Maturational costs of reproduction due to clutch size and ontogenetic conflict as revealed in the invisible fraction

Abstract

Reproduction is thought to entail costs, but assessing survival costs associated with maturation as organisms express reproductive genes for the first time is problematic because many will die prior to expressing a phenotype. We quantified selection acting on this invisible fraction by measuring selection on predicted breeding values for clutch size estimated from a multigenerational pedigree of side-blotched lizards in which clutch size was heritable (h 2 Z0.25G0.04). The survival effects of predicted breeding values for clutch size during maturation, however, differed between males and females indicating ontogenetic conflict. Increased mortality during maturation was associated with lower predicted breeding values for clutch size for females, but higher predicted breeding values for males who do not produce a clutch. Genetic correlations between clutch size and male and female survival were consistent with calculated selection differentials. Experimental yolk removal did not affect progeny survival during maturation, indicating that selection on maturing progeny was not due to confounding yolk-volume maternal effects, and hormone manipulations confirmed clutch size as the target of viability selection during maturation. Such episodes of selection prior to phenotypic expression of the trait will have important consequences for the evolution of reproductive investment.

Offspring size and timing of hatching determine survival and reproductive output in a lizard

“…Such traits include timing of reproduction, length of breeding season, egg size and number, egg composition, nest site choice, and developmental rate. Differences in selection, and its temporal and spatial variability within species, may partly explain interspecific variation in mating systems Sinervo and McAdam 2008), sex allocation and sex determination (Calsbeek and Sinervo 2004;Uller and Olsson 2006b;Warner and Shine 2008a;Warner et al 2009) and other fundamental aspects of the biology of short-lived lizards. Notably, U. stansburiana show complex dynamics of color morphs linked to mating strategies and reproductive investment, with associated non-linear fitness surfaces Sinervo and Lively 1996).…”

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

“…Bennington & McGraw (1995) showed that selection on plant height of jewelweed is significantly altered when the invisible fraction is taken into account. Sinervo & McAdam (2008) assessed the survival of side-blotched lizards before sexual maturity and revealed non-random mortality prior to clutch-size expression. Hadfield (2008) recently considered a variety of invisible fraction scenarios, and questioned whether any non-manipulative method can accurately estimate selection when individuals die before trait expression.…”

Introduction. Evolutionary dynamics of wild populations: the use of long-term pedigree data

“…The ability to incorporate real-world variability can therefore become a strength rather than a weakness of the studies of natural populations. As an illustration of this awareness, the studies presented in this issue explore the effects of ecological or environmental heterogeneity on: genetic variance (Brommer et al 2008), natural and sexual selection (Cockburn et al 2008;Sinervo & McAdam 2008), life-history trade-offs (Gillespie et al 2008), and inbreeding (Szulkin & Sheldon 2008). Growing awareness of the effects of anthropogenic climate change has also greatly encouraged interest in the impact of changing environmental conditions ( Visser 2008).…”

“…In many cases, careful analyses can do no more than to conclude that while there is some support for the phenomenon being tested, the current data have insufficient power to distinguish between relevant hypotheses (e.g. Brommer et al 2008;Keller et al 2008;Nussey et al 2008;Sinervo & McAdam 2008). Many such studies aim to quantify the magnitude of some form of variance component, for example additive genetic variance or differences between individuals in reaction norms in a changing environment.…”

“…This may be via selection acting on other correlated traits, which are effectively invisible if not incorporated into analyses, or simply because viability selection on the focal trait prior to census alters that trait's distribution; the dead are similarly invisible. Hadfield (2008) quantifies the dramatic effect that such invisibility can have on estimation procedures, and the concept is explored empirically with long-term data from a lizard population (Sinervo & McAdam 2008).…”