Spherillo, GROSSUS

Lee, Timothy R. C., Ho, Simon Y. W., Wilson, George D. F. & Lo, Nathan, 2014, Phylogeography and diversity of the terrestrial isopod Spherillo grossus (Oniscidea: Armadillidae) on the Australian East Coast, Zoological Journal of the Linnean Society 170 (2), pp. 297-309 : 305-306

SPHERILLO GROSSUS

We found high levels of genetic divergence between the different S. grossus populations sampled in this study (mean interlocality p-distances up to 15, 14, and 0.7% for 16S, COI, and 18S, respectively). These results are similar to those found in other studies of terrestrial isopods. In the rocky-shore oniscid species Ligia occidentalis ( Dana, 1853) , COI p-distances of up to 26% between populations in the Gulf of California have been reported ( Hurtado et al., 2010), and in the same species a Kimura two-parameter distance of up to 25% between populations was found by Eberl et al. (2013), and of up to 26.7% between populations was found by Markow & Pfeiler (2010). The p-distances of up to 14% in the 16S gene were found in the cosmopolitan oniscid Porcellionides pruinosus ( Brandt, 1833) ( Michel-Salzat et al., 2001) . In a study of the genus Haloniscus ( Chilton, 1919) , cave-dwelling oniscids found in Western Australia, p-distances of up to 10.7% in COI sequences were found between localities ( Cooper et al., 2008). In all these cases, the high levels of genetic diversity were regarded as indicating species-level divergences between lineages. We find that S. grossus exhibits a similar range of diversity to these. Our finding of variation between the Woy Woy specimens and all others in the 18S gene fragment raises the possibility that they are different species, because differences in this gene fragment have been used to distinguish between beetle species ( Raupach et al., 2010). For these reasons, the taxonomy of S. grossus probably needs revision.

The deep genetic divergences found among lineages of S. grossus contrast with the apparent lack of gross morphological variation. The most variable character measured was the shape of the penes cover, but this variation did not correlate with genetic clade or collection locality. Therefore, we tentatively conclude that the morphological variation that we have studied among the populations of S. grossus is limited (a result comparable with studies such as Hurtado et al., 2010 and Eberl et al., 2013), and that none of the observed variation appears to be phylogenetically significant. The observed variation in S. grossus may be a consequence of phenotypic plasticity. Because S. grossus has a range with a north–south axis over 1000 km in length, variation in local environments may be driving different plastic responses in different populations. Morphological plasticity is a well-known phenomenon in the crustacean Daphnia ( Boersma, Spaak & De Meester, 1998) , and phenotypic plasticity driven by temperature has been found in the terrestrial isopod A. vulgare ( Helden & Hassall, 1998) .

Mitochondrial gene phylogenies can be complicated by introgression (the introduction of genes from a related lineage; e.g. Wilson et al., 2009) and incomplete lineage sorting (where different clades are not reciprocally monophyletic for all genes; Freeland, Kirk & Peterson, 2011). Because our nuclear phylogeny does not conflict with our mitochondrial phylogenies, we did not find any evidence that either of these processes has led to different gene trees in S. grossus , although the resolution provided by our 18S phylogeny was low. The skewed sex ratio in our specimens ( Table 1) potentially indicates the presence of Wolbachia in these populations ( Bouchon, Rigaud & Juchault, 1998; Cordaux et al., 2004), and would be a potential focus for future research.