Limited population genetic structure in the littoral gastropod Nerita tessellata (Neritimorpha, Neritidae) suggests high dispersal across the Caribbean Sea

Abstract

The Caribbean Sea is characterized by an incredible biodiversity, including several endemic mollusk species, most of which have larval dispersal as their main mechanism of gene flow. It is known that the present-day population structure of a species reflects the combination of oceanographic currents, life-history traits, and historical events. Nerita tessellata is a common gastropod species in coastal, rocky, and exposed shores across the Caribbean Sea; however, little is known about the mechanisms that have shaped its distribution. Here, we tested potential barriers to gene flow and the associated genetic structure of N. tessellata in 12 populations across the Caribbean using digest restriction-site associated DNA sequencing (ddRAD-seq). Likewise, we evaluated demographic history and migration patterns through two coalescence approaches using Approximate Bayesian Computation (ABC) combined with supervised machine learning. The global analysis, based on 26,421 single nucleotide polymorphism (SNP) markers derived from ddRAD-seq, revealed low nucleotide diversity with high levels of gene flow and a lack of significant population differentiation within the survey area, indicating that N. tessellata is panmictic across the Caribbean Sea. Our results reveal that a pattern of north to south movement along Caribbean currents could potentially explain the limited genetic structure and high gene flow among N. tessellata populations. The scenarios simulated with ABC showed a constant effective population size for the ancestral population. Additionally, the four populations tested experienced demographic expansions that date to the Pleistocene. An extended pelagic larval stage could explain the large-scale genetic uniformity of this species across its distribution. Our findings contribute to understanding genetic diversity and population structure in a common gastropod within the Caribbean Sea.