Abstract
Alien predators are a major cause of decline and extinction of species worldwide, since native organisms are rarely equipped with specific antipredatory strategies to cope with them. However, phenotypic plasticity and learned predator recognition may help prey populations to survive novel predators. Here we examine geographical variation in the learning ability of larval spadefoot toads (Pelobates cultripes) to recognize invasive predatory crayfish (Procambarus clarkii). We compare the learning-mediated behavioural responses of tadpoles from six populations across two regions in Spain (central and southern), with different histories of exposure to the presence of the invasive species. Two of the populations showed innate recognition of chemical cues from the invasive crayfish, whereas three of them learned to recognize such cues as a threat after conditioning with conspecific alarm cues. Learning abilities did not differ among southern populations, but they did among central populations. We assessed patterns of genetic variation within and among these two regions through microsatellite markers and found low genetic divergence among the southern populations but greater differentiation among the central ones. We hypothesize that similar responses to the invasive crayfish in southern populations may have arisen from a combination of extended historical exposure to this introduced predator (~ 50 y) and higher levels of gene flow, as they inhabit a highly interconnected pond network. In contrast, populations from central Spain show lower connectivity, have been exposed to the invasive crayfish for a shorter period of time, and are more divergent in their plastic responses.
Similar content being viewed by others
Introduction
Alien predators are considered to be one of the major threats to global biodiversity loss, causing declines and extinction of species worldwide1,2,3. Introduced predators can create novel ecological contexts, posing new threats to which antipredatory responses of native prey may lack adaptive value4,5,6. Native prey are usually equipped with adaptive morphologies and/or behaviours to cope with local, coexisting predators. However, prey are often naïve to the hunting tactics of novel predators with whom they lack a shared evolutionary past1, 7. Because of this, alien predators frequently cause more severe impacts to prey populations than native predators8.
Despite the initial advantage of alien predators over naïve prey, prey populations enduring predator invasions may avoid extinction by adapting to the new threat9. Conditions favouring the persistence of local prey populations include moderate levels of predation pressure, large enough population size, the existence of sufficient genetic variation and/or phenotypic plasticity in the response to the novel predator within the population10,11,12. Adaptive variation, both genetic and phenotypic, appears then critical for native prey to evolve strategies to cope with alien predators, allowing the transition to their novel selective regimes. Nonetheless, because genetic shifts generally require multiple generations to occur, they are often too slow to keep pace with such a rapid environmental change13. In that light, phenotypic plasticity may be an essential mechanism for prey populations to survive novel predators, tempering the immediate impact of invasions and buying time for genetic responses to evolve, or be co-opted from defences against native predators14,15,16,17,18. In particular, behavioural plasticity –the ability of organisms to vary their behaviour in response to internal or external stimuli– constitutes the most rapid way to achieve behavioural shifts and improve individual fitness in response to human-induced environmental change exceeding the evolutionary response rate of the populations, and it may therefore represent the first line of defence for native prey to persist to introduced predators19,20,21,22.
Amphibians are the most threatened group of vertebrates with ca. 41% of the species endangered23, 24. Over the last decades, numerous studies have linked the introduction of alien predators with global amphibian declines, and even local extinctions25,26,27,28,29,30,31,32,33. Amphibian eggs and tadpoles are particularly vulnerable to alien aquatic predators, which can consume them intensively28,29,30,31. Naïve tadpoles, like many freshwater organisms, typically respond to the presence of water-borne cues from local predators by developing defensive morphologies and adjusting their behaviour34, 35 reviewed in36, 37. In contrast, tadpoles usually fail at inducing adaptive responses against alien predators, since activation of plastic defences necessarily requires predator recognition, and naïve tadpoles may be unable to recognize introduced predators with which they lack evolutionary history38,39,40,41,42. However, experimental studies have shown that many aquatic organisms including tadpoles can learn to recognize new predators as a threat by associating the unknown predator stimulus with conspecific alarm cues41, 43,44,45,46. Alarm cues are released when prey skin is damaged during a predatory attack, warning nearby individuals of imminent risk of predation and being crucial tools in associative learning40, 47, 48.
Hence, learning might be key to enabling the use of inducible defences against introduced predators, which can prove critical for amphibian populations until innate recognition (i.e. genetic adaptation) evolves. In this regard, tadpoles in some amphibian populations have been reported to recognize introduced predators39, 49,50,51,52, suggesting that, given enough time, native amphibians may evolve the ability to innately detect and avoid novel predators over generations, presumably assisted by behavioural plasticity through recurrent individual learning during the initial exposure. Geographic variation in plastic or innate responses against novel predators are likely to arise among prey populations, mostly due to variation in local predator abundance and history of exposure to the novel predators9, 53. Moreover, among-population variation in their behavioural plasticity and learning capacity may be influenced by available genetic diversity and gene flow with other populations with varying degrees of exposure to the novel predators. Thus, given sufficient genetic variation and selection from the novel predator, adaptive plasticity and even innate recognition can evolve locally, and even be exported to neighbouring populations with less predation pressure54, 55. Conversely, the evolution of such adaptations may be hindered by incoming gene flow from non-adapted populations54, 56, 57.
Here we compare innate responses and the ability to learn to detect chemical cues from a harmful invasive predator, the red swamp crayfish, Procambarus clarkii (Girard 1852), across multiple populations of the western, or Iberian, spadefoot toad, Pelobates cultripes (Cuvier 1829), with different histories of exposure to the presence of this invasive crayfish. Taking into account differences in the extent (abundance and history) of the invasion among toad populations and their genetic structure, we experimentally compare behavioural plasticity of tadpoles (innate and learning-mediated). According to the ‘plasticity-first’ evolution hypothesis14,15,16, the predatory pressure posed by the invasive crayfish would select for plasticity to increase in the populations in a first step, whereas plasticity would decrease in a second step when adaptive responses become fixed (i.e. the adaptation in the cue recognition system of tadpoles and the evolution of innate responses might occur at a later time). Given the short time elapsed since crayfish were first brought to the Iberian Peninsula (ca. 50 years ago), we predict that the populations are mostly in the first step (increasing plasticity). Thus, we expected learning-mediated behavioural plasticity of tadpoles to be influenced by the level of predatory impact posed by the crayfish, so that populations under stronger predatory pressure would have experienced stronger selection in favour of genotypes with greater learning ability58,59,60. We also analysed variation in the underlying genetic structure of the populations using neutral microsatellite markers to assess their genetic variation and patterns of among-population connectivity, so as to understand the population structure within which the among population differences in plasticity would have evolved.
Methods
Study system and study animals
The red swamp crayfish, Procambarus clarkii, is a worldwide invasive predator causing huge biodiversity loss in freshwater ecosystems. Native to south-eastern North America, P. clarkii is currently present in up to forty countries in four continents61. In Spain, it was introduced in the early 1970’s for commercial aquaculture purposes, in Badajoz province in 1973 and in the Lower Guadalquivir in 1974, following multiple translocations and gradually expanding its populations throughout almost the entire Iberian Peninsula62, 63. Procambarus clarkii is a voracious species with a broad trophic niche that can completely alter the trophic structure of invaded ecosystems, causing special damage to native amphibians through intense predation of eggs and tadpoles28, 64,65,66,67. Changes in morphology, behaviour, and life cycles of tadpoles have been observed in some amphibian populations in response to P. clarkii52, especially when crayfish cues were paired with alarm cues from attacked conspecific tadpoles38, 64, 68, 69. In contrast, populations of the common frog, Pelophylax perezi, and the western spadefoot toad, Pelobates cultripes, in southern Spain have consistently shown lack of innate antipredatory responses to chemical cues from the same invasive crayfish38, 41. Further, we have demonstrated that learned predator recognition via association with conspecific alarm cues successfully triggers antipredatory behaviour and improves survival of P. cultripes tadpoles in predation trials with the alien crayfish41.
Here we compare the ability to learn predator recognition in P. cultripes across six populations distributed between two regions of the Iberian Peninsula: three populations from Madrid and Segovia provinces (central Spain) –Manzanares (MAN), Colmenar (COL) and Sto. Tomé (STOME)–, and three populations from Huelva province (Doñana National Park, southern Spain) –Espajosas (ESP), Jabata (JAB) and El Llano (LLA). These populations were selected based on abundance and historical presence of invasive crayfish. The southern region around the Guadalquivir marshes was first invaded by P. clarkii in the 1970’s62, 63, whereas the central region was colonized more recently, likely by the end of the 1980’s70. Within each of both regions, we selected populations that in recent years have consistently shown different degrees of presence of the invasive crayfish, from ‘very abundant’ (southern Spain: ESP; central Spain: MAN) to ‘intermediate or intermittent’ presence (southern: JAB; central: COL), to ‘absence’ (southern: LLA; central: STOME). This information about crayfish abundance was based on previous fieldwork surveys in the southern region (databases from the Monitoring Program in the Doñana Natural Area, available since 2009; http://icts.ebd.csic.es/en/monitoring-program) and direct personal observations (I. Gomez-Mestre, C. Díaz-Paniagua and I. Martínez-Solano). Given the distinct histories of exposure to the invasive crayfish, and the likely (and confirmed, see below) genetic divergence between the two regions, we analysed each region independently to test for among-population divergence in antipredator responses and learning ability.
In spring 2017 we collected portions of 3–6 egg clutches in early stages of development (< 10 Gosner71) from each population. Eggs were transported to the Doñana Biological Station in Seville and housed in a walk-in climatic chamber to guarantee naïveté of experimental tadpoles to predator cues. Upon hatching, we raised tadpoles individually in 3 L plastic buckets with carbon-filtered dechlorinated tap water at 20 °C and 12:12 L:D photoperiod. Water was renewed twice weekly, and we subsequently fed tadpoles with ground rabbit chow and lightly boiled spinach. Additionally, we used fyke-nets to collect adult crayfish at the study populations to be used as predator cue donors. Donor crayfish were transported to the laboratory and housed individually in 3 L buckets in a climatic chamber separated from that of tadpoles to avoid chemical or visual contact with the predators prior to the experiments. Crayfish were fed spinach ad libitum, and temperature and photoperiod were the same as those of tadpoles. Crayfish and surviving tadpoles from Doñana National Park were euthanized after the experiments as indicated by the National Park authorities, whereas tadpoles from the northern populations were kept until metamorphosis and released as juveniles at their ponds of origin after standard prophylaxis procedures.
Preparation of chemical stimuli
To prepare predator chemical cues, we filled each donor crayfish aquarium with 1.5 L of dechlorinated tap water, to be pervaded with predator cues. To avoid potential confounding effects of the diet affecting conditioning or learning responses, we used starving crayfish to provide the cues (i.e. we examined tadpole responses to predator’s signature odour47; see also72 for definitions of the main cue types involved in risk perception). We kept crayfish unfed for 4 consecutive days before placing them in the donor aquaria, to ensure that no food remained in their digestive tracts73. Since predator cues last approximately 2–4 days in water74, we waited 2 additional days and then extracted and mixed the water from five donor aquaria and froze it in 10 mL aliquots until use. Ice aliquots containing predator cues have been previously used in experiments with P. cultripes and other anuran species, proving that tadpoles are able to detect and respond to such cues after freezing41, 42. Control water was prepared following the same procedure but without placing crayfish in the aquaria41, 42.
Tadpole alarm cues were prepared from three conspecific donor tadpoles. Tadpoles were euthanized by immersion in a highly concentrated solution of MS-222 and homogenized with a bench top homogenizer (Miccra D-1, Germany). We then diluted the homogenate in 600 mL of carbon-filtered, dechlorinated tap water and filtrated it with filter paper to remove solid particles. The water containing the alarm cues was immediately frozen in 10 mL aliquots until use75.
Behavioural plasticity
Behavioural plasticity was estimated as the capacity of tadpoles to adjust their antipredatory behaviour upon learning to recognize the novel predator. Since reduced activity is a common response to predation risk by larval amphibians, including P. cultripes41, 42, a reduction in tadpoles’ activity in the presence of predator cues was considered indicative of predator recognition. Hence, we compared the innate responses of tadpoles to water-borne chemical cues from the crayfish with their learning-mediated responses after conditioning by pairing crayfish cues with conspecific alarm cues. A total of 404 tadpoles were tested. A group of tadpoles from each population (n = 30–35) were randomly assigned to the ‘conditioned’ treatment and another group (n = 31–36) to the ‘non-conditioned’ treatment. Tadpoles in the ‘conditioned’ treatment were exposed to predator cues from crayfish coupled with conspecific alarm cues to induce conditioning, whereas tadpoles in the ‘non-conditioned’ treatment were exposed to predator cues alone. Thus, 10 mL test solution of crayfish cues plus 10 mL test solution of tadpole alarm cues were added in each 3 L housing bucket of tadpoles in the ‘conditioned’ treatment, whereas 10 mL test solution of crayfish cues plus 10 mL test solution of clean water were added in each 3 L housing bucket of tadpoles in the ‘non-conditioned’ treatment. Tadpoles were left undisturbed in their housing buckets overnight, and the next day, we tested basal activity levels of each tadpole both in clean water and in water with crayfish cues, in random order. Tadpoles were tested individually in grey, U-shaped, gutters (101 × 11.4 × 6.4 cm), sealed at both ends with plastic caps, and divided into five parts of equal surface by tracing four crossing lines inside. Batches of fifteen tadpoles (fifteen gutters) were tested at the same time. For the trials, gutters were filled with 3 L of carbon-filtered dechlorinated tap water, and we added 10 mL test solutions of clean water or crayfish cues to each end of each gutter (two frozen aliquots per gutter). We waited 5 min for the aliquots to thaw completely, and then placed a single tadpole in the middle of each gutter, waiting another 5 min before the trials began to allow tadpoles to acclimate. Tadpoles were monitored for 30 min, using the instantaneous scan sampling method, and recording every 1 min the quadrant that each tadpole occupied in the gutter (30 scans per tadpole in total). Activity levels were calculated from the number of lines crossed by each tadpole during each trial41, 42. Lack of response to crayfish cues by non-conditioned (naïve) tadpoles indicates lack of innate recognition. Then, if conditioned tadpoles significantly reduce their activity in the presence of crayfish cues, it indicates learned predator cue recognition. Change in tadpole activity in the presence of crayfish cues compared to clean water across ‘non-conditioned’ and ‘conditioned’ treatments was taken as a measure of learning-mediated behavioural plasticity or reaction norm for each population.
We analysed differences between conditioned and non-conditioned tadpoles in their responses to water-borne cues from the alien crayfish and compared innate and learning-mediated behavioural plasticity (i.e. reaction norms) of populations between regions by performing linear models with activity level (i.e. the number of lines crossed by tadpoles over the total observation time) as dependent variable, region, population nested in region, and conditioning treatment (‘conditioned’ vs. ‘non-conditioned’) as three between-subject factors, and the experimental chemical stimulus (‘clean water’ vs. ‘crayfish cues’) as a within-subject factor. Since central and southern populations formed two distinct genetic clusters (see below), and because the two regions were not analogous in their patterns of abundance and history of exposure to the invasive crayfish, we also analysed the responses of tadpoles from both regions separately. Finally, we analysed the effect of conditioning within each population by performing linear models with activity level as dependent variable, conditioning treatment as a between-subject factor, and the experimental chemical stimulus as a within-subject factor. Data normality was verified by Kolmogorov–Smirnov test, and Levene’s test indicated homoscedasticity. Post-hoc pairwise comparisons were calculated using protected Fisher’s LSD tests76. Analyses were performed using Statistica v12.0 (StatSoft Inc., Tulsa, OK, USA).
Crayfish abundance
During springs 2017 and 2018, we sampled the study populations repeatedly (6–10 times each) using fyke-nets to measure abundance of red swamp crayfish. Unbaited nets were set underwater in the ponds at twilight and removed the next morning. Number of traps in the populations was adjusted according to pond size, and traps were distributed in the ponds homogeneously. Sampling effort in each population was calculated as the total number of traps multiplied by total sampling duration (i.e. total number of hours that all the fyke-nets were underwater). The number of crayfish of different size (carapace length) classes captured in each population was registered every sampling day. Then, we calculated crayfish density in each population as the total number of crayfish of each size class divided by the surface area of the pond and corrected by the sampling effort. Captured crayfish were removed from the ponds and euthanized following the AVMA Guidelines for invasive species77.
Molecular analyses
We assessed the pattern of genetic diversity of the study populations within and across regions through nuclear DNA microsatellite analysis from tissue samples of tadpoles. Thirty tadpoles (Gosner stage 2571) were collected in each population. A portion of the tail tip (the last 5 mm) was clipped, and we immediately released them back in the field. Tail clips were introduced in individualized tagged tubes with 70% ethanol and stored at − 20 °C for DNA extraction and genotyping.
Genomic DNA was extracted from tissue samples using a modified high-salt DNA extraction method78, 79. Twelve microsatellite loci from P. cultripes (Pc 3.1, Pc 3.2, Pc 3.23, Pc 3.24, Pc 3.25, Pc 3.4, Pc 3.7, Pc 3.9, Pc 4.1, Pc 4.4, Pc 4.5, Pc 4.9)80 were multiplexed in three polymerase chain reactions (PCRs), with forward primers labelled with fluorescent dyes. PCR reactions were performed using Type-it Microsatellite PCR kits (Qiagen), in a total volume of 15 μL, containing 7.5 μL of master mix, 1.2 μL of primer mix (0.12–0.4 μM of each primer), and RNase-free H2O up to 15 μL. PCR thermal cycling conditions were as follows: initial denaturation at 95 °C for 5 min; followed by 30 cycles of denaturation at 95 °C for 30 s, annealing at 60 °C for 90 s, extension at 72 °C for 30 s; and a final extension step of 30 min at 60 °C. PCR products were analysed by agarose gel electrophoresis (2%) on a 3130XL Genetic Analyzer (Applied Biosystems, Foster City, CA, USA), and fragments were scored using GeneMapper v5.0 (Applied Biosystems, Foster City, CA, USA).
Presence of null alleles was assessed with Micro-Checker v2.2.381, using a 99% confidence interval and 1000 randomizations. To check for deviations from Hardy–Weinberg equilibrium (HWE) and evidence of linkage disequilibrium (LD), we performed Fisher’s exact test on multilocus genotypes using Genepop v4.7.082, with 10 000 dememorization steps, 1000 batches and 10 000 iterations per batch. A sequential Bonferroni correction for multiple testing was applied83.
We estimated allelic richness (A), number of effective alleles (Ae), Shannon information index (I), observed (Ho) and expected (He) heterozygosity, unbiased expected heterozygosity (uHe), and the inbreeding coefficient –expressed as Wright’s fixation index (FIS)– for each locus and population using GenAlEx v6.51b284. Comparisons between pairs of populations were performed with the G-statistic subroutine, applying a sequential Bonferroni correction to test for significance. We performed Principal Coordinate Analysis (PCoA) based on pairwise Hedrick’s GST, Jost’s D and Nei’s genetic distance matrices among populations. To test for isolation by distance (IBD), we used paired Mantel tests assessing the correlation between genetic distance matrices and the geographic distance matrix. Genetic variation within and among populations was determined using Analysis of Molecular Variance (AMOVA) with 999 permutations. We also estimated the effective number of breeders (Nb) in the populations using the sibship frequency method implemented in Colony v2.0.6.885. Analyses were performed by assuming polygamy in both sexes86, with “very high” likelihood precision, “very long” run length and using no sibship prior. We also explored the probability of siblings, and we obtained similar results to our expectations: tadpoles come from between 5–9 egg clutches in every population, with some degree of polygamy.
To characterize population genetic structure across study populations we performed unsupervised Bayesian clustering analyses using Structure v2.3.487. The number of clusters (K) best explaining the genetic data was determined by performing ten replicates for each K value (1–10), using an admixture model with correlated allele frequencies and 50 000 burn-in and 50 000 post burn-in iteration steps87, 88. We summarized clustering results using the online version of Clumpak89 and explored the relative likelihood of different K values using the ΔK (‘Evanno’) method90 in Structure Harvester v0.6.9491.
Results
Behavioural plasticity
Overall activity of tadpoles was significantly higher in the southern than in the central region (mean ± SE = 46.5 ± 0.9 vs. 42.1 ± 0.9 number of lines crossed), but did not differ across populations (Table 1; Fig. 1). Activity levels of non-conditioned and conditioned tadpoles did not significantly differ overall, and the interactions between conditioning treatment and region or population nested in region were not significant (Table 1). However, we found a significant interaction between conditioning treatment and testing predator cues (Table 1). Behavioural plasticity did not significantly differ between regions (i.e., the interaction between region, conditioning treatment and testing predator cues was not significant), but it did across populations (i.e., the interaction between population nested in region, conditioning treatment and testing predator cues was significant) (Table 1). Behavioural plasticity significantly differed across central populations, but not across southern populations (Table 1). In central Spain, reaction norms were similar between MAN and COL and between MAN and STOME, but differed significantly between COL and STOME (Table 1; Fig. 1), the latter of which lacks crayfish.
Activity levels (mean ± SE number of lines crossed during 30 min) of non-conditioned (open circles) and conditioned (solid circles) Pelobates cultripes tadpoles, either in clean water or in the presence of chemical cues from invasive crayfish, in six populations from two different regions of the Iberian Peninsula, central and southern Spain. MAN Manzanares, COL Colmenar, STOME Sto. Tomé, ESP Espajosas, JAB Jabata, LLA El Llano.
Within the central region, the interaction between conditioning treatment and testing predator cues was not significant in MAN or STOME (Table 1; Fig. 1). In both populations, activity of tadpoles (conditioned and non-conditioned pooled) was reduced in water with crayfish cues with respect to clean water (i.e., the effect of testing predator cues was significant; Table 1), thus indicating innate recognition of these cues as a threat (Fig. 1). In COL, the interaction between conditioning treatment and testing predator cues was significant (Table 1; Fig. 1). Activity of non-conditioned tadpoles in the presence of crayfish cues did not change with respect to their activity in clean water (Fisher’s LSD, p = 0.36), indicating lack of innate recognition of chemical cues from the invasive crayfish. However, tadpoles conditioned with conspecific alarm cues in combination with crayfish cues significantly reduced their activity in the presence of crayfish cues compared to clean water (p < 0.0001), indicating learned cue recognition of the crayfish in this population (Fig. 1). Within the southern region, the interaction between conditioning treatment and testing predator cues was not significant in ESP (Table 1; Fig. 1), and activity of tadpoles (conditioned and non-conditioned pooled) was similar in the presence of crayfish cues and in clean water, (i.e., the effect of testing predator cues was not significant; Table 1), thus indicating lack of response –innate or learned– to crayfish cues in this population (Fig. 1). In contrast, the interaction between conditioning treatment and testing predator cues was significant in JAB and LLA (Table 1; Fig. 1). Activity of non-conditioned tadpoles was similar in the presence of crayfish cues and in clean water (Fisher’s LSD, JAB: p = 0.26; LLA: p = 0.16), indicating lack of innate recognition of crayfish cues in both populations (Fig. 1). In JAB, conditioned tadpoles reduced their activity in the presence of crayfish cues compared to clean water, although this reduction did not reach statistical significance (p = 0.09). However, activity of conditioned tadpoles was significantly lower than activity of non-conditioned tadpoles in water with crayfish cues (p = 0.01), suggesting some degree of learned cue recognition of the invasive crayfish in this population (Fig. 1). Conditioned tadpoles from LLA significantly reduced their activity in the presence of crayfish cues compared to clean water (p < 0.001), indicating learned cue recognition of the invasive predator in this population (Fig. 1). Behavioural plasticity of tadpoles was not associated with the abundance of crayfish estimated in the populations (Fig. 2).
Abundance of crayfish (total individuals/m2/h) of different carapace length classes estimated in the populations. MAN Manzanares, COL Colmenar, STOME Sto. Tomé, ESP Espajosas, JAB Jabata, LLA El Llano.
Population genetics
There were significant deviations from Hardy–Weinberg equilibrium (HWE) associated with an excess of heterozygotes in loci Pc4.1, Pc4.4 and Pc4.5 in MAN, and locus Pc3.4 in LLA. Loci Pc3.24 and Pc3.1 presented an excess of homozygotes in ESP, likely due to the existence of null alleles. We also found evidence of linkage disequilibrium (LD) between loci Pc3.1–Pc4.5 in MAN and Pc3.2–Pc4.4 in LLA. Since disequilibria occurred in different populations, these loci were not discarded for subsequent analyses.
Analysis of microsatellite loci showed strong differences across regions in genetic diversity of the populations. Southern populations showed higher allelic richness, number of effective alleles, Shannon information index, and heterozygosity than the central populations, which in turn presented higher FIS values (Table 2). Allelic richness and heterozygosity were low to moderate, with scarce or inexistent inbreeding (Ho > He, except for ESP and LLA). Estimates of effective number of breeders were similar between central and southern populations, ranging from 9 to 17 reproductive individuals (Table 2). Within regions, genetic differentiation among southern populations was very low, whereas higher genetic divergence was observed among central populations (Table 3). IBD was not significant among central (Mantel test, Hedrick’s GST: Rxy = 0.86, p = 0.36; Jost’s D: Rxy = 0.83, p = 0.33; Nei’s: Rxy = 0.81, p = 0.3) or southern (Mantel test, Hedrick’s GST: Rxy = 0.97, p = 0.15; Jost’s D: Rxy = 0.94, p = 0.16; Nei’s: Rxy = 0.9, p = 0.17) populations (Table 3).
Partitioning of overall genetic variation within and among populations by AMOVA indicated that 82% of genetic variation was distributed within populations, whereas 18% was distributed among populations (AMOVA, FST = 0.18, p = 0.001; FIS = − 0.04, p = 0.99; FIT = 0.15, p = 0.001). Separated analyses by region yielded similar results for central populations (81% within vs. 19% among populations; AMOVA, FST = 0.22, p = 0.001; FIS = − 0.14, p = 0.99; FIT = 0.11, p = 0.001), but indicated much lower genetic structure among southern populations (96% within vs. 2% among populations; AMOVA, FST = 0.02, p = 0.001; FIS = 0.02, p = 0.17; FIT = 0.04, p = 0.02).
Number of clusters best explaining genetic data according to Evanno method (ΔK) was K = 2, simply corresponding to the central and southern regions (Fig. 3a). When performing separated analyses by region, the optimal number of clusters in the central region was K = 2, with STOME clearly separated from the other two central populations, but closely followed by K = 3, grouping individuals into three separate populations (Fig. 3b). In the southern region, the optimal number of clusters was K = 2, with individuals admixed at approximately the same proportions (Fig. 3c).
Summary results of the Bayesian clustering assignment implemented in Structure, with colours indicating clusters, or populations. (a) Number of K clusters best explaining genetic data of the six Pelobates cultripes populations from two different regions of the Iberian Peninsula, central and southern Spain. (b) Separated analysis for central region. Optimal number of clusters was K = 2 (upper panel), closely followed by K = 3 (lower panel). (c) Separated analysis for southern region. MAN Manzanares, COL Colmenar, STOME Sto. Tomé, ESP Espajosas, JAB Jabata, LLA El Llano.
Discussion
Our findings demonstrate widespread learning abilities of spadefoot toad tadpoles to recognize and respond to water-borne cues from a new predator, the invasive crayfish P. clarkii. We found lack of innate recognition of crayfish odour in four out of the six populations across the two study regions, and three out of these four were able to recognize it as a threat after conditioning with conspecific alarm cues. The lack of innate recognition of invasive crayfish by Iberian spadefoot toad populations is not unexpected, given that P. clarkii was introduced in the Iberian Peninsula ca. 50 years ago, a relatively short evolutionary time for adaptation to occur in temperate amphibians with long generation times (1–2 years). In our previous studies, P. cultripes and P. perezi tadpoles from Doñana National Park also failed to innately recognize invasive P. clarkii chemical cues38, 41. Here we extend this observation to other regions of the Iberian Peninsula. Naïve tadpoles of several anuran species, including P. cultripes and P. perezi, from southern Portugal have been reported to exhibit antipredatory behaviour in response to joint crayfish and attacked conspecific cues64, 68, 69, but responses to crayfish cues alone remain to be tested. Recently, Melotto et al.11 found that tadpoles of several amphibian species, especially those sharing coevolutionary history with native crayfish, strongly responded to visual cues from P. clarkii, whereas their responses to chemical cues from invasive crayfish were weak and contrasting. Altogether, our study reinforces the idea that responses of amphibians to chemical cues from novel exotic predators are largely mediated by consumed conspecifics68.
Different histories of coexistence with predators may also lead to dissimilar evolved responses to invasive crayfish among populations. In fact, generalization of predator recognition (i.e. when prey lacking innate recognition of novel predators have the ability to label them as predatory if they are phylogenetically closely related to already known predators92) has been demonstrated in larval amphibians93,94,95. In the Iberian Peninsula, the native crayfish Austropotamobius pallipes has been historically absent from Doñana area and almost from the entire Madrid region, but this indigenous species was present in the area of STOME population (in the limits between Segovia and Madrid provinces) about 50 years ago, before Iberian crayfish populations were drastically decimated by the crayfish plague caused by the pathogen Aphanomyces astaci96,97,98. Interestingly, we observed a significant reduction in activity of naïve tadpoles in response to water-borne cues from P. clarkii in the STOME population (Fig. 1). This suggests that a certain degree of generalized predator recognition of the alien crayfish linked to the presence of a native crayfish in the recent past might be taking place in this non-invaded population. However, an innate response to crayfish cues was observed also in the MAN population (Fig. 1), where A. pallipes has been historically absent. Although the arrival of P. clarkii to central Spain is fairly recent (ca. 35 years), we cannot completely discard that innate recognition of crayfish cues could have evolved in this population under the predatory pressure posed by the alien crayfish during the last decades.
Predator diet seems to be a critical factor in the recognition of alien predators by naïve amphibian larvae, and the consumption of conspecific tadpoles is precisely the ecological scenario in which learned recognition would take place. Even though innate responses may fail to be triggered against novel predators, prey can still rely on learning to reduce their impact. Learning of new threats through cognitive association with alarm cues has been observed in a variety of aquatic prey (see47 for an extended review), including amphibians44,45,46, 95. In a previous study, we demonstrated that learning via association with conspecific alarm cues allows successful activation of antipredatory responses by spadefoot toad tadpoles against P. clarkii, increasing larval survival in predatory assays41. Here we show that such learning ability is common to multiple populations of P. cultripes regardless of the intensity of the invasion by crayfish. This widespread learned predator recognition suggests that amphibian larvae might broadly benefit from associative learning to recognize and avoid new predatory threats, thus modulating the initial advantage of alien predators in amphibian assemblages.
According to the ‘plasticity-first’ evolution hypothesis14,15,16, we expected the level of predatory threat posed by the crayfish (i.e. abundance and history of exposure) to be positively associated with learning ability across populations58,59,60. A rapid shift towards learning-mediated antipredator responses might be facilitated by differential survival of individuals prone to learning. In addition, higher levels of predation mean higher concentration of conspecific alarm cues in the environment, presumably resulting in learning reinforcement43, 99,100,101,102. However, we did not find evidence for correlation between the crayfish abundance and the behavioural plasticity of tadpoles across populations. Reaction norms were similar across southern populations, even though abundance of crayfish was considerably higher in ESP and JAB (Figs. 1 and 2), likely due to higher gene flow and lack of genetic substructuring. Further, the separated analysis for ESP indicated lack of learned response to crayfish cues in this population. Among central populations, behavioural plasticity of tadpoles differed significantly between the non-invaded STOME and the intermediate COL, but not between STOME and the most heavily invaded MAN (Figs. 1 and 2). Also, the most responsive population (COL) was not the one with the highest abundance of crayfish (MAN). Predator learning therefore does not seem to be associated with history of coexistence with crayfish, suggesting that selection by the invader is likely not the main factor explaining population divergence in learning abilities. Amphibian populations facing P. clarkii might be co-opting pre-existing antipredatory adaptations evolved to face current or ancestral predators (such as the native A. pallipes in STOME). Further, the capacity for learning itself may have also evolved under selective pressures imposed by additional factors varying across populations, consequently affecting larval skills to acquire recognition of new predatory threats103.
Learning abilities and behavioural plasticity of tadpoles also vary according to genetic divergence. The similar behavioural responses to P. clarkii observed within the southern region may have arisen from a combination of (1) longer history of exposure to this invasive predator –crayfish were firstly introduced in the Guadalquivir marshes, reaching the Spanish central plateau later– and (2) higher levels of gene flow, as southern populations inhabit a highly interconnected pond network. In contrast, a lower connectivity and a higher genetic differentiation seem to be responsible for the more divergent plastic responses found among the central populations. In consequence, these more isolated populations may be at a greater risk from invasive predatory crayfish.
Our results emphasize the importance of integrating phenotypic plasticity and behavior of native organisms in the management of biological invasions, in order to achieve the conservation goal of long-term persistence. Indeed, the capacity to plastically modify behavior in response to new or unusual challenges (i.e., the cognitive buffer104) is an essential mechanism for animals to cope with rapid environmental changes such as the introduction of novel predators. By enabling tadpoles to adjust defensive behaviour and activate inducible defences, widespread learned predator recognition may be decisive for amphibian populations to persist in the new ecological context posed by aliens, soothing the impact of invasions and buying time for innate recognition to evolve17, 18.
Data availability
Data supporting the findings are available from Dryad Digital repository (https://datadryad.org/stash/share/OiStTZZeDejQEnu0VF9gm-hkI1Rwa0J4b2yLeiPi9-k).
References
Cox, J. G. & Lima, S. L. Naiveté and an aquatic-terrestrial dichotomy in the effects of introduced predators. Trends Ecol. Evol. 21, 674–680 (2006).
Doherty, T. S., Glen, A. S., Nimmo, D. G., Ritchie, E. G. & Dickman, C. R. Invasive predators and global biodiversity loss. Proc. Natl. Acad. Sci. U. S. A. 113, 11261–11265 (2016).
Vitousek, P. M., Mooney, H. A., Lubchenco, J. & Melillo, J. M. Human domination of Earth’s ecosystems. Science 277, 494–499 (1997).
Callaway, R. M. & Aschehoug, E. T. Invasive plants versus new and old neighbours: A mechanism for exotic invasion. Science 290, 521–523 (2000).
Carthey, A. J. R. & Banks, P. B. Naïveté in novel ecological interactions: Lessons from theory and experimental evidence. Biol. Rev. 89, 932–949 (2014).
Shea, K. & Chesson, P. Community ecology theory as a framework for biological invasions. Trends Ecol. Evol. 17, 170–176 (2002).
Schlaepfer, M. A., Sherman, P. W., Blossey, B. & Runge, M. C. Introduced species as evolutionary traps. Ecol. Lett. 8, 241–246 (2005).
Salo, P., Korpimäki, E., Banks, P. B., Nordström, M. & Dickman, C. R. Alien predators are more dangerous than native predators to prey populations. Proc. R. Soc. Lond. B 274, 1237–1243 (2007).
Melotto, A., Manenti, R. & Ficetola, G. F. Rapid adaptation to invasive predators overwhelms natural gradients of intraspecific variation. Nat. Commun. 11, 1–10 (2020).
Kokko, H. & Sutherland, W. J. Ecological traps in changing environments, ecological and evolutionary consequences of a behaviourally mediated Allee effect. Evol. Ecol. Res. 3, 537–551 (2001).
Melotto, A., Ficetola, G. F., Alari, E., Romagnoli, S. & Manenti, R. Visual recognition and coevolutionary history drive responses of amphibians to an invasive predator. Behav. Ecol. 32, 1352–1362 (2021).
Schlaepfer, M. A., Runge, M. C. & Sherman, P. W. Ecological and evolutionary traps. Trends Ecol. Evol. 17, 474–480 (2002).
Meyers, L. A. & Bull, J. J. Fighting change with change. Trends Ecol. Evol. 17, 551–557 (2002).
Garland, T. Jr. & Kelly, S. A. Phenotypic plasticity and experimental evolution. J. Exp. Biol. 209, 2344–2361 (2006).
Gomez-Mestre, I. & Jovani, R. A heuristic model on the role of plasticity in evolution: Plasticity increases adaptation, population viability, and genetic variation. Proc. R. Soc. Lond. B 280, 20131869 (2013).
Levis, N. A., Isdaner, A. J. & Pfennig, D. W. Morphological novelty emerges from pre-existing phenotypic plasticity. Nat. Ecol. Evol. 2, 1289–1297 (2018).
Losos, J. B., Schoener, T. W. & Spiller, D. A. Predator induced behaviour shifts and natural selection in field experimental lizard populations. Nature 432, 505–508 (2004).
Strauss, S. Y., Lau, J. A. & Carroll, S. P. Evolutionary responses of natives to introduced species: What do introductions tell us about natural communities?. Ecol. Lett. 9, 357–374 (2006).
Mery, F. & Burns, J. G. Behavioural plasticity: An interaction between evolution and experience. Evol. Ecol. 24, 571–583 (2010).
Snell-Rood, E. An overview of the evolutionary causes and consequences of behavioural plasticity. Anim. Behav. 85, 1004–1011 (2013).
West-Eberhard, M. J. Developmental Plasticity and Evolution (Oxford University Press, 2003).
Wong, B. B. M. & Candolin, V. Behavioural responses to changing environments. Behav. Ecol. 26, 665–673 (2015).
Catenazzi, A. State of the world’s amphibians. Annu. Rev. Environ. Resour. 40, 91–119 (2015).
Hoffmann, M. et al. The impact of conservation on the status of the world’s vertebrates. Science 330, 1503–1509 (2010).
Bradford, D. F., Graber, D. M. & Tabatabai, F. Population declines of the native frog, Rana muscosa, in Sequoia and Kings Canyon National Parks, California. Southwest. Nat. 39, 323–327 (1994).
Cruz, M. J., Rebelo, R. & Crespo, E. G. Effects of an introduced crayfish, Procambarus clarkii, on the distribution of south-western Iberian amphibians in their breeding habitats. Ecography 29, 329–338 (2006).
Cruz, M. J., Segurado, P., Sousa, M. & Rebelo, R. Collapse of the amphibian community of the Paul do boquilobo natural reserve (central Portugal) after the arrival of the exotic American crayfish Procambarus clarkii. Herpetol. J. 18, 197–204 (2008).
Gamradt, S. C. & Kats, L. B. Effect of introduced crayfish and mosquitofish on California newts. Conserv. Biol. 10, 1155–1162 (1996).
Gamradt, S. C., Kats, L. B. & Anzalone, C. B. Aggression by non-native crayfish deters breeding in California newts. Conserv. Biol. 11, 793–796 (1997).
Gillespie, G. R. The role of introduced trout in the decline of the spotted tree frog (Litoria spenceri) in South-eastern Australia. Biol. Conserv. 100, 187–198 (2001).
Kats, L. B. & Ferrer, R. P. Alien predators and amphibian declines, review of two decades of science and the transition to conservation. Divers. Distrib. 9, 99–110 (2003).
Kiesecker, J. M. & Semlitsch, R. D. Invasive species as a global problem. Toward understanding the worldwide decline of amphibians. In Amphibian Conservation (R.D. Semlitsch ed). Harper Collins Publisher (2003), pp. 113–126.
Matthews, K. R., Pope, K. L., Preisler, H. K. & Knapp, R. A. Effects of non-native trout on Pacific treefrogs (Hyla regilla) in the Sierra Nevada. Copeia 2001, 1130–1137 (2001).
Holomutzki, J. R. Ovoposition sites and fish-deterrent mechanisms in two stream anurans. Copeia 1995, 607–613 (1995).
Kiesecker, J. M., Chivers, D. P. & Blaustein, A. R. The use of chemical cues in predator recognition by western toad tadpoles. Anim. Behav. 52, 1237–1245 (1996).
Chivers, D. P. & Smith, R. J. F. Chemical alarm signalling in aquatic predator/prey systems. A review and prospectus. Ecoscience 5, 338–352 (1998).
Kats, L. B. & Dill, L. M. The scent of death: Chemosensory assessment of predation by prey animals. Ecoscience 5, 361–394 (1998).
Gomez-Mestre, I. & Diaz-Paniagua, C. Invasive predatory crayfish do not trigger inducible defences in tadpoles. Proc. R. Soc. Lond. B 278, 3364–3370 (2011).
Kiesecker, J. M. & Blaustein, A. R. Population differences in responses of red-legged frogs (Rana aurora) to introduced bullfrogs. Ecology 78, 1752–1760 (1997).
Marquis, O., Saglio, P. & Neveu, A. Effects of predators and conspecific chemical cues on the swimming activity of Rana temporaria and Bufo bufo tadpoles. Arch. Hydrobiol. 160, 153–170 (2004).
Polo-Cavia, N. & Gomez-Mestre, I. Learned recognition of introduced predators determines survival of tadpole prey. Funct. Ecol. 28, 432–439 (2014).
Polo-Cavia, N., Gonzalo, A., López, P. & Martín, J. Predator-recognition of native but not invasive turtle predators by naïve anuran tadpoles. Anim. Behav. 80, 461–466 (2010).
Ferrari, M. C. O., Messier, F. & Chivers, D. P. Threat-sensitive learning of predators by larval mosquitoes Culex restuans. Behav. Ecol. Sociobiol. 62, 1079–1083 (2008).
Ferrari, M. C. O., Messier, F. & Chivers, D. P. Larval amphibians learn to match antipredator response intensity to temporal patterns of risk. Behav. Ecol. 19, 980–983 (2008).
Gonzalo, A., López, P. & Martín, J. Iberian green frog tadpoles may learn to recognize novel predators from chemical alarm cues of conspecifics. Anim. Behav. 74, 447–453 (2007).
Mirza, R. S., Ferrari, M. C. O., Kiesecker, J. M. & Chivers, D. P. Responses of American toad tadpoles to predation cues: Behavioural response thresholds, threat-sensitivity and acquired predation recognition. Behaviour 143, 877–889 (2006).
Ferrari, M. C. O., Wisenden, B. D. & Chivers, D. P. Chemical ecology of predator-prey interactions in aquatic ecosystems: A review and prospectus. Can. J. Zool. 88, 698–724 (2010).
Summey, M. R. & Mathis, A. Alarm responses to chemical stimuli from damaged conspecifics by larval anurans: Test of three neotropical species. Herpetologica 54, 402–408 (1998).
Chivers, D. P. & Smith, R. J. F. Free-living fathead minnows rapidly learn to recognize pike as predators. J. Fish Biol. 46, 949–954 (1995).
Chivers, D. P., Wildy, E. L., Kiesecker, J. M. & Blaustein, A. R. Avoidance response of juvenile pacific tree frogs to chemical cues of introduced predatory bullfrogs. J. Chem. Ecol. 27, 1667–1676 (2001).
Moore, R. D., Griffiths, R. A., O’Brien, C. M., Murphy, A. & Jay, D. Induced defences in an endangered amphibian in response to an introduced snake predator. Oecologia 141, 139–147 (2004).
Pearl, C. A., Adams, M. J., Schuytema, G. S. & Nebeker, A. V. Behavioural responses of anuran larvae to chemical cues of native and introduced predators in the Pacific Northwestern United States. J. Herpetol. 37, 572–576 (2003).
Bytheway, J. P. & Banks, P. B. Overcoming prey naiveté: Free-living marsupials develop recognition and effective behavioral responses to alien predators in Australia. Glob. Chang. Biol. 25, 1685–1695 (2019).
Bridle, J. R. & Vines, T. H. Limits to evolution at range margins: When and why does adaptation fail?. Trends Ecol. Evol. 22, 140–147 (2007).
Ronco, F. et al. Drivers and dynamics of a massive adaptive radiation in cichlid fishes. Nature 589, 76–81 (2021).
Storfer, A. & Sih, A. Gene flow and ineffective antipredator behavior in a stream-breeding salamander. Evolution 52, 558–565 (1998).
Bachmann, J. C., van Jansen Rensburg, A., Cortazar-Chinarro, M., Laurila, A. & Van Buskirk, J. Gene flow limits adaptation along steep environmental gradients. Am. Nat. 195, E67–E86 (2020).
Arendt, J. D. & Reznick, D. N. Evolution of juvenile growth rates in female guppies (Poecilia reticulata): Predator regime or resource level?. Proc. R. Soc. Lond. B 272, 333–337 (2005).
Langerhans, R. B., Layman, C. A., Shokrollahi, A. M. & DeWitt, T. J. Predator-driven phenotypic diversification in Gambusia affinis. Evolution 58, 2305–2318 (2004).
Trussell, G. C. & Smith, L. D. Induced defenses in response to an invading crab predator: An explanation of historical and geographic phenotypic change. Proc. Natl. Acad. Sci. U. S. A. 97, 2123–2127 (2000).
Oficialdegui, F. J., Sánchez, M. I. & Clavero, M. One century away from home: How the red swamp crayfish took over the world. Rev. Fish Biol. Fisher. 30, 121–135 (2020).
Acevedo-Limón, L., Oficialdegui, F. J., Sánchez, M. I. & Clavero, M. Historical, human, and environmental drivers of genetic diversity in the red swamp crayfish (Procambarus clarkii) invading the Iberian Peninsula. Freshw. Biol. 65, 1460–1474 (2020).
Habsburgo-Lorena, A. S. Present situation of exotic species of crayfish introduced into Spanish continental waters. Freshw. Crayfish 4, 175–184 (1979).
Cruz, M. J. & Rebelo, R. Vulnerability of Southwest Iberian amphibians to an introduced crayfish, Procambarus clarkii. Amphib.-Reptil. 26, 293–303 (2005).
Ficetola, G. F. et al. Early assessment of the impact of alien species: Differential consequences of an invasive crayfish on adult and larval amphibians. Divers. Distrib. 17, 1141–1151 (2011).
Ficetola, G. F., Siesa, M. E., De Bernardi, F. & Padoa-Schioppa, E. Complex impact of an invasive crayfish on freshwater food webs. Biodivers. Conserv. 21, 2641–2651 (2012).
Gherardi, F. & Acquistapace, P. Invasive crayfish in Europe: the impact of Procambarus clarkii on the littoral community of a Mediterranean lake. Freshw. Biol. 52, 1249–1259 (2007).
Nunes, A. L., Richter-Boix, A., Laurila, A. & Rebelo, R. Do anuran larvae respond behaviourally to chemical cues from an invasive crayfish predator? A community—Wide study. Oecologia 171, 115–127 (2013).
Nunes, A. L., Orizaola, G., Laurila, A. & Rebelo, R. Rapid evolution of constitutive and inducible defenses against an invasive predator. Ecology 95, 1520–1530 (2014).
Grijalbo, J. L. laguna de San Juan y Demás Zonas Húmedas del Tajuña (Agencia de Medio Ambiente, Comunidad de Madrid, 1991).
Gosner, K. L. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16, 183–190 (1960).
Mitchell, M. D., Bairos-Novak, K. R. & Ferrari, M. C. O. Mechanisms underlying the control of responses to predator odours in aquatic prey. J. Exp. Biol. 220, 1937–1946 (2017).
McGaw, I. J. & Curtis, D. L. A review of gastric processing in decapod crustaceans. J. Comp. Physiol. B 183, 443–465 (2012).
Peacor, S. D., Allesina, S., Riolo, R. L. & Pascual, M. Phenotypic plasticity opposes species invasions by altering fitness surface. PLoS Biol. 4, e372 (2006).
Woody, D. R. & Mathis, A. Acquired recognition of chemical stimuli from an unfamiliar predator: Associative learning by adult newts. Notophthalmus Viridiscens Copeia 1998, 1027–1031 (1998).
Sokal, R. R., & Rohlf, F. J. (1995). Biometry: Nested analysis of variance. Biometry. Freeman WH. 3rd ed., pp. 272–342.
American Veterinary Medical Association. AVMA Guidelines on Euthanasia (2007).
Aljanabi, S. M. & Martinez, I. Universal and rapid salt-extraction of high quality genomic DNA for PCR-based techniques. Nucleic Acids Res. 25, 4692–4693 (1997).
Miller, S. A., Dykes, D. D. & Polesky, H. F. A simple salting out procedure for extracting DNA from human nucleated cells. Nucleic Acids Res. 16, 1215 (1988).
Gutiérrez-Rodríguez, J. & Martínez-Solano, Í. Isolation and characterization of sixteen polymorphic microsatellite loci in the Western Spadefoot, Pelobates cultripes (Anura: Pelobatidae) via 454 pyrosequencing. Conserv. Genet. Resour. 5, 981–984 (2013).
Van Oosterhout, C., Hutchinson, W. F., Wills, D. P. M. & Shipley, P. Micro-checker: Software for identifying and correcting genotyping errors in microsatellite data. Mol. Ecol. Notes 4, 535–538 (2004).
Rousset, F. Genepop’007: A complete reimplementation of the Genepop software for Windows and Linux. Mol. Ecol. Resour. 8, 103–106 (2008).
Rice, W. R. Analyzing tables of statistical tests. Evolution 43, 223–225 (1989).
Peakall, R. & Smouse, P. E. GenAlEx 65: genetic analysis in Excel. Population genetic software for teaching and research—An update. Bioinformatics 28, 2537–2539 (2012).
Jones, O. R. & Wang, J. COLONY: A program for parentage and sibship inference from multilocus genotype data. Mol. Ecol. Resour. 10, 551–555 (2010).
Gutiérrez-Rodríguez, J., Sánchez-Montes, G. & Martínez-Solano, Í. Effective to census population size ratios in two near threatened Mediterranean amphibians: Pleurodeles waltl and Pelobates cultripes. Conserv. Genet. 18, 1201–1211 (2017).
Pritchard, J. K., Stephens, M. & Donnelly, P. Inference of population structure using multilocus genotype data. Genetics 155, 945–949 (2000).
Falush, D., Stephens, M. & Pritchard, J. K. Inference of population structure using multilocus genotype data: Linked loci and correlated allele frequencies. Genetics 164, 1567–1587 (2003).
Kopelman, N. M., Mayzel, J., Jakobsson, M., Rosenberg, N. A. & Mayrose, I. CLUMPAK: A program for identifying clustering modes and packaging population structure inferences across K. Mol. Ecol. Resour. 15, 1179–1191 (2015).
Evanno, G., Regnaut, S. & Goudet, J. Detecting the number of clusters of individuals using the software STRUCTURE: A simulation study. Mol. Ecol. 14, 2611–2620 (2005).
Earl, D. A. & VonHoldt, B. M. Structure harvester: A website and program for visualizing STRUCTURE output and implementing the Evanno method. Conserv. Genet. Resour. 4, 359–361 (2012).
Sih, A. et al. Predator-prey naivete, antipredator behaviour, and the ecology of predator invasions. Oikos 119, 610–621 (2010).
Ferrari, M. C. O. & Chivers, D. P. Sophisticated early life lessons: Threat-sensitive generalization of predator recognition by embryonic amphibians. Behav. Ecol. 20, 1295–1298 (2009).
Ferrari, M. C. O., Brown, G. E., Messier, F. & Chivers, D. P. Threat-sensitive generalization of predator recognition by larval amphibians. Behav. Ecol. Sociobiol. 63, 1369–1375 (2009).
Ferrari, M. C. O., Crane, A. L. & Chivers, D. P. Certainty and the cognitive ecology of generalization of predator recognition. Anim. Behav. 111, 207–211 (2016).
Alcorlo, P. & Diéguez-Uribeondo, J. E. cangrejo señal y el declive de las poblaciones de cangrejo autóctono. Ambienta 109, 52–61 (2014).
Martín-Torrijos, L., Kokko, H., Makkonen, J., Jussila, J. & Diéguez-Uribeondo, J. Mapping 15 years of crayfish plague in the Iberian Peninsula, the impact of two invasive species on the endangered native crayfish. PLoS ONE 14, e0219223 (2019).
Torre, M. & Rodríguez, P. E. Cangrejo de río en España (Ministerio de Agricultura, Servicio Nacional de Pesca Fluvial y Caza, 1964).
Dupuch, A., Magnan, P. & Dill, L. M. Sensitivity of northern redbelly dace, Phoxinus eos, to chemical alarm cues. Can. J. Zool. 82, 407–415 (2004).
Ferrari, M. C. O., Trowell, J. J., Brown, G. E. & Chivers, D. P. The role of learning in the development of threat-sensitive predator avoidance in fathead minnows. Anim. Behav. 70, 777–784 (2005).
Ferrari, M. C. O., Kapitania-Kwok, T. & Chivers, D. P. The role of learning in the development of threat-sensitive predator avoidance: The use of predator cue concentration by fathead minnows. Behav. Ecol. Sociobiol. 60, 522–527 (2006).
Kesavaraju, B., Damal, K. & Juliano, S. A. Threat-sensitive behavioural responses to concentrations of water-borne cues from predation. Ethology 113, 199–206 (2007).
Snell-Rood, E. C. & Steck, M. K. Behaviour shapes environmental variation and selection on learning and plasticity: Review of mechanisms and implications. Anim. Behav. 147, 147–156 (2019).
Godfrey-Smith, P. Environmental complexity and the evolution of cognition. In The Evolution of Intelligence (eds Sternberg, R. & Kaufman, J.) 233–249 (Lawrence Erlbaum, 2002).
Acknowledgements
We thank the editor and two anonymous reviewers for helpful comments. C. Díaz-Paniagua and Í. Martínez-Solano helped in selecting the study populations. Í. Martínez-Solano, G. Sánchez-Montes and A. Piriz provided useful advice on genetic analyses. V. Castaño, L. Hyeun-Ji, L. Asencio, A. Trillo and G. Jiménez helped with field work and animal husbandry. Laboratory facilities were provided by ICTS-RBD. Casa del Infantado allowed free access to one of the Madrid populations located in private land. Experiments were carried out in accordance with all current European directives and Spanish laws, and under permission of the Consejerías de Medio Ambiente from Comunidad de Madrid and Junta de Andalucía. Procedures conformed to the recommended guidelines for use of live amphibians and reptiles in laboratory research. All experimental protocols were approved by the ‘Comité de Ética de Experimentación Animal CEEA-EBD’. Financial support was provided by the Spanish Ministry of Science and Innovation (MICINN), Grants CGL2015-68670-R and PID2020-119517GB-I00. CC-D acknowledges the Comunidad de Madrid/European Social Fund for the predoctoral contract PEJD-2019-PRE/AMB-14950 funded by the Youth Employment Initiative (YEI).
Author information
Authors and Affiliations
Contributions
N.P–C. and I.G-M. conceived the ideas and designed the study. R.A. and N.P–C. performed the behavioral experiments and collected the tissue samples. N.P–C. analyzed the behavioral data and R.A. and C.C-D. analyzed the genetic data. All authors discussed the analyses. N.P–C. wrote the original draft and all authors reviewed and edited the last version of the manuscript.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Polo-Cavia, N., Arribas, R., Caballero-Díaz, C. et al. Widespread learned predator recognition to an alien predator across populations in an amphibian species. Sci Rep 13, 14599 (2023). https://doi.org/10.1038/s41598-023-41624-1
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41598-023-41624-1
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.
