Estrus and Estrogen Changes in Mated and Unmated Free-Living European Ground Squirrels

The course of behavioral and vaginal estrus and patterns of circulating estrogens were followed in free-living European ground squirrels (Spermophilus citellus) after their emergence from hibernation. Normally mating females were compared to a second group in an area where males had been removed fro...

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Bibliographic Details
Published in:Hormones and behavior 2000-05, Vol.37 (3), p.190-197
Main Authors: Millesi, Eva, Huber, Susanne, Pieta, Katharin, Walzl, Manfred, Arnold, Walter, Dittami, John P.
Format: Article
Language:English
Subjects:
Animals
Animals, Wild
Copulation - physiology
Diestrus - physiology
Estradiol - blood
estrogen changes
estrus
Estrus - physiology
Female
ground squirrel
Hibernation
Male
Metestrus - physiology
Ovulation - physiology
Proestrus - physiology
Sciuridae - physiology
Seasons
Spermophilus
Spermophilus citellus
Vagina - cytology
Vagina - physiology
vaginal cytology
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Summary:The course of behavioral and vaginal estrus and patterns of circulating estrogens were followed in free-living European ground squirrels (Spermophilus citellus) after their emergence from hibernation. Normally mating females were compared to a second group in an area where males had been removed from the population before female emergence. Both groups showed vaginal estrus, but the patterns differed. Mating shortened vaginal estrus to a 3-day period compared to 8 days in unmated females. The extent (cell number) of cell cornification during estrus and the cellular components (percentage distribution) of metestrus did not differ between the two groups. Females in the area without males had significantly higher estrogen levels during estrus and metestrus compared to those in the control area. European ground squirrels were found to be monestrous, as none of the unmated females reentered estrus after met- or diestrus was detected. The prolongation of vaginal estrus in unmated females can be viewed as either a physiological inevitability or an adaptation to low mate availability. The extension is still relatively short compared to other sciurid species and perhaps a product of constraints producing a strict time frame for reproduction.
ISSN:0018-506X
1095-6867
DOI:10.1006/hbeh.2000.1574