REPRODUCTION

1. REPRODUCTION Ovis canadensis MATING SYSTEMS SEXUAL SELECTION

2. Hatchlings are PRECOCIAL require no further maternal provisioning Oviparity Ancestral reproductive mode of amniotes Turtles & Crocodilians Large clutches of small eggs (relative to adult size) Sea Turtle – no maternal care Aligator – basic maternal care (nest guarding)

3. Ovoviviparity (egg retention) lizards and snakes Live birth of small well-developed young, Small number of eggs hatch internally (maternal protection) Young are PRECOCIAL independent at birth requiring no further maternal provisioning Rattlesnakes (Crotalus) Horned lizard (Phrynosoma) Rattlesnakes (Crotalus) Protection of young-- frequency of ovoviviparity increases with increasing environmental stress Extra provisioning-- some degree of “viviparity” (internal transfer of nutrients from mother to young)

4. Bald eagle 1-3 American Robin 3-4 Gray partridge 10-20 Blue-winged teal 4-16 Oviparity in birds In general, birds produce relatively large eggs (with large yolk) Clutch size is highly variable Active birds – small clutches More sedentary birds – larger clutches

5. A solution : Barn Owl Kiwi Flightless birds have larger relative egg mass egg 8x the mass of a similar-sized flying bird Oviparity in birds Reproductive constraints imposed by flight Limitations on egg size & clutch size sequential laying AND sequential hatching

6. Altricial Precocial Oviparity in birds Relative development of young In birds, even relatively precocial young require continued parental investment

7. Small clutch (1-2); eggs very small relative to maternal size. Prehatching incubation period is very short compared to birds Oviparity in monotremes Young are extremely Atricial at hatching Require extended postnatal provisioning Postnatal care is strictly maternal (protection & lactation)

8. Life history of Mesozoic prototherians Conjecture based on comparison to living groups Morganucodon Ptilodus Oviparous – some possibly ovoviviparous Altricial young Extended post-hatching maternal care Lactation

9. Marsupials “ovoviviparous” or “semi-viviparous” Retention of egg shell membranes Limited placentation Neonate extremely altricial, requiring extended postnatal provisioning Postnatal care is strictly maternal (protection and lactation) Little developmental flexibility – fixed short gestation and extended lactation Wide variation in litter size

10. Placentals – evolution of complete viviparity Elaborate placentation Prolonged gestation period Considerable developmental flexibility – gestation and lactation periods are variable

11. Ailurops highly altricial-- Equus -- to highly precocial Placentals – viviparity Neonatal development is variable, from: but ALWAYS requiring extended postnatal provisioning Postnatal provisioning is exclusively maternal (lactation)

12. Why not male lactation? Dyacopterus spadiceus Francis. et al; "Lactation in Male Fruit Bats," Nature, 367:691, 1994. Lactation Pre-weaning provisioning by females

13. Monogamy is rare in mammals (only 3 to 5% of all species) Dolichotis Campephilus Males can directly increase their fitness through paternal care What limits PATERNAL care in mammals? Generally FACULTATIVE (involving mate guarding, or due to scarcity of potential mates) Not OBLIGATE (involving direct paternal investment) IN CONTRAST Monogamy is common in birds (90% of all species) Monogramy is OBLIGATE Often involves mating for life Why the difference?

14. LACTATION makes maternal care absolutely essential in ALL mammals (to ensure direct fitness) Females may also help female kin rear offspring (indirect fitness) Cooperative female kin (the foundation of social behavior) Paternal care is restricted even in species that are monogamous Parental Care in Mammals

15. Pteropus Haliaeetus Lasiurus Most bats have small litters of 1-2 young (in a few species up to 4 young) Reproductive constraints of flight in bats Constraints of flight are much greater in viviparous mammals compared to oviparous birds Females have an unavoidable and prolonged mass increase during pregnancy Altricial young require protection and nursing (are often are carried in flight) RESULT: Bats have very low reproductive output compared to other mammals of similar size (e.g. rodents) BUT they are much longer-lived

16. Male-male competition for mating opportunities Sexual strategies The sexes have different fitness perspectives: Females – mate quality, resource availability Males – mating opportunities Result: Female choice of mates (and often associated resources)

17. Harem polygyny -- male “control” of female groups to achieve exclusive matings Mating systems Polygyny Single male mating with multiple females Polyandry Single female mating with multiple males, AND males take on rearing responsibilities (i.e., “role reversal”) uncommon in birds (2% of species) Impossible (?) in mammals due to lactation

18. Promiscuity Both sexes mating with multiple partners Many (most?) mammal species are promiscuous Multiple mating, but NOT necessarily indiscriminate mating May reflect male-male competition (“sperm competition”) e.g. – “copulatory plugs” in rodents May involve active selection by females For multiple mates (i.e., advantages of multiple-sired litters)

19. Size dimorphism Sexual combat structures Display behavior and structures Sexual Selection Differential selection for traits in one sex (males) through the action of male-male competition and female choice