The Role of Haldane's Rule in Sex Allocation

Abstract

Sex allocation theory predicts that parents should bias their reproductive investments toward the offspring sex generating the greatest fitness return. When females are the heterogametic sex (e.g., ZW in butterflies, some lizards, and birds), production of daughters is associated with an increased risk of offspring inviability due to the expression of paternal, detrimental recessives on the Z chromosome. Thus, daughters should primarily be produced when mating with partners of high genetic quality. When female sand lizards (Lacerta agilis) mate with genetically superior males, exhibiting high MHC Class I polymorphism, offspring sex ratios are biased towards daughters, possibly due to recruitment of more Z-carrying oocytes when females have assessed the genetic quality of their partners. If our study has general applicability across taxa, it predicts taxon-specific sex allocation effects depending on which sex is the heterogametic one.

Differential sex allocation in sand lizards: bright males induce daughter production in a species with heteromorphic sex chromosomes

“…Furthermore, if one sex were particularly sensitive to maternal effects or genetic viability enhancement from a particularly good or compatible partner genome, then females would be predicted to overproduce that sex. In sand lizards (Lacerta agilis), as in birds, females are the heteromorphic sex and, hence, sex-linked genetic pathology probably occurs more in females than in males (Olsson et al , 2005. This is based on the fact that deleterious recessives on the hemizygous part of the Z chromosome are free to express their direct or epistatic negative effects (Olsson et al 2005).…”

“…In sand lizards (Lacerta agilis), as in birds, females are the heteromorphic sex and, hence, sex-linked genetic pathology probably occurs more in females than in males (Olsson et al , 2005. This is based on the fact that deleterious recessives on the hemizygous part of the Z chromosome are free to express their direct or epistatic negative effects (Olsson et al 2005). Furthermore, female sand lizards that mate with more major histocompatibility complex (MHC) diverse males overproduce daughters, and more MHC diverse males have more nuptial colouration (Olsson et al 2005).…”

Disentangling the complexities of vertebrate sex allocation: a role for squamate reptiles?

“…Thus, how sex determining mechanisms may constrain or otherwise affect sex ratio adjustment (e.g. due to sex-specific genetic effects coupled to sex chromosomes, Olsson et al 2004Olsson et al , 2005a can be tested from meta-analytical and comparative perspectives once such data become available (Mayhew andPen 2002, West et al 2005). The presence of temperature-dependent sex allocation patterns in some squamates further provides a possibility to experimentally test adaptive scenarios of sex allocation and its role in the evolution of sex determination.…”

“…1). However, squamate reptiles offer a suite of advantages (outlined below) that make them a potentially excellent model system that may provide novel insights into sex allocation biology as evident by recent publications (Uller et al 2004, Wapstra et al 2004, Langkilde and Shine 2005, Olsson et al 2005a, 2005b, Le Galliard et al 2005, Warner and Shine 2005, Allsop et al 2006, Uller and Olsson 2006). Here we provide a five-point argument for why biologists that typically use squamate models should consider sex allocation as a field of interest and why biologists with an interest in sex allocation could benefit from considering squamate reptiles as an alternative model system.…”

Sons are made from old stores: sperm storage effects on sex ratio in a lizard

“…For example, if the haploid genotype of the sperm is genetically compromised through ageing (e.g. due to higher free radical attacks on their mitochondria ;Harman 1956), their genes may be more suited for the production of a given sex offspring (typically the homogametic, which may suffer the least from genetic pathology; Olsson et al 2004Olsson et al , 2005a. Thus, if sperm characteristics change with sire age or prolonged storage, this warrants investigation of sperm storage effects on life-history traits in species where pronounced sperm storage forges a link between copulatory tactics and life-history evolution.…”