Patterns of sperm damage in Chernobyl passerine birds suggest a trade-off between sperm length and integrity.

Interspecific variation in sperm size is enigmatic, but generally assumed to reflect species-specific trade-offs in selection pressures. Among passerine birds, sperm length varies sevenfold, and sperm competition risk seems to drive the evolution of longer sperm. However, little is known about factors favouring short sperm or constraining the evolution of longer sperm. Here, we report a comparative analysis of sperm head abnormalities among 11 species of passerine bird in Chernobyl, presumably resulting from chronic irradiation following the 1986 accident. Frequencies of sperm abnormalities varied between 15.7 and 77.3% among species, more than fourfold higher than in uncontaminated areas. Nonetheless, species ranked similarly in sperm abnormalities in unpolluted areas as in Chernobyl, pointing to intrinsic factors underlying variation in sperm damage among species. Scanning electron microscopy of abnormal spermatozoa revealed patterns of acrosome damage consistent with premature acrosome reaction. Sperm length, but not sperm competition risk explained variation in sperm damage among species. This suggests that longer spermatozoa are more susceptible to premature acrosome reaction. Therefore, we hypothesize a trade-off between sperm length and sperm integrity affecting sperm evolution in passerine birds.

Malaria infection and feather growth rate predict reproductive success in house martins.

Carry-over effects take place when events occurring in one season influence individual performance in a subsequent season. Blood parasites (e.g. Plasmodium and Haemoproteus) have strong negative effects on the body condition of their hosts and could slow the rate of feather growth on the wintering grounds. In turn, these winter moult costs could reduce reproductive success in the following breeding season. In house martins Delichon urbica captured and studied at a breeding site in Europe, we used ptilochronology to measure growth rate of tail feathers moulted on the winter range in Africa, and assessed infection status of blood parasites transmitted on the wintering grounds. We found a negative association between haemosporidian parasite infection status and inferred growth rate of tail feathers. A low feather growth rate and blood parasite infections were related to a delay in laying date in their European breeding quarters. In addition, clutch size and the number of fledglings were negatively related to a delayed laying date and blood parasite infection. These results stress the importance of blood parasites and feather growth rate as potentially mechanisms driving carry-over effects to explain fitness differences in wild populations of migratory birds.

Individual responses in spring arrival date to ecological conditions during winter and migration in a migratory bird.

1. We studied lifetime arrival patterns in the barn swallow (Hirundo rustica L.) in relation to variation in ecological conditions, as reflected by the normalized difference vegetation index (NDVI) in the Sub-Saharan winter quarters and at stopover sites in North Africa. 2. Migratory birds have recently advanced their arrival dates, but the relative role of microevolution and phenotypic plasticity as mechanisms of response to changing environmental conditions remains unknown. To distinguish between these two possibilities, we investigated the change in the arrival date using cross-sectional and longitudinal analyses. 3. We predicted that the effect (i.e. slopes) of environmental conditions in stopover or winter areas on arrival date should be similar using cross-sectional and longitudinal analyses in case phenotypic plasticity is the underlying mechanism, or they should differ in case microevolution is the mechanism. 4. As expected according to a previous cross-sectional study, we found an advance in the arrival date when ecological conditions improve in stopover areas and a delay in the arrival date when ecological conditions improve in the winter quarters. 5. Change in the arrival time at the breeding grounds due to ecological conditions found en route and, in the winter areas, was mainly due to phenotypic plasticity as shown by similarities in the slopes found in these relationships using cross-sectional and longitudinal analyses. 6. We also investigated sex and age of barns swallows as sources of variation in the arrival time with respect to conditions experienced in winter and stopover areas. We found that earlier arrival at the breeding grounds due to prevailing ecological conditions found en route in North Africa was similar for males and females of all age-classes. In contrast, individuals tended to delay departure when ecological conditions improved in the winter quarters, but this delay differed among age classes, with old individuals delaying departure more than middle-aged and yearling birds. 7. The migratory response of individuals to changing climatic conditions experienced during different parts of their life provides evidence for individuals responding differently to prevailing conditions in the winter quarters depending on their age, but not to conditions experienced en route during spring migration.

Divergent patterns of impact of environmental conditions on life history traits in two populations of a long-distance migratory bird.

Some areas have experienced recent dramatic warming due to climate change, while others have shown no change at all, or even recent cooling. We predicted that patterns of selection on life history would differ between southern and northern European populations of a long-distance migratory bird, the barn swallow Hirundo rustica, because global patterns of weather as reflected by large-scale weather phenomena such as the North Atlantic Oscillation (NAO) and the El Niño-Southern Oscillation (ENSO) have different effects on environmental conditions in different parts of the world frequented during the annual cycle. We investigated relationships between mean arrival date, dispersal rate and yearling survival rate among years, using two long-term population studies in Spain and Denmark. We found evidence of a difference in the effects of normalized difference vegetation index in North and West Africa on mean arrival date of male barn swallows, with the effect differing significantly between populations. Second, there was a significant interaction between ENSO and population on dispersal rate, showing that conditions in Africa during winter differentially affected dispersal in the two populations. Finally, the NAO index in winter had an effect on yearling survival that differed between populations. These findings highlight the divergent patterns of response to climate change among populations, and they suggest that climate change can differentially affect important life history traits with potential implications for maintenance of viable populations and gene flow among populations.

Age-related change in breeding performance in early life is associated with an increase in competence in the migratory barn swallow Hirundo rustica.

1. We investigated age-related changes in two reproductive traits (laying date and annual fecundity) in barn swallows Hirundo rustica L. using a mixed model approach to di-stinguish among between- and within-individual changes in breeding performance with age. 2. We tested predictions of age-related improvements of competence (i.e. constraint hypothesis) and age-related progressive disappearance of poor-quality breeders (i.e. selection hypothesis) to explain age-related increase in breeding performance in early life. 3. Reproductive success increased in early life, reaching a plateau at middle age (e.g. at 3 years of age) and decreasing at older age (> 4 years). Age-related changes in breeding success were due mainly to an effect of female age. 4. Age of both female and male affected timing of reproduction. Final linear mixed effect models (LME) for laying date included main and quadratic terms for female and male age, suggesting a deterioration in reproductive performance at older age for both males and females. 5. We found evidence supporting the constraints hypothesis that increases in competence within individuals, with ageing being the most probable cause of the observed increase in breeding performance with age in early life. Two mechanisms were implicated: (1) advance in male arrival date with age provided middle-aged males with better access to mates. Yearling males arrived later to the breeding grounds and therefore had limited access to high-quality mates. (2) Breeding pairs maintaining bonds for 2 consecutive years (experienced pairs) had higher fecundity than newly formed inexperienced breeding pairs. 6. There was no support for the selection hypothesis because breeding performance was not correlated with life span. 7. We found a within-individual deterioration in breeding and migratory performance (arrival date) in the oldest age-classes consistent with senescence in these reproductive and migratory traits.