Meeting Abstract
26.3 Jan. 5 Ecomorphological diversification among snake populations on the Izu islands VINCENT, S.E.*; HASEGAWA, M.; MORI, A.; Stony Brook University ; Toho University; Kyoto University svincent@ethol.zool.kyoto-u.ac.jp
A recent review showed that insular snake body sizes are bimodal in their distribution, with giants evolving on islands with large prey sizes and dwarfs on islands with small prey sizes. Nonetheless, body size itself plays no direct role during ingestion in gape-limited snakes, and exhibits a strong plastic response to the amount of food consumed over ontogeny. Thus, the adaptive nature of these insular snake body size trends remains largely unclear. To address this issue, I first compared the relationships between maximum head and body size and consumed prey size among three insular populations of a dietary generalist snake (Elaphe quadrivirgata) from the Izu Islands off the central coast of Japan. I predicted that due to the markedly different prey fauna amongst islands, maximum head dimensions of adult snakes would closely match consumed prey size. A multivariate analysis of size revealed that adult snakes on Tadanae-jima have evolved gigantic head and body sizes compared to adult snakes from from Kozu-shima and Nii-jima. Coupled with this morphological divergence, Tadanae-jima adult snakes primarily consume large nestling seabird prey and seabird eggs, whereas Kozu-shima and Nii-jima adult snakes primarily consume smaller lizard prey. To test for environmental versus genetic effects, I compared head and body dimensions among hatchling snakes from these three islands born under standardized laboratory conditions. Hatchling data revealed a significant genotype-environment interaction for both head width and snout-vent length. Specifically, Tadanae-jima snakes are born with wider heads and larger body sizes, and their heads and bodies grow faster than other populations as well. This study further supports the hypothesis that head width has been a major axis of diversification among gape-limited snakes.
