Other things being equal, an asexual (clonal) organism will be able to reproduce twice
as fast as a sexual one, because asexuals do not have to produce males. This is known as the two-fold cost of sex. Nonetheless,
species that use sexual reproduction vastly outnumber those that utilize asexual reproduction. The apparent contradiction
between the two-fold cost of sex and the success of sexual reproduction is known as the 'paradox of sex'. How sexual
reproduction evolved and in maintained is a controversial topic in evolutionary biology.
As models in the evolution of
sex and parthenogenesis, aphids are especially interesting because they show diverse reproductive modes that can coexist
in the same population, including:
- cyclic parthenogenesis (asexual for most of the year with one sexual cycle)
- obligate asexuality (no sex possible)
- intermediate ('mix-and-match' strategy) and
- asexuality with male production.
Understanding
the relative costs and benefits of these different modes may be pivotal in understanding how they can co-exist, and thus
shed light on the maintenance of sexual reproduction in the face of demographically superior asexuals.
It has been suggested
that asexual organisms evolve too slowly to deal with environmental change, and indeed evolution of new ecological
traits has rarely been demonstrated in asexual organisms. However, this may be because few studies have been carried out.
In
this project I examined ecological evolution in an obligate asexual
Myzus persicae (the peach potato aphid) which
has been introduced into Australia since European settlement of the continent. To determine how much evolution occurs
in asexual aphids derived from a single recent common ancestor, experiments were completed comparing the fitness
under different conditions of host plant and temperature of two geographically-widespread clones. There were significant ecological differences between individual clone members, bu these differences showed rather little geographic pattern.
