Genetic structure and symbiotic profile of worldwide natural populations of the Mediterranean fruit fly, Ceratitis capitata

The sterile insect technique (SIT) is widely used in integrated pest management programs for the control of the Mediterranean fruit fly (medfly), Ceratitis capitata. The genetic interactions between the released individuals from the genetic sexing strains (GSS), used for SIT applications worldwide, and wild individuals have not been studied. Under the hypothesis that a number of Vienna GSS individuals released to the field might not be completely sterile and may produce viable offspring, we have analyzed medfly Spanish field populations to evaluate the presence of Vienna strain genetic markers. To this goal, we have used contrasted nuclear and mitochondrial genetic markers, and two novel sets of nuclear polymorphisms with the potential to be markers to discriminate between Vienna and wild individuals. Nuclear Vienna markers located on the 5th chromosome of Vienna males have been found in 2.2% (19 from 875) of the Spanish wild medfly females captured at the area where SIT is applied. In addition, a female-inherited mitochondrial Vienna marker has been found in two from the 19 females showing nuclear Vienna markers. The detection of several of these markers in single individuals represents evidence of the introgression of Vienna strain into natural populations. However, alternative explanations as their presence at low frequency in wild populations in the studied areas cannot be fully discarded. The undesired release of non-fully sterile irradiated GSS individuals into the field and their interactions with wild flies, and the potential environmental implications should be taken into account in the application of the SIT.

Euterpe precatoriais a palm tree belonging to the Arecaceae family, occurring in Western and Central Brazilian Amazonia. Its fruit, which is very appreciated in the Amazon region, produces pulp that is consumed in fresh form. Its production is carried out almost exclusively by extractive farmers. In order to establish adequate strategies to sustain this genetic resource, we need knowledge about the diversity and genetic structure in natural populations. This study aimed to evaluate the influence of geographic distance on genetic structure in the main extractive populations ofE. precatoriain the Brazilian Amazon. Leaves from 377 plants were collected in 19 populations located in 16 municipalities in the State of Amazonas and three in the State of Rondônia. Twelve microsatellite loci were used to genotype the plants. The diversity and genetic structure among populations were estimated. The average number of alleles per locus was 5.97. The observed heterozygosity means (HO) were higher than expected (HE) at the population level (HO= 0.72,HE= 0.66) and fixation index (f= -0.100) was negative. TheFSTvalue (0.1820) and the AMOVA results (Φ= 0.1796) showed population structure. The populations were clustered into three groups (K= 3) in the Bayesian analysis. The Discriminant Analysis of Principal Components (DAPC) confirmed eight clusters, with the populations close to those identified by the Bayesian analysis. The geographic differentiation was confirmed by the groupings obtained in the Structure analysis and the DACP function. Information related to phenotypic, genetic and environmental characterization of populations is important to guide conservation and management strategies and the formulation of public species management policies in Amazonia.

Simple SummaryThe Mediterranean fruit fly (medfly), Ceratitis capitata, is a major agricultural insect pest species worldwide. The sterile insect technique (SIT), as a component of area-wide integrated management (AW-IPM) programmes, is currently used to control populations of this pest. SIT is based on the mass production and release of sexually sterile insects, ideally males, over a target area. Male-only releases can be achieved by using genetic sexing strains (GSS) such as the medfly VIENNA 8 GSS. Females of this strain are homozygous for a mutation in the temperature-sensitive lethal (tsl) gene, which kills them when exposed to high temperatures during the embryonic stage. In the present study, we employed a temperature-sensitive lethal test (TSLT) to determine the temperature sensitivity or tolerance of twenty-seven Ceratitis capitata wild-type, genetic sexing, and tsl mutant strains. Significant differences were detected among the strains studied with respect to egg hatching, pupal, and adult recovery rates. We discussed our findings in the context of SIT applications and climate change. Area-wide integrated pest management (AW-IPM) programmes with a sterile insect technique component (SIT) are used to control populations of insect pests worldwide, including the Mediterranean fruit fly, Ceratitis capitata. SIT consists of the mass rearing, radiation-induced sterilization, handling, and release of sterile insects over the target area. Although SIT can be performed by using both sterile males and females, male-only releases significantly increase the efficiency and cost-effectiveness of SIT applications. Male-only releases can be achieved by using genetic sexing strains (GSS). The medfly VIENNA 8 GSS is based on two selectable markers, the white pupae (wp) gene, and the temperature-sensitive lethal (tsl) genes. The latter allows the elimination of females by exposing embryos to elevated temperatures. This study assessed the temperature sensitivity of twenty-seven medfly strains through a TSLT. Our results indicated significant differences among the strains regarding egg hatching as well as pupal and adult recovery rates due to the presence or absence of the tsl mutation and/or the genetic background of the strains. Our findings are discussed in the context of SIT applications, the importance of the tsl gene for developing genetic sexing strains, and climate change.

Developing GM insects for sustainable pest control in agriculture and human health

Preface: development and evaluation of improved strains of insect pests for sterile insect technique (SIT) applications.

With the increasing frequency of large‐scale restoration efforts, the need to understand the adaptive genetic structure of natural plant populations and their relation to heavily utilized cultivars is critical. Bouteloua gracilis (blue grama) is a wind‐dispersed, perennial grass consisting of several cytotypes (2n = 2×–6×) with a widespread distribution in western North America. The species is locally dominant and used regularly in restoration treatments. Using amplified fragment length polymorphism (AFLP) and cpDNA analyses, we assessed the genetic variability and adaptive genetic structure of blue grama within and among 44 sampling sites that are representative of the species’ environmental and habitat diversity in the southwestern United States. Five cultivars were also included to investigate genetic diversity and differentiation in natural versus cultivated populations. Three main findings resulted from this study: (a) Ninety‐four polymorphic AFLP markers distinguished two population clusters defined largely by samples on and off the Colorado Plateau; (b) substructure of samples on the Colorado Plateau was indicated by genetic divergence between boundary and interior regions, and was supported by cytotype distribution and cpDNA analysis; and (c) six AFLP markers were identified as “outliers,” consistent with being under selection. These loci were significantly correlated to mean annual temperature, mean annual precipitation, precipitation of driest quarter, and precipitation of wettest quarter in natural populations, but not in cultivated samples. Marker × environment relationships were found to be largely influenced by cytotype and cultivar development. Our results demonstrate that blue grama is genetically variable, and exhibits genetic structure, which is shaped, in part, by environmental variability across the Colorado Plateau. Information from our study can be used to guide the selection of seed source populations for commercial development and long‐term conservation management of B. gracilis, which could include genetic assessments of diversity and the adaptive potential of both natural and cultivated populations for wildland restoration.

Wild soybean (Glycine soja), a native species of East Asia, is the closest wild relative of the cultivated soybean (G. max) and supplies valuable genetic resources for cultivar breeding. Analyses of the genetic variation and population structure of wild soybean are fundamental for effective conservation studies and utilization of this valuable genetic resource. In this study, 40 wild soybean populations from China were genotyped with 20 microsatellites to investigate the natural population structure and genetic diversity. These results were integrated with previous microsatellite analyses for 231 representative individuals from East Asia to investigate the genetic relationships of wild soybeans from China. Analysis of molecular variance (AMOVA) revealed that 43·92 % of the molecular variance occurred within populations, although relatively low genetic diversity was detected for natural wild soybean populations. Most of the populations exhibited significant effects of a genetic bottleneck. Principal co-ordinate analysis, construction of a Neighbor-Joining tree and Bayesian clustering indicated two main genotypic clusters of wild soybean from China. The wild soybean populations, which are distributed in north-east and south China, separated by the Huang-Huai Valley, displayed similar genotypes, whereas those populations from the Huang-Huai Valley were different. The previously unknown population structure of the natural populations of wild soybean distributed throughout China was determined. Two evolutionarily significant units were defined and further analysed by combining genetic diversity and structure analyses from Chinese populations with representative samples from Eastern Asia. The study suggests that during the glacial period there may have been an expansion route between south-east and north-east China, via the temperate forests in the East China Sea Land Bridge, which resulted in similar genotypes of wild soybean populations from these regions. Genetic diversity and bottleneck analysis supports that both extensive collection of germplasm resources and habitat management strategies should be undertaken for effective conservation studies of these important wild soybean resources.

Understanding the principles that govern the mating behavior of insects that are the target of areawide integrated pest management (AW-IPM) programs by using the sterile insect technique (SIT) is a prerequisite to ensure optimal efficiency of such programs. Models were constructed to assess the effect of mating preference of insects, which display a female- or male-choice mating system, on the efficiency of SIT programs that release males only or programs that release both sexes. The model on preferential mating indicated that in a male choice mating system [e.g., screwworm, Cochliomyia hominivorax (Coquerel)], overcoming the discrimination of wild males against mating with sterile females would require a doubling of the number of sterile males compared with male-only releases. The model on female choice was incapable of distinguishing between reduced sterile male competitiveness and female preference for wild males and implied, in addition, that the release of both sexes and male-only releases required the same sterile to wild male overflooding ratio. Operational SIT projects have, however, shown a significant benefit with male-only releases against insects which have a female-choice mating system [e.g., Mediterranean fruit fly, Ceratitis capitata (Wiedemann)], and models were constructed to assess the potential effect of sterile female presence or absence on some parameters, i.e., reduced sterile sperm quantity with remating, reduced sterile sperm quality with aging and incomplete redistribution of the sterile males with the wild insects. The model suggests that in all three cases, male-only releases result in relatively more efficient sterile insects compared with programs releasing both sexes. The results of the models are discussed in relation to data available from operational screwworm and Mediterranean fruit fly AW-IPM programs with an SIT component.

BackgroundTsetse flies (Diptera: Glossinidae) are the vectors of African trypanosomosis, the causal agent of sleeping sickness in humans and nagana in animals. Glossina fuscipes fuscipes is one of the most important tsetse vectors of sleeping sickness, particularly in Central Africa. Due to the development of resistance of the trypanosomes to the commonly used trypanocidal drugs and the lack of effective vaccines, vector control approaches remain the most effective strategies for sustainable management of those diseases. The Sterile Insect Technique (SIT) is an effective, environment-friendly method for the management of tsetse flies in the context of area-wide integrated pest management programs (AW-IPM). This technique relies on the mass-production of the target insect, its sterilization with ionizing radiation and the release of sterile males in the target area where they will mate with wild females and induce sterility in the native population. It has been shown that Glossina pallidipes salivary gland hypertrophy virus (GpSGHV) infection causes a decrease in fecundity and fertility hampering the maintenance of colonies of the tsetse fly G. pallidipes. This virus has also been detected in different species of tsetse files. In this study, we evaluated the impact of GpSGHV on the performance of a colony of the heterologous host G. f. fuscipes, including the flies’ productivity, mortality, survival, flight propensity and mating ability and insemination rates.ResultsEven though GpSGHV infection did not induce SGH symptoms, it significantly reduced all examined parameters, except adult flight propensity and insemination rate.ConclusionThese results emphasize the important role of GpSGHV management strategy in the maintenance of G. f. fuscipes colonies and the urgent need to implement measures to avoid virus infection, to ensure the optimal mass production of this tsetse species for use in AW-IPM programs with an SIT component.

There is wide consensus that ongoing deforestation contributes to global warming and poses a threat to species diversity. Less understood is whether the practice of creating plantations might also erode genetic diversity and undermine the genetic structure of tree populations. We tested these hypotheses in natural and planted populations of Pinus brutia Ten. subsp. brutia and Cupressus sempervirens L. var. horizontalis (Mill.), 2 important forestry species in the Mediterranean region. We used plant material from 3 different bioclimatic regions in Syria. Using RAPD markers, we evaluated the genetic diversity and structure of 12 populations of P. brutia (6 natural, 6 planted) and 9 populations of C. sempervirens (3 natural, 6 planted). Expected heterozygosity (H_e) and percentage of polymorphic loci (PPL) were high in both species (P. brutia: H_e = 0.241, PPL = 81.2%; C. sempervirens: H_e = 0.241, PPL = 78.8%). In accordance with our assumptions, plantations of P. brutia manifested significant reduction in mean genetic diversity; this result, however, was not revealed in C. sempervirens. Analysis of molecular variance (AMOVA) demonstrated that the genetic structure of plantations differed from that of natural populations. Interestingly, plantations of both species harbored more genetic differentiation among them than natural populations. The partitions created by AMOVA also showed a significant differentiation between 2 groups, natural populations versus plantations in the 2 species, and among bioclimatic regions only in C. sempervirens. This result was corroborated by cluster analyses, which indicated a closer relationship among populations from the same geographic region. Genetic distance was positively related to geographic distance only in natural populations of P. brutia. Plantations in our research showed a significant reduction in genetic diversity, particularly in P. brutia, and stronger among-population genetic differentiation compared to natural populations. We recommend that forest management incorporates genetic diversity and differentiation as an important criterion for selecting appropriate tree stock material.

Summary 1 Classical evolutionary theory states that senescence should arise as a consequence of the declining force of selection late in life. Although the quantitative genetic predictions of hypotheses derived from this theory have been extensively tested in laboratory studies of invertebrate systems, relatively little is known about the genetics of ageing in the wild. 2 Data from long-term ecological studies is increasingly allowing quantitative genetic approaches to be used in studies of senescence in free-living populations of vertebrates. We review work to date and argue that the patterns are broadly consistent with theoretical predictions, although there is also a clear need for more empirical work. 3 We argue that further advances in this field of research might be facilitated by increased use of reaction norm models, and a decreased emphasis on attempting to discriminate between mutation accumulation and antagonistic pleiotropy models of senescence. We also suggest a framework for the better integration of environmental and genetic effects on ageing. 4 Finally, we discuss some of the difficulties in applying quantitative genetic models to studies of senescence outside the laboratory. In particular we highlight the problems that viability selection can cause for an accurate estimation of parameters used in the prediction of age-trajectory evolution.

The plant electrophoretic literature was reviewed to determine whether seed dispersal mechanisms effectively predict the distribution of genetic variation within and among plant populations. To consider the relationship between seed dispersal and genetic differentiation on a local scale, nine species of tropical trees from the same lowland forest community in Panama were examined electrophoretically. In both cases, the association between seed dispersal and the distribution of genetic variation was not as significant as expected. To better understand the processes underlying the development of genetic structure within plant populations, the genetic consequences of two generalized patterns of seed dispersal were explored. In the Platypodium model, seeds were wind disseminated and leptokurtically distributed, while the Piper model had the highly clumped dispersal pattern characteristic of many species with animalingested seeds. Variable breeding structures and the selective mortality of seeds and seedlings were also incorporated, since these factors can have important effects on population structure. The problem of obtaining quantitative estimates of these evolutionary parameters from natural populations is discussed. An analytical procedure (paternity exclusion analysis) is suggested which could be instrumental in elucidating those mechanisms which interact to produce genetic structure in natural plant populations.

Satureja bachtiarica Bunge (Lamiaceae) is a medicinal plant native to Iran which is widely used in traditional medicine, as a spice and as a vegetable. Understanding the patterns of genetic variation and structure of natural populations of the plant will be crucial for breeding and management purposes. However, until now, there has been no molecular tool with codominance inheritance available for studying genetic variation in this plant. In this study, we developed microsatellite markers for S. bachtiarica using a next-generation sequencing technique, and applied these markers to quantify the genetic variation and structure of natural populations. Sixty individuals collected from five natural populations were tested with 15 markers, 11 of which were fund to be polymorphic. The number of alleles per locus ranged from 4 to 17, with an average of 7.5 alleles per locus. The polymorphic information content of loci ranged from 0.41 to 0.89, with an average of 0.63. The average observed and expected heterozygosities over all populations were 0.62 (range 0.58 to 0.69) and 0.61 (range 0.60 to 0.63), respectively, and a low level of inbreeding (FIS) was observed in all populations (ranging from − 0.08 to 0.10) except Boli. None of the populations revealed any signature of recent reduction in population size. Private allelic richness was positively correlated with elevation (P < 0.05). The mean pairwise FST (± SD) among populations was 0.07 ± 0.01 (range 0.05 to 0.10). The clustering and Bayesian structure analyses exhibited genetic admixture between populations as supported by a weak population differentiation. The results of this study show the high efficiency of developed markers to investigate the genetics of natural populations of S. bachtiarica. The developed markers can also help to screen natural variation in diverse populations of closely related species, and can consequently be applied in conservation genetic and breeding programs.

Land use, genetic diversity and toxicant tolerance in natural populations of Daphnia magna

Dalmatian pyrethrum (Tanacetum cinerariifolium (Trevis.) Sch. Bip.) is an outcrossing plant species (2n = 18) endemic to the eastern Adriatic coast and source of the natural insecticide pyrethrin. Due to the high repeatability and large genome (1C-value = 9.58 pg) our previous attempts to develop microsatellite markers using the traditional method were unsuccessful. Now we have used Illumina paired-end whole genome sequencing and developed a specific procedure to obtain useful microsatellite markers. A total of 796,130,142 high-quality reads (approx. 12.5× coverage) were assembled into 6,909,675 contigs using two approaches (de novo assembly and joining of overlapped pair-end reads). A total of 31,380 contigs contained one or more microsatellite sequences, of which di-(59.7%) and trinucleotide (25.9%) repeats were the most abundant. Contigs containing microsatellites were filtered according to various criteria to achieve better yield of functional markers. After two rounds of testing, 17 microsatellite markers were developed and characterized in one natural population. Twelve loci were selected for preliminary genetic diversity analysis of three natural populations. Neighbor-joining tree, based on the proportion of shared alleles distances, grouped individuals into clusters according to population affiliation. The availability of codominant SSR markers will allow analysis of genetic diversity and structure of natural Dalmatian pyrethrum populations as well as identification of breeding lines and cultivars.