EFFECTS OF INBREEDING ON SKELETAL DEVELOPMENT OF RATTUS-VILLOSISSIMUS

In a species of Australian native rat, Rattus villosissimus, which exp eriences extreme population fluctuations and possibly episodes of loca l inbreeding in the wild, generations of inbreeding in a laboratory co lony led to altered skull shape and increased fluctuating asymmetry in some skeletal characters, Although inbreeding was closely associated with the number of generations in captivity, the effect of inbreeding after controlling statistically for the generation number was to decre ase skull length and width, The effect of generations in captivity aft er controlling for inbreeding was to increase skull length and width, The joint effect of these confounded determinants was to produce rats with increasingly broad and short skulls through generations of inbree ding, Developmental anomalies of the incisors and feet appeared in the population, The average effects of inbreeding on fluctuating asymmetr y were not strong, as most inbred and noninbred rats were not detectab ly asymmetric. Asymmetry appeared to be a threshold phenomenon, as sig nificantly asymmetric animals were more prevalent among the more highl y inbred rats of later generations, We detected no trend for a lesseni ng impact of inbreeding after many generations, as would have been exp ected if selection had been purging the population of its genetic load , Individual heterozygosity across five polymorphic allozyme loci was correlated with size and asymmetry metrics, but only in so far as coul d be accounted for by the correlation of sample heterozygosity with th e level of inbreeding and the effect of inbreeding on size and asymmet ry.