In many parts of the world, the tobacco specialist Myzus persicae nicotianae is isolated from the generalist Myzus persicae s . s . because either or both taxa reproduce parthenogenetically. Here we investigated how the genomic integrity of the tobacco specialist is maintained in Greece, where both taxa have a bisexual generation on peach. Microsatellite DNA analysis revealed greatest genetic divergence between populations in tobacco-growing regions and those in a region where tobacco is not cultivated. This was irrespective of reproductive mode, which has an important effect on population structure. Bayesian clustering and admixture analyses split the aphid genotypes into three groups, corresponding with persicae , bisexual nicotianae and unisexual nicotianae , respectively. Genetic distance parameters showed strong regional differentiation but marked year-on-year stability, indicating low interpopulation migration. Assortative mating between taxa is promoted by differences in the daily rhythm of female signalling behaviour, with peak activity coinciding with periods of consubspecific male searching activity. Males showed greater attraction to the sex pheromone of their own subspecies. Thus, despite relatively low overall genetic differentiation, processes are in place facilitating further genomic divergence and eventual speciation.

Microsatellite genotyping was used to identify common clones in populations of the Myzus persicae group from various hosts and regions in mainland Greece and southern Italy and to compare their distribution and occurrence on tobacco and other crops. Common clones were defined as genotypes collected at more than one time or in more than one population; and, therefore, unlikely to be participating in the annual sexual phase on peach. Sixteen common genotypes were found, accounting for 49.0% of the 482 clonal lineages examined. Eight of these genotypes were subjected, in the laboratory, to short days and found to continue parthenogenetic reproduction, i.e. they were anholocyclic. Four of the six commonest genotypes were red, and one of these accounted for 29.6% of the samples from tobacco and 29.4% of those from overwintering populations on weeds. All six commonest genotypes were found on weeds and five of them both on tobacco and on other field crops. In mainland Greece, the distribution of common clones corresponded closely with that of anholocyclic lineages reported in a previous study of life cycle variation. Common genotypes were in the minority in the commercial peach-growing areas in the north, except on weeds in winter and in tobacco seedbeds in early spring, but predominated further south, away from peach trees. This contrasts with the situation in southern Italy, reported in a previous paper, where peaches were available for the sexual phase, yet all samples from tobacco were of common genotypes.

The relationships among 207 squirrels from 12 locations in the UK and three in mainland Europe were examined using mitochondrial DNA (mtDNA) control region sequence. Twenty-six haplotypes were detected, many of which were population specific. Eighty per cent of the populations analysed contained two or more haplotypes. Hierarchical analysis of molecular variance showed the majority of genetic variation to be partitioned among populations. Genetic diversity varied considerably within the UK, and conformed to no obvious geographical trend. The populations in Argyll and Spadeadam Forest showed the highest levels of variation in the UK. However, the greatest genetic diversity was seen in Bavaria, southern Germany where six unique alleles were detected in a sample of 10 individuals. Phylogenetic analysis revealed no evolutionary divergence between UK and mainland European haplotypes. We conclude that, within the UK, the genetic patterns observed are most likely to be explained by the effects of genetic drift which has occurred since the isolation of populations during the past few hundred years, hence we cannot detect any underlying phylogeographic pattern. Therefore, the use of larger, geographically distinct populations within the UK for augmentation of small isolated populations is unlikely to pose problems of genetic incompatibility. Further, the role that demographic factors may have in complicating the application of current genetically based management unit criteria is likely to need further attention.

SUMMARYLittle is known about the mating behaviour of monogamous mammals. Here, we present behavioural and genetic evidence of fidelity in a socially monogamous dwarf antelope, Kirk's dik-dik. DNA microsatellite analysis revealed no evidence of extra-pair paternity (EPP) in dik-diks : mothers' partners matched the paternal genotype in all 12 juveniles tested. One likely reason for the absence of EPP is that males guard their mates closely during oestrus and over-mark all female scent, thereby reducing the likelihood of other males attempting to mate. In addition, males may be limited in their ability to search for extra-pair copulations (EPCs) by activities associated with pair-bond maintenance. Year-round, males maintained proximity within pairs, followed their females' activity patterns, and spent approximately 64 % of their time with their partners. However, males did attempt to obtain EPCs when the opportunity arose, and genetic monogamy in dik-diks is probably best explained by the behaviour of females : in contrast to many monogamous female birds, female dik-diks do not appear to seek EPC partners. We propose that females avoid extra-pair males because they are unable to mate with them without instigating a potentially dangerous conflict.

Mitochondrial DNA characterization of the sandfly Phlebotomus perniciosus has not resolved the population structure of its Iberian lineage. For this purpose, four AGC-and seven AGG-class microsatellite loci were characterized, after their isolation using Biotin-Avidin enrichment and the screening of plasmid libraries by polymerase chain reaction. Of the five polymorphic loci analysed in four Spanish populations, four showed patterns of allele diversity consistent with migration from a southern Ice Age refuge. Estimates of the historical migration rates of P. perniciosus will help to predict the effects of global warming on its range and that of Leishmania infantum , the parasitic protozoan it transmits.