Simulation of instability in genetic sexing strains: effects of male recombination in association with other biological parameters

Abstract

Genetic systems have been developed in several insect species for separating males and females prior to releasing sterilized males in pest control programmes using the sterile insect technique. The systems generally depend on translocating a readily selectable gene onto the Y chromosome. A potential source of instability in such a system is genetic recombination in the male. Although such recombination was originally thought to be absent in most cyclorrhaphous Diptera, low levels have recently been found. We have developed a computer model which simulates the progression of instability in the presence of male recombination, which can be used to assess the influence of rate of recombination in combination with a range of associated genetic and biological parameters. Male recombination alone or fitness of the Y-linked translocation were found to contribute relatively little to the rate of progression of instability. By contrast reduced fitness or mating competitiveness associated with the selectable gene had a strong effect. The sex ratio and the ratio of carriers to non-carriers of the selectable gene showed patterns characteristic of the parameters modelled. The relevance of such data to the development of suitable strains for genetic sex-separation and the replacement of strains under mass rearing conditions are discussed.

Simulation of instability in genetic sexing strains: effects of wild-type contamination in association with other biological parameters

“…A similar situation was observed during mass rearing of the phenotypically identical T:Y(wp + )30C strain, although the rate of progression of instability was much less in this strain (Busch-Petersen & Kafu, 1989); again, no instability had been observed in laboratory colonies. Similar instances of instability have been observed in at least ten other insect species (see Busch-Petersen & Baumgartner, 1991). In most cases it was not possible to determine whether the reported breakdowns were due to instability of the sexing mechanisms per se, to incomplete discrimination between the dimorphic sexes, to contamination, or to a combination of these or other causes.…”

“…Instability of the sexual dimorphism in genetic sexing strains has been observed during both laboratory and mass rearing of more than ten species of insects (see Busch-Petersen & Baumgartner, 1991). Generally, such genetic sexing strains have been developed as integral parts of integrated pest management programmes involving the sterile insect technique, i.e.…”

“…The GENSEX simulation model was described in detail by Busch-Petersen & Baumgartner (1991). The model uses discrete numbers in generation n to calculate the expected number of each genotype and karyotype in generation n x .…”

“…It is beyond the scope of this paper, however, to simulate all possible permutations of these parameters. Instead, we have simulated the expected breakdown of a hypothetical genetic sexing strain, utilizing data assembled from C. capitata by Busch-Petersen & Baumgartner (1991). These data include a fitness of the f/f genotype of 91.5% and a translocation fitness of 62%, here simulated in the presence of 0%, 0.01%, 1% and 10% contamination by both sexes (fig.…”

Spontaneous recombination between wp+ and the translocation breakpoint in the T:Y(wp+ )30C genetic sexing strain of Ceratitis capitata (Wied.)

“…However, a difference in recombination rate would fit in with the observation that the T:Y(wp)30C sexing strain is more stable than the T:Y(wp)101 strain under mass rearing conditions (Busch-Petersen & Kafu, 1989). At the same time, note must be taken of the fact that in computer simulations Hooper et al (1987) and Busch-Petersen & Baumgartner (1991) showed that the rate of breakdown in …”