Habitat structures and reproductive features suggesting a maintenance mechanism of reproductive isolation between ecomorphs of a herbivorous cichlid fish from Lake Tanganyika

Ecological speciation, driven by divergent selection across varying environments, is crucial for the evolution of biodiversity. To comprehend this phenomenon fully, investigating ongoing speciation events is imperative. Telmatochromis temporalis, a herbivorous cichlid endemic to Lake Tanganyika, recently revealed the existence of a slender morph inhabiting deep waters. Despite genetic similarity, it is reproductively isolated from the parapatric population of the normal morph inhabiting shallow waters. This study examined substrate features and life history traits to propose a mechanism that maintains the parapatric distribution, which likely contributes to reproductive isolation. The normal morph displayed a preference for natural shelters between rocks and invested significant energy on reproduction, likely well-adapted to shallow waters abundant in natural shelters and food resources. In contrast, the slender morph seemed to construct nests beneath rocks tailored to its body size and exhibited energy-saving reproduction, likely suited to deep waters with scarce natural shelters and food resources. These adaptive differences are likely responsible for parapatric distribution. Additionally, I discussed the potential for the slender morph and another morph, the dwarf morph, to have evolved in parallel from the normal morph through divergent natural selection, depending on the environmental challenges faced by the normal morph.