scholarly journals Comparing fitness measures and the influence of age of first reproduction in Columbian ground squirrels

2020 ◽  
Vol 101 (5) ◽  
pp. 1302-1312
Author(s):  
Kristin K Rubach ◽  
F Stephen Dobson ◽  
Bertram Zinner ◽  
Jan O Murie ◽  
Vincent A Viblanc
Keyword(s):  
Reproductive Success ◽  
Population Growth ◽  
Life Cycles ◽  
Ground Squirrels ◽  
Relative Fitness ◽  
Age At First Reproduction ◽  
Individual Fitness ◽  
First Reproduction ◽  
Fitness Measures ◽  
Columbian Ground Squirrels

Abstract The timing of life-history traits may have strong influences on the evolution of life cycles and on population demography. This is especially true of the age at which females first reproduce (Cole’s principle). We examined whether the age at which females first reproduce influences fitness in Columbian ground squirrels (Urocitellus columbianus), for which females varied in the age at which they initially produce weaned offspring, from ages 1 through 5 years. With 148 females with complete known life spans in a 28-year data set, we examined four fitness measures: individual fitness (λ ind), individual fitness relative to the pattern of growth of the population (λ rel), lifetime reproductive success (LRS), and LRS relative to the total LRS for each female’s cohort (LRSrel). These metrics were calculated for offspring produced at the time of weaning and offspring that survived to emerge after their first hibernation period. Individual fitness (λ ind) was significantly associated with population growth during a female’s lifetime (λ Leslie; R2 = 0.523, P < 0.0001), indicating the need to adjust individual fitness for demonstrated changes in population growth and thus producing a relative individual fitness index (λ rel). We regressed λ rel on age at first reproduction, and found significant selection favoring earlier reproductive success (β ± SE = −0.20 ± 0.06; R2 = 0.306, P < 0.0001). When using an earlier (offspring at weaning) versus later (those that survived their first hibernation) measure of fecundity, we found that the latter introduced considerable variation, likely environmental, into the estimate of selection. This greatly weakened the regression of relative fitness on the age at first successful reproduction. LRS and LRSrel exhibited nonsignificant changes with age at first reproduction. Finally, those females that reproduced successfully at younger ages had similar litter sizes but significantly shorter life spans than females that matured when older, perhaps reflecting costs to early reproduction.

Variation in reproductive success of male and female Columbian ground squirrels (Urocitellus columbianus)

2012 ◽  
Vol 90 (6) ◽  
pp. 736-743 ◽  
Author(s):  
Philip H. Jones ◽  
Jeffrey L. Van Zant ◽  
F. Stephen Dobson
Keyword(s):  
Reproductive Success ◽  
Mating System ◽  
Multiple Paternity ◽  
Ground Squirrels ◽  
Male Reproductive Success ◽  
Offspring Production ◽  
Bateman Gradient ◽  
Coefficients Of Variation ◽  
Males And Females ◽  
Columbian Ground Squirrels

The imbalanced reproductive success of polygynous mammals results in sexual selection on male traits like body size. Males and females might have more balanced reproductive success under polygynandry, where both sexes mate multiply. Using 4 years of microsatellite DNA analyses of paternity and known maternity, we investigated variation in reproductive success of Columbian ground squirrels, Urocitellus columbianus (Ord, 1815); a species with multiple mating by both sexes and multiple paternity of litters. We asked whether male reproductive success was more variable than that of females under this mating system. The overall percentage of confirmed paternity was 61.4% of 339 offspring. The mean rate of multiple paternity in litters with known fathers was 72.4% (n = 29 litters). Estimated mean reproductive success of males (10.27 offspring) was about thrice that of females (3.11 offspring). Even after this difference was taken into account statistically, males were about three times as variable in reproductive success as females (coefficients of variation = 77.84% and 26.74%, respectively). The Bateman gradient (regression slope of offspring production on number of successful mates) was significantly greater for males (βM = 1.44) than females (βF = 0.28). Thus, under a polygynandrous mating system, males exhibited greater variation in reproductive success than females.

scholarly journals Kin selection in Columbian ground squirrels ( Urocitellus columbianus ): littermate kin provide individual fitness benefits

2009 ◽  
Vol 277 (1684) ◽  
pp. 989-994 ◽  
Author(s):  
Vincent A. Viblanc ◽  
Coline M. Arnaud ◽  
F. Stephen Dobson ◽  
Jan O. Murie
Keyword(s):  
Kin Selection ◽  
Large Body ◽  
Group Living ◽  
Ground Squirrels ◽  
Evolution Of Cooperation ◽  
Major Life ◽  
Individual Fitness ◽  
Evolution Of Sociality ◽  
Fitness Benefits ◽  
Columbian Ground Squirrels

Since W. D. Hamilton's seminal work on the evolution of sociality, a large body of research has accumulated on how kin selection might explain the evolution of cooperation in many group-living species. Our study examined the evolutionary basis of philopatry and cooperation; specifically, whether individuals benefit from the presence of close kin. We applied an individual fitness approach to a 16-year study of Columbian ground squirrels ( Urocitellus columbianus ) to investigate potential causal paths by which the presence of kin might act on individual fitness. Our results indicate that individual fitness benefits resulted from associations of philopatric female kin, and support the hypothesis that increased tolerance of proximity of kin is a proximate mechanism for these benefits. The major life-history influence of kin on individual fitness was through improved reproductive success, and this benefit may have been owing to philopatric settlement of kin that were recognized through familiarization in the natal burrow. Thus, we demonstrated an evolutionary basis necessary for ongoing kin-selected cooperation in Columbian ground squirrels, though the mechanism of familiarity may determine which kin individuals benefit from cooperative behaviours.

scholarly journals Ectoparasites and fitness of female Columbian ground squirrels

2015 ◽  
Vol 370 (1669) ◽  
pp. 20140113 ◽  
Author(s):  
Shirley Raveh ◽  
Peter Neuhaus ◽  
F. Stephen Dobson
Keyword(s):  
Natural Selection ◽  
Reproductive Success ◽  
Ground Squirrels ◽  
Fitness Costs ◽  
Treatment Control ◽  
Free Living ◽  
Sham Treatment ◽  
Adult Females ◽  
And Control ◽  
Columbian Ground Squirrels

Parasites play an important role in the evolution of host traits via natural selection, coevolution and sexually selected ornaments used in mate choice. These evolutionary scenarios assume fitness costs for hosts. To test this assumption, we conducted an ectoparasite removal experiment in free-living Columbian ground squirrels ( Urocittelus columbianus ) in four populations over three years. Adult females were randomly chosen to be either experimentally treated with anti-parasite treatments (spot-on solution and flea powder, N = 61) or a sham treatment (control, N = 44). We expected that experimental females would show better body condition, increased reproductive success and enhanced survival. Contrary to our expectations, body mass was not significantly different between treatments at mating, birth of litter or weaning of young. Further, neither number nor size of young at weaning differed significantly between the two treatments. Survival to the next spring for adult females and juveniles was not significantly different between experimental and control treatments. Finally, annual fitness was not affected by the treatments. We concluded that females and their offspring were able compensate for the presence of ectoparasites, suggesting little or no fitness costs of parasites for females in the different colonies and during the years of our experiments.

Determinants of reproductive success in female Columbian ground squirrels

Oecologia ◽  
1991 ◽  
Vol 86 (4) ◽  
pp. 528-534 ◽  
Author(s):  
Wendy J. King ◽  
Marco Festa-Bianchet ◽  
Susan E. Hatfield
Keyword(s):  
Reproductive Success ◽  
Ground Squirrels ◽  
Columbian Ground Squirrels

Captive Ancestry Upwardly Biases Estimates of Relative Reproductive Success

2017 ◽  
Vol 108 (5) ◽  
pp. 583-587 ◽  
Author(s):  
Janna R Willoughby ◽  
Mark R Christie
Keyword(s):  
Reproductive Success ◽  
Captive Breeding ◽  
Wild Population ◽  
Relative Fitness ◽  
Declining Populations ◽  
In The Wild ◽  
Fitness Measures ◽  
Number Of Individuals ◽  
Mean Population Fitness

Abstract Supplementation programs, which release captive-born individuals into the wild, are commonly used to demographically bolster declining populations. In order to evaluate the effectiveness of these programs, the reproductive success of captive-born individuals released into the wild is often compared to the reproductive success of wild-born individuals in the recipient population (relative reproductive success, RRS). However, if there are heritable reductions in fitness associated with captive breeding, gene flow from captive-born individuals into the wild population can reduce the fitness of the wild population. Here, we show that when captive ancestry in the wild population reduces mean population fitness, estimates of RRS are upwardly biased, meaning that the relative fitness of captive-born individuals is over-estimated. Furthermore, the magnitude of this bias increases with the length of time that a supplementation program has been releasing captive-born individuals. This phenomenon has long-term conservation impacts since management decisions regarding the design of a supplementation program and the number of individuals to release can be based, at least in part, on RRS estimates. Therefore, we urge caution in the interpretation of relative fitness measures when the captive ancestry of the wild population cannot be precisely measured.

scholarly journals Subordinate male meerkats prospect for extra-group paternity: alternative reproductive tactics in a cooperative mammal

2007 ◽  
Vol 274 (1618) ◽  
pp. 1603-1609 ◽  
Author(s):  
Andrew J Young ◽  
Goran Spong ◽  
Tim Clutton-Brock
Keyword(s):  
Reproductive Success ◽  
Alternative Reproductive Tactics ◽  
Substantial Proportion ◽  
Reproductive Tactics ◽  
Age At First Reproduction ◽  
Suricata Suricatta ◽  
Cooperatively Breeding ◽  
First Reproduction ◽  
Fitness Benefits ◽  
Animal Societies

In cooperatively breeding species, subordinates typically suffer strong constraints on within-group reproduction. While numerous studies have highlighted the additional fitness benefits that subordinates might accrue through helping, few have considered the possibility that subordinates may also seek extra-group matings to improve their chances of actually breeding. Here, we show that subordinate males in cooperative meerkat, Suricata suricatta , societies conduct frequent extraterritorial forays, during periods of peak female fertility, which give rise to matings with females in other groups. Genetic analyses reveal that extra-group paternity (EGP) accrued while prospecting contributes substantially to the reproductive success of subordinates: yielding the majority of their offspring (approx. 70%); significantly reducing their age at first reproduction and allowing them to breed without dispersing. We estimate that prospecting subordinates sire 20–25% of all young in the population. While recent studies on cooperative birds indicate that dominant males accrue the majority of EGP, our findings reveal that EGP can also arise from alternative reproductive tactics employed exclusively by subordinates. It is important, therefore, that future attempts to estimate the fitness of subordinate males in animal societies quantify the distribution of extra-group as well as within-group paternity, because a substantial proportion of the reproductive success of subordinates may otherwise go undetected.

Effects of a late snowstorm and rain on survival and reproductive success in Columbian ground squirrels (Spermophilus columbianus)

1999 ◽  
Vol 77 (6) ◽  
pp. 879-884 ◽  
Author(s):  
Peter Neuhaus ◽  
Ron Bennett ◽  
Anne Hubbs
Keyword(s):  
Mortality Rate ◽  
Reproductive Success ◽  
Weather Conditions ◽  
Ground Squirrels ◽  
Mating Season ◽  
Spermophilus Columbianus ◽  
Adverse Weather Conditions ◽  
Adverse Weather ◽  
Body Mass Changes ◽  
Columbian Ground Squirrels

Body mass changes, reproductive success, and mortality were studied in Columbian ground squirrels (Spermophilus columbianus) in southern Alberta from 1994 to 1996. Spring weather conditions varied widely between years: 1994 was a dry, warm spring, 1995 was extremely rainy, and in 1996 a major snowstorm during the first 2 weeks of May stopped foraging by ground squirrels during the latter part of their mating season. We predicted that adverse weather conditions during the mating season in general, and this snowstorm specifically, would influence reproductive success and survival. Mass changes during the first 2 weeks of May varied from year to year and reflected major differences in spring weather. Female reproductive success was highest in 1994 and lowest in 1996. In 1996, we observed a higher mass loss during the first 2 weeks of May in females that subsequently did not wean a litter than in those that did. Weaning success was higher for females that mated after the snowstorm than for those that mated before or during the snowstorm. The mortality rate during mating in 1996 was higher in males than in females and was higher than in 1994 or 1995 for both sexes. Overall weaning success of females was highest in 1994 and lowest in 1996. We concluded that the energetic costs of mating can lead to a high mortality rate for males and low reproductive success for females.

scholarly journals Mating order and reproductive success in male Columbian ground squirrels (Urocitellus columbianus)

2010 ◽  
Vol 21 (3) ◽  
pp. 537-547 ◽  
Author(s):  
Shirley Raveh ◽  
Dik Heg ◽  
F. Stephen Dobson ◽  
David W. Coltman ◽  
Jamieson C. Gorrell ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Ground Squirrels ◽  
Mating Order ◽  
Columbian Ground Squirrels

Annual reproductive success in three cohorts of Columbian ground squirrels: founding immigrants, subsequent immigrants, and natal residents

1993 ◽  
Vol 71 (8) ◽  
pp. 1577-1584 ◽  
Author(s):  
Darwin R. Wiggett ◽  
David A. Boag
Keyword(s):  
Reproductive Success ◽  
Survival Rates ◽  
Ground Squirrels ◽  
Central Position ◽  
Adult Males ◽  
Male And Female ◽  
Reproductive Maturity ◽  
Active Season ◽  
Risk Of Predation ◽  
Columbian Ground Squirrels

We compared, over an 8-year period, the annual reproductive success (RS) of male and female founding immigrants (FIs) with that of subsequent immigrants (SIs), and the latter with that of natal residents (NRs) in two recently established colonies of Columbian ground squirrels (Spermophilus columbianus) in southwestern Alberta. For males, actual annual RS was unknown and so was estimated; for females, RS was measured directly. Among females, FIs had significantly more juveniles at litter emergence, and more yearlings present to age of emigration annually than did SIs. Juvenile and yearling offspring of SI females suffered higher annual rates of disappearance (presumed mortality) over the active season than did those of FIs. Additionally, the matrilines of FIs produced significantly more juveniles, more yearlings to time of emigration, and more daughters to reproductive maturity annually than did the matrilines of SI females. Male FIs had higher annual survival rates (and consequently lived and were territorial significantly longer), and had more female neighbours per year than did SIs, which suggests that the former had higher annual RS. We suggest that the higher annual RS of male and female FIs resulted mainly from their monopolization of the best resources and a lower risk of predation as a result of their more central position in the colony. Comparison of the annual RS of SIs and NRs showed that most (~70%) adult males present in the colonies were SIs. These males were significantly more likely to hold territories and to do so for significantly longer periods than their NR counterparts. Conversely, SI females annually brought above ground significantly fewer juveniles and had significantly fewer yearling offspring present to time of emigration than did NR females. Furthermore, the young of SI females suffered significantly higher rates of disappearance (presumed mortality) during the active season than did those of NR females, possibly because the former resided in more peripheral areas within the colony where predation rates may have been higher. We found no differences between these groups of females in the number of female offspring reaching reproductive maturity in the natal colony. These results provide preliminary support for the hypothesis that females, apart from FIs, benefit from philopatry; whereas males gain reproductive advantage through dispersal.

Sign in / Sign up

Export Citation Format

Share Document