Transcript Diversity of reproduction

Diversity of reproduction
Asexual reproduction
Parthenogenesis
Hermaphrodites
Sequential hermaphrodites - protogyny
(FM) or protoandry (MF)
Sexual reproduction
Why sex?
Cost & benefit of sex
Sex ratio
Local mate competition
Local resource competition
Maternal condition (Trivers/Willard
effect)
Male/female reproductive strategy
Asymmetrical gamete size (anisogamy)
means the sex with smaller gametes
should usually compete for access to the
sex with larger gametes.
This results in greater variation among
males than among females for
reproductive success.
Males should, therefore, fight over
females and females should select for
resources
Parental investment - whatever a parent
does to↑the probability that existing
offspring will survive to reproduce at the
cost of the parent's ability to generate
additional offspring
Sexual selection
The advantage which certain individuals
have over others of the same sex and
species, in exclusive relation to
reproduction (Darwin, 1871).
A form of natural selection that occurs
when individuals vary in their ability to
compete with others for mates or in their
attractiveness to members of the
opposite sex.
As with natural selection, sexual selection
leads to genetic changes in the
population over time
Intrasexual selection
Competition for copulation
Dominance
Alternatives:
• friendship with females
• male coalition
• female mimicry
• satellite males
• forced copulation
Game theory and Evolutionary Stable
Strategy (ESS)
Strategy = the behavioral response of an
individual
ESS = a strategy which if adopted by all
members of a population can not be
invaded by other strategy
Game theory is needed when fitness
consequences of a behavior depend on
what others are doing
Hawks and Doves
Possible behaviors
Display
Fight but risk injury
retreat
Possible strategies
Hawks: fight until injured of opponent retreats
Doves: display initially but retreats if opponent
fights
Payoff matrix
Actor
hawks
doves
Opponent
hawks
doves
(V-C)/2
V
0
V/2
Payoff of actors after confronting
opponents
V = values of resources being contested
C = cost of fighting due to injury
Pure ESS
Actor
hawks
doves
Opponent
hawks
doves
1/2
2
0
1
Resource = 2 > cost = 1
½ > 0, hawks resist dove invasion; 2 > 1,
doves are invaded by hawks  pure ESS
= all hawks
Mixed ESS
Actor
hawks
doves
Opponent
hawks
doves
-1/2
1
0
1/2
Resource = 1 < cost = 2
-½ < 0, doves can invade hawks ; 1 > ½ ,
hawks can invade dove  mixed ESS =
mix of hawks and doves
If frequency of hawks is p, and frequency
of doves is 1-p, and at the ESS the fitness
of hawks = the fitness of doves, then
(-1/2)p + (1-p) = (0)p + (1/2)(1-p)
1 – 3p/2 = 1/2 – p/2  1/2 = p
Either an individual can perform strategy
one or another w/ probability p or 1-p ; or
polymorphic state in which a fraction, p, of
the population adopts one strategy
Polymorphism in Ruff Grouse
16% light, 84% dark. Dark dominates
over light and is territorial. Only a few
dark mate. Light follows the female.
Reproductive success is the same.
Alternative sponge isopod
α♂ defend cavities and discard γ♂.
β♂behaves like♀. Morphs are due to 3
alleles at 1 genetic locus. Mating success is
1.51, 1.35, 1.37 for α, β and γ
Blue-gill Sunfish
3 male morphs: sneaker, female mimic,
territorial
Non-ESS alternative strategies
ESS predicts all strategies obtain equal fitness
Alternatively, strategies may be condition
dependent
Males in lower condition may adopt
alternative strategies to obtain some mating
Competition for fertilization
Sperm competition
physical: e.g. scrub out sperm, peck at the
cloaca
chemical: e.g. contraceptive douche,
copulatory plug, homosexual mating, antiaphrodisiac substance, eupyrene vs.
apyrene,
Mate guarding: cost and benefit
first-male vs. last-male
colonial vs. solitary
early vs. later season
Competition after fertilization
Bruce effect
Infanticide
Female choice
Unequivocal female preference, not
a result of male competition
Choice based on "genetic quality“
runaway selection — Fisher
good genes (survival skill)
handicap principle — Zahavi
rare male effect
Choice based on 'non-genetic'
benefit
resource defense
parental ability
Mating systems: monogamy,
polygyny, polyandry, promiscuity
Hypotheses on male monogamy
mate-guarding monogamy
mate-assistance monogamy
female-enforced monogamy
Extra-paired copulation (EPC)
fertility insurance hypothesis
better sperm hypothesis
material benefit hypothesis
more parental care hypothesis
Polyandry – polygynandry vs. sex role
reverse polyandry
Dunnocks - mating system changes with
access to resources
Polygyny occurs in small territories,
polyandry in large territories
Provisioning caused a reduction in female
territory size and a change from polyandry
(or polygynandry) to monogamy (or
polygyny)
Consequently, females have higher
reproductive success in poor environments
while successful males have higher
reproductive success in rich environments
Females solicit copulations from males to
keep them around
Male feeding rates are proportional to
their paternity
Polygyny
Emlen-Oring theory
Female defense polygyny
Resources defense polygyny
polygyny threshold model
deception hypothesis
The polygyny threshold model
Prediction of PTM
Polygyny should be most common in
patchy habitats
Male territory quality influences number
of females attracted
Females who mate with already mated
males should have at least as high
reproductive success as females
choosing unmated males
Blackbird experiments
Higher fledging success in larger harems
Harem size correlates with habitat quality
Female removals do not lower fledging
success; therefore, females do not pay
any cost to being secondarily polygynous
Scramble competition polygyny
scarce females
explosive breeding assemblage
Lek polygyny
central position hypothesis
hotshot satellite hypothesis
Factors favoring leks
No paternal care
Males cluster on traditional display sites
Mating aggregations occur away from any
resource required by females
Females are free to choose between displaying
males
In antelope & grouse, female home range↑
as male territory↓ and mating system
switches from resource defense to lekking.
Observed pattern
Monogamy
> 90% of birds, females disperse farther
presumably to pick best resource
< 10% of mammals (e.g. canids, beaver,
carnivorous bats)
Males help provision young - canids,
carnivorous bats, marmosets
Females solitary and males can only defend 1
female - dik-dik, some rodents
very rare in insects (carrion beetles), fishes
and herps
Polygyny
> 90% of mammals, males defend females
when they can, males disperse farther
presumably to find a female group
Females solitary, range of 2 or more defensible
by male - prosimian primates
Females solitary, range not defensible - moose,
orangutan
Females social, range defensible by male
seasonal harems - elephant seals, red deer
permanent harems - hamadryas baboons, spearnosed bats, zebra
Females social, range not defensible
Female movements predictable, males wait for
females on territories, e.g. topi, waterbuck,
Uganda kob - analogous to bird leks
Female movements unpredictable, males follow
estrous females, e.g. elephant, mountain
sheep
In polygynous birds, males defend food or
nesting sites (blackbirds, grouse)
Polyandry
Rare in birds, very rare in mammals, but fairly
common in fishes
This occurs in birds where resources are very
patchy and available for only a short period.
Sequential - sanderling, Temminck's stint, spotted
sandpiper
Simultaneous - phalarope, jacana
Cooperative - pukeko
Promiscuity - both sexes mate multiple times
Common in insects
Hibernating bats ??
Parental care
Types of care
Care before birth of offspring -- Ex.
preparation of nests, burrows, or
territories
Investment in gamete production -- Ex.
female katydids consume spermatophores
provided by males have larger eggs which
survive overwintering better
Care of eggs -- Ex. incubation by birds,
egg guarding by fish, carrying brood by
waterbugs and seahorses
Provisioning or protecting young -- Ex.
provisioning by birds, brooding fry in
mouth in some fish, lactation in mammals
Care following nutritional independence -Ex. support in conflicts in social primates
Who provides PC?
Terrestrial Arthropods
PC is uncommon - found in only 85 orders
Care by females much more common than
care by males
Bony Fish - male care more common than
female care
Amphibians - care-giving by males and
females fairly similar
Reptiles - care by females more common
Birds - 90% of over 9000 species show
biparental care
E. Mammals - 100% of species show care
by females (gestation, lactation) but less
than 5% show direct male care
Why is female care more common?
paternity certainty
the order of game release
the association with young
----------------------------------------internal external
----------------------------------------male care
2
61
female care
14
24
no care
5
100
--------------------------------------------
Parent-offspring conflict
Costs to parent and benefits to offspring
change over the period of offspring
dependency such that the B/C ratio shows
continual decrease
From a parent's point of view -- want to
terminate parental investment in offspring
as soon as it becomes more advantageous
to invest in future offspring (i.e. when B/C
ratio drops to 1.0)
From offspring's point of view -- want
parental investment to continue until costs
exceed 2X benefits (i.e. when B/C ratio
drops to 0.5)
This is because parents are related to both
current and future offspring by same
degree of relatedness (0.5) but offspring
are related by twice as much to
themselves as to future siblings (1.0 vs.
0.5)
This generates a conflict of interest
between parents and offspring over when
parent investment should be terminated
When future offspring are expected to be
half siblings rather than full siblings,
period of conflict should extend longer
Other predictions
Level of investment should be greater and
period of investment should be longer as
parental age↑ because of ↓ residual
reproductive value of the parent
Offspring should be selected to be
manipulators of parents and parents to
detect and resist manipulation by offspring
Prevalence of weaning conflict and
tantrums in many birds and mammals
Siblicide
(Am. Sci. 78:438-449, 1990)
Juvenile mortality resulted from the
overt aggression of sibling
Black eagle, osprey, blue-footed booby.
great egret, cattle egret
5 common characters
resource competition
provision of food in small units
weaponry
spatial confinement
competitive disparity between sibling
Younger ones are marginal
individual or replacement if elder
sibling died
Time to siblicide
own viability met
resource inadequate