Urinary gonadal steroid concentrations were measured and compared in the summer and winter for both the Cape mole-rat (Georychus capensis) and the Natal mole-rat (Cryptomys hottentotus natalensis). The Cape mole-rat breeds seasonally, with sexual activity and pregnancy recorded during the winter months in the southern hemisphere. Despite the fact that it has a distinct breeding season, the seas...

Puberty is defined as the awakening of the hypothalamic-pituitary gonadal axis. Sheep are seasonal breeders, experiencing an annual period of reproductive quiescence and renaissance that can be utilized as a model for the onset of puberty. Kisspeptin and gonadotropin-inhibitory hormone appear to be important for the seasonal shift in reproductive activity and the former is mandatory for puberty...

The laboratory rat, a non-photoperiodic rodent, exhibits seasonal fluctuations of melatonin. Melatonin has been found to be readily transferred from the maternal to the fetal circulation. No data exist on the possible influence of maternal pineal gland upon seasonal variations of the offspring. The aim of the present study was to asses the influence of the maternal melatonin rhythm on the offsp...

Life-history theory predicts that the trade-off between parasite defense and other costly traits such as reproduction may be most evident when resources are scarce. The strength of selection that parasites inflict on their host may therefore vary across environmental conditions. Collared flycatchers (Ficedula albicollis) breeding on the Swedish island Öland experience a seasonal decline in thei...

Nelson, Randy J., Joshua B. Fine, Gregory E. Demas, and Christopher A. Moffatt. Photoperiod and population density interact to affect reproductive and immune function in male prairie voles. Am. J. Physiol. 270 (Regulatory Integrative Comp. Physiol. 39): R571-R577, 1996.-Seasonal breeding of rodents is often associated with changes in adrenal function; altered adrenal function could account, in ...

The intensity of mating competition and the potential benefits for female of mating with certain males can be influenced by several extrinsic factors, such that behavioral decisions can be highly context-dependent. Short-lived species with a single reproductive season are a unique model to study context-sensitive mating decisions. Through exhaustive sampling in the field and simultaneous choice...

Seasonal declines in avian clutch size are well documented, but seasonal variation in other reproductive parameters has received less attention. For example, the probability of complete brood mortality typically explains much of the variation in reproductive success and often varies seasonally, but we know little about the underlying cause of that variation. This oversight is surprising given t...

Seasonal shifts in host use by mosquitoes from birds to mammals drive the timing and intensity of annual epidemics of mosquito-borne viruses, such as West Nile virus, in North America. The biological mechanism underlying these shifts has been a matter of debate, with hypotheses falling into two camps: (1) the shift is driven by changes in host abundance, or (2) the shift is driven by seasonal c...

Animals inhabiting non-tropical environments undergo seasonal changes in reproduction in order to improve their survival and chances of successful reproduction. For example, during certain periods of the year, food shortages and temperature extremes can make survival difficult. Adaptive physiological, behavioral and morphological changes are made to maintain a positive energy balance throughout...