A shell-brooding cichlid fish of Lake Tanganyika, Lamprologus callipterus, is unique in its reproductive behavior of constructing a breeding nest by actively gathering and accumulating a large number of empty gastropod shells as a spawning substrate. The breeding nest of this species is a typical example of interspecific niche construction, which provides a breeding substrate for a variety of other species. This species also exhibits a wide range of phenotypic diversity in male and female reproductive traits. Males from a single population have three distinctive reproductive tactics associated with their body sizes. Males from the largest size classes (96-130mm SL) perform a bourgeois tactic by gathering empty gastropod shells to build and maintain a breeding nest (territorial male) where females spawn and guard their young. The males of intermediate (51-75mm) and extremely small (24-46mm) size classes perform parasitic tactics by stealing fertilization from the large males. Sexually mature males and females show large geographical variations in body sizes. The sizes of mature females are mainly restricted by the sizes of locally available shells. Body sizes of territorial males positively correlate to densities of the breeding nests in each locality, possibly reflecting intensities of intra-sexual selection. However, we identified one exceptional population with extremely small territorial males. The males in this locality attain only 50mm in body size and lack the ability to gather the shells to build nests. The evolution of extremely small body sizes of territorial males may be related to the habitat structure of this locality, where the bottom across a wide area is completely covered with empty shells. The evolution of large intraspecific diversity of reproductive traits in this species and the implications of its breeding behavior for niche construction theory will be discussed in environmental and social contexts, together with other examples of interspecific niche construction found in the East African Great Lakes.
Tetsu Sato is the Professor of Ecology and Environmental Sciences at Nagano University Faculty of Tourism and Environmental Studies, studying evolutionary and environmental sciences for sustainable development. He studied the ecology and behavior of the cichlid fishes of Lakes Tanganyika and Malawi for twenty years, focusing in particular on mechanisms of rapid evolution and coexistence of cichlid fish communities. Through this experience in Africa, he expanded his research areas to community-based conservation and natural resource management.