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Diversity of reproduction
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Asexual reproduction
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Parthenogenesis
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Hermaphrodites
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Sequential hermaphrodites - protogyny
(FM) or protoandry (MF)
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Sexual reproduction
Male/female reproductive strategy
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Asymmetrical gamete size (anisogamy)
means the sex with smaller gametes
should usually compete for access to the
sex with larger gametes.
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This results in greater variation among
males than among females for
reproductive success.
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Males should, therefore, fight over
females and females should select for
resources
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Sexual selection - The advantage which
certain individuals have over others of
the same sex and species, in exclusive
relation to reproduction (Darwin, 1871)
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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.
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As with natural selection, sexual
selection leads to genetic changes in the
population over time
Intrasexual selection
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Competition for copulation
Dominance
Alternatives:
• friendship with females
• male coalition
• female mimicry
• satellite males
• forced copulation
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Competition for fertilization
Sperm competition
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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
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Choice based on 'non-genetic' benefit
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resource defense
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parental ability
Mating systems: monogamy, polygyny,
polyandry, promiscuity
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Cooperation or mutualism-- a mutually
helpful action
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Reciprocal altruism (reciprocity)-- a
helpful action that will be repaid in the
future by the recipient
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Altruism-- helpful behavior that raises
the recipient's direct fitness while
lowering the donor's direct fitness
Kin selection
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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
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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
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inclusive fitness-- the sum of an
individual's direct and indirect fitness
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B/C > 1/ r or rB - C > 0
Cooperative breeding
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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
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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
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found in only about 3% of birds and
mammals (roughly 200-300 bird species
and about 120 mammal species)
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Helper's duties--feeding, carrying,
huddling, babysitting, grooming, defense,
teaching, incubation, etc.
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Do helpers really help?
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Increase breeding success
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correlation approach
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exp. removal of helper
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Increase number of breeding free
females from caring fledgling
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Increase breeder survivorship
Social behavior
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Societies--groups of conspecifics organized
in a cooperative manner
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Evolutionary advantages of living in groups
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Protection from physical factors
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Protection against predator
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Assembling for mates
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Finding resources, beater effect, overwhelm
prey
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Group defense of resources
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Division of labors among specialists
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Richer learning environment for young
that develop slowly, social facilitation
Cooperative defense against predator
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Increase vigilance, alarm
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Dilution effect
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Selfish herd hypothesis
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Mobbing, fight back
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Evolutionary disadvantages of group living
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Increase competition
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Increase chances of spreading diseases
and parasites
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Interference with reproduction
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Reduce fitness due to inbreeding
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Attracting predators
Eusocial insect
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cooperative care of young
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reproductive castes
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overlap between generations
Possible explanations for
worker sterility
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Kin selection – haplodiploidy
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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
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If mothers are polyandrous (mate
multiple times), then workers may be
more closely related to their brothers than
to half-nephews (r=1/8).
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Expect workers to kill unfertilized eggs
laid by other workers. Example:
honeybees and yellowjackets are
polyandrous and have low levels of
worker reproduction
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What about diploid eusocial animals
(e.g. termites, naked mole rats)?
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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.
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But high levels of inbreeding can lead to
inbreeding depression
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Thus inbreeding might alternate with
some dispersal.
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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