Biology Reference
In-Depth Information
Therefore, one advantage of choosing redder males is that females get a healthy male,
better able to fan and protect her eggs and young. However, further experiments showed
that healthy males were also likely to provide 'good genes' for the female's offspring,
namely alleles which confer resistance to current infections, just as hypothesized by
Hamilton and Zuk (1982). The Major Histocompatibility Complex (MHC for short) is a
cluster of genes which codes for MHC molecules (glycoproteins) which help fight parasite
infections. Different MHC molecules recognize and bind different foreign peptides, which
are then destroyed (the details are complex and Milinski (2006a) provides a good review).
The MHC contains the most polymorphic gene loci known in vertebrates, so individuals
vary enormously in their MHC profile. Females are able to assess a male's MHC profile by
odour, because MHC gene products are fragrant. In laboratory experiments where
females were given choices between the odours of different males, they preferred the
odours of males whose MHC alleles provided the optimal complement to their own
alleles, including alleles that provided resistance against the current prevailing infections
(Reusch
et al
., 2001; Eizaguirre
et al
., 2009). Therefore, by choosing healthy males,
females gain genetic benefits for their offspring as well as better parental care.
… and males
whose MHC
alleles provide a
good compliment
to their own. So
female choice
leads to genetic
benefits as well
as better
parental care
Sexual selection in females
and male choice
Female ornaments
When males make a large contribution to parental investment, males may be choosy
about whom they mate with; this can lead to sexual selection in females, who evolve
traits to increase their access to males (Fig. 7.13a). For example, in monogamous birds
(a)
(b)
Fig. 7.13
Sexual ornaments in females. (a) In great crested grebes, both sexes have head-feather
ornaments, likely to have evolved through mutual mate choice. Photo © osf.co.uk. All rights reserved.
(b) Sexual swellings in a female Chacma baboon,
Papio ursinus
, from the Cape Peninsula, South Africa.
Photo © Esme Beamish.
