Half-chromatid mutation as a possible cause of mosaic males and females in Hymenoptera and rare fertile male tortoiseshell cats.

Half-chromatid mutations occur when a single base change in a gamete is transmitted to the zygote, which, after DNA replication and cleavage, will result in a mosaic individual. These mutations will be passed on through the germ plasm and also may be expressed somatically. Half-chromatid mutation has been suggested to account for the observed lower frequency of males than expected for lethal X-linked recessive disorders in humans, such as Lesch-Nyhan syndrome, incontinentia pigmenti, and Duchene muscular dystrophy. Although attention has been paid to half-chromatid mutation in humans, it otherwise has been ignored. Here I show that half-chromatid mutation in haplodiploid organisms, such as Hymenoptera, has some interesting and important consequences: (i) since all genes follow the X-linked pattern of inheritance, half-chromatid mutations should be relatively easier to detect; (ii) recessive mutations of all viabilities may be expected; (iii) mosaics of both sexes are expected in haplodiploids with half-chromatid mutation; (iv) gynandromorphs could result from half-chromatid mutation at the sex-determination locus, in species with single-locus complementary sex-determination. Finally, half-chromatid mutation can account for the rare fertile male tortoiseshell phenotype observed in the domestic cat, Felis catus, and which still has not been fully accounted for by other mechanisms.

Discrimination of the bumble bee species Bombus occidentalis Greene and B. terricola Kirby by morphometric, colour and RAPD variation.

The taxonomic status of B. terricola Kirby and B. occidentalis Greene has long been questioned. However recent COI gene sequence data suggests that B. occidentalis and B. terricola do represent good biological species. In this paper we test the hypothesis that B. terricola and B. occidentalis are conspecific by using independent morphometric and genetic (RAPD) data. For comparison we also analyzed one consubgeneric species, B. moderatus (now B. crytptarum), and one non-consubgeneric species B. (Pyrobombus) perplexus. Discriminant function analysis of wing morphometric data correctly classified over 85% of the specimens of B. occidentalis and B. terricola. Analysis of molecular variance of the RAPD data showed a significant difference (P < 0.0001) between B. occidentalis and B. terricola. Colour variation from laboratory reared colonies of B. occidentalis suggests that probably two gene locus inheritance is likely but that hybridization as the sole basis for the colour variation seen in the nominate taxon B. occidentalis can be excluded. We conclude that B. terricola and B. occidentalis should be regarded as distinct species which have recently diverged, and that they can be distinguished by wing morphometrics and RAPD genotypes. Where they are sympatric (e.g. in Alberta) colour pattern variation is confined to B. occidentalis.

Genetic and morphometric evidence for the conspecific status of the bumble bees, Bombus melanopygus and Bombus edwardsii.

The taxonomic status of closely related bumble bee species is often unclear. The relationship between the two nominate taxa, Bombus melanopygus Nylander (Hymenoptera: Apidae) and Bombus edwardsii Cresson (Hymenoptera: Apidae), was investigated using genetic (enzyme electrophoretic) and morphometric analyses. The taxa differ in the color of the abdominal terga two and three, being ferruginous in B. melanopygus and black in B. edwardsii. B. edwardsii occurs throughout California, while B. melanopygus extends north through Oregon, to Alaska and Canada. They are sympatric only in southern Oregon and northern California. The taxonomic status of these taxa was questioned when Owen and Plowright (1980) reared colonies from queens collected in the area of sympatry, and discovered that pile coloration was due to a single, biallelic Mendelian gene, with the red (R) allele dominant to the black (r). Here it is shown that all the taxa, whether from California, Oregon, or Alberta, have the same electrophoretic profile and cannot be reliably distinguished by wing morphometrics. This strongly supports the conclusion that B. melanopygus and B. edwardsii are conspecific and should be synonymized under the name B. melanopygus. Hence, there is a gene frequency cline running from north to south, where the red allele is completely replaced by the black allele over a distance of about 600 km.

Sex ratio adjustment in Asobara persimilis (Hymenoptera: braconidae), a parasitoid of Drosophila.

Sex ratios of offspring in forty-one broods of Asobara persimilis (an hymenopteran parasitoid of Drosophila) were analysed. A single female wasp was introduced per tube of Drosophila larvae so that local mate competition would be expected to occur amongst their offspring. The parental population had a sex ratio of 1:1 (87F:102M), the offspring sex ratio was 787F:296M (2.66:1) highly female biased and not significantly different from 3:1 (P>0.05). The sex ratio was approximately constant regardless of the total brood size which ranged from 5 to 100 (mean 26.2). Females were therefore able to adjust their offspring sex ratios in the predicted direction and the number of males in each brood was determined binomially.