Biology Reference
In-Depth Information
produce an intermediate pheromone blend. Analysis of the F
2
and backcross
progeny indicates pheromone type is controlled by two alleles at a single auto-
somal locus, although one or more modifier genes control the precise ratio of
the isomers in heterozygous females. Males of the two
O. nubilalis
strains are
attracted to the appropriate pheromone blends in the field, and hybrid males
respond preferentially to the pheromone produced by heterozygous females
rather than to the pheromones produced by the two parental female types.
A single-sex-linked gene with two alleles determines the response of males to
the pheromone. The olfactory sensillae of the two types of males are different,
which is controlled by an autosomal locus with two alleles. Hybrid males give
intermediate results when tested for their electrophysiological responses, with
E- and Z-cells yielding approximately equal spike amplitudes. The genes deter-
mining variation in pheromone production and organization of male olfactory
sensillae are not closely linked and are probably on different chromosomes
(
Löfstedt 1990
).
Yasukochi et al. (2011)
found sex-linked pheromone receptor
genes of
Ostrinia nubilalis
were present in tandem array on the Z chromosome.
In addition, an autosomal locus responsible for male response to the sex phero-
mone contains at least four odorant-receptor genes, suggesting that additional
copies of odorant-receptor genes can increase the potential for male moths to
acquire altered specificity for pheromone components and facilitate differentia-
tion of sex pheromones (
Yasukochi et al. 2011
).
Sexual isolation between the moths
Heliothis subflexa
and
H. virescens
was
determined to be due to a single quantitative trait locus (QTL) that consists of at
least four odorant receptor genes (
Gould et al. 2010
).
11.4.2 Selection Experiments
Selection experiments provide another traditional method to determine the
degree to which a given behavior is determined genetically. In a selection exper-
iment, individuals with a specific behavioral attribute are allowed to reproduce
and this process is repeated over succeeding generations. Eventually, the behav-
ior of the selected population is altered
if
genetic variation for the attribute is
present in the initial colony
and
the selection procedures were appropriate. The
response of the population to selection can be analyzed to estimate the herita-
bility of the trait.
11.4.2.1 Migratory Behavior in
Oncopeltus fasciatus
Migratory behavior of
Oncopeltus fasciatus
is under genetic control (
Palmer and
Dingle 1989
). Strains of
O. fasciatus
were selected for wing length and propen-
sity to fly. Bidirectional selection on wing length (selection for increased and
