Conservation implications of significant population differentiation in an endangered estuarine seahorse
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The spatial distribution of a species’ genetic diversity can provide insights into underlying evolutionary, ecological and environmental processes, and can contribute information towards the delineation of conservation units. The Knysna seahorse, Hippocampus capensis, is endangered and occurs in only three estuaries on the warm-temperate south coast of South Africa: Knsyna, Keurbooms and Swartvlei. Population sizes in the latter two estuaries have been very small for a prolonged period of time, and the populations residing in them may thus benefit from translocations as a means of increasing population sizes and possibly also genetic diversity. However, information on whether these three estuaries constitute distinct conservation units that warrant separate management is presently lacking. Here, we used genetic information from mitochondrial (control region) and nuclear microsatellite loci to assess the genetic diversity and spatial structure across the three estuaries, and also whether translocations should be included in the management plan for the Knysna seahorse. Although each population had a unique combination of alleles, and clustering methods identified the Swartvlei Estuary as being distinct from the others, levels of genetic admixture were high, and there was no evidence for reciprocal monophyly that would indicate that each estuary has a unique demographic history. On these grounds, we suggest recognising the three populations as a single evolutionarily significant unit (ESU), and encourage translocations between them to ensure the species’ long-term survival.
KeywordsEvolutionarily significant units (ESU) Endangered estuarine fish Population differentiation Seahorse Hippocampus capensis South Africa
We are grateful to Louw Claassens (Knysna Basin Project), Zeen Weight, Fatima Daniels and Sophie Bader for assisting in the acquisition of samples from the Knysna and Keurbooms estuaries, and to an anonymous benefactor for providing free accommodation for the duration of the fieldwork. Sampling permits were granted by SANParks and CapeNature. This study received funding from the Rufford Foundation (small grant 14490-1 awarded to PR Teske), and from the University of Johannesburg (URC Grant). T. K. M. acknowledges the University of Johannesburg for awarding him a Global Excellence and Stature (GES) scholarship.
Compliance with ethical standards
Conflict of interest
The authors have declared no conflict of interest.
Ethical approval to collect genetic samples was granted by the Ethics Committee of the University of Johannesburg, South Africa. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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