Competition-driven speciation in cichlid fish

Abstract

Theoretically, competition can initiate divergence in habitat use between individuals of a species, leading to restricted gene flow and eventual speciation. Evidence that sister species differ in habitat use is commonplace and consistent with this mechanism, but empirical experimental support is surprisingly scarce. Here we provide evidence that competition has taken a key role in the evolution of genetically distinct ecomorphs of the Lake Tanganyika cichlid fish Telmatochromis temporalis. Experiments show that differences in substrate use between a large-bodied rock-living ecomorph and a neighbouring small-bodied shell-living ecomorph are mediated by size-dependent competition that drives assortative mate-pair formation. Specifically, adults of the larger ecomorph outcompete adults of the smaller ecomorph on favoured rock substrate, compelling the smaller adults to use shell habitat. These results support a role for competition in maintaining reproductive isolation, and highlight the need to identify ecological processes that impose selection to improve our understanding of speciation and adaptive radiation.

Asymmetric dominance and asymmetric mate choice oppose premating isolation after allopatric divergence

“…In contrast to the above examples, asymmetries in competitive abilities can also launch processes which promote assortative mating, for example when asymmetric dominance relationships between taxa underlie their segregation into different habitats (Vallin and Qvarnström 2011; Vallin et al., 2012b; Winkelmann et al. 2014). We cannot rule out the possibility that asymmetric dominance relationships between Tropheus morphs in secondary contact would also result in habitat segregation and thereby strengthen rather than weaken reproductive isolation.…”

Ecological opportunity leads to the emergence of an alternative behavioural phenotype in a tropical bird

“…Similarly, Winkelmann and others (Winkelmann et al . ) conclude that competition played an important role in speciation and in maintenance of ecomorphs in cichlid fish in Lake Tanganyika, while Bailey and others (Bailey et al . ) found the extent of diversification in experimentally altered Pseudomonas microcosms to be determined by the strength of resource competition by conspecifics, in relation to the degree of ecological opportunity provided by levels of interspecific competitors.…”

Depth and substratum differentiations among coexisting herbivorous cichlids in Lake Tanganyika

“…Furthermore, repeated lake-level fluctuation is thought to drive diversification of Tanganyikan cichlids through the repetitive shrinking and expansion of habitats [75]. A Tanganyikan cichlid, T. temporalis , has diversified into two genetically distinct ecomorphs: a large-bodied rock-living ecomorph and a small-bodied shell-living ecomorph [76,77]. This diversification occurred repeatedly in places where rocky habitats and shell beds were neighbouring.…”

“…This diversification occurred repeatedly in places where rocky habitats and shell beds were neighbouring. Therefore, a variant that was small in size when mature, originating from the original population in the rocky habitat, is thought to have shifted to the shell bed when the shell bed reached a suitable depth due to lake-level changes [77]. …”