Mammals – Part IV
VERTEBRATE ZOOLOGY (VZ Lecture32 – Spring 2012 Althoff - reference PJH Chapter 21)
Bill Horn
Reproduction
Direct vs. indirectevidence 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
embryoembryo
Chorionic villi:penetrate theendometrium,providing mechanicalsupport & increased surface areafor rapid & efficient exchange
pigdiffuse
cowcotyledonary
canids, felids,genet, seal
raccoon
ZO
NA
RY
“unraveled”
villi connected
Endometrium (“horn”)
________ “connections”
Terms….terms….terms
• Afterbirtha) nondeciduousb) deciduous
• Estrous cycle• Pregnancy• Partuition• Follicle, ovum, corpura luteum
• Post-partum
• Litter
• Altricial
• Precocial
• Sexual maturity
And more terms….
• Estrous cycles:a) polyestrousb) monestrousc) 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 folliclecorpus luteum
Four Phases of Estrous Cycle
DIESTRUS - lowest hormone levelsPROESTRUS - “pre-heat”ESTRUS (without an “___” )- heat
a) highest hormone levelsb) ovulationc) LH “spikes”
METESTRUS - progesterone peaks
1
2
3
45
6 7
Developing, ovulating,…and gone!
Theovary
Estrous Cycle - more key points
• PRE-OVULATIONa) follicle growthb) endometrial growth (gets readyuterus ready for anticipated
“fertilized” embryo• POST-OVULATION
a) after “heat,” after release of ovumb) corpus luteum (CL) kicks in &
helps maintain pregnancy…otherwise it regresses….
...more key points
• POST-OVULATIONc) 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 fertilizationvs.
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 asa) nutritional, respiratory, and
excretory interchangeb) barrier to bacteriac) 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 bypituitary stimulates mammary glanddevelopment and milk secretion (initially)
• Milk production under neural controlthereafter
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 inseminationand 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
1st1st
2nd 3rd 4th 5th 6th2nd 3rd 4th 5th 6th
Pregnant
Nursing
days days days days days days
Growth of Young
• For some species, growth & development is rapidex. least shrew doubles weight in 4 daysex. 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
73.5 9.7 8.1 3.1 1.5Kangaroo
71.3 12.3 13.1 1.9 2.3Rabbit
43.8 11.9 42.8 0.0 0.9Harp seal
65.9 10.4 19.7 2.6 1.4W.t. deer
88.0 1.2 3.8 7.0 0.2Human
72.9 9.2 12.6 3.3 1.4Rat
44.9 10.6 34.9 0.9 0.5B-n dolphin
Note: ASH = not water & not organic
77.1 5.8 12.5 3.4 0.9Giraffe