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