Sex differences in the response to environmental cues regulating seasonal reproduction in birds

Abstract

Although it is axiomatic that males and females differ in relation to many aspects of reproduction related to physiology, morphology and behaviour, relatively little is known about possible sex differences in the response to cues from the environment that control the timing of seasonal breeding. This review concerns the environmental regulation of seasonal reproduction in birds and how this process might differ between males and females. From an evolutionary perspective, the sexes can be expected to differ in the cues they use to time reproduction. Female reproductive fitness typically varies more as a function of fecundity selection, while male reproductive fitness varies more as a function sexual selection. Consequently, variation in the precision of the timing of egg laying is likely to have more serious fitness consequences for females than for males, while variation in the timing of recrudescence of the male testes and accompanying territory establishment and courtship are likely to have more serious fitness consequences for males. From the proximate perspective, sex differences in the control of reproduction could be regulated via the response to photoperiod or in the relative importance and action of supplementary factors (such as temperature, food supply, nesting sites and behavioural interactions) that adjust the timing of reproduction so that it is in step with local conditions. For example, there is clear evidence in several temperate zone avian species that females require both supplementary factors and long photoperiods in order for follicles to develop, while males can attain full gonadal size based on photoperiodic stimulation alone. The neuroendocrine basis of these sex differences is not well understood, though there are many candidate mechanisms in the brain as well as throughout the entire hypothalamo-pituitary-gonadal axis that might be important.

Optimal annual routines: behaviour in the context of physiology and ecology

“…They may also differ in behaviour. For example, male and female birds may have different responses to cues (Ball & Ketterson 2008) or different patterns of migration (e.g. Ketterson & Nolan 1979;Kjellen 1992;Mueller et al 2000).…”

Seasonal variation in corticosterone receptor binding in brain, hippocampus, and gonads in House Sparrows (Passer domesticus)

“…Tissue mass (for gonads) and GR and MR binding were compared among life history stages using analysis of variance (ANOVA). Because females are often more sensitive to environmental cues related to breeding (Ball and Ketterson 2008), which could include stressors, we also looked for sex differences in GR and MR binding in brain and hippocampus. In a full model that included sex, life history stage, and possible interactions, we found no sex effect (all P ≥ 0.11), which is consistent with previous studies in this species (Breuner and Orchinik 2001).…”

Individual variation in avian reproductive physiology does not reliably predict variation in laying date

“…many animals (of only one sex) per room or cage, as well as for shorter and less complex experimental designs, as the laying stage does not have to be reached. The most widely used proxies in avian research are, on one hand, gonadal growth, which means the increase in volume of the male left testis, or, more rarely [2] the development of the largest follicle in the female ovary, as well as plasma concentrations of gonadotropins, prolactin, or sex steroids, measured either in the blood or in feces. These measures can be taken at regular intervals during different reproductive stages.…”