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

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

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 _____________________________

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

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

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

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

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

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

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

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

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

Developing, ovulating, …and gone! The ovary

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….

...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.

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

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

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 _______________

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)

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

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

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

Typical Fertilization Most 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

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

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

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

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 1st 2nd3rd4th5th6th 2nd3rd4th5th6th Pregnant  Nursing  days

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 %

MILK CONTENT (%) by Species (selected from FDVM Table 5.1, p64) Water Protein Fat Sugar Ash Kangaroo Rabbit Harp seal W.t. deer Human Rat B-n dolphin Note: ASH = not water & not organic Giraffe