Ph. D. defense of Mr Sèdjro Gilles Armel Nago, GTI trainee

Abstract:

In the actual context of worldwide amphibian decreasing, several explanations are given stretching from habitat alteration or degradation, overharvesting, water quality to diseases. Most scientific studies are regionally or geographically restricted to forest ecosystems in the tropics. However Africa harbours drier habitat amphibian species than forest-dwelling ones. Moreover, savannas are at least under equal human pressure as forests. This lack of exploration limits our global comprehension of effects of human land-use on these taxa. We investigated these issues with taxonomical, ecological and parasitological aspects to assess local patterns in amphibian responses to land-use modification and discussed the biomonitoring and conservation implications in a protected area of Northern Benin, West Africa.

Through potential habitats and vegetation of temporary puddles, we survey amphibian fauna with various methods. We report 32 species for the Pendjari Biosphere Reserve and succeed in adding 17 species to the countries’amphibian list. Those species are Bufo pentoni, Hildebrantia ornata, Pyxicephalus cf. edulis, Ptychadena bibroni, P. cf. schillukorum, P. tellini, P. tournieri, P. trinodis, Phrynobatrachus latifrons, P. francisci, P. gutturosus, Arthrolepsis sp., Kassina cassinoides, K. senegalensis, K. fusca, Leptopelis bufonides and Hyperolius nasutus. Pendjari Biosphere Reserve ranks within the most diverse African savanna regions. The found species are mainly composed of typical West African savanna frogs, especially those that are restricted to drier habitats. However, especially along the mountainous Atakora chain in the South of the area, rare and unsual species are recorded and they are dependant on higher humidity, e.g. Arthrolepsis sp. and Hyperolius sp. The single endemic frog of the Volta basin, P. francisci, is also present in the reserve. Within these local amphibian fauna, belong two for which clutch and larvae are not described yet. They are Leptopelis bufonides and P. cf. schillukorum. After captured an amplectant couple of them in the field, a clutch is received from both. Larval stages were obtained in captive breeding for the latter pair. Based both on living and preserved specimens, its tadpole is described. The concern tadpole is a typical West African Ptychadena tadpole and can potentially be mistaken with its congeners.

Across three ecological parts of the reserve, we studied a land-use modification gradient stretching from pristine area, buffer zone to agricultural region in Pendjari Biosphere. We determined species richness, abundance and diversity indexes in all habitat types. For this study, in general, occurrence and abundance of larval and adult stages differ among species and between habitat types from the undisturbed places to the most preserve areas. Diversity in tadpoles is in a favour of the pristine area but abundance patterns are contrary. Concerning adults, some of the species (Ptychadena tournieri, Phrynobatrachus gutturosus, Kassina cassinoides and Hildebrandtia ornata) are found exclusively in undisturbed savanna whereas others (Leptopelis bufonides and Pyxicephalus cf. edulis) live predominantly in pristine zone of Pendjari. It highlights the role of the reserve in the region concerning biodiversity conservation. On parasitological way, amphibians from the undisturbed zone, generally, seem to be more infected than those from the altered sites. This is perhaps due either to a strong impact of land use on parasite transmission or to the small samples of amphibians. Finally, through this study, an evidence for the negative link exists between human land use and individual and population characteristics of frogs in the savanna breeding pools. Also amphibians prove their sensitivity to edge-effetcs. Then amphibians can be considered as valuable bio-indicators in savanna ecosystems.

Keywords: Amphibians, species distribution, tadpole assemblage, savanna, agriculture, Biosphere reserve, land-use change, bio-indicator species, edge-effect, amphibian parasites, prevalence and intensity of infection rates, pesticide contaminants.

Director: Professeur Brice SINSIN (Université d'Abomey-Calavi, Bénin)

Co-director: PD Dr Mark-Oliver RÖDEL (Musée d'Histoire Naturelle de Berlin, Germany)

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