Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans

Recent studies of mitochondrial DNA (mtDNA) variation in mammals and Drosophila have shown an excess of amino acid variation within species (replacement polymorphism) relative to the number of silent and replacement differences fixed between species. To examine further this pattern of nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5 genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans. Of interest are the frequency spectra of silent and replacement polymorphisms, and potential variation among genes and taxa in the departures from neutral expectations. The Drosophila ND3 and ND5 data show no significant excess of replacement polymorphism using the McDonald-Kreitman test. These data are in contrast to significant departures from neutrality for the ND3 gene in mammals and other genes in Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however, both Drosophila and human mtDNA show very significant excesses of amino acid polymorphism. Silent polymorphisms at ND5 show a significantly higher variance in frequency than replacement polymorphisms, and the latter show a significant skew toward low frequencies (Tajima's D = -1.954). These patterns are interpreted in light of the nearly neutral theory where mildly deleterious amino acid haplotypes are observed as ephemeral variants within species but do not contribute to divergence. The patterns of polymorphism and divergence at charge-altering amino acid sites are presented for the Drosophila ND5 gene to examine the evolution of functionally distinct mutations. Excess charge-altering polymorphism is observed at the carboxyl terminal and excess charge-altering divergence is detected at the amino terminal. While the mildly deleterious model fits as a net effect in the evolution of nonrecombining mitochondrial genomes, these data suggest that opposing evolutionary pressures may act on different regions of mitochondrial genes and genomes.      

Diadegma insulare development is altered by Plutella xylostella reared on water‐stressed host plants

Natural enemies of herbivores function in a multitrophic context, and their performance is directly or indirectly influenced by herbivores and their host plants. Very little is known about tritrophic interactions between host plants, pests and their parasitoids, particularly when the host plants are under any stress. Herbivores and their natural enemies’ response to plants under stress are diverse and variable. Therefore, in this study we investigated how diamondback moth, Plutella xylostella (L.), reared on water‐stressed host plants (Brassica napus L. and Sinapis alba L.) influenced the development of its larval parasitoid, Diadegma insulare (Cresson). No significant differences were observed in development of P. xylostella when reared on water‐stressed host plants. However, all results indicated that water stress had a strong effect on developmental parameters of D. insulare. Development of D. insulare was delayed when the parasitoid fed on P. xylostella, reared on stressed host plants. Egg to adult development of D. insulare was faster on non‐stressed B. napus than non‐stressed S. alba followed by stressed B. napus and S. alba. Female parasitoids were heavier on non‐stressed host plants than stressed counterparts. Furthermore, the parasitoid lived significantly longer on stressed B. napus. However, body size was not affected by water treatment. Most host plant parameters measured were significantly lower for water‐stressed than non‐stressed treatments. Results suggest that development of this important and effective P. xylostella parasitoid was influenced by both water stress and host plant species.     

Associations of physical activity with gut microbiota in pre-adolescent children

[Purpose] To determine whether physical activity (PA), primarily the recommended 60 minutes of moderate-to-vigorous PA, is associated with gut bacterial microbiota in 10-year-old children.[Methods] The Block Physical Activity Screener, which provides minutes/day PA variables, was used to determine whether the child met the PA recommendations. 16S rRNA sequencing was performed on stool samples from the children to profile the composition of their gut bacterial microbiota. Differences in alpha diversity metrics (richness, Pielou’s evenness, and Faith’s phylogenetic diversity) by PA were determined using linear regression, whereas beta diversity (unweighted and weighted UniFrac) relationships were assessed using PERMANOVA. Taxon relative abundance differentials were determined using DESeq2.[Results] The analytic sample included 321 children with both PA and 16S rRNA sequencing data (mean age [SD] =10.2 [0.8] years; 54.2% male; 62.9% African American), where 189 (58.9%) met the PA recommendations. After adjusting for covariates, meeting the PA recommendations as well as minutes/day PA variables were not significantly associated with gut richness, evenness, or diversity (p ≥ 0.19). However, meeting the PA recommendations (weighted UniFrac R² = 0.014, p = 0.001) was significantly associated with distinct gut bacterial composition. These compositional differences were partly characterized by increased abundance of Megamonas and Anaerovorax as well as specific Christensenellaceae_R-7_group taxa in children with higher PA.[Conclusion] Children who met the recommendations of PA had altered gut microbiota compositions. Whether this translates to a reduced risk of obesity or associated metabolic diseases is still unclear.     

Fitness of the parasitoid Diadegma insulare is affected by its host's food plants

The diamondback moth, Plutella xylostella (L.) is considered a specialist on Brassicaceae, but it is capable of expanding its food range by incorporation of non-brassicaceous plants into its diet. The use of a new food plant may change food availability and vulnerability of P. xylostella to its natural enemies, especially specialist parasitoids. In this laboratory study, we evaluated the bottom-up effects of two Brassicaceae viz. Brassica napus L. and Descurainia sophia (L.) Webb ex Prantl and two non-Brassicaceae viz. Tropaeolum majus L. and Cleome hassleriana Chodat on several fitness correlates of the specialist parasitoid, Diadegma insulare (Cresson) reared on P. xylostella larvae. Percentage of parasitism of host larvae by D. insulare varied among the plant species and was highest on T. majus and lowest on D. sophia. Values of several fitness correlates for D. insulare differed when the host was feeding on various plant species. Egg to adult development was fastest on B. napus followed by C. hassleriana, D. sophia and T. majus. Female wasps reared on C. hasseleriana lived the longest in absence of food. The response of D. insulare to potential food-plant expansion by its host P. xylostella is discussed.     

Resistance of some cultivated Brassicaceae to infestations by Plutella xylostella (Lepidoptera: Plutellidae)

Selecting insect-resistant plant varieties is a key component of integrated management programs of oligophagous pests such as diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), but rigorous research on important life history parameters of P. xylostella in relation to host plant resistance is rare. We evaluated six conventional brassicaceous species, namely, Brassica napus L. 'Q2', B. rapa L., B. juncea (L.) Czern., B. carinata L., B. oleracea L., and Sinapis alba L., and two herbicide-tolerant cultivars, namely, B. napus 'Liberty' and B. napus 'Conquest' for their resistance against P. xylostella. Brassicaceae species and cultivars varied considerably in their susceptibilities as hosts for P. xylostella. Sinapis alba and B. rapa plants were highly preferred by ovipositing females and trichome density on adaxial and abaxial leaf surfaces had nonsignificant effects on P. xylostella oviposition. Larval survival was similar on the genotypes we tested, but host plants significantly affected larval and pupal developmental time, herbivory, pupal weight, silk weight, adult body weight, forewing area and longevity (without food) of both male and female P. xylostella. Larval and pupal development of females was fastest on B. juncea and S. alba, respectively. Specimens reared on B. napus Liberty and B. oleracea, respectively, produced the lightest female and male pupae. Defoliation by both female and male larvae was highest on B. rapa, whereas least herbivory occurred on S. alba. Females reared on S. alba were heavier and lived longer in the absence of food than their counterparts raised on other tested host plants. Brassica oleracea could not compensate for larval feeding to the level of the other species we evaluated. B. napus Conquest, B. napus Q2, B. carinata, B. rapa, and S. alba produced, respectively, 1.6-, 1.8-, 1.8-, 3.9-, and 5.5-fold heavier root systems when infested than their uninfested counterparts, suggesting that these species were better able to tolerate P. xylostella infestations.     

Role of maximum rate of depolarization in predicting action potential duration during ventricular fibrillation

During ventricular fibrillation (VF) only 39% of the variation in action potential duration (APD) is accounted for by the previous diastolic interval [DI((n-1))], i.e., restitution, and the previous APD [APD((n-1))], i.e., memory. We tested the hypothesis that a characteristic of the AP upstroke, the maximum rate of depolarization (V(max)), also helps account for its APD. A floating microelectrode was used to make transmembrane recordings at 16,000 samples/s from the anterior left ventricular wall during four 20-s episodes of VF in each of six pigs. V(max), time from V(max) to 60% repolarization (APD(60)), and DI were calculated throughout all episodes. Stepwise linear regression was used to determine how well each APD(60) (APD(60n)) was predicted by V(max) of that AP, the four previous DIs (n-1, n - 2, n - 3, n - 4), and the three previous APD(60)s (n-1, n - 2, n - 3). V(max) entered in the regression equation significantly more often (86% of VF episodes) than either APD((n-1)) (47% of episodes) or DI((n-1)) (58% of episodes). When these three variables entered first or second, their coefficients were almost always positive, consistent with a longer APD associated with 1) a larger V(max), 2) a longer APD((n-1)), and 3) a longer DI((n-1)). R(2) of the regression for all entered variables was 0.51 +/- 0.01 (mean +/- SD). During the first 20 s of VF in swine, V(max) is a more important determinant of APD than the previous DI (restitution) or the previous APD (memory). All variables together account for only one-half of APD variation during VF.     

Identification of potential natural enemies of the pea leaf weevil,Sitona lineatus L. in western Canada

Sitona lineatus L., the pea leaf weevil, is an invasive pest of Pisum sativum L. (field pea) that has recently become established in Alberta, Canada. Adults consume seedling foliage and larvae feed on Rhizobium root nodules thereby reducing nitrogen fixation; both life stages can reduce yield. Eggs and adults are vulnerable to predators and parasitoids. In 2009, a series of experiments was undertaken to identify potential indigenous natural enemies of S. lineatus in southern Alberta. In three test arenas, eggs were exposed to starved ground beetles in no‐choice tests for 48 h. Egg debris was observed when eggs were exposed to Bembidion quadrimaculatum L., Microlestes linearis (LeConte), Bembidion rupicola (Kirby), Bembidion timidum (LeConte), Poecilus scitulus LeConte, and staphylinid beetles. Of the two most abundant carabid species, the smaller B. quadrimaculatum consistently removed significantly more eggs (94.6%) than the larger Pterostichus melanarius (17.4%). Similar results were observed in Petri dish and egg card tests. No egg debris was observed in tests with Pt. melanarius. Presence of the larger beetle, Pt. melanarius, resulted in a lower rate of egg removal by the smaller B. quadrimaculatum relative to the rates observed for B. quadrimaculatum alone. Intraguild predation of B. quadrimaculatum by Pt. melanarius was observed in 47% of tests. These results suggest that B. quadrimaculatum is a potential predator of S. lineatus eggs in field pea agroecosystems and should be considered for use in conservation biological control and integrated pest management programs.