Biology Reference
In-Depth Information
15
Parthenogenesis
Associated
with
Wolbachia
Martinus E. Huigens and Richard Stouthamer
CONTENTS
Wolbachia
-Induced Parthenogenesis in Haplodiploids .................................................................248
Distribution and Density of
Wolbachia
in Parthenogenetic Wasps...............................................254
Phylogenetics: No Clustering of PI-
Wolbachia
.............................................................................255
Host Fitness: Higher Costs of Carrying
in Mixed Populations ..................................256
Dynamics of PI-
Wolbachia
and the Evolution of ÑVirginityÒ Mutants ........................................259
Wolbachia
PARTHENOGENESIS MEDIATED BY MICROBIAL INFECTIONS
Since the 19th century biologists have been puzzled by the fact that sexual reproduction is so
common and that only some, mostly lower, organisms have parthenogenetic reproduction. Parthe-
nogenetic reproduction has advantages due to its simplicity, efÝciency, effectiveness, and low cost
(Crow, 1994). For an individual, many disadvantages are associated with sex, such as Ýnding a
mate, competition for mates, and the chance of obtaining sexually transmitted diseases. In one of
the many reviews on the advantages of sexual reproduction, Crow (1994) mentions two of the most
plausible explanations. The ÑoldestÒ explanation is that greater genetic variability in a population
through sex can keep the population level at pace with changes in the environment. Second, harmful
mutations can be eliminated more easily through recombination and do not accumulate according
to the MullerÔs ratchet (Felsenstein, 1974), as happens in parthenogenetic populations (Muller,
1964). Most studies on the advantages of sexual reproduction are theoretical, and hypotheses remain
very difÝcult to test experimentally.
Recent studies on different modes of reproduction have forced us to change our perspective
because the evolutionary forces behind parthenogenetic reproduction are often not the genes of the
organism itself but those of their bacterial symbionts (Stouthamer et al., 1990a). In this chapter,
we will focus on microbe-induced parthenogenesis.
Studies on extraordinary sex ratios by Hamilton (1967, 1979) and Cosmides and Tooby (1981)
suggested that the differences in inheritance of cytoplasmic factors and nuclear genes could result
in a conÞict over offspring sex ratios. While cytoplasmic factors that are maternally inherited beneÝt
from an offspring sex ratio of 100% females, nuclear genes located on autosomal chromosomes
favor an optimal sex ratio with at least some male offspring in populations that are able to reproduce
