Expressed Sequence Tags from Cephalic Chemosensory Organs of the Northern Walnut Husk Fly, Rhagoletis suavis, Including a Putative Canonical Odorant Receptor

Rhagoletis fruit flies are important both as major agricultural pests and as model organisms for the study of adaptation to new host plants and host race formation. Response to fruit odor plays a critical role in such adaptation. To better understand olfaction in Rhagoletis, an expressed sequence tag (EST) study was carried out on the antennae and maxillary palps of Rhagoletis suavis (Loew) (Diptera: Tephritidae), a common pest of walnuts in eastern United States. After cDNA cloning and sequencing, 544 ESTs were annotated. Of these, 66% had an open reading frame and could be matched to a previously sequenced gene. Based on BLAST sequence homology, 9% (49 of 544 sequences) were nuclear genes potentially involved in olfaction. The most significant finding is a putative odorant receptor (OR), RSOr1, that is homologous to Drosophila melanogaster Or49a and Or85f. This is the first tephritid OR discovered that might recognize a specific odorant. Other olfactory genes recovered included odorant binding proteins, chemosensory proteins, and putative odorant degrading enzymes

Variation in life history traits and transcriptome associated with adaptation to diet shifts in the ladybird Cryptolaemus montrouzieri

Background: Despite the broad diet range of many predatory ladybirds, the mechanisms involved in their adaptation to diet shifts are not completely understood. Here, we explored how a primarily coccidophagous ladybird Cryptolaemus montrouzieri adapts to feeding on aphids. Results: Based on the lower survival rate, longer developmental time, and lower adult body weight and reproduction rate of the predator, the aphid Megoura japonica proved being less suitable to support C. montrouzieri as compared with the citrus mealybug Planococcus citri. The results indicated up-regulation of genes related to ribosome and translation in fourth instars, which may be related to their suboptimal development. Also, several genes related to biochemical transport and metabolism, and detoxification were up-regulated as a result of adaptation to the changes in nutritional and non-nutritional (toxic) components of the prey. Conclusion: Our results indicated that C. montrouzieri succeeded in feeding on aphids by regulation of genes related to development, digestion and detoxification. Thus, we argue that these candidate genes are valuable for further studies of the functional evolution of ladybirds led by diet shifts

Ecological Niche Dimensionality and the Evolutionary Diversification of Stick Insects

The degree of phenotypic divergence and reproductive isolation between taxon pairs can vary quantitatively, and often increases as evolutionary divergence proceeds through various stages, from polymorphism to population differentiation, ecotype and race formation, speciation, and post-speciational divergence. Although divergent natural selection promotes divergence, it does not always result in strong differentiation. For example, divergent selection can fail to complete speciation, and distinct species pairs sometimes collapse (‘speciation in reverse’). Widely-discussed explanations for this variability concern genetic architecture, and the geographic arrangement of populations. A less-explored possibility is that the degree of phenotypic and reproductive divergence between taxon pairs is positively related to the number of ecological niche dimensions (i.e., traits) subject to divergent selection. Some data supporting this idea stem from laboratory experimental evolution studies using Drosophila, but tests from nature are lacking. Here we report results from manipulative field experiments in natural populations of herbivorous Timema stick insects that are consistent with this ‘niche dimensionality’ hypothesis. In such insects, divergent selection between host plants might occur for cryptic colouration (camouflage to evade visual predation), physiology (to detoxify plant chemicals), or both of these niche dimensions. We show that divergent selection on the single niche dimension of cryptic colouration can result in ecotype formation and intermediate levels of phenotypic and reproductive divergence between populations feeding on different hosts. However, greater divergence between a species pair involved divergent selection on both niche dimensions. Although further replication of the trends reported here is required, the results suggest that dimensionality of selection may complement genetic and geographic explanations for the degree of diversification in nature

Simple sequence repeats in Puccinia graminis: abundance, cross-formae specialis and intra-species utility, and development of novel markers

We evaluated the abundance and nature of simple sequence repeats (SSRs) in the causal agent of stem rust of wheat, Puccinia graminis f. sp. tritici, in order to characterize and develop SSR markers. A strategy was tested in which publicly available genome datasets extracted from genome sequences of P. graminis f. sp. tritici were searched for abundance and mined for candidate novel SSR markers that could be applied to a wide range of Puccinia species. The genome analysis from 393 supercontigs yielded a total of 34,359 SSR repeat motifs. A majority of these (98 %) were mononucleotide, dinucleotide, and trinucleotide repeats. The AG/GA dinucleotide motifs were the most common, and a TTGTT motif was the longest of all SSRs. From a total of 500 primer pairs designed, 460 produced bands within the expected size range and 56 SSR markers were eventually developed. Most of these were tetranucleotide and pentanucleotide motifs with PIC values ranging from 0.40 to 0.91 with an average PIC value of 0.71. The cross amplification of these markers in 11 isolates representing five Puccinia species and six formae speciales of P. graminis was also investigated. The frequency of PCR amplifications was lower for the species P. coronata, P. striiformis and P. triticina, and consequently, no significant polymorphisms were detected. In contrast 10, 10, and 11 polymorphic SSR loci were identified in P. graminis f. sp. secalis, P. graminis f. sp. avenae, and the “Scabrum” rust, respectively. The SSR markers reported here will be useful to characterize and profile global diversity in the important pathogen P. graminis