Variation in Litter Size: A Test of Hypotheses in Richardson's Ground Squirrels

Risch, Thomas S.; Michener, Gail R.; Dobson, F. Stephen

doi:10.1890/06-0249

Cited by 39 publications

(25 citation statements)

References 56 publications

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“…Positive correlation between litter size and body size has been well established in the literature, as predicted by Darwin's fecundity advantage (Bünger et al, 2005;Risch et al, 2007). In contrast, we found a nonlinear, quadratic relationship between litter size and body carcass mass.…”

Section: Discussionsupporting

confidence: 69%

Litter sizes of Daurian ground squirrels peak at intermediate body sizes

et al. 2016

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a b s t r a c tLitter size and body size of animals may coevolve under the concomitant pressures of sexual selection, fecundity selection, and viability selection. Studies have demonstrated the positive relationship between body size and litter size, consistent with Darwin's fecundity advantage of large body size. However, the counterbalancing selection hypothesis predicts fecundity selection would result in a positive correlation between litter size and body size initially, whereas the opposite pressure by viability selection would decrease litter size with further increasing body size beyond a threshold size. Moreover, the reproduction senescence hypothesis predicts that litter size of old, large females would decline with deteriorating body conditions. In this study, we tested the predictions of the counterbalancing selection hypothesis and the reproduction senescence hypothesis concerning the quadratic relationship between body size and litter size in Daurian ground squirrels (Spermophilus dauricus). Litter size increased initially with increasing carcass weight of females, and then decreased with further increases in carcass weight, supporting the prediction of the counterbalancing hypothesis. However, litter size was not related to body condition index of females, and body conditions improved with increasing body weight, suggesting that the reproduction senescence hypothesis alone cannot explain the observed quadratic relationship between litter size and carcass weight of female S. dauricus.

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Section: Discussionsupporting

confidence: 69%

Litter sizes of Daurian ground squirrels peak at intermediate body sizes

et al. 2016

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“…Indeed, female mammals have been shown to adjust their litter size in relation to their condition (Risch et al . ; Servanty et al . ).…”

Section: Discussionmentioning

confidence: 99%

Sex differences in relationships between habitat use and reproductive performance in Soay sheep (Ovis aries)

et al. 2015

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The role of habitat use in generating individual variation in fitness has rarely been examined empirically in natural populations of long-lived mammals, particularly for both sexes simultaneously. This is the case despite the increase in studies attempting to understand evolutionary change in such populations. Using data from the St. Kilda Soay sheep population, we quantified the association between lifetime reproductive performance (lifetime breeding and reproductive success) and the proportion of the home range covered by a key grass species, H. lanatus, for 490 females and 304 males. Increased H. lanatus cover was associated only with increased female lifetime reproductive success, but increased lifetime breeding success for both sexes, arising through increased male longevity and increased female fecundity. This work suggests that improved understanding of the causes and consequences of fitness differences will likely require us to better account for habitat-derived individual variation, and to do so for the sexes appropriately.

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“…; Risch et al. ). Females in good condition may also show improved survival and concurrent subsequent breeding through increased somatic effort.…”

Section: Introductionmentioning

confidence: 97%

Testing the reproductive and somatic trade‐off in female Columbian ground squirrels

Rubach

Abebe

et al. 2016

Ecology and Evolution

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Energetic trade‐offs in resource allocation form the basis of life‐history theory, which predicts that reproductive allocation in a given season should negatively affect future reproduction or individual survival. We examined how allocation of resources differed between successful and unsuccessful breeding female Columbian ground squirrels to discern any effects of resource allocation on reproductive and somatic efforts. We compared the survival rates, subsequent reprodction, and mass gain of successful breeders (females that successfully weaned young) and unsuccessful breeders (females that failed to give birth or wean young) and investigated “carryover” effects to the next year. Starting capital was an important factor influencing whether successful reproduction was initiated or not, as females with the lowest spring emergence masses did not give birth to a litter in that year. Females that were successful and unsuccessful at breeding in one year, however, were equally likely to be successful breeders in the next year and at very similar litter sizes. Although successful and unsuccessful breeding females showed no difference in over winter survival, females that failed to wean a litter gained additional mass during the season when they failed. The next year, those females had increased energy “capital” in the spring, leading to larger litter sizes. Columbian ground squirrels appear to act as income breeders that also rely on stored capital to increase their propensity for future reproduction. Failed breeders in one year “prepare” for future reproduction by accumulating additional mass, which is “carried over” to the subsequent reproductive season.

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Variation in Litter Size: A Test of Hypotheses in Richardson's Ground Squirrels

Cited by 39 publications

References 56 publications

Litter sizes of Daurian ground squirrels peak at intermediate body sizes

Litter sizes of Daurian ground squirrels peak at intermediate body sizes

Sex differences in relationships between habitat use and reproductive performance in Soay sheep (Ovis aries)

Testing the reproductive and somatic trade‐off in female Columbian ground squirrels

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