Biology Reference
In-Depth Information
Table 10.3: Examples of Nonnuclear Influences on Sex Determination or Sex Ratio in Arthropods. a
(Continued)
Microorganism
Arthropod species (order)
Effect reference(s)
(Hymenoptera)
Thelytoky lost
Trichogramma species
Cure with antibiotics results in
bisexual (arrhenotokous) populations.
maternally inherited
(Hymenoptera)
Stouthamer et al. 1990, Stouthamer
and Werren 1993, Stouthamer and
Luck 1993
Wolbachia
Leptopilina hetrotoma
Tri-infected strain males crossed
with uninfected or monoinfected
females result in killed female eggs;
monoinfected males crossed with
uninfected females result in reduced
progeny and more males
(Hymenoptera)
Vavre et al. 2000
a Wolbachia also causes cytoplasmic incompatibility and other effects (see Chapter 4).
inherited). Cytoplasmic agents that can manipulate their host's sex ratio and
promote their own spread are called cytoplasmic sex-ratio distorters . The
spread of a cytoplasmic sex-ratio distorter often reduces the fitness of its host
and can drive populations to extinction ( Cordaux et al. 2011 ). Sex-ratio distort-
ers are usually suspected if crosses produce a heavily female-biased sex ratio,
although meiotic drive and hybrid dysgenesis agents are other possible mecha-
nisms ( Hurst 1993 ). Cordaux et al. (2011) evaluated the impact of symbionts on
the evolution of sex-determination mechanisms in their hosts and noted that
there are four types of reproductive mechanisms caused by symbionts: cytoplas-
mic incompatibility (as discussed in Chapter 4), male killing (increase in the pro-
portion of females through targeted death of male progeny), feminization of
genetic males (conversion of genetic males to functional females), and induction
of asexual daughter development (thelytoky).
Ebbert (1991, 1993) described > 50 cases in which cytoplasmically inherited
organisms alter sex ratios in the Diptera, Heteroptera, Coleoptera, Lepidoptera,
and Acari (mites). Such sex-ratio distorters may be widespread, but undiscov-
ered, in other arthropods because scientists rarely assess sex ratios by mak-
ing single-pair crosses. Transmission rates of these agents typically are high,
although a few progeny may fail to become infected. The altered sex-ratio con-
ditions are found in natural populations at frequencies ranging from low to
high. The infections may reduce fitness of the hosts, and reduce egg hatch or
larval survival in the progeny of infected females. Some examples are described
in Sections 10.11.1-10.11.5.
Search WWH ::




Custom Search