Diergedrag
Campbell 52.3 Selection for individual survival and reproductive
success can explain diverse behaviours
Evolution of foraging behaviour
An experiment on fruit flies allows us to examine one way that foraging behaviour might have
evolved.
For (= forager gene) dictates how far larvae travel when foraging. Larvae carrying the forR allele
travel nearly twice as far as larvae with the forS allele. Both the forR and forS alleles are present in
natural populations. Larvae in populations kept at a low density foraged over shorter distances than
those in populations kept at high density. Furthermore, the forS allele increased in frequency in the
low-density populations, whereas the forR allele increased in frequency in the high-density group.
An interpretable evolutionary change in behaviour occurred during the experiment.
Optimal foraging model: This idea proposes that foraging behaviour is a compromise between the
benefits of nutrition and the costs of obtaining food (energy expenditure, risk of being eaten).
According to this, natural selection should favour a foraging behaviour that minimalizes the cost of
foraging and maximizes the benefits.
Balancing risk and reward: One of the most significant potential costs to a forager is risk of
predation. Predation risk influences foraging behaviour.
Mating behaviour and mate choice
These behaviours include seeking or attracting mates, choosing among potential mates, competing
for mates, and caring for offspring.
Mating systems and sexual dimorphism: In the context of reproduction there are differences in
mating systems, the length and number of relationships between males and females.
▫ Promiscuous: no strong pair-bonds
▫ Monogamous: one male mating with one female
▫ Polygamous: individual of one sex mating with several of the others
Polygyny: a single male and many females
Polyandry: a single female and multiple males
Sexual dimorphism is the extent to which males and females differ in appearance; this varies with
the type of mating system. Among monogamous species, males and females often look very similar.
Among polygamous species, the sex that attracts multiple mating partners is typically showier and
larger than the opposite sex.
Mating systems and parental care: the needs of the young are an important factor constraining
the evolution of mating systems
▫ Birds:
Young cannot care for themselves, require a large, continuous food supply, the male
usually stays to help, most of these species are monogamous
Young can care for themselves, males derive less benefit from staying with their partner,
they seek other mates.
▫ Mammalian species
Lactating female is the only food source, no male needed in raising the young.
Males protect the females and young, a male or small group of males typically cares for a
harem of many females.
Another factor influencing mating behaviour and parental care is certainty of paternity. Young born
to or eggs laid by a female definitely contain the female’s genes, but the father may be uncertain.
The certainty of paternity is relatively low in most species with internal fertilization because the acts
,of mating and birth are separated over time. With external fertilization the certainty of paternity is
high.
Sexual selection and mate choice: Sexual selection is a form of natural selection in which
differences in reproductive success among individuals are a consequence of differences in mating
success.
Intersexual selection: members of one sex choose mates on the basis of characteristics of the other
sex.
Intrasexual selection: involves competition between members of one sex for mates.
Mate choice by females: A female whose mate choice is a healthy male is likely to produce more
offspring that survive to reproduce. As a result, males may compete with each other in ritualized
contests to attract female attention. Mate choice can also be influenced by imprinting. Mate-choice
copying is a behaviour in which individuals in a population copy the mate choice of others.
Male competition for mates: Male competitions may involve agonistic behaviour, a contest,
typically ritualized, that determines which competitor gains access to a recourse or a mate.
Applying game theory: Game theory evaluates alternative strategies in situations where the
outcome depends on the strategies of all the individuals involved. Game theory provides a way to
think about complex evolutionary problems in which relative performance (reproductive success
relative to other phenotypes), not absolute performance, is the key to understanding the evolution
of behaviour.
Campbell 52.4 Genetic analyses and the concept of inclusive fitness
provide a basis for studying the evolution of behavior
Genetic basis of behaviour
In many cases, differences in behaviour arise not from gene inactivation, but from variation in the
activity or amount of a gene product. A few examples in the book.
Genetic variation and the evolution of behaviour
Behavioural differences between closely related species are common. When behavioural variation
between populations of a species correlates with variation in environmental conditions, it may
reflect natural selection. Two case studies in the book.
Altruism
We typically assume that behaviours are selfish (they benefit the individual at the expense of
others). In discussing selflessness, we use the term altruism to describe a behaviour that reduces an
animal’s individual fitness but increases the fitness of other individuals in the population. A few
examples in the book.
Inclusive fitness
How does altruistic behaviour arise during evolution? The easiest case to consider is that of parents
sacrificing for their offspring, this act increases the fitness of the parents because it maximizes their
genetic representation in the population. By this logic, altruistic behaviour can be maintained by
evolution. Inclusive fitness (= the total effect an individual has on proliferating its genes by
producing its own offspring and by providing aid that enables other close relatives to produce
offspring).
Hamilton’s rule and kin selection: According to Hamilton, the three key variables in an act of
altruism are: the benefit of the recipient, the cost to the altruist, and the coefficient of relatedness.
Benefit (B): the average number of extra offspring that the recipient of an altruistic act produces.
Cost (C): how many fewer offspring the altruist produces.
The coefficient of relatedness (r): equals the fraction of genes that, on average, are shared.
Hamilton’s rule: rB>C natural selection favours altruism if rB>C
, Kin selection: Natural selection that thus favours altruism by enhancing the reproductive success of
relatives. Kin selection weakens with hereditary distance.
Reciprocal altruism: reciprocal altruism (= altruism that occurs between animals who are not
relatives.) is rare and limited to species with social groups stable enough that individual have many
chances to exchange aid. “Cheating”: not returning favours to individuals who had been helpful in
the past. “tit-for-tat strategy”: an individual treats another in the same way it was treated the last
time they met.
Evolution and human culture
?
Goodenough Perspectives on Animal Behaviour
9. Biological Clocks
Life evolved under cyclical conditions orchestrated by the relative movements of the earth, moon,
and sun, and the ecological conditions under which animals find themselves differ tremendously at
different times of the cycle. Life is exposed to rhythmic variations in light intensity, temperature,
relative humidity, barometric pressure, geomagnetism, cosmic radiation, and the electrostatic field.
Tidal cycles cause changes in the environment of intertidal organisms. Biological locks may have
evolved as adaptations to environmental cycles, and they provide a mechanism to synchronize
various internal processes with other internal processes.
Defining properties of clock-controlled rhythms
Biological clocks measure time at the same rate under nearly all conditions, and they have
mechanisms that reset them as needed to keep them synchronized with environmental cycles.
Persistence in constant conditions
A defining property of clock-controlled rhythms is that cycles continue in the absence of
environmental cues such as light-dark and temperature cycles. We attribute the ability to keep time
without external cues to an internal, (endogenous) biological clock.
Period: the interval between two identical points in the cycle
Circadian: daily rhythm, about 24 hours.
Circalunidian: A lunar day (tidal) rhythm
Circamonthly: monthly rhythm
Circannual: annual rhythm
When an animal is kept in constant conditions in the laboratory, the period length of its rhythms
generally deviates from that observed in nature.
Free running: the circadian period length is no longer manipulated by environmental cycles.
Entrainment by environmental cycles
Biological rhythms are generally not exactly the same length as the natural cycle. To keep from
getting wildly out of synchrony with the natural cycle, biological clocks need to be reset, or
entrained, to the cycle. Phase resetting occurs because a cue affects the clock differently depending
on when in the clock’s cycle it occurs. Entrainment is important for all organisms because it adjusts
biological rhythms to prevailing environmental cycles, it is especially important for animals living in
temperate regions.
Temperature compensation
Environmental temperature has only a slight effect on the rate at which the clock runs. This property
is called temperature compensation. It should be apparent that if the clock were as sensitive as most
other chemical reactions are to temperature changes, it would function as a thermometer, indicating
the ambient temperature by its rate of running, rather than as a timepiece. Some possible
consequences if the biological clock were affected by changes in temperature:
