Sociality and the adaptive value of helpful behavior

ZOL 313

June 17, 2008

Sociality and the adaptive value of helpful behavior

ZOL 313

June 17, 2008

Objectives:

1. Become familiar with some of the costs and benefits of social living.

2. Understand the differences between cooperation, reciprocity, and altruism and be able to generate hypotheses and predictions.

3. Understand why altruism usually occurs between kin and be able to use Hamilton’s rule to calculate whether altruistic behaviors are adaptive.

Costs and benefits of social living

Foraging

Costs:

Benefits:

Predation

Costs:

Benefits:

Costs and benefits of social living

Costs and benefits of social living

Disease/parasitism

Costs:

Benefits:

Mating

Costs:

Benefits:

Costs and benefits of social living

Parental Care

Costs:

Benefits:

Costs and benefits of social living

Prediction: Parasitic coot eggs that look less like their host’s eggs will be more likely to be rejected.

Donor Recipient

Selfish behavior

Spiteful behavior

Mutualism/ Cooperation

Reciprocity

Altruism

The adaptive value of helpful behavior

Types of social interactions between animals

The adaptive value of helpful behavior:

Example: Bubble net hunting by humpback whales

Example:

Cooperation: A mutually beneficial interaction between two members of the same species.

http://youtube.com/watch?v=-_IYBJjnw2U&feature=related

The adaptive value of helpful behavior:

Example: Cooperative courtship in the long-tailed manakin

The beta male helps the alpha male display to receptive females but NEVER gets to mate with any of them.

How can this be cooperation?

Cooperation: A mutually beneficial interaction between two members of the same species.

Example: Cooperation among competitors in the lazuli bunting

The adaptive value of helpful behavior

Cooperation: A mutually beneficial interaction between two members of the same species.

Bright, dominant males allow dull competitors to claim high quality territories next to them but drive away intermediate colored males.

Benefit to bright males:

Benefit to dull males:

Problem: Vulnerable to cheating. Why should the recipient repay

the donor?

Reciprocity: The recipient of a helpful action repays the donor later in time.

The adaptive value of helpful behavior

Game theory shows that reciprocity is more likely to occur when

Example:

The adaptive value of helpful behavior

Reciprocity: The recipient of a helpful action repays the donor later in time.

Hypothesis 1: Reciprocity. Meerkat sentinels help others at a personal cost now because

The adaptive value of helpful behavior

Reciprocity: The recipient of a helpful action repays the donor later in time.

Hypothesis 2: Personal Safety. Meerkat sentinels are the animals that are sated, so they obtain

Example: Meerkats forage in groups. Sometimes an individual will stop foraging and act as a “sentinel”, watching for predators and giving an alarm.

The adaptive value of helpful behavior

Reciprocity: The recipient of a helpful action repays the donor later in time.

Sentinels are not more likely to be preyed on than foragers.

Meerkats that are given food supplements spend more time as sentinels.

Prediction:

The adaptive value of helpful behavior

Reciprocity: The recipient of a helpful action repays the donor later in time.

Example: Belding’s ground squirrels alarm calls

1. Squirrels that alarm call are more likely to be killed by predators than non-callers.

2. The probability that an individual will alarm call is not correlated with familiarity/length of association with recipient.

3. Females with kin (sisters, aunts, cousins) nearby

The adaptive value of helpful behavior

Altruism: Helpful behavior that lowers the direct fitness of the donor and raises the fitness of the recipient

Most (non-human) altruistic behaviors that we know of are performed toward relatives.

Is this really altruism?

Altruism: Helpful behavior that lowers the direct fitness of the donor and raises the fitness of the recipient

C=cost to donor B=benefit to receiver

R=relatedness (between donor and recipient)

Hamilton’s Rule: R x B > C

2

Inclusive fitness=

The adaptive value of helpful behavior

Example: A Belding’s ground squirrel who gives alarm calls will have 2 fewer offspring over her lifetime than if she never called. However, by calling when she sees a predator she will save the lives of 5 of her sisters. Is this “altruistic” behavior adaptive?

R= B= C=

Altruism: Helpful behavior that lowers the direct fitness of the donor and raises the fitness of the recipient

C=cost to donor B=benefit to receiver

R=relatedness (between donor and recipient)

Hamilton’s Rule: R x B > C

2

The adaptive value of helpful behavior

Prediction:

The adaptive value of helpful behaviorCooperative breeding: “altruistic” helpers increase their inclusive fitness

In pied kingfishers, some yearling males are not able to find a mate. Options:

Primary helper: Help parents breed Secondary helper: Help non-related birds breed Delay: Wait until next year

The adaptive value of helpful behaviorCooperative breeding: “altruistic” helpers increase their inclusive fitness

Prediction:

Example: Cooperatively breeding paper wasps.

Subordinate females help care for the brood and defend the nest against predators.

One dominant female monopolizes the egg laying.

The adaptive value of helpful behaviorCooperative breeding: “altruistic” helpers increase their inclusive fitness

Based on what you know about altruism, when might it be adaptive for subordinate females to help instead of trying to reproduce on their own?

Transactional Theory Dominants and subordinates “negotiate” their reproductive rights within the group.

A dominant might allow a non-relative subordinate a small amount of reproduction to secure her help.

The adaptive value of helpful behaviorHow can cooperative breeding among non-relatives be adaptive?

Prediction: