Abstract
Population differentiation and diversification depend in large part on the ability and propensity of organisms to successfully disperse. However, our understanding of these processes in organisms with high dispersal ability is biased by the limited genetic resolution offered by traditional genotypic markers. Many neustonic animals disperse not only as pelagic larvae, but also as juveniles and adults while drifting or rafting at the surface of the open ocean. In theory, the heightened dispersal ability of these animals should limit opportunities for species diversification and population differentiation. To test these predictions, we used next‐generation sequencing of genomewide restriction‐site‐associated DNA tags (RADseq) and traditional mitochondrial DNA sequencing, to investigate the species‐level relationships and global population structure of Planes crabs collected from oceanic flotsam and sea turtles. Our results indicate that species diversity in this clade is low—likely three closely related species—with no evidence of cryptic or undescribed species. Moreover, our results indicate weak population differentiation among widely separated aggregations with genetic indices showing only subtle genetic discontinuities across all oceans of the world (RADseq F ST = 0.08–0.16). The results of this study provide unprecedented resolution of the systematics and global biogeography of this group and contribute valuable information to our understanding of how theoretical dispersal potential relates to actual population differentiation and diversification among marine organisms. Moreover, these results demonstrate the limitations of single gene analyses and the value of genomic‐level resolution for estimating contemporary population structure in organisms with large, highly connected populations.
Highlights
Population differentiation and diversification depend in large part on the ability and propensity of organisms to success‐ fully disperse (Palumbi, 1994, 2003 )
For Planes, the ability to disperse as pelagic larvae and as adults associated with oceanic flotsam and sea turtles should facilitate transoceanic ge‐ netic exchange, limiting both species diversity within this group of crabs and intraspecific genetic differentiation among widely sepa‐ rated populations
A major challenge in phylogeography is predicting the role that dis‐ persal mode plays in shaping population structure and species diversification (Palumbi, 1994, 2003 )
Summary
Population differentiation and diversification depend in large part on the ability and propensity of organisms to success‐ fully disperse (Palumbi, 1994, 2003 ). For Planes, the ability to disperse as pelagic larvae and as adults associated with oceanic flotsam and sea turtles should facilitate transoceanic ge‐ netic exchange, limiting both species diversity within this group of crabs and intraspecific genetic differentiation among widely sepa‐ rated populations. To test this hypothesis, we conducted an analysis of the global species diversity and population‐level differentiation using ‐generation sequencing of genomewide restriction‐site‐ associated DNA tags (RADseq) and traditional mitochondrial DNA (mtDNA) sequencing, to address three main questions. At the spe‐ cies level: (a) Is species diversity low with no evidence of cryptic spe‐ cies? At the population level: (b) Is population differentiation weak among widely separated aggregations? (c) If genetic discontinuities exist, where are there biogeographic corridors and barriers to rafting dispersal at a global scale?
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