Evolution, 4th Edition

258 CHAPTER 10

nothing but make sexual displays (FIGURE 10.14). Their complex courtship

display shows off the males’ elaborate plumage. Females visit the lek, mate

with the male of their choice, and then leave to rear the offspring with no

help from their mate. In lekking species, the females receive no direct ben-

efit whatsoever from the males. There must be some other cause for the

evolution of female preferences for these elaborate male displays.

One such cause is natural selection acting on pleiotropic effects of genes

that affect female mate choice [27]. Recall from Chapter 4 that virtually all

genes have pleiotropic effects, meaning they affect multiple traits. An allele

that changes a female’s mating preference will typically also change other

things about her. The guppy (Poecilia reticulata) is a small tropical freshwater

fish with brightly colored males. Females have mating preferences for males

with more orange on their body (see Figure 6.11). Experiments show that

both females and males are attracted to small orange discs, which they peck

at as if to eat [43]. A plausible hypothesis is that guppies evolved an attrac-

tion to round orange objects because they feed on orange fruit, and as a side

effect females are now attracted to orange males.

Mating preferences that evolved by selection on pleiotropic effects are

called perceptual biases [44]. These biases are sometimes surprising:

experiments with fishes, frogs, and birds show that females of some species

are attracted to signals that males of their own species do not even make

(FIGURE 10.15). In these cases, it appears that the female mating prefer-

ences are side effects of features of the sensory system that evolved for rea-

sons unrelated to mating, before the male signals were even present.

Mating preferences can arise as side effects of how the courtship signals

interact with the environment. As signals propagate, they are filtered by

the environment they pass through. Colors are transmitted differentially

through water depending on depth and the amount of sediment in the

water, for example, and sounds with different frequencies attenuate at different rates

in open habitat and forest. As a result, different mating displays can be favored by

sexual selection depending on the habitat where they are performed [44].

A third way that female mating preferences evolve is called the good genes

mechanism. Some male displays are correlated with traits that increase lifetime

FIGURE 10.14 Males of the Andean cock-of-

the-rock (Rupicola peruvianus) perform mating

displays together on leks. Females visit the lek,

mate with the male of their choice, and then leave

to raise the offspring alone. There is no opportu-

nity for direct benefits to females in lek-breeding

species.

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_10.15.ai Date 01-25-17

Preference for

sword evolves

Sword

evolves Swordtails

Priapella

Xiphophorus (^) m
m
FIGURE 10.15 Some female mating preferences are perceptual
biases that evolved before the origin of the male trait on which
they act. Males of swordtails (such as this green swordtail, Xiphoph-
orus helleri) have dramatic swords that attract females. Males of a
closely related species (Priapella olmecae) lack the sword, but the
females prefer males with a sword that has been surgically added
[6]. The phylogeny of these fishes (in green) shows that the prefer-
ence for the sword evolved before the sword itself did. (Xiphoph-
orus photo courtesy of Alexandra Basolo.)
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