A．Adult female wasps are capable of storing sperm.B．Fem……
TEXT F
The evolution of sex
ratios has produced, in most plants and animals with separate sexes,
approximately equal numbers of males and females. Why should this be so Two
main kinds of answers have been offered. One is couched in terms of advantage to
population. It is argued that the sex ratio will evolve so as to maximize the
number of meetings between individuals of the opposite sex. This is essentially
a "group selection" argument. The other, and in my view correct, type of answer
was first put forward by Fisher in 1930. This "genetic" argument starts from the
assumption that genes can influence the relative numbers of male and female
offspring produced by an individual carrying the genes. That sex ratio will be
favored which maximizes the number of descendants an individual will have and
hence the number of gene copies transmitted. Suppose that the population
consisted mostly of females: then an individual who produced sons only would
have more grand children. In contrast, if the population consisted mostly of
males, it would pay to have daughters. If, however, the population consisted of
equal numbers of males and females, sons and daughters would be equally
valuable. Thus a one-to- one sex ratio is the only stable ratio; it is an
"evolutionarily stable strategy". Although Fisher wrote before the mathematical
theory of games had been developed, his theory incorporates the essential
feature of a game—that the best strategy to adopt depends on what others are
doing.
Since Fisher’s time, it has been realized that genes can
sometimes influence the chromosome or gamete in which they find themselves so
that the gamete will be more likely to participate in fertilization. If such a
gene occurs on a sex-determining ( X or Y) chromosome, then highly aberrant sex
ratios can occur. But more immediately relevant to game theory are the sex
ratios in certain parasitic wasp species that have a large excess of females. In
these species, fertilized eggs develop into females and unfertilized eggs into
males. A female stores sperm and can determine the sex of each egg she lays by
fertilizing it or leaving it unfertilized. By Fisher’s argument, it should still
pay a female to produce equal numbers of sons and daughters. Hamilton, noting
that the eggs develop within their host—the larva of another insect—and that the
newly emerged adult wasps mate immediately and disperse, offered a remarkably
cogent analysis. Since only one female usually lays eggs in a given larva,
it would pay her to produce one male only, because this one male could fertilize
all his sisters on emergence. Like Fisher, Hamilton looked for an
evolutionarily stable strategy, but he went a step further in recognizing that
he was looking for a strategy.
Which of the following is NOT true of the species of parasitic wasps discussed in the passage
A．Adult female wasps are capable of storing sperm.
B．Female wasps lay their eggs in the larvae of other insects.
C．The adult female wasp can be fertilized by a male that was hatched in the same larva as herself.
D．So few male wasps are produced that extinction is almost certain.
