Eco‐morphological differentiation in Lake Magadi tilapia, an extremophile cichlid fish living in hot, alkaline and hypersaline lakes in East Africa

Abstract

Ecological diversification through divergent selection is thought to be a major force during the process of adaptive radiations. However, the large sizes and complexity of most radiations such as those of the cichlids in the African Great Lakes make it impossible to infer the exact evolutionary history of any population divergence event. The genus Alcolapia, a small cichlid lineage endemic to Lakes Magadi and Natron in East Africa, exhibits phenotypes similar to some of those found in cichlids of the radiations of the African Great Lakes. The simplicity within Alcolapia makes it an excellent model system to investigate ecological diversification and speciation. We used an integrated approach including population genomics based on RAD-seq data, geometric morphometrics and stable isotope analyses to investigate the eco-morphological diversification of tilapia in Lake Magadi and its satellite lake Little Magadi. Additionally, we reconstructed the demographic history of the species using coalescent simulations based on the joint site frequency spectrum. The population in Little Magadi has a characteristically upturned mouth possibly an adaptation to feeding on prey from the water surface. Eco-morphological differences between populations within Lake Magadi are more subtle, but are consistent with known ecological differences between its lagoons such as high concentrations of nitrogen attributable to extensive guano deposits in Rest of Magadi relative to Fish Springs Lagoon. All populations diverged simultaneously only about 1100 generations ago. Differences in levels of gene flow between populations and the effective population sizes have likely resulted in the inferred heterogeneous patterns of genome-wide differentiation.

Magadi tilapia ecological specialization: filling the early gap in the speciation continuum

“…Kavembe et al . () conclude that this rapid trophic diversification accompanied by morphological and genetic divergence is compatible with early stages of ecological speciation.…”

“…Using diverse approaches, Kavembe et al . () provide relevant insights about ecological specialization and genetic differentiation in this species (Fig. ).…”

“…In this issue of Molecular Ecology, Kavembe et al . () report very recent genetic diversification accompanied by ecological specialization in cichlids of the small and ecologically extreme Lake Magadi, in Kenya. Combining geometric morphometrics, stable isotope analysis, population genomics using RADS eq data and coalescent‐based modelling techniques, the authors characterize the eco‐morphological differences between genetically distinct populations of Magadi tilapia ( Alcolapia grahami ), which are consistent with the different environmental conditions they experience, and infer their history of divergence.…”

Gene(s) and individual feeding behavior: Exploring eco‐evolutionary dynamics underlying left‐right asymmetry in the scale‐eating cichlid fish Perissodus microlepis

“…Similar or lower sample sizes had previously been successful in detecting feeding differences in other fish species (e.g., Ford et al., 2016; Kavembe et al., 2016; Manousaki et al., 2013) and the selection of the most extreme specimens contributes to maximize the power of finding differences between groups. The diet during the period over which a tissue is synthesized determines the stable isotope signatures of the tissue.…”

“…Stable isotope analysis is the identification of the distribution of chemical isotopes within organisms’ tissues. It has been successfully used to address many issues in ecology, supplementing measures from stomach contents (reviewed in Araújo, Bolnick, & Layman, 2011; Bearhop, Adams, Waldron, Fuller, & MacLeod, 2004; examples from cichlid fish: Ford et al., 2016; Hata, Shibata, Omori, Kohda, & Hori, 2015; Kavembe, Kautt, Machado‐Schiaffino, & Meyer, 2016; Malinsky et al., 2015), and it is particularly useful to analyze diet differences among individuals, as variation in feeding behavior is reflected in their isotopic differences (Araújo, Bolnick, Machado, Giaretta, & Dos Reis, 2007; Fry et al., 1999). Trophic studies typically use the naturally occurring carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope.…”