Data from: Body size evolution on islands: are adult size variations in tiger snakes a non-adaptive consequence of selection on birth size?

Mean adult size has been used as the traditional measure of body size to explain trends of insular gigantism and dwarfism in a wide array of taxa. However, patterns of variation in body size at birth have received surprisingly little attention, leaving open the possibility that adult body-size differences are nonadaptive consequences of selection acting on neonate body size. Here I used an empirical and correlative approach to test this hypothesis in a mosaic of 12 island and mainland snake populations in Australia. Data collected on 597 adult and 1,084 neonate tiger snakes showed that (1) both adult and neonate mean body sizes varied strongly across populations; (2) prey diversity and size convincingly explained birth-size variations: birth size—notably, gape size—correlated with prey size; (3) neonate snout-vent length was significantly correlated with neonate gape size; and (4) neonate snout-vent length was significantly correlated with adult snout-vent length. Postnatal growth rates recorded under common-garden conditions differed across populations and were correlated with mean prey size. These data collectively suggest that (1) prey size is the main driver for the evolution of body size at birth in gape-limited predators, (2) adult size variations may reflect selective forces acting on earlier life stages, and (3) adult size variations may also reflect resource availability during ontogeny (notably, prey diversity).成年个体平均体型长期以来被视作身体大小的经典衡量指标，用于阐释众多类群（taxa）的岛屿巨型化（insular gigantism）与岛屿侏儒症（insular dwarfism）演化趋势。然而，新生个体身体大小的变异模式却极少受到学界关注，这使得“成年体型差异是选择作用于新生个体体型的非适应性演化结果”这一假说始终缺乏实证支撑。本研究采用经验分析与相关性分析相结合的方法，在澳大利亚12个岛屿与大陆蛇类种群构成的镶嵌分布样地中对该假说进行检验。针对597条成年虎蛇与1084条新生虎蛇的野外采集数据显示：（1）不同种群间的成年与新生个体平均体型均存在显著差异；（2）猎物多样性与猎物大小可有效解释新生体型的变异：新生体型——尤其是口裂大小（gape size）——与猎物大小显著相关；（3）新生个体吻肛长（snout-vent length）与新生个体口裂大小显著相关；（4）新生个体吻肛长与成年个体吻肛长显著相关。在同质园（common-garden）条件下测定的产后生长速率在不同种群间存在差异，且与平均猎物大小呈显著相关。综合上述数据，本研究得出以下结论：（1）对于口裂限制型捕食者（gape-limited predators）而言，猎物大小是新生个体体型演化的核心驱动因素；（2）成年体型的变异可能反映了作用于更早生活史阶段的选择压力；（3）成年体型的变异同时也可能反映个体发育（ontogeny）过程中的资源可获得性，尤其是猎物多样性。