Abstract
Tripneustes is one of the most abundant and ecologically significant tropical echinoids. Highly valued for its gonads, wild populations of Tripneustes are commercially exploited and cultivated stocks are a prime target for the fisheries and aquaculture industry. Here we examine Tripneustes from the Kermadec Islands, a remote chain of volcanic islands in the southwest Pacific Ocean that mark the boundary of the genus’ range, by combining morphological and genetic analyses, using two mitochondrial (COI and the Control Region), and one nuclear (bindin) marker. We show that Kermadec Tripneustes is a new species of Tripneustes. We provide a full description of this species and present an updated phylogeny of the genus. This new species, Tripneustes kermadecensis n. sp., is characterized by having ambulacral primary tubercles occurring on every fourth plate ambitally, flattened test with large peristome, one to two occluded plates for every four ambulacral plates, and complete primary series of interambulacral tubercles from peristome to apex. It appears to have split early from the main Tripneustes stock, predating even the split of the Atlantic Tripneustes lineage. Its distinction from the common T. gratilla and potential vulnerability as an isolated endemic species calls for special attention in terms of conservation.
Highlights
The upsurge of molecular genetic data being generated over the past two decades has facilitated major advances in our understanding of speciation and biogeography across the tree of life
Considering the large morphological variability observed for Tripneustes across its vast range, it seems probable that the genus may contain additional highly localized endemic species, around the periphery of its range
T. gratilla gratilla from the Indian Ocean and the Coral Triangle shows strikingly different color and spine posture patterns in addition to differing corona shape and ambulacral tuberculation. Based on their morphological characters (Table 1), Tripneustes from the Kermadec Islands clearly belong to a novel, yet undescribed species
Summary
The upsurge of molecular genetic data being generated over the past two decades has facilitated major advances in our understanding of speciation and biogeography across the tree of life. Apart from its role as an ecological keystone species in many tropical regions[7], T. gratilla is unique in being one of the most commercially valued echinoid species to date and is a prime target for the fisheries and aquaculture industry[8] In some localities, such as Oahu Island in Hawaii, T. gratilla are being propagated as agents of environmental control to regulate the expansion of invasive alien seaweeds (http://dlnr.hawaii.gov/ais/invasivealgae/urchn-hatchery). A recent study, combining molecular genetics (mitochondrial and nuclear DNA sequences), morphological, fossil, and ecological evidence demonstrated that the Red Sea (RS) Tripneustes is a distinct clade, endemic to the RS13. This clade was likely formed at a time when gene flow between the RS Tripneustes and the wider Indian Ocean population was constricted. Several endemic fishes and marine invertebrates have been described[14], the majority of shallow reef marine species found at the Kermadec Islands have broader New Zealand, Australasian, and even Indo-Pacific wide distributions[14,15,16]
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