Introgression patterns between divergent lineages are often characterized by asymmetry in the direction and among-marker variation in the extent of gene flow, and therefore inform on the mechanisms involved in differentiation and speciation. In the present study, we test the hypothesis that unidirectional introgression between two phenotypically and genetically distinct lineages of the littoral, rockdwelling cichlid fish Tropheus moorii across a wide sandy bay is linked to observed differences in mate preferences between the two lineages. This hypothesis predicts bi-directional nuclear gene flow and was rejected by congruent patterns of introgression in mtDNA, AFLP and microsatellite markers, with admixture confined to the populations west of the bay. This pattern can be explained on the basis of habitat changes in the course of lake level fluctuations, which first facilitated the development of a symmetric admixture zone including the area corresponding to the present sand bay and then shaped asymmetry by causing local extinctions and cessation of gene flow when this area became once more inhabitable. This conforms with previous assumptions that habitat dynamics are a primary determinant of populationlevel evolution in Tropheus. In this respect, Tropheus may be representative of species whose preferred habitat is subject to frequent re-structuring.

Intraspecific variability in mating behaviour and disparities between social and reproductive behaviour add complexity to the description of animal mating systems. A previously published field study on a population of the maternally mouthbrooding cichlid fish Ctenochromis horei in the north of Lake Tanganyika suggested mate monopolization by the most dominant male. In the present study, genetic reconstructions of paternity in a population in the south of the lake provided no evidence for male mate monopolization, as none of the inferred sires had offspring in more than one brood. The ability to reconstruct sire genotypes from offspring alleles was confirmed by computer simulations. Multiple paternity occurred in several broods and was significantly more frequent in the sample taken in the rainy season than in the dry season sample (100% of broods vs. 14%, respectively; P = 0.005). The data suggest geographical and temporal variation in the mating behaviour of C. horei despite its continuous year-round reproduction, invariable brood care behaviour and habitat-specific distribution in the relatively constant and confined environment of a tropical lake. Moreover, our data show that inferences on the distribution of male reproductive success, if based on each geographical or temporal data set alone, would fail to describe the potential for sexual selection in this species.

Female mate preferences for male traits and resource characteristics affect trait evolution and diversification. Here, we test the effects of male body traits and territory characteristics on within-population female preferences and on population–assortative mating in the cichlid Tropheus moorii. Within-population preferences of females were independent of male body size, coloration and territory size but were strongly dependent on territory quality and co-varied with male courtship activity. Courtship activity of individual males was contingent on the quality of their assigned territory, and therefore, courtship may not only indicate intrinsic male quality. On the basis of these results we suggest that female preferences for high-quality territories reinforce the outcome of malemale competition and ensure male mating success. Mating preferences of females for males of their own color variant (ascertained in a previous experiment) were not overturned when males of another color variant were presented in a superior territory, indicating that within- and between-population mate preferences of females depend on different cues.

Uniparental maternal brood care often coincides with multiple paternity and single maternity of broods, possibly reflecting benefits of polyandry and costs of uniparental care. Genetic data from the maternally mouthbrooding cichlid fish Simochromis pleurospilus revealed the opposite pattern – low polyandry and allomaternal care. More than 70% of the investigated females had mated with a single male, and 14% of the females had unrelated fry in their broods. Broods with foreign fry were in the late stage of brood care, in which females guard free‐swimming fry and recall the broods into their mouths for protection. With one exception, fostering females were related to their adopted fry at the level of first cousins (RQG > 0.12), but relatedness between fosters and adopted fry was not significantly higher than between fosters and fry tended by other females. Relatedness among breeders extended to the level of first‐order relatives. Mean relatedness among contemporaneously breeding dams (RQG = 0.08) was significantly higher than among dams breeding in different seasons (RQG = −0.04), which suggests a temporal or spatial concentration of mouthbrooding relatives. Indeed, females sometimes brood in small groups. This behaviour may reduce brood predation but will increase the risk of brood mixing, which is possibly mitigated by low costs of brood care and indirect benefits accrued by relatedness among the breeders in the group. Remarkably, the apparent inbreeding potential did not give rise to bet‐hedging polyandry or active avoidance of relatives, as half of the mated individuals were related at RQG > 0.13 and polyandry did not coincide with high within‐pair relatedness.

Phylogenetic analysis identified haplochromine cichlids from isolated water bodies in the eastern branch of the East African Rift system as an ancient lineage separated from their western sister group in the course of the South Kenyan-North Tanzanian rift system formation. Within this lineage, the close phylogenetic relatedness among taxa indicates a recent common ancestry and historical connections between now separated water bodies. In connection with a total lack of local genetic diversity attributable to population bottlenecks, the data suggest cycles of extinction and colonization in the unstable habitat provided by the small lakes and rivers in this geologically highly active area.