Natalina quekettiana

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 : 51-54

Natalina quekettiana complex

In addition to the large and conspicuous Natalina s.s. species discussed thus far, are three further species described from KwaZulu-Natal. These are all of smaller size and appear to be rare. In two cases they are known solely from the original samples, and only N. quekettiana has been collected again subsequent to its original description. However, on-going field work has brought to light additional small-shelled, but clearly adult Natalina specimens from a number of other localities in KwaZulu-Natal ( Fig. 33 ). These are similar to the described taxa, but not clearly conspecific with any one of them. We have attempted to clarify this matter through analysis of DNA sequence data, but have been hindered in this by being unable to obtain fresh topotypic material of two of the described species ( N. inhluzana and N. reenenensis ), despite targeted attempts. We have, however, been able to obtain sequence data from topotypic material of N. quekettiana and a number of the indeterminate specimens from other localities.

From analyses of these data ( Moussalli et al. 2009), it is clear that the small-shelled specimens collectively comprise a monophyletic lineage within Natalina , which we term the N. quekettiana complex. This is sister to the clade comprising N. cafra and N. beyrichi ( Fig. 1 ). In terms of shell morphology, radula dentition, body coloration and genetic make up, this complex exhibits considerable internal diversity, although, with the exception of the epiphallus, the genital anatomy is the same. The spermatophore is known for only one subspecies, but this differs greatly from that of the larger Natalina s.s. species and Natalina (Tongalina) in bearing well-developed, lobate, scale-like spines. This differing spermatophore morphology is reflected in the internal structure of the epiphallus and, since this is similar in all members of the complex for which preserved material is available, it is likely that the presence of scale-like spines on the spermatophore will prove to be an autapomorphic trait for this clade as a whole (the spines on the Afrorhytida spermatophore are of a very different form).

The molecular data identified four allopatric subclades ( Fig. 1 ), one comprising material from central and south-western Zululand, a second from the mist-belt regions of the KwaZulu-Natal Midlands, and two others from the central KwaZulu-Natal Drakensberg.The first two are sister taxa and can be differentiated from each other morphologically in terms of size and radula dentition. As a pair they comprise a mid-altitude radiation (600–1500 m).The two other subclades, from higher altitude forests in the foothills of the central Drakensberg (1350–1650 m), however, show no obvious or consistent differences in shell form (which is confusingly variable in the few specimens available) or radula dentition. Yet despite this and their geographical proximity, they are evidently not closely related, the one being sister to the mid-altitude subclade and the other representing a deeply divergent lineage arising at the base of the N. quekettiana clade. Neither appear to be referable to the similarly high altitude taxon N. reenenensis on account of differences in radula dentition.

This situation is clearly complicated and in need of further investigation, but for the present, we chose to treat this material as a single complex. However, in order to recognise the lineages identified through analyses of molecular data (in some cases supported by morphology), we propose to treat these as subspecies within a broadly interpreted Natalina quekettiana , the earliest available species-group name within the complex. We maintain Natalina reenenensis as a distinct species simply because we have no data upon which to base a change in its status. It is unique within the N. quekettiana complex in having only five pairs of lateral teeth per transverse row of the radula. We also have no new data concerning N. inhluzana , and treat this as a separate entity too, but we strongly suspect that it is a synonym of N. quekettiana quekettiana (see below).

In addition to the above, are further small-shelled specimens ( Fig. 34 ) from escarpment-edge habitats in Mpumalanga and Swaziland (locality details given below). These are shell-only samples and while we can be moderately confident that they belong to the N. quekettiana complex, we cannot reliably assign them to any of the taxa discussed below. They do, however, indicate that this complex ranges beyond KwaZulu-Natal along the north-eastern Drakensberg escarpment.

As a whole, the N. quekettiana complex is evidently confined to wet forest habitats, primarily Afrotemperate (montane) and mist-belt forests, but extends also into lower altitude scarp forest in southern Zululand ( Fig. 33 ). Given this habitat specialisation, the distribution of the taxon is likely to be highly fragmented with many populations and perhaps species restricted to isolated forest islands within the rainforest archipelago. This patchy pattern is concordant with the considerable genetic diversity mentioned above, even between geographically proximate populations, for example those in central KwaZulu-Natal Drakensberg (Cathedral Peak vs Injasuthi–Monk’s Cowl). It is thought that this derives from sequential isolation events associated with Plio-Pleistocene glacial cycles (see biogeographic summary).

Unidentified material belonging to the Natalina quekettiana complex: SOUTH AFRICA: Mpumalanga: Mariepskop Forest (24.56683°S: 30.86232°E), 1520 m, mist-belt forest, J. Horn, 28/ii/2005 ( NMSA W4720 ) ; nr Pienaar’s R., between Pretoria and Lydenburg, ‘ Transvaal’ ( BMNH 78.1.30.3); Lydenburg area, 25 km south, Buffelskloof Nat. Res. (25.3°S: 30.5°E), 1500 m, indigenous forest, in leaf-litter, D. Plowes ( NMSA W6104 ) ; Wakkerstroom, 40 km ENE of, Paardeplaats Forest (27.23683°S: 30.50250°E), 1472 m, indigenous forest, in leaf-litter, J. Horn & M. Lotter, 06/xi/2006 ( NMSA W5569 ) . SWAZILAND: Mbabane (26.330°S: 31.133°E),> 1250 m, L.D. Brongersma, 17/x/1938 (cited Bruggen (2004: 46) as Natalina cafra ; RMNH.MOL.109689) .

Figures

Fig. 33. Distribution of Natalina quekettiana complex; contours at 1000 m and 1500 m.

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)

Fig.34. Natalina quekettiana complex, unidentified material from the north-eastern escarpment:(A) Mbabane, Swaziland, diameter 28.0 mm (RMNH.MOL.109689); (B) Buffelskloof Nat. Res., Mpumalanga, diameter 30.1 mm (NMSA W6104).