Individual repeatability and heritability of divorce in a wild population

Understanding micro-evolutionary responses of mating systems to contemporary selection requires estimating sex-specific additive genetic variances and cross-sex genetic covariances in key reproductive strategy traits. One key trait comprises the occurrence of divorce versus mate fidelity across sequential reproductive attempts. If divorce represents an evolving behavioural strategy that responds to selection it must have non-zero individual repeatability and heritability, but quantitative estimates from wild populations are scarce. We used 39 years of individual breeding records and pedigree data from free-living song sparrows ( Melospiza melodia ) to quantify sex-specific permanent individual and additive genetic variances, and hence estimate repeatability and heritability, in liability for divorce. We estimated moderate repeatability among females, but little repeatability among males. Estimates of additive genetic variance were small in both sexes, and the cross-sex genetic covariance was close to zero. Consequently, the total heritability was small but likely non-zero, indicating low potential for micro-evolutionary response to selection. Rapid micro-evolutionary change of divorce rate, therefore, appears unlikely, even if there were substantial fitness benefits of divorce and resulting selection.

Individual repeatability and heritability of divorce in a wild population

ABSTRACTUnderstanding micro-evolutionary responses of mating systems to contemporary selection requires estimating sex-specific additive genetic variances and cross-sex genetic covariances in key reproductive strategy traits. One key trait comprises the occurrence of divorce versus mate-fidelity across sequential reproductive attempts. If divorce represents an evolving behavioural strategy it must have non-zero individual repeatability and heritability, but quantitative estimates from wild populations are scarce. We used 39 years of individual breeding records and pedigree data from free-living song sparrows (Melospiza melodia) to quantify sex-specific permanent individual and additive genetic variances, and hence estimate repeatability and heritability, in liability for divorce. We estimated moderate repeatability in females, but little repeatability in males. Estimates of additive genetic variance were small in both sexes, and the cross-sex genetic covariance was close to zero. However, the total heritability was likely non-zero but small, indicating low potential for micro-evolutionary response to selection. Rapid micro-evolution of divorce rate therefore appears unlikely, even if there were substantial fitness benefits of divorce and resulting selection.

Breeding of White-tailed Tropicbirds (Phaethon lepturus) in the western South Atlantic

Basic information on natural history is crucial for assessing the viability of populations, but is often lacking for many species of conservation concern. One such species is the White-tailed Tropicbird, Phaethon lepturus (Mathews, 1915). Here, we address this shortfall by providing detailed information on reproductive biology, distribution and threats on the Fernando de Noronha archipelago, Brazil – the largest colony of P. lepturus in the South Atlantic. We assessed reproduction from August 2011 to January 2012 by monitoring tropicbird nests and their contents. A population estimate was obtained through a combination of active searches for nests and by census at sea between 2010 and 2012. Breeding success was calculated by traditional methods. The growth curve of chicks and life table were also calculated. Additional information on nest and mate fidelity and on age of breeding birds was obtained from the banded birds. Our results indicate that the unusual nest form (limestone pinnacles) and predation by crabs may be responsible for the observed patterns of hatching and fledging success. Although the Fernando de Noronha population appears to be stable (at between 100-300 birds), a long term monitoring program would be desirable to assess fluctuations in this globally important population. Conservation strategies should focus on controlling predation by land crabs and tegu lizards.

Male-biased sex ratios and plasticity in post-insemination behaviour in the New Zealand stick insect Micrarchus hystriculeus

The duration of mate guarding by males is predicted to vary in accordance with the risk of sperm competition or mate encounter rate. Mate guarding is predicted to be prolonged under a male-biased sex ratio because the risk of sperm competition is high or the mate encounter rate is low. A consistently male-biased sex ratio should thus select for greater mate fidelity, and reduced plasticity in guarding behaviour, by males. Micrarchus hystriculeus Westwood (Phasmatodea) is a sexually size dimorphic stick insect in which males form prolonged post-insemination associations with their mates and whose populations have a consistently male-biased sex ratio. My laboratory experiments showed, as predicted, little plasticity by males in the duration of their post-insemination association. Although mate guarding duration is similar under male- and female-biased sex ratios, males clasped the genitalia of their mates significantly more often under a male-biased sex ratio, suggesting that males intensify their guarding with increasing risk of sperm competition.