Freshwater crabs and Simulium neavei in east Africa. III. Morphological variation in Potamonautes loveni (Decapoda: Potamidae).

Potamonautes loveni (Colosi) is the valid name for the species also described as P. granviki, P. harvardi and P. loveni longimerus, and incorrectly identified as P. berardi berardi. Potamonautes jeanelli and P. idjwiensis may be allied to P. loveni, but are geographically separated and show sufficient morphological distinction not to be considered conspecific. Potamonautes loveni occurs in the upper reaches of rivers on the highlands of western Kenya and eastern Uganda. Its replacement by other species, principally P. niloticus, at lower altitudes is probably determined by the temperature range of the water. Potamonautes loveni has been observed to coexist with P. niloticus within the range of altitude 1280-1950 m. Distinct forms of P. loveni, differing in colour, size and the expression of the post-frontal crest, occur on the western side of Mt. Elgon and in the former ochocerciasis foci of Kenya. Hybridization is evident in populations from between these areas. Morphological divergence within P. loveni may be the result of past climatic change. Periods of generally lower temperature have been accompanied by increased aridity and reduction of forest cover. It is suggested that these conditions are such as to promote a disjunct distribution of P. loveni, and in particular the isolation of the Mt. Elgon population.