BIOC54H3 Study Guide - Midterm Guide: Polygyny Threshold Model, Lek Mating, Scramble Competition

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Reading 2- Genes, Behaviour, Selection (Chapter 2)
Nature or nurture fallacy : No trait is purely genetic. Environmental signals have an influence on
all traits. Similarly, no trait is purely environmentally determined. Neither genotype nor
environment is more important that the other.
Imprinting : A young animal’s early social interactions, usually with its parents, lead to its
learning such things as what constituted an appropriate sexual partner. Example : When Blue
Tits (BT) and Great Tits (GT) were cross fostered (BTs were reared by GTs and vice versa),
misimprinting occurred differentially. Cross fostered BTs almost all mated with GTs. But only
some of the cross fostered GTs mated with BTs. Hence mis-imprinting occurred but the extent
to which it occurred differed between species.
Birds are able to remember where they store seeds- an example of specialized traits in birds.
The birds even remember the size of the seeds stored. This is only possible by genes required to
construct the learning system and genes that respond to key sensory stimuli in the environment.
Genetic differences and Behavioural differences : Migratory birds- is migration an inherited
behavior ? experimenters in the UK kept blackcap birds confined and let them breed to make a
generation that had never experienced migration. They observed that these new birds were
restless at migration time- indicating that they wanted to migrate. When placed in a funnel
shaped cage, they kept trying to go West, an indication of their migration direction. Hence
migration is inherited. Later data confirmed that these birds migrated from Germany to Britain
(west).
Genetic basis for differential feeding : Garter snakes from 2 different areas seem to eat
different prey (both eats toads but one type eats banana slugs which are available in its area).
When young were reared such that they had never eaten anything, the ones that typically eat
banana slugs ate slugs when offered but the other did not, showing that this preference for food
was genetically based. When both types of snakes were sexually crossed, their offspring ate
both food well. Further proof that genetics is at work.
Single gene effects on development : The ability of a single gene to have a strong influence on
phenotype. Knock out experiments can be done to verify this.
Reading 3- Chapter 10- Sexual selection I : Males vs females, Intra-Sex competition
Changes in the way males and females behave when it comes to reproduction have evolved in
response to the difference in size and number of gametes produced by the sexes. Both types of
gametes are good at different things and so specialized into egg and sperm. An “intermediate”
gamete for both sexes would be less efficient.
Evolutionary change by sexual selection : The advantage which certain individuals have over
others of the same sex and species, in exclusive relation to reproduction.
Intrasexual selection : Members of one sex compete with each other for access to the other sex.
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Continuing from page 350
Discrete mating strategies : The marine isopod Paracerceis sculpta. Females look the same.
Males come in different sizes, large (alpha), medium (beta) and small (gamma), each with its
own behavioral phenotype. Alpha males protect sponges which contain females. If another
alpha male arrives, they fight. If a gamma male arrives, alpha throws the gamma out. When
alpha and beta meet in a sponge, the beta behaves like a female and the alpha courts him
(female mimicry). Through female mimicry, beta males coexist with their much larger and
stronger rivals and thereby gain access to the real females. Is this behavior conditional or
distinct? Experimenters first showed that the difference in SIZE was controlled by a single gene
with 3 alleles. To determine the reproductive success of each type of male, they put different
numbers of males and females together. The reproductive success of a male depended on the
number of females and males present in the sponge. The reproductive success of each male was
found to be almost the same. Hence this is an example of 3 distinct strategies.
Sperm competition : Evidence of competition among males with respect to the fertilization
success of their sperm. If the sperm of some males have a consistent advantage in the race to
fertilize eggs, then counting up a male’s spawning or copulatory partners will not measure his
fitness accurately.
Example : The black winged damselfly removes rival sperm from a female before mating, using a
spiky penis that acts as a scrub. He removes between 90 and 100% of sperm from the female
before inseminating her.
Mate Guarding: males may keep female occupied after mating, lure away competitiors or seal
the tract of females after mating. There is some cost as the male can’t go around and fuck more
females and pass on his sperm but he is more likely to be the daddy of the donkeys that he
actually guards.
Example :Wablers : Experimenter placed a fake egg in the nest just before the female was due
to lay an egg. The male stopped guarding once he saw the egg. She could then be fertilized by
another male.
Reading 4- Chapter 10- Sexual Selection II : Inter-sex Mate Choice, Mating Systems
Sexual selection and mate choice : eg. Redback males offer themselves as a “nuptial gift”
because the cost of being eaten is low- it is unlikely they will find another mate. Females select
for males that offer themselves and these males tend to fertilize more eggs.
Good Parent theory: A male’s color, ornamentation and courtship behavior are sexually
selected indicators of a male’s capacity to provide parental care.
Long tailed widowbird : Experiment done where tails were shortened or lengthened. Longer
tailed males had better success.
Cryptic female choice: choice generally hidden from view of researchers that is based on the
internal workings of the female’s reproductive machinery.
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