Abstract Ecological and life-history variation and both interspecific and intraspecific brood parasitism contribute to diversity in egg phenotype within the same species. In this study, Barn Swallows (Hirundo rustica erythrogaster) laid eggs with high intraclutch repeatability in egg size, shape, and maculation. Despite this high intraclutch repeatability, last-laid eggs had consistently less of the eggshell covered in spots and fewer spots than earlier-laid eggs in the clutch. We examined sources of interclutch and intraclutch variation using both direct measurements and custom software (SpotEgg, NaturePatternMatch) that provide detailed information on egg characteristics, especially maculation measures. In addition to our main findings, maculation on different sides of the egg was highly repeatable; however, only shape, proportion of the eggshell maculated, and average spot size were repeatable between first and replacement clutches. Low intraclutch variation in maculation could allow females to recognize their clutch and this may be adaptive for colonial nesting species, such as the Barn Swallow. Characterizing intraspecific variation in egg size, shape, and maculation is the first step in understanding whether intraclutch variation is low enough—and interclutch variation high enough—such that eggs could serve as identity signals.
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Environmental drivers of female reproductive investment in egg quantity and quality in a grassland sparrow
Female investment in reproduction is a critical component of life history that influences both the fitness of the female and her offspring. Oviparous females can allocate energy into egg size and/or clutch size, and this allocation can vary over lifetimes, within populations and among species. However, we know little about whether investment decisions shift within breeding seasons and the factors that influence female reproductive strategies. We studied endogenous and exogenous factors associated with variation in female reproductive investment by measuring 860 eggs from 240 clutches laid by Grasshopper Sparrows
- PAR ID:
- 10557250
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Ibis
- ISSN:
- 0019-1019
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Age and environment are important determinants of reproductive parameters in long‐lived organisms. These factors may interact to determine breeding responses to environmental change, yet few studies have examined the environmental dependence of aging patterns across the entire life span. We do so, using a 20‐yr longitudinal data set of reproductive phenotypes in long‐lived female Nazca boobies (
Sula granti ), a monogamous seabird breeding in the eastern tropical Pacific. Young and old females may suffer from inexperience and senescence, respectively, and/or practice reproductive restraint. Breeding performance (for breeding participation, breeding date, clutch size, egg volume, and offspring production) was expected to be lower in these age classes, particularly under environmental challenge, in comparison with middle‐aged breeders. Sea surface temperature anomalies (SSTA) represented interannual variation in the El Niño–Southern Oscillation (ENSO) and were one proxy for environmental quality (a population count of clutch initiations was a second). Although only females lay eggs, both sexes care for eggs and nestlings, and the male partner’s age, alone or in interaction with female age, was evaluated as a predictor of breeding performance. Middle‐aged females performed better than young and old birds for all reproductive traits. Pairing with a young male delayed breeding (particularly for old females) and reduced clutch size, and pairing with an old male reduced offspring production. Challenging environments increased age effects on breeding probability and breeding date across young to middle ages and for offspring production across middle to old ages. However, important exceptions to the predicted patterns for clutch size and fledging success across young to middle ages suggested that trade‐offs between fitness components may complicate patterns of trait expression across the life span. Relationships between breeding participation, environment, and individual quality and/or experience in young females may also contribute to unexpected patterns for clutch size and fledging success, traits expressed only in breeders. Finally, independent of age, breeding responses of female Nazca boobies to the ENSO did not follow expectations derived from oceanic forcing of primary productivity. During El Niño‐like conditions, egg‐laying traits (clutch size, breeding date) improved, but offspring production declined, whereas La Niña‐like conditions were “poor” environments throughout the breeding cycle. -
The number of offspring parents rear varies considerably among closely related lineages, individuals, and even reproductive events by one individual. Constraints can come at any point, from the costs of producing a large clutch to the cost of caring for a large brood of dependent young. We report here on observations of the early phase of a reproductive cycle in a captive colony of Oophaga pumilio, a poison frog with offspring entirely dependent on maternally provisioned trophic eggs. We tracked reproductive clutches, and found that while clutch and egg size were variable, neither predicted the success of a clutch; there was also no evidence of a trade-off between clutch and egg size. Larger eggs did, however, produce larger tadpoles, and when parents transported only a subset of the brood to nurseries, the tadpoles they moved were larger than the ones they did not. Adaptive adjustment of parental investment is a key life-history trait, and a complete accounting of the way families are constructed is key to understanding the evolution of parental care, parental favoritism, and cooperation and conflict among closely related individuals.more » « less
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Abstract Multigenerational effects can have important and sex‐dependent effects on offspring. Sex allocation theory predicts that females should differentially invest in sons and daughters depending on sex‐specific fitness returns and costs of investment. Maternal stress‐relevant (glucocorticoid) hormones may be one mechanism driving this effect. We investigated how maternal stress hormones differentially affected sons and daughters by manipulating levels of the glucocorticoid, corticosterone (CORT), in gravid female eastern fence lizards (
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Abstract Sex can influence patterns of parasitism because males and females can differ in encounter with, and susceptibility to, parasites. We investigate an isopod parasite (
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