The annual reproductive cycles of the Japanese sipunculans Siphonosoma cumanense (Keferstein) and Phascolosoma scolops (Selenka, de Man & Biilow) were studied based on size, density, and frequency distribution of gametes from May 1989 to November 1990 and October 1989 to February 1991, respectively. Aliquots from the total volume of the diluted coelomic fluid from each individual were analyzed....

Breeding periodicity allows organisms to synchronise breeding attempts with the most favourable ecological conditions under which to raise offspring. For most animal species, ecological conditions vary seasonally and usually impose an annual breeding schedule on their populations; sub-annual breeding schedules will be rare. We use a 16-year dataset of breeding attempts by a tropical seabird, th...

For vertebrates, annual cycles are organized into a series of breeding and non-breeding periods that vary in duration and location but are inextricably linked biologically. Here, we show that our understanding of the fundamental ecology of four vertebrate classes has been limited by a severe breeding season research bias and that studies of individual and population-level responses to natural a...

An experiment was conducted to investigate the annual reproductive cycle of a Korean endemic species, Acheilognathus majusculus, from Jeokseong-myeon located in Seomjin River. The reproductive cycle is examined histologically regarding water temperature and day length of the habitat, the gonadosomatic index (GSI), the female ovipositor length index (OLI), monthly variation in egg diameter distr...