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The African clawed frog, Xenopus laevis (Daudin, 1802) is native to southern Africa but is invasive on four different continents. This study aimed to understand four major aspects of the African clawed frogs’ invasion in western France. Firstly, I assessed for the level of phenotypic plasticity and local adaptation of X. laevis tadpoles from the two contrasting rainfall regions in the native range, as this could provide information on the level of phenotypic plasticity in the French invasive range. The winter rainfall region is characterised by colder temperature and a winter rainfall pattern whereas the summer rainfall region is characterised by warmer temperatures and a summer rainfall pattern. I performed a reciprocal exchange experiment using outdoor mesocosms. I found that both phenotypic plasticity and local adaptation determined the tadpole phenotype in the winter and summer rainfall regions. I also identified a survival cost in individuals translocated to the other region. However, the cost was lower for winter rainfall tadpoles. Thus, the interaction between phenotypic plasticity and local adaptation likely explains the persistence of this species in contrasting environments. Secondly, in amphibians, tadpole phenotypic traits can be coupled or decoupled to dispersal traits in adults. Spatial sorting has been observed in adults of X. laevis in western France. Thus, I tested whether spatial sorting altered the morphology and life-history traits of tadpoles due to the coupling of traits between stages. I conducted common garden experiments in laboratory microcosms and outdoor mesocosms. I compared body size, timing of metamorphosis and survival between tadpoles from the core and from the periphery of the invasive range but found no effects of the position in the invasive range on tadpole phenotype. The only difference in both the outdoor and laboratory experiments was the larger body size of post-metamorphic individuals at the periphery. These findings support the hypothesis of decoupling between adult traits and tadpole phenotypic traits. Decoupling can allow each stage of the complex life cycle to respond independently to environmental conditions. Thirdly, I assessed whether the degree of phenotypic plasticity changed between the core and the periphery during the expansion process. I tested this hypothesis for invasive X. laevis in western France. I measured the critical thermal limits and modelling the thermal performance curves of the burst swimming performance (velocity, acceleration, and sinuosity) of core and periphery tadpoles reared at three developmental temperatures (low, intermediate, and high). I found that both the position in the distribution (core/ periphery) and the developmental temperature was significant in determining burst swimming performance. However, no differences were identified between the performance of core and periphery tadpoles reared in the same developmental temperature. Tadpoles reared at the high temperature acclimated their performance to warmer temperatures, however, tadpoles displayed limited acclimation to cooler temperatures. Finally, I tested whether tadpoles identified and responded to novel predators in their invasive range. In western France, X. laevis can encounter novel aquatic predators. I tested whether naïve tadpoles from the invasive French population exhibited anti-predator response to local predators, and whether the response depended on the degree of relatedness with predators in the native range. I exposed naïve lab-reared tadpoles to a non-predatory water snail, Planorbarius corneus, a native predatory beetle, Dytiscus dimidiatus, and an invasive predatory crayfish, Procambarus clarkii. I found that tadpoles innately reduced their activity when exposed to beetle and crayfish olfactory cues, but not to snail cue. This demonstrates that invasive tadpoles respond to known and novel predators regardless of the evolutionary history of the prey-predator interaction, Le Xénope lisse, Xenopus laevis (Daudin, 1802) est originaire d'Afrique australe et envahissante sur quatre continents. Cette étude visait à comprendre quatre aspects majeurs de l’invasion du Xénope lisse. Premièrement, j'ai évalué le niveau de plasticité phénotypique et d'adaptation locale des têtards de X. laevis des deux régions pluviométriques de l'aire de répartition d’origine, car cette connaissance pourrait fournir des informations sur le niveau de plasticité phénotypique au sein de l'aire colonisée en France. J'ai effectué une expérience d'échange réciproque en utilisant des mésocosmes en milieu extérieur. J'ai mesuré la taille du corps, le moment de la métamorphose et la survie des têtards (stade NF 45 - 66). J'ai trouvé que la plasticité phénotypique et l'adaptation locale déterminaient le phénotype du têtard dans les régions deux régions pluviométriques (précipitations hivernales ou estivales). J'ai également identifié un coût à la survie chez les individus transférés dans l'autre région climatique. Deuxièmement, chez les amphibiens, les caractères phénotypiques des têtards peuvent être couplés ou découplés des caractères liés à la dispersion chez les adultes. Un processus de spatial sorting a été observé chez des adultes de X. laevis. J'ai ainsi testé si ce processus modifiait la morphologie et les traits d'histoire de vie des têtards en raison d’un couplage traits entre les stades. J'ai mené des expériences en environnement commun dans des microcosmes au laboratoire et des mésocosmes en milieu extérieur. J'ai comparé la taille du corps, le moment de la métamorphose et la survie entre les têtards du centre et de la périphérie de la zone colonisée, mais je n'ai trouvé aucun effet de la position dans la zone colonisée sur le phénotype du têtard. La seule différence détectée dans les deux expériences réalisées en mésocosme et en laboratoire était la plus grande taille corporelle des individus post-métamorphiques à la périphérie. Ces résultats soutiennent l'hypothèse d'un découplage entre les traits adultes et les traits phénotypiques têtards.Troisièmement, j'ai évalué si le degré de plasticité phénotypique avait changé entre le noyau et la périphérie pendant le processus d'expansion. J'ai testé cette hypothèse pour la population invasive de X. laevis. J'ai mesuré les limites thermiques critiques et modélisé les courbes de performances thermiques pour le comportement de déclenchement de la nage (vitesse, accélération et sinuosité) des têtards du centre et de la périphérie ayant été élevés à trois températures de développement (basse, intermédiaire et élevée). J'ai trouvé que la position dans la distribution et la température de développement avaient des effets significatifs. Cependant, aucune différence n'a été détectée entre les performances de nage des têtards du centre et de la périphérie s’étant développés à la même température. Les têtards élevés à la température élevée se sont acclimatés à des températures plus chaudes. En revanche, les têtards ont montré une capacité d’acclimatation limitée à des températures basses. Enfin, j'ai testé si les têtards identifiaient et répondaient à de nouveaux prédateurs dans leur zone colonisée. Xenopus laevis peut rencontrer de nouveaux prédateurs aquatiques. J'ai testé si les têtards naïfs de la population invasive française présentaient une réponse anti-prédatrice aux prédateurs locaux et si la réponse dépendait du degré de parenté avec les prédateurs de l'aire d’origine. J'ai exposé des têtards naïfs élevés en laboratoire à un gastéropode aquatique non-prédateur, un coléoptère prédateur indigène, et une écrevisse prédatrice invasive. J'ai trouvé que les têtards réduisaient naturellement leur activité lorsqu'ils étaient exposés à des signaux olfactifs du coléoptère et de l'écrevisse, mais pas à des signaux du gastéropode

MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2017 South Africa has a diverse anuran fauna consisting of 161 described species. Amphibians are suffering large-scale regressions due to various threats: (1) pollution, (2) habitat engineering and (3) invasive species. The endangered Western Leopard toad (Sclerophrys pantherina) endemic to the Western Cape is currently experiencing major external pressures from these above-mentioned threats. The latter being a local invader, namely the Guttural toad (Sclerophrys gutturalis), which (through human-assisted translocation) was introduced from KwaZulu-Natal into the native range of the Western Leopard Toad. The direct effects such as predation and competition have received extensive attention, seeing that invasive species can have devastating effects on native fauna. However, a more neglected field of research is the indirect threats invasive species pose to the native fauna such as interactions with infectious agents, which include spill back and spill over of parasites. The present study aimed to understand this interaction by focusing on the relationship between parasites, native species, and invasive species. The research examined mechanisms such as spill back and spill over for a better understanding of the indirect drives and consequences invasive species may hold. Morphological markers (light microscopy and scanning electron microscopy) as well as molecular markers (COI and 28S) were applied to survey parasites found in collected toads from five populations: (1) native Guttural Toad in KwaZulu-Natal; (2) invasive Guttural Toad isolated in Western Cape; (3) invasive Guttural Toad and native Western Leopard Toad in Western Cape; (4) native Western Leopard Toad isolated in Western Cape; and (5) native Guttural Toad from Potchefstroom. Parasites that were observed was a nasal mite Lawrencarus eweri (Lawrence, 1952); a lung nematode Rhabdias cf. africana Kuzmin, 2001; intestinal nematode Cosmocerca sp. Diesing, 1861; intestinal trematode Mesocoelium cf. monodi Dolfus, 1929; two blood parasites Hepatozoon ixoxo Netherlands, Cook, & Smit 2014, as well as Trypanosoma sp. Gruby, 1843. It was found that the introduced species may have vacated their parasites throughout the invasion, possibly due to the ‘enemy release hypothesis’ (Marr et al. 2008). This can enhance the invaders competitive ability as defence costs against parasites can be decreased and reproductive rates can increase (Hatcher & Dunn, 2011). The native Western Leopard Toad population co-existing with invasive Guttural Toad was found to contain less parasites than the isolated native Western Leopard Toad population. In this case, it is possible that the invader decreased the parasite loads of the native population by acting as a ‘sink’ for native parasites (Kelly et al., 2009). If so, native parasites are taken up by the invader but fail to complete their life cycle due to disorientation and lack of co-evolutionary history (Hempel et al., 2003). Encysted nematodes (presumably third-stage larvae), collected from native Western Leopard Toads and invasive Guttural Toads from the Western Cape, appear to have a host-size and niche specificity rather than a specificity to the host itself. Few life cycles have been described for nematodes in South African fauna to which a toad acts as an intermediate host for the third-stage larvae. Thus, without further identification and molecular studies it is uncertain whether these cysts in native Western Leopard Toads and invasive Guttural Toads are a result of spill back or spill over. However, each case of parasite-host relationship is unique since the relationship can be dynamic. This makes it difficult to predict the consequences. Furthermore, as is the case with restoration ecology, irreversible changes may have to be accepted in certain ecosystems that are subject to invading parasites and their introduced hosts (Dunn & Hatcher, 2014). Masters

Bibliography: leaves 74-78., Saldanha Bay, which lies on the west coast of South Africa, has undergone major development over the last 30 years, including breakwater and harbour construction, harbour extension, dredging, mining, fishing, fish-processing and mussel culture. The aims of this study were to determine whether the benthic macrofaunal communities in the Bay have been altered over this period and to explore the benthic community patterns within the Bay prior to and after harbour development.