Gradients of genetic diversity and differentiation across the distribution range of a Mediterranean coral: Patterns, processes and conservation implications

José Templado,Mathilde Horaud,Nathaniel Bensoussan,Cristina Linares,Agostinho Antunes,Jean‐Baptiste Ledoux,Jamila Ben Souissi,Annie Machordom,Paula López‐Sendino,Raouia Ghanem,Daniel Gómez‐Gras,Joaquim Garrabou,Raphaêl Leblois,Valèria Romero‐Soriano,Oscar Ocaña

doi:10.1111/ddi.13382

Abstract

AbstractAimHow historical and contemporary eco‐evolutionary processes shape the patterns of genetic diversity and differentiation across species’ distribution range remains an open question with strong conservation implications. Focusing on the orange stony coral, Astroides calycularis, we (a) characterized the pattern of neutral genetic diversity across the distribution range; (b) gave insights into the underlying processes; and (c) discussed conservation implications with emphasis on a national park located on a hotspot of genetic diversity.LocationSouth Mediterranean Sea and Zembra National Park.MethodsWe combined new data from 12 microsatellites in 13 populations located in the Centre and in the Western Periphery of the distribution range with a published dataset including 16 populations from the Western and Eastern Peripheries. We analysed the relationship among parameters of genetic diversity (He, Ar(g)) and structure (population‐specific FST) and two measures of geographic peripherality. We compared two estimators of pairwise genetic structure (GST, DEST) across the distribution range. The evolutionary and demographic history of the populations following the Last Glacial Maximum was reconstructed using approximate Bayesian computations and maximum‐likelihood analyses. We inferred the contemporary connectivity among populations from Zembra National Park and with the neighbouring area of Cap Bon.ResultsWe demonstrate a decrease in genetic diversity and an increase in genetic differentiation from the Centre to the Eastern and Western Peripheries of the distribution range. Populations from Zembra show the highest genetic diversity reported in the species. We identified a spillover effect towards Cap Bon.Main conclusionsThe patterns of genetic diversity and differentiation are most likely explained by “the postglacial range expansion hypothesis” rather than the “central–peripheral hypothesis.” Enforcement of conservation measures should be considered to protect this genetic diversity pattern, in particular when considering the low effective population size inferred at many sites.

Highlights

Genetic diversity is at the heart of populations’ resilience and evolutionary potential (Fisher, 1930)
We demonstrate a decrease in genetic diversity and an increase in genetic differentiation from the Centre to the Eastern and Western Peripheries of the distribution range
The “postglacial range expansion hypothesis” suggests that historical processes such as serial founder event recolonization following the Last Glacial Maximum (LGM 24–18,000 years ago; Lambeck & Purcell, 2005) shape negative genetic gradients from the source to the edge of the expansion range. This pattern is mainly driven by an increase in genetic drift along the axis of expansion due to contrasted demographic histories when comparing peripheral versus central populations

Summary

| INTRODUCTION

Genetic diversity is at the heart of populations’ resilience and evolutionary potential (Fisher, 1930). While these studies greatly improved our knowledge regarding the ecology of A. calycularis, they were mainly focused on populations located at the Eastern and Western Peripheries Whether those genetic patterns can be generalized to the Centre of the species range remains an open question with critical implication for the species’ conservation. We sampled and genotyped 13 populations from two parts (Centre vs Western Periphery) of A. calycularis’ distribution range Combining these data with the dataset of Casado-Amezúa et al (2012), which covered Western and Eastern range peripheries, we: i) characterized the spatial pattern of genetic diversity across the species’ distribution range; ii) reconstructed the species evolutionary and demographic history to test for the impact of historical processes on the observed pattern. | 5 implications of these results for the conservation of the species and for the management of the Zembra National Park

| METHODS

| DISCUSSION

Findings

| CONCLUSION