Rm. Kliman et al., Differences in (G + C) content between species: a commentary on Forsdyke's"chromosomal viewpoint" of speciation, J THEOR BIO, 209(2), 2001, pp. 131-140
Forsdyke (1999) has recently argued that differences in (G + C)%, or G + C
content, may trigger new species formation. He further argues that the geni
c model has shortcomings that can be overcome by his "chromosomal" thereaft
er, "G + C") model. We disagree on several counts. First, we do not accept
that the genic model has the shortcomings suggested by Forsdyke. There is a
n abundance of empirical support for the contribution of individual genes,
as well as of mapped chromosomal regions, to post-zygotic reproductive isol
ation land Haldane's rule). Further, we argue that the G + C model suffers
from the same theoretical difficulties as other speciation models based on
underdominance. We also question the evidence Forsdyke uses to support his
model. Finally, we describe analyses of G + C content in a well-studied mod
el system of speciation (the Drosophila melanogaster species complex), the
results of which are incompatible with the G + C model. Thus, while Forsdyk
e's G + C model cannot be explicitly ruled out, it is not directly supporte
d by empirical data. In contrast, the genic model is well supported by empi
rical data, holds up on theoretical grounds, and does not require any assis
tance from the G + C model. (C) 2001 Academic Press.