Tetsumi Takahashi

Abstract Lake Tanganyika harbours an exceptionally diverse fauna of cichlids that has arisen through explosive adaptive radiation. During a recent survey at Kasenga and Kombe, Zambia, we discovered an undescribed species of the genus Neolamprologus . The new species is readily distinguished from its congeners by its uniquely developed upper lip, which protrudes conspicuously beyond the lower lip, along with several additional morphological characters. Phylogenetic analysis of the mitochondrial NADH dehydrogenase subunit 2 gene showed that specimens of the new species were not recovered as monophyletic; instead, they formed a clade together with Neolamprologus mustax . Nevertheless, the new species is morphologically clearly distinct from N. mustax despite their sympatric occurrence. This discovery highlights the still underestimated diversity of cichlids in Lake Tanganyika and underscores the importance of documenting its fauna in the face of increasing anthropogenic pressures on the lake's ecosystem.

Abstract The evolution of sexual dimorphism is widely acknowledged as a manifestation of sex-specific genetic architecture. Although empirical studies suggested that sexual dimorphism evolves as a joint consequence of constraints arising from genetic architecture and sexually divergent selection, it remains unclear whether and how these established microevolutionary processes scale up to the macroevolutionary patterns of sexual dimorphism among taxa. Here, we studied how sexual selection and parental care drive sexual dimorphism in cichlid fishes from Lake Tanganyika. We found that male–male competition, female choice, and maternal mouthbrooding are associated with sexual dimorphism in body length, body colour, and head length, respectively, despite strong allometric relationships between body length and head length. Within-species (static) allometry of head length on body length evolved as sex-specific responses to mouthbrooding, where females evolved higher intercepts while males evolved steeper slopes. Thus, selection to increase mouth size in mouthbrooders may have broken down and reorganized the pattern of allometric constraints that are inherently strong and concordant between sexes. Furthermore, sex-specific responses to mouthbrooding left a remarkably clear signature on the macroevolutionary pattern, resulting in a decoupling of co-evolution in parameters of static allometries between sexes observed exclusively within maternal mouthbrooders. Our study provides multiple lines of evidence that are consistent with the idea that macroevolutionary patterns of sexual dimorphism in Lake Tanganyika cichlids result from sexually divergent selection. Our approach illustrates that an examination of within-population phenotypic variance in the phylogenetic comparative framework may facilitate nuanced understandings of how macroevolutionary patterns are generated by underlying microevolutionary processes.