Article: Evolutionary biology: Males from Mars

Nature 435, 1167-1168 (30 June 2005) | doi: 10.1038/4351167a

Evolutionary biology: Males from Mars
David Queller

In an ant species - or is it two species? - females are produced only by
females and males only by males. Explanations of this revelation have to
invoke some decidedly offbeat patterns of natural selection.

That men and women sometimes seem like different species is the stock in
trade of pop psychologists and relationship gurus. Some go even farther: men
are from Mars and women are from Venus. But in reality, human sexual
differences are rather small. Even a naturalist freshly arrived from Mars or
Venus would have little trouble binning specimens of men with women, and not
with female chimpanzees or gorillas. There are species where males and
females are different enough to have fooled real earthly naturalists. But no
population geneticist would be misled - males and females mix their genes in
their progeny, and as a result male and female genes comprise a common,
well-mixed pool. A fascinating exception to this rule is described by
Fournier et al. (Clonal reproduction by males and females in the little fire
ant)1. Males and females each reproduce clonally and, like independent
species, follow separate evolutionary branches.

The surprise comes from the little fire ant, Wasmannia auropunctata, which
is hardly obscure. An invasive pest in tropical habitats, it earns a place
on a list of the 100 worst alien species2. Its ancestor, like other
haplodiploid social insects, must have already had two other varieties of
asexuality, which together set the stage for this story. Haplodiploid
species produce males asexually from unfertilized eggs (Fig. 1a), so the
males are haploid - they have only one copy of each gene. Fertilized eggs
become diploid females with two gene copies (Fig. 1b). In social
haplodiploids, environmental differences usually induce females to
differentiate into one of two castes (Fig. 2, overleaf) - 'gynes' become
reproducing queens (Fig. 1c), whereas workers (Fig. 1d) are not just asexual
but non-reproductive; they pass on their genes only by helping to rear
relatives in their colony, a process known as kin selection.

Full Text at Nature:
http://www.nature.com/nature/journal/v435/n7046/full/4351167a.html

Posted By
Robert Karl Stonjek


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