Genomic and morphological evidence of distinct populations in the endemic common (weedy) seadragon Phyllopteryx taeniolatus (Syngnathidae) along the east coast of Australia.

O Selma Klanten,David J Booth,Samuel Greaves,Rob Mckinnon,Michelle R Gaither,Kristine O’Keeffe,Kade Mills,John Turnbull,Tzen-Yuh Chiang

doi:10.1371/journal.pone.0243446

Abstract

The common or weedy seadragon, Phyllopteryx taeniolatus, is an iconic and endemic fish found across temperate reefs of southern Australia. Despite its charismatic nature, few studies have been published, and the extent of population sub-structuring remains poorly resolved. Here we used 7462 single nucleotide polymorphisms (SNPs) to identify the extent of population structure in the weedy seadragon along the temperate southeast coast of Australia. We identified four populations, with strong genetic structure (FST = 0.562) between them. Both Discriminant Analysis of Principle Components (DAPC) and Bayesian clustering analyses support four distinct genetic clusters (north to south: central New South Wales, southern NSW, Victoria and Tasmania). In addition to these genetic differences, geographical variation in external morphology was recorded, with individuals from New South Wales shaped differently for a few measurements to those from the Mornington Peninsula (Victoria). We posit that these genetic and morphological differences suggest that the Victorian population of P. taeniolatus was historically isolated by the Bassian Isthmus during the last glacial maximum and should now be considered at least a distinct population. We also recorded high levels of genetic structure among the other locations. Based on the genomic and to a degree morphological evidence presented in this study, we recommend that the Victorian population be managed separately from the eastern populations (New South Wales and Tasmania).

Highlights

Marine fishes often inhabit wide geographic ranges, have large populations with high genetic diversity, and display low levels of genetic structuring due to high larval dispersal capacity [1,2,3,4,5]
Our results report a high degree of genetic separation similar to that found in a study based on just two mtDNA loci [29], which reported some shared haplotypes of seadragon populations between New South Wales (NSW) and Tasmania
Combining genomics and morphological data, we demonstrate that weedy seadragon populations are highly structured along the southeast coast of Australia

Summary

Introduction

Marine fishes often inhabit wide geographic ranges, have large populations with high genetic diversity, and display low levels of genetic structuring due to high larval dispersal capacity [1,2,3,4,5]. Conservation and management of these fish resources is often based on the assumption that population connectivity over large geographic scales confers some level of resilience even in the face of anthropogenic stressors. Under this logic, endemic species with restricted ranges, smaller population sizes, and lower genetic diversity [6] face increased extinction risk due to environmental stressors such as habitat loss and climate change [7, 8]. The family Syngnathidae are a unique group of fishes found in temperate and tropical oceans around the world and includes 321 species of seahorses, pipefishes, and seadragons [17, 18]. The weedy seadragon’s status on the IUCN Red List was changed in 2017 from “Near Threatened” (NT) to “Least Concern” (LC) but their population trend is still considered as “Decreasing” (https://www.iucnredlist.org/species/17177/67624517)

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Discussion

Conclusion