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Diversity of reproduction
Asexual reproduction
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
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
• 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
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
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