Historical translocations by M\u0101ori may explain the distribution and genetic structure of a threatened surf clam in Aotearoa (New Zealand)

Philip M Ross,James Williams,Huhana Smith,Matthew A Knox,Ian D Hogg,Shade Smith

doi:10.1038/s41598-018-35564-4

Abstract

The population genetic structure of toheroa (Paphies ventricosa), an Aotearoa (New Zealand) endemic surf clam, was assessed to determine levels of inter-population connectivity and test hypotheses regarding life history, habitat distribution and connectivity in coastal vs. estuarine taxa. Ninety-eight toheroa from populations across the length of New Zealand were sequenced for the mitochondrial cytochrome c oxidase I gene with analyses suggesting a population genetic structure unique among New Zealand marine invertebrates. Toheroa genetic diversity was high in Te Ika-a Māui (the North Island of New Zealand) but completely lacking in the south of Te Waipounamu (the South Island), an indication of recent isolation. Changes in habitat availability, long distance dispersal events or translocation of toheroa to southern New Zealand by Māori could explain the observed geographic distribution of toheroa and their genetic diversity. Given that early-Māori and their ancestors, were adept at food cultivation and relocation, the toheroa translocation hypothesis is plausible and may explain the disjointed modern distribution of this species. Translocation would also explain the limited success in restoring what may in some cases be ecologically isolated populations located outside their natural distributions and preferred niches.

Highlights

Dispersal and connectivity among populations of marine organisms are strongly influenced by a species’ life history characteristics[1]
Haplotype and nucleotide diversity was comparable across North Island populations with 12 haplotypes recorded for NMB/Ripiro and 10 at Waitarere (HD = 0.56, π = 0.0036)
This study provides support for the hypothesis that southern toheroa are isolated from toheroa in the North Island

Summary

Introduction

Dispersal and connectivity among populations of marine organisms are strongly influenced by a species’ life history characteristics[1]. Open-coast taxa are often better connected, through either larval or post-settlement dispersal, over similar geographic scales because their habitat is more continuous, allowing greater mixing among populations[12]. For species which occur under a relatively narrow range of environmental conditions, distances between populations may be great and inter-population dispersal rare[9,13]. One such open-coast organism that occurs in geographically discrete populations and is hypothesised to experience www.nature.com/scientificreports/. In contrast to other New Zealand bivalves, such as the surf clam Paphies subtriangulata (tuatua) or the estuarine clam Paphies australis (pipi), toheroa appear to have habitat requirements that limit their geographic distribution[17]. Despite having been protected for over 40 years, toheroa populations nationwide have, for unknown reasons, failed to recover, with some populations continuing to decline[14]

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