The basic structures (if there) are frequently modified. Frequently the penis is retracted into a sheath.

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1 Reproduction: Combining anatomy with material from chapter 20. Unlike some of the other systems we've looked at, there is considerable variation here (and humans aren't the best model). Table 20-1, p. 393 is a good start (I don't expect you to memorize the table!) Male anatomy: The basic structures (if there) are frequently modified. Make sure you know about the basic function of the various structures: seminal vesicles, bulbourethral glands, epidimys, vas deferens, testes, urethra, etc. Frequently the penis is retracted into a sheath. In monotremes and some marsupials, penis may be bifid ( Often (rodents, bats, carnivores, non-human primates, others) penis includes a bone or baculum that sits inside the penis. Baculum can be diagnostic in identifying to species. Collections of bacula exist, and some mammalogists have made extensive studies of these. (Females may also have an os clitoridis, or clitoral bone, but it's not quite clear if it's always found in the same groups that have a baculum). Usually, testes sit outside the body (lower temperature), but some groups keep testes inside the body: Female anatomy: monotremes, cetaceans, elephants, etc. But many mammals (e.g. deer) can retract testes into the body during nonbreeding season. Structure of uterus and associated features varies widely: Monotremes: Resembles reptiles - have a cloaca that combines urinary, digestive and reproductive tracts.

2 Marsupials: Therians: Fertilization takes place in oviducts, and as zygote travels further down oviducts/uterus, shell is eventually added. Ovaries are larger than usual in mammals due to the amount of yolk needed. However, eggs are generally smaller and young hatch earlier than in reptiles or related groups (rely heavily on parental care and milk). Young are born in an extremely primitive state. Look like worms with legs. Crawl out of birth canal, up mothers abdomen and into pouch, where they attach to a nipple and continue development. As they develop, they eventually start moving out of pouch for longer and longer periods. Text mentions special anatomy that allows young to breathe while suckling. Reproductive tract includes two vaginas (males have a bifid penis). Sperm travels up vaginas to get to uterus and tubes. Young exit through a pseudovaginal central canal. Placenta is formed from yolk sac and is very simple, which contributes to the short time spent inside the mother's body. In brief: it's not a good placenta. Young are born in a much more complete state of development: Although even here, things are quite variable: precocial - young are born ready to run. Basically miniature versions of the adult. Many ungulates are examples, but also cetaceans, many primates and other groups. altricial - young are born in primitive condition, and need much help and nourishment before becoming mobile. Often born

3 Estrous cycle: hairless and without fully functioning eyes. Lots of rodents, shrews, etc. Many carnivores also fit this pattern. One could argue humans fit this pattern as well. Not sure the books summary of life history strategies really applies in all cases (seems that there are a lot of exceptions). Placenta is formed from chorion and allantois (other membranes that can be tracked back to egg). This allows for much longer development inside mother's body. Structure of the uterus varies considerably: Duplex - two uteri, each with own oviduct Bipartite - mostly separate uteri, but share common cervix Bicornuate - combined lower part, separated upper part. Simplex - one uterus, with oviducts leading away from upper corners Hormones fluctuations are essentially similar to menstrual cycle, but there are two important differences: 1) Mammals with an estrous cycle re-absorb the uterine lining instead of sloughing it off. 2) Changes in behavior are much more pronounced in mammals with an estrous cycle: Females are only reproductively active during estrous (heat). Will not mate at other times. In contrast, females with a menstrual cycle can be reproductively active at any time (though there is often a peak near ovulation). Most mammals have an estrous cycle. Mammals with menstrual cycles include: Many (most) primates, some bats, and elephant shrews.

4 Other issues related to reproduction: Delayed fertilization: May occur in some other animals, but it's not clear. Many males (particularly bats) can store sperm. (This is a bit different than storing sperm in epididimys) Delayed implantation: Sperm are fully functional and stored for considerable time after being formed. Spermatogenesis takes place at the optimal time of year (food abundance, etc.) Mating takes place late in the fall or winter (even hibernating females may be mated with). Females can store sperm. Fertilization and implantation take place as early as possible in the year giving the young as along a period as possible to develop (before hibernation). Similar, but egg is fertilized. Zygote may complete a few early stages of development, but then becomes dormant. Female can then implant zygote to finish development at opportune time (e.g., food, temperatures, etc). May be facultative (mother can control this) or obligative (happens all the time). Delayed development is similar, but in this case zygote implants, and then becomes dormant. Seen in some bats. Reproductive timing: Can be controlled by a number of different factors including: Photoperiod

5 Length of day can influence timing through pineal gland and melatonin levels. temperature energy nutrition Other reproduction related issues: Direct effect is hard to measure, but indirectly affects energy reserves which can change reproductive activity. Energy requirements due to gestation/lactation are huge. So timing of reproduction is often tied directly to: Availability of nutrition is important in both timing of reproduction and in quality of reproduction. Later in the semester (given time), we may discuss such things as: Infanticide Inbreeding Litter size Life history strategies Energetic cost of reproduction (One could spend the whole semester on reproduction!)