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Season- and Age-related Reproductive Changes Based on Fecal Androgen Concentrations in Male Koalas, Phascolarctos cinereus

Satoshi KUSUDA, Hisashi HASHIKAWA, Masato TAKEDA, Hideki, Atsushi GOTO, Jun OGUCHI and Osamu DOI

'Laboratory of Animal Reproduction, Faculty of Applied Biological Sciences, Gifu University, Gifu 501-1193, Japan

lagoya Higashiyama Zoo, Aichi 464-0804, Japan

0saka Municipal Tennoji Zoological Gardens, Osaka 543-0063, Japan

Awaji Farm Park England Hill Zoo, Hyogo 656-0443, Japan


Abstract. The purposes of the present study were to clarify age- and season- related androgen patterns, and to compare the reproductive physiology between Japanese captive koala populations and Australian populations. To measure fecal androgens, feces were collected from male koalas (4.2 to 13.8 years of age) kept in Japanese zoos. Fecal androgens were extracted with methanol from the lyophilized samples and determined by enzyme immunoassay using 4-androstene-3,17-dione antibody. Fecal androgen concentration in male koalas increased after sexual maturation and remained relatively high until old age. In the survey with the Japanese zoo studbook of koalas, copulation (conception) month showed a pyramid shape with a peak in March to June (60.7%) in koalas born and reared in Japanese zoos and from July to April with the highest concentration in September to January (69.7%) in Australian institutes. Japanese zoo koala populations have a characteristic physiological cycle adapted to Japan's seasonal changes. The suitable month of year for copulation or conception in Japan is diametrically opposed to that in Australia. Mean fecal androgen concentrations by month in the males born and reared in Japan indicated annual changes with the highest concentration in May and the lowest value in November. Fecal androgen analysis may be a noninvasive alternative tool to monitor circulating testosterone and may be helpful in understanding reproductive activity and physiology in male koalas.