Cryptic speciation in pan-tropical sea urchins: a case study of an edge-of-range population of Tripneustes from the Kermadec Islands

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.

Mind the gap! The mitochondrial control region and its power as a phylogenetic marker in echinoids

“…Apart from the general advantages of mitochondrial markers in animal phylogenetic studies, namely their maternal inheritance, lack of recombination, and fast rate of evolution [ 9 , 10 ], several unique qualities make the CR a favoured marker sequence for genetic diversity analyses, in particular, its exceptionally fast evolutionary rate (even in comparison to the rest of the mitochondrial genome [ 11 , 12 ]), polymorphic nature [ 13 ] and presumed selective neutrality as a non-coding region (but see [ 14 , 15 ]). Consequently, this region has been widely used as a genetic marker in phylogenetic studies of various animals including vertebrate classes such as fish (e.g., [ 16 , 17 ]), amphibians [ 18 ], reptiles [ 19 ], birds [ 20 ] and mammals [ 21 , 22 ] as well as numerous invertebrate taxa (e.g., [ 23 – 26 ]. Nevertheless, despite being extremely useful for some species, several factors may hinder the utility of this marker in others.…”

Genetic Diversity and Connectivity of Sea Urchin Tripneustes gratilla in Region Surrounding Cenderawasih Bay, Papua-Indonesia and Indo-Pacific

“…Tridacna maxima (Nuryanto and Kochzius 2009), T. crocea and T. maxima (DeBoer et al 2014), Haptosquilla pulchella (Barber et al 2002). Liggin et al (2014) determined 23 haplotypes of COI gene of T. gratilla from Kermadec Island (Southwest Pacific), now this species under the name Tripneustes kermadecensis (Bronstein et al 2017). The analyzing of 82 COI gene fragment sequences of T. gratilla from 11 locations in Indo-Pacific accessed from the GenBank data (Lessios et al 2003) resulted in 34 haplotypes.…”

Hidden in plain sight: Tripneustes kermadecensis (Echinodermata: Echinoidea) is a junior synonym of the eastern Australian sea urchin Evechinus australiae described in 1878

“…31052). These sequences were complemented with publicly available data from the original description of T. kermadecensis and T. g. elatensis (Bronstein et al 2016, 2017, 2019). We subsequently created a COI dataset with these 69 sequences and our nine novel sequences, including the Evechinus australiae material.…”

“…The misidentification of the Tripneustes species in NSW highlights a knowledge gap in our understanding of the biology and ecology of these species in Australia. Tripneustes kermadecensis was first identified as a distinct species by morphological and molecular genetic analysis of specimens from the Kermadec Islands, New Zealand (Bronstein et al 2017). Subsequently, T. kermadecensis was confirmed to be the species that also commonly occurs in the subtropical and temperate regions of NSW, locally as the ‘lamington urchin’ (Bronstein et al 2017, 2019).…”