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Ecological, evolutionary and social constraints on reproductive effort: are hoary marmots really biennial breeders?

Patil VP, Karels TJ, Hik DS - PLoS ONE (2015)

Bottom Line: Hoary marmots were neither obligate nor facultative biennial breeders, and breeding probability was insensitive to evolved, environmental, or social factors.However, newly mature females were significantly less likely to breed than older individuals.Annual breeding did not result in increased mortality.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, 99775, United States of America; Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada.

ABSTRACT
Biennial breeding is a rare life-history trait observed in animal species living in harsh, unproductive environments. This reproductive pattern is thought to occur in 10 of 14 species in the genus Marmota, making marmots useful model organisms for studying its ecological and evolutionary implications. Biennial breeding in marmots has been described as an obligate pattern which evolved as a mechanism to mitigate the energetic costs of reproduction (Evolved Constraint hypothesis). However, recent anecdotal evidence suggests that it is a facultative pattern controlled by annual variation in climate and food availability (Environmental Constraint hypothesis). Finally, in social animals like marmots, biennial breeding could result from reproductive competition between females within social groups (Social Constraint hypothesis). We evaluated these three hypotheses using mark-recapture data from an 8-year study of hoary marmot (Marmota caligata) population dynamics in the Yukon. Annual variation in breeding probability was modeled using multi-state mark-recapture models, while other reproductive life-history traits were modeled with generalized linear mixed models. Hoary marmots were neither obligate nor facultative biennial breeders, and breeding probability was insensitive to evolved, environmental, or social factors. However, newly mature females were significantly less likely to breed than older individuals. Annual breeding did not result in increased mortality. Female survival and, to a lesser extent, average fecundity were correlated with winter climate, as indexed by the Pacific Decadal Oscillation. Hoary marmots are less conservative breeders than previously believed, and the evidence for biennial breeding throughout Marmota, and in other arctic/alpine/antarctic animals, should be re-examined. Prediction of future population dynamics requires an accurate understanding of life history strategies, and of how life history traits allow animals to cope with changes in weather and other demographic influences.

No MeSH data available.


Model-averaged breeding probability.Probability of breeding (Ψ) for adult female hoary marmots was modeled as a function of age, previous breeding state, and time. Results are based on 6 years of trapping data (1999–2004) for marmots from 10 social groups in a single valley in the Ruby Range, Yukon. Values are model-averaged annual parameter estimates ± 1 SE.
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pone.0119081.g001: Model-averaged breeding probability.Probability of breeding (Ψ) for adult female hoary marmots was modeled as a function of age, previous breeding state, and time. Results are based on 6 years of trapping data (1999–2004) for marmots from 10 social groups in a single valley in the Ruby Range, Yukon. Values are model-averaged annual parameter estimates ± 1 SE.

Mentions: For females who were reproductively mature during the previous year, the mean probability of breeding in the current year was 0.51 (SE = 0.05) for previous-year breeders and 0.50 (SE = 0.05) for previous nonbreeders (Fig. 1). The top model did not include previous breeding state as a covariate, but models with previous breeding state as a predictor of Ψ (the probability of moving into the ‘Breeder’ state) had a combined AIC weight of 0.48, and 3 models containing this covariate were within 2 AICc of the top model. Model selection therefore provided a moderate degree of support for effects of previous breeding state on current breeding effort (Table 3). However, the model-averaged effect size (difference in Ψ probability between breeders and nonbreeders from the previous year) was < 0.01 (Fig. 1). Model selection did not support PDO as a predictor of Ψ (Table 4). Social group size had a combined AIC weight of 0.28 (Table 4), but the Group covariate was only present in one model within 2 AICc of the top model. The best model did not include annual variation in breeding probability (Table 3), and model-averaged Ψ estimates varied by less than 1 SE from year to year in both age-classes (Fig. 1). Age-class had the strongest support of any model covariates, and had the largest effect size (Table 4; Fig. 1). Annual variation in Ψ was more pronounced for females in their first year of reproductive maturity, but the uncertainty in parameter estimates was also greater for this age-class (Fig. 1). On average, the breeding probability of females four years old or older was 0.33 greater than that of three-year-old individuals (Fig. 1).


Ecological, evolutionary and social constraints on reproductive effort: are hoary marmots really biennial breeders?

Patil VP, Karels TJ, Hik DS - PLoS ONE (2015)

Model-averaged breeding probability.Probability of breeding (Ψ) for adult female hoary marmots was modeled as a function of age, previous breeding state, and time. Results are based on 6 years of trapping data (1999–2004) for marmots from 10 social groups in a single valley in the Ruby Range, Yukon. Values are model-averaged annual parameter estimates ± 1 SE.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4359141&req=5

pone.0119081.g001: Model-averaged breeding probability.Probability of breeding (Ψ) for adult female hoary marmots was modeled as a function of age, previous breeding state, and time. Results are based on 6 years of trapping data (1999–2004) for marmots from 10 social groups in a single valley in the Ruby Range, Yukon. Values are model-averaged annual parameter estimates ± 1 SE.
Mentions: For females who were reproductively mature during the previous year, the mean probability of breeding in the current year was 0.51 (SE = 0.05) for previous-year breeders and 0.50 (SE = 0.05) for previous nonbreeders (Fig. 1). The top model did not include previous breeding state as a covariate, but models with previous breeding state as a predictor of Ψ (the probability of moving into the ‘Breeder’ state) had a combined AIC weight of 0.48, and 3 models containing this covariate were within 2 AICc of the top model. Model selection therefore provided a moderate degree of support for effects of previous breeding state on current breeding effort (Table 3). However, the model-averaged effect size (difference in Ψ probability between breeders and nonbreeders from the previous year) was < 0.01 (Fig. 1). Model selection did not support PDO as a predictor of Ψ (Table 4). Social group size had a combined AIC weight of 0.28 (Table 4), but the Group covariate was only present in one model within 2 AICc of the top model. The best model did not include annual variation in breeding probability (Table 3), and model-averaged Ψ estimates varied by less than 1 SE from year to year in both age-classes (Fig. 1). Age-class had the strongest support of any model covariates, and had the largest effect size (Table 4; Fig. 1). Annual variation in Ψ was more pronounced for females in their first year of reproductive maturity, but the uncertainty in parameter estimates was also greater for this age-class (Fig. 1). On average, the breeding probability of females four years old or older was 0.33 greater than that of three-year-old individuals (Fig. 1).

Bottom Line: Hoary marmots were neither obligate nor facultative biennial breeders, and breeding probability was insensitive to evolved, environmental, or social factors.However, newly mature females were significantly less likely to breed than older individuals.Annual breeding did not result in increased mortality.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, 99775, United States of America; Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada.

ABSTRACT
Biennial breeding is a rare life-history trait observed in animal species living in harsh, unproductive environments. This reproductive pattern is thought to occur in 10 of 14 species in the genus Marmota, making marmots useful model organisms for studying its ecological and evolutionary implications. Biennial breeding in marmots has been described as an obligate pattern which evolved as a mechanism to mitigate the energetic costs of reproduction (Evolved Constraint hypothesis). However, recent anecdotal evidence suggests that it is a facultative pattern controlled by annual variation in climate and food availability (Environmental Constraint hypothesis). Finally, in social animals like marmots, biennial breeding could result from reproductive competition between females within social groups (Social Constraint hypothesis). We evaluated these three hypotheses using mark-recapture data from an 8-year study of hoary marmot (Marmota caligata) population dynamics in the Yukon. Annual variation in breeding probability was modeled using multi-state mark-recapture models, while other reproductive life-history traits were modeled with generalized linear mixed models. Hoary marmots were neither obligate nor facultative biennial breeders, and breeding probability was insensitive to evolved, environmental, or social factors. However, newly mature females were significantly less likely to breed than older individuals. Annual breeding did not result in increased mortality. Female survival and, to a lesser extent, average fecundity were correlated with winter climate, as indexed by the Pacific Decadal Oscillation. Hoary marmots are less conservative breeders than previously believed, and the evidence for biennial breeding throughout Marmota, and in other arctic/alpine/antarctic animals, should be re-examined. Prediction of future population dynamics requires an accurate understanding of life history strategies, and of how life history traits allow animals to cope with changes in weather and other demographic influences.

No MeSH data available.