Abstract
Pleurobranchaea maculata is a rarely studied species of the Heterobranchia found throughout the south and western Pacific–and recently recorded in Argentina–whose population genetic structure is unknown. Interest in the species was sparked in New Zealand following a series of dog deaths caused by ingestions of slugs containing high levels of the neurotoxin tetrodotoxin. Here we describe the genetic structure and demographic history of P. maculata populations from five principle locations in New Zealand based on extensive analyses of 12 microsatellite loci and the COI and CytB regions of mitochondrial DNA (mtDNA). Microsatellite data showed significant differentiation between northern and southern populations with population structure being associated with previously described regional variations in tetrodotoxin concentrations. However, mtDNA sequence data did not support such structure, revealing a star-shaped haplotype network with estimates of expansion time suggesting a population expansion in the Pleistocene era. Inclusion of publicly available mtDNA sequence sea slugs from Argentina did not alter the star-shaped network. We interpret our data as indicative of a single founding population that fragmented following geographical changes that brought about the present day north-south divide in New Zealand waters. Lack of evidence of cryptic species supports data indicating that differences in toxicity of individuals among regions are a consequence of differences in diet.
Highlights
The grey side-gilled sea slug (Pleurobranchaea maculata) is an opportunistic carnivore that feeds on invertebrates including sea anemones, marine worms and other molluscs [1] and on algae [2]
18 slugs were obtained from WL of which eight randomly chosen individuals were subject to TTX assay
We observed marked signals of population structure; the population structure suggested by microsatellite versus mitochondrial DNA (mtDNA) data differed
Summary
The grey side-gilled sea slug (Pleurobranchaea maculata) is an opportunistic carnivore that feeds on invertebrates including sea anemones, marine worms and other molluscs [1] and on algae [2]. Japan where it is found in habitats ranging from sandy sediments to rocky reefs, and from shallow sub-tidal flats to depths of 300 m [1, 3]. In late 2009 this otherwise little-known sea slug attracted attention after it was implicated in dog deaths on beaches in Auckland [5]. Analyses of vomit and gastrointestinal contents revealed that deaths were a consequence of tetrodotoxin (TTX) poisoning associated with ingestion of P. maculata [5]. This was the first time that TTX had been reported in NZ and in a species of the taxonomic clade Heterobranchia [5]. P. maculata that have recently invaded coastal waters of Argentina contain TTX [6, 7]
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