Question

Name the reproductive cycle that occurs in seasonal breeders. Give an example.

Answer 1

Animals that only mate during certain periods are called seasonal breeders. Mainly non-primates such as cows and mice are seasonal breeders and they have an oestrous cycle and primates such as monkeys have a menstrual cycle.

Complete answer: Seasonal breeders are those animals that only mate during a certain period of time in the year. This period of time has optimum temperature, food, water and changes in predation. Animals show their sexual behaviour and interest-only during this phase. During this phase, males show a change in testes weight, testosterone levels and fertility and females have an oestrous cycle and are receptive to mating. In the oestrous cycle, the endometrium is reabsorbed and the females are sexually active. It is also referred to as ‘heat’. Animals having oestrous cycles display their receptivity through large coloured genitals and mating calls. The oestrous cycle is the reproductive cycle in the female of the non-primates, e.g. mouse, cow while menstrual cycle occurs in female primates eg; monkey, the gorilla. There are 4 phases in the oestrous cycle:
i. Proestrus: Follicle begins to grow and endometrium thickens under influence of estrogen. Corpus luteum degenerates, uterus and vagina are filled with fluid and sanguineous fluid is released. Females are not sexually receptive and this phase lasts for days ranging from 1 day to as long as 3 weeks.
ii. Estrus phase: In this phase, the female is sexually receptive. Levels of gonadotropic hormones and estrogen increases. Ovarian follicles mature and ovulation may occur.
iii. Metestrus or diestrus phase: Corpus luteum produces progesterone and estrogen level decreases. The uterine lining appears. If pregnancy doesn’t occur, corpus luteum is regressed.
iv. Anestrus phase: In this phase, the sexual cycle rests. Melatonin released by the pineal gland stimulates reproduction in short-day breeders and represses reproduction in long-day breeders.

Note: Estrous cycles start after sexual maturity in females and are interrupted by anestrous phases or by pregnancies. Typically, oestrous cycles continue until death. Some animals may display bloody vaginal discharge, often mistaken for menstruation.