Abstract
Phenotypic differences may have genetic and plastic components. Here, we investigated the contributions of both for differences in body shape in two species of Lake Malawi cichlids using wild‐caught specimens and a common garden experiment. We further hybridized the two species to investigate the mode of gene action influencing body shape differences and to examine the potential for transgressive segregation. We found that body shape differences between the two species observed in the field are maintained after more than 10 generations in a standardized environment. Nonetheless, both species experienced similar changes in the laboratory environment. Our hybrid cross experiment confirmed that substantial variation in body shape appears to be genetically determined. The data further suggest that the underlying mode of gene action is complex and cannot be explained by simple additive or additive‐dominance models. Transgressive phenotypes were found in the hybrid generations, as hybrids occupied significantly more morphospace than both parentals combined. Further, the body shapes of transgressive individuals resemble the body shapes observed in other Lake Malawi rock‐dwelling genera. Our findings indicate that body shape can respond to selection immediately, through plasticity, and over longer timescales through adaptation. In addition, our results suggest that hybridization may have played an important role in the diversification of Lake Malawi cichlids through creating new phenotypic variation.
Highlights
Understanding the drivers of phenotypic diversification remains one of the central goals of evolutionary biology
We performed a common garden experiment and hybrid crosses to estimate the potential of plasticity and transgressive segregation contributing to body shape variation in a sympatric pair of
Transgressive phenotypes resemble some other taxa within the Lake Malawi cichlid radiation suggesting that some of the radiation may have been seeded by variation resulting from hybridization
Summary
Understanding the drivers of phenotypic diversification remains one of the central goals of evolutionary biology. Recently separated species driven apart by consistent divergent selection are not expected to exhibit transgressive segregation (Albertson & Kocher, 2005) Due to their potential to generate phenotypic variation, both phenotypic plasticity and transgressive segregation have been suggested to play crucial roles in adaptive radiations (Genner & Turner, 2012; Seehausen, 2004; Selz et al, 2014). A classic axis of body shape divergence in fishes is the divergence into deep-bodied and slender-bodied morphs associated with adaptation to benthic and limnetic macrohabitats This pattern has been documented in a variety of species (e.g., Schluter, 1993; Willacker, Hippel, Wilton, & Walton, 2010) including Lake Malawi cichlids (Hulsey et al, 2013). We anticipated to gain an insight into the roles of plasticity and transgression for body shape divergence in the adaptive radiation of Lake Malawi cichlids
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