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Mammals – Part IV

VERTEBRATE ZOOLOGY (VZ Lecture32 – Spring 2012 Althoff - reference PJH Chapter 21). Reproduction. Mammals – Part IV. ?. Bill Horn. Direct vs. indirect evidence of reproductive success. Mammalian Reproduction. More advanced than any other class of vertebrates

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Mammals – Part IV

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  1. VERTEBRATE ZOOLOGY (VZ Lecture32 – Spring 2012 Althoff - reference PJH Chapter 21) Reproduction Mammals – Part IV ? Bill Horn Direct vs. indirect evidence of reproductive success

  2. Mammalian Reproduction • More advanced than any other class of vertebrates • Except monotremes, young remain in uterus during embryonic and fetal life • Under most conditions, high survival rates of fetuses

  3. and… • After birth, young nourished with milk • Parental care until reasonably capable of taking care of one’s self …compare to arthropods, fish, reptiles, etc. RESULT  High survival of fetuses and extended post-partum care is an _________ in efficiency of reproduction in terms of energy expenditure per young that reaches _____________________________

  4. Chorionic villi: penetrate the endometrium, providing mechanical support & increased surface area for rapid & efficient exchange embryo Placental mammal -reduced yolk sac

  5. ________ “connections” “unraveled” pig diffuse cow cotyledonary Endometrium (“horn”) ZONARY canids, felids, genet, seal raccoon villi connected

  6. Terms….terms….terms • Post-partum • Litter • Altricial • Precocial • Sexual maturity • Afterbirth a) nondeciduous b) deciduous • Estrous cycle • Pregnancy • Partuition • Follicle, ovum, corpura luteum

  7. Hormones • GnRH (gonadotropin- releasing hormone) • FSH (folloicle- stimulating hormone) • estrogen • LH (lutenizing hormone) • progesterone • relaxin • testosterone • oxytocin • prolactin And more terms…. • Estrous cycles: a) polyestrous b) monestrous c) menstrual cycle • Fertilization • Delayed fertilization • Delayed implantation • Induced ovulation

  8. Themes • Timing of reproduction • Reproductive cycles • Physiological changes • Productivity relative to energy investment • Environmental influences on reproduction

  9. Ovarian Cycle • Growth of follicle and release of ovum • Development of corpus luteum (CL) which results in production of progesterone Follicle growth and development of CL both under control of pituitary & ovarian hormones

  10. Estrous Cycle - Key Hormones • FSH - produced by pituitary • LH - produced by pituitary *FSH & LH stimulate follicle & estrogen production • PROGESTERONE - produced by CL • ESTROGEN - produced by ovary

  11. GnRH (HT) FSH (AP) LH (AP) ESTROGEN (OV) PROGESTERONE (OV) HT =hypothalamus AP = anterior pituitary OV = ovary (oocyte folliclecorpus luteum

  12. Four Phases of Estrous Cycle • DIESTRUS - lowest hormone levels • PROESTRUS - “pre-heat” • ESTRUS (without an “___” )- heat a) highest hormone levels b) ovulation c) LH “spikes” • METESTRUS - progesterone peaks

  13. Developing, ovulating, …and gone! 5 4 6 7 The ovary 3 2 1

  14. Estrous Cycle - more key points • PRE-OVULATION a) follicle growth b) endometrial growth (gets ready uterus ready for anticipated “fertilized” embryo • POST-OVULATION a) after “heat,” after release of ovum b) corpus luteum (CL) kicks in & helps maintain pregnancy… otherwise it regresses….

  15. ...more key points • POST-OVULATION c) when CL regresses (if no implantation) it shrinks and is essentially “finished”…only one estrous cycle per follicle d) if pregnancy goes full-term (or nearly full- term, CL will remain “enlarged” (but not producing progesterone) well past partuition…useful for fertility est.

  16. Copulation • Internal fertilization (important adaptation for reproduction for terrestrial species) • Sperm reaches oviduct, usually within minutes • Fertilization occurs “sometime” • Zygotes (then embryos) move down oviducts by contractions of oviducts until it reaches uterus

  17. Post-copulation • Embryo “implants” (i.e., attaches) in uterine wall in the ENDOMETRIUM • Delayed fertilization vs. Delayed implantation

  18. Few notes about the Placenta • Not unique to mammals…certain fishes & a few reptiles have similar structures • the “connecting structure” between the fetus and the uterus • Functionally, serves as a) nutritional, respiratory, and excretory interchange b) barrier to bacteria c) produces some _______________

  19. Pre-partum • Key hormone: ________ --its levels increase at the end of pregnancy, causes relaxation of the pelvic ligaments and public symphysis (in pocket gophers [Geomyidae], connective tissue is resorbed at puberty so relaxin not as “necessary”) • Relaxin produced by uterus, placenta, or ovaries (varies by species)

  20. Pre-partum…con’t • Besides relaxin, __________ production increases at end of pregnancy: a) initiates contractions of uterus b) promotes milk “letdown” post-partum • Produced by hypothalamus, stored in pituitary • Production blocked by progesterone during pregnancy

  21. Partuition • = birthing process • Highest levels of relaxin and oxytocin --oxytocin promotes further contraction of uterus after placenta expelled… collaspe reduces bleeding • Increased (h) levels of estrogen • Decreased (h) levels of progesterone

  22. Post-partum • = time after “birth” of young • Hormone PROLACTIN, produced by pituitary stimulates mammary gland development and milk secretion (initially) • Milk production under neural control thereafter

  23. Typical FertilizationMost mammal species exhibit “typical” fertilization pattern • Egg fertilized shortly after copulation (i.e., in the presence of sperm in oviduct) • Embryo implants shortly after fertilization

  24. Delayed Fertilization • Copulation occurs but fertilization delayed for months • Typical among bats • NOTE: male & female reproductive status ___ _________; viable sperm remain in male long after spermatogenesis; female does not ovulate until long after insemination

  25. Delayed Implantation • Fertilization occurs shortly after insemination and some changes in blastocyst occur but… • Implantation does not take place for 12 days up to 11 months (varies by species) • Some bats, mustelids, some insectivores, some rodents

  26. Advantages of VARIATION • Not at all well understood, but reasonably a … • Response to changing climate (i.e. seasonal variation) • Response to nutritional status &/or food availability • Response to potential “over-winter” loss of healthy males

  27. 1st 2nd 3rd 4th 5th 6th Pregnant 1st 2nd 3rd 4th 5th 6th Nursing days days days days days days Cottontail Rabbits …. TALK ABOUT A DEMANDING! • Polygamous • Breeding “activity” start in late Feb in Midwest • Reproductive season may extend to Aug-Sep • 4-6 young per litter common (max 15?) • 28 day gestation period

  28. Growth of Young • For some species, growth & development is rapid ex. least shrew doubles weight in 4 days ex. evening bat doubles weight in 18 days • Impacted by amount of time… a) suckling (i.e each day) b) quality of milk ex. pinnipeds have high fat %

  29. MILK CONTENT (%) by Species(selected from FDVM Table 5.1, p64) WaterProteinFatSugarAsh Kangaroo 73.5 9.7 8.1 3.1 1.5 Human 88.0 1.2 3.8 7.0 0.2 Rabbit 71.3 12.3 13.1 1.9 2.3 Rat 72.9 9.2 12.6 3.3 1.4 Harp seal 43.8 11.9 42.8 0.0 0.9 B-n dolphin 44.9 10.6 34.9 0.9 0.5 W.t. deer 65.9 10.4 19.7 2.6 1.4 Giraffe 77.1 5.8 12.5 3.4 0.9 Note: ASH = not water & not organic

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