Parentage analyses via molecular markers have revealed multiple paternity within the broods of polytocous species, reshaping our understanding of animal behavior, ecology, and evolution. In a meta-analysis of multiple paternity in bird and mammal species, we conducted a literature search and found 138 bird and 64 mammal populations with microsatellite DNA paternity results. Bird populations averaged 19.5% multiple paternity and mammals more than twice that level (46.1%). We used a Bayesian approach to construct a null model for how multiple paternity should behave at random among species, under the assumption that all mated males have equal likelihood of siring success, given mean brood size and mean number of sires. We compared the differences between the null model and actual probabilities of multiple paternity. While a few bird populations fell close to the null model, most did not, averaging 34.0-percentage points below null model predictions; mammals had an average probability of multiple paternity 13.6-percentage points below the null model. Differences between bird and mammal species were also subjected to comparative phylogenetic analyses that generally confirmed our analyses that did not adjust for estimated historical relationships. Birds exhibited extremely low probabilities of multiple paternity, not only compared to mammals, but relative to other major animal taxa. The generally low probability of multiple paternity in birds might be produced by a variety of factors, including behaviors that reflect sexual selection (extreme mate guarding or unifocal female choice) and sperm competition (e.g., precedence effects favoring fertilization by early or late matings).

Seasonal dormancy (e.g. diapause, hibernation) is widely considered an adaptation for surviving life-threatening conditions during part of the year. However, the selective pressures acting on dormancy are poorly studied. An underestimated common aspect is the high survival rate during dormancy compared to the active period, perhaps due to the reduced risk of predation and competition. We hypothesize that dormancy phenology is influenced by a trade-off between the reproductive benefits of being active and the survival benefits of being dormant. Using a phylogenetic comparative method and more than 20 hibernating mammals, we find that the sex difference in hibernation phenology is explained by sex differences in physiological constraints that may influence this trade-off. Consistent with the trade-off hypothesis, the sex that spends more time in an activity directly associated with reproduction (e.g. testicular maturation, gestation) or indirectly (e.g. recovery from reproductive stress) spends less time in hibernation. Some of the tested parameters such as testes maturation or a late mating period during the active season also influence the sex difference in dormancy phenology among ectotherms (e.g. reptiles, invertebrates). We then gathered evidence that dormancy in non-life-threatening periods that are unfavorable for reproduction may be more widespread than previously thought.

Telomeres, the terminal repetitive DNA sequences at the ends of linear chromosomes, have strong associations with longevity in some major taxa. Longevity has been linked to rate of decline in telomere length in birds and mammals, and absolute telomere length seems to be associated with body mass in mammals. Using a phylogenetic comparative method and 30 species of birds, we examined longevity (reflected by maximum lifespan), absolute telomere length, the rate of change in telomere length (TROC), and body mass (often strongly associated with longevity) to ascertain their degree of association. We divided lifespan into two life-history components, one reflected by body size (measured as body mass), and a component that was statistically independent of body mass. While both lifespan and body mass were strongly associated with a family tree of the species (viz., the phylogeny of the species), telomere measures were not. Telomere length was not significantly associated with longevity or body mass, or our measure of mass-independent lifespan. TROC, however, was strongly associated with mass-independent lifespan, but to a lesser degree with body mass. Our results supported an association of TROC and longevity, in particular longevity that was independent of body size and part of the pace-of-life syndrome of life histories.

Longevity is highly variable among animal species, and has coevolved with other of life-history traits, like body size and rates of reproduction. Telomeres, through their erosion over time, are one of the cell mechanisms that produce senescence at the cell level, and might even have an influence on the rate of ageing in whole organisms. However, uneroded telomeres are also risk factors of cell immortalization. The associations of telomere lengths, their rate of change, and life-history traits independent of body size are largely underexplored for birds. To test associations of life-history traits and telomere dynamics, we conducted a phylogenetic meta-analysis using studies of 53 species of birds. We restricted analyses to studies that applied the telomere restriction fragment length (TRF) method, and examined relationships between mean telomere length at the chick (Chick TL) and adult (Adult TL) stages, the mean rate of change in telomere length during life (TROC), and life-history traits. We examined 3 principal components of 12 life-history variables that represented: body size (PC1), the slow-fast continuum of pace-of-life (PC2) and post-fledging parental care (PC3). Phylogeny had at best a small-to-medium influence on Adult and Chick TL (r² = 0.190 and 0.138, respectively), but a substantial influence on TROC (r² = 0.688). Phylogeny strongly influenced life histories: PC1 (r² = 0.828), PC2 (0.838), and PC3 (0.613). Adult TL and Chick TL were poorly associated with the life-history variables. TROC, however, was negatively and moderate-to-strongly associated with PC2 (unadjusted r = -0.340; with phylogenetic correction, r = -0.490). Independent of body size, long-lived species with smaller clutches and slower embryonic rate of growth may exhibited less change in telomere length over their lifetimes. We suggest that telomere lengths may have diverged even among closely avian related species, yet telomere dynamics are strongly linked to the pace of life.