Populations ofD Research Articles

Evolution of sex-specific heat stress tolerance and larval Hsp70 expression in populations of Drosophila melanogaster adapted to larval crowding.

The ability to tolerate temperature stress is an important component of adult fitness. In holometabolous insects like Drosophila melanogaster, adult stress resistance can be affected by growth conditions experienced during the larval stages. Although evolution under crowded larval conditions is known to lead to the correlated evolution of many adult traits, its consequences on adult heat stress tolerance have not been investigated. Therefore, in the present study, we assessed the adult heat stress tolerance in populations of D. melanogaster adapted to a stressful larval crowding environment. We used replicate populations ofD. melanogaster, selected for adaptation to larval crowding stress (MCUs), for more than 230 generations, and their respective controls (MBs). Larvae from selected and control populations were grown under crowded and uncrowded conditions, and their adult heat shock resistance at two different temperatures was measured. Further, we compared Hsp70 expression in crowded and uncrowded larvae of both populations and also measured the Hsp70 expression after a mild heat treatment in adults of selected and control populations. Our results showed that adaptation to larval crowding leads to the evolution of Hsp70 gene expression in larval stages and improves adult heat stress tolerance ability in males, but not in females.

Target Region Amplification Polymorphism (TRAP) for Assessing Genetic Diversity and Relationships Among Cultivated Populations of Dendrobium officinale

Dendrobium officinale (Orchidacesae) is one of the rare and endangered species of herbs in China. Therefore, it will be beneficial to investigate the genetic diversity and relationships of cultivated populations of D. officinale for quality improvement. In this study, eight target region amplification polymorphism (TRAP) primer combinations were selected from fifty-four combinations, which were designed based on the related genes of the polysaccharides and alkaloids. A total of 148 fragments were scored in nine cultivated populations of D. officinale, including 130 (87.84%) polymorphic fragments. The analysis of genetic diversity revealed high level of genetic diversity in cultivated populations of D. officinale (H = 0.4125, I = 0.5985). Based on analysis of genetic structure, there was a moderate variation (Gst = 0.4706) and lower gene flow (Nm = 0.5625) among the cultivated populations due to some isolated measures, and domestication of excellent cultivars. Moreover, UPGMA dendrogram and Principal Coordinate Analysis (PCoA) indicated that nine cultivated populations were divided into four major groups. The results suggested that genetic relationships were associated with geographical germplasm sources instead of cultivation locations. Therefore, TRAP markers can be effectively employed to analyze genetic diversity and relationships among cultivated populations of D. officinale.

Fitness costs associated with thiamethoxam and imidacloprid resistance in three field populations of Diaphorina citri (Hemiptera: Liviidae) from Florida.

Insecticide resistance is an increasing problem in citrus production. The Asian citrus psyllid, Diaphornia citri Kuwayama, is recognized as one of the most important citrus pests worldwide and it has developed resistance in areas where insecticides have been overused. The development of insecticide resistance is often associated with fitness costs that only become apparent in the absence of selection pressure. Here, the fitness costs associated with resistance to thiamethoxam and imidacloprid were investigated in three agricultural populations of D. citri as compared with susceptible laboratory colonies. Results showed that all field populations had greater resistance than laboratory susceptible colonies. For both thiamethoxam and imidacloprid, a Candidatus Liberibacter asiaticus-positive (CLas+) colony was more susceptible than the CLas- colony. Resistance ratios ranged from 7.65-16.11 for imidacloprid and 26.79-49.09 for thiamethoxam in field populations as compared with a susceptible, CLas- laboratory strain. Among three resistant field populations, a significantly reduced net reproductive rate and finite rate of population increase were observed in a population from Lake Wales, FL as compared to both susceptible strains. The fecundity of field populations from Lake Wales, FL was statistically lower than both laboratory susceptible populations. Certain changes in morphological characteristics were observed among resistant, as compared, with susceptible strains. Our data suggest fitness disadvantages associated with insecticide resistance in D. citri are related to both development and reproduction. The lower fitness of D. citri populations that exhibit resistance to neonicotinoid insecticides should promote recovery of sensitivity when those populations are no longer exposed to thiamethoxam and/or imidacloprid in the field. The results are congruent with a strategy of insecticide rotation for resistance management.

Population viability analysis of common marsupials,Didelphis marsupialisandDidelphis virginiana, in a scenario of constant loss of native vegetation

AbstractWe studied the population viability of two common marsupials,Didelphis marsupialisandDidelphis virginiana, based on field data and published ecological and genetic information. Using the VORTEX v. 10. 2.6 program, a 100-year simulation was performed with 1000 iterations for five populations ofD. marsupialisand six ofD. virginiana. A low probability of extinction was observed in both species, particularly forD. virginiana(0.000–0.007). Population size is higher considering a metapopulation dynamics approach versus individual populations for the two marsupials: 498.25 individuals forD. marsupialisand 367.41 individuals forD. virginiana. The estimated mean genetic diversity was high for bothD. marsupialis(He = 0.77–0.78) andD. virginiana(He = 0.79–0.82). The survival of both species over time could be expected to increase if a metapopulation dynamics is favored over the coming decades, despite a 1.3% loss rate of forest cover. The monitoring of population size and genetic diversity is highly recommended to validate the trends suggested by the model; this is especially true forD. marsupialis, a species associated with conserved areas that are becoming progressively less abundant. This research provides information on the responses of common mammalian species to environmental changes such as deforestation.

Global warming and chromosomal inversion adaptation in isolated islands:Drosophila subobscurapopulations from Madeira

AbstractGlobal warming is an environmental phenomenon to which species must adapt to survive.Drosophila subobscurapresents an adaptive capacity due to its chromosomal inversion polymorphism. Until now, the impact of global warming on this polymorphism has been studied inD. subobscurapopulations located either on a continental mainland or on islands not far from a continent. In this context, gene flow could be a relevant mechanism allowing the movement of thermally adapted inversions between populations. Our aim was to sample and study the chromosomal polymorphism on Madeira, a small isolated island in the Atlantic Ocean. We compared our findings with those reported in the same location approximately four and five decades ago. Moreover, we studied whether global warming has occurred on this island by analyzing mean, maximum and minimum temperatures over a 55‐year period. All atmospheric parameters have increased significantly, consistent with climate change expectations. Frequencies and chromosomal thermal index values of thermal adapted inversions remained quite stable over years. Furthermore, J, U and O chromosomes are almost fixed for “warm” adapted inversions. Thus, if there is little genetic variability remaining and temperatures continue increasing, island populations ofD. subobscuramight be on the threshold of endangerment. However, apart from selection, genetic drift and inbreeding, other processes, such as phenotypic plasticity or thermoregulatory behavior, could be involved in the survival of the species’ populations. Finally, although in danger,D. subobscurais a generalist that lives in humanized environments, and this fact could favor its persistence on Madeira Island.

Diplolepis Rosae (L.) (Hymenoptera: Cynipidae): Development, Ecology and Galls in the Brno Region

The paper results from two years of studying development and formation of the galls ofDiplolepis rosae(L.) onRosa canina(L.) in the Brno region (Czech Republic). Following the extremely warm and dry growing season of 2015, 70 % of prepupae and 30 % of grown‑up 2ndinstar larvae hibernated. After the climatically milder growing period of 2016, only 47 % of prepupae and 53 % of grown‑up larvae hibernated. Pupae were recorded from mid‑March to mid‑July and imagoes occurred from April to July. The average percentage of males in the populations was 4.5 %. Eggs were found in the galls from May to July. Larvae of the 1stand 2ndinstars were found in the galls from June to August and from July to October (or to next March), respectively. Average cranium width in the 1stinstar larvae increased during the growth of larvae from 0.25 to 0.35 mm, i.e. by 38 %. Average cranium width in the 2ndinstar larvae was 0.55 mm and practically did not change during the growth of the larvae. 85.1 % of galls were formed on budding leaves, 14.9 % on flowers and fruits. The galls were growing most rapidly in June and July, and their growth ended in October when they reached average height and width of 40 mm and 47 mm, respectively. They consisted of 1 to 20 (on average 7) ± intergrown parts with 1 to 225 (on average 54) cells. 63.5 % of them were localized along the sides of shoots and 36.5 % were found on the shoot tips. The largest cells (3.9 x 3.1 mm) were those with the completed development of gall wasp larvae. Cells inhabited by parasitoids were by 15.0 % smaller and by 24.5 % smaller were cells with dead gallwasp larvae due to natural reasons. As compared with the cells with the completed development of gall wasp, cells with the larvae of inquilinePericlistus brandtii(Ratz.) were by 43.6 % shorter and by 50.6 % narrower. The inquiline was found in 10 % of galls and in 3.6 % of cells. In 2015, parasitoids inhabited on average 15.0 % (in 2016 22.1 %) of cells. Approximately 50 % of the population ofD. rosaedied in the galls during the preimaginal development.

New problems in dendropathology – new and invasive pathogens

AbstractDuring the last decades, several new and invasive tree pathogens have arrived in the northern Europe, damaging forest and verdant trees. New and invasive species (e.g.Lecanosticta acicola,Dothistroma septosporum, Diplodia sapinea,Hymenoscyphus fraxineus) are considered to cause economic loss and be an important threat to biodiversity. Once the alien species have entered into ecosystem, then it is very difficult to eliminate them. Therefore, it is important to discover new and invasive pathogens from forests and from imported plant material as early as possible. For that reason, the research team of Estonian forest pathologists has worked out a survey strategy with permanent plots across Estonia – for early detection of new pathogens, which essentially includes molecular monitoring of pathogens. An important task in developing of early detection methods for new and invasive pathogens is working out of quick detection methods by creating original PCR primers. Crucial is also the analyses of pathogens biology, of their spreading and finding of all their potential hosts in new for them environment in northern Europe. In cooperation studies with our foreign partners, the Estonian forest pathologists have analysed populations ofD. septosporum,L. acicolaandH. fraxineus. The population genetic methods give data about the pathogens diversity, vitality and betray potential pathways of them to northern Europe. This information serves for building up the control strategy and helps to find and test resistant tree species progenies. Early detection, molecular monitoring and pathways detection of new and invasive pathogens are currently the most important research tasks of the forest pathology team working in Estonian University of Life Sciences.

Genomic analysis of P elements in natural populations of Drosophila melanogaster.

The Drosophila melanogaster P transposable element provides one of the best cases of horizontal transfer of a mobile DNA sequence in eukaryotes. Invasion of natural populations by the P element has led to a syndrome of phenotypes known as P-M hybrid dysgenesis that emerges when strains differing in their P element composition mate and produce offspring. Despite extensive research on many aspects of P element biology, many questions remain about the genomic basis of variation in P-M dysgenesis phenotypes across populations. Here we compare estimates of genomic P element content with gonadal dysgenesis phenotypes for isofemale strains obtained from three worldwide populations of D. melanogaster to illuminate the molecular basis of natural variation in cytotype status. We show that P element abundance estimated from genome sequences of isofemale strains is highly correlated across different bioinformatics approaches, but that abundance estimates are sensitive to method and filtering strategies as well as incomplete inbreeding of isofemale strains. We find that P element content varies significantly across populations, with strains from a North American population having fewer P elements but a higher proportion of full-length elements than strains from populations sampled in Europe or Africa. Despite these geographic differences in P element abundance and structure, neither the number of P elements nor the ratio of full-length to internally-truncated copies is strongly correlated with the degree of gonadal dysgenesis exhibited by an isofemale strain. Thus, variation in P element abundance and structure across different populations does not necessarily lead to corresponding geographic differences in gonadal dysgenesis phenotypes. Finally, we confirm that population differences in the abundance and structure of P elements that are observed from isofemale lines can also be observed in pool-seq samples from the same populations. Our work supports the view that genomic P element content alone is not sufficient to explain variation in gonadal dysgenesis across strains of D. melanogaster, and informs future efforts to decode the genomic basis of geographic and temporal differences in P element induced phenotypes.

Aggressiveness Changes in Populations of Didymella pinodes over Winter and Spring Pea Cropping Seasons.

Ascochyta blight, caused by the necrotrophic ascomycete Didymella pinodes, is responsible for severe losses in winter and spring pea crops. Despite different climatic conditions, epidemics on winter and spring crops are due to a single population of D. pinodes, suggesting gene flow either between the two crops or from reservoir sources during the cropping season. This should lead to similar pathogenicity characteristics in isolates sampled from the two crops. However, these hypotheses have never been formally tested. We therefore sampled a total of 520 D. pinodes strains throughout a growing season from winter and spring pea plots (WP and SP, respectively) and from winter and spring trap plants (TWP and TSP). Amplified fragment length polymorphism (AFLP) markers revealed high genetic diversity within subpopulations, whereas pathogenicity tests showed that mean aggressiveness increases over the course of an epidemic. These results support the idea that alloinoculum contributes to the carryover of epidemics between winter and spring crops and that the most aggressive isolates are selected as an epidemic progresses. Ascochyta blight, caused by Didymella pinodes, is responsible for severe losses in pea crops. While previous studies have shown that ascochyta blight epidemics on winter and spring crops are due to a single population of D. pinodes, suggesting that isolates from the two crops present similar pathogenicity characteristics, that hypothesis have never been tested. Genetic analysis of subpopulations sampled throughout a growing season from winter and spring pea plots revealed high genetic diversity within subpopulations, whereas pathogenicity tests showed that mean aggressiveness increases over the course of an epidemic.

Unraveling the evolutionary scenario of the hobo element in populations of Drosophila melanogaster and D. simulans in South America using the TPE repeats as markers.

Transposable elements (TEs) are nucleotide sequences found in most studied genomes. These elements are highly diversified and have a large variation in nucleotide structure and mechanisms of transposition. hobo is a member of class II, belonging to hAT superfamily, described inDrosophila melanogaster, and it presents in its Open Reading Frame, a repetitive region encoding the amino acids threonine-proline-glutamic acid (TPE), which shows variability in the number of repeats in some regions of the world. Due to this variability some evolutionary scenarios of the hobo element are discussed, such as the scenario of the invasion of hobo element in populations ofD. melanogaster. In the present study, we investigated 22 DNA sequences of D. melanogaster and seven sequences ofD. simulans, both from South America, to check the number of repetitions of TPE, in order to clarify the evolutionary scenario of thehobo element in these populations. Our results showed a monomorphism in populations of both species in South America, with only three TPE repeats. Hence, we discuss and propose an evolutionary scenario of the invasion of the hobo element in populations of D. melanogaster and D. simulans.

The distribution ofDothistroma septosporumand its mating types in Poland

SummaryDothistroma needle blight (DNB), one of the most dangerous foliar diseases of pines, is the cause of much economic loss in pine plantations worldwide. The threat to pine‐dominated Polish forestry from this disease is therefore very large. However, the impact ofDNBhas not been high mainly due to the planting ofP. sylvestris, a less susceptible native species. Until now,DNBwas recorded in Poland only on highly susceptible exoticP. nigra. The current situation concerning the disease in Poland is described in this article. This disease, caused byDothistroma septosporum, was first recorded in a single location (Domiarki) in southern Poland in 1990. This study reports the occurrence ofD. septosporumin 37 new locations, demonstrating that the disease has now spread across the whole country.Pinus nigraremains the predominant host species in Poland. However, three new hosts for this fungus are reported, that isP. sylvestris,P. mugoandP. ponderosa. The ratio ofD. septosporummating types varies significantly between sites, ranging from an equal proportion of each mating type to single mating type populations. For the oldest known Polish population ofD. septosporum,the mating type ratio has shifted towards equilibrium over time.

Body size and age structure of the endangered Clark’s lizard (Darevskia clarkorum) populations from two different altitudes in Turkey

We investigated age structure, body size and longevity in two breeding populations ofDarevskia clarkoruminhabiting altitudes ranging from 450 m a.s.l. (Kamilet) to 2250 m a.s.l. (Başyayla) in Turkey by skeletochronology performed on the phalanges. The mean age was found to be 6 years in the Kamilet population and 7 years in the Başyayla population. The maximum life span was 10 years in the lowland population while it was 12 years in the highland population. Age at sexual maturity of both males and females was 1-2 years in the lowland population while it was 2-3 for both sexes in the highland population. Both age and SVL of specimens from the Kamilet population were significantly different between the sexes while age and SVL did not differ significantly between the sexes in Başyayla population. As a conclusion, we observed that the mean age, longevity and age at maturity were increased by altitude while there was a decrease based on the mean SVL in the highland population ofD. clarkorum. Our data on body size, longevity and age at sexual maturity may contribute to conservation efforts for this endangered species.

Does kin selection moderate sexual conflict in Drosophila?

Two recent studies provide provocative experimental findings about the potential influence of kin recognition and cooperation on the level of sexual conflict in Drosophila melanogaster. In both studies, male fruit flies apparently curbed their mate-harming behaviours in the presence of a few familiar or related males, suggesting some form of cooperation mediated by kin selection. In one study, the reduction in agonistic behaviour by brothers apparently rendered them vulnerable to dramatic loss of paternity share when competing with an unrelated male. If these results are robust and generalizable, fruit flies could be a major new focus for the experimental study of kin selection and social evolution. In our opinion, however, the restrictive conditions required for male cooperation to be adaptive in this species make it unlikely to evolve. We investigated these phenomena in two different populations of D. melanogaster using protocols very similar to those in the two previous studies. Our experiments show no evidence for a reduction in mate harm based upon either relatedness or familiarity between males, and no reduction in male reproductive success when two brothers are in the presence of an unfamiliar, unrelated, 'foreign' male. Thus, the reduction of sexual conflict owing to male cooperation does not appear to be a general feature of the species, at least under domestication, and these contrasting results call for further investigation: in new populations, in the field and in the laboratory populations in which these phenomena have been reported.

Infection Density Dynamics of the Citrus Greening Bacterium "Candidatus Liberibacter asiaticus" in Field Populations of the Psyllid Diaphorina citri and Its Relevance to the Efficiency of Pathogen Transmission to Citrus Plants.

Huanglongbing, or citrus greening, is a devastating disease of citrus plants recently spreading worldwide, which is caused by an uncultivable bacterial pathogen, "Candidatus Liberibacter asiaticus," and vectored by a phloem-sucking insect, Diaphorina citri. We investigated the infection density dynamics of "Ca. Liberibacter asiaticus" in field populations of D. citri with experiments using field-collected insects to address how "Ca. Liberibacter asiaticus" infection density in the vector insect is relevant to pathogen transmission to citrus plants. Of 500 insects continuously collected from "Ca. Liberibacter asiaticus"-infected citrus trees with pathological symptoms in the spring and autumn of 2009, 497 (99.4%) were "Ca. Liberibacter asiaticus" positive. The infections were systemic across head-thorax and abdomen, ranging from 10(3) to 10(7) bacteria per insect. In spring, the infection densities were low in March, at ∼ 10(3) bacteria per insect, increasing up to 10(6) to 10(7) bacteria per insect in April and May, and decreasing to 10(5) to 10(6) bacteria per insect in late May, whereas the infection densities were constantly ∼ 10(6) to 10(7) bacteria per insect in autumn. Statistical analysis suggested that several factors, such as insect sex, host trees, and collection dates, may be correlated with "Ca. Liberibacter asiaticus" infection densities in field D. citri populations. Inoculation experiments with citrus seedlings using field-collected "Ca. Liberibacter asiaticus"-infected insects suggested that (i) "Ca. Liberibacter asiaticus"-transmitting insects tend to exhibit higher infection densities than do nontransmitting insects, (ii) a threshold level (∼ 10(6) bacteria per insect) of "Ca. Liberibacter asiaticus" density in D. citri is required for successful transmission to citrus plants, and (iii) D. citri attaining the threshold infection level transmits "Ca. Liberibacter asiaticus" to citrus plants in a stochastic manner. These findings provide valuable insights into understanding, predicting, and controlling this notorious citrus pathogen.

Micro‐geographical scale variation inDrosophila melanogasterlarval olfactory behaviour is associated with host fruit heterogeneity

AbstractOrganisms utilize environmental cues to deal with heterogeneous environments. In this sense, behaviours that mediate interactions between organisms and their environment are complex traits, especially sensitive to environmental conditions. In animals, olfaction is a critical sensory system that allows them to acquire chemical information from the environment. The genetic basis and physiological mechanisms of the olfactory system ofDrosophila melanogasterMeigen (Diptera:Drosophilidae) are well known, but the effects of ecological factors on the olfactory system have received less attention. In this study, we analysed the effect of environmental heterogeneity (different host fruits) on variation in larval olfactory behaviour in a natural population ofD. melanogaster. We generated half‐sib lines ofD. melanogasterderived from two nearby fruit plantations,Vitis viniferaL. (Vitaceae) (‘grape’) andPrunus persicaL. (Rosaceae) (‘peach’), and measured, using a simple behavioural assay, larval olfactory response to natural olfactory stimuli. Results indicate that patterns of variation for this trait depend on host fruit plantation where lines were collected. In fact, only lines derived from ‘grape’ showed phenotypic plasticity for larval olfaction, whereas a genotype*environment interaction was detected solely in lines derived from ‘peach’. Therefore, our results demonstrate the existence of genetic differences inD. melanogasterlarval olfactory behaviour at a micro‐geographical scale and also reveal that the trait studied presents a dynamic genetic architecture which is strongly influenced by the environment.

Morphobiochemical Variability and Selection Strategies for the Germplasm ofDactylorhiza hatagirea(D. Don) Soo: An Endangered Medicinal Orchid

Dactylorhiza hatagirea(D. Don) Soo (Orchidaceae) is an important endangered medicinal herb, distributed in subalpine to alpine regions of the Himalayas. Its tubers are important constituents of many medicines and health tonics. Overexploitation for medicinal uses has decreased availability in natural habitats and this species has been enlisted as endangered, making conservation and cultivation studies necessary. Variability studies may serve as an important tool for effective conservation and for a crop improvement program. Therefore, natural populations ofD. hatagireawere analyzed for variability on the basis of morphological, biochemical, and isoenzyme patterns. The studied populations were grouped into two clusters. Existing variability among different populations opens up new areas for conservation and perspectives for a genetic improvement program forD. hatagirea.

Adaptive divergence of a transcriptional enhancer between populations ofDrosophila melanogaster

As species colonize new habitats they must adapt to the local environment. Much of this adaptation is thought to occur at the regulatory level; however, the relationships among genetic polymorphism, expression variation and adaptation are poorly understood. Drosophila melanogaster, which expanded from an ancestral range in sub-Saharan Africa around 15 000 years ago, represents an excellent model system for studying regulatory evolution. Here, we focus on the gene CG9509, which differs in expression between an African and a European population of D. melanogaster. The expression difference is caused by variation within a transcriptional enhancer adjacent to the CG9509 coding sequence. Patterns of sequence variation indicate that this enhancer was the target of recent positive selection, suggesting that the expression difference is adaptive. Analysis of the CG9509 enhancer in new population samples from Europe, Asia, northern Africa and sub-Saharan Africa revealed that sequence polymorphism is greatly reduced outside the ancestral range. A derived haplotype absent in sub-Saharan Africa is at high frequency in all other populations. These observations are consistent with a selective sweep accompanying the range expansion of the species. The new data help identify the sequence changes responsible for the difference in enhancer activity.

Diet composition and food habits ofDiplodus puntazzo(Sparidae) from the Gulf of Gabès (Central Mediterranean)

The diet and feeding habits of the sharpsnout seabream,Diplodus puntazzo, from the Gulf of Gabès were investigated using stomach contents of 490 specimens ranging from 12.6 cm to 26.1 cm total length in size and from 29.95 g to 230.83 g in weight collected from commercial catches between April 2008 and March 2009. Of the total number of examined stomachs, 279 were empty (%VI = 56.94). This percentage varied significantly with months, attaining a maximum in spring (74.88%) and a minimum in autumn (37.38%). Eight major taxa were identified (Plantae, Spongia, Tunicata, Echinodermata, Crustacea, Annelida, Mollusca and Teleostei) in stomach contents ofD. puntazzo. Plants were the most important food source, constituting 89.88% of the total Index of relative importance. The other groups, such as teleosts, molluscs, crustaceans and annelids represented accessory food. Significant differences in diet were observed in relation to season. Plants were the most important food source item in all seasons, especially during the autumn. The estimation of trophic level gave an average of 2.57 ± 0.2 for the whole population ofD. puntazzoin the Gulf of Gabès. Based on the composition of its diet, this species may be considered as an omnivorous fish with a preference for vegetable material, and showing specialist feeding strategy.

Dynamic Insecticide Susceptibility Changes in Florida Populations of <I>Diaphorina citri</I> (Hemiptera: Psyllidae)

Five field populations of Diaphorina citri Kuwayama from various regions of Florida were evaluated in 2011 for resistance to commonly used insecticides. Three diagnostic doses (LD50, LD75, and LD95), developed in 2009 using a laboratory susceptible population, were used to measure changes in susceptibility levels of field-collected populations as compared with a susceptible laboratory population. Further reductions in the susceptibility levels of D. citri to chlorpyriphos and fenpropathrin were determined, compared with results obtained in 2010. Mean percent mortality obtained from all five locations was significantly lower than observed with the laboratory susceptible population for all insecticides tested. Previously, expression of five CYP4 genes was implicated in contributing to insecticide metabolism in D. citri. In the current study, we compared the relative expression of these five CYP4 genes and their associated levels of protein expression among field-collected and laboratory susceptible populations. Expression of all CYP4 genes investigated was higher in field-collected populations when normalized against the laboratory susceptible population. There was an increased signal of a band corresponding to a 45 kDa protein in four of the five field populations as measured by the Western blot assay, which suggests increased production of cytochrome P450 enzymes. The current results indicate that insecticide resistance continues to increase in Florida populations ofD. citri, particularly to chlorpyriphos and fenpropathrin. However, there was no further decrease in susceptibility of Florida populations of D. citri to neonicotinoid insecticides in 2011 as compared with previous years.

Phylogeography of the Christmas Island blue crab,Discoplax celeste(Decapoda: Gecarcinidae) on Christmas Island, Indian Ocean

The land crab,Discoplax celeste(Gecarcinidae) is endemic to Christmas Island in the Indian Ocean. Due to a freshwater-dependant life history, in which the megalopae migrate from the ocean up freshwater streams to their adult terrestrial/freshwater habitat,D. celesteinhabits only a few isolated locations on the island. This restricted distribution is one of a number of factors which has previously highlighted the vulnerability of this species to outside threats. A number of anthropogenic factors including the introduction of multiple invasive species and habitat destruction have led to drastic ecosystem change on Christmas Island. The aim of this study was to investigate whether the restricted geographical distributions ofD. celestepopulations contribute to significant genetic structuring across Christmas Island, with an objective to inform future conservation strategies for this species on Christmas Island. Fragments of the mitochondrial cytochrome oxidase I gene and the control region were sequenced from 95 individuals collected from all five locations on Christmas Island known to be inhabited byD. celeste. Analyses using analysis of molecular variance revealed no evidence of population sub-structuring, indicating that despite any geographical isolation, there is a single population ofD. celesteon Christmas Island. This lack of population differentiation is probably explained by the oceanic dispersal of larvae, rather than terrestrial migration ofD. celeste. Therefore, based on these results, for conservation purposes,D. celesteon Christmas Island can be considered a single management unit.