Trophic specialization drives morphological evolution in sea snakes

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 smallheaded,
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.