Oviposition preferences, Bt susceptibilities, and tissue feeding of fall armyworm (Lepidoptera: Noctuidae) host strains.

BACKGROUND: The fall armyworm, Spodoptera frugiperda (Smith), is a pest of many economically essential crops across several continents. Documentation of resistance to Bt toxins has caused growing concern in agricultural communities regarding the ability to keep fall armyworm populations below economic thresholds. The existence of two host strains referred to as the 'rice' and 'corn' strains is a complicating and under-researched factor of fall armyworm biology and management. It is essential to characterize the differences between the host strains, as well as their rice/corn hybrid offspring, to elucidate their contributions to field-evolved resistance. RESULTS: Corn was a preferred oviposition host for both rice and corn strain fall armyworm, and a suitable larval host plant for each of the four populations tested. Corn strain females displayed a significant preference towards oviposition on plants that lacked mechanical damage. The rice strain population was generally less tolerant to Cry1F corn tissue than the corn strain and hybrid populations, which performed in a similar way to one another. CONCLUSION: The preference for corn as an ovipositional host may have an impact on resistance management when coupled with differential host strain Bt tolerances, though more studies are needed. Hybrid tolerance to Bt toxins could possibly contribute to the evolution of Bt resistance. This is the first study to compare the larval fitness and survival of rice/corn hybrid fall armyworm to that of pure host strains using a tissue-based approach.

Trans-Atlantic Distribution and Introgression as Inferred from Single Nucleotide Polymorphism: Mussels Mytilus and Environmental Factors.

Large-scale climate changes influence the geographic distribution of biodiversity. Many taxa have been reported to extend or reduce their geographic range, move poleward or displace other species. However, for closely related species that can hybridize in the natural environment, displacement is not the only effect of changes of environmental variables. Another option is subtler, hidden expansion, which can be found using genetic methods only. The marine blue mussels Mytilus are known to change their geographic distribution despite being sessile animals. In addition to natural dissemination at larval phase-enhanced by intentional or accidental introductions and rafting-they can spread through hybridization and introgression with local congeners, which can create mixed populations sustaining in environmental conditions that are marginal for pure taxa. The Mytilus species have a wide distribution in coastal regions of the Northern and Southern Hemisphere. In this study, we investigated the inter-regional genetic differentiation of the Mytilus species complex at 53 locations in the North Atlantic and adjacent Arctic waters and linked this genetic variability to key local environmental drivers. Of seventy-nine candidate single nucleotide polymorphisms (SNPs), all samples were successfully genotyped with a subset of 54 SNPs. There was a clear interregional separation of Mytilus species. However, all three Mytilus species hybridized in the contact area and created hybrid zones with mixed populations. Boosted regression trees (BRT) models showed that inter-regional variability was important in many allele models but did not prevail over variability in local environmental factors. Local environmental variables described over 40% of variability in about 30% of the allele frequencies of Mytilus spp. For the 30% of alleles, variability in their frequencies was only weakly coupled with local environmental conditions. For most studied alleles the linkages between environmental drivers and the genetic variability of Mytilus spp. were random in respect to "coding" and "non-coding" regions. An analysis of the subset of data involving functional genes only showed that two SNPs at Hsp70 and ATPase genes correlated with environmental variables. Total predictive ability of the highest performing models (r2 between 0.550 and 0.801) were for alleles that discriminated most effectively M.trossulus from M.edulis and M.galloprovincialis, whereas the best performing allele model (BM101A) did the best at discriminating M.galloprovincialis from M. edulis and M.trossulus. Among the local environmental variables, salinity, water temperature, ice cover and chlorophyll a concentration were by far the greatest predictors, but their predictive performance varied among different allele models. In most cases changes in the allele frequencies along these environmental gradients were abrupt and occurred at a very narrow range of environmental variables. In general, regions of change in allele frequencies for M.trossulus occurred at 8-11 psu, 0-10 C, 60%-70% of ice cover and 0-2 mg m-3 of chlorophyll a, M. edulis at 8-11 and 30-35 psu, 10-14 C and 60%-70% of ice cover and for M.galloprovincialis at 30-35 psu, 14-20 C.

Stromule extension along microtubules coordinated with actin-mediated anchoring guides perinuclear chloroplast movement during innate immunity.

Dynamic tubular extensions from chloroplasts called stromules have recently been shown to connect with nuclei and function during innate immunity. We demonstrate that stromules extend along microtubules (MTs) and MT organization directly affects stromule dynamics since stabilization of MTs chemically or genetically increases stromule numbers and length. Although actin filaments (AFs) are not required for stromule extension, they provide anchor points for stromules. Interestingly, there is a strong correlation between the direction of stromules from chloroplasts and the direction of chloroplast movement. Stromule-directed chloroplast movement was observed in steady-state conditions without immune induction, suggesting it is a general function of stromules in epidermal cells. Our results show that MTs and AFs may facilitate perinuclear clustering of chloroplasts during an innate immune response. We propose a model in which stromules extend along MTs and connect to AF anchor points surrounding nuclei, facilitating stromule-directed movement of chloroplasts to nuclei during innate immunity.

Survivorship of Z-Pheromone Race European Corn Borer (Lepidoptera: Crambidae) on a Range of Host Plants Varying in Defensive Chemistry.

The European corn borer, Ostrinia nubilalis (Hübner), was introduced in North America in the early 1900s and became a major pest of corn. After its introduction, it was found on > 200 other plant hosts, but corn remained its primary host. Early life history studies indicated that European corn borer had the potential of a wide host range. For nearly 80 yr before the introduction of Bt corn, the European corn borer was a major pest of corn in North America. This study investigated the growth and survivorship of the Z-pheromone race European corn borer on a range of hosts that vary in defensive chemistries and historic degree of infestation to better understand the current host plant range of Z-pheromone race of O. nubilalis. The plants tested include sweet corn, cry1F Bt field corn, non-Bt corn, cucumber, tomato, and green bean. Experiments were conducted in the growth chamber, greenhouse, and field to determine survival under different conditions. In most cases, results supported the expected outcome, with significantly higher survival on non-Bt corn hosts than the other hosts tested. Neonate larvae fed exclusively on leaves of green bean exhibited intermediate survival, whereas third-instars fed on only leaves of cucumber survived intermediately. Larvae on Bt corn and tomato had comparable low survival rates, overall suggesting that the defensive features of tomato are about as effective as Cry1F Bt corn. Non-Bt corn was found to be the most suitable host plant, overall for European corn borer among those tested.

Loss of Sip1 leads to migration defects and retention of ectodermal markers during lens development.

SIP1 encodes a DNA-binding transcription factor that regulates multiple developmental processes, as highlighted by the pleiotropic defects observed in Mowat-Wilson syndrome, which results from mutations in this gene. Further, in adults, dysregulated SIP1 expression has been implicated in both cancer and fibrotic diseases, where it functionally links TGFß signaling to the loss of epithelial cell characteristics and gene expression. In the ocular lens, an epithelial tissue important for vision, Sip1 is co-expressed with epithelial markers, such as E-cadherin, and is required for the complete separation of the lens vesicle from the head ectoderm during early ocular morphogenesis. However, the function of Sip1 after early lens morphogenesis is still unknown. Here, we conditionally deleted Sip1 from the developing mouse lens shortly after lens vesicle closure, leading to defects in coordinated fiber cell tip migration, defective suture formation, and cataract. Interestingly, RNA-Sequencing analysis on Sip1 knockout lenses identified 190 differentially expressed genes, all of which are distinct from previously described Sip1 target genes. Furthermore, 34% of the genes with increased expression in the Sip1 knockout lenses are normally downregulated as the lens transitions from the lens vesicle to early lens, while 49% of the genes with decreased expression in the Sip1 knockout lenses are normally upregulated during early lens development. Overall, these data imply that Sip1 plays a major role in reprogramming the lens vesicle away from a surface ectoderm cell fate towards that necessary for the development of a transparent lens and demonstrate that Sip1 regulates distinctly different sets of genes in different cellular contexts.

Statistical tests for measures of colocalization in biological microscopy.

Colocalization analysis is the most common technique used for quantitative analysis of fluorescence microscopy images. Several metrics have been developed for measuring the colocalization of two probes, including Pearson's correlation coefficient (PCC) and Manders' correlation coefficient (MCC). However, once measured, the meaning of these measurements can be unclear; interpreting PCC or MCC values requires the ability to evaluate the significance of a particular measurement, or the significance of the difference between two sets of measurements. In previous work, we showed how spatial autocorrelation confounds randomization techniques commonly used for statistical analysis of colocalization data. Here we use computer simulations of biological images to show that the Student's one-sample t-test can be used to test the significance of PCC or MCC measurements of colocalization, and the Student's two-sample t-test can be used to test the significance of the difference between measurements obtained under different experimental conditions.

Ovarian abnormalities in a mouse model of fragile X primary ovarian insufficiency.

FMR1 premutation (PM) alleles have 55-200 CGG·CCG-repeats in their 5' UTR. PM carriers are at risk of fragile X-associated tremor and ataxia syndrome (FXTAS). Females are also at risk for FX primary ovarian insufficiency (FXPOI). PM pathology is generally attributed to deleterious properties of transcripts with long CGG-tracts. For FXPOI, hormone changes suggest a reduced residual follicle pool. Whether this is due to a smaller than normal original follicle pool or an increased rate of follicle depletion is unclear. A FX-PM mouse the authors generated with 130 CGG·CCG-repeats in the endogenous Fmr1 gene recapitulates features of FXTAS. Here the authors demonstrate that the gross development of the ovary and the establishment of the primordial follicle pool is normal in these mice. However, these animals show a faster loss of follicles of all follicle classes, suggesting that the problem is intrinsic to the ovary. In addition, many oocytes show aberrant nuclear accumulation of FMRP and elevated levels of ubiquitination. Furthermore, PM follicles are smaller and have fewer granulosa cells (GCs) than normal. Thus, these animals have ovarian abnormalities involving both the oocytes and GCs that may shed light on the molecular basis of FXPOI in humans.

A practical guide to evaluating colocalization in biological microscopy.

Fluorescence microscopy is one of the most powerful tools for elucidating the cellular functions of proteins and other molecules. In many cases, the function of a molecule can be inferred from its association with specific intracellular compartments or molecular complexes, which is typically determined by comparing the distribution of a fluorescently labeled version of the molecule with that of a second, complementarily labeled probe. Although arguably the most common application of fluorescence microscopy in biomedical research, studies evaluating the "colocalization" of two probes are seldom quantified, despite a diversity of image analysis tools that have been specifically developed for that purpose. Here we provide a guide to analyzing colocalization in cell biology studies, emphasizing practical application of quantitative tools that are now widely available in commercial and free image analysis software.

Temperature adaptation at homologous sites in proteins from nine thermophile-mesophile species pairs.

Whether particular amino acids are favored by selection at high temperatures over others has long been an open question in protein evolution. One way to approach this question is to compare homologous sites in proteins from one thermophile and a closely related mesophile; asymmetrical substitution patterns have been taken as evidence for selection favoring certain amino acids over others. However, most pairs of prokaryotic species that differ in optimum temperature also differ in genome-wide GC content, and amino acid content is known to be associated with GC content. Here, I compare homologous sites in nine thermophilic prokaryotes and their mesophilic relatives, all with complete published genome sequences. After adjusting for the effects of differing GC content with logistic regression, 139 of the 190 pairs of amino acids show significant substitutional asymmetry, evidence of widespread adaptive amino acid substitution. The patterns are fairly consistent across the nine pairs of species (after taking the effects of differing GC content into account), suggesting that much of the asymmetry results from adaptation to temperature. Some amino acids in some species pairs deviate from the overall pattern in ways indicating that adaptation to other environmental or physiological differences between the species may also play a role. The property that is best correlated with the patterns of substitutional asymmetry is transfer free energy, a measure of hydrophobicity, with more hydrophobic amino acids favored at higher temperatures. The correlation of asymmetry and hydrophobicity is fairly weak, suggesting that other properties may also be important.

Apparent trends of amino Acid gain and loss in protein evolution due to nearly neutral variation.

It has recently been claimed that certain amino acids have been increasing in frequency in all living organisms for most of the history of life on earth, while other amino acids have been decreasing in frequency. Three lines of evidence have been offered for this assertion, but each has a more plausible alternative interpretation. Here I show that unequal patterns of gains and losses for particular pairs of amino acids (such as more leucine --> phenylalanine than phenylalanine --> leucine substitutions in humans and chimpanzees since they split from a common ancestor) are consistent with a simple neutral model at equilibrium amino acid frequencies. Unequal numbers of gains and losses for particular amino acids (such as more gains than losses of cysteine) are shown by simulations to be consistent with a model of nearly neutral evolution. Unequal numbers of gains and losses for particular amino acids in human polymorphism data are shown by simulations to be explainable by the nearly neutral model as well. In a comparison of protein sequences from four strains of Escherichia coli, polarized by one outgroup strain of Salmonella, the disparity in number of gains and losses for particular amino acids is strong in terminal branches but weaker or nonexistent in internal branches, which is inconsistent with the universal trend model but as expected under the nearly neutral model.

Positive selection on an acrosomal sperm protein, M7 lysin, in three species of the mussel genus Mytilus.

Marine invertebrate sperm proteins are particularly interesting because they are characterized by positive selection and are likely to be involved in prezyogotic isolation and, thus, speciation. Here, we present the first survey of interspecific and intraspecific variation of a bivalve sperm protein among a group of species that regularly hybridize in nature. M7 lysin is found in sperm acrosomes of mussels and dissolves the egg vitelline coat, permitting fertilization. We sequenced multiple alleles of the mature protein-coding region of M7 lysin from allopatric populations of mussels in the Mytilus edulis species group (M. edulis, M. galloprovincialis, and M. trossulus). A significant McDonald-Kreitman test showed an excess of fixed amino acid replacing substitutions between species, consistent with positive selection. In addition, Kolmogorov-Smirnov tests showed significant heterogeneity in polymorphism to divergence ratios for both synonymous variation and combined synonymous and nonsynonymous variation within M. galloprovincialis. These results indicate that there has been adaptive evolution at M7 lysin and, furthermore, show that positive selection on sperm proteins can occur even when postzygotic reproductive isolation is incomplete.

Evidence for balancing selection from nucleotide sequence analyses of human G6PD.

Glucose-6-phosphate dehydrogenase (G6PD) mutations that result in reduced enzyme activity have been implicated in malarial resistance and constitute one of the best examples of selection in the human genome. In the present study, we characterize the nucleotide diversity across a 5.2-kb region of G6PD in a sample of 160 Africans and 56 non-Africans, to determine how selection has shaped patterns of DNA variation at this gene. Our global sample of enzymatically normal B alleles and A, A-, and Med alleles with reduced enzyme activities reveals many previously uncharacterized silent-site polymorphisms. In comparison with the absence of amino acid divergence between human and chimpanzee G6PD sequences, we find that the number of G6PD amino acid polymorphisms in human populations is significantly high. Unlike many other G6PD-activity alleles with reduced activity, we find that the age of the A variant, which is common in Africa, may not be consistent with the recent emergence of severe malaria and therefore may have originally had a historically different adaptive function. Overall, our observations strongly support previous genotype-phenotype association studies that proposed that balancing selection maintains G6PD deficiencies within human populations. The present study demonstrates that nucleotide sequence analyses can reveal signatures of both historical and recent selection in the genome and may elucidate the impact that infectious disease has had during human evolution.