Amanda Lane

Host Adaptation of a Wolbachia Strain after Long-Term Serial Passage in Mosquito Cell Lines

ABSTRACT The horizontal transfer of the bacterium Wolbachia pipientis between invertebrate hosts hinges on the ability of Wolbachia to adapt to new intracellular environments. The experimental transfer of Wolbachia between distantly related host species often results in the loss of infection, presumably due to an inability of Wolbachia to adapt quickly to the new host. To examine the process of adaptation to a novel host, we transferred a life-shortening Wolbachia strain, wMelPop, from the fruit fly Drosophila melanogaster into a cell line derived from the mosquito Aedes albopictus. After long-term serial passage in this cell line, we transferred the mosquito-adapted wMelPop into cell lines derived from two other mosquito species, Aedes aegypti and Anopheles gambiae. After a prolonged period of serial passage in mosquito cell lines, wMelPop was reintroduced into its native host, D. melanogaster, by embryonic microinjection. The cell line-adapted wMelPop strains were characterized by a loss of infectivity when reintroduced into the original host, grew to decreased densities, and had reduced abilities to cause life-shortening infection and cytoplasmic incompatibility compared to the original strain. We interpret these shifts in phenotype as evidence for genetic adaptation to the mosquito intracellular environment. The use of cell lines to preadapt Wolbachia to novel hosts is suggested as a possible strategy to improve the success of transinfection in novel target insect species.

Genomic evolution of the pathogenic Wolbachia strain, wMelPop

Most strains of the widespread endosymbiotic bacterium Wolbachia pipientis are benign or behave as reproductive parasites. The pathogenic strain wMelPop is a striking exception, however: it overreplicates in its insect hosts and causes severe life shortening. The mechanism of this pathogenesis is currently unknown. We have sequenced the genomes of three variants of wMelPop and of the closely related nonpathogenic strain wMelCS. We show that the genomes of wMelCS and wMelPop appear to be identical in the nonrepeat regions of the genome and differ detectably only by the triplication of a 19-kb region that is unlikely to be associated with life shortening, demonstrating that dramatic differences in the host phenotype caused by this endosymbiont may be the result of only minor genetic changes. We also compare the genomes of the original wMelPop strain from Drosophila melanogaster and two sequential derivatives, wMelPop-CLA and wMelPop-PGYP. To develop wMelPop as a novel biocontrol agent, it was first transinfected into and passaged in mosquito cell lines for approximately 3.5 years, generating wMelPop-CLA. This cell line-passaged strain was then transinfected into Aedes aegypti mosquitoes, creating wMelPop-PGYP, which was sequenced after 4 years in the insect host. We observe a rapid burst of genomic changes during cell line passaging, but no further mutations were detected after transinfection into mosquitoes, indicating either that host preadaptation had occurred in cell lines, that cell lines are a more selectively permissive environment than animal hosts, or both. Our results provide valuable data on the rates of genomic and phenotypic change in Wolbachia associated with host shifts over short time scales.

Effects of Land Use on Threatened Species

There is widespread agreement that biodiversity loss must be reduced, yet to alleviate threats to plant and animal species, the forces driving these losses need to be better understood. We searched for explanatory variables for threatened-species data at the country level through land-use information instead of previously used socioeconomic and demographic variables. To explain the number of threatened species in one country, we used information on land-use patterns in all neighboring countries and on the extent of the countrys sea border. We carried out multiple regressions of the numbers of threatened species as a function of land-use patterns, and we tested various specifications of this function, including spatial autocorrelation. Most cross-border land-use patterns had a significant influence on the number of threatened species, and land-use patterns explained the number of threatened species better than less proximate socioeconomic variables. More specifically, our overall results showed a highly adverse influence of plantations and permanent cropland, a weaker negative influence of permanent pasture, and, for the most part, a beneficial influence of nonarable lands and natural forest. Surprisingly, built-up land also showed a conserving influence on threatened species. The adverse influences extended to distances between about 250 km (plants) and 2000 km (birds and mammals) away from where the species threat was recorded, depending on the species. Our results highlight that legislation affecting biodiversity should look beyond national boundaries.

New insights into the role of MHC diversity in devil facial tumour disease.

Background Devil facial tumour disease (DFTD) is a fatal contagious cancer that has decimated Tasmanian devil populations. The tumour has spread without invoking immune responses, possibly due to low levels of Major Histocompatibility Complex (MHC) diversity in Tasmanian devils. Animals from a region in north-western Tasmania have lower infection rates than those in the east of the state. This area is a genetic transition zone between sub-populations, with individuals from north-western Tasmania displaying greater diversity than eastern devils at MHC genes, primarily through MHC class I gene copy number variation. Here we test the hypothesis that animals that remain healthy and tumour free show predictable differences at MHC loci compared to animals that develop the disease. Methodology/Principal Findings We compared MHC class I sequences in 29 healthy and 22 diseased Tasmanian devils from West Pencil Pine, a population in north-western Tasmania exhibiting reduced disease impacts of DFTD. Amplified alleles were assigned to four loci, Saha-UA, Saha-UB, Saha-UC and Saha-UD based on recently obtained genomic sequence data. Copy number variation (caused by a deletion) at Saha-UA was confirmed using a PCR assay. No association between the frequency of this deletion and disease status was identified. All individuals had alleles at Saha-UD, disproving theories of disease susceptibility relating to copy number variation at this locus. Genetic variation between the two sub-groups (healthy and diseased) was also compared using eight MHC-linked microsatellite markers. No significant differences were identified in allele frequency, however differences were noted in the genotype frequencies of two microsatellites located near non-antigen presenting genes within the MHC. Conclusions/Significance We did not find predictable differences in MHC class I copy number variation to account for differences in susceptibility to DFTD. Genotypic data was equivocal but indentified genomic areas for further study.

Intraspecific variation in the direction and degree of sex-biased dispersal among sea-snake populations.

Higher rates of dispersal in one sex than the other are widespread, and often attributed to the genetic advantages of reduced inbreeding. The direction of sex‐biased dispersal shows strong phylogenetic conservatism (e.g. males disperse more than females in most mammals, but the reverse is true in most birds). By contrast, our genetic data reveal strong inter‐population variation in the relative dispersal rates of two species of sea snakes (Laticauda saintgironsi and L. laticaudata) in the Noumea Lagoon of New Caledonia. Assignment methods using microsatellite data identified parallel variation in sex‐specific dispersal in both species: dispersal was female‐biased in the north‐west of the sampling area (in islands far from the main island), but male‐biased in the south‐east (in islands closer to the main island). This flexibility may reflect sex differences in diets, with spatial variation in sex‐specific resources generating spatial variation in sex‐specific dispersal distances.

Flexible mate choice: A male snake's preference for larger females is modified by the sizes of females encountered

Why do males exert strong mate choice in some taxa but not others? Theory suggests that mate discrimination will enhance male fitness when encounter rates with potential mates are high, when those potential mates vary in the fitness consequences likely to accrue from an attempted insemination, and when courting one female reduces the male’s opportunity to court other females. One widespread form of mate choice involves a trend for males of many ectothermic species to court larger (and thus, more fecund) females. To test whether such preferences are dynamically adjusted to local conditions, we studied male preference for larger females in red-sided garter snakes, Thamnophis sirtalis parietalis, near a communal den in Manitoba, Canada. Courting a small female imposes a high opportunity cost for a male in the centre of the den, because many large and easily located females are nearby. In the surrounding woodland, in contrast, a male that neglects a small female is unlikely to encounter a larger substitute partner. In arena trials, male snakes from the den selected larger females more than did males from the surrounding woodland. Manipulating a den male’s exposure to females (none, large, small) for 60 min led males to adjust their criteria for courtship depending upon the sizes of females encountered. Hence, the local environment can modify courtship criteria, with male garter snakes adjusting their mate choice selectivity based upon spatial and temporal factors that affect the opportunity costs of courtship.

Trends in socioeconomic inequalities in mortality from ischaemic heart disease and stroke in Australia, 1979–2006

Background: This study investigates secular trends in ischaemic heart disease (IHD) and stroke mortality by socioeconomic status (SES) in Australia to determine if absolute and relative differences between low and high SES areas have changed over time. Methods: IHD and stroke mortality data for adults aged 35–74 years and corresponding population data from Australian censuses for 1979–2006 were stratified into quintiles using an area-based measure of SES and analysed by quinquennia (and 2004–06). IHD and stroke (rates per 100,000) adjusted for age, country of birth, and rurality were compared across SES strata (separately by sex) using Poisson regression. Results: Mortality declined monotonically over the study period in all SES groups and both sexes. Absolute differences between low and high SES groups narrowed for IHD in females (27 to 23 per 100,000) and stroke in males and females (16 to 13, and 13 to 7 per 100,000, respectively), although absolute differences widened for IHD in males (52 to 63 per 100,000). Relative declines were greater in high compared to low SES groups for IHD (28% average quinquennial decline in high SES; compared with 21% in low SES for males; 30% and 21% for females), and for stroke (25% average quinquennial decline in high SES; 21% in low SES for males; 26% and 23% for females). Conclusion: Differences in mortality rates between lower and higher SES groups narrowed for both IHD (in females) and stroke (in males and females) from 1979–2006, indicating that the epidemic decline is now at a late stage when low SES groups are benefiting more, in absolute terms, than high SES groups. However males in the lower SES groups are still at an earlier stage of the epidemic decline in IHD mortality.

Evidence of a Spotted Fever-Like Rickettsia and a Potential New Vector from Northeastern Australia

Abstract A spotted fever-like rickettsia was identified in a Hemaphysalis tick by polymerase chain reaction (PCR) amplification and sequencing of the 16S rDNA, ompA, and ompB genes. A comparison of these nucleotide sequences with those of other spotted fever group (SFG) rickettsiae revealed that the Hemaphysalis tick rickettsia was distinct from other previously reported strains. Phylogenetic analysis based on both ompA and ompB also indicates that the strain’s closest relatives are the agents of Thai tick typhus (Rickettsia honei strain TT-118) and Flinders Island spotted fever (R. honei). This study represents the first report of an R. honei-like agent from a Hemaphysalis tick in Australia and of a spotted fever group rickettsia from Cape York Peninsula, Queensland.

Microsatellite loci for laticaudine sea kraits

We report the development of 11 polymorphic microsatellite loci (three dinucleotides, one trinucleotide and seven tetranucleotides) that are useful for the detection of population subdivision and the study of philopatry, migration and mating biology in laticaudine sea kraits Laticauda saintgironsi and Laticauda laticaudata. Five loci are highly polymorphic and amplify reliably in both L. saintgironsi and L. laticaudata. An additional three are useful in L. saintgironsi and another three in L. laticaudata.

Sex-biased dispersal of a frog (Odorrana schmackeri) is affected by patch isolation and resource limitation in a fragmented landscape.

Sex-biased dispersal is widespread in the animal kingdom and is affected by numerous factors including mating system, social factors and environmental conditions. Unlike birds and mammals, there is no common trend in amphibians and explaining the direction and degree of sex-biased dispersal in species-specific cases is difficult. We conducted a study on dispersal of the Chinese piebald odorous frog (Odorrana schmackeri) in a fragmented landscape associated with dam construction. Ten microsatellite loci were used to analyze 382 samples sourced from 14 fragmented ‘islands’. Assignment tests indicated a significant pattern of female-biased dispersal on one island with inconsistencies in the strength and direction of this pattern between nearby islands. The effects of four island attributes and two potential impact factors on the pattern of sex-biased dispersal were examined. We found that the extent of isolation from the mainland and the number of breeding sites both showed a negative correlation with female biased dispersal, such that the closer an island is to the mainland the more likely it is to display female biased dispersal, and the more breeding sites on an island the more male immigrants. Based on these results, we conclude that geographic isolation and limited breeding resources are the most likely explanation for the patterns of dispersal observed in this fragmented population of amphibians.