Ch. 10: Adaptation
Adaptive Behaviour
Definition: Adaptive behaviour refers to an evolutionary framework for studying behaviour.
Concepts:
Non-adaptive and maladaptive traits: Traits that do not aid in survival or reproduction.
Empirical methods for testing the adaptive basis of behaviour include:
Observation
Comparative methods
Experimental approaches
Evolution by Natural Selection
Historical Context: The concept of evolution by natural selection was proposed by Charles Darwin in 1859.
Key Components of Natural Selection:
A trait must exhibit natural variation among individuals.
Some of that variation must be heritable, passed down to offspring.
There must be a struggle for existence, leading to competition among individuals.
Different variants of the trait should confer different probabilities of survival and reproduction.
Darwin’s Evolutionary Framework
Definition: Natural selection is described as the differential survival and reproduction of individuals due to genetically based variations in their behaviour, morphology, and physiology.
Evolution: Refers to the change that occurs as the heritable traits of successful individuals spread throughout the population while those of less successful individuals are lost.
Citation: Goodenough et al. (2001).
Adaptive Basis of Behaviour
Genetic Basis of Behaviour:
All behaviours have a genetic basis, indicating that they can evolve over time.
This makes traits subject to natural selection.
Adaptive traits tend to increase in frequency within a population.
Maladaptive traits tend to decrease in frequency through natural selection.
So, we can assume behaviour is adaptive.
Definitions in Adaptive Behaviour
Adaptation:
Definition: A trait that enhances an individual's ability to survive and reproduce compared to individuals that lack the trait.
Subject to natural selection: Over time, adaptive traits become more common in the population.
Fitness:
Definition: A measure of an individual's relative success in propagating its genes into the next generation through the production of surviving descendents.
Subject to natural selection: High fitness traits are favored over generations.
Inclusive Fitness:
Definition: A measure of an individual’s success in propagating its genes into the next generation via both descendents and non-descendants that survive to reproduce.
Citation: W. D. Hamilton (1964).
Subject to natural selection: It acknowledges the impact of an individual's relatives on its own reproductive success.
Examples of Inclusive Fitness
Cooperative Courtship in Wild Turkeys:
Observed behaviour: Subordinate male turkeys assist dominant males in courtship. They are brothers, and the subordinate brother helps to chase invading males away so the dominant turkey has more chances to reproduce.
Benefits:
Increases reproductive success of dominant males.
Provides indirect benefits to subordinates, which must outweigh the costs of assisting. While they themselves don’t get to mate, his dominant brother gets to which actually spreads both their genes further.
Hamilton's Rule: inclusive fitness explains evolution of apparently altruistic behaviour where rB>C, relatedness, additional reproductive benefit to help the recipient, c+ reproductive cost to actor
Dominant gets net increase of 40 when he becomes dominant, but he loses 10 if he chooses to help his brother
Citation: Krakauer (2005).
Reference of publication: Kin selection and cooperative courtship in wild turkeys, Nature, 434, 69-72.
Fruit fly example: Related males may coordinate in the context of courtship. When related, males exhibit much less competition between one another and less aggressive courtship, leading to the female being unharmed and having more offspring overall. Related = less fighting = more offspring = longer lifespan for both males and females. (as adults and as juveniles)
Central Principle of Behavioural Biology: Animals behave in a way that maximizes propagation of copies of their genes
But… is everything we observe adaptive? NO!
Non-Adaptive or Maladaptive Traits
Causes for expression of maladaptive traits:
Domestication
Context-dependence: most evident with transplantation
Developmental anomalies
Diseases/pathologies
Parasitism-induced behavioral changes
Gene Flow and Behavioural Adaptation
Example: Gene Flow in an Aridlands Spider:
Example scenario: Desert populations vs. riparian woodland populations.
Desert populations are aggressive due to resource limitations.
Riparian populations are expected to be non-aggressive due to resource abundance, yet both aggressive and non-aggressive behaviours are present.
Methodology: Drift fence analysis revealed patterns of gene flow affecting behaviour. Migrations between populations exist. This can explain the maladaptive behaviour we see.
Citation: Reichert (1993).
Reference of publication: Investigation of potential gene flow limitation of behavioral adaptation in an aridlands spider, Behav. Ecol. Sociobiol. 32, 355-363.
Parasites and Behaviour
Behavioral Changes Induced by Parasites:
Example: The acanthocephalan (spiny-headed worm) parasites influence the behaviour of Gammarus lacustris (a type of amphipod).
Normally photophobic and repelled from water disturbances, but parasite infection turns them photophilic (attracted to light) and attracted to water disturbances, increasing susceptibility to predation by fish and waterfowl. So the parasite can find a vertebrate host.
Indicates adaptive manipulation of host behaviour by parasites to enhance transmission.
Specific Effects of Toxoplasma Infection on Rodents
Study Findings: The protozoan parasite Toxoplasma gondii alters the innate aversion of rats towards cat urine, creating an attraction instead.
Implications:
Increases the likelihood of predation by cats, which is vital for Toxoplasma’s reproduction within feline hosts.
Support for the “behavioral manipulation” hypothesis, which suggests that parasites manipulate host behavior to enhance transmission efficacy.
Research details: Toxoplasma infection affects aversion to feline pheromones without impacting learned fear or overall anxiety.
“Zombie ant” study
Retaining Non-Adaptive Traits
Mechanisms through which maladaptive traits are retained:
Selectively neutral behaviours
Conflicts between natural and sexual selection (e.g., Irish elk antlers, super large antlers caused its extinction)
Linkage between genetic loci (genes close to one another that are highly adaptive)
Pleiotropic gene effects (gene influences expression of multiple traits. While gene may be maladaptive, net package of behaviours may be positive). Tame foxes also had floppy ears and curly tails.
Evolutionary time lags “arms race”
Evolutionary Arms Race
Definition: Natural selection may render previous adaptations ineffective.
Example:
Predator-prey interactions where efficient predation causes improved antipredator behaviours and vice versa, creating a continuous cycle of evolution between species.
Eg. cats vs. Birds. Most efficient cats create most efficient birds and vice versa
Coevolution
Definition: Refers to reciprocal adaptations in interacting species due to the natural selection each species imposes on the other.
Contexts:
Predator-prey relationships
Host-parasite dynamics. Host does not recognize foreign eggs from brood parasites, and the parasite even lays eggs that looks like host’s eggs (cuckoo). Parasite evolves to lay more similar eggs.
Some hosts have evolved to recognize and remove parasites
The Red Queen Hypothesis
Concept: Animals must continually evolve to maintain their adaptive state relative to their changing environments.
Quote by van Valen (1973): "Animals must constantly evolve to maintain the same state of adaptation relative to their environment"
Red queen quote
Implication: Continuous evolutionary change is necessary for survival, illustrating the dynamic nature of natural selection and adaptation.