Mechanical Transgressive Segregation and the Rapid Origin of Trophic Novelty

Abstract

Hybrid phenotypes are often intermediate between those of parental species. However, hybridization can generate novel phenotypes when traits are complex. For instance, even when the morphologies of individual musculo-skeletal components do not segregate outside the parental range in hybrid offspring, complex functional systems can exhibit emergent phenotypes whose mechanics exceed the parental values. To determine if transgression in mechanics could facilitate divergence during an adaptive radiation, we examined three functional systems in the trophic apparatus of Lake Malawi cichlid fishes. We conducted a simulation study of hybridization between species pairs whose morphology for three functional systems was empirically measured, to determine how the evolutionary divergence of parental species influences the frequency that hybridization could produce mechanics that transgress the parental range. Our simulations suggest that the complex mechanical systems of the cichlid trophic apparatus commonly exhibit greater transgression between more recently diverged cichlid species. Because (1) all three mechanical systems produce hybrids with transgressive mechanics in Lake Malawi cichlids, (2) hybridization is common, and (3) single hybrid crosses often recapitulate a substantial diversity of mechanics, we conclude that mechanical transgressive segregation could play an important role in the rapid accumulation of phenotypic variation in adaptive radiations.

Evolution of a soft‐tissue foraging adaptation in African cichlids: Roles for novelty, convergence, and constraint

“…The relationships and divergence times of our Lake Malawi and Lake Tanganyika cichlids (Fig. S3) are broadly congruent with previously published trees (e.g., Hulsey et al 2007;Day et al 2008;Sturmbauer et al 2010;Mcgee et al 2016;Holzman and Hulsey 2017). In general, nodes in Lake Tanganyika were well supported with high posterior probability (%PP).…”

“…S3) are broadly congruent with previously published trees (e.g., Hulsey et al 2007;Day et al 2008;Sturmbauer et al 2010;Mcgee et al 2016;Holzman and Hulsey 2017). S3) are broadly congruent with previously published trees (e.g., Hulsey et al 2007;Day et al 2008;Sturmbauer et al 2010;Mcgee et al 2016;Holzman and Hulsey 2017).…”

High-resolution Linkage Map with Allele Dosage Allows the Identification of an Apomixis Region and Complex Traits in Guinea Grass (Megathyrsus maximus)

“…Traits related to the productivity and quality of forage used for cattle fattening are categorized as complex traits, which are determined by both genetic and environmental factors. The transgressive segregation observed in these traits in M. maximus suggests quantitative and polygenic inheritance, consistent with the inheritance of non-Mendelian traits (Miles and Wayne, 2008;Holzman and Hulsey, 2017). For the characterization of the genetic architecture of such traits, a QTL mapping approach is required.…”

Evolutionary diversity as a catalyst for biological discovery

“…are genetic mosaics of the parent species, and can be used for quantitative trait loci (QTL) mapping of genes contributing to species-specific behaviors. QTL mapping has been used to identify genetic loci associated with many traits of interest in Malawi cichlids (Holzman & Hulsey, 2017; Husemann et al, 2017; Nandamuri et al, 2017; O’Quin et al, 2012; Parnell et al, 2008; 2012; Parsons et al, 2015; Selz et al, 2014; Svensson et al, 2011); and has recently been used to discover genetic loci contributing to extended phenotypes (burrow structures) and social behaviors in Peromyscus mice (Bendesky et al, 2017; Metz et al, 2017; Weber et al, 2013). …”