Biology Reference
In-Depth Information
10.9 Hybrid Sterility
When different species are crossed, hybrid progeny sometimes are produced.
However, the progeny may have altered sex ratios, with one sex absent, rare, or
sterile. The missing or sterile sex is usually the heterogametic sex ( Laurie 1997 ).
This phenomenon is known as Haldane's Rule , which is “one of a few general
rules in evolutionary biology” ( Sawamura 1996 ). However, Sawamura (1996)
indicates some exceptions do exist to Haldane's rule, caused by maternal effects.
Hurst and Pomiankowski (1991) suggest that Haldane's Rule only occurs in taxa
with sex chromosome-based meiotic drive, such as the Lepidoptera and Diptera.
Thus, Haldane's rule may be accounted for in some insects by a loss of suppres-
sion of sex-ratio distorters when in the novel nuclear cytotype of the hybrid.
Sex-ratio distorters that result in unisexual sterility in crosses between dif-
ferent species have been found in many species of Drosophila , the dipterans
Musca domestica and Glossina morsitans , the hemipteran Tetraneura ulmi , and
Lepidoptera ( Acraea encedon , Maniola jurtina , Danaus chrysippus , Philudoria
potatoria , Mylothris spica , Abraxus grossulariata , and Talaeporia tubulosa )
( Hurst and Pomiankowski 1991 ).
10.10 Medea in Tribolium
A class of selfish genes, Medea , was found in the red flour beetle, Tribolium
castaneum ( Beeman et  al. 1992 ). Medea causes a “ M aternal- E ffect D ominant
E mbryonic A rrest” that results in the death of zygotes that do not carry it. If a
mother carries Medea , any of her offspring that lack this gene die before they
pupate. Females who are heterozygous for Medea lose half their progeny if
they mate with a wild-type male and ¼ of their progeny when mated to a het-
erozygous male. It was hypothesized that Medea could lead to reproductive iso-
lation and speciation in T. castaneum populations.
A survey of wild populations of T. castaneum from Europe, North and South
America, Africa, and Southeast Asia showed that four different Medea alleles
were widespread, but absent or rare in Australia and the Indian subcontinent
( Beeman and Friesen 1999 ). Thomson and Beeman (1999) suggest that Medea
factors are absent from India because a hybrid incompatibility factor (H) is
found in the T. castaneum populations in India. Apparently, H and Medea strains
of T. castaneum are incompatible due to suppression by the H factor of the self-
rescuing activity of the lethal Medea genes.
10.11 Cytoplasmic Agents Distort Normal Sex Ratios
Many cytoplasmically transmitted organisms (bacteria, viruses, and protozoa)
alter the “normal” sex-determining mechanism(s) in arthropods ( Table 10.3 ).
Most are inherited primarily through the oocyte of the mother (cytoplasmically
 
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