Reproductive Morphology

Male

Semeniferous tubules

Reproductive Morphology

MalePosition of testes varies:

May remain in abdominal cavity permanently (Monotremes, Xenarthrans, &most marine mammals)

May reside in abdominal cavity but descend into scrotum during breeding seasonthrough inguinal canal (bats and rodents)

May be permanently housed in scrotum (most primates and terrestrial carnivorans)

Many marsupials have a bifurcate penis:

Variation in BaculaChipmunks Ground squirrels

Reproductive MorphologyFemale

Marsupials

Reproductive Cycles

Almost all mammals are iteroparous - >1 cycle per lifetime

A few insectivorous marsupials are semelparous – 1 cycle per lifetime

Antechinus - Males all die after a single frantic bout of reproduction. This is driven by extreme sperm competition.

Fisher et al., 2013. Sperm competition drives the evolution of suicidalreproduction in mammals. PNAS 110:17910-1791

Reproductive Cycles

Ovarian Cycle Uterine Cycle

Estrous Cycle

Spermatogenic Cycle

Control of Cyclicity

Primarily, all cycles are under control of pituitary hormones.

Many cues that induce the pituitary to initiate cycles.

1. Visual Cues - In some mammals, the sight of scrotal testicles actually induces female estrous cycle.

L'Hoest's monkeyCercopithecus lhoesti

2. Behavioral Cues may trigger hormonal responses.

Control of Cyclicity

suckling – macropodids

copulation in felids

Microtus montanus

Dipodomys ingens

Control of Cyclicity

3. Environmental cues operate external to cycles may confer seasonality.

Mechanisms for Optimizing Timing of Birth

Artibeus lituratus (Big fruit-eating bat)

2) Delayed development

Myotis ciliolabrum (Western small-footed myotis)

1) Delayed fertilization

3) Delayed implantation (Chiroptera, Carnivora, Xenarthra, Cetartiodactyla)

Zona Pellucida

Mechanisms for Optimizing Timing of Birth

Obligate

Ursus americanus

Facultative

Many Rodents

3) Delayed implantation (Chiroptera, Carnivora, Xenarthra, Cetartiodactyla)

Mechanisms for Optimizing Timing of Birth

Well-studied in Mustelidae(Thom et al. 2004. Evolution 58:175)

Mustela erminea

4) Embryonic diapause (Macropodids)

Mechanisms for Optimizing Timing of Birth

General Trends Relating to Body Size

1. Total number of offspring per lifetime decreases with increasing body size

Peromyscus maniculatus

P. truei

P. californicus

General Trends Relating to Body Size

2. Small mammals tend to have higher basal metabolic rates

a. Large litters

b. Short gestation times

c. Altricial young

d. High post-natal growth rate

e. Reach reproductive age very quickly

General Trends Relating to Body Size

3. Large mammals tend to have lower BMR and tend to have much longer lives.

a. Long estrous cycles.

b. Small litter size.

c. Precocial young.

d. Grow much more slowly.

Exceptions to Body Size/Reproduction Trends

1) Microchiroptera

- only 1 or 2 young annually.

- low metabolic rates for their size

- first reproduction is at 18 months

- very long life spans.

Exceptions to Body Size/Reproduction Trends

2) Macroscelidids

Elephantulus

- Small litters : 1-2

- Precocial young

- Long gestation (~ 60 days)

Exceptions to Body Size/Reproduction Trends

3) Hystricognaths

Tuco-tuco, Ctenomys sociabilis

- Large/small trends break down in this group.

- In general, hystricognaths have longer gestation time than sciurognaths.

Exceptions to Body Size/Reproduction Trends

4) Marine carnivores (Pinnipeds)

Mirounga

- have incredibly rapid post-natal growth rates