Lazy males? Bioenergetic differences in energy acquisition and metabolism help to explain sexual size dimorphism in percids

Abstract

Summary1. Differences in energy use between genders is a probable mechanism underlying sexual size dimorphism (SSD), but testing this hypothesis in the field has proven difficult. We evaluated this mechanism as an explanation for SSD in two North American percid species -walleye Sander vitreus and yellow perch Perca flavescens . 2. Data from 47 walleye and 67 yellow perch populations indicated that SSD is associated with the onset of maturation: typically, males of both species matured smaller and earlier and attained a smaller asymptotic size than females. Males also demonstrated equal (perch) or longer (walleye) reproductive life spans compared with females. 3. To examine whether reduced post-maturation growth in males was due to lower energy acquisition or higher reproductive costs we applied a contaminant mass-balance model combined with a bioenergetics model to estimate metabolic costs and food consumption of each sex. Mature males exhibited lower food consumption, metabolic costs and food conversion efficiencies compared with females. 4. We propose that slower growth in males at the onset of maturity is a result of decreased feeding activity to reduce predation risk. Our finding that SSD in percids is associated with the onset of maturity is supported by laboratory-based observations reported elsewhere, showing that changes in growth rate, consumption and food conversion efficiency were elicited by oestrogen (positive effects) or androgen (negative effects) exposure in P. flavescens and P. fluviatilis . 5. Researchers applying bioenergetic models for comparative studies across populations should use caution in applying bioenergetic models in the absence of information on population sex ratio and potential differences between the sexes in energetic parameters.

Temperature tolerance and energetics: a dynamic energy budget-based comparison of North Atlantic marine species

“…However, males can also have additional 'reproduction-related' costs, namely territorial behaviour or parental care, which should be accounted. Differences in energy acquisition and assimilation seem to be the underlying cause for sexual differences in some flatfishes like dab L. limanda (Lozán 1992) and in percids (Rennie et al 2008).…”

The influence of external subsidies on diet, growth and Hg concentrations of freshwater sport fish: implications for management and fish consumption advisories

“…McClain et al 2006 observed similar patterns in male and female walleye growth and Hg concentrations and alluded to Henderson et al 2003 to explain these findings. Rennie et al 2008 suggested that differences in male and female walleye growth and Hg concentrations were likely attributable to ''laziness'', suggesting that male walleye foraging was greatly reduced at the onset of maturity presumably to avoid predation as posited by Roff 1983, though the authors did not discount the importance of the supposition by Henderson et al 2003. Our results indicate that another mechanism may be influencing walleye sexual dimorphism and Hg concentrations.…”

“…For example, fish sex (Henderson et al 2003;Rennie et al 2008), size (Harris and Bodaly 1998), diet and trophic position (Harris and Bodaly 1998;Power et al 2002;Sackett et al 2010) and growth (Simoneau et al 2005;Ward et al 2010) have all been shown to play a role in Hg bioaccumulation. Anthropogenic manipulation of food webs can alter the dynamics of these factors.…”

“…This mechanism, known as growth dilution, occurs when, ceteris paribus, fish that accumulate somatic tissue more efficiently and achieve larger sizes more quickly have lower contaminant concentrations than smaller, less efficient, slower-growing individuals (Verta 1990;Ward et al 2010). Growth dilution has been observed in sport fish, where females of the species grew more efficiently and had lower Hg concentrations relative to males with similar diets (Rennie et al 2008). Similarly, biomass dilution occurs in individual or populations of sport fish when, ceteris paribus (e.g., prey Hg concentration, availability, etc.)…”

Target size and optimal life history when individual growth and energy budget are stochastic

“…However, if 321 there are additional sex-specific differences in consumption, assimilation, metabolism or 322 mortality, the optimal growth trajectories of males and females may diverge earlier in life, 323 and before final structural size is attained. When such differences are caused by differences in 324 behavior between males and females (e.g., Rennie et al, 2008), the model may be extended 325 to include reversible behavioral transitions (which can then be optimized separately for males 326 and females), in addition to the irreversible structural growth, as presented and discussed in 327…”