1. Reproduction The Mammalian Strategy:
Relatively few intrauterine young (higher survival rate)
Nourish neonates with milk (high survival early; bonding)
Young remains with mother (or parents) at minimum until weaned (parental protection; learned behaviors)

2. Reproduction The Mammalian Strategy:
Amount of energy invested per young is lower than non-mammals;
Relatively few young produced but most survive to potentially reproduce

3. Costs of Lactation

4. Tradeoffs in Litter Size

5. Reproductive Endocrinology “Crash Course”

7. Reproductive Endocrinology “Crash Course”
Ovarian Cycle Influenced by:
Follicle stimulating hormone (FSH) and luteinizing hormone (LH) secreted by pituitary

8. Reproductive Endocrinology “Crash Course”
Ovarian Cycle Influenced by:
2) Estrogen secretion feeds-back to hypothalamus-pituitary; more LH secreted & less FSH
Ovulation & corpus luteum formation (spongy body which forms in place of ruptured follicle)

9. Reproductive Endocrinology “Crash Course”
Ovarian Cycle Influenced by:
3) No fertilization

10. Reproductive Endocrinology “Crash Course”
Ovarian Cycle Influenced by:
3) If fertilization occurs…

19. amnion
chorion
embryo
allantois

20. Four Major Parts of Embryonic Membranes
yolk sac: part of primitive intestine lying external to embryo; forms from endoderm
No nutritional value

21. Four Major Parts of Embryonic Membranes
2) amnion: forms from ectoderm & mesoderm around the embryo
Filled with serous fluid = prevent dessication/shock
3) allantois: out-pocket from hindgut of embryo
Movement of nutrients & O2

22. Four Major Parts of Embryonic Membranes
4) chorion: outer embryonic layer (ectoderm); envelopes entire assemblage
villi
placenta:

23. Types of Placenta
Placenta types based on villi distribution on chorion:
diffuse: villi scattered over entire surface of chorion = increased SA for absorption
2) polycotyledonary: islands of villi scattered over chorion

24. Types of Placenta
Placenta types based on villi distribution on chorion:
3) zonary: band of villi encircle center of blastocyst; lacking villi elsewhere
4) discoidal: regional restriction of villi

25. discoidal
zonary
diffuse

26. Types of Placenta
B) Placenta type based on connection between villi & endometrium:
nondeciduate: loose fitting of villi with endometrium; villi pull free without disrupting endometrium during parturition
2) deciduate: close fitting of villi-endometrium; villi pull free & cause erosion of endometrium during parturition

27. Types of Placenta
C) Placenta type based on degree of intimacy between embryonic & maternal parts:
1) choriovitelline: blastocyst lies in endometrium depression; does not embed
2) chorioallantoic: villi; blastocyst rests against endometrium at allantois-chorion contact point

28. Types of Placenta C) Chorioallantoic Placenta Types:
1) epitheliochorial – lemurs, cetaceans, equids, suids
- epithelial cells of chorion in contact with epithelial cells of uterus; villi in pockets in endometrium
2) syndesmochorial – artiodactyls
- lacking uterine epithelial barrier; contact uterine tissue

29. Types of Placenta C) Chorioallantoic Placenta Types:
3) endotheliochorial – carnivores
- epithelial cells of chorion in contact lining of uterine capillaries
4) hemochorial – insectivores, bats, higher primates
- villi in direct contact with maternal blood

30. Types of Placenta C) Chorioallantoic Placenta Types:
5) hemoendothelial – lagomorphs, some rodents
- lining of villi blood vessels only barrier to maternal blood

31. Reproductive Patterns
Continuous embryonic development (“typical”) a)

32. Reproductive Physiology
- Implantation of embryo in uterine wall for varying lengths of time
- Embryo supplied with nutrients via the placenta

33. Reproductive Patterns
2) Deviations from contiuous development strategy:
a) Delayed Fertilization:

34. Reproductive Patterns
Example
Fall
copulation
Winter
Sperm storage
Early spring
ovulation
Spring-summer
Embryo develops after fertilization
2) Deviations from contiuous development strategy:
a) Delayed Fertilization:

35. Reproductive Patterns
2) Deviations from contiuous development strategy:
b) Delayed Development: blastocyst embeds into endometrium & then becomes dormant; development delayed (e.g., bats)

36. Reproductive Patterns
2) Deviations from contiuous development strategy:
b) Delayed Development:
Example
Late summer
Blastocyst forms
Summer-Fall
Blastocyst dormant
Late fall-early winter
Development begins
Early spring
parturition

37. Reproductive Patterns
2) Deviations from contiuous development strategy:
c) Delayed Implantation:

38. Reproductive Patterns
Summer (Jun-Jul) 2004
Mating
March 2005
Implantation
(8-9 mo delay)
Spring
(Apr-May)
2005
Parturition
Summer (Jun-Jul) 2005
Mating (including 2005 females
2) Deviations from contiuous development strategy:
c) Delayed Implantation:
e.g., Mustela erminea
(avg age at death = 1.5 to 2 yrs)
*gestation period = 9-10 months

39. Reproductive Patterns
Spring-Summer (Apr-May) 2004
Mating
Spring-Summer (May-Jun) 2004
Parturition
Summer
(Jul-Aug)
2004
Mating?
Sexually Mature 2004 Females
Summer-Fall
Aug-Sep 2004
Parturition (2nd litter)
Mustela nivalis
Delayed Implantation????
* NO
(avg age at death = <1 yrs)
* gestation period = days
2 litter per year possible
Relation to vole cycles

40. Types of Breeding Seasons
1) Continuous – year round breeding; no seasonality; common to tropics
2) Restricted
a) Regular – seasonal breeding; temperate regions
b) Irregular – discontiuous breeding during rainfall, etc…
desert/arid regions
Optimal timing for:
* mating (time with best availability of mates)
* birth (time with abundant resources

41. Seasonality to Mating & Parturition based on resource availability (i
Seasonality to Mating & Parturition based on resource availability (i.e, mates or food)
Fall
Winter
Spring
Summer
Mating
Birthing
Resources
Gestation Period

42. Body size relation to length of gestation period…
Body size relation to length of gestation period….What if mammal could “extend” the gestation period to birth in a more favorable time and/or insure mating opportunities? (e.g., weasels)
Fall
Winter
Spring
Summer
Mating
Birthing
Resources
Gestation Period
Delay
Major Development

43. Reproduction
Sexual Maturity (puberty) – age when capable of producing gametes
influence onset/cessation (restricted)
*environmental factors
efficiency of reproduction (continuous)

44. Influences on Puberty & Reproduction
Light (photoperiod)
Rattus norvegicus (continuous breeder)

45. Influences on Puberty & Reproduction
Light (photoperiod)
Microtus arvalis
(seasonal breeder)
breeds 21 Mar – 24 Jun
simulate photoperiod during (22 Sep – Dec)
Natural light
Artificial light
Uniform 16-h daylength
Uniform 8-h daylength until Nov, then 13-h day
Control (“out of season”)
Results….
#1-4 = reached puberty
>60% females = pregnant
Control = no reproduction/puberty
*Light (photoperiod) linked to reproductive development

46. Influences on Puberty & Reproduction
2) Temperature
rodents
Temp
Puberty
1st Estrus
Experimental Animals
-3oC
33 days
61 days
Control
21oC
26 days
38 days
**Growth rates lowered due indirectly to low temps. Thus, results directly in delayed puberty

47. Influences on Puberty & Reproduction
Nutrition – under-nutrition delays puberty in both females and males
Precipitation – deer in Texas (Knowlton)
- “high” rainfall lead to shorter breeding season, more synchronous breeding & fawning
- lower predation rates (functional response of coyotes)
# prey consumed
Prey density

48. Influences on Puberty & Reproduction
Whitten Effect: synchronized estrus cycles when male introduced into population of females
Bruce Effect: implantation blocked, pregnancy aborted if females exposed to strange, new male
* Male urine stimulates FSH & LH secretion (pheromones)
Social Effects/Density
(examples from captive mice)
Lee-Boot Effect: pseudo-pregnancy induced among crowded females; may go anestrus

49. Readings Reproductive Cycles & Life-History Strategies, pp. 354-356
Litter Size & Reproductive “Seasons”, pp
Lactation and Postnatal Growth, pp