Ovulation rates and oestrous cycle lengths in several species of Australian native rats (Rattus spp.) from various habitats

Abstract

Ovulation rates, as determined by the number of recently formed corpora lutea, and oestrous cycle lengths have been determined for several species of native Australian rats (Rattus spp.) from diverse habitats. Ovulation rates vary significantly between species: R. leucopus cooktownensis had the lowest ovulation rate; those for two subspecies of R. fuscipes, R. lutreolus lutreolus, R. tunneyi tunneyi, R. sordidus sordidus and R. sordidus colletti were significantly higher and all similar to each other; the highest ovulation rate occurred in R. sordidus villosissimus. However, all species of rats had short, 4- to 6-day, oestrous cycles. The possible ecological and evolutionary significance of these findings is briefly discussed.