Chapter 18Evolution of

reproductive behavior(2nd lecture)

A male Resplendent Quetzal

Male-male competition in red deer

Males engage in fiercecompetition to secure

the best breedingterritories

Once a male has secured its breeding territory, he performs aprotracted and exhausting sessions of bellowing. Females “prefer” to

mate with males that have the best territory and bellowing ability.

The relationship between social dominance and reproductive success is not straightforward

Some males adopt an alternative mating tactics. For instance, they play

a nonaggressive role as a satellite male, and sneak copulations whenever

possible

A satellite male Great Plains toad (left) crouches by a calling male

(right), waiting to intercept females attracted by his signals

Six subordinate male bighorn sheep trail after a dominant male, who

stands between them and the female with whom he will mate at intervals

Ways in which females and males attempt to control reproduction while interacting with each other

Female mate choice in relation to bower size in a cichlid fish

Males in this species build volcano-like bowers of sand in which they court visiting females. Females

enter tall bowers (mean height = 25 cm) more frequently than they do small ones (mean height = 10 cm)

and mate with the male.

On the value of a large prenuptial giftIn the hangingfly

A male hangingfly has just captured a moth, and is advertising the availability of this gift by releasing a pheromone from abdominal glands

The larger the prenuptial gift, the

longer the mating, and hence the more sperm

the male is able to pass to the female

Post-copulatory mate choice

Rooster fowl

Female fowl eject the sperm of

subdominant males, while retaining the sperm of preferred, dominant roosters

Males can provide for offspring in a variety of waysHere a female katydid is eating the large and nutritious spermatophore that was attached to

her ovipositor by a male during copulation. As she ingests the spermatophore, sperm from theampulla enter her reproductive tract. When she finishes the spermatophore, she ingests the

sperm ampulla. Thus, the larger the spermatophore, the more sperm enter her reproductive tract.

Sperm ampulla

Spermatophore

The effect of spermatophore consumption on the weight and number of eggs produced by female katydids

Three theories to explain why extreme male ornamentation and striking courtship displays

evolved in species in which males fail to provide parental care or any other material benefits to their

mates

How can we evaluate the merits of the healthy mate hypothesis?

Anders Moller conducted a rigorous test of this hypothesis with barnswallows. Males contain long tail feathers that that they display prominently to

females in courtship flights prior to pair bonding.

Moller hypothesized that females should prefer males with traits that demonstratetheir resistance to ectoparasites. Accordingly, extravagant tail feathers could be a

“parasite resistance indicator”

Natural variation in tail feather length

Moller tested 4 predictions

1. Barn swallows must be afflicted by parasites that reduce fitness

2. There must be heritable variation among males in resistance to some of these parasites

3. Variation in parasite infestation must be expressed visually in the ornaments that they possess

4. Females must prefer males with traits that signal reduced parasite load

He obtained evidence consistent with all of these predictions, thereby providingrobust support for the “”healthy mate” (and good genes) hypothesis in barn swallows

Do female peacocks prefer the males with the most elaborate tail

feather display?If so, do these males have “good

genes”—i.e., ones that confer higher survivorship on offspring?

After 20 eyespots were removed from each male’s feather display (Expmtl.), they

averaged significantly fewer copulations than they had during the previous year (Control)

Male peacocks with more eyespots on their tails sired offspring that survived better when

released from captivity into an English woodland park

So, where do we stand with respect to these hypotheses?