BIO220H1 Lecture Notes - Lecture 16: Social Animal, Cooperative Breeding, Eusociality

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Cooperation, Conflict, and the Evolution of Complex Animal Societies
Organisms are inherently competitive, yet cooperation is widespread. Genes cooperate
in genomes; cells cooperate in tissues; individuals cooperate in societies.
animal societies are not only common in insects, mammals, and birds, but exist even in
simple species like amoebas.
social associations can be temporary (unstable) or permanent (stable, interactions
among members often appear to be altruistic).
The Costs and Benefits of Group Living
Group-living typically have benefits and costs to group members
-benefits: more eyes to provide vigilance and forage, assistance to deal with pathogens,
easier mating opportunities, better conservation of heat, and reduced energetic costs
of movements.
-cost: increased attack rates by predators, increased parasite burdens, misdirected
parental care, and greater reproductive competition and food competition
*When the benefits of living together outweigh the costs of living alone, animals will
tend to form groups
*altruistic behavior in situations where individuals interact repeatedly, which typically
occurs when animals live in stable groups
Kin Selection and Living in Families
Altruistic behavior can benefit individuals even when it is not reciprocated.
Hamilton : the extent to which an individual is willing to help another should be
determined by the degree to which those individuals are related.
relatives share many genes. evolutionary fitness : is determined by the fraction of an
individual’s genes that enter the next generation’s gene pool, regardless of whether
those genes come from that particular individual or from identical copies in its
relative. If the cousin who is saved goes on to reproduce, then the altruistic act of
saving that relative increases the evolutionary fitness of the rescuer by passing on
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shared genes. Although organisms can enhance their direct fitness by reproducing
themselves, Hamilton realized that they can also enhance their own indirect fitness by
helping relatives.
Kin selection theory is particularly relevant to social insect societies because many
insects are haplodiploid (Diploid fertilized eggs become females, while unfertilized
haploid eggs become males).
Patterns of relatedness in
haplodiploid and diploid species
In singly mated haplodiploid
species, females are more closely
related to their sisters (r = 0.75)
than they are to their brothers (r =
0.25).
Haplodiploid females are also more
related to their nieces (r = 0.375,
Figure 1b) than diploid females are
to their nieces (r = 0.25, Figure 1b).
Kin selection theory suggests that the sex-determined differences in relatedness
among individuals (Figure 3) provide incentives for young females to stay at home and
help raise their sisters. However, initial excitement over this explanation as a primary
reason for sociality was tempered by observations of non-social haplodiploid species,
as well as subsequent discovery of eusocial diploid species like termites.
Eusociality in Insect Societies
The enormous and highly complex societies formed by some insects(most notably in
bees, wasps, and termites) is called eusociality. Eusociality is characterized by 3 key
criteria:
(1) cooperative care of young
(2) overlapping generations (i.e., parents and offspring cohabitating);
(3) a reproductive division of labor
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BIO220H1 Full Course Notes
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Document Summary

Cooperation, conflict, and the evolution of complex animal societies. Organisms are inherently competitive, yet cooperation is widespread. Group-living typically have benefits and costs to group members. Benefits: more eyes to provide vigilance and forage, assistance to deal with pathogens, easier mating opportunities, better conservation of heat, and reduced energetic costs of movements. Cost: increased attack rates by predators, increased parasite burdens, misdirected parental care, and greater reproductive competition and food competition. *when the benefits of living together outweigh the costs of living alone, animals will tend to form groups. *altruistic behavior in situations where individuals interact repeatedly, which typically occurs when animals live in stable groups. If the cousin who is saved goes on to reproduce, then the altruistic act of saving that relative increases the evolutionary fitness of the rescuer by passing on shared genes. 0. 25): haplodiploid females are also more related to their nieces (r = 0. 375,