Maternal Traits and Reproduction in Richardson's Ground Squirrels

Abstract

Differences among conspecifics in body mass result from underlying differences in structural size and physiological condition. To determine whether the structural or physiological component of body mass has a stronger influence on reproductive traits at parturition, we studied the body composition (lean dry mass and fat content), structural size (1st principal component scores computed from 10 skeletal measurements), and body condition (residuals from regression of body mass on structural size) of yearling and older female Richardson's ground squirrels (Spermophilus richardsonii). At parturition, differences among yearlings in body mass primarily reflected differences in structural size associated with continuing structural growth. Older females appeared to reach a deterministic adult structural size, and body mass of older females was most strongly associated with body condition. Structural size of yearling females and body condition of older females had significant positive effects on litter mass. For older females, date of parturition had a significant negative influence on litter size. Both yearling and older females exhibited significant positive effects of parturition date and body condition on neonate mass. In older females, trade—off resulted in smaller litters of heavier neonates as the breeding season progressed, perhaps reflecting the need for rapid growth of offspring before hibernation. Maternal size, maternal condition, and seasonal timing were important aspects of reproduction in Richardson's ground squirrels, but these characteristics are seldom considered concurrently in studies of life histories.

Timing of Hibernation and Molt in Female Columbian Ground Squirrels

“…To ensure that I did not use data from females that died before going into hibernation, I used only immergence dates of animals that did emerge the following spring. Growing immature females may exhibit different patterns of reproduction and associated characteristics than adult animals (Dobson and Michener 1995). Because 2-year-old Columbian ground squirrels are still growing in body mass and body size (Boag and Murie 1981), I included only individuals that were Ն3 years old in analyses.…”

Sex–biased maternal investment in voles: importance of environmental conditions

“…Dobson & Michener 1995). The linear regression was used as it was significant (R 2 = 0.51, F 1,36 = 35.74, p Ͻ 0.001), whereas quadratic or cubic parameters were not significantly different from zero (t-tests, p Ͼ 0.5).…”

Maternal Traits and Reproductive Effort in Northern Elephant Seals

“…E-mail: crocker@sonoma.edu location, a good measure of reproductive effort should consider variation in individual activity and foraging efficiency (Stearns 1992) and consider that energy expenditure is recoverable (Drent and Dann 1980). Body size exerts an important influence on patterns of animal life-history traits, within (e.g., Martin 1987, Patton and Brylski 1987, Dobson 1992, Dobson and Michener 1995 and among species (Western 1979, Western and Ssemakula 1982, Stearns 1983, Dunham and Miles 1985, Costa 1991, 1993. Many studies have used mass as a preferred indicator of body size, but few have examined the impacts of both body mass and body condition on reproductive effort (e.g., Dobson and Michener 1995).…”