Turning induced plasticity into refined adaptations during range expansion

Robustness against environmental fluctuations within an adaptive state should preclude exploration of new adaptive states when the environment changes. Here, we study transitions between adaptive associations of feather structure and carotenoid uptake to understand how robustness and evolvability can be reconciled. We show that feather modifications induced by unfamiliar carotenoids during a range expansion are repeatedly converted into precise coadaptations of feather development and carotenoid accommodation as populations persist in a region. We find that this conversion is underlain by a uniform and coordinated increase in the sensitivity of feather development to local carotenoid uptake, indicative of cooption and modification of the homeostatic mechanism that buffers feather growth in the evolution of new adaptations. Stress-buffering mechanisms are well placed to alternate between robustness and evolvability and we suggest that this is particularly evident in adaptations that require close integration between widely fluctuating external inputs and intricate internal structures.


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MRI-based neuroimaging
We evaluated structural transformation of feathers associated with uptake of 19 carotenoid compounds across study populations.
Male house finches were sampled for 3-5 feathers per three ornamental areas to provide sufficient substrate to extract carotenoids samples per ornament while not affecting the ornament of the bird. All captured males from 43 study populations were sampled and included in analyses (Supplementary Table 1 lists locations and sample sizes).
All captured males were sampled. For some analyses (Supplementary Table 1), data from study populations were combined into nine regions that shared the origin, general geographic location, and colonization route.
Field data were collected following identical field protocols in all populations, where data were recorded in both a hard copy and a digital copy. All feather structural analyses were conducted following an established protocol by a single observer, where data were uploaded continuously to a digital backup. HPLC and other biochemical analyses were conducted following established laboratory protocols by technicians working under the one supervisor, with data uploaded continuously to a digital backup. Data were collected a part of routine field work in long-term study populations and caused minimal disturbance to animals or habitats. Males were captured and released at permanent feeding stations maintained across study sites.