chapter 14 the evolution of social behavior (1 lecture)most insects are not social. however, some...
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SocietyA group of individuals of the same species that is organized in a cooperative manner, extending beyond sexual and parental care
Colonial invertebrates form aggregations of individuals
for mutual benefit
For instance, to the right is a man-of-war (phylum Coelenterata). It consists of four different types of polyps, which specialize in either
flotation, feeding, defense, or reproduction
Sociality in FishForm complex schools
Some form colonies that actively defend nest sitesSome species are territorial
A school of fish changes leadership when it changes direction
The leaders at the left (stippled) are shifted to the flank when the schoolmakes at 90 degree turn, as shown in the sequence in the center and at
the right
The colonial bluegill nests in groups
Each male defends a territory bordered by the nest sites of other males. He attempts to protect his nest against bass (blue circle), bullhead catfish (green
arrow), snails, and pumpkin-seed sunfish (red arrow)
Sociality in amphibians and reptiles
Amphibians and reptilesDevelop large communal sites for calling females
Some exhibit parental careSome species form hibernacula (garter snakes)
Some species spend considerable time and energy engaged interritorial defense
Males of a tropical frog (Dendrobates galindoi)wrestle for possession of a territory
In most cases, spacing between frogsis maintained by repetitious calling
Sociality in birds
The majority of bird species are monogamous territorial breeders
Many aggregate in feeding, migratory and roosting flocks
Well-organized breeding colonies are common
The most complex avian social systems are those involving cooperative breeding, in which non-parents share in the rearing
of young
Sociality in mammals
Majority of species are solitary, where the most complex social unit is the mother with her young
Some species are social during the mating season, when a male monopolizes several females (= polygynous mating system)
However, complex social organizations have evolved in species within virtually all mammalian orders, especially in marsupials,carnivores, ungulates and primates that live in relatively open
habitats. ==> This indicates that social behavior evolved largely as a defense against predators and protection of resources through group territory
Social behavior in the Hamadryas baboon
A large group of baboons is departing from the communal sleeping rock (leftbackground) on the way the the feeding and watering sites. The procession is
beginning to break up into the basic social units, which consist of single males andtheir harems of females and offspring. Aggressive interactions are frequent and
animated. The 2 males in the foreground threaten each other--the one on the right isusing a hostile stare, while his opponent responds with a more intense gaping display.
Sociality in insectsMost insects are not social. However, some species of insects (e.g., bees, ants, termites, and wasps) display a
remarkable type of social organization, referred to as eusociality
Eusocial insect colonies consist of:sterile workers that labor on behalf of reproductive individuals
sterile worker that cooperate in the care of youngat least two generations of individuals
Colony members use a variety of visual and chemical signals forAlarm
Simple attractionRecruitment of individuals to a new food source or nest site
GroomingGreeting rituals consisting of the exchange of oral and anal liquid food
Exchange of solid food particlesRecognition of nestmates and members of particular castes
The high proportion of genetic relatedness between sisters promotes the evolution of altruism among sisters, and hence
the evolution of eusociality.
Altruism: helpful behavior that raises the recipient’s direct fitness, while lowering the donor’s direct fitness
Accordingly, altruistic females are presumed to be really helping their sisters (future queens) and only incidentally
helping their mothers
Altruism in bees
A female bee that has just stung a human. Notice that she devisceratesherself as she tries to leave her victim.
The Naked mole rat: an example of a eusocial mammal
Found in Ethiopia and KenyaIn the Family Bathyergidae (includes Guinea pigs, chinchillas, porcupines)
Colonies: Typically 75 - 80 rats, including workers, defenders, and a breeder (queen)
Queen is very aggressive (other females reproductively suppressed until queen removed)
Inbreeding high, relatedness = 0.81 (0.50 = siblings)
Control over reproductive suppression: Not pheromonal, but instead due tophysical contact (when queen removed, reproductivity released)
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