Convergent Evolution within an Adaptive Radiation of Cichlid Fishes

Abstract

The recurrent evolution of convergent forms is a widespread phenomenon in adaptive radiations (e.g., [1-9]). For example, similar ecotypes of anoles lizards have evolved on different islands of the Caribbean, benthic-limnetic species pairs of stickleback fish emerged repeatedly in postglacial lakes, equivalent sets of spider ecomorphs have arisen on Hawaiian islands, and a whole set of convergent species pairs of cichlid fishes evolved in East African Lakes Malawi and Tanganyika. In all these cases, convergent phenotypes originated in geographic isolation from each other. Recent theoretical models, however, predict that convergence should be common within species-rich communities, such as species assemblages resulting from adaptive radiations. Here, we present the most extensive quantitative analysis to date of an adaptive radiation of cichlid fishes, discovering multiple instances of convergence in body and trophic morphology. Moreover, we show that convergent morphologies are associated with adaptations to specific habitats and resources and that Lake Tanganyika's cichlid communities are characterized by the sympatric occurrence of convergent forms. This prevalent coexistence of distantly related yet ecomorphologically similar species offers an explanation for the greatly elevated species numbers in cichlid species flocks.

Community assembly in Lake Tanganyika cichlid fish: quantifying the contributions of both niche‐based and neutral processes

“…Hence, it seems likely that we have missed some relevant traits and that some niche axes that are potentially important to explain diversity are not included in our analysis. In order to minimize this effect, we have focused here on traits associated with shifts in diet (total length, gut length, pharyngeal jaw shape, and body shape), which are known to differ most between habitats, as they are related to trade‐offs regarding resource uptake (McGee et al., 2015; Muschick et al., 2012). Furthermore, we have included stable isotope ratios of carbon and nitrogen, which are known to reflect trophic level and food type (Muschick et al., 2012).…”

“…In order to minimize this effect, we have focused here on traits associated with shifts in diet (total length, gut length, pharyngeal jaw shape, and body shape), which are known to differ most between habitats, as they are related to trade‐offs regarding resource uptake (McGee et al., 2015; Muschick et al., 2012). Furthermore, we have included stable isotope ratios of carbon and nitrogen, which are known to reflect trophic level and food type (Muschick et al., 2012). Our choice of traits therefore focuses on adaptations related to food uptake and diet, which we expected to be important drivers of diversity.…”

The Geography of Ecological Niche Evolution in Mammals

“…However, parallelism and convergence are part of a continuum, hampering any clear distinction among them [1,4], thus, we use the term convergence for all phylogenetic scales (as proposed by ref [4], 'parallelism' should be restricted to characterize the degree of molecular similarities underlying phenotypic convergences). Convergent evolution leads to higher ecological niche and trait similarity between unrelated species than expected under neutral evolution, where niches or traits shift along a continuous axis or between discrete states in a random way through evolutionary time [2,3,6,7]. While these neutral-like evolution can be generated by randomly fluctuating natural selection [8] typical random walk models still represent the most realistic macroevolutionary models of neutral evolution so far.…”

“…While these neutral-like evolution can be generated by randomly fluctuating natural selection [8] typical random walk models still represent the most realistic macroevolutionary models of neutral evolution so far. There is empirical evidence of convergent trait and niche evolution in all major kingdoms [3,[9][10][11][12]] but this has not yet been quantified at the species scale for large clades, or at the scale of entire species assemblages at broad spatial scales (e.g. grid-based assemblages).…”

“…the appearance of similar niches in independent lineages-is the result of natural selection acting on niche-related species traits ('traits' hereafter) and contrasts with neutral evolution [1][2][3][4]. While trait convergences are recognized as being of importance at the species scale, we still know little about the impact of species convergence on the overall trait and niche structure of entire biotas at large spatial scales [5].…”