Low Spatial Genetic Differentiation Associated with Rapid Recolonization in the New Zealand Fur SealArctocephalus forsteri

Abstract

Population declines resulting from anthropogenic activities are of major consequence for the long-term survival of species because the resulting loss of genetic diversity can lead to extinction via the effects of inbreeding depression, fixation of deleterious mutations, and loss of adaptive potential. Otariid pinnipeds have been exploited commercially to near extinction with some species showing higher demographic resilience and recolonization potential than others. The New Zealand fur seal (NZFS) was heavily impacted by commercial sealing between the late 18th and early 19th centuries, but has recolonized its former range in southern Australia. The species has also recolonized its former range in New Zealand, yet little is known about the pattern of recolonization. Here, we first used 11 microsatellite markers (n = 383) to investigate the contemporary population structure and dispersal patterns in the NZFS (Arctocephalus forsteri). Secondly, we model postsealing recolonization with 1 additional mtDNA cytochrome b (n = 261) marker. Our data identified 3 genetic clusters: an Australian, a subantarctic, and a New Zealand one, with a weak and probably transient subdivision within the latter cluster. Demographic history scenarios supported a recolonization of the New Zealand coastline from remote west coast colonies, which is consistent with contemporary gene flow and with the species' high resilience. The present data suggest the management of distinct genetic units in the North and South of New Zealand along a genetic gradient. Assignment of individuals to their colony of origin was limited (32%) with the present data indicating the current microsatellite markers are unlikely sufficient to assign fisheries bycatch of NZFSs to colonies.

Reduced representation sequencing detects only subtle regional structure in a heavily exploited and rapidly recolonizing marine mammal species

“…For our analyses of population structure, we evaluated genetic variation at the colony and genetic cluster levels. Three main clusters were defined based on previous NZFS genetic studies (Dussex et al., ; Salis et al., ) as well as the results presented here: NZ‐North‐West (OBI: Open Bay Island; CF: Cape Foulwind; WP: Wekakura Point), NZ‐North‐East (CP: Cape Palliser; OP: Ohau Point), previously identified as a zone of admixture (Dussex et al., ) and NZ‐South (East Coast to south coast colonies; HB: Horseshoe Bay; VB: Victory Beach; NP: Nugget Point) (Figure ).…”

“…We then tested for correlations between estimates of H e and F ST derived from microsatellite loci by Dussex et al. () and the biallelic SNPs genotyped here. For H e , we calculated the Pearson correlation coefficient (“cor.test” in R; R Development Core Team ) and for F ST , we used a Mantel test for matrix correspondence for correlation (“mantel.rtest” in R; R Development Core Team ).…”

“…Here, we did not attempt to reiterate the demographic model comparisons described in these studies, but rather to estimate demographic parameters based on SNP data for the most likely scenarios inferred in these studies. We thus designed a scenarios including a Polynesian‐induced decline (~500–1,000 years ago; Emami‐Khoyi et al., ), and a European‐induced decline (~125–250 years ago; Dussex et al., ) followed by range‐wide recolonization from a single refugium and subsequent population divergence with a NZ‐North (OBI, CF, WK, CP, OP) and NZ‐South cluster (HB,VB,NP) (Dussex et al., ; Salis et al., ) (Supporting Information Figure , Table ). We also designed a null model of constant effective population size though time followed by the same population divergence.…”

“…The dashed line represents the genetic clusters based on Dussex et al. () and Salis et al. () microsatellite and mt DNA results, and the dotted line represents the approximate limit of the admixture zone between the two main clusters.…”

“…() microsatellite and mt DNA results, and the dotted line represents the approximate limit of the admixture zone between the two main clusters. Arrows depict the post‐sealing recolonization scenario from hypothetical south‐western South Island refugia depicted with a star inferred by ABC analyses (Dussex et al., ; this study) [Colour figure can be viewed at wileyonlinelibrary.com]…”