Haploniscus rostratus ( Menzies, 1962 )

Brix, Saskia, Riehl, Torben & Leese, Florian, 2011, First genetic data for species of the genus Haploniscus Richardson, 1908 (Isopoda: Asellota: Haploniscidae) from neighbouring deep-sea basins in the South Atlantic, Zootaxa 2838, pp. 79-84 : 81

Haploniscus rostratus ( Menzies, 1962)

The known distribution of H. rostratus is restricted to abyssal depths of 4577–5647 m, geographically extending from the southern part of the Cape Basin over the Angola Basin to the Guinea Basin. The type locality of the species is in the Cape Basin. Using a morphological approach, Brökeland (2010a) studied specimens of H. rostratus collected north and south of the Walvis Ridge. The role of the ridge as a potential barrier to gene flow and hence allopatric divergence or speciation has been discussed ( Brandt et al. 2005). For H. rostratus, Brökeland (2010a) found no significant morphological differences across the Walvis Ridge and consequently stated that populations on either side do not represent allopatric sibling species but rather are members of a single species distributed across the ridge. However, since distinct species may be morphologically very similar or even indistinguishable (e.g. Held & Wägele 2005; Raupach & Wägele 2006), genetic data provide important independent information to test species hypotheses. The data of the 658 bp CO1 alignment from this study adds genetic support in favor of Brökeland´s (2010a) conclusion of gene flow across the Walvis Ridge. Our data resolve a single, well-supported H. rostratus group (posterior probability 0.95, ML Bootstrap 98) including both, the specimen from the Angola Basin (DIVA2-HA469, station 45) as well as those from the Cape Basin (16 sequences from stations 40 and 41). Interestingly, the single specimen available for analysis from the Guinea Basin (DIVA2-HA497, station 89), which is far more to the north, forms the sister group to the Cape and Angola Basin group and is genetically distinct (about 7% uncorrected p -distance; Fig. 1 ). This specimen was clearly identified as H. rostratus by Brökeland (pers. comm.), indicating possible barriers to gene flow among the southern basins and the northern Guinea Basin or even the presence of yet overlooked species. We conclude that although our dataset is rather small, it supports Brökeland’s (2010a) hypothesis of recent or ongoing gene flow across the Walvis Ridge as specimens from the Angola Basin and the Cape Basin share a single CO1 haplotype. In addition, our data support the possible existence of cryptic or yet overlooked species occurring in the deep Guinea Basin.

Figures

FIGURE 1. CO 1 Bayesian phylogenetic tree based on the 658 bp alignment. Branch support shows the ML / MP bootstrap values / posterior probabilities, respectively. (CB) = Cape Basin, (AB) = Angola Basin, (GB) = Guinea basin, (ARB) = ArgentinianBasin.