Downwind migration of the African army worm moth, Spodoptera exempta, studied by mark-and-capture and by radar

Abstract. 1. About 166,000 African armyworm moths, Spodoptera exempta (Walk.), were marked at an emergence site near Nairobi when they fed at night on trees baited with dyed molasses.
2. Six marked moths were captured in pheromone traps, including one at 90 km after flying for only one night, and another at 147 km.
3. Moth flight trajectories deduced from radar and from marking showed that migration was downwind.
4. During migration, moths become dispersed; hence the high densities that lead to outbreaks must be produced by concentration.
5. Some moths were ready to mate on the same night they completed their long-distance flight.     

Onset and spread of an African army worm upsurge

Abstract. 1. Onset and spread of the severe outbreaks of African armyworm, Spodoptera exempta (Walk.), over Ethiopa, Kenya, Tanzania and Burundi in late 1984 have been analysed in relation to trap and weather records.
2. Although first outbreaks in each country appeared progressively further south, winds on the best estimated dates of moth concentration and egg laying blew from directions precluding moth movements between them.
3. Such independently developing outbreaks are called 'primary' to distinguish them from any 'secondary' outbreaks that may develop from them.
4. Parent moths giving rise to all seven areas of primary outbreaks were derived from low-density populations that had persisted through the dry season, probably near the coast of East Africa.
5. Primary outbreaks developed on the south-eastern sides of individual rainstorms over the highlands, most likely because windborne moths were concentrated there by convergent winds.
6. Of the secondary outbreaks within Kenya, Tanzania and Burundi, most were derived from only one area of primary outbreaks in Kenya, which were therefore critical for effective control of spread; the paucity of other secondaries was presumably due to a lack of timely rainstorms or other concentrating mechanisms.     

Selection often overrides the effects of random processes in island populations of Philaenus spumarius (Homoptera)

The influence of various evolutionary factors on the populations of the colour polymorphic meadow spittlebug, Philaenus spumarius (Homoptera), was investigated on islands in the Gulf of Finland. Long-term (30-year) investigations showed that the populations can survive through very narrow bottlenecks, but after strong reduction in the size of a population, random genetic drift may remove alleles or change allele frequencies. One of the factors sustaining the presence of almost all the colour polymorphism alleles in almost all the populations is gene flow. Migration seems to be largely by air and by the sea surface (anemohydrochoric). On one rocky island, gene flow was able to carry the top dominant allele, p^T, to a number of scattered plant stands. However, it was not powerful enough to alter the differences in allele frequencies between populations living on the same island in meadows of different types 3 m or 12 m from each other. It is highly probable that the factor operating is meadow-specific selection. Its action appears to be based on the ecological character of the meadow. In the different meadows, the coverages of the food plants of the spittlebug are dissimilar. Differences in plant assemblages are possibly of importance in maintaining the meadow-specific allele frequencies in the spittlebug populations.     

Exact moment calculations for genetic models with migration,mutation, and drift

Using properties of moment stationarity we develop exact expressions for the mean and covariance of allele frequencies at a single locus for a set of populations subject to drift, mutation, and migration. Some general results can be obtained even for arbitrary mutation and migration matrices, for example: (1) Under quite general conditions, the mean vector depends only on mutation rates, not on migration rates or the number of populations. (2) Allele frequencies covary among all pairs of populations connected by migration. As a result, the drift, mutation, migration process is not ergodic when any finite number of populations is exchanging genes. In addition, we provide closed-form expressions for the mean and covariance of allele frequencies in Wright's finite-island model of migration under several simple models of mutation, and we show that the correlation in allele frequencies among populations can be very large for realistic rates of mutation unless an enormous number of populations are exchanging genes. As a result, the traditional diffusion approximation provides a poor approximation of the stationary distribution of allele frequencies among populations. Finally, we discuss some implications of our results for measures of population structure based on Wright's F-statistics.     

温带气旋对一代粘虫迁飞的影响:2015年个例分析

【目的】一代粘虫Mythimna separate(Walker)蛾大多在5月中旬至6月中旬集群外迁,而此时我国温带气旋活动较为频繁,由气旋活动引起的风场条件的变化会对一代粘虫的迁入区分布造成极大影响,因此阐明温带气旋对一代粘虫迁飞过程的影响是预测2代粘虫发生的重要前提。【方法】通过在江苏姜堰、安徽金安和山东宁津设立高空灯监测点,获取三地粘虫空中种群过境动态,结合WRF(Weather Research and Forecast)模式输出的精细风温场资料分析2015年温带气旋对一代粘虫迁飞的影响。【结果】2015年5月东亚反气旋频繁过境,一代粘虫在反气旋影响下多往西南和西北方向迁飞。6月上旬在东北低涡和蒙古气旋的影响下,一代粘虫可迁入东北地区为害。【结论】春夏之交频发的温带气旋是导致我国二代粘虫大范围为害的重要原因。     

Red cell enzyme polymorphisms in three Iranian population samples: Tabriz,Yazd, Mashhad

Three population samples from Iran (Tabriz, Yazd, Mashhad) have been typed for four enzyme group polymorphisms: ACP1, ESD, AK, and PGD. The phenotype and allele frequencies are presented and compared with other Iranian populations. The AK allele frequencies do not show significant intergroup heterogeneity, whereas ACP1, ESD and PGD allele frequencies disclose obvious heterogeneity. The possible reasons therefore are discussed.     

Microgeographic genetic variation in the apple maggot rhagoletis pomonella

We examined electrophoretic variability at five enzyme loci in the apple maggot fly, Rhagoletis pomonella, on a microgeographic scale. Treating flies from individual hawthorn trees as separate populations, we estimated F(ST) values from allele frequencies. The results indicate that there is significant allele frequency heterogeneity among fly populations over a small spatial scale at some loci but not at others. This variation among loci in degree of differentiation is itself statistically significant, casting doubt on the role of genetic drift in maintaining the heterogeneity. There is also heterogeneity between years in flies from a given tree. These data provide a baseline with which future work on genetic differentiation among apple maggot populations associated with different species of host plants may be compared.     

Biosystematic studies onCapsella bursa-pastoris (Brassicaceae): Enzyme polymorphism in natural populations

The genetic variability of natural populations ofCapsella bursapastoris in North- and Middle-Europe has been estimated by means of enzyme assays. Zymograms of 81 populations have been developed. 17 loci could be identified, and 8 of them can be heterozygous. Genetic variability is greater between populations than within. No correlation between actual population sizes and genetic heterogeneity could be detected. Some electromorphs shift their frequencies proportionally to increasing adversity of climatic conditions, some appear to be constant over the whole area, and others are characterized by an apparently irregular variation pattern. Marginal populations comprise a significantly higher proportion of heterozygous plants than central ones. Apart from this clinal variation pattern, a mosaic pattern, strongly related to habitat conditions, was observed: genetic heterogeneity is greater in more intensively disturbed sites. The pattern of genetic variation in natural populations ofCapsella bursa-pastoris is rather highly influenced by the breeding system.     

How Ebola Impacts Genetics of Western Lowland Gorilla Populations

Background

Emerging infectious diseases in wildlife are major threats for both human health and biodiversity conservation. Infectious diseases can have serious consequences for the genetic diversity of populations, which could enhance the species'' extinction probability. The Ebola epizootic in western and central Africa induced more than 90% mortality in Western lowland gorilla population. Although mortality rates are very high, the impacts of Ebola on genetic diversity of Western lowland gorilla have never been assessed.

Methodology/Principal Findings

We carried out long term studies of three populations of Western lowland gorilla in the Republic of the Congo (Odzala-Kokoua National Park, Lossi gorilla sanctuary both affected by Ebola and Lossi''s periphery not affected). Using 17 microsatellite loci, we compared genetic diversity and structure of the populations and estimate their effective size before and after Ebola outbreaks. Despite the effective size decline in both populations, we did not detect loss in genetic diversity after the epizootic. We revealed temporal changes in allele frequencies in the smallest population.

Conclusions/Significance

Immigration and short time elapsed since outbreaks could explain the conservation of genetic diversity after the demographic crash. Temporal changes in allele frequencies could not be explained by genetic drift or random sampling. Immigration from genetically differentiated populations and a non random mortality induced by Ebola, i.e., selective pressure and cost of sociality, are alternative hypotheses. Understanding the influence of Ebola on gorilla genetic dynamics is of paramount importance for human health, primate evolution and conservation biology.     

Genetic structure of an isolated native population group of northern Sibiria, the Nganasani (Tavgi) of the Taimyr. II. An analysis of intrapopulation variability

Chi-square contingency table analysis of phenotypic (genotypic) and gene frequencies of erythrocyte and blood serum groups and enzymes in a group of reindeer hunter and fishermen revealed heterogeneity within the population studied. Four out of twelve loci which have been compared were found to be involved in the process of differentiation into two local subgroups (subpopulations). No statistical differences have been observed between samples arbitrarily representing three generations. The data obtained support the hypothesis that the whole population still preserves the state of the stability. Traditional migration from adjacent populations close to nganasans by language and culture has made an important contribution into heterogeneity found in nganasans.     

云南省粘虫二代虫源探讨

首先设定常年有一代粘虫发生的印度北部、云南省和我国江淮地区为云南省粘虫主害代（二代）的可能虫源地。然后,讨论各个可能虫源地一代粘虫发生量及迁出时期空中走廊气流方向和强度对云南省二代粘虫发生量的影响;分析云南二代粘虫迁入期与各个一代区成虫迁出期的对应关系。结果表明：云南二代粘虫虫源主要来自于江淮地区一代粘虫发生区;小部分来自于云南一代粘虫发生区,但其基数甚小,仅此成分不致造成对作物的危害;没有包含印度一代粘虫的成分。此结论在1994～1995年的异地测报应用中得到验证。     

Molecular diagnosis and frequencies of primary hypolactasia in populations of Russia and neighboring countries

Normally, the ability to digest milk sugar (lactose) is present in every child, but not in every adult. The decrease in lactase synthesis (hypolactasia) results in the inability to digest whole milk. Recent studies of the Finnish population have associated lactase persistence in adults with allele T of the C/T_?13910 polymorphism located upstream of the lactase gene; a 100% correlation of primary hypolactasia with genotype C/C has been proved. In this study, the allele and genotype frequencies of C/T_?13910 were determined in populations of Russia. The frequencies of genotype C/C, varying from 36.6% in Russians to 88.2% in Chukchi, were close to the published medical and epidemiological data on the hypolactasia frequencies in these populations. Genotyping was carried out by three different methods to determine the optimal one. Genotype C/C proved to be the key determinant of primary hypolactasia. It was assumed that DNA diagnosis of genotype C/C provides a predictive test to detect primary hypolactasia long before its clinical manifestation.     

Staphylococcus aureus and its food poisoning toxins: characterization and outbreak investigation

Staphylococcal food poisoning (SFP) is one of the most common food-borne diseases and results from the ingestion of staphylococcal enterotoxins (SEs) preformed in food by enterotoxigenic strains of Staphylococcus aureus. To date, more than 20 SEs have been described: SEA to SElV. All of them have superantigenic activity whereas half of them have been proved to be emetic, representing a potential hazard for consumers. This review, divided into four parts, will focus on the following: (1) the worldwide story of SFP outbreaks, (2) the characteristics and behaviour of S. aureus in food environment, (3) the toxinogenic conditions and characteristics of SEs, and (4) SFP outbreaks including symptomatology, occurrence in the European Union and currently available methods used to characterize staphylococcal outbreaks.     

Genetic differentiation among North Atlantic killer whale populations

Population genetic structure of North Atlantic killer whale samples was resolved from differences in allele frequencies of 17 microsatellite loci, mtDNA control region haplotype frequencies and for a subset of samples, using complete mitogenome sequences. Three significantly differentiated populations were identified. Differentiation based on microsatellite allele frequencies was greater between the two allopatric populations than between the two pairs of partially sympatric populations. Spatial clustering of individuals within each of these populations overlaps with the distribution of particular prey resources: herring, mackerel and tuna, which each population has been seen predating. Phylogenetic analyses using complete mitogenomes suggested two populations could have resulted from single founding events and subsequent matrilineal expansion. The third population, which was sampled at lower latitudes and lower density, consisted of maternal lineages from three highly divergent clades. Pairwise population differentiation was greater for estimates based on mtDNA control region haplotype frequencies than for estimates based on microsatellite allele frequencies, and there were no mitogenome haplotypes shared among populations. This suggests low or no female migration and that gene flow was primarily male mediated when populations spatially and temporally overlap. These results demonstrate that genetic differentiation can arise through resource specialization in the absence of physical barriers to gene flow.     

Population subdivision and molecular sequence variation: theory and analysis of Drosophila ananassae data

Population subdivision complicates analysis of molecular variation. Even if neutrality is assumed, three evolutionary forces need to be considered: migration, mutation, and drift. Simplification can be achieved by assuming that the process of migration among and drift within subpopulations is occurring fast compared to mutation and drift in the entire population. This allows a two-step approach in the analysis: (i) analysis of population subdivision and (ii) analysis of molecular variation in the migrant pool. We model population subdivision using an infinite island model, where we allow the migration/drift parameter Theta to vary among populations. Thus, central and peripheral populations can be differentiated. For inference of Theta, we use a coalescence approach, implemented via a Markov chain Monte Carlo (MCMC) integration method that allows estimation of allele frequencies in the migrant pool. The second step of this approach (analysis of molecular variation in the migrant pool) uses the estimated allele frequencies in the migrant pool for the study of molecular variation. We apply this method to a Drosophila ananassae sequence data set. We find little indication of isolation by distance, but large differences in the migration parameter among populations. The population as a whole seems to be expanding. A population from Bogor (Java, Indonesia) shows the highest variation and seems closest to the species center.     

Population genetic studies of the crown-of-thorns starfish,Acanthaster planci (L.), in the Great Barrier Reef region

Seven populations of the crown-of-thorns starfish, Acanthaster planci, were compared genetically using starch gel electrophoresis in order to investigate the extent of genetic exchange throughout the Great Barrier Reef (GBR) region. These populations extended from Lizard Island in the north to One Tree Island in the south, a distance of approximately 1300 km. Thirteen of 36 enzymes assayed were genetically interpretable, and 10 (77%) of these were polymorphic. Mean heterozygosity over all loci was 0.225. An analysis of the gene frequency heterogeneity between the populations using Wright's F _ST statistic gave an overall F _ST of 0.019. The mean unbiased value of Nei's genetic distance between the populations was 0.009. These values indicate a homogeneous genetic composition throughout the range, and are consistent with the hypothesis that gene flow between these populations is high, and that A. planci throughout the GBR region are members of a single, effectively panmictic population. Within this group, the Green Island population was most distinct genetically because of differences in allele frequencies at the MDH-1 locus. Although there is no rigorous method for determining the selective basis for such differences, it is argued that the differences observed in the Green Island population were the result of selection. The basis for selective differences was possibly food availability since, at the time of sampling, the Green Island A. planci were the remnants of a large, high-density population that caused extensive coral mortality, and suffered severe population decline as food became scarce. These findings are consistent with observations of a relatively ordered sequence of outbreaks from north to south along the GBR, suggesting that all outbreaks but the first are secondary. Control measures, both on the GBR and elsewhere, have been unsuccessful except on a very small scale. Unless a vulnerable part of the A. planci life cycle can be identified, it would seem that the greatest chance for successful control would be to identify and control the causes of the primary population outbreak.     

Physical defences wear you down: progressive and irreversible impacts of silica on insect herbivores

1. Silica in the leaves of grasses can act as a defence against both vertebrate and invertebrate herbivores. The mechanisms by which silica affects herbivore performance are not well characterized. Here we expose an insect herbivore Spodoptera exempta to high-silica diets and test two mechanisms by which silica has been proposed to act as a defence. First, that silica reduces the digestibility of leaves and second, that silica causes wear to insect mandibles, both of which could potentially impact on herbivore performance. 2. Silica reduced the efficiency with which S. exempta converted ingested food to body mass and the amount of nitrogen absorbed from their food, leading to reduced insect growth rates. The measure of how efficiently herbivores utilize digested food (ECD) was unaffected by silica. 3. These effects occurred even with short-term exposure to silica-rich diets, but they also increased markedly with the duration of exposure and affected late instars more than early instar larvae. This appears to be due to the progressive impacts of silica with longer exposure times and suggests that herbivores cannot adapt to silica defences, nor do they develop a tolerance for silica with age. 4. Exposure to silica-rich diets caused increased mandible wear in S. exempta. This effect was extremely rapid, occurring within a single instar, further reducing feeding efficiency and growth rates. These effects on insect growth and feeding efficiency are nonreversible, persisting after the herbivore has switched diets. Up to a third of this residual impact can be explained by the degree of mandible wear caused by previous silica-rich diets. 5. The impacts of silica on S. exempta larvae were progressive with exposure time and could not be compensated for, even by switching to a different diet. Thus, herbivores cannot easily adapt to physical defences such as silica, suggesting this defence will have major implications for herbivore fitness.     

Segregation and conditional probability association of molecular markers with traits in autotetraploid alfalfa

The complications introduced by the autotetraploid, outcrossing nature of alfalfa (Medicago sativa L.) as related to detecting associations of marker loci and traits of interest are discussed, and a new method of detecting marker-trait associations is suggested. This method utilizes plant populations that are likely to have been produced through the plant breeding process: populations selected for one trait, and the base, unselected population. Marker allele frequency shifts between the populations are indicative of genomic regions involved in trait expression, and may indicate alleles that have reached the triplex or homozygous state and do not segregate in S₁ or F₁ populations. However, because many, perhaps hundreds, of sequential frequency comparisons are needed to detect fragments in significantly different proportions in the two populations, the type I error rate is very high. A resampling-based analysis method is proposed to address the concern of the type I error rate, and identify marker alleles associated with this trait of interest. The utility of marker-trait associations thus defined for identifying individual plants from heterogeneous populations was investigated through model-building and conditional probability studies. Factors investigated that influenced the utility of the marker associations and (in the base population) the frequencies of the trait and marker, and the frequencies of the markers in plants exhibiting the trait and in the plants not exhibiting the trait. The frequency of occurrence of a marker in undesirable plants profoundly influenced the efficiency with which the marker could be used to select desirable plants, however, under some circumstances, markers or combinations of markers can be highly efficient for selecting rare, desirable plants from a heterogeneous base population.     

Evidence for ecological divergence across a mosaic of soil types in an Amazonian tropical tree: Protium subserratum (Burseraceae)

Soil heterogeneity is an important driver of divergent natural selection in plants. Neotropical forests have the highest tree diversity on earth, and frequently, soil specialist congeners are distributed parapatrically. While the role of edaphic heterogeneity in the origin and maintenance of tropical tree diversity is unknown, it has been posited that natural selection across the patchwork of soils in the Amazon rainforest is important in driving and maintaining tree diversity. We examined genetic and morphological differentiation among populations of the tropical tree Protium subserratum growing parapatrically on the mosaic of white‐sand, brown‐sand and clay soils found throughout western Amazonia. Nuclear microsatellites and leaf morphology were used to (i) quantify the extent of phenotypic and genetic divergence across habitat types, (ii) assess the importance of natural selection vs. drift in population divergence, (iii) determine the extent of hybridization and introgression across habitat types, (iv) estimate migration rates among populations. We found significant morphological variation correlated with soil type. Higher levels of genetic differentiation and lower migration rates were observed between adjacent populations found on different soil types than between geographically distant populations on the same soil type. P_ST‐F_ST comparisons indicate a role for natural selection in population divergence among soil types. A small number of hybrids were detected suggesting that gene flow among soil specialist populations may occur at low frequencies. Our results suggest that edaphic specialization has occurred multiple times in P. subserratum and that divergent natural selection across edaphic boundaries may be a general mechanism promoting and maintaining Amazonian tree diversity.     

Reasons for failure of genetic classifications of South Amerind populations

Previous attempts to classify South American Indian tribes according to genetic characteristics have failed to yield a hierarchical system of relationships. This can be explained by the facts that (1) tribal populations did not evolve through sequential fissions but through frequent fusions of groups with diverse histories and (2) allele frequencies have been held at nearly common values by intertribal migration or balancing selection. A valid model must allow for fusion and mixed populations as well as for fission; factor analysis or newer methods of fuzzy mathematics permit this. The effects of migration and balancing can be made more manageable by partitioning them according to the limited time periods recorded by haplotypes. An initial attempt using factor analysis and HLA haplotype data on 19 rain forest tribes revealed two overlapping clusters that are largely but not neatly separated by the lower Amazon River. Several tribes, especially in the west, were excluded from these clusters.