Population structure of the blacklegged tick Ixodes scapularis revealed by SSCP data using the mitochondrial Cyt b and the nuclear ITS1 markers

The population genetic structure of the blacklegged tick Ixodes scapularis was analyzed using 853 individual ticks collected from 12 sites along the eastern seaboard of the United States. PCR-based DNA single strand conformation polymorphism(SSCP) was used for analysis of one haploid locus, the mitochondrial cytochrome b(Cyt b), and one diploid locus, the internal transcribed spacer 1(ITS1) of nuclear ribosomal RNA. Seven haplotypes in the Cyt b locus and 13 genotypes in the ITS1 locus were identified. Population differentiation and isolation by distance were found. Distribution of haplotype and genotype frequencies across geographic regions suggests that two distinct populations exist along the Eastern Coast of the US. However, genetic variation among individuals within regions was large. This degree of variation suggests frequent gene flow between regions. Moreover, overall genetic diversity among individuals was much higher in ticks from the southern population.

Population structure of the Atlantic sand fiddler crab Uca pugilator along the eastern coast of US revealed by molecular data

The Atlantic sand fiddler crab Uca pugilator is an extremely abundant crab found along the eastern coast of the United States. Fiddler crabs have a life cycle with an obligatory planktonic larval phase of 30-90 days,which might be expected to lead to widespread larval dispersal and consequent genetic homogeneity over considerable distances. However,a large amount of morphological and behavioral variation is found between northern and southern populations along the eastern coast. This study was undertaken to determine the population genetic structure of U.pugilator and to determine whether these differences may have a genetic basis. The population structure of the fiddler crab was analyzed using 472 individuals collected from 12 sites along the eastern coast. PCR-based single stand conformation polymorphism (SSCP) was used to investigate between-site variation in the mitochondrial 16S rRNA gene of these individuals. Analysis of genetic variation indicated frequent gene flow between nearby localities,but much reduced levels between populations separated by larger geographic distances. Thus,despite the potential for high dispersal by planktonic larvae,population differentiation and isolation by distance is evident between northern and southern populations of U.pugilator. A high amount of genetic differentiation (F ST =0.3468) was found between northern and southern regions suggesting that the morphological and behavioral differences between these two regions have a genetic basis and may represent subspecies.

The phylogenetic relationships of introduced Aphelinus （Hymenoptera： Aphelinidae）, biological control agents of the Russian wheat aphid （Homoptera： Aphididae）

Several species of Aphelinus have been introduced to the US from the Old World for biological control of the Russian wheat aphid, Diuraphis noxia （Modvilko）. Reproductive incompatibility has been observed among populations collected from different geographic areas. We examined whether or not the reproductive incompatibility between strains of A. asychis was caused by distant phylogenetic relationships. Ribosomal DNA sequences of internal transcribed spacers 2 （ITS2） were analyzed in several species of Aphelinus collected from multiple sites of Europe and Asia. Yhe phylogenetic analysis showed that strains within the species A. albipodus and A. asychis are not monophyletic, and two clearly divergent clades were revealed among sequenced samples. Our results suggest that the reproductive incompatibility between three exotic strains ofA. asychis was more likely caused by divergence of phylogeny than by symbiotic bacteria.