The influence of birth date via body mass on individual fitness in a long‐lived mammal

Reproductive synchrony tends to be widespread in diverse species of plants and animals, especially at higher latitudes. However, for long‐lived mammals, birth dates for different individuals can vary by weeks within a population. A mother's birth timing can reveal useful information about her reproductive abilities and have important implications for the characteristics and survival of her offspring. Despite this, our current knowledge of factors associated with variation in birth dates is modest. We used long‐term data for known‐age Weddell seals in Antarctica and a Bayesian hierarchical modeling approach to study how birth dates varied with fixed and temporally varying features of mothers, whether sex allocation varied with birth timing, and annual variation in birth dates. Based on birth dates for 4465 pups born to 1117 mothers aged 4–31, we found that diverse features of mothers were associated with variation in birth dates. Maternal identity was the most important among these. Unlike most studies, which have reported that birth dates occur earlier as mothers age, we found that birth dates progressively occurred earlier in the year in the early part of a mother's reproductive life, reached a minimum at age 16, and then occurred later at later ages. Birth dates were positively related to a mother's age at primiparity and recent reproductive effort. The earliest birth dates were for pups born to prime‐age mothers who did not reproduce in the previous year but began reproduction early in life, suggesting that females in the best condition gave birth earlier than others. If so, our finding that male pups tended to be born earlier than females provides support for the Trivers–Willard sex‐allocation model. Average birth dates were quite consistent across years, except for 2 years that had notable delays and occurred during the period when massive icebergs were present and disrupted the ecosystem.

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“…; Plard et al. ). Sex ratios of offspring born on different dates have also proven to be a particularly interesting subject of study.…”

Section: Introductionmentioning

confidence: 97%

Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high‐latitude marine mammal

Rotella

Paterson

Garrott

2016

Ecology and Evolution

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“…It can be strongly affected by demographic structure generating individual heterogeneity in the vital rates of individuals (Vindenes et al ). Some important sources of individual heterogeneity include spatial heterogeneity (Beckage and Clark , Reid et al ), genetic variation (Postma and van Noordwijk , Coulson et al ) and lasting effects of early life conditions (Beckerman et al , Plard et al ). Earlier studies have shown that the demographic variance can be positively or negatively affected by individual heterogeneity (demographic structure), as compared to a model where the structure is ignored (Vindenes et al , Vindenes and Langangen 2015).…”

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confidence: 99%

Demographic stochasticity and temporal autocorrelation in the dynamics of structured populations

Vindenes

Engen

2017

Oikos

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Populations can show temporal autocorrelation in the dynamics arising from different mechanisms, including fluctuations in the demographic structure. This autocorrelation is often treated as a complicating factor in the analyses of stochastic population growth and extinction risk. However, it also reflects important information about the demographic structure. Here, we consider how temporal autocorrelation is related to demographic stochasticity in structured populations. Demographic stochasticity arises from inherent randomness in the demographic processes of individuals, like survival and reproduction, and the resulting impact on population growth is measured by the demographic variance. Earlier studies have shown that population structure have positive or negative effects on the demographic variance compared to a model where the structure is ignored. Here, we derive a new expression for the demographic variance of a structured population, using the temporal autocorrelation function of the population growth rate. We show that the relative difference in demographic variance when the structure is included or ignored (the effect of structure on demographic variance) is approximately twice the sum of the autocorrelations. We demonstrate the result for a simple hypothetical example, as well as a set of empirical examples using age‐structured models of 24 mammals from the demographic database COMADRE. In the empirical examples, the sum of the autocorrelation function was negative in all cases, indicating that age structure generally has a negative effect on the demographic variance (i.e. the demographic variance is lower compared to that of a model where the structure is ignored). Other kinds of structure, such as spatial heterogeneity affecting fecundity, can have positive effects on the demographic variance, and the sum of the autocorrelations will then be positive. These results yield new insights into the complex interplay between population structure, demographic variance, and temporal autocorrelation, that shapes the population dynamics and extinction risk of populations.

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“…For instance, we have previously shown that earlier birth dates can result in larger size at maturation in N. ocellatus (Pen et al., ). This pattern of early birth date conferring an advantage later in life is observed across vertebrates, with evidence in some species of mammals and many bird species (e.g., Arnold, Hatch, & Nisbet, ; Green & Rothstein, ; Plard et al., ; Saino et al., ). While growth rates were affected by birth date, we found no effect on offspring survival over the first winter.…”

Section: Discussionmentioning

confidence: 79%

Plastic rates of development and the effect of thermal extremes on offspring fitness in a cold‐climate viviparous lizard

et al. 2018

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Populations at the climatic margins of a species' distribution can be exposed to conditions that cause developmental stress, resulting in developmental abnormalities. Even within the thermal range of normal development, phenotypes often vary with developmental temperature (i.e., thermal phenotypic plasticity). These effects can have significant consequences for organismal fitness and, thus, population persistence. Reptiles, as ectotherms, are particularly vulnerable to thermal effects on development and are, therefore, considered to be at comparatively high risk from changing climates. Understanding the extent and direction of thermal effects on phenotypes and their fitness consequences is crucial if we are to make meaningful predictions of how populations and species will respond as climates warm. Here, we experimentally manipulated the thermal conditions experienced by females from a high-altitude, cold-adapted population of the viviparous skink, Niveoscincus ocellatus, to examine the consequences of thermal conditions at the margins of this population's normal temperature range. We found strong effects of thermal conditions on the development of key phenotypic traits that have implications for fitness. Specifically, we found that offspring born earlier as a result of high temperatures during gestation had increased growth over the first winter of life, but there was no effect on offspring survival, nor was there an effect of developmental temperature on the incidence of developmental abnormalities. Combined, our results suggest that advancing birth dates that result from warming climates may have positive effects in this population via increased growth.

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The influence of birth date via body mass on individual fitness in a long‐lived mammal

Cited by 59 publications

References 93 publications

Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high‐latitude marine mammal

Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high‐latitude marine mammal

Demographic stochasticity and temporal autocorrelation in the dynamics of structured populations

Plastic rates of development and the effect of thermal extremes on offspring fitness in a cold‐climate viviparous lizard

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