Naturwissenschaften (2000) 87 : 312–314 Q Springer-Verlag 2000 R. Apfelbach (Y) Zoologisches Institut/Tierphysiologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany e-mail: raimund.apfelbach6uni-tuebingen.de Tel.: c49-7071-2972624 N.Y. Vasilieva 7 E.V. Cherepanova Institute of Ecology and Evolution, Russian Academy of Sciences, Prospect St 33, 11071 Moscow, Russia D. von Holst Lehrstuhl für Tierphysiologie, Universität Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany SHORT COMMUNICATION N.Y. Vasilieva 7 E.V. Cherepanova 7 D. von Holst R. Apfelbach Predator odour and its impact on male fertility and reproduction in Phodopus campbelli hamsters Received: 31 January 2000 / Accepted in revised form: 6 June 2000 Abstract This study investigated the influence of cat urine odour in suppressing development and fertility in Campbell’s hamster males. Exposure to this odour from postnatal day 11 until day 45 (sexual maturation) resulted in reduced sex organ weights, reduced testoste- rone levels and in an increase in abnormalities of the synaptonemal complex in both sex chromosomes and autosomes. Subsequent breeding experiments revealed a significant decrease in litter size. All these data indi- cate a severe effect of predator odour on the breeding success of potential prey species. It is assumed that these effects are caused by the sulphurous compounds in the urine; however, the underlying mechanisms are not yet known. Predator odours are known to repel potential prey spe- cies (Stoddart 1980; Berton et al. 1998). Wild-living rats may even shift their nocturnal activity phases to diur- nal, presumably to avoid contact with predators or their odours (Fenn and Macdonald 1996). In fact, predator odours are considered to be potential ecologically clean repellents for pest control. Besides their repellent ef- fect, predator odours affect litter size, sex ratio and postnatal development of different rodent species (Va- silieva 1995; Voznessenskaya 1995). Yet, the mecha- nisms behind this breeding suppression are not well un- derstood. Likewise, the effective component or compo- nents of a predator odour are not known; sulphurous components and/or their metabolites in the urine are likely candidates (Nolte et al. 1994). When exposed to mustelid odour, female Clethrionomys voles aggressive- ly avoid male advances (Ylönen 1989; Ylönen and Ron- kainen 1994). Male Microtus voles may themselves show less sexual activity in high-risk situations (Koske- la and Ylönen 1995). To reveal a possible role of preda- tor urine odour in regulating the development and breeding success of Phodopus campbelli hamster males, we estimated the testosterone level in cat urine odour- treated prepubertal males and analysed whether preda- tor odour influences meiosis in males. Males were taken from litters with 5–7 pups of both sexes and were randomly assigned to experimental and control groups according to a tandem sequence with the constraints that (1) one half of the male pups from each litter served as experimental subjects, the other half served as controls and (2) the difference in body weight of individual siblings assigned to the experimen- tal or control groups did not exceed 0.5 g at the begin- ning of the experiment. Due to the lack of natural pre- dators, cats as obligate carnivores served as urine do- nors; cats were feed with cat-chew, fish and beef. Cat urine (experimental group) or water (control group) was applied directly onto the external nares of the hamsters and around the home cage every other day from postnatal day 11 until day 45 (sexual maturity). Bedding was changed weekly. After termination of the experiment, the weights of the body, testes and epididy- mis were obtained from ten control and ten experimen- tal males. Body weights were not affected by the urine odour exposures. However, there were significant dif- ferences in testes and epididymis weights: in experi- mental males both organs were significantly lighter than in the controls (Table 1). Thirty control and 22 experimental males were used for testosterone analyses. To avoid interference be- tween blood sampling and predator odour exposure ex- periments, the basal testosterone levels were deter- mined by measuring the hormone amounts excreted in 24-h urine. Urine was extracted with ether in glass co-