Invasions of ecosystems by exotic species are increasing and they may often act as a significant driver of the homogenization of the Earth’s biota, resulting in global biodiversity loss. Moreover, the addition of exotic species may have dramatic effects on ecosystem structure and functioning which may result in the extirpation of indigenous species. In 2004, a large population of an unknown lymnaeid was found in the Amatikulu Hatchery, northern KwaZulu-Natal, South Africa, and was subsequently found in few garden fish ponds in Durban. In 2007, it was identified using molecular techniques as Radix rubiginosa (Michelin, 1831) – a species widespread in southeast Asia. An invasion by R. rubiginosa is however likely to go unnoticed because its shell morphology resembles some forms of the highly variable and widely distributed indigenous lymnaeid, Lymnaea natalensis Krauss, 1848. Accurate and “easy” species identifications would permit the ready assessment of introduction histories and distributions, but in the present case identification was difficult due to unclear and contradicting accounts of the indigenous L. natalensis in the literature. A redescription of L. natalensis with emphasis on conchological and anatomical characteristics was therefore presented. This will help to distinguish variation between R. rubiginosa and L. natalensis and also assist those carrying out rapid bioassessment (SASS) surveys in South African rivers in recognising R. rubiginosa should it spread. For this, shells of R. rubiginosa and L. natalensis from both the UKZN Pond and the Greyville Pond were selected into either size class 1 (shell length < 10 mm) or size class 2 (shell length ≥ 10 mm). Six shell characters, shell length (height), shell width, aperture length (height), aperture width, length of last body whorl and spire height for each specimen was measured and analysed using principal component analysis (PCA) and The invasive potential of the freshwater snail Radix rubiginosa recently introduced into South Africa discriminant functions analysis (DFA). The most useful discriminant conchological characters were shell length, length of the last body whorl and aperture width. Use of these shell characters provided simple yet effective criteria for the separation of R. rubiginosa and L. natalensis. For both size classes R. rubiginosa had larger, more broadly ovate shells with longer (higher) body whorls than either of the two populations of L. natalensis that exhibited smaller, elongated shells with shorter (lower) body whorls. Also, R. rubiginosa had a narrower aperture width compared to the larger, wider aperture of the UKZN Pond L. natalensis population. The Greyville L. natalensis population was found to have narrower apertures than both R. rubiginosa and L. natalensis (UKZN Pond). The morphology of the radula and the reproductive anatomy of R. rubiginosa and L. natalensis from both the UKZN and Greyville Ponds showed little variation. The species did however vary in the relative numbers of radula teeth in each field and this serves as an additional useful diagnostic character. Both L. natalensis populations had similar mantle pigmentation patterns but that of R. rubiginosa was different. The mantle surface of R. rubiginosa was mottled black with patches of pale white to yellow. There were also large unpigmented fields and stripes that were not observed in L. natalensis. Having found characters to conveniently separate the alien R. rubiginosa from the indigenous L. natalensis, it became increasingly important to assess the potential invasiveness of this introduced species and its likely impact. The potential invasiveness of R. rubiginosa was assessed in relation to the already invasive North American Physidae Physa acuta Draparnaud, 1805 and the indigenous L. natalensis. This was particularly important in view of the success of P. acuta as an invader in South Africa. The hatching success, frequency of egg abnormalities, embryonic development, growth, survivorship, fecundity and life history parameters (GRR, Ro, rm, T and λ) for the four snail populations were assessed at three experimental temperatures (20oC, 25oC and 30oC). The invasive potential of the freshwater snail Radix rubiginosa recently introduced into South Africa The results showed that R. rubiginosa and P. acuta had a higher growth coefficient (K), longer survivorship, higher fecundity (higher hatching success, fewer egg abnormalities, longer duration of oviposition), shorter incubation period, greater life history parameters (GRR, Ro, rm and λ) and wider temperature tolerances than the two L. natalensis populations tested. The high adaptability of P. acuta to changing environmental factors such as temperature, is in agreement with the fact that it is now more widespread in South Africa than the indigenous species L. natalensis. This has important implications for R. rubiginosa, since this species displayed reproductive attributes and a temperature tolerance that were similar and in certain cases even exceeded the performance of the invasive P. acuta. This therefore implies that R. rubiginosa has the potential to colonize a wider geographical and altitudinal range than L. natalensis, and perhaps even P. acuta. Also, the superior reproductive ability of R. rubiginosa over L. natalensis is likely to present a situation that allows for its rapid spread as well as a possible impact on the indigenous L. natalensis that might render it vulnerable. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

Invasions of ecosystems by alien species is a worldwide problem. Man, with his constant travelling, introduces organisms to places they have never occurred in before. The introductions may be accidental or deliberate. Some of the introduced organisms become invasive and some of these also become pests. Two aquatic pulmonate snails, Physa acuta (Physidae) and Lymnaea columella (Lymnaeidae), were introduced to South Africa probably through the aquarium industry in the 1940s and have now spread to most of the country's freshwater systems. A third invasive pulmonate, and second physid provisionally called Aplexa cf. marmorata, has recently been found in South African freshwaters. Comparison between A.. cf. marmorata found in Durban and P. acuta from Pietermaritzburg as an example of the genus Physa, confirmed that they belong to different genera and are therefore different species. Features compared were the shell, radula, foot, mantle, male genitalia and sperm morphology. Aplexa cf. marmorata is characterized by its foot having a pointed posterior end with a dark mid-dorsal stripe while that of P. acuta does not have these features. The mantle edge ofA.cf. marmorata has short triangular dentations while that of P. acuta has long finger-like projections. Aplexa cf. marmorata does not have an externally visible preputial gland whereas P. acuta does. The penis of A.cf. marmorata has a lateral opening while that of P. acuta has a sub-terminal outlet. TEM sections of the spermatozoon of A.cf. marmorata showed that it has a maximum of two glycogen helices around the mid-piece while P. acuta is known to have three. A study of the population dynamics of A.cf. marmorata in Durban showed it to produce three overlapping generations within a 14 month period whereas P. acuta has been shown to produce as many as eight over a similar time period. Further comparisons between South African A. cf. marmorata and similar material from the West Indies, Nigeria and St Lucia (KwaZulu-Natal) showed that they shared the same features with the specimens collected in Durban and are therefore considered to belong to the same species , Aplexa marmorata (Guilding, 1828). This species is indigenous to the Caribbean and northern parts of South America. The picture is however complicated by the fact that Dr L Paraense, doyen of the Brazilian school of freshwater malacology, does not recognize the genus Aplexa and redescribed this species under the name Physa marmorata in 1986. / Thesis (M.Sc.)-University of Natal, Durban, 2000.