Dispersal Patterns and Processes in Littorinid Snails along the Indian Coastline

Abstract

Dispersal has important ecological and evolutionary consequences for a species. Marine dispersal is unique because of facilitation by ocean currents, where oceanography interacts with species traits and environmental heterogeneity to determine connectivity between populations. However, marine dispersal research has largely focussed on coral reefs and temperate shores, while tropical coastlines remain poorly studied. To address this gap in knowledge, we studied dispersal patterns and processes along the Indian coastline using two genera of intertidal littorinid snails (Littoraria and Echinolittorina) as a model system. We used a comparative framework to study the influence of species traits on patterns of mitochondrial phylogeography and deduced environmental correlates of range using species distribution models. We also performed larval dispersal simulations to derive estimates of coastal connectivity. We found that all species showed signatures of demographic expansion in the Pleistocene, and only two species with wide environmental tolerance showed population genetic structure. Gradients in sea surface salinity and tidal range along the coastline were important in predicting distribution patterns across species and scales. There were seasonal differences in oceanic connectivity patterns, where certain sections remained isolated from the rest of the coastline. Regions predicted to have poor connectivity overlapped with observed species turnover for a range of marine taxa. These multiple lines of evidence suggest that variation in environment and oceanographic connectivity can influence dispersal patterns along tropical coastlines. This study presents hypotheses related to species-environment relationships and population genetic connectivity, which can be tested in other taxa to arrive at a unified framework of coastal biogeography for this region