Insights from genetic and demographic connectivity for the management of rays and skates

Pascal Lorance,Florianne Marandel,Verena M Trenkel,Grégory Charrier,Marco Andrello,Sabrina Le Cam,Sigrid Lehuta

doi:10.1139/cjfas-2017-0291

Abstract

Studying demographic and genetic connectivity can help assess marine metapopulation structure. Rays and skates have no larval phase; hence, population connectivity can only result from active movement of individuals. Using thornback ray (Raja clavata) in European waters as a case study, demographic and genetic connectivity were studied for 11 putative populations with unequal population abundances and two hypotheses of dispersal rates. Genetic simulation results highlighted three large metapopulations: in the Mediterranean, around the Azores, and on the Northeast Atlantic shelf. Demographic results highlighted a finer population structure indicating that several pairs of putative populations might be demographically linked. Results were highly sensitive to dispersal assumptions and relative population abundances, which provided insights into the potential magnitude of genetic and demographic connectivity differences. Accounting for demographic connectivity appears to be crucial for managing and conserving rays and skates, while genetic connectivity provides a longer-term perspective and less subtle spatial structures. Moreover, accounting for heterogeneity in population abundances is a key factor for determining or interpreting metapopulation connectivity.

Highlights

Population connectivity is a crucial parameter to take into account when defining population units relevant for management and conservation purposes (Stearns and Hoekstra 2005; Sinclair et al 2006; Schwartz et al 2007)
Local elasticity analysis identified the survival of stage 3 individuals (S3) as the parameter to which intrinsic population growth was the most reactive, while it was least reactive to the rate of fecundity increase from stage 3 to 4 (H3) (Fig.3a); similar results were obtained for the set of alternative parameter values and when varying parameter values by ±10%
Analyzing the elasticity and sensitivity of the intrinsic population growth rate in the Usher matrix model for a thornback ray-like species we found that it was most sensitive to the survival from egg laying to stage 1 (S0), followed by the survival of stages 1 and 2 (S1 and S2) and least sensitive to the maturation rate (H3), that is to the proportion of mature individuals moving to stage 4 with higher fecundity

Summary

Introduction

Population connectivity is a crucial parameter to take into account when defining population units relevant for management and conservation purposes (Stearns and Hoekstra 2005; Sinclair et al 2006; Schwartz et al 2007). Population units relevant for management purposes are commonly defined using ecological and genetic information. By reproducing in the population they joined, these individuals contribute to the local demography and transfer their genetic material into the gene pool, inducing gene flow among populations. A meta-population is a network of local populations where local populations are populations exchanging individuals but having somewhat independent dynamics (Levins 1969). Determining how many local or meta-populations exist and characterizing the relationships among them is a challenging task

Objectives

Methods

Results

Discussion

Conclusion