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REPRODUCTION. Ovis canadensis. MATING SYSTEMS. SEXUAL SELECTION. 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).

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Presentation Transcript
slide1

REPRODUCTION

Ovis canadensis

MATING SYSTEMS

SEXUAL SELECTION

slide2

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)

slide3

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)

slide4

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

slide5

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

slide6

Altricial

Precocial

Oviparity in birds

Relative development of young

In birds, even relatively precocial young require continued

parental investment

slide7

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)

slide8

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

slide9

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

slide10

Placentals – evolution of complete viviparity

Elaborate placentation

Prolonged gestation period

Considerable developmental flexibility –

gestation and lactation periods are variable

slide11

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)

slide12

Why not male lactation?

Dyacopterus spadiceus

Francis. et al; "Lactation in Male Fruit Bats," Nature, 367:691, 1994.

Lactation

Pre-weaning provisioning by females

slide13

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?

slide14

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

slide15

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

slide16

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)

slide17

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

slide18

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)

slide19

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