The relationship of telomere length to baseline corticosterone levels in nestlings of an altricial passerine bird in natural populations.

BackgroundEnvironmental stressors increase the secretion of glucocorticoids that in turn can shorten telomeres via oxidative damage. Modification of telomere length, as a result of adversity faced early in life, can modify an individual's phenotype. Studies in captivity have suggested a relationship between glucocorticoids and telomere length in developing individuals, however less is known about that relationship in natural populations.MethodsIn order to evaluate the effect of early environmental stressors on telomere length in natural populations, we compared baseline corticosterone (CORT) levels and telomere length in nestlings of the same age. We collected blood samples for hormone assay and telomere determination from two geographically distinct populations of the Thorn-tailed Rayadito (Aphrastura spinicauda) that differed in brood size; nestlings body mass and primary productivity. Within each population we used path analysis to evaluate the relationship between brood size, body mass, baseline CORT and telomere length.ResultsWithin each distinct population, path coefficients showed a positive relationship between brood size and baseline CORT and a strong and negative correlation between baseline CORT and telomere length. In general, nestlings that presented higher baseline CORT levels tended to present shorter telomeres. When comparing populations it was the low latitude population that presented higher levels of baseline CORT and shorter telomere length.ConclusionsTaken together our results reveal the importance of the condition experienced early in life in affecting telomere length, and the relevance of integrative studies carried out in natural conditions

Anaesthetic induced relaxation of the winged pearl oyster, Pteria penguin, varies with oyster size and anaesthetic concentration

Stress and mortality of pearl oysters during nucleus implanting for round pearl and mabé pearl production can be reduced using appropriate anaesthetics that allow improved access to nucleus implanting sites. This study evaluated the efficacy of three different concentrations of benzocaine (0.25, 0.50 and 1.20 g L-1) and 1-propylene phenoxetol (2.50, 3.00 and 3.50 mL L-1) when presented to ‘small’ (dorso-ventral height [DVH], 78.7 ± 1.6 mm), ‘medium’ (DVH, 118.2 ± 2.0 mm) and ‘large’ (DVH, 149.3 ± 1.1 mm) cohorts of the winged pearl oyster, Pteria penguin. Results showed the following general trends across treatments with both anaesthetics: (1) greater proportions of large oysters became relaxed compared to small oysters; (2) large oysters required shorter exposure times to become relaxed than small oysters; (3) for each size class of oyster, an increase in anaesthetic concentration resulted in an increased proportion of relaxed oysters; and (4) ‘mantle collapse’ (where the mantle collapses away from the shell) was only recorded in large oysters in treatments with higher concentrations of anaesthetics. The most effective concentration of benzocaine to use with small, medium and large Pt. penguin was the highest level tested in this study (1.20 g L-1). Similarly, the highest concentration of 1-propylene phenoxetol tested (3.5 mL L-1) was also the most effective with all three size classes of Pt. penguin. These treatments caused mantle collapse in large oysters, for which use of lower, less effective anaesthetic concentrations may be considered preferable, to avoid potentially negative impacts of mantle collapse on subsequent mabé pearl production. As well as efficacy, choice of anaesthetic should consider ease of preparation and preparation time. Benzocaine requires dissolving in methyl alcohol and heating to 88–92˚C, while 1-propylene phenoxetol is readily soluble in seawater

Testosterone and Group Size in Cliff Swallows: Testing the “Challenge Hypothesis” in a Colonial Bird

The “challenge hypothesis” states that increases in testosterone levels of male animals during the breeding season are directly related to the extent of intrasexual competition for resources or mates that they experience. Although often tested in territorial species, the challenge hypothesis has not been evaluated for colonial animals that live in groups of different sizes and that thus experience different intensities of intrasexual competition. We measured circulating testosterone levels of male and female cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, where these birds nest in colonies of widely different sizes. Males had significantly higher testosterone levels than females, as expected. For males especially, there was a seasonal rise in testosterone levels early in the nesting cycle, corresponding to the period when birds were establishing nest ownership and egg laying, and then a fall as they switched to parental duties. Testosterone levels varied significantly with colony size; for both sexes, birds in larger colonies had higher levels of testosterone than those in smaller colonies when controlling for date. Age and body mass were not related to testosterone levels. Higher levels of testosterone for birds of both sexes in larger colonies probably reflect greater com-petition for matings, often extra pair, in the more social nesting situations. The results support the predictions of the challenge hypothesis

Testosterone and Group Size in Cliff Swallows: Testing the “Challenge Hypothesis” in a Colonial Bird

The “challenge hypothesis” states that increases in testosterone levels of male animals during the breeding season are directly related to the extent of intrasexual competition for resources or mates that they experience. Although often tested in territorial species, the challenge hypothesis has not been evaluated for colonial animals that live in groups of different sizes and that thus experience different intensities of intrasexual competition. We measured circulating testosterone levels of male and female cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, where these birds nest in colonies of widely different sizes. Males had significantly higher testosterone levels than females, as expected. For males especially, there was a seasonal rise in testosterone levels early in the nesting cycle, corresponding to the period when birds were establishing nest ownership and egg laying, and then a fall as they switched to parental duties. Testosterone levels varied significantly with colony size; for both sexes, birds in larger colonies had higher levels of testosterone than those in smaller colonies when controlling for date. Age and body mass were not related to testosterone levels. Higher levels of testosterone for birds of both sexes in larger colonies probably reflect greater com-petition for matings, often extra pair, in the more social nesting situations. The results support the predictions of the challenge hypothesis

Glucocorticoid Hormone Levels Increase with Group Size and Parasite Load in Cliff Swallows

Animals often cope with adverse events by releasing glucocorticoid hormones, which in turn promote increased energy assimilation. In captive animals, crowding also leads to increased glucocorticoid activity, probably because of increased levels of social competition. We investigated how group size and ectoparasite infestations affected endogenous levels of the glucocorticoid hormone, corticosterone, in colonial cliff swallows, Petrochelidon pyrrhonota, in southwestern Nebraska, USA. Parasites were removed from some colonies by fumigating nests. Baseline levels of corticosterone in breeding adults varied significantly with whether parasites were present, colony size (measured by total number of active nests at a site), and nesting stage. Across all analyses, birds from fumigated colonies averaged significantly lower baseline levels of corticosterone. These levels in adults increased with colony size at nonfumigated sites, especially during the period when nestlings were being fed, but no relation or the opposite one was found for birds in fumigated colonies. Baseline corticosterone levels were unrelated to sex, age, body weight, or testosterone levels in adults. Corticosterone concentrations tended to increase during a bad-weather event when food was scarce. Patterns in nestling and recently fledged juveniles were consistent with those in adults. The increased baseline levels of corticosterone in birds of larger colonies appear related to the larger number of parasites there. Higher levels of corticosterone probably facilitate increased allocation of time and energy to foraging and greater energy assimilation during challenging events such as bad weather, parasitism by blood-feeding bugs in large colonies, and the period when young are becoming independent of their parents

Effects of Endogenous Steroid Hormone Levels on Annual Survival in Cliff Swallows

The hormone corticosterone is an important part of animals’ response to environmental stress, modulating short-term adaptive changes in behavior and physiology. The hormone testosterone is also critical, especially for males, in regulating the expression of sexual behavior and parental care. These hormones can have costly consequences, however, and within populations individuals show variation in endogenous levels of both corticosterone and testosterone. We studied how annual survival varied as a function of natural levels of these hormones in colonially breeding Cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, USA, in 2000–2003. We sampled hormone levels of birds caught at colonies and using mark–recapture, monitored their survival through subsequent years in the study area. Maximum-likelihood estimation and model fitting (with program MARK) revealed that birds sampled for corticosterone in colonies of all sizes late in the season had curvilinear survival; individuals with very low and very high levels of corticosterone had lower survival than those with intermediate levels. Annual survival of birds sampled earlier in the season, however, generally declined with increasing corticosterone level. More birds than expected, given the survival functions, had the very low corticosterone levels in nonfumigated colonies later in the year, suggesting perhaps a compensatory benefit unrelated to survival for very low corticosterone levels. In a more limited analysis, testosterone appeared to have little effect on annual survival, although some evidence suggested that females with endogenous testosterone levels below the mean for a given date might have survived better

Effects of Endogenous Steroid Hormone Levels on Annual Survival in Cliff Swallows

The hormone corticosterone is an important part of animals’ response to environmental stress, modulating short-term adaptive changes in behavior and physiology. The hormone testosterone is also critical, especially for males, in regulating the expression of sexual behavior and parental care. These hormones can have costly consequences, however, and within populations individuals show variation in endogenous levels of both corticosterone and testosterone. We studied how annual survival varied as a function of natural levels of these hormones in colonially breeding Cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska, USA, in 2000–2003. We sampled hormone levels of birds caught at colonies and using mark–recapture, monitored their survival through subsequent years in the study area. Maximum-likelihood estimation and model fitting (with program MARK) revealed that birds sampled for corticosterone in colonies of all sizes late in the season had curvilinear survival; individuals with very low and very high levels of corticosterone had lower survival than those with intermediate levels. Annual survival of birds sampled earlier in the season, however, generally declined with increasing corticosterone level. More birds than expected, given the survival functions, had the very low corticosterone levels in nonfumigated colonies later in the year, suggesting perhaps a compensatory benefit unrelated to survival for very low corticosterone levels. In a more limited analysis, testosterone appeared to have little effect on annual survival, although some evidence suggested that females with endogenous testosterone levels below the mean for a given date might have survived better

Germ-furrow morphology and storage conditions determine the degree of viability of Pinus caribaea pollen

This study has found a correlation between Pinus caribaea pollen morphology and viability. Eighteen different P. caribaea pollen families were screened to determine the effect of environmental conditions during storage on germination. The results indicated that there was a direct decrease in viability with an increase in the age of the pollen, temperature at which the pollen was stored, and exposure to high humidity during storage. Scanning electron microscopy was used to investigate the dimensions of the 18 families. Upon statistical analysis of the dimensional data, the families were found to group into three clusters. Pollen families displaying narrow germ furrows clustered with those displaying wide germ furrows, while those pollen families displaying intermediate germ furrows clustered into a second group. When the clusters were compared with the germination data obtained it was found that the pollen families displaying highest germination percentages fell into the intermediate cluster, while the pollen families displaying low to intermediate germination percentages fell into the narrow/wide cluster