scholarly journals The stress of parenthood? Increased glucocorticoids in birds with experimentally enlarged broods

2011 ◽  
Vol 7 (6) ◽  
pp. 944-946 ◽  
Author(s):  
Frances Bonier ◽  
Ignacio T. Moore ◽  
Raleigh J. Robertson
Keyword(s):  
Positive Relationship ◽  
Reproductive Effort ◽  
Reproductive Investment ◽  
Tachycineta Bicolor ◽  
Relative Fitness ◽  
Allocation Of Resources ◽  
Tree Swallows ◽  
Parental Behaviour ◽  
Poor Condition ◽  
Before And After

Variation in baseline glucocorticoid (cort) levels can be attributed, at least in part, to differences in energetic demands confronting individuals. Elevated baseline cort levels are routinely interpreted as indicating individuals in poor condition, with low relative fitness. However, when greater reproductive effort increases energetic demands, individuals with high cort might paradoxically be those with the highest fitness. Here, we experimentally test the hypothesis that increased reproductive demand causes increases in baseline cort (the Cort-Adaptation hypothesis). We measured maternal baseline cort before and after experimentally enlarging and reducing brood sizes in tree swallows ( Tachycineta bicolor ). Females with experimentally enlarged broods had greater increases in baseline cort and fledged more offspring than females with reduced broods. Additionally, females with greater increases in baseline cort had higher offspring-provisioning rates than females with lower changes in cort. These findings demonstrate that increased reproductive demand can cause increased baseline cort. As yet, we do not know if these increases in cort cause increased allocation of resources towards reproduction, but the positive relationship between parental behaviour and cort suggests that increased cort does not always interfere with reproductive investment, and might instead facilitate it.

Transgenerational effects of maternal immune challenge in tree swallows (Tachycineta bicolor)

2002 ◽  
Vol 80 (5) ◽  
pp. 918-925 ◽  
Author(s):  
G A Lozano ◽  
R C Ydenberg
Keyword(s):  
Egg Laying ◽  
Tachycineta Bicolor ◽  
Cell Mediated Immunity ◽  
Immune Challenge ◽  
Ecological Context ◽  
Allocation Of Resources ◽  
Tree Swallows ◽  
Immune Development ◽  
Nestling Growth ◽  
Better Than

The fact that avian eggs contain antibody of maternal origin is well documented, but only recently has this phenomenon been considered in an ecological context. We used tree swallows (Tachycineta bicolor) to examine the possibility of transgenerational immunity and its effect on nestling growth and immune development. We measured cell-mediated immunity with a delayed-hypersensitivity assay and antibody-mediated immunity with a hemagglutination test with sheep red blood cells (SRBCs). We tested for differences in immunocompetence and growth between nestlings from females who had been exposed to a novel antigen prior to egg laying and nestlings from unexposed females. To determine whether the effect, if any, resulted from something transferred to the eggs prior to egg laying or from subsequent changes in parental behaviour, nestlings were exchanged so that at each nest half the nestlings were from females who had been injected with SRBCs and half were from females who had not been exposed to SRBCs. Finally, brood sizes were independently manipulated to either 4 or 6 nestlings. We failed to detect maternal antibodies in any nestlings, and whether a female was exposed to SRBCs or not had no effect on the growth or cell-mediated immunity of her brood. However, nestlings in smaller broods grew better than nestlings in larger broods, though we did not find the expected differences in cell-mediated immunity. Furthermore, within each nest, nestlings whose mothers had been exposed to SRBCs grew better than nestlings whose mothers had not been exposed. These results are contrary to the idea of a simple trade-off in the allocation of resources between parasite protection and reproduction; however, they support the idea that exposure of females to parasites prior to egg laying leads to better nestling growth, and are congruous with the possibility of mithridatic parental care.

scholarly journals Maternal glucocorticoid levels during incubation predict breeding success, but not reproductive investment, in a free-ranging bird

2019 ◽  
Author(s):  
Devin Fischer ◽  
Robby R. Marrotte ◽  
Eunice H. Chin ◽  
Smolly Coulson ◽  
Gary Burness
Keyword(s):  
Breeding Success ◽  
Positive Relationship ◽  
Negative Relationship ◽  
Reproductive Investment ◽  
Egg Laying ◽  
Tree Swallows ◽  
Female Tree ◽  
Adaptation Hypothesis ◽  
Breeding Seasons ◽  
Free Ranging

ABSTRACTThe hormone corticosterone (CORT)) has been hypothesized to be linked with fitness, but the directionality of the relationship is unclear. The “CORT-fitness hypothesis” proposes that high levels of CORT arise from challenging environmental conditions, resulting in lower reproductive success (a negative relationship). In contrast, the “CORT-adaptation hypothesis” suggests that, during energetically demanding periods, CORT will mediate physiological or behavioural changes that result in increased reproductive investment and success (a positive relationship). During two breeding seasons, we experimentally manipulated circulating CORT levels in female tree swallows (Tachycineta bicolor) prior to egg laying, and measured subsequent reproductive effort, breeding success, and maternal survival. When females were recaptured during egg incubation and again during the nestling stage, the CORT levels were similar among individuals in each treatment group, and maternal treatment had no effect on indices of fitness. By considering variation among females, we found support for the “CORT-adaptation hypothesis”; there was a significant positive relationship between CORT levels during incubation and hatching and fledging success. During the nestling stage CORT levels were unrelated to any measure of investment or success. Within the environmental context of our study, relationships between maternal glucocorticoid levels and indices fitness vary across reproductive stages.SUMMARY STATEMENTMaternal corticosterone levels predict breeding success of female tree swallows.

The costs of reproduction in tree swallows (Tachycineta bicolor)

1991 ◽  
Vol 69 (10) ◽  
pp. 2540-2547 ◽  
Author(s):  
Nathaniel T. Wheelwright ◽  
Joanna Leary ◽  
Caragh Fitzgerald
Keyword(s):  
Life History ◽  
Clutch Size ◽  
Brood Size ◽  
Life History Theory ◽  
Tachycineta Bicolor ◽  
Laying Date ◽  
Tree Swallows ◽  
Costs Of Reproduction ◽  
Return Rates ◽  
Trade Offs

We investigated the effect of brood size on nestling growth and survival, parental survival, and future fecundity in tree swallows (Tachycineta bicolor) over a 4-year period (1987–1990) in an effort to understand whether reproductive trade-offs limit clutch size in birds. In addition to examining naturally varying brood sizes in a population on Kent Island, New Brunswick, Canada, we experimentally modified brood sizes, increasing or decreasing the reproductive burdens of females by two offspring. Unlike previous studies, broods of the same females were enlarged or reduced in up to 3 successive years in a search for evidence of cumulative costs of reproduction that might go undetected by a single brood manipulation. Neither observation nor experiment supported the existence of a trade-off between offspring quality and quantity, in contrast with the predictions of life-history theory. Nestling wing length, mass, and tarsus length were unrelated to brood size. Although differences between means were in the direction predicted, few differences were statistically significant, despite large sample sizes. Nestlings from small broods were no more likely to return as breeding adults than nestlings from large broods, but return rates of both groups were very low. Parental return rates were also independent of brood size, and there was no evidence of a negative effect of brood size on future fecundity (laying date, clutch size). Reproductive success, nestling size, and survival did not differ between treatments for females whose broods were manipulated in successive years. Within the range of brood sizes observed in this study, the life-history costs of feeding one or two additional nestlings in tree swallows appear to be slight and cannot explain observed clutch sizes. Costs not measured in this study, such as the production of eggs or postfledging parental care, may be more important in limiting clutch size in birds.

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