Giant males or dwarf females: what determines the extreme sexual size dimorphism in Lamprologus callipterus?

Abstract

In the Lake Tanganyika cichlid Lamprologus callipterus, males were >12 times heavier than females, the most extreme sexual size dimorphism in this direction among animals. L. callipterus males construct nests of empty snail shells in which the females breed. If the ancestors of L. callipterus were small cichlids, both sexes may have used shells for shelter. If the ancestors were larger, snail shells could not be used as shelters and would be important only for reproduction. In the field and the laboratory, females bred only in shells and the largest spawned in the largest shells. In the field, females chose larger shells than the average available in males' territories and did not copy the mate choice of other females. They never hid from predators in snail shells and they occurred commonly in areas without any potential shell shelters. In laboratory experiments females used shells only for reproduction and hardly for shelter. Therefore, it seems unlikely that L. callipterus descended from small shell-brooding cichlids which used shells for shelter, but more likely that the ancestors were of large or intermediate size, and that female size is constrained by the sizes of snail shells, which appear to be optimal breeding substrata. 2000 The Fisheries Society of the British Isles

Interspecific variation of body shape and sexual dimorphism in three coexisting species of the genus Petrotilapia (Teleostei: Cichlidae) from Lake Malawi

“…; PG, Petrotilapia genalutea Lamprologus callipterus where males are more than 12 times heavier than females (Schutz and Taborsky, 2000). Even though the degree of sexual dimorphism is expected to depend on a balance of natural and sexual selection (see Schutz and Taborsky, 2000), in our study, as well as the studies mentioned above, sexual selection seems to be the most applicable explanation, as such dimorphism promotes success in male-male competition or female choice (see Fryer and Iles, 1972;Barlow, 2000). This success means that only the bigger males will have the chance to mate with as many females as possible, because such males will be able to defend their territories.…”

Some evidence for different ecological pressures that constrain male and female body size

“…If optimal body size or strength is different between ecological pressure on one sex and other forces on the other sex, it may accelerate evolution of sexual size dimorphism (SSD). In a population of Lamprologus callipterus (cichlid fish) from Lake Tanganyika, which shows the most extreme male-biased SSD (males [ females) among animals (Schütz & Taborsky, 2000), the body size of females appears to be restricted by the ability to spawn eggs inside empty snail shells of a gastropod. Mature males of this species (except for sneakers) are too large to enter shells, and no ecological pressures limiting body size have been reported, although the large body size may be a result of sexual selection and natural selection so that the males could carry the shells with their mouths to make breeding nests (Schütz & Taborsky, 2005;Schütz et al, 2006).…”

Ecology and mating competition influence sexual dimorphism in Tanganyikan cichlids

“…For instance, the shellbreeding cichlids often have extreme SSD with remarkably small females in relation to males. In fact, the highest reported male-biased SSD in any animal is found in a Tanganyikan cichlid, Lamprologus callipterus, where larger males with higher reproductive success are able to carry shells to their territories in which females brood the eggs resulting in males being [12 times larger than females (Sato and Gashagaza 1997;Schütz and Taborsky 2000;Schütz et al 2006). As such, we propose that a combination of sexual selection and natural selection have caused the sometimes extreme levels of SSD, at least in these species (see also Schütz et al 2006 for a more exhaustive discussion on this topic) and this highlights the need to consider many selective pressures to fully explain the causes of SSD (Blanckenhorn 2005).…”

“…For instance, in species with uni-parental care, natural selection against predation can lead to the evolution of cryptic colouration or smaller size in the caring parent and thus to sexual dimorphism in colour or size (e.g. Promislow et al 1994;Cuervo and Møller 1999;Schütz and Taborsky 2000;Doucet and Mennill 2009). This means it is important to consider not only differences in mating-specific behaviours but also potential differences in general ecology among the sexes to fully understand the factors leading to the evolution of sexual dimorphism.…”