Phylogeography of a specialist insect, Adelges cooleyi: historical and contemporary processes shape the distribution of population genetic variation.

Adelges cooleyi is a host-alternating, gall-making insect native to the Rocky Mountains and Cascade Mountains in western North America. The insect's primary hosts are Picea (spruce) species, and its secondary host is Pseudotsuga menziesii, Douglas fir. To determine whether there are large-scale patterns of genetic variation in this specialist insect, we created molecular phylogenies of geographically separate samples of A. cooleyi using sequence data from two mitochondrial (mtDNA) genes and amplified fragment length polymorphisms (AFLPs). Three divergent mtDNA lineages were identified. Analysis of mtDNA and AFLP genetic variation revealed that samples from southeastern Arizona are genetically isolated from all other samples. AFLP data identified possible gene flow between individuals from divergent mtDNA lineages in an area in the central Rocky Mountains. Factors that likely affected divergence within A. cooleyi were identified by comparing our conclusions with well-known changes in the distribution of vegetation in response to glaciations and previous phylogeographical work conducted on this specialist insect's host-plants. In addition to documenting previously unknown patterns of genetic variation in A. cooleyi, our work provides the basis for a testable hypothesis regarding the extent to which the distribution of variation in Picea and Pseudotsuga hosts mediates the distribution of genetic variation for this specialist insect.

Ahern RG ，Hawthorne DJ ，Raupp MJ 《-》

Phylogeography of spruce beetles (Dendroctonus rufipennis Kirby) (Curculionidae: Scolytinae) in North America.

Tree-feeding insects that are widespread in north temperate regions are excellent models for studying how past glaciations have impacted differentiation and speciation. We used mitochondrial DNA (mtDNA) sequences and allele frequencies at nine microsatellite loci to examine genetic population structure across the current range of the spruce beetle (Dendroctonus rufipennis), an economically important insect in North America. Two major haplotype groups occur across northern North America, from Newfoundland to Alaska, on white spruce (Picea glauca), and a third distinctive haplotype group occurs throughout the Rocky Mountains on Engelmann spruce (Picea engelmannii). The two mtDNA lineages found in northern populations are 3-4% divergent from each other and from the lineages found in the Rocky Mountains. Analyses of microsatellite data also suggest the existence of major population groupings associated with different geographical regions. In the Pacific Northwest, concordant contact zones for genetically distinct populations of spruce beetles and their principal hosts appear to reflect recent secondary contact. Although we could detect no evidence of historical mtDNA gene flow between allopatric population groups, patterns of variation in the Pacific Northwest suggest recent hybridization and introgression. Together with the pollen record for spruce, they also suggest that beetles have spread from at least three glacial refugia. A minimum estimate of divergence time between the Rocky Mountain and northern populations was 1.7 Myr (million years), presumably reflecting the combined effects of isolation during multiple glacial cycles.

Maroja LS ，Bogdanowicz SM ，Wallin KF ，Raffa KF ，Harrison RG ... -  《MOLECULAR ECOLOGY》

Phylogeography of Douglas-fir based on mitochondrial and chloroplast DNA sequences: testing hypotheses from the fossil record.

The integration of fossil and molecular data can provide a synthetic understanding of the ecological and evolutionary history of an organism. We analysed range-wide maternally inherited mitochondrial DNA and paternally inherited chloroplast DNA sequence data with coalescent simulations and traditional population genetic methods to test hypotheses of population divergence generated from the fossil record of Douglas-fir (Pseudotsuga menziesii), an ecologically and economically important western North American conifer. Specifically, we tested (i) the hypothesis that the Pliocene orogeny of the Cascades and Sierra Nevada caused the divergence of coastal and Rocky Mountain Douglas-fir varieties; and (ii) the hypothesis that multiple glacial refugia existed on the coast and in the Rocky Mountains. We found that Douglas-fir varieties diverged about 2.11 Ma (4.37 Ma-755 ka), which could be consistent with a Pliocene divergence. Rocky Mountain Douglas-fir probably resided in three or more glacial refugia. More variable molecular markers would be required to detect the two coastal refugia suggested in the fossil record. Comparison of mitochondrial DNA and chloroplast DNA variation revealed that gene flow via pollen linked populations isolated from seed exchange. Postglacial colonization of Canada from coastal and Rocky Mountain refugia near the ice margin at the Last Glacial Maximum produced a wide hybrid zone among varieties that formed almost exclusively by pollen exchange and chloroplast DNA introgression, not seed exchange. Postglacial migration rates were 50-165 m/year, insufficient to track projected 21st century warming in some regions. Although fossil and genetic data largely agree, each provides unique insights.

Gugger PF ，Sugita S ，Cavender-Bares J 《-》

Phylogeography of a parasitoid wasp (Diaeretiella rapae): no evidence of host-associated lineages.

The exceptional diversity of insects is often attributed to the effects of specialized relationships between insects and their hosts. Parasite-host interactions are influenced by current natural selection and dispersal, in addition to historical effects that may include past selection, vicariance, and random genetic drift. Both current and historical events can lead to reduced fitness on some hosts. If trade-offs in fitness on alternate hosts are common, adaptation to one host can prevent adaptation to another, giving rise to genetic differentiation among host-associated lineages. Previous studies of Diaeretiella rapae (Hymenoptera: Aphidiidae), a parasitoid of aphids, have revealed additive genetic differences in performance between populations that parasitize different aphid host species. To determine whether D. rapae populations collected from different aphid hosts have diverged into genetically independent lineages, we constructed a haplotype network based on sequence variation in mitochondrial DNA (mtDNA). We used single strand conformation polymorphism (SSCP) analysis to examine 2041 base pairs of mtDNA and to identify nucleotide sequences of 42 unique SSCP haplotypes. We found no association between mtDNA haplotypes and host species in either the ancestral range (Europe, Mediterranean region, Middle East, Asia) or part of the introduced range (western North America). Haplotypes likely to be ancestral were geographically widespread and found on both hosts, suggesting that the ability to use both hosts evolved prior to the diversification of the mtDNA. Ongoing gene flow appears to prevent the formation of host races.

Baer CF ，Tripp DW ，Bjorksten TA ，Antolin MF ... -  《MOLECULAR ECOLOGY》

The voyage of an invasive species across continents: genetic diversity of North American and European Colorado potato beetle populations.

The paradox of successful invading species is that they are likely to be genetically depauperate compared to their source population. This study on Colorado potato beetles is one of the few studies of the genetic consequences of continent-scale invasion in an insect pest. Understanding gene flow, population structure and the potential for rapid evolution in native and invasive populations offers insights both into the dynamics of small populations that become successful invaders and for their management as pests. We used this approach to investigate the invasion of the Colorado potato beetle (Leptinotarsa decemlineata) from North America to Europe. The beetles invaded Europe at the beginning of the 20th century and expanded almost throughout the continent in about 30 years. From the analysis of mitochondrial DNA (mtDNA) and amplified fragment length polymorphism (AFLP) markers, we found the highest genetic diversity in beetle populations from the central United States. The European populations clearly contained only a fraction of the genetic variability observed in North American populations. European populations show a significant reduction at nuclear markers (AFLPs) and are fixed for one mitochondrial haplotype, suggesting a single successful founder event. Despite the high vagility of the species and the reduction of genetic diversity in Europe, we found a similar, high level of population structure and low gene flow among populations on both continents. Founder events during range expansion, agricultural management with crop rotation, and selection due to insecticide applications are most likely the causes partitioning genetic diversity in this species.

Grapputo A ，Boman S ，Lindström L ，Lyytinen A ，Mappes J ... -  《MOLECULAR ECOLOGY》