Evolutionary
dynamics of ‘the’ bdelloid and monogonont rotifer life history patterns
Ch.E.
King, C. Ricci, J. Schonfeld, M. Serra-2003
Abstract:
Substantial
differences in both life table characteristics and reproductive patterns
separate bdelloid from monogonont rotifers. Bdelloids reproduce only
asexually, whereas most monogononts are cyclical parthenogens. We explore
some of the adaptive consequences of these life history differences using a
computer model to simulate the evolutionary acquisition of nex beneficial
mutations. A one-locus mutation-selection regime based on the life history
characteristics of bdelloids indicates that asexuals can have higher rates
of evolutionary change and maintain higher levels of genetic diversity over
a longer time period that obligate sexuals. These results are produced by
differences in the magnitude of random genetic drift that are associated
with the different types of reproduction. Cyclical parthenogens have
significantly higher evolutionary rates in the single locus model than
either obligate sexuals or asexuals; they also maintain the lowest levels of
genetic diversity. The relative rates of evolutionary change between
asexuals and sexuals in a one-locus model disappear when the modeled
population is undergoing simultaneous selection for beneficial mutations at
two or more loci. Using monogonont life table parameters in a two-locus
simulation, both obligate sexuals and cyclical parthenogens have much higher
rates of evolution that obligate asexuals. However, the asexuals still
ratain much higher levels of genetic variation over longer time periods than
the other groups. Our results are strongly influenced by both the number of
loci being evaluated and the quantitative characteristics of the life table
inputs. We end with an attempt to use our model to help understand the
adaptive basis of the remarkably divergent life histories found in typical
bdelloid and monogonont rotifers.
(Department
of Zoology, Oregon State University, Corvallis, OR 97331, USA, kingc@mail.science.orst.edu)