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.

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.

Reproduction in yearling female Columbian ground squirrels (Spermophilus columbianus)

1981 ◽  
Vol 59 (6) ◽  
pp. 1032-1035 ◽  
Author(s):  
M. Festa-Bianchet
Keyword(s):  
Weight Gain ◽  
Sexual Development ◽  
Weather Conditions ◽  
Ground Squirrels ◽  
Lower Weight ◽  
Spermophilus Columbianus ◽  
Adult Females ◽  
Lower Weight Gain ◽  
Columbian Ground Squirrels ◽  
Similar Growth

In 1980, 4 of 13 yearling female Columbian ground squirrels in a colony in southwestern Alberta raised litters. Mean litter size was not significantly smaller than that of adult females. Breeding and nonbreeding yearling females had similar growth rates as juveniles in 1979, but the former had a lower weight gain in 1980 before their young were weaned. Breeding yearling females were more aggressive and played less than nonbreeders. A combination of apparently good habitat quality in the study area and favourable weather conditions during summer of 1979 and in May of 1980 may have produced early sexual development of these females.

The proximate causes of male-biased natal emigration in Columbian ground squirrels

1993 ◽  
Vol 71 (1) ◽  
pp. 204-218 ◽  
Author(s):  
Darwin R. Wiggett ◽  
David A. Boag
Keyword(s):  
Ground Squirrels ◽  
Home Ranges ◽  
Adult Males ◽  
Spermophilus Columbianus ◽  
Adult Females ◽  
Study Support ◽  
Proximate Causes ◽  
Natal Home ◽  
And Behavior ◽  
Columbian Ground Squirrels

The results of this study support the hypothesis that male-biased emigration of yearling male Columbian ground squirrels (Spermophilus columbianus) is socially induced. The likelihood of emigration from both the natal site and the natal colony was correlated with parameters of social structure and behavior. Agonism by the mother and (or) neighboring adult females, in association with parturition and lactation, apparently caused the initial shifts of yearling males away from their natal home ranges. After these shifts, yearling males that lived in areas where the number of neighboring males (both adult and yearling) was high relative to the number of females emigrated to areas within the natal colony that were more female-biased (intracolony emigration), or emigrated from the natal colony (intercolony emigration). Reduced numbers of adult males apparently resulted in lower rates of emigration by yearling males. Among the latter, emigrants appeared to be subordinate to non-emigrants. We discuss these findings in light of current hypotheses concerning the proximate and ultimate causes of emigration in ground-dwelling sciurids.

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.

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

scholarly journals The timing of birds' breeding seasons: a review of experiments that manipulated timing of breeding

2007 ◽  
Vol 363 (1490) ◽  
pp. 399-410 ◽  
Author(s):  
Simon Verhulst ◽  
Jan-Åke Nilsson
Keyword(s):  
Reproductive Success ◽  
Fitness Costs ◽  
Fitness Component ◽  
Free Living ◽  
Breeding Time ◽  
Weak Points ◽  
Per Se ◽  
Seasonal Decline ◽  
Breeding Seasons ◽  
Cross Fostering

Reproductive success usually declines in the course of the season, which may be a direct effect of breeding time, an effect of quality (individuals with high phenotypic or environmental quality breeding early), or a combination of the two. Being able to distinguish between these possibilities is crucial when trying to understand individual variation in annual routines, for instance when to breed, moult and migrate. We review experiments with free-living birds performed to distinguish between the ‘timing’ and ‘quality’ hypothesis. ‘Clean’ manipulation of breeding time seems impossible, and we therefore discuss strong and weak points of different manipulation techniques. We find that the qualitative results were independent of manipulation technique (inducing replacement clutches versus cross-fostering early and late clutches). Given that the two techniques differ strongly in demands made on the birds, this suggests that potential experimental biases are limited. Overall, the evidence indicated that date and quality are both important, depending on fitness component and species, although evidence for the date hypothesis was found more frequently. We expected both effects to be prevalent, since only if date per se is important, does an incentive exist for high-quality birds to breed early. We discuss mechanisms mediating the seasonal decline in reproductive success, and distinguish between effects of absolute date and relative date, for instance timing relative to seasonal environmental fluctuations or conspecifics. The latter is important at least in some cases, suggesting that the optimal breeding time may be frequency dependent, but this has been little studied. A recurring pattern among cross-fostering studies was that delay experiments provided evidence for the quality hypothesis, while advance experiments provided evidence for the date hypothesis. This indicates that late pairs are constrained from producing a clutch earlier in the season, presumably by the fitness costs this would entail. This provides us with a paradox: evidence for the date hypothesis leads us to conclude that quality is important for the ability to breed early.

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

The resident fitness hypothesis and dispersal by yearling female Columbian ground squirrels

1992 ◽  
Vol 70 (10) ◽  
pp. 1984-1994 ◽  
Author(s):  
Darwin Wiggett ◽  
David A. Boag
Keyword(s):  
Resource Availability ◽  
Ground Squirrels ◽  
Home Ranges ◽  
Adult Males ◽  
Data Set ◽  
Individual Basis ◽  
Spermophilus Columbianus ◽  
Adult Females ◽  
Fitness Benefits ◽  
Columbian Ground Squirrels

The emigratory behavior of yearling female Columbian ground squirrels (Spermophilus columbianus) in southwestern Alberta was studied for 25 active seasons among five colonies. From this data set we tested six predictions of the resident fitness hypothesis. The data strongly supported all six predictions: (1) yearling females were highly philopatric; (2) mothers behaved cohesively towards their yearling daughters (adult females tended to shift their home ranges in the presence of yearling daughter(s), often facilitating the recruitment of the latter to the natal site); (3) as densities of adult resident females rose and resource availability on an individual basis presumably declined, agonism from parous mothers and neighboring females caused greater proportions of yearling females to emigrate; (4) sibling daughters competed for access to the natal site when this space became vacant (parous yearlings were more successful than their nonparous siblings, and among the latter, dominant individuals were more successful than their subordinate siblings); (5) resident adult females were highly aggressive towards immigrant yearling females; and (6) resident adult males behaved cohesively with all yearling females, whether resident or immigrant, and were significantly more cohesive towards yearling females than towards yearling males. The results of this study suggest that emigration is not adaptive for yearling female Columbian ground squirrels. Rather, we suggest that female Columbian ground squirrels gain fitness benefits through philopatry and the retention of daughter(s) on the natal site when resources are not limiting.

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