Lecture_9-1

Lecture_9-1 - - Castration of young males eliminated sexual...

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Lecture 9 – The Reproductive Axis – Males Within the breeding season, males undergo the following reproductive stages: 1 – Male-male competition and aggression (in some species) 2- Courtship of females 3—Incubation feeding of the female 4 – Parental care *the degree and even presence of the last two stages differ depending on whether the male is monogamous or polygynous. Many of the courtship and other sexual behaviors exhibited by males are modified forms of aggressive behavior *VIDEO EXAMPLES Male reproductive behaviors are controlled by the hypothalamic-pituitary-gonadal axis, also called the “reproductive” axis. Release of gonadotropic releasing hormone (GnRH) Release of Luteinizing hormone (LH) and Follicle Stimulating Hormone Release of sex steroids from the testes The idea that hormones are necessary for production of reproductive traits came about in 1840 with Berthold’s experiment with cockerels.
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Unformatted text preview: - Castration of young males eliminated sexual behaviors- Implantation of testes from same male or other males into the peritoneal cavity restored sexual behavior In later experiments, it became clear that testosterone is one of the primary hormones involved in this control of reproductive behavior.-When looking at a model of average testosterone levels in males over the course of the year, there are seasonal differences. Low during overwintering/migration and molt, high during the breeding season. If we focus on breeding season levels, we see a within-season pattern as well. Testosterone concentrations increase dramatically at the onset of the breeding season, and this is followed by increases in courtship and related aggressive activities. The same cycle can happen several times within the same breeding season, particularly when birds have more than one reproductive cycle per season. EUROPEAN STARLING EXAMPLE SONG SPARROW EXAMPLE...
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Lecture_9-1 - - Castration of young males eliminated sexual...

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