Golden hamsters, Mesocricetus auratus , are important models for studying season

Question

Golden hamsters, Mesocricetus auratus, are important models for studying seasonal reproduction. In autumn, increasing night-length is associated with increasing duration of melatonin-rich intervals. For golden hamsters, this inhibits reproduction by increasing the negative feedback effects of gonadal-steroid hormones on the hypothalamic-pituitary axis. Normally, the hamster begins hibernation after gonadal regression. After a set interval of time passes, gonadal recrudescence occurs spontaneously, i.e., without any explanation except the passage of time. For a time, the recrudesced animal is insensitive to long nights (photorefractory), but after a few weeks of the long days of summer, photorefractoriness is terminated. This is described on the graph.

For the annual cycle portrayed, you will make predictions for the reproductive outcomes of the MALE golden hamster of pineal gland surgery. Your predictions should state what is expected for the 45 days following the indicated time points. State two predictions for each point in the cycle: A, B, C, and D. For the first prediction, state what is happening in the normal reproductive cycle for the next 45 days. For the second prediction, state what would happen to the MALE reproductive outcome for the next 45 days if the pineal gland was surgically removed at that point in the cycle. While limiting this assignment to male reproductive outcomes appears to cut females out of the picture, and, believe me, females are CENTRAL to the picture, the limitation makes the assignment more straightforward, as your answers can be simply focus on testes size.

After completing your predictions, describe, in one sentence, the overall dependence of seasonal reproduction in golden hamsters on the hamsters having a functional pineal gland.

normal   pineal gland removed

Prediction for time A - _____________ _______________

Prediction for time B - _____________ _______________

Prediction for time C - _____________ _______________

Prediction for time D - _____________ _______________

Explanation / Answer

Based on the given data, the reproduction of Golden hamster reproduction is regulated by negative feedback of gonadal-steroid hormones during autumn, which is associated with long melatonin-rich intervals. They have full reproductive capacity in autumn and summer, which is period A and after D. Pineal gland is an endocrine gland located inferior to the diencephalon roof and secretes the hormone melatonin.

Increased amounts of light would inhibit melatonin production from the pineal gland. Melatonin is a hormone affected by light reaching the body’s visual centers. Melatonin may inhibit reproductive function. It slows the maturation of reproductive organs and cells.

Therefore, in winter season the melatonin production increases, which lead to decrease of reproductive capability. The removal of Pineal gland results improper production of melatonin, and therefore the reproductive would be altered.

The predictions are as follows:

Prediction for time A – Due to removal of penal gland, results increased production of male reproductive hormones takes place.

Prediction for time B – Negative feedback inhibition takes place, due to increased gonadal-steroid hormones.

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