6: Animal reproductive strategies

intra specific

within a species

inter specific

among species

intra specific processes

- group living

- competition for mates and food

- reproduction

- sexual conflict

inter specific processes

- predation and herbivory

- competition for space and food

- mutualisms

- parasitism and disease

- pollination

external fertilisation

fertilisation that takes place outside the body, such as marine species releasing sperm and eggs into water

why do marine species release sperm and eggs into water

mass spawning is energetically cheap, potential to have many offspring, overwhelms predators and has no mate choice

mate choice is common in populations where

the number of offspring a female can have at one time is limited

monogamy

marriage to a single mate

what species perform monogamy

humans and most birds

polygyny

one male, several females

what species perform polygyny

most insects and mammals

polyandry

one female and many males

what species perform polyandry

few birds and fish

promiscuity

having many sexual partners

what species are promiscuous?

chimps and bonobos

females choosing a mate

intersexual selection

males competing for a mate

intrasexual selection

sexual selection ____ a form of natural selection

is

- traits selected for in natural selection are those that influence survival

- traits selected for in sexual selection are those that directly influence mating success

intersexual selection

selection for traits that increase attractiveness to females

eg. colours in birds of paradise, manikin birds performing a dance and bowerbirds building bowers/using optical illusions to attract females

INTRAsexual selection

selection for traits that increase success at fighting e.g. antlers

males often use ____ to indicate their strength without combate

ornaments eg. antlers - this reduces the need for costly, unnecessary battles

2 hypotheses for the evolution of mate choice

1. good genes hypothesis

2. sexy sons hypothesis

good genes hypothesis

display traits are energetically costly, so give the female an honest signal about how good the male is at getting food or resisting disease - choosing a mate with good genes maximises the females fitness

sexy sons hypothesis

traits used in fights/display are passed on to the female's sons, increasing their likelihood of mating in the future - choosing a mate who will produce sexy sons means the females genes are more likely to be passed down

sexual selection can drive

speciation - different females can mate with different partners, causing speciation

to ensure fertilisation, the sperm and egg must be

as close together as possible

how do animals ensure sperm and egg are as close together as possible?

many animals have an intromittent organ

intromittent organs in invertebrates are often very

distinctive and can be used to identify different species

intromittent organ

an external organ in a male that is specialised to deliver sperm during copulation

cephalopod intromittent organ

hectocotylus

insect intromitten organ

aedeagus

squamate (snake, lizard) intromittent organ

hemipenes

baculum

found within the penis of many mammals

which species has the largest penis?

blue whales have the largest penis in absolute terms

barnacles have the largest in relative terms

methods of ensuring sperm fertilises the female

mate guarding to prevent other males inseminating

damselflies in the wheel position is an example of

reproduction: male deposits sperm in one location and female picks it up

love bugs copulation length

several days: most of their adult life span

How do damselflies avoid reproductive competition?

damselflies use a modified copulatory organ to remove the sperm of other males (removes 90-100% of competing sperm)

how do golden orb's ensure reproductive success?

golden orb web spiders copulatory palp breaks off during mating acting as a post-copulatory plug

females invest _____ energy in offspring than males

MORE!

eggs are bigger and need incubation

internal development of young

parental care is often the mothers job

in mammals, females produce milk

how can males maximise fitness?

have as many offspring as possible

how can females maximise fitness?

have few, high quality offspring that survive

intersexual conflict

males and females have different ways to maximise fitness

drosophila intersexual conflict

male drosophila use chemicals that kill the sperm of other males - but these chemicals also damage the females

bed bug intersexual conflict

bed bug males have needle like structures for traumatic insemination of the females

ducks intersexual conflict

spiral shaped - only 3% are the offspring of other males

very few bird species have _____, except

penises, except ducks, geese and ostriches