Polygamy and an absence of fine-scale structure in Dendroctonus ponderosae (Hopk.) (Coleoptera: Curcilionidae) confirmed using molecular markers.

An understanding of mating systems and fine-scale spatial genetic structure is required to effectively manage forest pest species such as Dendroctonus ponderosae (mountain pine beetle). Here we used genome-wide single-nucleotide polymorphisms to assess the fine-scale genetic structure and mating system of D. ponderosae collected from a single stand in Alberta, Canada. Fine-scale spatial genetic structure was absent within the stand and the majority of genetic variation was best explained at the individual level. Relatedness estimates support previous reports of pre-emergence mating. Parentage assignment tests indicate that a polygamous mating system better explains the relationships among individuals within a gallery than the previously reported female monogamous/male polygynous system. Furthermore, there is some evidence to suggest that females may exploit the galleries of other females, at least under epidemic conditions. Our results suggest that current management models are likely to be effective across large geographic areas based on the absence of fine-scale genetic structure.

Effects of postfire salvage logging on deadwood-associated beetles.

In Canada and the United States pressure to recoup financial costs of wildfire by harvesting burned timber is increasing, despite insufficient understanding of the ecological consequences of postfire salvage logging. We compared the species richness and composition of deadwood-associated beetle assemblages among undisturbed, recently burned, logged, and salvage-logged, boreal, mixed-wood stands. Species richness was lowest in salvage-logged stands, largely due to a negative effect of harvesting on the occurrence of wood- and bark-boring species. In comparison with undisturbed stands, the combination of wildfire and logging in salvage-logged stands had a greater effect on species composition than either disturbance alone. Strong differences in species composition among stand treatments were linked to differences in quantity and quality (e.g., decay stage) of coarse woody debris. We found that the effects of wildfire and logging on deadwood-associated beetles were synergistic, such that the effects of postfire salvage logging could not be predicted reliably on the basis of data on either disturbance alone. Thus, increases in salvage logging of burned forests may have serious negative consequences for deadwood-associated beetles and their ecological functions in early postfire successional forests.

Molecular and Morphological Evidence for Interspecific Hybridization Between Cronartium ribicola and C. comandrae on Pinus flexilis in Southwestern Alberta.

In May 2003, a survey was conducted in southwestern Alberta, east of the Rocky Mountains, to determine the extent of the spread and genetic diversity of white pine blister rust, which is caused by Cronartium ribicola J.C. Fisch. Aeciospores were sampled from white pine blister rust cankers in three infected limber pine (Pinus flexilis James) stands separated from one another by 100 to 215 km. DNA genotypes were determined for 12 codominant PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism) loci representing genes derived from an EST library. At each site sampled, some aecia displayed DNA genotypes that were heterozygous at all loci and possessed novel alleles (GenBank Accession Nos. DQ009533-DQ009611). At Waterton Lakes, Kananaskis County, and Porcupine Hills, 29%, 11%, and 3% of sampled aecia and 38%, 33%, and 10% of sampled trees, respectively, possessed these unusual profiles. In May 2004, similar genetic profiles were found at two of these sites, Waterton Lakes and Kananaskis County, at 17 and 25% of sampled aecia (25% of sampled trees). In each of these aecia, genotyping and sequence analysis revealed this pattern was due to the presence of one C. ribicola and one C. comandrae Peck. allele at each of the 12 loci. Scanning electron microscopy (SEM) revealed aeciospore morphology that was intermediate between C. ribicola and C. comandrae. Aeciospores were longer (16 to 20 × 25 to 40 µm) than the expected range for C. ribicola (18 to 20 × 22 to 31 µm) (3). They were also fusiform, obovoid or short-to-long ellipsoid, but not pyriform-acuminate as in C. comandrae, and without a true conspicuous smooth spot as in C. ribicola. This provides evidence for interspecific hybridization between C. ribicola and C. comandrae, the causal agent of comandra blister rust. We hypothesize that the presence of nearby C. comandrae-infected lodgepole pine (P. contorta Dougl.) could have led to spermatization of C. ribicola receptive hyphae by C. comandrae pycniospores, resulting in the formation of hybrid aecia. An important question is whether these hybrids have a different host range that could potentially extend its geographic range in areas where the telial host, Ribes spp. L., is not abundant. The hybrid rust Melampsora × columbiana Newcombe was shown to exhibit virulence against certain hybrid poplar clones that had previously been reported as resistant against both parental rusts (M. medusae Thuem. and M. occidentalis Jacks) and abundant pathogenic variation has been observed (2). Furthermore, the ability to colonize unexpected hosts could provide fitness advantages over parental species, as was observed in Phytophthora spp. pathogenic on alder (1). Host range and virulence assays should be conducted to assess the potential impact of this hybrid. References: (1) C. M. Brasier et al. Proc. Natl. Acad. Sci. USA 96:5878, 1999. (2) G. Newcombe et al. Phytopathology 91:981, 2001. (3) W. G. Ziller. The Tree Rusts of Western Canada. Can. For Serv. No. 1329. Pacific Forestry Center, Victoria, BC, 1974.

Mitochondrial DNA sequence divergence in weevils of the Pissodes strobi species complex (Coleoptera:Curculionidae).

Mitochondrial DNA sequence divergence is unusually high between several species of the Pissodes strobi complex, in contrast to low allozyme and morphological divergences, and the ability to hybridize in the laboratory. We sequenced an 810 bp segment in seven individuals, representing four species in the P. strobi complex and one outgroup species, P. affinis Randall. The 810 bp segment covered the 3' half of the cytochrome oxidase subunit I (COI) gene. We also sequenced one specimen of P. strobi (Peck) over a 2301 bp region of mtDNA, extending from the 5' end of COI to the 3' end of COII. Uncorrected sequence divergences were below 1.1% among three specimens of P. schwarzi Hopkins, and between P. terminalis Hopping and P. nemorensis Germar. All other interspecific combinations in the P. strobi complex showed divergences of 6.0-7.5%. The outgroup species, P. affinis, had an average divergence of 12.8% from members of the P. strobi group. As in most other insects, A + T content in Pissodes mtDNA was high; transition:transversion ratio was high among lineages exhibiting low divergences, but declined with increasing sequence divergence; and inferred amino acid sequence divergences were low. The degree of sequence divergence differs markedly across different functional regions of the COI gene. The high mtDNA divergences within the P. strobi complex calculated from direct sequencing support earlier reports based on restriction site surveys; however, cladograms based on mtDNA sequence differ from those based on earlier work.