Chapter 18
Evolution of
reproductive behavior
(2nd lecture)
A male Resplendent Quetzal
Male-male competition
in red deer
Males engage in fierce
competition to secure
the best breeding
territories
Once a male has secured its breeding territory, he performs a
protracted 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 volcanolike 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 gift
In 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 ways
Here 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 the
ampulla 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 barn
swallows. 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 demonstrate
their 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 providing
robust 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?