Somatic senescence: evidence from female Richardson's ground squirrels

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

doi:10.1111/j.0030-1299.2005.13382.x

Cited by 22 publications

(23 citation statements)

References 62 publications

(91 reference statements)

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“…One- and two-year-old females did not significantly differ in the percentage of mated females that delivered litters and average litter size at birth. Similar results were obtained in Richardson's ground squirrel and Siberian lemming females (Erlinge et al, 2000; Broussard et al, 2005). However, in deer mice and white-footed mice (Millar, 1994; Morris, 1996), older females have decreased reproductive success.…”

Section: Discussionsupporting

confidence: 80%

Effects of seasonal, ontogenetic, and genetic factors on lifespan of male and female progeny of Arvicola amphibius

Назарова¹

2013

Front. Genet.

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The water vole (Arvicola amphibius) in the forest-steppe of West Siberia is known to have wide fluctuations in abundance. These fluctuations are accompanied by changes in birth and death rates, sex-age structure of the population, and individual morphophysiological and behavioral characteristics of the animals. Survival of the animals depends on season, phase of population cycle, and sex. Based on the data of long-term captive breeding of water voles, the maximal lifespan of males was found to be 1188 days and that of females, 1108 days. There were no differences between the sexes in mean lifespan. The probability of living 2 years or longer was 0.21. Individuals who began breeding at an older age had a significantly longer lifespan and produced more offspring. The survival curves of the spring-born animals were steeper than of those summer-/autumn-born. Maternal factors had a differential effect on males and females with respect to lifespan. Male lifespan correlated negatively with maternal age, parity, and litter size, whereas female lifespan did not correlate with these characteristics. To estimate heritability, parent-offspring correlations of lifespan were calculated, as well as full-sib intraclass correlations. No statistically significant correlation was found for lifespan between sons and mothers, sons and fathers, and daughters and fathers. Daughters' lifespan correlated positively with maternal lifespan (r = 0.21, p < 0.001). Female full-sibs and male full-sibs had the same intraclass correlations, 0.22, p < 0.001.

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Section: Discussionsupporting

confidence: 80%

Effects of seasonal, ontogenetic, and genetic factors on lifespan of male and female progeny of Arvicola amphibius

Назарова¹

2013

Front. Genet.

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“…In contrast to the prediction of Lack's optimum clutch size hypothesis, the most productive litter size for Richardson's ground squirrels was larger than both the mean litter size and the most common litter size. Yearling Richardson's ground squirrels produce litters similar in size to older females (Michener 1989 a , Broussard et al 2005), so the divergence of the most productive litter from mean litter size was not attributable to lower fecundity in the first year of reproduction, as has been suggested in birds (e.g., ).…”

Section: Discussionmentioning

confidence: 87%

“…In addition, when we compared mean litter size for mothers that did and did not survive to the next year (6.47 ± 0.07, n = 575, and 6.50 ± 0.10, n = 424, respectively), the difference was not significant (Satterthwaite t 861 = 0.25, P > 0.80). Because yearling Richardson's ground squirrels produce litters similar in size to older females (Michener 1989 a , Broussard et al 2005), we included females of all ages in the analysis of year‐to‐year changes in litter size; for those females with data available for more than two consecutive years, we randomly selected one pair of years for analysis. Mother's litter size in one year was weakly and positively associated with her litter size in the following year (Fig.…”

Section: Resultsmentioning

confidence: 99%

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

Risch

Michener

Dobson

2007

Ecology

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We studied litter size variation in a population of Richardson's ground squirrels (Spermophilus richardsonii) in Alberta, Canada, from 1987 to 2004. Litter size at first emergence of juveniles from the natal burrow ranged from 1 to 14; the most common litter sizes, collectively accounting for 41.0% of 999 litters, were 6 and 7. The number of offspring surviving to adulthood (attained on emergence from hibernation as yearlings) increased with increasing litter size, a result that was not predicted by Lack's "optimal litter size" hypothesis, Mountford's "cliff-edge" effect, or the "bad-years" effect. Contrary to the negative effects predicted by the "cost of reproduction" hypothesis, litter size had no significant influence on survival of mothers to the subsequent year or on the size of the subsequent litter. Rather, our results best fit the predictions of the "individual optimization" hypothesis, which suggests that litter size is determined by the body condition and environmental circumstances of each mother. Supporting this hypothesis, survival of individual offspring was not significantly associated with litter size. Additionally, year-to-year changes in maternal body mass at mating were positively associated with concurrent changes in litter size (r = 0.56), suggesting that litter size depends on the body condition of the mother. Because the mean number of recruits to adulthood increased as litter size increased (r2 = 0.96) and litter size increased with maternal condition, offspring productivity was greater for mothers in better body condition.

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“…In females that survive to old age, a general deterioration in reproduction is evidence of senescence (Newton 1989; Gustafsson & Pärt 1990; Broussard et al . 2005), which we found evidence for in the cross‐sectional analysis.…”

Section: Discussionmentioning

confidence: 99%

Age‐specific variation in reproduction is largely explained by the timing of territory establishment in the New Zealand stitchbird Notiomystis cincta

Low

Pärt

Forslund

2007

Journal of Animal Ecology

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Summary1. Using data from 327 nests over a consecutive 8-year period we examined age-specific variation in reproduction in a population of stitchbirds (or hihi) Notiomystis cincta and related how differences in reproductive performance were linked to the timing of territory establishment and breeding. 2. Across the population all reproductive parameters showed a quadratic relationship with an increase mainly between the first and second breeding season and a decline after the fourth year. A longitudinal analysis showed evidence of senescence by the sixth year in the numbers of chicks fledged and recruited. 3. Reproductive increases between years 1 and 2 were the result of poor-quality females dying after their first breeding season (differential selection hypothesis) in combination with surviving females showing improvements in reproduction in their second year (individual improvement/constraint hypothesis). 4. There was no effect of mate experience or territory quality on improvements in breeding between years. 5. The key variable influencing reproductive output was the timing of breeding. Birds that started laying earlier were more likely to lay multiple clutches in any given season. This was the main difference between first-year and older birds; generally first-year birds initiated egg laying later and consequently laid fewer clutches. 6. Approximately half of all first-year birds did not establish their territory until after the breeding season had begun. This delay in territory establishment resulted in these birds delaying breeding, which resulted in them having a lower reproductive output relative to all other birds. First-year birds that managed to establish their territory before breeding commenced, had similar rates of reproduction as older birds. 7. There was a positive relationship between the timing of territory establishment during a female's first year and her hatching date in the previous breeding season. We hypothesize that this was because late-hatched females were less able to effectively compete for territories against earlier-hatched members of their cohort, and this delayed their establishment and breeding in their first year. Thus, this social constraint is likely to be a major factor driving age-specific reproductive variation in this population.

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Somatic senescence: evidence from female Richardson's ground squirrels

Cited by 22 publications

References 62 publications

Effects of seasonal, ontogenetic, and genetic factors on lifespan of male and female progeny of Arvicola amphibius

Effects of seasonal, ontogenetic, and genetic factors on lifespan of male and female progeny of Arvicola amphibius

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

Age‐specific variation in reproduction is largely explained by the timing of territory establishment in the New Zealand stitchbird Notiomystis cincta

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