Constraints on reproductive investment: a comparison between aquatic and terrestrial snakes

Abstract

Biomechanical models suggest that reproductive investment in aquatic snakes may be constrained by the important locomotory role of the posterior part of the body during swimming: carying eggs or offspring in this region would more seriously impair locomotory efficiency in swimming than in terrestrial lateral undulation. If this constraint is important, aquatic snakes would be expected to have lower clutch masses relative to body mass than terrestrial species and to carry the clutch in a more anterior position. Comparisons between aquatic and terrestrial snakes of several families confirm predictions. Phylogenetic analysis suggests that his pattern of reduced reproductive investment has evolved independently in each of the 4 ophidian lineages that contain marine species (acrochordids, homalopsine colubrids, laticaudid sea snakes, and hydrophiid sea snakes). Although if thus seems likely that these patterns represent adaptations to aquatic versus terrestrial life, the nature of the selective forces involved remains speculative. The hypothesis based on locomotory impairment of gravid females has better empirical support than any alternative hypothesis, as it successfully predicts modifications in the position of the clutch within the female's body, as well as overall reduced reproductive investment. -from Author