Sibling recognition in thirteen-lined ground squirrels: effects of genetic relatedness, rearing association, and olfaction

I investigated sibling-sibling recognition in captive thirteen-lined ground squirrels ( Spermophilus tridecemlineatus ) by cross-fostering lab-born pups shortly after birth. When young reached about 45 days of age, I observed dyadic interactions in a test arena of pairs from four relatedness X rearing groups, and recorded the frequency of “exploratory” encounters between individuals. Sibs-reared together and nonsibs-reared together exhibited significantly fewer exploratory encounters than either sibs-reared apart or nonsibsreared apart. Young reared together were equally exploratory, regadless of relatedness; similarly, young reared apart, whether they were sibs or nonsibs, showed similar levels of exploration. Thus, the differential treatment of siblings in the lab appears to be based on rearing association and not genetic relatedness per se. I interpret this recognition based on association (rearing familiarity) in the context of the species' social organization and compare my results on S. tridecemlineatus with similar studies on S. beldingi, S. parryii , and S. richardsonii . I also used an olfactory impairment technique (zinc sulfate) and found that differential treatment in thirteen-lined ground squirrels was influenced by olfactory cues.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46871/1/265_2004_Article_BF00299622.pd

Efficient age determination: how freezing affects eye lens weight of the small rodent species Arvicola terrestris

Age determination of animals by measuring the weight of their eye lenses is a widely used method in wildlife biology. In general, it is recommended to prepare lenses immediately after trapping to avoid errors in the age estimation due to decomposition of lens tissue. However, in many field studies, large numbers of animals need to be trapped over long periods of time in huge areas and by many different field workers. Therefore, the immediate preparation of eye lenses imposes a considerable logistic constraint that could be avoided by prior freezing of trapped animals. To assess the impact of freezing, weights of lens of frozen and unfrozen eyes of 114 Arvicola terrestris were compared pair wise. The frozen lenses weighed at average 3.3% (95% CI: 2.4–4.1%) more than the unfrozen ones from the same animals. Freezing time, weight of lenses and mean temperature of the trapping day as an indicator of decomposition speed did not affect the freezing-induced weight increase. Age estimates based on weights of unfrozen lenses varied between 24 and 445 days. Estimates based on frozen lenses were systematically higher. Applying a constant correction factor of 1.033−1 for the weight of frozen lenses corrects this overestimation of age. We conclude that age determination with frozen lenses of small rodents can yield valid age estimates if a correction factor for freezing is applied. Thus, age determination can be organised much more efficiently in field studies, which is highly advantageous for many ecological, agricultural and epidemiological research projects