Metabolic consequences of sex-reversal in two lizard species: a test of the like genotype and like phenotype hypotheses

Abstract

Vertebrate sex is typically determined genetically, but in many ectotherms sex can be determined by genes (Genetic Sex Determination: GSD), temperature (Temperature-dependent Sex Determination: TSD), or interactions between genes and temperature during development. Temperature dependent sex determination may involve GSD systems with either male or female heterogamety (XX/XY or ZZ/ZW) where temperature overrides chromosomal sex determination to cause a mismatch between genetic sex and phenotypic sex (sex-reversal). In these temperature-sensitive lineages, phylogenetic investigations point to recurrent evolutionary shifts between genotypic and temperature-dependent sex determination. These evolutionary transitions in sex determination can occur rapidly if selection favours the reversed sex over their concordant phenotypic sex. To investigate the consequences of sex-reversal on offspring fitness, we measured two energy-driven traits often linked to fitness (metabolism and growth-rate) and 6-month survival in two species of reptile with different patterns of temperature-induced sex-reversal. Male sex-reversal occurs in Bassiana duperreyi when chromosomal females (femaleXX) develop male phenotypes (maleSRXX), while female sex-reversal occurs in Pogona vitticeps when chromosomal males (maleZZ) develop female phenotypes (femaleSRZZ). We show metabolism in maleSRXX was like that of maleXY, that is, reflective of phenotypic sex and lower than genotypic sex. In contrast, for Pogona vitticeps, femaleSRZZ metabolism was intermediate between maleZZ and femaleZW metabolic rate. For both species, our data indicate differences in metabolism become more apparent as individuals become larger. Our findings provide some evidence for a fitness advantage from sex-reversal in both species but do not exclude energetic processes as a constraint on the distribution of sex-reversal in nature.

Interactive effects of intrinsic and extrinsic factors on metabolic rate

“…[24,[38][39][40][41][42]44,93,94]) life-history stage (e.g. [20,32,40,[47][48][49][50]66,91,123,126,[129][130][131][132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147]) interactive effects of intrinsic factors ecological life style pelagic versus benthic (e.g. [20,24,34,40,92,93]) food habits (e.g.…”

“…[255,256]) body size and taxonomic affinity variable related to differences in physiological/ecological lifestyle that are described below [1,9,20,23,25,[28][29][30][31][32][33][34][35][36] body size and cell size or cellular mode of growth variable mass-scaling of metabolism depends on cell size and the cellular mode of growth (i.e. cell enlargement versus multiplication, which affects metabolically relevant cellular surface area to body volume ratios) [24,32,[36][37][38][39][40][41][42] body size and genome size variable mass-scaling of metabolism relates to genome size, presumably because of its association with cell size (see above) [32,41] body size and genotype variable mass-scaling of metabolism differs between genotypes for unknown reasons [43][44][45][46][47] body size and gender size variable mass-scaling of metabolism differs between males and females often for unknown reasons. Gender-related differences in body composition may be involved in some cases (e.g.…”