Helpful behaviour

Helpful behaviour

Helpful behaviour

Facultative altruismIn Long-tailed Manakins, males conduct an elaborate display, but only the alpha male receives copulations.

Visiting display male (up to 10 years) -> beta -> alpha

Facultative altruism

In Florida scrub jays, helpers at the nest povide food for the young, defense of the territory, and protection from predators. Helpers may also gain direct fitness benefits through inheriting the territory or indirect fitness benefits through helping raise kin.

Helpful behaviour

The puzzle of altruism

Natural selection causes a particular behaviour to increase in a population if its fitness benefits outweigh its costs

Then why do members of some species help other members without any obvious fitness benefits?

For example, Belding’s ground squirrels increase their risk of being spotted by an intruder by barking an alarm, but nevertheless do so, allowing others in the area to reach safety.

Male wild turkeys form coalitions to court females and defend them against other groups, but only the dominant males sire offspring. Subordinates expend effort in the display, but with no apparent benefit

Dwarf mongooses take food to the young of others and guard the den from predators.

Eusocial insects (ants, termites, some wasps and bees) have worker castes that work in constant care of the colony, dying in defense of the nest, and helping rear offspring that are not their own, as they are sterile.

Altruism is a behaviour that raises the fitness of another individual at the expense of the altruists direct fitness (number of offspring it leaves).

How could altruism evolve?W.D. Hamilton: helping genetically similar individuals (i.e., relatives) to reproduce can indirectly increase fitness.

Can examine coefficient of relatedness (r)

Helping relative reproduce and indirectly increasing your own fitness is considered indirect selection or kin selection

When to help?Hamilton’s Rule:

BC

1r>

When to help?Hamilton’s Rule:

BC

1r>

Example: When should an individual forego reproduction to help its sister reproduce?

If you’re going to help kin, you better be able to discriminate kin from non-kin.

Belding’s ground squirrel pups identify their siblings because they learn each other’s odors while still in the same nest. When cross-fostered, unrelated pups treat each other like siblings

Paper wasps discriminate kin and nonkin through the odor of hydrocarbons present in the nest that become locked into the insect’s cuticle. Odors differ among colonies, depending on plant fibre used to build the nest. Wasps can recognize kin away from the nest.

Kin phenotype matching

Self-referent Phenotype matching

Female golden hamsters cross-fostered on their day of birth (not enough time to learn phenotype of relatives). As adults, could discriminate the odors of kin from non-kin, suggesting that they use their own odor to form a template to reference.

Tim

2 males – parentals and cuckolders

Offspring of parentals have high relatedness (as expected) compared to cuckolder offspring

Offspring of parental males show no association preference for full-sibling odors over nonkin/halfsibs

Offspring of cuckolder males show a significant preference for association with full-sibs (both familiar and unfamiliar) over nonkin/half-sibs

Offspring of parental males show no association preference for full-sibling odors over nonkin/halfsibs

Offspring of cuckolder males show a significant preference for association with full-sibs (both familiar and unfamiliar) over nonkin/half-sibs