APS 209 Animal Behaviour

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APS 209 Animal Behaviour
Francis L. W. Ratnieks Laboratory of Apiculture
Social Insects
Department of Animal Plant Sciences University
of Sheffield
Lecture 2 Counter Intuitive Darwinian Logic of
Natural Selection on Behaviour
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Aims Objectives
Aims 1. To present the logic behind group
selection and individual level selection (
between group and within group) and why group
selection is unlikely to be a major force in
evolution. 2. To give examples of
counter-intuitive Darwinian logic. 3. To present
scientific papers on animal behaviour and to
assist students in understanding these.
Objectives 1. Understand group versus
individual level selection. 2. Read and
understand the scientific papers, particularly
their conclusions and the way the data are
presented. 3. Learn examples of
counter-intuitive Darwinian logic.
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• Why do humans eat so much candy and drink so many
  soft drinks? Which of the following explanations
  are proximate hypotheses, and which are ultimate
  hypotheses?
• P proximate (How) U ultimate (Why)
• Candy and soft drinks contain sugar , which
  tastes sweet to people.
• Sweet taste is remembered as good the memory of
  pleasure leads people to eat or drink more of the
  same.
• Sugar, which is present in candy and soft
  drinks, is an energy source that helps keep
  people alive.
• Our primate ancestors depended on sugar-rich
  fruits from these ancestors. we have inherited
  the same kind of taste perceptions that they had.
  
• The genetic information in our bodies shapes the
  development of nerve cells that provide
  perceptions of sweetness and pleasure.
• In the past, those individuals who liked sugar
  left more descendants that those who were
  indifferent to sweet-tasting foods.
• The sensory input from taste receptors in the
  tongue to selected brain cells leads to a
  positively reinforcing sensation of sweetness.

P
P
U
U
P
U
P
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Group Selection Selection Within Between Groups
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Infanticide in Hanuman langurs
Live in social groups 1 large male, several
females, young Males gets displaced Violent
struggle Infants die New males the prime
suspect in most cases
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Infanticide Natural Selection
Why do males kill offspring? Risky behaviour
females may attack them Does infanticide advance
a males reproductive success? If so how? Three
different kinds of hypothesis
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Infanticide Natural Selection
H 1 Non-evolutionary Social pathology bought on
by overcrowding H 2 Favoured by natural
selection, at individual level Infanticide makes
females able to get pregnant sooner. Male becomes
a father sooner, and has more offspring before he
is himself overthrown by another male. H 3
Favoured by natural selection, group
level Infanticide reduces overcrowding which
would cause the group to overexploit its food or
other resources.
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Group Selection
Group selection arguments are sometimes
identifiable because of a specific set of words
used such as for the good of the species. More
usually, there is an implicit assumption that
something is good for the species, or the
long-term survival of the population. Although
group selection can occur, the circumstances
which favour group selection as a major selective
force are rare.
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The Logic of Group Selection
Many behaviours of individuals are adaptations
which assist the survival of their group. For
example, reproducing less to avoid
overexploitation of resources. How can this be
selectively favoured? Answer. By selection of
groups. Groups with more individuals who practice
self restraint or do something else beneficial to
the group survive better. Problem. Within group
selection will often be stronger. Groups of the
necessary sort are rare.
Many behaviours previously given a group
selection logic can be adequately explained by
selection acting at the individual level.
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Within Group Selection Advantage to
Time 1
Time 2
Time 3
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Between Group Selection Advantage to
Competition between groups for space or resources
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The Logic of Group Selection
The previous two slides show the logic of
selection at both the within group ( among
individuals) and between group levels. The
example is not particularly realistic but shows
the essence of the logic. There are two types of
individuals. One (red solid circles) does not
restrain its own reproduction. The other (blue
open circles) spends time defending the group and
so does not reproduce as rapidly. Within group
selection favours the red individuals. But if two
groups are competing for space, the group with
more blue individuals has the advantage. So red
is favoured at the within group level and blue at
the between group level. The blue individuals
will only be favoured if individual are
relatively long lived in relation to the life
span of groups, if groups are well
differentiated, and if inter-group competition is
important. These circumstances are not common in
nature.
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Infanticide
Pages 17-18 discuss infanticide which occurs
widely, with examples in mammals, birds, and
insects.
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Infanticide in Meerkats (Special Reading Young
Clutton-Brock 2006)
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Infanticide in Meerkats
The survival of litters of dominant females was
significantly greater when there were no other
pregnant females in the group than when there
were other pregnant females. P lt 0.001
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Infanticide in Meerkats
The survival of litters of subordinate females
was significantly greater when there were no
other pregnant females in the group than when
there were other pregnant females. P lt 0.001
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Infanticide in Meerkats
In lions and langurs infanticide is carried out
by males. In giant water bugs by females.
Infanticide also occurs in meerkats, a social
mammal found in South Africa. In meerkat groups,
there is a dominant female and a few subordinate
females who may breed. Infanticide is carried out
by pregnant females. By killing another females
litter, her own offspring probably have a higher
chance of surviving given that the group probably
does not have the resources to rear two litters
at the same time. Infanticide of the dominants
newly born litter is more likely if one of the
subordinates is pregnant. Infanticide of a
subordinates newly born litter is more likely if
another female is also pregnant. Young, A. J.,
Clutton-Brock, T. 2006. Infanticide by
subordinates influences reproductive sharing in
cooperatively breeding meerkats. Biology Letters
(published on line).
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Self Sacrifice Sting Autotomy in Worker Honey
Bees
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Worker Honey Bee Sting Autotomy
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Detachable Sting
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Barbed Sting
Easy to go in Hard to get out
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Barbed Sting
Easy to go in Hard to get out
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Pumping Venom Releasing Alarm Pheromone
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Worker Alarm Pheromone 1
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Self Sacrifice by Honey Bee Workers
Insect workers normally do not reproduce
directly. Instead, they rear their brothers and
sisters. This reproductive altruism is favoured
by natural selection because workers normally
rear close relatives. In this way the workers
genes are passed on indirectly. Worker altruism
reaches its most spectacular level when workers
deliberately sacrifice their life for the colony.
This occurs in many species in several different
ways. The sting of the honey bee has
backward-pointing barbs, and lodges firmly into
the flesh of an attacking vertebrate. The worker
then walks away and the sting tears out, leaving
the worker to die soon after. This is not a
mistake. It is designed to happen. What is the
advantage of this sting autotomy (self
cutting). The sting continues to pump venom after
being detached from the workers body, and also
releases an alarm pheromone (which smells of
banana) which guides more workers to the
intruder.
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Self Sacrifice Forelius Ants That Close the Nest
Entrance
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(No Transcript)
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Unusual Reproductive Behaviours
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Sexual Selection
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Strange Darwinian Logic
Sex change in Anthias fish
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Self Sacrifice Self Sacrifice by Male Redback
Spiders (Special Reading Andrade 1996)
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Garden spider Waiting for Female to Mature
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Tied Down Female
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Nuptial gift
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Nephila Female Dwarf Male
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Black Widow
Latrodectus mactans black widow N.
America Latrodectus hasselti redback
spider Australia Latin Latro, servant, robber
Greek Dektes, a biter
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Redback Spider Background Information
A species of black widow spider from Western
Australia Females much larger than males (c. 450
v 5 mg) Mature female lives much longer than
male c. 2 years v 2-4 months Males mature at a
younger age Many males per female up to 6 males
in a females web Multiple mating by female does
occur in nature 17 wild caught had mated to 2
or 3 males Male deliberately places himself in
females jaws Andrade, M. C. B. 1996. Sexual
selection for male sacrifice in the Australian
redback spider. Science 271 70-72.
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Redback Spider Background Information
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Redback Spider Copulation
(A) The male first aligns himself facing forward
on the underside of the females abdomen while he
inserts his sperm-transferring organ into her
reproductive tract. (B) He then elevates his
body and (C) somersaults backwards into the
jaws of his partner. She may oblige by consuming
him while sperm transfer takes place. After
Forster 391.
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Benefit of Being Cannibalised to 2nd male
Effect of copulation duration on second male
paternity (female already mated)
Means C (cannibalised)
y 0.0710.034x r2 0.49 P 0.025 n 10
Means NC (not cannibalised)
0
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Benefit of Being Cannibalised to 1st male
Effect of cannibalism on first male
paternity Female is unmated Male is
cannibalised 6/9 females reject second male
(67) Male is not cannibalised 1/23 females
reject second male (4) Difference is highly
significant Female less likely to remate if first
male cannibalised P 0.001 (Fisher Exact Test)
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Genital Damage, Kicking, and Early Death (Special
Reading Crudginton Siva-Jothy 2000)
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Callosbruchus maculatus
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Aedeagus (Penis) of Bean Beetle Callosobruchus
maculatus
This SEM photo shows the male beetles spiny
penis. Crudgington, H., Siva-Jothy, M. T. 2000.
Genital damage, kicking and early death. Nature
407 855-856.
receiver (tongue extended)
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Battle of the Sexes
Mating is in many ways a mutualistic act (both
partners benefit), but there are also conflicts
between the male and the female. For example, the
male would prefer it if the female does not mate
with another male but rather uses his sperm to
fertilize her eggs. Male intromittent organ
carries spines This is not to remove the sperm
of other males, as happens in some species such
as damselflies Examination of in situ genitalia
showed that the spines penetrate the lining of
the genital tract Females kick males towards the
end of copulation Why do females kick their
mates?
receiver (tongue extended)
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Data from Bean Beetle Paper
Genital damage to females (Area damaged,
mm2) Virgin females 0 Once mated females 113 n
20 P lt0.0001 Copulation duration
(seconds) 1) Non-kicking females 867 2)
Kicking females (control operated) 501 3)
Kicking females (untreated) 587 P lt0.001 (group
1 copulations take longer than either 2 or
3) Genital damage of kicking v non-kicking
females (mm2) Kicking 147 non-kicking 272 P
lt0.02 Female fecundity no difference, twice v.
once mated (P gt0.05) Female lifespan Single
mated live significantly longer than double mated
(P lt 0.02)
receiver (tongue extended)