Development of Behavior • Development is an interactive process in which the genes are turned on and off both in response to environmental change and simultaneously creating change. • This demonstrated by changes in behavior shown by honeybees over the course of their lives.
Development of Behavior • Honeybees when they emerge as adults first work at cleaning cells then as they age they shift to other tasks. • Eventually at about age 3 weeks they begin foraging outside the hive.
Development of Behavior • As the bee goes through these changes in behavior it appears that predictable changes in the genes being actively expressed occur. • Microarray technology makes it possible to scan for activity levels of many genes by detecting mRNA made when genes are turned on.
Development of Behavior • Comparisons of arrays of nurse and forager bees shows substantial differences in genes turned on at each stage.
Development of Behavior • Transition to worker role appears to be strongly influenced by level of a hormone called juvenile hormone, which is produced by a gene. • The juvenile hormone gene turns on apparently in response to activity of other genes during 1st three weeks of adulthood , but can also be turned on in response to conditions in the hive.
Development of Behavior • If colonies are artificially made up of only young workers some become foragers much sooner and others remain as nurse bees much longer. • It may be social encounters that stimulate these changes. • Lack of encounters with older foragers appears to hasten nurse bees transition to forager role.
Development of Behavior • Adding numbers of older bees to hives that contain only young bees reduces the number of young bees that become foragers. • In contrast, adding more young bees does not slow rate at which young bees become foragers.
Development of Behavior • Inhibiting agent believed to be a chemical called ethyl oleate that foragers manufacture and store in their crop. • When foragers transfer food to nurse bees they transfer the chemical, which slows the nurses transition to foragers.
Development of Behavior • In honeybees, therefore, sequence of behavioral changes is determined by continuous interactions between genes and both chemical and social environments.
Nature vs Nurture Debate • Nature: genetic contribution to behavior. • Nurture: environmental contribution to molding behavior. • There is a false dichotomy in popular discussions in which traits are considered to be genetically or environmentally determined.
Nature vs Nurture Debate • In reality, all traits are the product of gene-environment interactions. • As we saw in the process of song learning there is considerable gene-environment interaction.
Nature vs Nurture Debate • Environmental or genetic differences among individuals can lead to differences in development and finally differences in behavior.
What causes individuals to develop differently? • Environmental differences and behavioral differences. • Many behavioral differences result from differences in experience. • For example, marsh tits fed whole sunflower seeds, which they can hide and later retrieve, develop a larger hippocampus in their brain than birds fed only powdered sunflower seeds. Practice of storing and retrieving seeds alters brain development.
Learning of nestmates in Polistes wasps • Polistes wasps learn to identify the smell of their natal nest and tolerate individuals that smell like the nest (whether or not they are relatives). • Individuals with a different smell are attacked. Differences in how wasps behave towards each other thus are based on the smells they learned when young.
Similar discrimination between individuals reared together versus apart has been shown in Belding’s Ground Squirrels. • Non-relatives reared together act nicely towards each other. However, relatives reared apart also act nicely towards each other.
Ground squirrels apparently learn what they themselves smell like and use this information to evaluate their relatedness to other individuals. • Trials in which squirrels provided with cubes smeared with dorsal gland secretions of other individuals respond more strongly to those of non-relatives and discriminate between different degrees of relatedness.
Genetic differences and behavioral differences • Breeding experiments can show whether behavioral differences between populations have a genetic basis.
Funnel Web Spiders • Spiders in different habitats differ in their speed of reaction to food being caught in their webs. • Streamside spiders react slowly. • Desert grassland spiders react quickly. • Is difference largely environmental or genetic?
Funnel Web Spiders • Spiders bred in lab. • Offspring of both populations kept equally well fed. Then offered food. • Desert spider reaction time: 3s. • Streamside spider reaction time: 60s. • Most of the difference in behavior apparently due to genetic differences between populations.
Migratory behavior of European Blackcaps • Blackcaps are small European warblers, most of which migrate to Africa to winter. However, some spend the winter in Britain. • What causes this difference in behavior?
Migratory behavior of European Blackcaps • Peter Berthold caught wintering blackcaps in Britain. • He then bred these birds in central Germany in outdoor cages.
Migratory behavior of European Blackcaps • In fall Berthold looked at migratory direction selected by birds. • Used an Emlen funnel to record orientation.
Blackcaps oriented in a westerly direction. Conclusion? British birds from where?
Migratory behavior of European Blackcaps • Based on orientation birds not from Scandinavia or northern Britain. • Birds probably from due east of Britain Belgium or Germany.
Migratory behavior of European Blackcaps • Could environmental influences be responsible? • Perhaps, just being in Germany causes westward orientation.
Migratory behavior of European Blackcaps • To check birds from SW Germany were bred in captivity. • Migratory orientation was checked.
Migratory behavior of European Blackcaps • Differences in orientation between populations largely determined by genetic differences. • Southwest German birds migrate SW traveling west of the Mediterranean via Spain.
Migratory behavior of European Blackcaps • Andreas Helbig has shown that Blackcaps from Austria orient southeast. • They travel east of the Mediterranean via Turkey and Israel.
Migratory behavior of European Blackcaps • Helbig crossed birds from Austria with birds from southwest Germany. • What direction did they orient?
Mean orientation of offspring south. Inner ring Adults. Outer ring Offspring.
Migratory behavior of European Blackcaps • Due south is a poor choice. Requires bird to cross the Alps and the make a long sea crossing over the Mediterranean.
Single gene effects on development • In theory a single gene difference could be responsible for difference in orientation on different Blackcap populations. • Note a single gene does not encode migratory choices, but a change in a single gene can result in many gene-environment effects and ultimately produce a large behavioral difference.
Two strains of Drosophila differ in larval foraging behavior. Rovers move a lot when feeding. Sitters move very little. Rover Sitter
Rover/sitter behavior in Drosophila • When the two strains were crossed in the F1 generation all of the larvae were rovers. • A cross of members of the F1 generation produced a 3:1 ratio of rovers to sitters.
Rover/sitter behavior in Drosophila • One gene appears to be responsible for difference between phenotypes. • The rover allele is dominant and the sitter allele is recessive. Gene that affects rover/sitter behavior affects the olfactory system and may affect fly’s ability to sense its environment.
Rover/sitter behavior in Drosophila • Many other single gene effects in Drosophila. • E.g. Stuck: males don’t dismount after normal 20 minutes of copulation. • Coitus interruptus: male copulates for only 10 minutes.
Single gene examples from lab mice • Mice homozygous for allele for defective form of calmodulin kinase have poor learning ability.
Single gene examples from lab mice • Mouse placed in water-filled container. • Submerged platform available for rest. • Normal and mutant mice tested with platform in random locations and original testing position. • Time to find platform measured.