Brood size is associated with apparent telomere lengthening in nestling barn swallows.

Early life for animals is often a time of rapid growth and development. In a resource-limited environment, life history theory predicts that there must be trade-offs between resource sinks in ways that optimize future survival and reproductive success. Telomeres have emerged as putative indicators of these early life trade-offs, but there are conflicting accounts as to how developmental traits and conditions impact telomere length and dynamics. For 2 years, we studied the nestlings of a breeding population of barn swallows from day 6 to day 12 of life, measuring various ontogenetic factors to understand to what extent they explain variation in telomere length and dynamics. We unexpectedly found that telomeres lengthened between the two sampling points. Nestlings in large broods had shorter telomeres, but surprisingly, individuals that grew faster from day 6 to day 12 had longer telomeres and more telomere lengthening. Nestlings with higher mass relative to their nestmates on d6 had shorter telomeres, suggesting that the relatively fast growth barn swallows experience early in development is more costly than the relatively slower growth later in development. These effects were only found in the first year of study. Telomere lengthening may be due to the initiation of new hematopoietic cell lines during development or the expression of telomerase early in life. Favorable early life conditions and high parental investment could allow for more growth with little to no cost to telomere length or dynamics.

Experimental manipulation of a signal trait reveals complex phenotype-behaviour coordination.

Animals use morphological signals such as ornamental traits or weaponry to mediate social interactions, and the extent of signal trait elaboration is often positively associated with reproductive success. By demonstrating relationships between signal traits and fitness, researchers often make inferences about how behaviour operates to shape those outcomes. However, detailed information about fine-scale individual behaviour, and its physiological basis, can be difficult to obtain. Here we show that experimental manipulations to exaggerate a signal trait (plumage colour) and concomitant changes in testosterone and stress-induced corticosterone levels altered social interactivity between manipulated males and their social mates. On average, darkened males did not have higher levels of interactivity than unmanipulated males; however, males who experienced a greater shift in colour (pale to dark), a larger, positive change in testosterone levels, and a dampened stress-induced corticosterone response had a larger increase in the number of interactions with their social mate post-manipulation compared to pre-manipulation. This work provides new insights into the integration and real-time flexibility of multivariate phenotypes and direct evidence for the role of social interactions in pair bond maintenance.

Host immune responses to experimental infection of Plasmodium relictum (lineage SGS1) in domestic canaries (Serinus canaria).

Understanding the complexity of host immune responses to parasite infection requires controlled experiments that can inform observational field studies. Birds and their malaria parasites provide a useful model for understanding host-parasite relationships, but this model lacks a well-described experimental context for how hosts respond immunologically to infection. Here, ten canaries (Serinus canaria) were infected with the avian malaria parasite Plasmodium relictum (lineage SGS1) in a controlled laboratory setting with ten uninfected (control) birds. A suite of immunological blood parameters, including the concentration of four white blood cell types, the concentration of the acute phase protein haptoglobin, and the bacteria-killing ability of blood plasma, were repeatedly measured over a 25-day period covering the acute phase of a primary infection by P. relictum. Three infected and one control bird died during the course of the experiment. A multivariate statistical analysis of the immune indices revealed significant differences between infected and uninfected individuals between 5 and 14 days postinfection (dpi). Group differences corresponded to reduced concentrations of lymphocytes (5 dpi), heterophils (8 dpi), and monocytes (11 and 14 dpi), and an increase in haptoglobin (14 dpi), in infected birds relative to uninfected controls, and no change in bacteria-killing. Upon re-running the analysis with only the surviving birds, immunological differences between infected and control birds shifted to between 11 and 18 dpi. However, there were no clear correlates relating immune parameters to the likelihood of surviving the infection. The results presented here demonstrate the dynamic and complex nature of avian immune function during the acute phase of malaria infection and provide a context for studies investigating immune function in wild birds.