Midterm Answer key

1) Progeny are on average half related and they can be even unrelated because the transmission of alleles from parents to progeny is probabilistic and for any gene there is a ¼ chance of the progeny sharing exactly the same two identical alleles, a ½ change of receiving only one allele that is identical, and ¼ chance of not sharing any alleles. A simple diagram with each of the four possible alleles labeled illustrates these probabilistic outcomes: Each line (from top parent row to bottom progeny row) reflects a ½ chance of that outcome:

2) The degree of elaboration in some signaling trait is under selection in males and the preference for these traits is under selection in females.

The more elaborate trait is favored in males because they mate with all choosy females and half of the females that are indifferent (random) in their choice, thus receiving more copulations than the male with the less elaborate trait.

Likewise, females with the choosy trait will produce sexy sons with elaborate traits in the next generation, thereby receiving a fitness boost from their choice of an eleaborate mate.

Runaway is an example of maladaptive evolution because even if the elaborate trait has a fitness cost to the males (in survival) females will still be favored to pick them and thus increase the frequency of these debilitating ornaments from one generation to the next.

You can also supply a diagram of the fitness of males (or the verbal explanation above)

Table 3.1 Fitness of males.		Male Trait
		Elaborate Male (E)	Normal male (N)
Female Choice	Choosy (C)	3/2	0
	Non-choosy (+)	1/2	1/2

3) The costs of territoriality reflect the energy required to defend a larger and larger space (linear costs per area). The benefits of territorial are governed by the marginal value theorem and the benefits asymptote at higher territory areas.

The costs and benefits of a territory determine the economic defendability of a territory and reflect a tradeoff. A territory size of A would be the minimum size of territory in which the cost of defense equals the benefit from territoriality. Conversely, a territory size of B would be the maximum size territory at which the benefit still exceeds the cost. A territory of size X would maximize energy gain because net gain = benefits-costs is the greatest possible (double-headed arrow).

4) The three basic strategies of males in mating are aggressive territory holding male that has high Resource Holding Potential able to hold onto a large harem, a more cooperative territorial male type that tends towards monogamy, and a male strategy that abandons territorial in favor of a sneak/female mimicry strateg

No strategy wins in the long run because each is beaten by a second while at the same time beating a third, which can be illustrated with a payoff matrix:

Common type in the population

Rare type:	Rock	Paper	Scissors
Rock	1	½	2
Paper	2	1	½
Scissors	½	2	1

Where W_P,R > W_R,R > W_S,R, W_S,P > W_P,P > W_R,P, W_R,S > W_S,S > W_P,S (inequalities are not strictly necessary, a verbal explanation of such intransitive payoffs would suffice).

In biological terms the orange lizards are strong and have high testosterone but they are vulnerable to a sneaky strategy that can invade their harem

The cooperate blue strategy does not have to fight with their cooperative neighbors and can thus defend against sneak, but each is vulnerable to invasion by the aggressive orange

The sneaky yellow can use mimicry and does not have to defend a territory but this strategy is only effective against the harem holding orange, not the cooperative blue

(or something similar)