Robert quotes:

>Why is sex so unpopular in the Australian desert?
>
>Sex is by far the most predominant mode of reproduction among eukaryotes.
>Nevertheless, two new discoveries of asexual reproduction in a lizard and a
>plant from the Australian arid zone highlight an emerging trend toward the
>loss of sex in this region. Efforts to understand the processes leading to
>this pattern should provide important information about the relative
>advantages and disadvantages of sexual reproduction.

A long-proposed reason for the "commonality' of asexual reproduction among
lizards in deserts -- whether that desert resides in the Australia, North
America or Asia -- is the "weed species" concept of John Wright
and Chuck Lowe:

WRIGHT, J. W. AND C. H. LOWE. 1968. WEEDS, POLYPLOIDS, PARTHENOGENESIS, AND THE
GEOLOGICAL AND ECOLOGICAL DISTRIBUTION OF ALL-FEMALE SPECIES OF CNEMIDOPHORUS.
COPEIA 1968(1)- 128-138.

The hypothesis is simple enough: once a fully sexual species' population
density falls to a critical level, it faces the exigencies of demographic
extinctions (local populations composed of all one gender, individuals too
dispersed to easily find each other, etc.). When this occurs, species go
locally extinct. 

The situation is made even more difficult for a sexual species if the habitat
is episodically (but not predictably) disturbed (flash floods, etc.). Under
these conditions, asexual congeners, which are often the result of
interspecific hybridizations, prove themselves to be more demographically
"competitive" in the sense that they can invade newly disturbed
habitat faster
and persist more easily as viable populations at extremely low densities, even
though they are often otherwise physiologically, ecologically and behaviorally
incompetent competitors.

In ecogeographic conditions that essentially prohibit the persistence of sexual
species, asexuals -- if they exist at all -- are given the chance to dominate
in a manner that they never could given more clement conditions.

Wirt Atmar
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