Quantitative genetic parameters of agronomic and quality traits in a global germplasm collection reveal excellent breeding perspectives for Jatropha curcas L.

Jatropha curcas L. (jatropha) is an undomesticated plant, which has received great attention in recent years for its potential in biofuel production and in greening and rehabilitation of wastelands. Yet the absence of improved cultivars and the lack of agronomic knowledge are limiting factors for successful jatropha cultivation. The objectives of the present study were to investigate the perspectives of a worldwide jatropha breeding program and specifically to (i) estimate variance components and heritabilities for agronomic and quality traits in the early phase of cultivation; (ii) assess phenotypic and genetic correlations among those traits; and (iii) discuss strategies for breeding high yielding jatropha cultivars. Data on various traits was collected from 375 jatropha genotypes, which were tested at seven locations during the first 3 years of growth. The accumulated seed yields and the seed yields per harvest year differed significantly among the testing locations. The estimates of genetic and genotype‐by‐environment interaction variances were significant and estimates of heritabilities were high for all yield parameters. The estimates of genetic correlations indicated a strong association among yield parameters. Oil yield was strongly correlated with seed yield and only weakly with oil content in seeds. The perspectives of a jatropha breeding program are excellent. Improved cultivars, definition of favorable environmental factors and refinement of agronomic management practices are needed to secure sustainable jatropha cultivation.     

Exotic ladybirds for biological control of herbivorous insects – a review

Since the late 19th century, exotic ladybirds (Coleoptera: Coccinellidae) have been used extensively for suppressing herbivorous insects of economic importance. In recent decades, the introduction of non‐native biological control (BC) agents has been greatly limited due to the awareness of the potential non‐target effects of introductions. Nonetheless, recent episodes of biological invasions of economically important pests have raised the need to carefully consider whether the expected benefits of pest control go beyond the possible environmental risks of introduction. To better understand the factors that contributed to successful BC programs, here we review the literature behind classical and augmentative BC using exotic ladybirds. Additionally, by means of case studies, we discuss the BC efficacy of selected exotic species, e.g., Coccinella septempunctata L., Harmonia axyridis (Pallas), and Hippodamia variegata (Goeze), and their position within the communities of predators in the introduced areas of USA, Canada, and Chile. In Europe, much of the research on exotic ladybirds has been conducted on the undesired impact of H. axyridis. Therefore, we summarize the risk assessment data for this species and review the field research investigating the ecological impact on European aphidophagous predators. According to the BIOCAT database of classical BC programs, 212 ladybird species belonging to 68 genera have been released in about 130 years of BC activity, with 14.6% of introductions having resulted in partial, substantial, or complete control of the target pest. However, because post‐release evaluation of establishment and BC success has not always been conducted, this rate could underestimate the successful cases. Among other factors, ladybird establishment and pest suppression mostly depend on (1) intrinsic factors, i.e., high voracity, synchronized predator‐prey life cycle, and high dispersal ability, and (2) extrinsic factors, i.e., adaptability to the new environment and landscape composition. This review contributes to improved understanding of ladybirds as exotic BC agents.     

Effects of larval crowding on quantitative variation for development time and viability in Drosophila melanogaster

Competition between individuals belonging to the same species is a universal feature of natural populations and is the process underpinning organismal adaptation. Despite its importance, still comparatively little is known about the genetic variation responsible for competitive traits. Here, we measured the phenotypic variation and quantitative genetics parameters for two fitness‐related traits—egg‐to‐adult viability and development time—across a panel of Drosophila strains under varying larval densities. Both traits exhibited substantial genetic variation at all larval densities, as well as significant genotype‐by‐environment interactions (GEIs). GEI was attributable to changes in the rank order of reaction norms for both traits, and additionally to differences in the between‐line variance for development time. The coefficient of genetic variation increased under stress conditions for development time, while it was higher at both high and low densities for viability. While development time also correlated negatively with fitness at high larval densities—meaning that fast developers have high fitness—there was no correlation with fitness at low density. This result suggests that GEI may be a common feature of fitness‐related genetic variation and, further, that trait values under noncompetitive conditions could be poor indicators of individual fitness. The latter point could have significant implications for animal and plant breeding programs, as well as for conservation genetics.     

Quarantine host range of Bikasha collaris,a potential biological control agent of Chinese tallowtree (Triadica sebifera) in North America

Chinese tallowtree, Triadica sebifera (L.) Small (Euphorbiaceae), is one of the worst invasive weeds of the southeastern USA impacting coastal wetlands, forests, and natural areas. Traditional mechanical and chemical controls have been unable to limit the spread, and this invasive species continues to expand its range. A proposed biological control candidate, the flea beetle Bikasha collaris (Baly) (Coleoptera: Chrysomelidae), shows high specificity for the target weed Chinese tallowtree. Results from a series of no‐choice and choice feeding tests of B. collaris adults and larvae indicated that this flea beetle was highly specific to Chinese tallowtree. The larvae of B. collaris feed by tunneling in the roots, whereas the adults feed on the leaves of Chinese tallowtree. A total of 77 plant taxa, primarily from members of the tallow plant family Euphorbiaceae, were tested in numerous test designs. Larval no‐choice tests indicated that larvae completed development only on two of the non‐target taxa. Of 80 B. collaris larvae fed roots of Hippomane mancinella L. and 50 larvae fed roots of Ricinus communis L., two and three larvae completed development, respectively. The emerging adults of these five larvae died within 3 days without reproducing. Larval choice tests also indicated little use of these non‐target taxa. Adult no‐choice tests indicated little leaf damage by B. collaris on the non‐targets except for Ditrysinia fruticosa (Bartram) Govaerts & Frodin and Gymnanthes lucida Sw. When given a choice, however, B. collaris adults consumed much less of the non‐targets D. fruticosa (7.4%) and G. lucida (6.1%) compared with the control leaves. Finally, no‐choice oviposition tests indicated that no eggs were produced when adults were fed all non‐target taxa, except those fed G. lucida. These B. collaris adults fed G. lucida leaves produced an average of 4.6 eggs compared with 115.0 eggs per female when fed Chinese tallowtree. The eggs produced from adults fed G. lucida were either inviable or the emerging larvae died within 1 day. These results indicate that the flea beetle B. collaris was unable to complete its life cycle on any of the non‐target taxa tested. If approved for field release, B. collaris will be the first biological control agent deployed against Chinese tallowtree in the USA. This flea beetle may play an important role in suppressing Chinese tallowtree and contribute to the integrated control of this invasive weed.     

Ecological interactions and the fitness effect of water‐use efficiency: Competition and drought alter the impact of natural MPK12 alleles in Arabidopsis

The presence of substantial genetic variation for water‐use efficiency (WUE) suggests that natural selection plays a role in maintaining alleles that affect WUE. Soil water deficit can reduce plant survival, and is likely to impose selection to increase WUE, whereas competition for resources may select for decreased WUE to ensure water acquisition. We tested the fitness consequences of natural allelic variation in a single gene (MPK12) that influences WUE in Arabidopsis, using transgenic lines contrasting in MPK12 alleles, under four treatments; drought/competition, drought/no competition, well‐watered/competition, well‐watered/no competition. Results revealed an allele × environment interaction: Low WUE plants performed better in competition, resulting from increased resource consumption. Contrastingly, high WUE individuals performed better in no competition, irrespective of water availability, presumably from enhanced water conservation and nitrogen acquisition. Our findings suggest that selection can influence MPK12 evolution, and represents the first assessment of plant fitness resulting from natural allelic variation at a single locus affecting WUE.     

Environmental origins of sexually selected variation and a critique of the fluctuating asymmetry-sexual selection hypothesis

Identifying sources of phenotypic variability in secondary sexual traits is critical for understanding their signaling properties, role in sexual selection, and for predicting their evolutionary dynamics. The present study tests for the effects of genotype, developmental temperature, and their interaction, on size and fluctuating asymmetry of the male sex comb, a secondary sexual character, in Drosophila bipectinata Duda. Both the size and symmetry of elements of the sex comb have been shown previously to be under sexual selection in a natural population in northeastern Australia. Two independent reciprocal crosses were conducted at 25 degrees and 29 degrees C between genetic lines extracted from this population that differed in the size of the first (TC1) and third (TC3) comb segments. These temperatures are within the documented range experienced by the species in nature. Additive and dominance genetic effects were detected for TC1, whereas additive genetic, and Y-chromosomal effects were detected for TC3. TC2 and TC3 decreased sharply with increasing temperature, by 10% and 22%, respectively. In contrast, positional fluctuating asymmetry (PFA) significantly increased with temperature, by up to 38%. The results (1) document an important source of environmental variance in a sexual ornament expected to reduce trait heritability in field populations, and thus act to attenuate response to sexual selection, (2) suggest that variation in ornament size reflects differences in male condition; and (3) support the general hypothesis that asymmetry in a sexual ornament is indicative of developmental instability arising from environmental stress. The "environmental heterogeneity" (EH) hypothesis is proposed, and supportive evidence for it presented, to explain negative size-FA correlations in natural populations. Data and theory challenge the use of negative size-FA correlations observed in nature to support the FA-sexual selection hypothesis, which posits that such correlations are driven by differences in genetic quality among individuals.     

Selection in a fluctuating environment leads to decreased genetic variation and facilitates the evolution of phenotypic plasticity

Changes in the environment are expected to induce changes in the quantitative genetic variation, which influences the ability of a population to adapt to environmental change. Furthermore, environmental changes are not constant in time, but fluctuate. Here, we investigate the effect of rapid, continuous and/or fluctuating temperature changes in the seed beetle Callosobruchus maculatus, using an evolution experiment followed by a split-brood experiment. In line with expectations, individuals responded in a plastic way and had an overall higher potential to respond to selection after a rapid change in the environment. After selection in an environment with increasing temperature, plasticity remained unchanged (or decreased) and environmental variation decreased, especially when fluctuations were added; these results were unexpected. As expected, the genetic variation decreased after fluctuating selection. Our results suggest that fluctuations in the environment have major impact on the response of a population to environmental change; in a highly variable environment with low predictability, a plastic response might not be beneficial and the response is genetically and environmentally canalized resulting in a low potential to respond to selection and low environmental sensitivity. Interestingly, we found greater variation for phenotypic plasticity after selection, suggesting that the potential for plasticity to evolve is facilitated after exposure to environmental fluctuations. Our study highlights that environmental fluctuations should be considered when investigating the response of a population to environmental change.     

Drift,selection and adaptive variation in small populations of a threatened rattlesnake

An important goal of conservation genetics is to determine if the viability of small populations is reduced by a loss of adaptive variation due to genetic drift. Here, we assessed the impact of drift and selection on direct measures of adaptive variation (toxin loci encoding venom proteins) in the eastern massasauga rattlesnake (Sistrurus catenatus), a threatened reptile that exists in small isolated populations. We estimated levels of individual polymorphism in 46 toxin loci and 1,467 control loci across 12 populations of this species, and compared the results with patterns of selection on the same loci following speciation of S. catenatus and its closest relative, the western massasauga (S. tergeminus). Multiple lines of evidence suggest that both drift and selection have had observable impacts on standing adaptive variation. In support of drift effects, we found little evidence for selection on toxin variation within populations and a significant positive relationship between current levels of adaptive variation and long‐ and short‐term estimates of effective population size. However, we also observed levels of directional selection on toxin loci among populations that are broadly similar to patterns predicted from interspecific selection analyses that pre‐date the effects of recent drift, and that functional variation in these loci persists despite small short‐term effective sizes. This suggests that much of the adaptive variation present in populations may represent an example of “drift debt,” a nonequilibrium state where present‐day levels of variation overestimate the amount of functional genetic diversity present in future populations.     

Selective breeding of Steinernema feltiae (Filipjev) (Nematoda: Steinernematidae) for improved efficacy in control of a mushroom fly,Lycoriella solani Winnertz (Diptera: Sciaridae)

A method of selecting a Steinernema feltiae strain that is effective against a mushroom fly, Lycoriella solani, is described in detail. The pest control efficacy of the selected nematode strain was evaluated and compared with the efficacy of two unselected strains. The selection procedure was designed to give preference to nematode individuals with the greatest ability (1) to search effectively for the target insect larvae in their natural habitat, (2) to infect them shortly after application and (3) to reproduce in their haemocoel. Thirty‐four rounds of selection achieved a 4‐fold improvement in nematode ability to find and parasitize third‐ and fourth‐instar larvae of the pest in the mushroom substrate. In 24‐h laboratory experiments, mortality of the insect caused by nematode juveniles rose from 22.5%, recorded for the original unselected isolate, to 92.5% for the selected strain. In a 51‐day experiment conducted on a mixed age mushroom house population of L. solani, the enhanced pest control ability of the selected strain was detected shortly after nematode application and remained high throughout the experimental period. During the first 4 weeks of the trial the selected nematode strain was significantly better than both unselected strains and caused 91.1–92.7% reduction of the fly emergence from the mushroom substrate. No difference was observed between the efficacy of the selected nematodes applied at 1 × 10⁶ and 3 ×10⁶ infective juveniles per m², while the unselected strains performed significantly better at the higher concentration. All the nematodes examined showed good persistence in the mushroom casing apparently due to recycling in the insect host.     

The strength of the association between heterozygosity and probability of interannual local recruitment increases with environmental harshness in blue tits

The extent of inbreeding depression and the magnitude of heterozygosity–fitness correlations (HFC) have been suggested to depend on the environmental context in which they are assayed, but little evidence is available for wild populations. We combine extensive molecular and capture–mark–recapture data from a blue tit (Cyanistes caeruleus) population to (1) analyze the relationship between heterozygosity and probability of interannual adult local recruitment and (2) test whether environmental stress imposed by physiologically suboptimal temperatures and rainfall influence the magnitude of HFC. To address these questions, we used two different arrays of microsatellite markers: 14 loci classified as neutral and 12 loci classified as putatively functional. We found significant relationships between heterozygosity and probability of interannual local recruitment that were most likely explained by variation in genomewide heterozygosity. The strength of the association between heterozygosity and probability of interannual local recruitment was positively associated with annual accumulated precipitation. Annual mean heterozygosity increased over time, which may have resulted from an overall positive selection on heterozygosity over the course of the study period. Finally, neutral and putatively functional loci showed similar trends, but the former had stronger effect sizes and seemed to better reflect genomewide heterozygosity. Overall, our results show that HFC can be context dependent, emphasizing the need to consider the role of environmental heterogeneity as a key factor when exploring the consequences of individual genetic diversity on fitness in natural populations.     

The influence of landscape configuration and environment on population genetic structure in a sedentary passerine: insights from loci located in different genomic regions

The study of the factors structuring genetic variation can help to infer the neutral and adaptive processes shaping the demographic and evolutionary trajectories of natural populations. Here, we analyse the role of isolation by distance (IBD), isolation by resistance (IBR, defined by landscape composition) and isolation by environment (IBE, estimated as habitat and elevation dissimilarity) in structuring genetic variation in 25 blue tit (Cyanistes caeruleus) populations. We typed 1385 individuals at 26 microsatellite loci classified into two groups by considering whether they are located into genomic regions that are actively (TL; 12 loci) or not (NTL; 14 loci) transcribed to RNA. Population genetic differentiation was mostly detected using the panel of NTL. Landscape genetic analyses showed a pattern of IBD for all loci and the panel of NTL, but genetic differentiation estimated at TL was only explained by IBR models considering high resistance for natural vegetation and low resistance for agricultural lands. Finally, the absence for IBE suggests a lack of divergent selection pressures associated with differences in habitat and elevation. Overall, our study shows that markers located in different genomic regions can yield contrasting inferences on landscape‐level patterns of realized gene flow in natural populations.     

The combined use of raw and phylogenetically independent methods of outlier detection uncovers genome‐wide dynamics of local adaptation in a lizard

Local adaptation is a dynamic process by which different allele combinations are selected in different populations at different times, and whose genetic signature can be inferred by genome‐wide outlier analyses. We combined gene flow estimates with two methods of outlier detection, one of them independent of population coancestry (CIOA) and the other one not (ROA), to identify genetic variants favored when ecology promotes phenotypic convergence. We analyzed genotyping‐by‐sequencing data from five populations of a lizard distributed over an environmentally heterogeneous range that has been changing since the split of eastern and western lineages ca. 3 mya. Overall, western lizards inhabit forest habitat and are unstriped, whereas eastern ones inhabit shrublands and are striped. However, one population (Lerma) has unstriped phenotype despite its eastern ancestry. The analysis of 73,291 SNPs confirmed the east–west division and identified nonoverlapping sets of outliers (12 identified by ROA and 9 by CIOA). ROA revealed ancestral adaptive variation in the uncovered outliers that were subject to divergent selection and differently fixed for eastern and western populations at the extremes of the environmental gradient. Interestingly, such variation was maintained in Lerma, where we found high levels of heterozygosity for ROA outliers, whereas CIOA uncovered innovative variants that were selected only there. Overall, it seems that both the maintenance of ancestral variation and asymmetric migration have counterbalanced adaptive lineage splitting in our model species. This scenario, which is likely promoted by a changing and heterogeneous environment, could hamper ecological speciation of locally adapted populations despite strong genetic structure between lineages.     

Climatic drivers of leaf traits and genetic divergence in the tree Annona crassiflora: a broad spatial survey in the Brazilian savannas

The Cerrado is the largest South American savanna and encompasses substantial species diversity and environmental variation. Nevertheless, little is known regarding the influence of the environment on population divergence of Cerrado species. Here, we searched for climatic drivers of genetic (nuclear microsatellites) and leaf trait divergence in Annona crassiflora, a widespread tree in the Cerrado. The sampling encompassed all phytogeographic provinces of the continuous area of the Cerrado and included 397 individuals belonging to 21 populations. Populations showed substantial genetic and leaf trait divergence across the species' range. Our data revealed three spatially defined genetic groups (eastern, western and southern) and two morphologically distinct groups (eastern and western only). The east‐west split in both the morphological and genetic data closely mirrors previously described phylogeographic patterns of Cerrado species. Generalized linear mixed effects models and multiple regression analyses revealed several climatic factors associated with both genetic and leaf trait divergence among populations of A. crassiflora. Isolation by environment (IBE) was mainly due to temperature seasonality and precipitation of the warmest quarter. Populations that experienced lower precipitation summers and hotter winters had heavier leaves and lower specific leaf area. The southwestern area of the Cerrado had the highest genetic diversity of A. crassiflora, suggesting that this region may have been climatically stable. Overall, we demonstrate that a combination of current climate and past climatic changes have shaped the population divergence and spatial structure of A. crassiflora. However, the genetic structure of A. crassiflora reflects the biogeographic history of the species more strongly than leaf traits, which are more related to current climate.     

Temporal and host-related variation in frequencies of genes that enable Phyllotreta nemorum to utilize a novel host plant, Barbarea vulgaris

The flea beetle, Phyllotreta nemorum L. (Coleoptera: Chrysomelidae), is an intermediate specialist feeding on a small number of plants within the family Brassicaceae. The most commonly used host plant is Sinapis arvensis L., whereas the species is found more rarely on Cardaria draba (L.) Desv., Barbarea vulgaris R.Br., and cultivated radish (Raphanus sativus L.). The interaction between flea beetles and Barbarea vulgaris ssp. arcuata (Opiz.) Simkovics seems to offer a good opportunity for experimental studies of coevolution. The plant is polymorphic, as it contains one type (the P‐type) that is susceptible to all flea beetle genotypes, and another type (the G‐type) that is resistant to some genotypes. At the same time, the flea beetle is also polymorphic, as some genotypes can utilize the G‐type whereas others cannot. The ability to utilize the G‐type of B. vulgaris ssp. arcuata is controlled by major dominant genes (R‐genes). The present investigation measured the frequencies of flea beetles with R‐genes in populations living on different host plants in 2 years (1999 and 2003). Frequencies of beetles with R‐genes were high in populations living on the G‐type of B. vulgaris ssp. arcuata in both years. Frequencies of beetles with R‐genes were lower in populations living on other host plants, and declining frequencies were observed in five out of six populations living on S. arvensis. Selection in favour of R‐genes in populations living on B. vulgaris is the most likely mechanism to account for the observed differences in the relative abundance of R‐genes in flea beetle populations utilizing different host plants. A geographic mosaic with differential levels of interactions between flea beetles and their host plants was demonstrated.