Natural selection can only work on genetic differences

• Therefore, for behaviour to evolve:

  • There must be behavioural alternatives in the population
  • The differences must be (or must have been) heritable, so some influence on the behaviour must be genetic (but not necessarily all)
  • Some behavioural alternatives must confer more success than others
    (these are essentially the three pillars of Darwin's Natural Selection and natural selection theory reworded to be about behaviour)

• Remember that this is almost never just one gene influencing behaviour, often many work in concert, and there is an environmental factor as well

Three other important points

• The molecular path linking genes to behaviour is very complicated and not always easy to trace
• Genes and behaviour are linked both ways - genes influence behaviour, but behaviour can influence gene expression.
• Just because genes influence behaviour does not imply that genes alone produce the behaviour.

Example of Drosophila and honeybees

Background

• In Drosophila, there are two feeding behvaiours - rovers and sitters - about their overall mobility. These behvaiours exist in both larval and adult stage
• In absence of food, rovers and sitters don't differ in behvaiour
• This difference is caused by just one gene called for, with alleles ${for}^R$ and $fo{r}^S$, where $fo{r}^R$ increases production of enzyme PKG.
• Rovers have better short-term memory for olfactory stimuli
• Sitters are better at long-term memory for odor cues

Competition example

• A wild population at a Toronto orchard had 70% rovers and 30% sitters.
• Rovers do better in areas with many larvae and patchy food, sitters better with uniform food and low larval density.
• When food is scarce, Competition is most intense between individuals in the same morph.
  • In this case, the advantage goes to whichever type is rarest:
  • Negative frequency-dependent selection
• This explains why both morphs persist in the population

Honeybee example

• This gene $for$ also exists in Apis mellifera and regulates age changes
• Young bees mostly stay inside the hive, and older workers travel long distances to collect pollen and nectar
• The expression of $for$ changes in this period, increasing production of the enzyme (PKG) that makes them rovers
• If older bees are removed, young bees will begin foraging early (changing gene expression)
• This gene expression is influenced by both age and social information
• Experiments that in elevating PKG level in young workers also makes them foragers

Drosophila Courtship song

• Temporal pattern of courtship song varies between species
• A gene called period affects this pattern
• Gene editing can cause one species to make the song of another species

Example of MC1R

• Melanin variations determine darkness or lightness of skin, hair or feathers
• In vertebrates this is encoded by MC1R gene
• Lesser snow geese homozygous for one allele in MC1R are white and others are blue. There is no evidence of any selective advantage, but whites usually mate with whites and vice versa.
• In the rock pocket mouse, there are also two forms. Dark live on lava flows and light live on sandy habitat. Owls selectively predate the mice which don't match their background.

Example of blackcap warblers

• Migratory birds in captivity show "restlessness" at their natural species migration time
• Duration of restlessness correlates with migration distance
• Two populations of blackcaps studied: Sedentary population and migratory
• Cross-bred, hand-raised individuals showed migratory restlessness, suggesting genetic control
• Selective breeding could result in 100% migratory or non-migratory populations within 3 - 6 generations
• Milder winters in Britain have created a whole new migratory pattern which is also genetic and heritable