Sneaker males are not necessarily similar to females in colour in a sexually monochromatic cichlid

Abstract

In species with alternative reproductive tactics (ARTs), males employing different tactics usually have different appearance. The clearest difference is body size: bourgeois males that monopolize access to females are larger than sneaker males that steal fertilizations from them. Sneakers are also known to be often dull in colour compared with bourgeois males and rather resemble females. However, this typical colour pattern is unlikely in the Lake Tanganyika cichlid Neolamprologus mondabu: we observed sneaking by two distinctive colour morphs, namely, black (which is apparently conspicuous against the background) and white (which is apparently background-matching). Because breeding females are black, this observation indicates that one type of sneakers contrasts female appearance. In this study, we conducted field studies to determine the expression of body colour in relation to ARTs in this fish. Body colour was dependent on size, but not sex and maturation, with black individuals being larger than white ones. Together with the presence of intermediate grey colour expressed by intermediate-sized individuals, this fish could ontogenetically changes their body colour from white to black. Both sexes of black individuals occupied feeding territories, but white individuals were non-territorial, indicating that the black body signals the possession of a feeding territory. Sexually active females were invariably black, whereas sexually active males were both black and white in colour. Few of the largest black males held harems, which included several female territories, whereas the remaining males were bachelors with no female territories. These bachelor males invested more in testes than harem males, suggesting that bachelors employ sneaking tactics, which is corroborated by our sneaking observations. To our knowledge, this is the first study showing that sneakers are entirely dissimilar to females in appearance. Herein, we discuss why sneakers are dichromatic in relation to their life histories.