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Rapid morphological change of a top predator with the invasion of a novel prey


Invasive exotic species are spreading rapidly throughout the planet. These species can have widespread impacts on biodiversity, yet the ability for native species, particularly long-lived vertebrates, to respond rapidly to invasions remains mostly unknown. Here we provide evidence of rapid morphological change in the endangered snail kite (Rostrhamus sociabilis) across its North American range with the invasion of a novel prey, the island apple snail (Pomacea maculata), a much larger congener of the kite’s native prey. In less than one decade since invasion, snail kite bill size and body mass increased substantially. Larger bills should be better suited to extracting meat from the larger snail shells, and we detected strong selection on increased size through juvenile survival. Using pedigree data, we found evidence of both genetic and environmental influences on trait expression and discovered that additive genetic variation in bill size increased with invasion. However, trends in predicted breeding values emphasize that recent morphological changes have been driven primarily by phenotypic plasticity rather than micro-evolutionary change. Our findings suggest that evolutionary change may be imminent and underscore that even long-lived vertebrates can respond quickly to invasive species. Furthermore, these results highlight that phenotypic plasticity may provide a crucial role for predators experiencing rapid environmental change.

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We thank J. Orrock, B. Reichert, E. Robertson and M. Morrissey for providing comments on earlier versions of this manuscript. This project was funded by USGS’s Greater Everglades Priority Ecosystems Science (GEPES), the US Army Corps of Engineers, and US Fish and Wildlife Service.

Author information

C.E.C. conducted the study; C.E.C., R.J.F., R.T.K. and C.W.M. analysed data; C.E.C. and R.J.F. wrote the initial manuscript; C.E.C., R.J.F., R.T.K., C.W.M. and W.M.K. edited the manuscript; W.M.K. and R.J.F. secured funding.

Competing interests

The authors declare no competing financial interests.

Correspondence to Robert J. Fletcher Jr.

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Further reading

Fig. 1: The endangered snail kite, its novel prey and the invasion across the kite’s geographic range.
Fig. 2: Rapid change in morphology, but not predicted breeding values, of fledgling snail kites with the invasion of P. maculata.
Fig. 3: Snail kites with large bills and larger mass were more likely to survive the first year of life since the invasion of P. maculata.
Fig. 4: Variance components of morphology of snail kites in invaded and uninvaded wetlands suggest cryptic genetic variation for morphology.