A6 Ethology Flashcards
Ethology
is the scientific study of animal behaviour under natural conditions (i.e. observational not experimental)
As it is a biological perspective, behaviour is considered to be an evolutionary adaptive trait developed via natural selection
Natural selection - animal behaviour
Natural selection is a mechanism of evolution by which the frequency of inherited traits change as a result of external agents
Characteristics which promote survival and reproduction (i.e. beneficial alleles) become more prevalent in a population
Any behaviour that has a genetic basis (i.e. innate) and confers reproductive success will become more common
Learned behaviours may also evolve via natural selection if the capacity for learning has a genetic basis (e.g. language)
Natural selection will promote “optimal” behaviours for the given set of environmental conditions in which the organism lives
As these external conditions change, the frequency of certain behavioural responses will vary accordingly
Genetic basis of migration in blackcaps
The migratory behaviours in blackcaps has been demonstrated to have a genetic basis via a number of experiments
Chicks raised in isolation will follow the migratory routes of their parents (hence it is an innate trait and not learned)
Hybrid chicks of parents with different migration routes will migrate in a direction between the two parental directions
This suggests heterozygote hybrids exhibit a combination of the migratory tendencies from each homozygous parent
Natural selection affect on migration of blackcaps
Blackcaps occupy summer breeding grounds in Germany, but migrate to different locations during the winter months
Historically, most birds migrated south to Spain in the winter, with a minority migrating west to the UK
Spain is further away but has generally had a more temperate winter climate than the UK, improving reproductive success
With an increase in global temperatures, the migratory patterns of blackcaps are changing due to natural selection
Blackcap populations in the UK are rising, as warmer temperatures are improving survival rates during the winter months
UK blackcaps are reproducing more, as the shorter migration allows them to select the best breeding territories in Germany
Altruism
is behaviour which benefits another individual at the cost of the performer
Ostensibly, it is in opposition to natural selection as it reduces the potential for the altruistic individual passing on their genes
However, it improves the chances of the other individual passing on genes into the same gene pool (i.e. inclusive fitness)
Kin selection
Enhancing the reproductive success of relatives who share common genes
Reciprocal altruism
Organisms that live in social clusters will also promote the conservation of altruistic genes
Blood sharing among vampire bats
Vampire bats commonly regurgitate blood to share with unlucky roost mates who were unable to gain independent sustenance
Vampire bats cannot survive multiple successive days without food, however food can often be difficult to find
The small cost of sharing blood (lost time until starvation) is less than the benefit received (time gained)
Hence sharing blood improves the fitness of the entire brood (via reciprocal altruism), increasing the occurrence of altruism
Foraging
is the act of searching for (and potentially finding) food resources in nature
Shore crabs - foraging
Shore crabs demonstrate selectivity in the type of mussel foraged when the mussel population is abundant:
Crabs will ignore smaller mussels (as the energy yield is less than that obtained from larger mussels)
Crabs will also ignore larger mussels (difficult to crush, also risks potential damage to the crab’s claws)
Crabs will selectively identify and feed on mid-sized mussels (provided the mussel supply is in abundance)
Breeding strategies in coho salmon
Male coho salmon form two different breeding populations according to the strategy used for passing on genes:
All males initially undergo a development phase as juveniles in which they grow within freshwater rivers (~12 months)
Following that, the males migrate out to the ocean for a period of maturation, whereby they differentiate into two populations
Some of the male salmon develop into ‘jacks’, while other male salmon will develop into ‘hooknoses’
Jacks are smaller and well camouflaged – they only require ~ 6 months in the seawater to reach maturity
Hooknoses are larger and brightly coloured – they require ~ 18 months in the seawater to reach maturity
Jacks and hooknoses employ different breeding strategies in order to successfully reproduce with female coho salmon:
Jacks sneak out from behind rocks or recesses in the riverbed and attempt to stealthily mate with a female
Hooknoses swim within the open water and fight aggressively amongst one another for the opportunity to mate
Having two breeding pathways improves the rates of successful reproduction and also increases levels of genetic variation
Jacks have higher rates of survival (as they spend less time in seawater), but have more competition for reproduction
Hooknoses have lower rates of survival but consequently experience less direct competition for successful mating
Courtship
Courtship describes a set of behavioural patterns whereby potential mates inform each other of a readiness to reproduce
Courtship stimuli may be species-specific and will be performed differently by different individuals
Courtship stimuli are often competitive among males and form the basis of assessment by females
Courtship behaviour in the birds of paradise
Whereas females appear drab, males will have bright plumage and display fancy behaviours to demonstrate their virility
While these features make them a target for predators, they improve chances of attracting female attention (mate selection)
Any exaggerated trait that improves reproductive fitness will become more prominent in future generations (sexual selection)
Synchronised oestrus
Female lions synchronise their sexual receptiveness (oestrus) to increase chances of survival and reproduction of offspring
Lionesses remain in the same pride their entire lives, living with genetic relatives (sisters, aunts, nieces)
Male lions leave their birth group at a young age and in order to reproduce must replace males in existing prides
Upon establishing dominance within a pride, a male lion will kill all cubs already present
The loss of cubs triggers an innate, synchronised response whereby all lionesses enter a period of oestrus
This synchronised oestrus is mediated by pheromone signals
Advantages to synchronised oestrus
It increases the number of offspring the male lion can produce (risks of displacement are always present)
It allows for shared lactation and nursing of cubs within the pride (all female lions nurse indiscriminately)
It is easier for the lionesses to hunt and defend the pride if all cubs are of a comparable age
