Social dominance and rainfall predict telomere dynamics in a cooperative arid-zone bird.

In many vertebrate societies dominant individuals breed at substantially higher rates than subordinates, but whether this hastens ageing remains poorly understood. While frequent reproduction may trade off against somatic maintenance, the extraordinary fecundity and longevity of some social insect queens highlight that breeders need not always suffer more rapid somatic deterioration than their nonbreeding subordinates. Here, we used extensive longitudinal assessments of telomere dynamics to investigate the impact of dominance status on within-individual age-related changes in somatic integrity in a wild social bird, the white-browed sparrow-weaver (Plocepasser mahali). Dominant birds, who monopolise reproduction, had neither shorter telomeres nor faster telomere attrition rates over the long-term (1-5 years) than their subordinates. However, over shorter (half-year) time intervals dominants with shorter telomeres showed lower rates of telomere attrition (and evidence suggestive of telomere lengthening), while the same was not true among subordinates. Dominants may therefore invest more heavily in telomere length regulation (and/or somatic maintenance more broadly); a strategy that could mitigate the long-term costs of reproductive effort, leaving their long-term telomere dynamics comparable to those of subordinates. Consistent with the expectation that reproduction entails short-term costs to somatic integrity, telomere attrition rates were most severe for all birds during the breeding seasons of wetter years (rainfall is the key driver of reproductive activity in this arid-zone species). Our findings suggest that, even in vertebrate societies in which dominants monopolise reproduction, dominants may experience long-term somatic integrity trajectories indistinguishable from those of their nonreproductive subordinates.

Longitudinal evidence that older parents produce offspring with longer telomeres in a wild social bird.

As telomere length (TL) often predicts survival and lifespan, there is considerable interest in the origins of inter-individual variation in TL. Cross-generational effects of parental age on offspring TL are thought to be a key source of variation, but the rarity of longitudinal studies that examine the telomeres of successive offspring born throughout the lives of parents leaves such effects poorly understood. Here, we exploit TL measures of successive offspring produced throughout the long breeding tenures of parents in wild white-browed sparrow weaver (Plocepasser mahali) societies, to isolate the effects of within-parent changes in age on offspring TLs. Our analyses reveal the first evidence to date of a positive within-parent effect of advancing age on offspring TL: as individual parents age, they produce offspring with longer telomeres (a modest effect that persists into offspring adulthood). We consider the potential for pre- and post-natal mechanisms to explain our findings. As telomere attrition predicts offspring survival to adulthood in this species, this positive parental age effect could impact parent and offspring fitness if it arose via differential telomere attrition during offspring development. Our findings support the view that cross-generational effects of parental age can be a source of inter-individual variation in TL.

Altruistic bet-hedging and the evolution of cooperation in a Kalahari bird.

Altruism is globally associated with unpredictable environments, but we do not understand why. New theory has highlighted that unpredictable environments could favor the evolution of altruism if altruistic acts reduce environmentally induced variance in the reproductive success of relatives ("altruistic bet-hedging"). Here, we show that altruism does indeed reduce environmentally induced reproductive variance in a wild cooperative bird. Our decade-long field study reveals that altruistic helping actually has no overall effect on the mean reproductive success of relatives but instead reduces their reproductive variance. This remarkable pattern arises because helpers improve reproductive performance in dry conditions but reduce it in wet conditions. Helpers thereby specifically reduce rainfall-induced reproductive variance, the very mechanism required for altruistic bet-hedging to explain the enigmatic global association between avian altruism and unpredictable rainfall.

Agreement of stall-side and laboratory major crossmatch tests with the reference standard method in horses.

BACKGROUND: Crossmatching is used to prevent life-threatening transfusion reactions in horses. Laboratory methods are laborious and technically challenging, which is impractical during emergencies. HYPOTHESIS/OBJECTIVES: Evaluate agreement between a stall-side crossmatch kit (KIT) and a laboratory method (LAB) in horses with known and unknown blood types. ANIMALS: Twenty-four blood-typed and alloantibody-screened healthy adult horses (Aim 1) and 156 adult horses of unknown blood type (Aim 2). METHODS: Prospective, blinded study. Expected positive (n = 35) and negative (n = 36) crossmatches among 24 antibody and blood-typed horses were used to determine sensitivity and specificity of KIT and LAB against the reference method. Agreement in 156 untyped horses was evaluated by reciprocal crossmatch (n = 156). RESULTS: Sensitivity (95% confidence interval [CI]) for LAB and KIT compared with expected reactions was 77.1% (59.9%-90.0%) and 91.4% (77.0%-98.2%), and specificity 77.8% (60.9%-89.9%) and 73.5% (55.6%-87.1%), respectively. The KIT was 100% sensitive for Aa reactions; LAB was 100% sensitive for Qab; and both were 100% sensitive for Ca. Cohen's κ agreement for LAB and KIT with expected positive and negative reactions (n = 71) was moderate (0.55 [0.36-0.74]) and substantial (0.65 [0.47-0.82]), respectively. Agreement was fair comparing LAB with KIT in Aim 1 (0.30 [0.08-0.52]) and in untyped horses in Aim 2 (0.26 [0.11-0.41]). CONCLUSIONS AND CLINICAL IMPORTANCE: Agreement between KIT and LAB with expected reactions was blood type dependent. Performance of both methods depends on blood type prevalence.

Telomere attrition predicts reduced survival in a wild social bird, but short telomeres do not.

Attempts to understand the causes of variation in senescence trajectories would benefit greatly from biomarkers that reflect the progressive declines in somatic integrity (SI) that lead to senescence. While telomere length has attracted considerable interest in this regard, sources of variation in telomere length potentially unrelated to declines in SI could, in some contexts, leave telomere attrition rates a more effective biomarker than telomere length alone. Here, we investigate whether telomere length and telomere attrition rates predict the survival of wild white-browed sparrow-weaver nestlings (Plocepasser mahali). Our analyses of telomere length reveal counterintuitive patterns: telomere length soon after hatching negatively predicted nestling survival to fledging, a pattern that appears to be driven by differentially high in-nest predation of broods with longer telomeres. Telomere length did not predict survival outside this period: neither hatchling telomere length nor telomere length in the mid-nestling period predicted survival from fledging to adulthood. Our analyses using within-individual telomere attrition rates, by contrast, revealed the expected relationships: nestlings that experienced a higher rate of telomere attrition were less likely to survive to adulthood, regardless of their initial telomere length and independent of effects of body mass. Our findings support the growing use of telomeric traits as biomarkers of SI, but lend strength to the view that longitudinal assessments of within-individual telomere attrition since early life may be a more effective biomarker in some contexts than telomere length alone.