Phenotypic variation contrasts with genetic homogeneity across scattered sea snake colonies
Résumé
Aim In philopatric species distributed across wide geographical areas, each
population is influenced by local factors. We assessed the expected spatial
genetic and phenotypic structure across a set of colonies of a highly philopatric
sea snake.
Location South Lagoon of New Caledonia, Western Pacific Ocean.
Methods We used body size (N = 4915 individuals) to assess phenotypic variations
across 11 islet colonies of the amphibious sea kraits (L. saintgironsi)
spread throughout the South Lagoon of New Caledonia. We also used 11
microsatellite markers in a subsample of 302 individuals to examine the demographic
history and genetic structure.
Results A major colonization event and rapid population expansion occurred
during the mid-Pleistocene. Mean body size increased significantly along the
north–south gradient investigated, suggesting that each colony is relatively
independent and responds to local conditions. However, our data revealed a
total lack of genetic structure despite a substantial genetic diversity.
Main conclusions A peculiar reproductive system likely underlies this pattern
that combines a marked phenotypic gradient with a lack of geographical
genetic structure. Gravid females from colonies scattered throughout the South
Lagoon converge towards few communal coastal nesting sites to lay their eggs.
Hatchlings disperse randomly in the lagoon and supply islets with recruits.
This process homogenizes the overall genetic structure. However, because when
settled snakes are philopatric, the mean body size of each colony presumably
reflects the influence of local conditions. This system resembles those documented
in various organisms (e.g. fish) but was not previously described in
any amniotic lineage.