Evidências morfológicas sustentam divergência evolutiva mediada por alagamento sazonal de florestas na Amazônia

Abstract

Spatial variation in morphological traits emerges in response to different selective pressures experienced when geographic range crosses heterogeneous habitats. In seasonally flooded habitats, animal adaptation is conspicuously demonstrated by the ability to swim among tops of hills that form islands during flooding, or by the ability to climb treetops above the water level. We have noticed that a widely distributed terrestrial snake is forced to climb treetops in flooded várzea forests of eastern Amazonia. We hypothesized that seasonal flooding of habitats selects morphotypes by the levels of adaptation to use treetops as foraging and resting sites. We measured seven morphological variables on 30 Bothrops atrox specimens from floodable várzea forests, and 25 specimens from non-floodable terra firme forests. Models of Discriminant Analysis of Principal Components (DAPC) separately by sex showed morphological differences between these habitat types, which were independent of geographic distance. We found longer tail and wider head in females and lower head and slender body in males from the várzea forests sampled. Despite sex-biased divergences in selected morphological traits, our results converge to natural selection toward arboreality in seasonally flooded habitats. We ultimately show an intermediary stage of evolutionary divergence, although speciation is not clear as in island-isolated populations.