diversity of reproduction asexual reproduction parthenogenesis hermaphrodites sequential...
TRANSCRIPT
Diversity of reproduction Asexual reproduction
Parthenogenesis
Hermaphrodites
Sequential hermaphrodites - protogyny (FM) or protoandry (MF)
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 re
sult 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
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
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 non-colony members. Once settled reverts to xenophobia and loses fat stores