SuGGESTIoNS FoR FuRTHER READING
As with so many topics in evolutionary biology,
Charles Darwin wrote not only the first but also
some of the most insightful thoughts on sexual
selection. He laid out the principles of sexual
selection in On the Origin of Species (John
Murray, london, 1859), then elaborated them
in his longest book, The Descent of Man and
Selection in Relation to Sex (John Murray, lon-
don, 1871). both books have many important
ideas that still have not been fully explored.
Insects are by far the most diverse group of
animals, so it is not surprising that they have a
remarkable range of strange and fascinating
forms of sexual selection. The book by D. M.
Shuker and l. W. Simmons, The Evolution of In-
sect Mating Systems (oxford university Press,
oxford, 2014) is a recent collection of articles
by leading researchers in that field.
Males have evolved a remarkable variety of
weapons to fight each other. These weapons,
and their implications for humans, are ex-
plored (and beautifully illustrated) in a book by
D. J. Emlen, Animal Weapons: The Evolution of
Battle (Henry Holt, New York NY, 2014).An overview of the diversity and evolution of
sex determination mechanisms is given by D.
bachtrog and colleagues in “Sex determina-
tion: Why so many ways of doing it?” (PLOS
Biology 12: e1001899, 2014).
A witty yet scholarly exploration of some of the
more interesting and unusual sides of sex in
the animal kingdom is olivia Judson’s popular
book, Dr. Tatiana’s Sex Advice to All Creation
(Henry Holt, New York NY, 2013).
The definitive work on the evolution of sex ratios
and sex allocation is S. West’s Sex Alloca-
tion (Princeton university Press, Princeton NJ,
2009).
The evolution of sexual reproduction and re-
combination is one of the most fascinating but
difficult topics in evolutionary genetics. lucid
introductions have been written by several of
the leading researchers in the field: S. P. otto
(“The evolutionary enigma of sex,” Amer. Nat.
174: S1–S14, 2009), N. H. barton (“Why sex and
recombination?”, Cold Spring Harbor Symp.
Quant. Biol. 74: 187–195, 2009), and C. M.
lively and l. T. Morran (“The ecology of sexual
reproduction,” J. Evol. Biol. 27: 1292–1303).PRoblEMS AND DISCuSSIoN ToPICS
- Populations of some species of fish, insects, and
crustaceans consist of both sexually and asexu-
ally reproducing individuals. Would you expect
such populations to become entirely asexual or
sexual? What factors might maintain both repro-
ductive modes? How might studies of these
species shed light on the factors that maintain
sexual reproduction? - Many parthenogenetic species of plants and ani-
mals are known to be genetically highly variable.
What processes might account for this variation? - The text says that asexual, parthenogenetic spe-
cies are typically found on the tips of the tree
of life: their closest relatives reproduce sexually.
Explain this pattern. - Would you expect sexual selection to increase or
decrease adaptation of a population to its envi-
ronment? Do the pleiotropic effects and good
genes mechanism for the evolution of female
preferences differ in their implications for adap-
tation to the environment? - In many socially monogamous species of par-
rots, both sexes are brilliantly colored. Is sexual
selection likely to be responsible for the color-
ation in both sexes? How can there be sexual
selection in pair-bonding species with a 1:1 sex
ratio, given that every individual presumably
obtains a mate? Which of the types of sexual
selection described in this chapter might
account for bright coloration in both sexes of
these species?- In many reptiles, including crocodiles and many
turtles, sex is determined by temperature during
early development. Many scientists expect that
as Earth’s climate warms, the sex ratios in these
species may become highly biased, further
endangering these animals. Do some outside
research and conclude whether this concern
is warranted and what might happen to these
populations as a result. - Anisogamy is the term for sexual dimorphism in
gamete size. Discuss the evolution of anisogamy
from an ancestor in which gametes had equal
sizes. What factors would lead to a divergence
in gamete size among members of a popula-
tion? Are females of one lineage homologous
with the females of distantly related lineages
(for example, female birds and female flowering
plants)? That is, how many times might the sex
roles have evolved? - What aspects of human behavior, physiology,
and morphology might be explained by sexual
selection? What are the alternative hypotheses,
and how might we determine which is (or are)
correct?
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