Afrorhytida kraussi ( Pfeiffer, 1846 )

Herbert, D. G. & Moussalli, A., 2010, Revision of the larger cannibal snails (Natalina s. l.) of southern Africa - Natalina s. s., Afrorhytida and Capitina (Mollusca: Gastropoda: Rhytididae), African Invertebrates 51 (1), pp. 1-1 : 89

Afrorhytida kraussi ( Pfeiffer, 1846)

Moussalli et al. (2009) have shown that Afrorhytida material occurring in the mountains of the southern Cape Fold Belt (Langeberge to Port Elizabeth) and adjacent coastal regions constitutes a monophyletic lineage which was identified as the A. kraussi complex. From a morphological perspective this complex includes two clearly distinct forms. Firstly, a form with an essentially brown shell, representing typical A. kraussi , which is widespread and occurs in a variety of habitats from southern Afrotemperate forest to montane sandstone fynbos, and secondly a smaller form with a thicker, paler shell which is evidently confined to coastal habitats in the De Hoop region. Since this latter form is clearly and consistently diagnosable we describe it as a new taxon, choosing for the present to rank it as a subspecies within a broadly interpreted A. kraussi , primarily on account of the molecular data which shows it to cluster within this complex.

As a whole, the A. kraussi complex has high genetic diversity (mean uncorrected Pdistances of 0.44 for the protein coding mitochondrial gene COI; refer to Fig. 1 ) and exhibits strong west-east phylogeographic structure ( Moussalli et al. 2009). This structure is more consistent with the predominantly west-east distribution of the material, than it is with the habitat of origin (i.e. forest vs fynbos). However, other than for the De Hoop material, we have been unable to identify any clear morphological characters which could serve to discriminate between the constituent subclades, and which might thus justify further specific or subspecific division. This notwithstanding, there is some evidence that the genetically divergent lineage occurring in isolated Afrotemperate forest patches at the western limit of the range (i.e. Grootvadersbosch and Tradoupas) exhibits a discernable trend toward larger size and frequently has a distinct reddish head-foot coloration (see below). In contrast, morphologically similar and geographically proximate specimens from sandstone fynbos in the mountains inland of Mossel Bay are widely disjunct genetically, yet there is no obvious physical feature in this area which stands out a potential biogeographic barrier. Given apparently anomalous patterns such as this, and the paraphyly resulting from the nesting of the morphologically distinct De Hoop lineage within the typical A. kraussi clade, it is evident that resolution of taxonomic uncertainties and phylogenetic relationships within the A. kraussi complex must await more detailed study of material more broadly representative the distribution of the species, particularly with respect to DNA sequence data.

Figures

Fig. 1. All compatible Bayesian consensus tree based on mixed model partitioned analysis of the combined nucleotide dataset (16S and COI = GTR + IΓ, ITS2 = GTR+I). Asterisk indicates nodal support>95 % posterior probability (PP); PP below 95 % are not shown. (From Moussalli et al. 2009)