Effects of Inbreeding on Reproduction and Sex Ratio of Rattus villosissimus

A retrospective study of the breeding records of a laboratory colony of an Australian rodent, Rattus villosissimus , demonstrated significant inbreeding depression in the number of young bom per litter, with a 3.4% decrease for each 10% increase in the inbreeding coefficient. This inbreeding depression showed no evidence of amelioration as the laboratory population became highly inbred over 25 generations. Inbreeding had no effect on survival or growth rate of juveniles. There was a significant relationship between the number of young and the sex ratio of a litter, with larger litters having a higher proportion of females. Inbreeding, while decreasing the number of young per litter, did not result in a significant shift in the sex ratio.

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