A Matter of Scale: Population Genomic Structure and Connectivity of Fisheries At-Risk Common Dolphins (Delphinus delphis) From Australasia

Andrea Barceló,Nikki Zanardo,Karen A Stockin,Kerstin Bilgmann,Krista Hupman,Gabriela Tezanos-Pinto,Jonathan Sandoval-Castillo,Isabella M Reeves,Emma L Betty,Guido J Parra,Luciana M Möller,Catherine R M Attard,Luciano B Beheregaray

doi:10.3389/fmars.2021.616673

Abstract

An understanding of population structure and connectivity at multiple spatial scales is required to assist wildlife conservation and management. This is particularly critical for widely distributed and highly mobile marine mammals subject to fisheries by-catch. Here, we present a population genomic assessment of a near-top predator, the common dolphin (Delphinus delphis), which is incidentally caught in multiple fisheries across the Australasian region. The study was carried out using 14,799 ddRAD sequenced genome-wide markers genotyped for 478 individuals sampled at multiple spatial scales across Australasia. A complex hierarchical metapopulation structure was identified, with three highly distinct and genetically diverse regional populations at large spatial scales (&gt;1,500 km). The populations inhabit the southern coast of Australia, the eastern coast of Australia, New Zealand, and Tasmania, with the latter also showing a considerable level of admixture to Australia's east coast. Each of these regional populations contained two to four nested local populations (i.e., subpopulations) at finer spatial scales, with most of the gene flow occurring within distances of 50 to 400 km. Estimates of contemporary migration rates between adjacent subpopulations ranged from 6 to 25%. Overall, our findings identified complex common dolphin population structure and connectivity across state and international jurisdictions, including migration and gene flow across the Tasman Sea. The results indicate that inter-jurisdictional collaboration is required to implement conservation management strategies and mitigate fisheries interactions of common dolphins across multiple spatial scales in the Australasian region.

Highlights

Genetic connectivity and the delineation of populations, including their boundaries, are fundamental issues in conservation biology, because such information can advise on the scale of which to conserve and manage wildlife species (Leslie and Morin, 2016; Taylor et al, 2017; Dunn et al, 2019; Pierre, 2019; Sousa et al, 2019; Taft et al, 2020; Tulloch et al, 2020)
Integrating genomic technology for answering these questions can inform about the dolphin populations and scale at which anthropogenic activities may impact upon them (e.g., Leslie and Morin, 2016)
This study revealed a hierarchical metapopulation structure for Australasian common dolphins, with high levels of genomewide diversity and negligible inbreeding among them

Summary

Introduction

Genetic connectivity and the delineation of populations, including their boundaries, are fundamental issues in conservation biology, because such information can advise on the scale of which to conserve and manage wildlife species (Leslie and Morin, 2016; Taylor et al, 2017; Dunn et al, 2019; Pierre, 2019; Sousa et al, 2019; Taft et al, 2020; Tulloch et al, 2020). There is still limited information about how geographic barriers and spatial scales impact on population genetic structure (Riginos et al, 2016). Population structure and the dispersal of marine species may be associated with a range of factors such as spatial distance, oceanographic features (e.g., currents, upwellings, environmental gradients) and ecological traits (e.g., feeding ecology and life history), making it difficult to disentangle these factors (Selkoe et al, 2016; Bernatchez et al, 2018), and establishing policies for conservation and management

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Results

Conclusion