General environmental heterogeneity as the explanation of sexuality? Comparative study shows that ancient asexual taxa are associated with both biotically and abiotically homogeneous environments

Journal Article
Toman, J. & Flegr, J.
Ecology and Evolution, 1-19, 10.1002/ece3.3716.

Ecological theories of sexual reproduction assume that sexuality is advantageous in
certain conditions, for example, in biotically or abiotically more heterogeneous environments.
Such theories thus could be tested by comparative studies. However, the
published results of these studies are rather unconvincing. Here, we present the results
of a new comparative study based exclusively on the ancient asexual clades. The
association with biotically or abiotically homogeneous environments in these asexual
clades was compared with the same association in their sister, or closely related, sexual
clades. Using the conservative definition of ancient asexuals (i.e., age >1 million
years), we found eight pairs of taxa of sexual and asexual species, six differing in the
heterogeneity of their inhabited environment on the basis of available data. The difference
between the environmental type associated with the sexual and asexual species
was then compared in an exact binomial test. The results showed that the majority of
ancient asexual clades tend to be associated with biotically, abiotically, or both biotically
and abiotically more homogeneous environments than their sexual controls. In
the exploratory part of the study, we found that the ancient asexuals often have durable
resting stages, enabling life in subjectively homogeneous environments, live in the
absence of intense biotic interactions, and are very often sedentary, inhabiting benthos,
and soil. The consequences of these findings for the ecological theories of sexual
reproduction are discussed.

Microevolutionary, macroevolutionary, ecological and taxonomical implications of punctuational theories of adaptive evolution

Journal Article
Flegr, J.
Biology Direct

Punctuational theories of evolution suggest that adaptive evolution proceeds mostly, or even entirely, in the distinct periods of existence of a particular species. The mechanisms of this punctuated nature of evolution suggested by the various theories differ. Therefore the predictions of particular theories concerning various evolutionary phenomena also differ.
Punctuational theories can be subdivided into five classes, which differ in their mechanism and their evolutionary and ecological implications. For example, the transilience model of Templeton (class III), genetic revolution model of Mayr (class IV) or the frozen plasticity theory of Flegr (class V), suggests that adaptive evolution in sexual species is operative shortly after the emergence of a species by peripatric speciation – while it is evolutionary plastic. To a major degree, i.e. throughout 98-99% of their existence, sexual species are evolutionarily frozen (class III) or elastic (class IV and V) on a microevolutionary time scale and evolutionarily frozen on a macroevolutionary time scale and can only wait for extinction, or the highly improbable return of a population segment to the plastic state due to peripatric speciation.
The punctuational theories have many evolutionary and ecological implications. Most of these predictions could be tested empirically, and should be analyzed in greater depth theoretically. The punctuational theories offer many new predictions that need to be tested, but also provide explanations for a much broader spectrum of known biological phenomena than classical gradualistic evolutionary theories.
This article was reviewed by Claus Wilke, Pierre Pantarotti and David Penny (nominated by Anthony Poole).

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