WEEK 1 – Jan 15th and 16th 2014 Natural selection

WEEK 1 – Jan 15th and 16th 2014
Natural selection and how it works
Raghav Rajan
Bio 335 – Animal Behavior
Jan 15th 2014
16th January 2014
Bio 335 - Animal behavior - Week 2 - Lecture 4
1
Ultimate questions – how did the behavior
evolve?
Proximate
mechanisms
What causes the behavior? How does it
change over development?
Can be answered but in the lab (not natural
settings
BEHAVIOR
What are the effects on survival, reproductive
success?
Can be answered in various ways – sometimes
practically difficult
How did it evolve?
Difficult to answer, but we can compare across
livingspecies and guess
16th January 2014
Bio 335 - Animal behavior - Week 2 - Lecture 4
Ultimate
mechanisms
2
Foundations of ethology
●
Natural selection
–
Any trait that provides a reproductive advantage
would be favoured
–
How does natural selection work?
●
Individual learning
●
Cultural transmission
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Another case study for natural selection – guppy
evolution
●
Guppies breed quickly
●
Ideal for studies of natural selection and behavior
●
Widely distributed
●
Have also been introduced in many different
habitats
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Guppies often present in two different habitats
on either side of a waterfall
●
Upstream, low predation stream
●
Downstream high-predation stream
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Natural selection has produced different results
at two sites with different predation levels
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Guppy predators differ in size upstream and
downstream
●
Larger predators downstream
●
Smaller predator upstream – can only eat small guppies
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Predation has also affected other behaviors
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Predation affects schooling (group size) and
predator watching behavior
●
●
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Bio 335 - Animal behavior - Week 2 - Lecture 4
More dense
schools in
high
predation
sites
High
predation
sites
associated
with more
and closer
predator
inspection
9
Testing hypothesis regarding evolution of guppy
anti-predator behavior - transplants
●
CP Haskins, guppy population biology researcher
transferred 200 guppies from high to low predation
site (guppy free)
●
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Change in characteristics according to level of
predation
●
Transplanted guppies showed characteristics of lowpredation site guppies
●
Also, they colonized downstream high predation site
●
And showed high-predation site characteristics
●
Did they colonize slowly?
–
●
Lose behaviors and re-evolve them?
Did they colonize fast?
–
Retained original behavior?
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Guppy – evolution of behaviors can be pretty
quick too!
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Result of natural selection - adaptations
●
●
Adaptations are traits associated with highest
fitness among a specified set of behaviors in a
specified environment
Reeve and Sherman argued that adaptations need
not be only the result of natural selection
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Brood parasitism in wood ducks – an example of
maladaptive behavior
●
●
●
16th January 2014
Brood parasitism – laying
eggs in a different nest
Don't have to take care of
them
But your genes are passed
on
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Wood ducks – an example
●
●
Female lays an egg per day and then spends rest of
day foraging
Males stay during egg-laying and then abandon
nest when females begin to incubate
●
Full clutch – about 10-12 eggs
●
Approx. 75% of female body mass
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A number of man-made nests were parasitized
and abandoned
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Why are so many nests parasitised when empty
nest boxes are available?
●
Semel and Sherman formulated different
hypothesis
–
Dump eggs to reduce predation on all their eggs at
once
–
Forced to parasitize for lack of suitable, hidden nests
–
Parasitize when own nest is destroyed
–
Benefit from placing eggs in relatives' nests
–
Enhance reproductive success by laying eggs in any
available nest
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Infact, level of nest parasitism affects both
number of eggs and proportion that hatch
●
Greater parasitism is associated with higher clutch
size and fewer offspring (more eggs abandoned)
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Egg dumping might be a maladaptive behavior
due to visible man-made nests
●
●
●
In the wild, nests are well
concealed
Parasitic females may have
benefited from egg dumping in
such concealed nests
Continued such behavior, but
now so many visible nests
confused the birds
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Finally, phylogeny and the study of animal
behavior
●
●
●
Common ancestor or convergent evolution?
Construct phylogenetic trees are first constructed –
based on homologies (not homoplasies)
–
polarity of direction of historical change in a trait
–
DNA sequence similarties and differences
Map behavioral traits onto this tree
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Wings - Homoplasy (analogy) not homology
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Phylogeny, mating systems and male aggression
●
●
●
●
Theories that males are more aggressive when
sexually receptive females are present
Wasps of genus Nasonia
Parasitic – lay between 20-140 eggs in pupae of
flesh flies, blow flies
Males emerge and remain on pupae surface to
court emerging females
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Male-male aggression higher in some species
●
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Bio 335 - Animal behavior - Week 2 - Lecture 4
Measured
by watching
males on a
fly pupa for
upto 30
mins
23
Level of within-host mating differs in these 3
species
●
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Bio 335 - Animal behavior - Week 2 - Lecture 4
And so
number of
sexually
receptive
females
emerging
varies in
these 3
species
24
Male-male aggression and female receptivity
present in oldest species
●
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Others intermediate and
derived states
Bio 335 - Animal behavior - Week 2 - Lecture 4
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Ultimate questions – how did the behavior
evolve?
Proximate
mechanisms
What causes the behavior? How does it
change over development?
Can be answered but in the lab (not natural
settings
BEHAVIOR
What are the effects on survival, reproductive
success?
Can be answered in various ways – sometimes
practically difficult
How did it evolve?
Difficult to answer, but we can compare across
livingspecies and guess
16th January 2014
Bio 335 - Animal behavior - Week 2 - Lecture 4
Ultimate
mechanisms
26
Foundations of ethology
●
Natural selection
–
Any trait that provides a reproductive advantage
would be favoured
–
How does natural selection work?
●
Individual learning
●
Cultural transmission
16th January 2014
Bio 335 - Animal behavior - Week 2 - Lecture 4
27