A review of the reproductive biology of the only known matrotrophic viviparous anuran, the West African Nimba toad, Nimbaphrynoides occidentalis

Amphibians, and anurans in particular, show the highest diversity of reproductive modes among tetrapods. Nevertheless, viviparity is scarce in anurans and its occurrence is even more often assumed rather than confirmed. Probably the best studied viviparous amphibian is the Nimba toad, Nimbaphrynoides occidentalis. During more than 40 years of research, the Nimba toad's reproductive morphology, endocrine activity of the ovary as well as the pituitary gland, and to some extent the ecological impact (seasonality, humidity, food availability) on reproduction was examined. Due to the Nimba toad's unique reproductive mode, summaries are usually included in reviews discussing amphibian reproduction and articles on reproductive biology often discuss the exceptional reproductive system of Nimba toads. However, to our knowledge a detailed synthesis, summarising all the different original studies on the toad's reproduction, is so far missing. In this paper we review and summarise all available initial publications, which often have been published in French and/or are difficult to access. A short overview is given of the climatic and environmental conditions experienced by Nimba toads and the key findings supporting a " true" viviparous reproduction with matrotrophy (maternal provision of nutrition during the gestation) and pueriparity (birth of juveniles). Then foetal development (morphological, gonad and pituitary development), and the female (ovary, oviduct, pituitary and their endocrine interactions) and the male reproductive system (testes and pituitary) are reviewed. Finally, the reproductive cycle and its link to the Nimba mountains' seasonality and ecological/conservation implications are discussed.