Geminivirus transmission and biological characterisation of Bemisia tabaci (Gennadius) biotypes from different geographic regions

Eighteen populations of Bemisia tabaci, collected from different geographic locations (North & Central America, the Caribbean, Africa, the Middle East, Asia and Europe), were studied to identify and compare biological and genetic characteristics that can be used to differentiate biotypes. The morphology of the fourth instar/pupal stage and compound eye structures of adults were investigated using scanning electron microscopy and found to be typical of the species among all biotypes and populations studied. Setae and spines of B. tabaci larval scales from the same colony were highly variable depending on the host plant species or leaf surface characteristics. The location and the morphology of caudal setae, characteristic of all B. tabaci studied to date, were present in all colonies. However, differences in adult body lengths and in the ability to induce phy to toxic disorders in certain plant species were found between biotypes or populations. The recently identified “B” biotype, characterised by a diagnostic esterase banding pattern and by its ability to induce phytotoxic responses in squash, honeysuckle and nightshade was readily distinguished from non-“B” biotype populations. None of the non-“B” biotypes studied, were found to induce phytotoxic responses. Nine populations examined showed typical “B” biotype characteristics, regardless of country of origin. All tested populations, determined as “B” or “B”-like biotypes successfully mated with other “B” biotype colonies from different geographic areas. Non-“B” biotype colonies did not interbreed with other biotypes. The B. tabaci populations were tested for their ability to transmit 15 whitefly-transmitted geminiviruses (WTGs) from different geographic areas with a wide range of symptom types. All WTGs were transmitted by the “B” biotype colonies and by most non-“B” biotype colonies, with the exception of three viruses found in ornamental plants which were non-transmissible by any colony. Some non-“B” biotypes would not transmit certain geminiviruses and some geminiviruses were more efficiently transmitted than were others.     

REGIONAL,LOCAL AND MICROGEOGRAPHIC ALLELE FREQUENCY VARIATION BETWEEN APPLE AND HAWTHORN POPULATIONS OF RHAGOLETIS POMONELLA IN WESTERN MICHIGAN

In the preceding study (Feder et al., 1990), we report that paired apple and hawthorn infesting populations of Rhagoletis pomonella are genetically differentiated for six allozymes. Here, we show that patterns of intra- and inter-host allele frequency variation seen for these six loci across the eastern United States are consistent on a more fine grained spatial scale in western Michigan. Malic enzyme, Aconitase-2, Mannose phosphate isomerase, and Hydroxyacid dehydrogenase all displayed significant linear relationships with latitude among five “regional” hawthorn populations sampled along a north-south transect between the cities of Cadillac and Portage, Michigan. Clines were not as evident among “regional” apple populations in western Michigan, although allele frequencies for Malic enzyme¹⁰⁰, Mannose phosphate isomerase¹⁰⁰ and Aconitase-2⁹⁵ varied with latitude among six “local” apple populations within a 60 km² area near the town of Grant. Significant allele frequency differences were observed between hawthorn and apple populations at all “regional” and “local” collecting sites analyzed in the study (a total of 20 different apple and hawthorn populations). As was the case in the geographic survey of the eastern United States, the magnitude and pattern of inter-host frequency differences at “regional” and “local” sites were a function of latitude. Host related genetic differentiation was consistent on a “microgeographic” scale as well. Allele frequencies for Malic enzyme¹⁰⁰ and Aconitase-2⁹⁵ were significantly higher over a four-year period (1984 to 1987) for flies sampled from individual hawthorn trees (N = 6) than apple trees (N = 7) within an old field (0.09-km² area) located near Grant. The fine level of genetic subdivision between hawthorn and apple populations of R. pomonella in western Michigan substantiates the existence of host associated polymorphism in the fly and supports a sympatric mode of divergence for the “apple race”.     

Morphological clines across a karyotypic zone of house mice in Central Italy

Multivariate morphometric differentiation between chromosomal races of the mouse Mus domesticus in Central Italy was investigated using a population of 2n = 22 “CB” karyotype, three populations of standard 2n = 40 karyotype, five populations of 2n = 22 “CD” karyotype and three populations from the hybrid zone between the latter two karyotypes. Whilst populations of different karyotype generally have significantly different morphometry, canonical analysis does not reveal that the populations ordinate into distinct aggregations based on karyotype, largely because the 2n = 22 “CD” populations are so diverse. Nevertheless, canonical analysis does reveal a significant cline in morphology across the contact zone between the 2n = 40 and 2n = 22 “CD” mice. The nature of this transition, i. e. a cline 1. within the 2n = 40 range, 2. within the hybrid range (but unrelated to chromosome number) and 3. within the 2n = 22 “CD” range, tends to indicate that the morphometric divergence is due to adaptation to the different ecological regimes across which these mice are distributed rather than the phylogenetic divergence of the karyotypic races.     

Isolation and biodiversity in Cytisus villosus Pourret (Fabaceae,Genisteae): enzyme polymorphism in disjunct populations

ABSTRACT

The genetic diversity of isolated populations of Cytisus villosus has been studied by means of enzyme polymorphism analysis. Two types of isolated populations were studied: “terrestrial islands” in Sicily, and “true islands” in the Aeolian archipelago. In the populations of “true islands” the number of alleles and the heterozygosity are lower than in “terrestrial islands”. Isolation amongst Sicilian populations seems to be more recent than isolation of the Aeolian populations, and may be attributed to climatic changes which occurred during the Holocene and/or to human activities. The disjunction of the Aeolian populations seems much more recent than the origin of the isles themselves; the colonization of the archipelago is attributed to a single, recent dispersal event not followed by local evolution. In view of the biological structure of the Aeolian populations, C. villosus must be regarded as a locally endangered species.     

LEAF CAVITY SIZE DIFFERENTIATION AND WATER RELATIONS IN CAREX ELEOCHARIS

Carex eleocharis leaves contain large intercellular cavities that traverse the length of the leaf above rows of stomata and are roughly constant in size throughout a leaf. Semithin sections (1–2 μm) demonstrate that the substomatal chambers are directly continuous with the intercellular cavities. Leaves of plants inhabiting moist swale regions of the shortgrass steppe, in northeastern Colorado, were found to have larger cavities as compared to leaves of plants inhabiting dry hilltops. Plants collected from a common hilltop site were grown in a controlled environment chamber, and, by manipulating the watering schedule, we obtained water potentials similar to those in the field. Leaves of “well-watered” plants were found to have larger intercellular cavities as compared to “water-stressed” plants. Leaf mesophyll cell sizes did not differ significantly between “well-watered” and “water-stressed” plants, suggesting that cavity size differences are not the result of developmental differences. Leaf cavities were shown to contain gases and to occur along the leaf length above rows of stomata. Additionally, the cavities in unstressed plants were continuous with substomal chambers. It is proposed that the reduction of cavity size is a mechanism to reduce water loss from the leaves during periods of plant water stress.     

Very low pressures drive ventilatory flow in chimaeroid fishes

Chimaera (Holocephali) are cartilaginous fishes with flexible operculi rather than external gill slits, suggesting ventilation occurs in a manner different from other fishes. We examined holocephalan ventilation morphology, behavior, and performance by anatomical investigations, high‐speed video, and in vivo pressure measurements from the buccal and parabranchial cranial cavities in Hydrolagus colliei and Callorhinchus callorynchus. Ventilatory modes ranged from quiet resting breathing to rapid “active” breathing, yet external cranial movements—excepting the passive movement of the opercular flap—were always extremely subtle, and pressures generated were one to two orders of magnitude lower than those of other fishes. To explain ventilation with such minimal pressure generation and cranial motion, we propose an “accordion” model, whereby rostrocaudal movement of the visceral arches drives pressure differentials, albeit with little lateral or ventral movement. Chimaeroids have comparatively large oropharyngeal cavities, which can move fluid with a smaller linear dimension change than the comparatively smaller cavities of other fishes. Orobranchial pressures are often less than parabranchial pressures, suggesting flow in the “wrong” direction; however, the long gill curtains of chimaeroids may passively restrict backflow. We suggest that constraints on holocephalan jaw and hyoid movements were compensated for evolutionarily by novel visceral arch mechanics and kinematics. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc.     

THREE SELECTIONS ARE BETTER THAN ONE: CLINAL VARIATION OF THERMAL QTL FROM INDEPENDENT SELECTION EXPERIMENTS IN DROSOPHILA

We report the results of two independent selection experiments that have exposed distinct populations of Drosophila melanogaster to different forms of thermal selection. A recombinant population derived from Arvin California and Zimbabwe isofemale lines was exposed to laboratory natural selection at two temperatures (T_AZ: 18°C and 28°C). Microsatellite mapping identified quantitative trait loci (QTL) on the X‐chromosome between the replicate “Hot” and “Cold” populations. In a separate experiment, disruptive selection was imposed on an outbred California population for the “knockdown” temperature (T_KD) in a thermal column. Microsatellite mapping of the “High” and “Low” populations also uncovered primarily X‐linked QTL. Notably, a marker in the shaggy locus at band 3A was significantly differentiated in both experiments. Finer scale mapping of the 3A region has narrowed the QTL to the shaggy gene region, which contains several candidate genes that function in circadian rhythms. The same allele that was increased in frequency in the High T_KD populations is significantly clinal in North America and is more common at the warm end of the cline (Florida vs. Maine; however, the cline was not apparent in Australia). Together, these studies show that independent selection experiments can uncover the same target of selection and that evolution in the laboratory can recapitulate putatively adaptive clinal variation in nature.     

GROWTH AND CELL CYCLE OF TWO CLOSELY RELATED RED TIDE-FORMING DINOFLAGELLATES: GYMNODINIUM NAGASAKIENSE AND G. CF. NAGASAKIENSE1

Small-sized vegetative cells were found to co-occur with normal-sized cells in populations of the European bloom-forming dinoflagellate Gymnodinium cf. nagasakiense Takayama et Adachi, currently known as Gyrodinium aureolum Hulburt, but not in populations of the closely related Japanese species Gymnodiniumn agasakiense. We examined how cell size differentiation may influence growth and cell cycle progression under a 12:12-h light: dark cycle in the European taxon, as compared to the Japanese one. Cell number and volume and chlorophyll red fluorescence in both species varied widely during the photocycle. These variations generally appeared to be related lo the division period, which occurred at night, as indicated by the variations of the fraction of binucleated cells (mitotic index) as well as the distribution of cellular DNA content. “Small” cells of G. cf. nagasakiense divided mainly during the first part of the dark period, although a second minor peak of dividing cells could occur shortly before light onset. In contrast, “large” cells displayed a sharp division peak that occurred 9 h after the beginning of the dark period. The lower degree of synchrony of “small” cells could be a consequence of their faster growth. Alternatively, these data may suggest that cell division is lightly controlled by an endogenous clock in “large” cells and much more loosely controlled in “small” cells. Cells of the Japanese species, which were morphologically similar to “large” cells of the European taxon, displayed an intermediate growth pattern between the two cell types of G. cf. nagasakiense, with a division period that extended to most of the dark period.     

The Occurrence of Vascular Cavities and Specialized Parenchyma Cells in the Roots of Cool-season Legumes

The seeds of 20 legume species were grown in the greenhouse or in growth chambers at different temperatures. Under warm temperature conditions (above 15 °C), six species, pea (Pisum sativum), broadbean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinaris), wild lupine (Lupinus latifolius), and soybean (Glycine max), formed cavities in the vascular cylinder of their primary roots, which in turn became filled by the ingrowth of specialized parenchyma cells (SP cells). When these species were grown at low temperature (below 15 °C), however, a “normal” vascular cylinder formed in the primary roots with late-maturing metaxylem vessel members differentiating in the center. These species were all cool-season legumes except soybean, a warm-season legume, which sometimes also formed cavities and SP cell ingrowths. The occurrence of cavities and SP cells therefore was restricted to the cool-season legumes (except soybean) when they were grown under warm temperature conditions. The position and size of cavities varied among these species. Pea and broadbean usually formed large, axially elongated cavities in the central vascular cylinder, or in the xylem poles. Others formed smaller cavities of various lengths.     

Blessed are the meek for they shall inherit the earth: quietness component of introversion is associated with single nucleotide polymorphisms in two circadian clock genes

Individual differences studied by chronobiologists and personality psychologists are usually shaped by polygenic selection occurring by small allele frequency shifts spreading across many loci. Therefore, the candidate gene association studies suffer from increased likelihood of false positive findings. We previously associated a PER3 single nucleotide polymorphism (SNP, rs228697) with self-ratings on personality-relevant nouns exemplifying personality dimension of Extraversion/Introversion in a sample of 88 female students. To replicate and extend this finding, we genotyped three more SNPs in three circadian clock genes. The results indicated that the minor alleles of PER3 rs228697 and PER2 rs934945 were rather similar in terms of their association with a personality type nicknamed “demure persona” (i.e. described by such nouns as “quietness”, “restraint”, “taciturnity”, “bashfulness”, “timidity”, “constraint”, and “reticence”). Analysis of data from populations of the 1000 Genomes Project suggested that, like frequencies of the minor alleles of many SNPs in circadian clock genes, the frequencies of these two SNPs were higher in populations of out-of-African ancestry compared to populations of African ancestry. We suggested that genetic candidates for Extraversion/Introversion can be prioritized in future association studies by means of identification of genetic signatures of polygenic selection imposed by out-of-Africa expansion of ancestral populations.     

CELL SIZE DIFFERENTIATION IN THE BLOOM-FORMING DINOFLAGELLATE GYMNODINIUM CF. NAGASAKIENSE1

Two subpopulations differing essentially by their mean cell size were observed regularly in cultures and natural samples of the naked dinoflagellate Gymnodinium cf. nagasakiense Takayama et Adachi (currently known as Gyrodinium aureolum Hulburt), a species which frequently forms red tides in North European seas. “Large” cells represented the typical forms; they were morphologically similar to cells of the closely related Japanese species G. nagasakiense, which did not form any subpopulation of reduced size. “Small” and “large” cells of G. cf. nagasakiense had the same DNA content, but the nucleus of the former appeared to be much more condensed during interphase. Each cell type was able to divide and had its own growth dynamics; therefore, any intermediary between pure populations of “small” and of “large” cells were observed in culture. The “large” form generated a “small” cell by an atypical budding-like division, whereas the “small” form gave back a “large” form, once it ceased to divide, by simple enlargement of its cell body. Factory inducing cell size differentiation are yet unclear. Neither nitrogen nor phosphorus starvation induced a significant increase in the relative proportion of “small” and budding cells. Although cell size differentiation is associated with the formation of gametes in a variety of dinoflagellates, we demonstrated that “small” cells of G. cf. nagasakiense are able to divide asexually, in contrast to gametes of most other species. The high proliferative power of “small” cells as compared with normal cells suggests that they could play a significant role during red tides of G. cf. nagasakiense; in contrast, cells of the Japanese species G. Nagasakiense could sustain high growth rates with larger cell size because this species generally blooms in waters much warmer than those found in northern Europe.     

A Selection Procedure for Selecting Good Exponential Populations

Consider k independent exponential populations with location parameters μ₁,…, μ_k and a common scale parameter or standard deviation θ. Let μ_(k) be the largest of the μ's and define a population to be good if its location parameter exceeds μ_(k) –Δ₁. A selection procedure is proposed to select a subset of the k populations which includes the good populations with probability at least P*, a pre-assigned value. Simultaneous confidence intervals, that can be derived with the proposed selection procedure, are discussed. Moreover, if populations with locations below μ_(k) –δ₂, (δ₂ > δ₁) are “bad”, a selection procedure is proposed and a sample size is determined so that the probability of omitting a “good” population or selecting a “bad” population is at most 1 – P*.     

Growth and fecundity of fertile Miscanthus × giganteus (“PowerCane”) compared to feral and ornamental Miscanthus sinensis in a common garden experiment: Implications for invasion

Perennial grasses are promising candidates for bioenergy crops, but species that can escape cultivation and establish self‐sustaining naturalized populations (feral) may have the potential to become invasive. Fertile Miscanthus × giganteus, known as “PowerCane,” is a new potential biofuel crop. Its parent species are ornamental, non‐native Miscanthus species that establish feral populations and are sometimes invasive in the USA. As a first step toward assessing the potential for “PowerCane” to become invasive, we documented its growth and fecundity relative to one of its parent species (Miscanthus sinensis) in competition with native and invasive grasses in common garden experiments located in Columbus, Ohio and Ames, Iowa, within the targeted range of biofuel cultivation. We conducted a 2‐year experiment to compare growth and reproduction among three Miscanthus biotypes—”PowerCane,” ornamental M. sinensis, and feral M. sinensis—at two locations. Single Miscanthus plants were subjected to competition with a native grass (Panicum virgatum), a weedy grass (Bromus inermis), or no competition. Response variables were aboveground biomass, number of shoots, basal area, and seed set. In Iowa, all Miscanthus plants died after the first winter, which was unusually cold, so no further results are reported from the Iowa site. In Ohio, we found significant differences among biotypes in growth and fecundity, as well as significant effects of competition. Interactions between these treatments were not significant. “PowerCane” performed as well or better than ornamental or feral M. sinensis in vegetative traits, but had much lower seed production, perhaps due to pollen limitation. In general, ornamental M. sinensis performed somewhat better than feral M. sinensis. Our findings suggest that feral populations of “PowerCane” could become established adjacent to biofuel production areas. Fertile Miscanthus × giganteus should be studied further to assess its potential to spread via seed production in large, sexually compatible populations.     

ISOLATING A ROLE FOR NATURAL SELECTION IN SPECIATION: HOST ADAPTATION AND SEXUAL ISOLATION IN NEOCHLAMISUS BEBBIANAE LEAF BEETLES

Muller (1942) and Mayr (1963) hypothesized that natural selection indirectly causes the evolution of reproductive barriers between allopatric populations by causing adaptive genetic divergence that pleiotropically promotes prezygotic or postzygotic incompatibility. Under this mechanism, herbivorous insect populations should be more prone to speciate if they are adapting to different host plants, because the evolution of reproductive isolation will be accelerated above the rate promoted by genetic drift and host-independent sources of selection alone. Although the Muller-Mayr hypothesis is widely accepted, little direct evidence has been collected in support of selection's role in allopatric speciation. This paper offers a method for isolating and evaluating the contribution of host plant-related natural selection pressures to the reproductive isolation between allopatric herbivore populations. The host-related selection hypothesis (HRSH) predicts that herbivore populations using different host plants should be more reproductively isolated than those using the same host, other things being equal. Here, I test this hypothesis using Neochlamisus bebbianae, an oligophagous leaf beetle with a geographically variable host range. In each of two sets of experiments (contrast I, contrast II), I compared two beetle populations (Georgia and New York) that use the same host (Acer) in nature and a third population that natively uses a different host (Betula in Oklahoma [CI], Salix in Ontario [CII]). Experiments showed that “different-host” populations were more strongly differentiated in host-use traits (oviposition, host fidelity, feeding response, larval performance) than were “same-host” populations and that each population most readily uses foliage from its native host. As predicted by the HRSH, sexual isolation was also greater between the adaptively divergent different-host populations (from Betula vs. Acer, from Salix vs. Acer) than between the same-host populations (from Acer), which were undifferentiated in host-use traits. Interpreting these results in a historical context provided by mtDNA sequences from test populations indicated: (1) that Acer- and Betula-associated N. bebbianae represent separate sibling species whose causal origins have been lost to history, and whose incomplete sexual isolation is fortified by host-associated ecological and “physiological” isolation; and (2) that incipiently speciating Acer- and Salix-associated populations are more closely related to each other than are the two Acer-associated populations, which is consistent with the HRSH. This study thus illustrates the consequences of host-related selection for both the origin and maintenance of reproductive isolation. More important, it provides evidence that the pleiotropic effects of natural selection promote allopatric speciation.     

Genetics and modern human origins

The past decade has brought considerable debate on the subject of modern human origins. The nature of the transition from Homo erectus to archaic Homo sapiens to modern H. sapiens has been examined primarily in terms of the relative contribution of archaic populations to later moderns, both within and among geographic regions. The recent African origin model proposes that modern humans appeared first in Africa between 100,000 and 200,000 years ago, and then spread through the rest of the Old World, replacing preexisting populations.^1–6 This model has been referred to by a variety of names, including “replacement”, “Garden of Eden”, “Noah's Ark”, and “out of Africa”. The recent African origin model contrasts with the multiregional model, which proposes a species-wide transition to modern humans throughout the Old World during the past million years or more.^7–10 Indeed, some proponents of the multiregional model advocate placing Homo erectus and all subsequent species of Homo in the evolutionary species Homo sapiens.¹¹ This contrasts with the view that there were multiple hominid species during the Middle Pleistocene. The debate continues.^12,13 Although the multiregional model is often portrayed as proposing a simultaneous transition to anatomically modern humans in different geographic regions, it explicitly allows for varying degrees of continuity across time and space.¹⁰ This model, in the broad sense, does not rule out the possibility that modern human morphology appeared first in Africa and then spread through the rest of the Old World through gene flow. However, not all advocates of the multiregional model adhere to this specific subset of the general model.⁹ Comparison of the African and multiregional models is complicated by considering other, less extreme, hypotheses. Some versions of the recent African origin model imply a speciation event associated with the initial origin of modern humans. Another version, which suggests the possibility of some admixture between “moderns” leaving Africa and preexisting “archaics” elsewhere in the Old World,^14,15 is similar to some variants of the multiregional model, which also suggest that modern morphology appeared first in Africa, but involved admixture with other Old World populations.¹⁶ The major difference between these views appears to be the extent of admixture, although the exact level is never specified. A further complication is the possibility that multiple dispersals from Africa produced a more complicated pattern of worldwide variation.¹⁷     

ECOLOGICAL GENETICS OF A MOSAIC HYBRID ZONE: MITOCHONDRIAL,NUCLEAR, AND REPRODUCTIVE DIFFERENTIATION OF CRICKETS BY SOIL TYPE

We investigated the effects that habitat variation has on the structure and dynamics of a hybrid zone between two closely related crickets in Connecticut. A collecting protocol was developed in which crickets were sampled from characteristic habitats on either side of the hybrid zone and from two distinct habitat types within the zone. Presumptive pure Gryllus pennsylvanicus were sampled from fields in northwestern Connecticut and represent “inland” populations. “Pure” Gryllus firmus were sampled from beaches along the coast and represent the “coastal” populations. Crickets from within the hybrid zone were sampled from two different soil types: the “loam” populations from loamy soils and the “sand” populations from sandy soils. Moreover, an attempt was made to identify closely adjacent sand and loam localities to determine the scale of habitat variation and its possible effects on hybrid-zone structure. In general, there was little variation in morphological traits or in allozyme and mtDNA genotype frequencies among localities from within each of the four habitat types. Between each of the closely situated sand and loam localities within the hybrid zone, however, there were very significant differences in each of these sets of markers. In addition, crickets from hybrid-zone populations were tested for reproductive isolation. The asymmetric outcome of hybrid crosses that exists across the zone (Harrison, 1983) also exists on a finer ecological scale within the zone. Thus, this hybrid zone is a mosaic of strikingly differentiated populations. The dynamics of hybrid zones with mosaic structures are discussed in contrast to the traditional clinal models. The data are also discussed in light of the semipermeable nature of species boundaries. The extent to which a species boundary is permeable varies not only from one genetic marker to the next, but also with the ecological and geographic context of species interaction.     

Pathways of introduction of the invasive aquatic plant Cabomba caroliniana

The pathway and frequency of species' introductions can affect the extent, impact, and management of biological invasions. Here, we examine the pathway of introduction of the aquatic plant Cabomba caroliniana (fanwort) into Canada and the northern United States using plastid DNA sequence (intergenic spacers atpF‐atpH, trnH‐psbA, and trnL‐trnF) and DNA content analyses. We test the hypothesis that the spread of fanwort is a result of commercial trade by comparing a Canadian population (Kasshabog Lake, ON) to native populations from southern U.S., introduced populations in northern U.S., and plants from commercial retailers. Thirteen plastid haplotypes were identified throughout North America, including one dominant haplotype, which was present in all C. caroliniana populations. Several rare haplotypes were used to infer shared colonization history. In particular, the Canadian population shared two rare alleles with a population from Massachusetts, suggesting range expansion of C. caroliniana from the northern U.S. However, the possibility of a commercial introduction cannot be excluded, as common alleles were shared between the Canadian population and both commercial and southern U.S. sources. Variation in C. caroliniana genome size was bimodal and populations were classified into “high” and “low” categories. The Canadian population had DNA contents similar to several northern U.S. populations (low DNA content). This may provide additional support for range expansion from these introduced populations rather than from commercial sources or populations in the southern U.S., which had high DNA content.     

Dmrt1 polymorphism and sex‐chromosome differentiation in Rana temporaria

Sex‐determination mechanisms vary both within and among populations of common frogs, opening opportunities to investigate the molecular pathways and ultimate causes shaping their evolution. We investigated the association between sex‐chromosome differentiation (as assayed from microsatellites) and polymorphism at the candidate sex‐determining gene Dmrt1 in two Alpine populations. Both populations harboured a diversity of X‐linked and Y‐linked Dmrt1 haplotypes. Some males had fixed male‐specific alleles at all markers (“differentiated” Y chromosomes), others only at Dmrt1 (“proto‐” Y chromosomes), while still others were genetically indistinguishable from females (undifferentiated X chromosomes). Besides these XX males, we also found rare XY females. The several Dmrt1 Y haplotypes differed in the probability of association with a differentiated Y chromosome, which we interpret as a result of differences in the masculinizing effects of alleles at the sex‐determining locus. From our results, the polymorphism in sex‐chromosome differentiation and its association with Dmrt1, previously inferred from Swedish populations, are not just idiosyncratic features of peripheral populations, but also characterize highly diverged populations in the central range. This implies that an apparently unstable pattern has been maintained over long evolutionary times.     

MITOCHONDRIAL DNA PHYLOGEOGRAPHY OF HOST RACES OF THE GOLDENROD BALL GALLMAKER,EUROSTA SOLIDAGINIS (DIPTERA: TEPHRITIDAE)

We determined the phylogenetic relationships and geographic distribution of mitochondrial haplotypes of two host races of the tephritid fly Eurosta solidaginis, a gallmaker that attacks species of goldenrod (Solidago). We performed a preliminary survey by sequencing 492 bp from the 3′ ends of the mitochondrial cytochrome oxidase I and II subunits from a single individual from eight S. gigantea- and 10 S. altissima-associated populations across their range in eastern North America and from two outgroup species, Eurosta comma (two populations) and E. cribrata. Eurosta solidaginis haplotypes fell into two groups (“E” and “W” clades), which differed by four substitutions, one of which occurred within the recognition site of the DdeI restriction enzyme. We used the presence or absence of the restriction site to survey a total of 11 S. gigantea (20 individuals) and 20 S. altissima (43 individuals) host-race populations. All gigantea-fly haplotypes regardless of geographic origin carried the E-clade haplotype, whereas altissima-fly haplotypes were geographically partitioned. Altissima flies east of Michigan were of haplotype E, whereas those west of Michigan were of haplotype W, with mixed populations found in lower Michigan. These patterns confirm an earlier allozyme survey that suggested that S. altissima is the ancestral host for the gallmaker, but also suggest that the gigantea fly populations were derived from eastern U.S. altissima fly populations. The data support the conclusions of behavioral and ecological studies indicating that the shift to the derived host was facilitated by escape from natural enemies.