Annual Breeding Cycle Research Articles

The fecundity of Raja clavata in British waters

The annual breeding cycle of Raja clavata in British waters is described. The ovarian cycle starts in December with the appearance of small, white ovarian eggs. Copulatory activity, based on the evidence of clasper wounds in the cloaca of one female, starts in February and reaches a peak in May-June, based on the occurrence of spermatophores in the nidamental glands. Egg laying starts in February, reaches a peak rate in June and ceases by September. Two methods of estimating the annual egg production are described, one based on the proportion of mature female rays with egg capsules and observed rates of egg laying and the other based on the decline in the number of ovarian eggs. Although the latter method is only valid for the period June to September, for these months it gives similar results to those of the alternative method. The estimated average production is 140 eggs a year. The number of ovarian eggs present in April and May equals the number of eggs laid after 1 June. Taking account of egg production before 1 June gives the relationship between annual egg production (y) and total maternal length in centimetres (x) as y = 1.19.x + 25.1 over the length range 77 to 105 cm. Although there is evidence that the duration of the breeding season may vary both annually and geographically, the limited data show that variations in annual egg production from year to year are small. It is suggested that length of daylight is the main factor controlling the ovarian cycle and that temperature controls the rate of egg laying. The length/fecundity relationship is linear and the reasons why it does not follow the more usual cubic relationship are discussed.

Seasonal variations in the reflexive release of oxytocin and in the effect of estradiol on the reflex in goats.

In a total of 142 experiments performed over a 3-year period, the amount of oxytocin released in response to vaginal distention was found to vary with the time of year. Stimulation increased plasma oxytocin by 41.7 ± 6.7 (SE) μU/ml in the 74 experiments performed during Dec-May, but by only 11.0 ± 2.2 u,U/ml in the 68 experiments performed during Jun-Nov. In the latter period, a high frequency of animals failed entirely to respond to distention. Hour-long infusions of estradiol (5-100 μg/hr) significantly potentiated oxytocin release in responsive animals but uniformly failed to activate the reflex in the 25 unresponsive cases tested. The relative frequency of animals responsive to distention appeared to have a sinusoidal distribution with annual period and a phase which followed that of the annual breeding cycle by about 4-5 months. An hypothetical explanation for this distribution in responsiveness, based partly upon the seasonally related, divergent effects of estradiol on oxytocin release is presented...

Response of the Testes of Purple Sea Urchins to Variations in Temperature and Light

STUDIES on the reproductive activity of the purple sea urchin, S. purpuratus, made during the past eight years at Pacific Grove, California, indicate the presence of an annual breeding cycle, with maximum gonadal activity occurring during the winter months. In the course of the present investigation, designed to examine the effect of latitude on the breeding activity of the sea urchin, it was observed that the sea urchin populations distributed over a 20° latitudinal range have a uniform spawning period. These observations suggest that the reproductive activity of the purple sea urchin might be independent of temperature over a physiological range represented by this distribution. Therefore a photoperiodic response was considered as a possible explanation for the breeding cycles observed.

The Bushy-Tailed Wood Rat: A Laboratory Colony

Gestation period, litter size, annual breeding cycle, growth rate, post-juvenal molt and rearing methods in captivity are given for the bushy-tailed wood rat, Neotoma cinerea acraia . Observations on territorialism and other related behavior patterns of breeding pairs are recorded.