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Transcript
Diversity of reproduction

Asexual reproduction

Parthenogenesis

Hermaphrodites

Sequential hermaphrodites - protogyny
(FM) or protoandry (MF)

Sexual reproduction
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

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

Competition for fertilization
Sperm competition


Physical, chemical, mate guarding, etc
Competition after fertilization
Bruce effect
Infanticide
Female choice
 Unequivocal
female preference, not a
result of male competition
 Choice
based on "genetic quality“
 runaway
 good
genes (survival skill)
 handicap
 rare
selection — Fisher
principle — Zahavi
male effect


Choice based on 'non-genetic' benefit

resource defense

parental ability
Mating systems: monogamy, polygyny,
polyandry, promiscuity

Cooperation or mutualism-- a mutually
helpful action

Reciprocal altruism (reciprocity)-- a
helpful action that will be repaid in the
future by the recipient

Altruism-- helpful behavior that raises
the recipient's direct fitness while
lowering the donor's direct fitness
Kin selection

A form of selection in which alleles
differ in their rate of propagation because
they influence the survival of kin who
carry the same allele

Indirect fitness-- the genes
contributed by an individual indirectly
by helping non-descendant kin, in
effect creating relatives that would not
have existed without the help

inclusive fitness-- the sum of an
individual's direct and indirect fitness

B/C > 1/ r or rB - C > 0
Cooperative breeding

a social systems in which some group
members defer their own reproduction,
even as adults, and help care for the
young of a few breeding individuals

Helpers are typically (but not always)
related to breeders and are often
individuals that do not disperse instead
aid in the rearing of their siblings

found in only about 3% of birds and
mammals (roughly 200-300 bird species
and about 120 mammal species)

Helper's duties--feeding, carrying,
huddling, babysitting, grooming, defense,
teaching, incubation, etc.

Do helpers really help?

Increase breeding success

correlation approach

exp. removal of helper

Increase number of breeding free
females from caring fledgling

Increase breeder survivorship
Social behavior

Societies--groups of conspecifics organized
in a cooperative manner

Evolutionary advantages of living in groups

Protection from physical factors

Protection against predator

Assembling for mates

Finding resources, beater effect, overwhelm
prey


Group defense of resources

Division of labors among specialists

Richer learning environment for young
that develop slowly, social facilitation
Cooperative defense against predator

Increase vigilance, alarm

Dilution effect

Selfish herd hypothesis

Mobbing, fight back

Evolutionary disadvantages of group living

Increase competition

Increase chances of spreading diseases
and parasites

Interference with reproduction

Reduce fitness due to inbreeding

Attracting predators
Eusocial insect

cooperative care of young

reproductive castes

overlap between generations
Possible explanations for
worker sterility

Kin selection – haplodiploidy

But, they are more closely related to
their own male offspring (r = 1/2) and
their nephews (r = 3/8) than their
brothers (r = 1/4). Therefore, expect
workers to lay unfertilized eggs

If mothers are polyandrous (mate
multiple times), then workers may be
more closely related to their brothers than
to half-nephews (r=1/8).

Expect workers to kill unfertilized eggs
laid by other workers. Example:
honeybees and yellowjackets are
polyandrous and have low levels of
worker reproduction

What about diploid eusocial animals
(e.g. termites, naked mole rats)?

One proposed hypothesis is that these
populations undergo cycles of
inbreeding. With high levels of
inbreeding-mother-son and sister
brother can rapid approach r>3/4 for
both males and females.

But high levels of inbreeding can lead to
inbreeding depression

Thus inbreeding might alternate with
some dispersal.

A rare disperser morph is found in mole
rats: it is fatter, attempts to disperse in
captive settings, solicits mating with noncolony members. Once settled reverts to
xenophobia and loses fat stores