BIO220H1 Lecture Notes - Lecture 3: Great Reed Warbler, Junglefowl, Barn Swallow

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16 Jan 2019
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Intersexual Selection & Mate Choice
Female Choice
Introduction to the problem
Examples of female choice in action
The benefit of female choice (direct and indirect benefits)
Why do they choose arbitrary traits? Why these traits?
Female Choice
Any female trait (behaviour, morphology) that biases the mating success of males
toward the “preferred” type (filtering males)
We will use mating bias, female preference, female choice to mean the
same thing
No implied sense of beauty
As we will see, male choice occurs in some species, and is simply the reverse.
By what mechanisms are females choosing?
Visual stimulation
Long‐tailed widowbird
Satin bower bird
Scorpionfly
Barn swallow
Cichlid fish
Field cricket
Jungle fowl
Acoustical stimulation
Field cricket
Woodhouse’s toad
Great reed warbler
Túngara frog
Olfactory stimulation
Mouse
Cockroach
Moth
Tactile stimulation
Sierra dome spider
Sex dimorphismdifferent elaborations
How to define which trait?
e.g. tail feather
Tail manipulation experiment
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QUESTION:
Are long tails preferred by females?
EXPERIMENT:
Manipulate tail length
Experiment (4 treatment groups)
Natural tail length (N) control
Reduced tail length (R)
Elongated tail length (L)
Sham surgery (S) cut the tail and glue it backadditional control
PREDICTIONS:
Mating success
(BEST) L > N = S > R (WORST)
Results:
Before treatment
R, N, S, L have about the same female nestsabout the same selection by females
After treatment
R, N are not significantly different
L has significant increase in female nests
This study also asked:
Does tail length impact male‐male competition?
Are long‐tailed males better at holding territory?
The answer was no.
Tail length seems only to influence female choice
Only affect intersexual selection
Female preference for eyespots in peacock tails
EXPERIMENT 1: Reduction of eye spot number (clipping tail feathers)
EXPERIMENT 2: Alter eye spot colour
Another experiment: Female preference for complex in Túngara Frog
Why doesn’t all males make complex call? Frog-eating bat prefer complex calls too!
Call complexity
predation against sex selection
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