Evolution of pleiotropic alleles for maturation and size as a consequence of predation

Abstract

Understanding life-history evolution requires knowledge about genetic interactions, physiological mechanisms and the nature of selection. For platyfish, Xiphophorus maculatus, extensive information is available about genetic and physiological mechanisms influencing lifehistory traits. In particular, alleles at the pituitary locus have large and antagonistic effects on age and size at sexual maturation. To examine how predation affects the evolution of these antagonistic traits, I examined pituitary allele evolution in experimental populations differing in predation risk. A smaller size, earlier maturation allele increased in frequency when predators were absent, while a larger size, later maturation allele increased in frequency when predators were present. Thus, predation favours alleles for larger size, at the cost of later maturation and reproduction. These findings are interesting for several reasons. First, predation is often predicted to favour early reproduction at smaller sizes. Second, few studies have shown how selection acts on alleles that affect age and size at sexual maturation. Finally, many studies assume that trade-offs between these life-history traits result from antagonistic pleiotropy, with alleles that positively affect one trait negatively affecting another, yet this is rarely known. This study unequivocally demonstrates that genetically based trade-offs affect life-history evolution in platyfish.

Selection for a dominant oncogene and large male size as a risk factor for melanoma in the Xiphophorus animal model

“…1990; Basolo 1998) and that larger males tend to be dominant to (Earley & Dugatkin 2006) and win fights against smaller males (Ribowski & Franck 1993). In addition to sexual selection, Xiphophorus with larger body sizes experience decreased predation risk in both natural (Basolo & Wagner 2004) and laboratory populations (Basolo 2008) compared to smaller individuals. Therefore, this result establishes selection for the Xmrk oncogene in the context of both sexual selection and natural selection.…”

Viability selection prior to trait expression is an essential component of natural selection

“…Most notably, there is a clear developmental connection between flower size and development rate. Antagonistic pleiotropy has been invoked as an explanation for the evolution of late-life fecundity (Rauser et al 2006), age and size of sexual maturation (Basolo 2008), senescence (Curtsinger et al 1994;Williams & Day 2003), and the maintenance of genetic variation (Charlesworth & Hughes 2000). Given that flower size exhibits abundant genetic variation within the Iron Mountain population and that this variation cannot be explained by mutation -selection balance (Kelly & Willis 2001;Kelly 2003;Lee 2009), antagonistic pleiotropy emerges as a potentially important mechanism.…”

Risk, resources and state-dependent adaptive behavioural syndromes

“…larger size or energy reserves, better condition or vigour) cope better with predators either by fleeing faster or by being better at defending themselves (e.g. Temple 1987;Chase 1999;Downes 2002;Iriarte-Diaz 2002;Caro 2005;Lindstrom et al 2006;Alzaga et al 2008;Basolo 2008;Hoefler et al 2008;Arendt 2009;Stankowich 2009). Accordingly, although foragers feeding on immobile prey often prefer larger prey with more energy (i.e.…”