12.1 Essential ideas

12.1.6 Applications of ethology (HL)

  • Ethology is the study of animal behaviour in natural conditions.
    • Ethology (study of animal behaviour) and ecology (study of the interaction of organisms with the environment) are both important for understanding how natural selection leads to the evolution of behaviour.
  • Natural selection can change the frequency of observed animal behaviour.
    • Behaviour, both innate and learned, affects an animal’s chance of survival and reproductive success.
    • Some behaviours are favoured in different environmental conditions, so the frequency of behaviours changes in response to natural selection. 
  • Behaviour that increases chances of survival and reproduction will become more prevalent in a population.
    • Both innate and learned behaviours become more prevalent if they increase an organism’s chance of survival and reproduction. 
  • Learned behaviour can spread through a population or be lost from it more rapidly than innate behaviour.
    • Many generations are needed for the frequency of innate, or genetic, behaviours to change.
    • A learned behaviour is quickly passed on by social interaction in a single generation, but if one generation doesn’t learn the skill from the previous generation, it may be lost forever.

Application: Synchronised oestrus in female lions – an innate behaviour

  • Lions do not have breeding seasons – instead the females of one pride all ovulate and are ready for mating at the same time.
  • Oestrus can be induced by the introduction of a new dominant male to the pride. Upon arrival, he kills any existing cubs and mates with females to ensure his own cubs are cared for.
  • Synchronised oestrus is an innate response that has survival advantages. For example:
    • Female lions care for each other’s cubs of about the same stage of development, e.g. suckling cubs while others are hunting.
    • Male cubs are about the same age when they are cast off from the pride, so they generally have an equal chance of competing for a new pride. 

Application: Milk-bottle feeding in blue tits – a learned behaviour

  • The Eurasian blue tit Cyanistes caeruleus is unable to digest lactose from milk, but is capable of digesting milk fat – a highly nutritious food source.
  • Between the 1920s and the 1940s, (unhomogenised) milk was widely delivered to doorsteps in glass bottles with cardboard caps in many parts of Europe. Blue tits were observed first in England, then as far away as Sweden, skimming the cream from the top of unclaimed milk bottles.
  • In the 1950s, milk bottles were fitted with aluminium seals, which the blue tits learned to pierce in order to get at the cream. Other birds, such as robins, were also seen at the bottles, but not with the same frequency as blue tits.
  • A possible explanation for the difference in frequency is the family structure and relative sociability of the two species. Blue tits travel in family groups of up to ten, whereas robins are solitary. Blue tits were able to learn from each other, whereas. cream-skimming behaviour would remain isolated to innovative robins.
  • Milk is no longer delivered in glass bottles, and is normally homogenised, so blue tits exposed to the food source do not exploit it. Cream-skimming was a learned behaviour that is now lost.

Application: Breeding strategies of coho salmon affect survival and reproduction

  • Pacific coho salmon Oncorhynchus kisutch migrate to estuaries from the open water annually during the spawning season.
  • Male coho salmon develop into one of two breeding phenotypes – each is associated with a different breeding behaviour: 

Phenotype

Hooknose

Jack

Appearance

Larger body mass
Bright colouration

Smaller
Less conspicuous colour

Maturation time

18 months

6 months

Dominant breeding strategy

Fight with other males for access to females and eggs

Sneak up on freshly laid eggs without being noticed by females or other males

Disadvantages

Large energy investment
More conspicuous to predators

Less able to defend themselves
Success depends on the number of suitable hiding places in the spawning area

 

  • The breeding success of either strategy is frequency-dependent:
    • When few males develop into jacks, jacks will be more successful at finding suitable hiding places.
    • When many males develop into hooknoses, competition will be greater.

12.1.6aFigure 12.1.6a – Life history of male coho salmon (Ecology 72(4) 1991, p.1181)

Application: Courtship in birds of paradise is an example of mate selection

  • Many species of birds display sexual dimorphism – males have very different morphological features (i.e. bright and colourful plumage) compared to females.
  • In addition to conspicuous plumage, male birds of paradise (about 40 species of the family Paradisaeidae) perform elaborate dances and calls in order to woo mates.
  • The basic moves are inherited genetically, but each male refines his own steps and calls to perform unique courtship behaviours. For example, the male in this video adds a leaf to his perch pivot to ‘add to the effect’: www.birdsofparadiseproject.org

Birds-of-paradise.org takes you through the courtship display of a male Carola’s parotia (binomial name: Parotia carolae).

  • Females choose males that perform elaborate displays and this choice has driven the evolution of increasingly complex courtship behaviour – this is an example of sexual selection.
  • The reason why females choose elaborate dancers is unclear although suggested hypotheses include the possibility that the more exhibitionist male dancers are stronger than their less elaborate competitors.

12.1.6bFigure 12.1.6b – Niko Tinbergen
Niko Tinbergen (1907–88) and his colleague Konrad Lorenz shared a Nobel Prize in 1973 for their contributions to the field of ethology.

Key questions

Using examples of both innate and learned behaviour, outline how behaviour either increases or decreases the chances of survival and reproduction.

12.1.6cFigure 12.1.6c – A pride of lions
Oestrus synchronisation means all the cubs in a pride of lions are the same age.

12.1.6dFigure 12.1.6d – Blue tit on a milk bottle
The Eurasian blue tit learned to pierce caps and feed on cream. 

12.1.6fFigure 12.1.6e – Homogenised milk
Homogenised cow's milk causes diarrhoea in blue tits.

Concept help

  • Other species of Pacific salmon, including Chinook Oncorhynchus tshawytscha, also have alternative male reproductive phenotypes. Human activity (i.e. fishing) may also affect the frequency and success of jacks vs hooknoses in both species.
  • Distinct layers of cream (fat) and watery milk are visible in unhomogenised milk. The process of homogenisation emulsifies the fats in milk so that they are more evenly distributed.

12.1.6dFigure 12.1.6f – Red salmon
The breeding strategy of male coho salmon affects the chances of survival and reproduction.

12.1.6gFigure 12.1.6g – Bird of paradise
Courtship behaviour is an example of mate selection in birds of paradise in Papua New Guinea.

Course link

Innate behaviours evolve as a result of natural selection. Review the mechanism in 5.1.2.

Further reading

A recent study has suggested that social learning in blue tits is affected by the age of birds and individual innovativeness, where younger birds are more likely to perform a new skill and to learn it from others. See:

Aplin, Lucy M., Sheldon, B. and Morand-Ferran, J. ‘Milk bottles revisited: social learning and individual variation in the blue tit, Cyanistes caeruleus’. Animal Behaviour 85(6), 1225-1232.