The ecology and evolution of endemic shrimp in Lake Tanganyika

Abstract

An exceptionally diverse group of shrimp species in the genera Atyella, Caridella, Limnocaridina and Macrobrachium is found in Lake Tanganyika, Africa, while the region is otherwise relatively poor in shrimp species. In this work the evolutionary and ecological diversity is explored among one palaemonid and twelve atyid shrimp species that are endemic to Lake Tanganyika. New insights in molecular phylogenetic relationships among Tanganyikan shrimp species largely support previous taxonomic assumptions based on morphological characters, however a single taxonomic modification is proposed to accommodate a genetic deviation from the current taxonomic classification of a very small species, Caridella minuta, for which morphological examination and description previously proved to be challenging. Additionally, the possibility of an atyid species flock, a single radiation with a common ancestor, is discussed in the light of the constructed phylogenies. Age estimates of evolutionary events based on dating methods are considered in relation to the estimated age of the ancient rift lake. Genetic diversification was observed in one population of the abundant benthic species Limnocaridina tanganyikae, which is the initial step towards speciation. The strong genetic deviation in one location among otherwise genetically homogeneous populations was related to topological gene flow barriers. An ecological treatise on species-specific niche space occupation and diversity, with a focus on habitat, morphology, and dietary preferences, revealed how the various niche aspects are linked. Ultimately, phylogenetic relationships are considered in the ecological framework, resulting in hypotheses about how niche partitioning may have contributed to the current diversity found in the Tanganyikan caridean shrimp species assemblage.