Abstract
Viviparous sea snakes are the most rapidly speciating reptiles known, yet the ecological factors underlying this radiation are poorly understood. Here, we reconstructed dated trees for 75% of sea snake species and quantified body shape (forebody relative to hindbody girth), maximum body length and trophic diversity to examine how dietary specialization has influenced morphological diversification in this rapid radiation. We show that sea snake body shape and size are strongly correlated with the proportion of burrowing prey in the diet. Specialist predators of burrowing eels have convergently evolved a ‘microcephalic’ morphotype with dramatically reduced forebody relative to hindbody girth and intermediate body length. By comparison, snakes that predominantly feed on burrowing gobies are generally short-bodied and small-headed, but there is no evidence of convergent evolution. The eel specialists also exhibit faster rates of size and shape evolution compared to all other sea snakes, including those that feed on gobies. Our results suggest that trophic specialization to particular burrowing prey (eels) has invoked strong selective pressures that manifest as predictable and rapid morphological changes. Further studies are needed to examine the genetic and developmental mechanisms underlying these dramatic morphological changes and assess their role in sea snake speciation.
Highlights
Speciating groups are found throughout the tree of life and have provided important insights into the mechanisms shaping biodiversity (e.g. [1])
Strong support was found for all primary clades, including reciprocal monophyly of the Aipysurus and Hydrophis groups 5, the placement of Ephalophis + Parahydrophis and Hydrelaps as successive sister lineages to the Hydrophis group, the relatively distant sister relationship between Microcephalophis gracilis and Hydrophis, and the H. ornatus and H. cyanocinctus groups
We find that trophic specialization has strongly influenced sea snake body shape and, to lesser extent, body size
Summary
Speciating groups are found throughout the tree of life and have provided important insights into the mechanisms shaping biodiversity (e.g. [1]). Speciating groups are found throughout the tree of life and have provided important insights into the mechanisms shaping biodiversity Approaches to explaining the disparity in clade speciation rates often focus on morphological diversification: divergent selection on ecologically relevant traits, 2018 The Authors. Key morphological traits implicated in species radiations often show accelerated rates of evolution and highly replicate (convergent or parallel) origins in response to ecological opportunity We investigated the tempo and mode of body size and shape evolution in relation to trophic diversity in the most rapidly speciating reptiles known—the viviparous sea snakes (Hydrophiinae)
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