High prevalence of <Emphasis Type="Italic">Yersinia pestis</Emphasis> in black-tailed prairie dog colonies during an apparent enzootic phase of sylvatic plague

Sylvatic plague (Yersinia pestis) was introduced into North America over 100 years ago. The disease causes high mortality and extirpations in black-tailed prairie dogs (Cynomys ludovicianus), which is of conservation concern because prairie dogs provide habitat for the critically endangered black-footed ferret (Mustela nigripes). Our goal was to help elucidate the mechanism Y. pestis uses to persist in prairie ecosystems during enzootic and epizootic phases. We used a nested PCR protocol to assay for plague genomes in fleas collected from prairie dog burrows potentially exposed to plague in 1999 and 2000. No active plague epizootic was apparent in the 55 prairie dog colonies sampled in 2002 and 2003. However, 63% of the colonies contained plague-positive burrows in 2002, and 57% contained plague-positive burrows in 2003. Within plague-positive colonies, 23% of sampled burrows contained plague-positive fleas in 2002, and 26% contained plague-positive fleas in 2003. Of 15 intensively sampled colonies, there was no relationship between change in colony area and percentage of plague-positive burrows over the two years of the study. Some seasonality in plague prevalence was apparent because the highest percentages of plague-positive colonies were recorded in May and June. The surprisingly high prevalence of plague on study area colonies without any obvious epizootic suggested that the pathogen existed in an enzootic state in black-tailed prairie dogs. These findings have important implications for the management of prairie dogs and other species that are purported to be enzootic reservoir species.     

Deltamethrin flea-control preserves genetic variability of black-tailed prairie dogs during a plague outbreak

Genetic variability and structure of nine black-tailed prairie dog (BTPD, Cynomys ludovicianus) colonies were estimated with 15 unlinked microsatellite markers. A plague epizootic occurred between the first and second years of sampling and our study colonies were nearly extirpated with the exception of three colonies in which prairie dog burrows were previously dusted with an insecticide, deltamethrin, used to control fleas (vectors of the causative agent of plague, Yersinia pestis). This situation provided context to compare genetic variability and structure among dusted and non-dusted colonies pre-epizootic, and among the three dusted colonies pre- and post-epizootic. We found no statistical difference in population genetic structures between dusted and non-dusted colonies pre-epizootic. On dusted colonies, gene flow and recent migration rates increased from the first (pre-epizootic) year to the second (post-epizootic) year which suggested dusted colonies were acting as refugia for prairie dogs from surrounding colonies impacted by plague. Indeed, in the dusted colonies, estimated densities of adult prairie dogs (including dispersers), but not juveniles (non-dispersers), increased from the first year to the second year. In addition to preserving BTPDs and many species that depend on them, protecting colonies with deltamethrin or a plague vaccine could be an effective method to preserve genetic variability of prairie dogs.     

<Emphasis Type="Italic">Catenaria anguillulae</Emphasis> Sorokin: a Natural Biocontrol Agent of <Emphasis Type="Italic">Meloidogyne graminicola</Emphasis> Causing Root Knot Disease of Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Summary Catenaria anguillulae parasitized and killed the eggs and second stage juveniles (J₂) of Meloidogyne graminicola under natural conditions. The percentage of infection in eggs was higher than J₂ of M.␣graminicola, which ranged between 0–50.3% and 0–18.9% in 2004 and 0–46.6% and 0–21.7% in 2005, respectively. The higher parasitism of eggs and J₂ was recorded from those fields in which plants were severely infected with M. graminicola. The degree of parasitism of eggs and J₂ by C. anguillulae varied with severity of root knot disease. The fields with a higher root gall index recorded a higher percentage of infection in eggs and J₂ of M. graminicola. In general, old galls when teased and incubated, recorded higher parasitism of eggs and juveniles than young galls.     

Transmission Efficiency of Two Flea Species (<Emphasis Type="Italic">Oropsylla tuberculata cynomuris</Emphasis> and <Emphasis Type="Italic">Oropsylla hirsuta</Emphasis>) Involved in Plague Epizootics among Prairie Dogs

Plague, caused by Yersinia pestis, is an exotic disease in North America circulating predominantly in wild populations of rodents and their fleas. Black-tailed prairie dogs (Cynomys ludovicianus) are highly susceptible to infection, often experiencing mortality of nearly all individuals in a town as a result of plague. The fleas of black-tailed prairie dogs are Oropsylla tuberculata cynomuris and Oropsylla hirsuta. We tested the efficiency of O. tuberculata cynomuris to transmit Y. pestis daily from 24 to 96 h postinfection and compared it to previously collected data for O. hirsuta. We found that O. tuberculata cynomuris has over threefold greater transmission efficiency (0.18 infected fleas transmit Y. pestis at 24 h postinfection) than O. hirsuta (0.05 fleas transmit). Using a simple model of flea-borne transmission, we combine these laboratory measurements with field data on monthly flea loads to compare the seasonal vectorial capacity of these two flea species. Coinciding with seasonal patterns of flea abundance, we find a peak in potential for flea-borne transmission in March, during high O. tuberculata cynomuris abundance, and in September–October when O. hirsuta is common. Our findings may be useful in determining the timing of insecticidal dusting to slow plague transmission in black-tailed prairie dogs.     

Changes in <Emphasis Type="Italic">Galleria mellonella</Emphasis> lysozyme level and activity during <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> infection

The level of lysozyme in fat body, hemocytes and cell-free hemolymph from Galleria mellonella larvae infected with Pseudomonas aeruginosa was determined and evaluated. In the samples of fat body and hemocytes, an increase in lysozyme content was detected 1 d after infection and then a significant decrease was observed after a prolonged infection time. In the case of cell-free hemolymph, an increase in the lysozyme level was noticeable during the first 30 h post injection and stayed at a similar level for 42 h. The smaller decrease of the lysozyme level after 42 h might be associated with the development of bacteremia of P. aeruginosa in insects. In addition, the gradual increase in the content of lysozyme correlated with the increase of its activity in the hemolymph of the infected larvae as a response to injection with P. aeruginosa. The G. mellonella lysozyme appeared to be insensitive to extracellular proteinases produced in vivo by P. aeruginosa.     

Colony founding and social parasitism in <Emphasis Type="Italic">Lasius</Emphasis> (<Emphasis Type="Italic">Acanthomyops)</Emphasis>

We investigated colony foundation behavior of three species of the Lasius claviger group, L. latipes, L. interjectus and L. claviger, using field observations and laboratory experiments. Laboratory studies included observing gyne behavior prior to interaction with host colonies (e.g. grouping, overwintering, feeding) and experiments in which gynes were introduced to putative host colonies. Observations of gyne parasitic behavior immediately after mating flights in the field and the discovery of mixed colonies both confirm the parasitic behavior of these species and point toward a wide host species range including two cases of hyperparasitism. L. interjectus and L. latipes enter the host colony immediately after the nuptial flight, while L. claviger may hibernate and enter in the spring. Laboratory experiments showed that L. interjectus gynes prefer to group and suffer lower mortality when in a group, which is consistent with field observations of L. interjectus gynes entering host colonies in large numbers. Details on behavior of L. latipes alpha and beta form gynes are also given.     

Phenology and parasitism rates in introduced populations of <Emphasis Type="Italic">Pseudacteon tricuspis</Emphasis>, a parasitoid of <Emphasis Type="Italic">Solenopsis invicta</Emphasis>

We documented patterns of seasonal abundance and rates of parasitism in introduced populations of Pseudacteon tricuspis Borgmeier, a phorid parasitoid of the red imported fire ant, Solenopsis invicta Buren. Adult P. tricuspis populations were censused at monthly intervals for 1 year at three sites in northern Florida. Censuses were conducted by aspirating phorids attracted to disturbed S. invicta mounds. Pseudacteon tricuspis adults were present in every month at all sites, although abundances varied greatly among sites and over time. The highest densities of flies (up to 453 censused at 10 disturbed S. invicta mounds in 30 min) were observed in November, and changes in abundance over time were positively correlated among sites. Sex ratios were usually male biased. Parasitism rates were evaluated by collecting workers from field colonies and monitoring them in the laboratory for evidence of parasitism. Parasitism rates were very low – always less than 1%. The average parasitism rate per colony over 16 colonies and 2 years was 0.058%. No pupariation occurred within the first 8 days of collection, suggesting parasitism by P. tricuspis induced behavioral changes in parasitized workers that precluded such workers from our collections. If so, true field parasitism rates may be several times higher than measured here, yet still low in an absolute sense. These low parasitism rates can be reconciled with observed adult phorid densities by considering the large number of host ants present at the study sites.     

Sand Pile Formation in <Emphasis Type="Italic">Dorymyrmex</Emphasis> Ants

We studied circular sand pile formation by two colonies of Brazilian Dorymyrmex ants, in which workers dumped sand excavated from their underground nest around the nest entrance hole. In most cases a worker dumped its load just beyond the ridge of the pile. Each dumped piece either stayed where it was deposited (81.9% in colony A and 73.0% in colony B) or rolled down the outer slope of the sand pile away from the entrance (17.9% in colony A and 27.0% in colony B). Ants almost never dumped in a way that resulted in the load rolling back to the entrance. When one side of the sand pile was experimentally removed, ants preferentially dumped soil on the now flat side, thereby restoring the original circular shape.     

<Emphasis Type="Italic">Drosophila melanogaster</Emphasis> as a polymicrobial infection model for <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> and <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

Non-mammalian infection models have been developed over the last two decades, which is a historic milestone to understand the molecular basis of bacterial pathogenesis. They also provide small-scale research platforms for identification of virulence factors, screening for antibacterial hits, and evaluation of antibacterial efficacy. The fruit fly, Drosophila melanogaster is one of the model hosts for a variety of bacterial pathogens, in that the innate immunity pathways and tissue physiology are highly similar to those in mammals. We here present a relatively simple protocol to assess the key aspects of the polymicrobial interaction in vivo between the human opportunistic pathogens, Pseudomonas aeruginosa and Staphylococcus aureus, which is based on the systemic infection by needle pricking at the dorsal thorax of the flies. After infection, fly survival and bacteremia over time for both P. aeruginosa and S. aureus within the infected flies can be monitored as a measure of polymicrobial virulence potential. The infection takes ~24 h including bacterial cultivation. Fly survival and bacteremia are assessed using the infected flies that are monitored up to ~60 h post-infection. These methods can be used to identify presumable as well as unexpected phenotypes during polymicrobial interaction between P. aeruginosa and S. aureus mutants, regarding bacterial pathogenesis and host immunity.     

Antibacterial characteristics of <Emphasis Type="Italic">Curcuma xanthorrhiza</Emphasis> extract on <Emphasis Type="Italic">Streptococcus mutans</Emphasis> biofilm

This study evaluated the antibacterial effects of a natural Curcuma xanthorrhiza extract (Xan) on a Streptococcus mutans biofilm by examining the bactericidal activity, inhibition of acidogenesis and morphological alteration. Xan was obtained from the roots of a medicinal plant in Indonesia, which has shown selective antibacterial effects on planktonic S. mutans. S. mutans biofilms were formed on slide glass over a 72 h period and treated with the following compounds for 5, 30, and 60 min: saline, 1% DMSO, 2 mg/ml chlorhexidine (CHX), and 0.1 mg/ml Xan. The Xan group exposed for 5 and 30 min showed significantly fewer colony forming units (CFU, 57.6 and 97.3%, respectively) than those exposed to 1% DMSO, the negative control group (P<0.05). These CFU were similar in number to those slides exposed to CHX, the positive control group. Xan showed similar bactericidal effect to that of CHX but the dose of Xan was one twentieth that of CHX. In addition, the biofilms treated with Xan and CHX maintained a neutral pH for 4 h, which indicates that Xan and CHX inhibit acid production. Scanning electron microscopy showed morphological changes in the cell wall and membrane of the Xan-treated biofilms; an uneven surface and a deformation in contour. Overall, natural Xan has strong bactericidal activity, inhibitory effects on acidogenesis, and alters the microstructure of S. mutans biofilm. In conclusion, Xan has potential in anti-S. mutans therapy for the prevention of dental caries.     

Protoplast isolation and culture for somatic hybridization of <Emphasis Type="Italic">Lupinus angustifolius</Emphasis> and <Emphasis Type="Italic">L</Emphasis>. <Emphasis Type="Italic">subcarnosus</Emphasis>

A method for isolation and shoot regeneration from electrofused protoplasts of L. angustifolius and L. subcarnosus was developed. Viable protoplasts were isolated from leaves of in-vitro grown seedlings at an average yield of 6 × 10⁵ protoplasts g⁻¹ fresh weight. Liquid and agarose solidified B5 media were used for protoplast culture. In the liquid-culture system, all tested media, VKM, P1 and KM8p, were applicable for inducing cell division (84% of all tested petri dishes at four weeks) and colony formation. Media containing additional carbohydrates were suitable to produce compact calli with green and brown pigmentations in different combinations. Analysis of callus with molecular markers allowed to identify six somatic hybrids. However, none of the parental-protoplast derived cell colonies could develop shoots. This is the first report on protoplast fusion of L. angustifolius and L. subcarnosus with subsequent shoot regeneration.     

Macronutrient regulation in the Rasberry crazy ant (<Emphasis Type="Italic">Nylanderia</Emphasis> sp. nr. <Emphasis Type="Italic">pubens</Emphasis>)

Animals grow and optimize performance when they collect foods in amounts and ratios that best meet their species-specific nutritional requirements. For eusocial organisms like ants, where only a small fraction of the colony members collect food, increasing evidence demonstrates that strong macronutrient regulation occurs at the colony level. Here, we explored regulation of protein and carbohydrate (p:c) intake in the Rasberry crazy ant, Nylanderia sp. nr. puben. We did this using dry artificial foods (14–42% total macronutrient content) having a range of fixed p:c ratios in a series of choice and no-choice laboratory experiments and used worker mortality to gauge colony-level costs associated with active nutrient regulation. Choice experiments revealed that colonies preferred carbohydrate-rich foods and self-selected a diet having a p:c ratio ~1:2. No-choice experiments demonstrated that food p:c ratio only moderately affected worker food collection behavior, likely because colonies regulated the intake of only the non-limiting nutrients. Absolute worker mortality was generally high, but lowest in colonies feeding on the food having a p:c ratio of 1:2 (the p:c ratio ants self-selected in the choice experiment), although mortality was not significantly affected by food p:c ratio. The self-selected p:c ratio in our study is consistent with that observed in other recent ant nutrient regulation studies. Taken together, the results from these combined studies reveal emerging commonalities among ants in macronutrient regulation strategies, and similarities in foraging behaviors and costs associated with macronutrient regulation. Finally, from a methodological perspective, the high mortality observed in our study, when compared with other recent studies, suggests that ant nutrient regulation studies should be conducted using foods having high moisture and total macronutrient content.     

Incongruent effects of two isolates of <Emphasis Type="Italic">Rickettsia conorii</Emphasis> on the survival of <Emphasis Type="Italic">Rhipicephalus sanguineus</Emphasis> ticks

Rickettsia conorii, the etiologic agent of Mediterranean spotted fever is widely distributed in Southern Europe, the Middle East, Africa, India and the Caspian region. In the Mediterranean region, the brown dog tick, Rhipicephalus sanguineus, is the recognized vector of R. conorii. To study tick-pathogen relationships and pathogenesis of infection caused in model animals by the bite of an infected tick, we attempted to establish a laboratory colony of Rh. sanguineus persistently infected with R. conorii. Rhipicephalus sanguineus ticks of North American and Mediterranean origin were exposed to R. conorii isolates of African (R. conorii conorii strain Malish) and Mediterranean (R. conorii israelensis strain ISTT) origin. Feeding of ticks upon infected mice and dogs, intra-hemocoel inoculation, and submersion in suspensions of purified rickettsiae were used to introduce the pathogen into uninfected ticks. Feeding success, molting success and the longevity of molted ticks were measured to assess the effects of R. conorii on the survival of Rh. sanguineus. In concordance with previously published results, Rh. sanguineus larvae and nymphs from both North American and Mediterranean colonies exposed to R. conorii conorii Malish experienced high mortality during feeding and molting or immediately after. The prevalence of infection in surviving ticks did not exceed 5%. On the other hand, exposure to ISTT strain had lesser effect on tick survival and resulted in 35–66% prevalence of infection. Rh. sanguineus of Mediterranean origin were more susceptible to infection with either strain of R. conorii than those from North America. Previous experimental studies had demonstrated transovarial and transstadial transmission of R. conorii in Rh. sanguineus; however, our data suggest that different strains of R. conorii may employ different means of maintenance in nature. The vertebrate host may be a more important reservoir than previously thought, or co-feeding transmission between different generations of ticks may obviate or lessen the requirement for transovarial maintenance of R. conorii.     

Natural patterns of caste and sex allocation in the stingless bees <Emphasis Type="Italic">Melipona favosa</Emphasis> and <Emphasis Type="Italic">M. trinitatis</Emphasis> related to worker behaviour

Summary. This paper is the report of a long-duration study of the production of gynes and males in Melipona stingless bees in Trinidad and Tobago, including a behavioural study of laying workers. In 167 brood samples (16342 pupae) of M. favosa, taken from 78 colonies in the natural environment over the years 1993-2001, workers represented 78.4% and males represented 17.3%. Gynes represented 5.1% of all female brood. Gyne proportion never exceeded 22.5%. Gynes were found to be common throughout the year. Like the gynes, males were present all year, but their occurrence varied over the months. Males were most common in the months of July and August. At the colony level male occurrence in the brood was characterized by very high values (maximum 74.2%), next to a frequent complete absence (in 26.5% of all samples). The finding of bout-like production of males at the colony level is supported by the observations on reproductive worker behaviour. The colonies appeared to be in different phases of male production. When male producing laying workers were present, they competed heavily for egg-laying opportunities. Various behaviours of laying workers and the queen are described and interpreted on the basis of reproductive competition and kin conflict theories. From these results, we conclude that in M. favosa, workers have a distinct influence on reproduction, including the production of gynes and males.     

Importance of early arrival of adult <Emphasis Type="Italic">Harmonia axyridis</Emphasis> for control of <Emphasis Type="Italic">Aphis spiraecola</Emphasis> on apple

The biological control of aphid populations may only be possible when natural enemies arrive soon after aphid colonization. This study was done to identify how quickly adult Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) need to arrive at newly established spirea aphid [Aphis spiraecola Patch (Homoptera: Aphididae)] colonies on apple (Malus domestica Borkh.) to provide population control. A total of 100 newly established spirea aphid colonies were caged in an experimental apple orchard in West Virginia, USA. A single adult H. axyridis was added to each of ten caged colonies at day 0, 5, 10, 15 and 20 days after caging. An additional ten caged colonies were opened for exposure to natural levels of predation at each of the treatment intervals as a control. The single H. axyridis eliminated the aphid colonies significantly more quickly than natural predation for up to ten days after colony establishment. The probability of an aphid colony producing alates was significantly lower in the presence of a single H. axyridis adult than when exposed to natural predation for the first ten days. Adult H. axyridis beetles are capable of completely controlling individual spirea aphid colonies on apple only if they are abundant enough to find colonies within one week of colony establishment.     

Distribution of <Emphasis Type="Italic">Paenibacillus larvae</Emphasis> Spores Among Adult Honey Bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>) and the Relationship with Clinical Symptoms of American Foulbrood

Knowledge of the distribution of Paenibacillus larvae spores, the causative agent of American foulbrood (AFB), among individual adult honey bees is crucial for determining the appropriate number of adult bees to include in apiary composite samples when screening for diseased colonies. To study spore distribution at the individual bee level, 500 honey bees were collected from different parts of eight clinically diseased colonies and individually analyzed for P. larvae. From the brood chamber and from the super, bees were randomly collected and individually put in Eppendorf vials. The samples were frozen as soon as possible after collection. Concurrently with sampling, each colony was visually inspected for clinical symptoms of AFB. The number of clinically diseased cells in the colony was visually estimated. All samples were cultured in the laboratory for P. larvae. The results demonstrate that the spores are not randomly distributed among the bees; some bees have much higher spore loads than others. It is also clear that as the proportion of contaminated bees increase, the number of spores from each positive bee also increases. The data also demonstrated a relationship between the number of clinically diseased cells and the proportion of positive bees in individual colonies. This relationship was used to develop a mathematical formula for estimating the minimum number of bees in a sample to detect clinical disease. The formula takes into account the size of the apiary and the degree of certainty with which one aims to discover clinical symptoms. Calculations using the formula suggest that adult bee samples at the colony level will detect light AFB infections with a high probability. However, the skewed spore distribution of the adult bees makes composite sampling at the apiary level more problematic, if the aim of the sampling is to locate lightly infected individual colonies within apiaries. The results suggest that false-negative culturing results from composite samples of adult bees from individual colonies with clinical symptoms of AFB are highly improbable. However, if single colonies have light infections in large apiaries, the dilution effect from uncontaminated bees from healthy colonies on the positive bees from diseased colonies may yield false-negative results at the apiary level.     

<Emphasis Type="Italic">Sporothrix inflata</Emphasis>, a root-inhabiting fungus of <Emphasis Type="Italic">Quercus robur</Emphasis> and <Emphasis Type="Italic">Q. petraea</Emphasis>

The anamorphic fungus Sporothrix inflata, known as a soil-borne fungus with worldwide distribution, was isolated for the first time from the cortex and central cylinder of living and dead roots of healthy and diseased oak trees (Quercus robur and Q. petraea). Isolation frequencies of S. inflata from oak roots varied according to the health status of trees, oak species, study sites, soil depth and root diameter. Colony morphology and growth rate of isolates are influenced by colony age and type of culture medium.     

Dispersal flight and colony development in the fungus-growing termites <Emphasis Type="Italic">Pseudacanthotermes spiniger</Emphasis> and <Emphasis Type="Italic">P. militaris</Emphasis>

Pseudacanthotermes spiniger and P. militaris are two African fungus-growing termites (Termitidae, Macrotermitinae) which may become pests in disturbed agrosystems where they often live in sympatry. To study their development and their reproductive strategies, colonies of both species were reared in the laboratory for 20 and 17 years, respectively, after their foundation from reproductive pairs. The first steps of development were in great part similar in both species, although P. spiniger favoured the defence during the juvenile period, while P. militaris tended to favour a rapid development. While P. spiniger colonies did not produce alates until year 7 of colony life, P. militaris colonies were able to produce a fertile progeny 4 years after their foundation. In contrast, major soldiers were more rapidly differentiated in the incipient colonies of P. spiniger. Dispersal flights occurred every year for 10 years in P. spiniger. In P. militaris, dispersal flights did not occur regularly although alates appeared yearly. The annual number of alates produced by P. spiniger increased with the colony age to reach a maximum of 25,000 individuals and global production of alates was estimated at ca. 150,000 individuals in the life of a colony. The longevity of P. spiniger and P. militaris colonies was around 20 years. These species were shown to be reproductively isolated by multiple pre-mating mechanisms. While chronological differences in dispersal flights contribute to reproductive isolation of the two species, the non-viability of experimental hybrid colonies also indicates the involvement of post-mating mechanisms of isolation.     

<Emphasis Type="Italic">Aphidius ervi</Emphasis> Preferentially Attacks the Green Morph of the Pea Aphid, <Emphasis Type="Italic">Acyrthosiphon pisum</Emphasis>

The pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae) is found in red and green color morphs. Previous work has suggested that the aphidiine parasitoid Aphidius ervi Haliday preferentially attacks green pea aphids in the field. It is not clear whether these results reflect a real preference, or some unknown clonal difference, such as in immunity, between the aphids used in the previous studies. We used three susceptibility-matched pairs of red and green morph pea aphid clones to test for preferences. In a no-choice situation, the parasitoids attacked equal proportions of each color morph. When provided with a choice, A. ervi was significantly more likely to oviposit into colonies formed from green morphs when the neighboring colony was formed from red morph aphids. In contrast, red morphs were less likely to be attacked when their neighboring colony was of the green morph. By preferentially attacking green colonies, A. ervi may reduce the likelihood of intraguild predation, as it is suggested that visually foraging predators preferentially attack red aphid colonies. Furthermore, if this host choice behavior is replicated in the field, we speculate that color morphs of the pea aphid may interact indirectly through their shared natural enemies, leading to intraspecific apparent competition.     

<Emphasis Type="Italic">Ty</Emphasis>1<Emphasis Type="Italic">/copia</Emphasis>- and <Emphasis Type="Italic">Ty</Emphasis>3<Emphasis Type="Italic">/gypsy</Emphasis>-like DNA sequences in <Emphasis Type="Italic">Helianthus </Emphasis>species

Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.