ICE 1: Why do females prefer nice plumage?

It has largely been accepted that females prefer a mate that has colorful, beautiful plumage.  This is no different for the wild jungle fowl.  Until a study was done that shows male plumage isn’t genetic at all.  In fact, it is due to indirect genetic effects.  That is, the male’s plumage is determined by the other male’s genetics that he surrounds himself with.  The question then becomes, “What do females actually prefer?”

Zach, Andrew, and I formed a team.  We were tasked with generating three hypotheses, and for one of them we were to set up an experiment to test the chosen hypothesis.  Our hypothesis centered on determining the offspring’s plumage type.  We thought this was more effective than determining the female’s indirect genetic effects.  Her fecundity ultimately relies on her offspring’s mating success.  If they failed, then her line would end.

Hypothesis 1: If a female fowl mates with a socially successful male, then her offspring have a higher chance of being socially successful leading to reproductive success.

This hypothesis is determined by Hamilton’s Rule which states that rB>C where r is the coefficient of relatedness, B is the benefit and C is cost.  We determined that r is negligible because the females are independent whereas the males are in cohorts, the assumption being that the female is not related to any of the males.  B is the mate’s indirect genetic effect, and C is the offspring’s indirect genetic effect.  Although the female is hoping for nice plumage for her offspring, there is a cost before mating as the indirect genetic effects for the offspring cannot be predicted.  We don’t know who the male offspring will form a cohort with!

Hypothesis 2: Relatedness between males will increase the focal individual’s indirect genetic effects.  

Female’s choose this male for safe cost and increased genetic diversity.

This is the outbreeding hypothesis.  The male fowl perform a plucking ritual in which the dominant male plucks feathers from other males to make them “ugly” and deter females from mating with them.  In this hypothesis the males are related, so the indirect genetic effect of the focal individual increases with relatedness.  Returning, to Hamilton’s Rule, this decreases the cost for the female.  This hypothesis is assuming that there is low relatedness between the female and other males so that the offspring have genetic diversity.

Hypothesis 3: The indirect genetic effect of the father could influence a higher susceptibility to indirect genetic effects in the offspring.

This is the susceptibility hypothesis, meaning indirect genetic effects are highly plastic.  This plasticity could pass down to the offspring.  However, this would only work in a static environment where the indirect genetic effects remain constant.  In a dynamic environment, the cost is high.  In this environment, the cohorts of the offspring will greatly affect their plumage and could go many different ways.  This is the hypothesis for which we decided to set up an experiment.

We designed two null hypotheses.  The first states that the offspring will be successful across environments.  The second states that the father’s indirect genetic effects are unlinked to offspring’s indirect genetic effects.  Figure 1 shows the breeding crosses designed for our experiment.

Parental Cross with Female	F1 Static Environment Expectations	F1 Dynamic Environment Expectations
Isolated male Control 1	Random	Random
Isolated male Control 2	Random	Random
Successful Male Experimental Group 1	Nice Plumage	Susceptible to Cohort
Successful Male Experimental Group 2	Nice Plumage	Susceptible to Cohort
Unsuccessful Male Experimental Group 1	Ugly Plumage	Susceptible to Cohort
Unsuccessful Male Experimental Group 2	Ugly Plumage	Susceptible to Cohort

The offspring of the isolated male control group account for randomness.  In a static environment, the offspring should mimic their fathers, and in a dynamic environment, the offspring’s indirect genetic effect depends on their choice of cohort.  After the offspring have reached maturity, their indirect genetic effects will be measured, and compared to their father.  If they are similar in the static environment and differ widely in the dynamic environment, we can conclude that the indirect genetic effect is highly plastic.  In this scenario, the female chooses the mate on the basis that the environment will remain constant.  But as we know, that is not always the case.  This poses a great cost for mate choice in the female.