| dc.description.abstract | Enzyme heterogeneity and genetic variation were studied
in Aedes (Stegomyia) aegypti L. in the Rabai area, Coast
Province Kenya. Mosquitoes were collected from inside houses
(domestic habitat), from the immediate vicinity of human
dwellings (peridomestic habitat), and from the woods far from
human dwellings (feral habitat). These were bred in the
laboratory.
Morphological variants were separated by examination
of anaesthetised adults under the dissecting microscope.
Biochemical variation was determined by starch gel electrophoretic
techniques and ultra-violet spectrophotometric
techniques.
The life cycle of Ae. aegypti was completed in at least
11 days. There were behavioural traits differing between - larvae "of Ae. aegypti type form and sub-species formosus
Walker. There was a slight excess of males, such that the
sex ratio was 1.07 males: 1 female. More eggs,were oviposited
in 1 male : 1 female crosses than in 2 'male~ : 1 female
crosses. 'The mean pupal expect~cy from eggs was 76%,
indicating larval ~ortality an~robably infertility of eggs.
Females generally l~~ed longer than males. Reciprocal crosses
between type form and ssp. formosus indicated the presence of
a partial sub-specific fertility barrier, operating in
matings of the type spp. formosus female X type form male.
With respect to the esterase loci, differences were
Preliminary data on a morphological phenotype, the extent of
wing cover over the terminal abdominal segments, suggested
that more variation exists between ssp. fonmosus and type form
than otherwise envisaged. A hypothetical explanation for the
observed data was advanced. More data is required for a
conclusive explanation.
More than one isozyme variant was found for esterases
(Est.), malate dehydrogenase QMDH), glutamate oxaloacetate
transaminase (GOT), peroxidases and tetrazolium oxidase (To).
The esterases were shown to exhibit some locus-enzymesubstrate
specificity. Genetic polymorphism was discovered
at the Est-3, Est-6, MDH-l, GOT-2, and malic enzyme OMe) loci.
found between type form Ae. aegypti and ssp. formosus on the
one hand and between domestic, peridomestic and feral
populat1ons on the other hand. These differences were in
terms of the types and frequencies of alleles present. The
same differences were also found to occur on a spatial basis,
i.e. between mosquito populations of the sampling localities.
The domestic, peridomestic and feral populations were shown
to be in Hardy-Weinberg equilibrium, even though there was poor
fitness in p~ridomes~~c populations. There was very little
evidence for gene flow between these populations.
Gene activity during enzyme ontogenesis was studied
by electrophoretic and spectrophotometric techniques. The
activity of a-glycerolphosphate dehydrogenase (a-GPDH)
was generally very high in pupae and adults, principally
due to the temporal activation of the locus responsible
for the major adult isozyme a-GPDH3. Lactate dehydrogenase
(LDH) activity was rather restricted to the early
larval stages, with the gene responsible either producing
an inactive enzyme or probably being under the control of
regular gene(s). Gene repression probably occurs after
the third larval instar. MDH activity is highest in pupae
with changes in activity mainly due to the MDH-2 locus,
and pupal peroxidases were found to be different from
adult peroxidases, suggesting that the temporal repression
and activation of genes, and vice-versa, is an important
mechanism during ontogenesis in insects.
Ae. aegypti has been shown to be a very variable
mosquito, both morphologically and biochemically. Only a
fe~ ~rlzymes have been studied here, and the variation
already found in adult populations and during ontogenesis
suggests great potential variability. Three esterase
alleles were found in Ae. aegypti ssp. formosus that were
absent in type form. More enzymes must be studied so that
differe~ces can b,e found which may form the basis of .
biochemical taxonomy.
Non-glucose..metabolising enzymes (esterases) were
more polymorphic than glucose-metabolizing enzymes (e.g.
LDH).
Enzymes acting on multiple substrates were the most
polymorphic group (esterases). This supports the theory
that selective forces have a role in the maintenance of
polymorphism. | en |
