Robin E. Owen

Allozyme variation, linkage disequilibrium and diploid male production in a primitively social bee Augochlorella striata (Hymenoptera; Halictidae)

A population of the primitively eusocial bee Augochlorella striata was surveyed for allozyme variation at 47 loci for 35 enzyme systems with a mean number of haploid genomes sampled of 76 per locus. The expected heterozygosity (mean ± S.E.) was 0·107 ± 0·004, the highest found for any bee species, solitary or social, studied to date. This result indicates that low levels of genetic variation are not ubiquitous in bees. No differences in allele frequencies between males and females were found. One diploid male was detected providing a maximum likelihood estimate of the frequency of diploid males in the population of 2·6 per cent. Strong linkage disequilibrium was detected between the loci Dia-2 and Lap. Under a genetic drift explanation for disequilibrium and realistic assumptions for the recombination rate between the two loci, the predicted population size is in broad agreement with that suggested from field studies

Contrasting frequencies of parasitism and host mortality among phorid and conopid parasitoids of bumble‐bees

Abstract 1. Phorid (Diptera, Phoridae) and conopid (Diptera, Conopidae) parasitism among four North American bumble‐bee (Hymenoptera, Apidae) species was investigated. Male bumble‐bees experienced a significantly higher incidence of parasitism by the phorid, Apocephalus borealis Brues, and a significantly lower incidence of parasitism by the conopid, Physocephala texana Williston, than did workers.

Gene frequency clines at X-linked or haplodiploid loci.

The equations governing gene frequency clines at X-linked or haplodiploid loci are derived. Clines at X-linked loci will be identical to corresponding clines at autosomal loci only under three restrictive conditions (a) no dominance, (b) dispersal distance the same in each sex, (c) average effect of alleles same in each sex. If any of these conditions are not met then the males and females will have different gene frequencies. Clinal variation in colour morph frequency in the bumble bee Bombus melanopygusis analysed. It is concluded that a minimum selection intensity acting on the queens on the order of 1 per cent or less is sufficient to maintain the cline.

Effective population size in social Hymenoptera with worker-produced males

In the social Hymenoptera, which have haplodiploid inheritance, a proportion, ψ of the (haploid) males can be produced by the workers. It is shown that, for the special case where each laying worker produces exactly one male that survives to maturity and mates, the variance effective population size Ne(v) = (3 − ψ)2FM/(2F + (2 − ψ)2M), where F and M are, respectively, the number of queens and males in the population. If the sex ratio is unity or female biased then Ne is reduced if there are worker-produced males, however with male biased sex ratios Ne is increased compared to its value with ψ = 0. An alternative situation, in which laying workers can each produce more than one male offspring, was investigated using computer simulations. In this case worker-produced males reduce Ne(v) regardless of sex ratio, although the effect is relatively the most weak with male biased sex ratios.A reduction in effective population size due to worker-produced males may contribute to the generally low levels of genetic variation found in the Hymenoptera.

Selection at two sex-linked loci

Recurrence equations are derived for selection at two sex-linked or haplodiploid loci, each with two alleles. Equilibrium equations containing only the female gametic frequencies are obtained by using a transformation that absorbs the male gametic frequencies. It is shown that gametic equilibria occur at a stationary point of the geometric mean viability if, and only if, ½rf[x1x4(v11+v44) − x2x3(v22+v33)]w22 = 0, where rf is the recombination fraction in females, w22 is the viability of the double heterozygote, x1, x2, x3, x4 are the frequencies of the female gametes AB, Ab, aB, ab respectively and v11, v22, v33, v44 are the corresponding male viabilities. Therefore, in general, linkage equilibrium is neither sufficient nor necessary for the mean viability to be at a stationary point and there will always be some linkage disequilibrium in the system, either in females or males or both. Symmetrical selection in females is analysed in some detail and it is shown that unless there is also a particular type of symmetrical selection in males then only asymmetrical equilibria can occur. The hitchhiking effect at sex-linked and autosomal loci is compared, and it is found that with no recombination in males at autosomal loci the effect can be stronger than at sex-linked loci.

Frequencies of Diploid Males in Natural Populations of Three North American Bumble Bee (Bombus) Species (Hymenoptera: Apidae)

ABSTRACT We used four DNA microsatellite markers and detected diploid males in two out of three species of North American bumble bees from Alberta, Canada. The estimated average proportion of diploid males, , in Bombus occidentalis Greene and Bombus perplexus Cresson was ≈ 3% (n = 112) and 6% (n = 104), respectively. However, there was no significant difference between these estimates. Because no diploid males were detected in the sample (n = 81) of Bombus terricola Kirby, no estimate of could be made directly, but the upper limit to that would be found in a sample of this size, was ≈ 4%. The average over the three species was ≈ 4%. This is the first report of diploid males in natural populations of North American bumble bees.