Tony D. Williams

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In species where offspring fitness is sex-specifically influenced by maternal reproductive condition, sex allocation theory predicts that poor-quality mothers should invest in the evolutionarily less expensive sex. Despite an accumulation of evidence that mothers can sex-specifically modulate investment in offspring in relation to maternal quality, few(More)
Twenty years ago, Albert Bennett published a paper in the influential book New directions in ecological physiology arguing that individual variation was an 'underutilized resource'. In this paper, I review our state of knowledge of the magnitude, mechanisms and functional significance of phenotypic variation, plasticity and flexibility in endocrine systems,(More)
T has long been a dichotomy of opinion as to whether egg production is biologically costly or not. On the one hand, many research articles have included statements such as “Egg production is energetically or nutritionally demanding,” based mainly on early theoretical estimates of energy and protein requirements (Carey 1996). In contrast, Lack (1947) set a(More)
Current research in birds suggests that a conflict should exist during reproduction for the role of the glucocorticoid corticosterone (CORT). While elevated levels have been correlated with the increased energetic demand of raising offspring, elevated CORT levels have traditionally been implicated in reproductive abandonment. We examined the relationship(More)
The question of why maternal stress influences offspring phenotype is of significant interest to evolutionary physiologists. Although embryonic exposure to maternally derived glucocorticoids (i.e., corticosterone) generally reduces offspring quality, effects may adaptively match maternal quality with offspring demand. We present results from an interannual(More)
Optimal functioning of the hypothalamo-pituitary-adrenal (HPA) axis is paramount to maximizing fitness in vertebrates. Research in laboratory mammals has suggested that maternally-induced stress can cause significant variation in the responsiveness of an offspring's HPA axis involving both pre- and post-natal developmental mechanisms. However, very little(More)
Corticosterone has received considerable attention as the principal hormonal mediator of allostasis or physiological stress in wild animals. More recently, it has also been implicated in the regulation of parental care in breeding birds, particularly with respect to individual variation in foraging behavior and provisioning effort. There is also evidence(More)
Although individual variation is a key requirement for natural selection, little is known about the magnitude and patterns of individual variation in endocrine systems or the functional significance of that variation. Here we describe (1) the extent and repeatability of inter-individual variation in adrenocortical responses and (2) its relationship to(More)
The metabolic cost of egg production in birds (passerines) has been measured as a 16-27% increase in basal or resting metabolic rate (BMR and RMR, respectively) when comparing non-breeding values with those in egg-producing individuals. However, available data to date have been obtained in free-living birds and may thus be confounded by the effect of(More)
Polyhalogenated aromatic hydrocarbons are global contaminants that are often considered to be endocrine disruptors and include 1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (p,p'-DDE), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). The present study examined these compounds and their hydroxylated metabolites or analogues and(More)