Morphometric and Genetic Description of Trophic Adaptations in Cichlid Fishes

Abstract

Since Darwin, biologists have sought to understand the evolution and origins of phenotypic adaptations. The skull is particularly diverse due to intense natural selection on feeding biomechanics. We investigated the genetic and molecular origins of trophic adaptation using Lake Malawi cichlids, which have undergone an exemplary evolutionary radiation. We analyzed morphological differences in the lateral and ventral head shape among an insectivore that eats by suction feeding, an obligate biting herbivore, and their F2 hybrids. We identified variation in a series of morphological traits—including mandible width, mandible length, and buccal length—that directly affect feeding kinematics and function. Using quantitative trait loci (QTL) mapping, we found that many genes of small effects influence these craniofacial adaptations. Intervals for some traits were enriched in genes related to potassium transport and sensory systems, the latter suggesting co-evolution of feeding structures and sensory adaptations for foraging. Despite these indications of co-evolution of structures, morphological traits did not show covariation. Furthermore, phenotypes largely mapped to distinct genetic intervals, suggesting that a common genetic basis does not generate coordinated changes in shape. Together, these suggest that craniofacial traits are mostly inherited as separate modules, which confers a high potential for the evolution of morphological diversity. Though these traits are not restricted by genetic pleiotropy, functional demands of feeding and sensory structures likely introduce constraints on variation. In all, we provide insights into the quantitative genetic basis of trophic adaptation, identify mechanisms that influence the direction of morphological evolution, and provide molecular inroads to craniofacial variation.

The transcriptional state and chromatin landscape of cichlid jaw shape variation across species and environments

“…Significant efforts over the past 20 years have focussed on characterizing the genetic basis of cichlid craniofacial variation (e.g. Albertson et al, 2005; DeLorenzo et al, 2022; Hu & Albertson, 2017; Powder et al, 2014; Roberts et al, 2011; Singh et al, 2017). In addition, cichlids have long been a model of phenotypic plasticity (Huysseune, 1995; Machado‐Schiaffino et al, 2014; Meuthen et al, 2018; Meyer, 1987; Navon et al, 2020; Schneider et al, 2014; Wimberger, 1991), which is defined as the ability of a single genotype to produce a range of phenotypes in response to environmental inputs.…”

Epigenetics and the evolution of form: Experimental manipulation of a chromatin modification causes species‐specific changes to the craniofacial skeleton

“…This phenotypic divergence, coupled with tractable genetics and development, makes them an excellent system for investigating the molecular regulators of phenotypic variation (reviewed in Henning & Meyer, 2014; Kocher, 2004; Powder & Albertson, 2015; Salzburger, 2018; Svardal et al, 2021). While genetic changes are a cornerstone of the genotype‐phenotype relationship and have been associated with species‐specific facial differences in cichlids (Albertson et al, 2005; DeLorenzo et al, 2022; Matthews & Albertson, 2017; Parsons et al, 2014; Powder & Albertson, 2015; Powder et al, 2014, 2015; Roberts et al, 2011), they collectively only explain part of the morphological diversity of this radiation.…”