BIONG Prelim #3 Study

Typical Group Size

How many individuals generally occur together

Social Organization

What is the nature of social interactions and who interacts

Philopatry

Remaining in a natal group or in a nata territory

• influences whether or not you will be around relatives.

• Family groups depend on philopatry

A non-exhaustive list of some axes of social structure variation

1. Presence/absence of in-group v. out-group behavior

2. Nature of interactions (cooperative, competitive, etc)

3. Types of individuals in the group (males, females, young)

4. Dominance hierarchy within the group

5. Reproductive division of labor and/or task specialization

Dispersal

Movement to a new group or territory to reproduce

Lots of variation in dispersal…but there are some broad patterns

1. Many species in the ocean have long distance dispersal of larvae driven by currents, so individuals are not near relatives

2. When dispersal is more directed by individual movement (as is the case on land) Generally, one sex disperses further than the other, this reduces inbreeding

Consequences of staying at home

• Families and cooperation

• Inbreeding

Helping behavior in families

• Meerkats are an example of a family where non-breeding individuals help raise the young

• Adult helpers:

• Babysit the pups

• Feed the pups

• Stand guard while group forages

Evolution favors individuals that have behaviors that promote their own success.

Altruism

Is when an individual’s behavior provides a benefit to another individual at a cost to itself.

Costs can be both negative consequences of a behavior or the missed opportunities caused by helping.

Hamilton's rule

In meerkats and other social species (e.g., bees, ants, termites, wasps, naked mole rats, wolves, etc.) helping is not random

Key to solving the conundrum:

• Help is given to related individuals.

• Helping raise relatives can pass on your genes because they share a recent common ancestor

Equation

A simple equation can tell us whether a behavior directing help to others may evolve:

r*b > c

r = relatedness

b = benefits

c = costs

Benefits

The additional offspring that the recipient will have as a result of the altruist’s behavior.

Costs

The loss in offspring that an altruist will have a result of the helping behavior.

r * b > c - Benefits and Costs

These are straightforward to define but difficult to measure in practice. In many cases, estimating b and c involves a counter factual, since it is added benefit and realized cost. It is hard to know what would have happened without the helping behavior.

Relatedness

The proportion of ancestry shared between two individuals through common descent.

For sexually reproducing species, this means that each pedigree link needed to connect individuals reduces relatedness by 50%

Relationship - r value

Parent & Child: 0.5

Full siblings: 0.5

Half siblings: 0.25

Grandparent & Grandchild: 0.25

Aunt/Uncle & Niece/Nephew: 0.25

1st Cousins: 0.125

Meerkats

• They (typically) raise their full siblings

• Pup production is easiest in large groups

• Leaving to start your own group means you will be in a small group and you will produce few pups

Inbreeding and deleterious alleles

• Mating with close relatives increases the chances that a negative genetic trait for which you are a carrier will be expressed

• Many negative mutations present in populations are recessive, meaning they have little or no impact on the phenotype when there is only one copy

• If one sex regularly leaves social groups that helps reduce inbreeding (i.e., breeding within a family line)

How lion social structure actually works

• Solitary males or coalitions compete for access to prides of females.

• When males are deposed, the new males will kill any nursing

• cubs present in the pride

• The core unit of the pride is group of related females. They cooperate to defend territory and hunt. They will also provide care for others’ cubs.

• Female lions compete for resources

• Male lions compete for access to mates

Genetic structure in lions

• Shared DNA similarity can be measured in many ways (in this classic work using DNA ‘fingerprints). The important point is to assess similarity of variable DNA elements among individuals.

• For lions, DNA shows that females within a pride are relatives.

• Male partners tend to be relatives.

• Breeding males and females are not related to each other.

Shared reproduction among males (lions)

• Male lion coalitions vary in size.

• Large coalitions a made of close relatives that dispersed single pride.

• Small coalitions may have unrelated males.

• Multiple males sire cubs when there are coalitions. There is no single ‘king’ of the pride that gets all the matings.

Brothers are everything for lion males!

• Larger coalitions can control prides for longer (avoid infanticide)

• They can hold larger prides

• And they sire more young