Evolution__3rd_Edition

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Study and review questions
1 What is the cost of sex in a species in which the sex
ratio at birth is: (a) 1 male : 2 females, and (b) 2 males :
1 female?
2 (a) What condition is required of the rate of
deleterious mutation for natural selection to favor
sexual over asexual reproduction? Does reason and
evidence suggest that the condition is met naturally?
(b) Draw the relation between the number of deleterious
mutations in an organism and its fitness that is required
for sex and recombination to be advantageous (include
a specification of the y-axis). What form is arguably true
in reality?
3 What would you investigate in order to determine
whether sex is favored by host–parasitic coevolution?
4 Why does a male character have to be costly
(a handicap) in order to signal genetic quality?
CHAPTER 12 / Adaptations in Sexual Reproduction 343
One further related theme is the possibility of destroying HIV by enhancing its mutation
rate: Holmes (2000a) is a popular piece on it.
The other main theory is parasitic. Hamilton (2001) is volume 2 of his collected
papers and contains all his key papers on sex, together with introductions that update
the literature reviews. Otto & Lenormand (2002) discuss the theory, as do Barton &
Charlesworth (1998). Lively (1996) introduces his research. Chapter 22 contains further
references on parasite–host coevolution generally; and see Simmons (1996) on the
genetics of parasite–host relations in plants.
The evolution of sex was the topic of special issues of three journals recently: Science
September 25, 1998 (vol. 281, pp. 1979–2008), Journal of Evolutionary Biology (vol. 12,
no. 6, 1999), and Nature Reviews Genetics (vol. 3, no. 4, 2002). The Journal of
Evolutionary Biology (sometimes informally referred to as the journal of evil biology)
special issue contains a “target” article by West et al., together with commentaries by
many expert authors. West et al. argue that the mutational and parasitic theories may
act jointly to maintain sex, rather than being alternatives.
For both sexual selection and the sex ratio, Dawkins (1989a) is a good introduction.
For sexual selection, Andersson (1994) is a comprehensive review; Cronin (1991) is
another clear introduction and is good on history and the broader context. Møller
(1994) describes his work on swallows. On female choice for good genes, see also
Wilkinson et al. (1998)’s work on stalk-eyed flies. On antagonistic coevolution, further
results in the same vein as Holland & Rice (1999) are reported by Hosken et al. (2001)
and by Civetta & Clark (2000).
On sex ratios, Fisher (1930) is the classic source. West et al. (2000) is a short review
and Hardy (2002) is an edited volume on modern research. Hewison & Gaillard (1999)
review another deviation a the Trivers & Willard (1973) effect a in ungulates.
5 In Fisher’s runaway theory, what maintains the female
preference for extreme males a why does the preference
not evolutionarily disappear?
6 If one male can fertilize several females in a species,
why do parents not produce a sex ratio of many
daughters per son?
7 In terms of the modes of selection (or fitness regimes)
discussed in Chapter 5, what kind of selection operates in
Fisher’s model of: (a) female choice, and (b) the sex ratio?
8 [This question draws on material in all three chapters
in Part 3.] If organisms in a polygynous species produce
a 50: 50 sex ratio in their offspring, is it a perfect
adaptation from the viewpoint of: (a) the individual
organism, and (b) the group of organisms? What general
moral about the perfection of adaptation does the
example illustrate?