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Presentation on theme: "REPRODUCTION MATING SYSTEMS SEXUAL SELECTION Ovis canadensis."— Presentation transcript:


2 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) Hatchlings are PRECOCIAL require no further maternal provisioning

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

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

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

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

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

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

9 Marsupials “ovoviviparous” or “semi-viviparous” Retention of egg shell membranes Limited placentation Postnatal care is strictly maternal (protection and lactation) Neonate extremely altricial, requiring extended postnatal provisioning 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 Neonatal development is variable, from: Placentals – viviparity but ALWAYS requiring extended postnatal provisioning highly altricial-- Ailurops -- to highly precocial Equus Postnatal provisioning is exclusively maternal (lactation)

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

13 What limits PATERNAL care in mammals? Monogamy is rare in mammals (only 3 to 5% of all species) Dolichotis Monogramy is OBLIGATE Often involves mating for life 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) Why the difference? Males can directly increase their fitness through paternal care Campephilus

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

15 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 Pteropus Females have an unavoidable and prolonged mass increase during pregnancy Altricial young require protection and nursing (are often are carried in flight) Bats have very low reproductive output compared to other mammals of similar size (e.g. rodents) BUT they are much longer-lived RESULT:

16 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) Male-male competition for mating opportunities

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

18 Promiscuity Both sexes mating with multiple partners 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) Many (most?) mammal species are promiscuous

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


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