Rapid Evolution of Assortative Fertilization between Recently Allopatric Species of Drosophila

The virilis group of Drosophila represents a relatively unexplored but potentially useful model to investigate the genetics of speciation. Good resolution of phylogenetic relationships and the ability to obtain fertile hybrid offspring make the group especially promising for analysis of genetic changes underlying reproductive isolation separate from hybrid sterility and inviability. Phylogenetic analyses reveal a close relationship between the sister species, Drosophila americana and D. novamexicana, yet excepting their contemporary allopatric distributions, factors that contribute to reproductive isolation between this species pair remain uncharacterized. A previous report has shown reduced progeny numbers in laboratory crosses between the two species, especially when female D. novamexicana are crossed with male D. americana. We show that the hatch rate of eggs produced from heterospecific matings is reduced relative to conspecific matings. Failure of eggs to hatch, and consequent reduction in hybrid progeny number, is caused by low fertilization success of heterospecific sperm, thus representing a postmating, prezygotic incompatibility. Following insemination, storage and motility of heterospecific sperm is visibly compromised in female D. novamexicana. Our results provide evidence for a mechanism of reproductive isolation that is seldom reported for Drosophila species, and indicate the rapid evolution of postmating, prezygotic reproductive barriers in allopatry

Inference of chromosomal inversion dynamics from Pool-Seq data in natural and laboratory populations of Drosophila melanogaster

Sequencing of pools of individuals (Pool-Seq) represents a reliable and cost- effective approach for estimating genome-wide SNP and transposable element insertion frequencies. However, Pool-Seq does not provide direct information on haplotypes so that for example obtaining inversion frequencies has not been possible until now. Here, we have developed a new set of diagnostic marker SNPs for 7 cosmopolitan inversions in Drosophila melanogaster that can be used to infer inversion frequencies from Pool-Seq data. We applied our novel marker set to Pool-Seq data from an experimental evolution study and from North American and Australian latitudinal clines. In the experimental evolution data, we find evidence that positive selection has driven the frequencies of In(3R)C and In(3R)Mo to increase over time. In the clinal data, we confirm the existence of frequency clines for In(2L)t, In(3L)P and In(3R)Payne in both North America and Australia and detect a previously unknown latitudinal cline for In(3R)Mo in North America. The inversion markers developed here provide a versatile and robust tool for characterizing inversion frequencies and their dynamics in Pool- Seq data from diverse D. melanogaster populations.Comment: 31 pages, 4 main figures, 1 main table, 7 supporting figures, 11 supporting table

Widespread Discordance of Gene Trees with Species Tree in Drosophila: Evidence for Incomplete Lineage Sorting

The phylogenetic relationship of the now fully sequenced species Drosophila erecta and D. yakuba with respect to the D. melanogaster species complex has been a subject of controversy. All three possible groupings of the species have been reported in the past, though recent multi-gene studies suggest that D. erecta and D. yakuba are sister species. Using the whole genomes of each of these species as well as the four other fully sequenced species in the subgenus Sophophora, we set out to investigate the placement of D. erecta and D. yakuba in the D. melanogaster species group and to understand the cause of the past incongruence. Though we find that the phylogeny grouping D. erecta and D. yakuba together is the best supported, we also find widespread incongruence in nucleotide and amino acid substitutions, insertions and deletions, and gene trees. The time inferred to span the two key speciation events is short enough that under the coalescent model, the incongruence could be the result of incomplete lineage sorting. Consistent with the lineage-sorting hypothesis, substitutions supporting the same tree were spatially clustered. Support for the different trees was found to be linked to recombination such that adjacent genes support the same tree most often in regions of low recombination and substitutions supporting the same tree are most enriched roughly on the same scale as linkage disequilibrium, also consistent with lineage sorting. The incongruence was found to be statistically significant and robust to model and species choice. No systematic biases were found. We conclude that phylogenetic incongruence in the D. melanogaster species complex is the result, at least in part, of incomplete lineage sorting. Incomplete lineage sorting will likely cause phylogenetic incongruence in many comparative genomics datasets. Methods to infer the correct species tree, the history of every base in the genome, and comparative methods that control for and/or utilize this information will be valuable advancements for the field of comparative genomics

Inference of chromosomal inversion dynamics from Pool-Seq data in natural and laboratory populations of Drosophila melanogaster

Sequencing of pools of individuals (Pool‐Seq) represents a reliable and cost‐effective approach for estimating genome‐wide SNP and transposable element insertion frequencies. However, Pool‐Seq does not provide direct information on haplotypes so that, for example, obtaining inversion frequencies has not been possible until now. Here, we have developed a new set of diagnostic marker SNPs for seven cosmopolitan inversions in Drosophila melanogaster that can be used to infer inversion frequencies from Pool‐Seq data. We applied our novel marker set to Pool‐ Seq data from an experimental evolution study and from North American and Australian latitudinal clines. In the experimental evolution data, we find evidence that positive selection has driven the frequencies of In(3R)C and In(3R)Mo to increase over time. In the clinal data, we confirm the existence of frequency clines for In(2L)t, In(3L)P and In(3R)Payne in both North America and Australia and detect a previously unknown latitudinal cline for In(3R)Mo in North America. The inversion markers developed here provide a versatile and robust tool for characterizing inversion frequencies and their dynamics in Pool‐Seq data from diverse D. melanogaster populations

Reefs at Risk: A Map-Based Indicator of Threats to the Worlds Coral Reefs

This report presents the first-ever detailed, map-based assessment of potential threats to coral reef ecosystems around the world. "Reefs at Risk" draws on 14 data sets (including maps of land cover, ports, settle-ments, and shipping lanes), information on 800 sites known to be degraded by people, and scientific expertise to model areas where reef degradation is predicted to occur, given existing human pressures on these areas. Results are an indicator of potential threat (risk), not a measure of actual condition. In some places, particularly where good management is practiced, reefs may be at risk but remain relatively healthy. In others, this indicator underestimates the degree to which reefs are threatened and degraded.Our results indicate that:Fifty-eight percent of the world's reefs are poten-tially threatened by human activity -- ranging from coastal development and destructive fishing practices to overexploitation of resources, marine pollution, and runoff from inland deforestation and farming.Coral reefs of Asia (Southeastern); the most species-rich on earth, are the most threatened of any region. More than 80 percent are at risk (undermedium and high potential threat), and over half are at high risk, primarily from coastal development and fishing-related pressures.Overexploitation and coastal development pose the greatest potential threat of the four risk categories considered in this study. Each, individually, affects a third of all reefs.The Pacific, which houses more reef area than any other region, is also the least threatened. About 60 percent of reefs here are at low risk.Outside of the Pacific, 70 percent of all reefs are at risk.At least 11 percent of the world's coral reefs contain high levels of reef fish biodiversity and are under high threat from human activities. These "hot spot" areas include almost all Philippine reefs, and coral communities off the coasts of Asia, the Comoros, and the Lesser Antilles in the Caribbean.Almost half a billion people -- 8 percent of the total global population -- live within 100 kilometers of a coral reef.Globally, more than 400 marine parks, sanctuaries, and reserves (marine protected areas) contain coral reefs. Most of these sites are very small -- more than 150 are under one square kilometer in size. At least 40 countries lack any marine protected areas for conserving their coral reef systems

Towards informed and multi-faceted wildlife trade interventions

International trade in wildlife is a key threat to biodiversity conservation. CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora, is the primary mechanism for controlling international wildlife trade and seeks to ensure it is sustainable, relying on trade bans and controls. However, there has been little comprehensive review of the effectiveness of CITES. Here, we review typical and atypical approaches taken to regulate wildlife trade in CITES and assert that it boasts few successes. We attribute this to: non-compliance, an over reliance on regulation, lack of knowledge of listed species, ignorance of the reality of market forces, and influence among CITES actors. To more effectively manage trade we argue that interventions need to go beyond regulation and should be multi-faceted, reflecting the complexity of wildlife trade. To inform such interventions we assert an intensive research effort is needed and we outline six key research areas: (1) factors undermining wildlife trade governance at the national level, (2) determining sustainable harvest rates for CITES species, (3) gaining the buy-in of local communities in implementing CITES, (4) supply and demand based market interventions, (5) means of quantifying illicit trade, and (6) political processes and influence within CITES

Increased Nucleotide Diversity with Transient Y Linkage in Drosophila americana

Recombination shapes nucleotide variation within genomes. Patterns are thought to arise from the local recombination landscape, influencing the degree to which neutral variation experiences hitchhiking with selected variation. This study examines DNA polymorphism along Chromosome 4 (element B) of Drosophila americana to identify effects of hitchhiking arising as a consequence of Y-linked transmission. A centromeric fusion between the X and 4(th) chromosomes segregates in natural populations of D. americana. Frequency of the X-4 fusion exhibits a strong positive correlation with latitude, which has explicit consequences for unfused 4(th) chromosomes. Unfused Chromosome 4 exists as a non-recombining Y chromosome or as an autosome proportional to the frequency of the X-4 fusion. Furthermore, Y linkage along the unfused 4 is disrupted as a function of the rate of recombination with the centromere. Inter-population and intra-chromosomal patterns of nucleotide diversity were assayed using six regions distributed along unfused 4(th) chromosomes derived from populations with different frequencies of the X-4 fusion. No difference in overall level of nucleotide diversity was detected among populations, yet variation along the chromosome exhibits a distinct pattern in relation to the X-4 fusion. Sequence diversity is inflated at loci experiencing the strongest Y linkage. These findings are inconsistent with the expected reduction in nucleotide diversity resulting from hitchhiking due to background selection or selective sweeps. In contrast, excessive polymorphism is accruing in association with transient Y linkage, and furthermore, hitchhiking with sexually antagonistic alleles is potentially responsible

Exploring the nature of resilience in paramedic practice: A psycho-social study

Previous research has identified that paramedics experience high levels of stress and sickness rates which have escalated in recent years due to changes to workforce restructuring. While a number of studies have investigated resilience among healthcare professionals, there is little research exploring how paramedics address work challenges and how they become resilient. Using psychosocial methodology, seven paramedics participated in Free Association Narrative interviewing; all were based at one regional centre. In line with the study design, data analysis adopted a psycho-social approach that generated four themes and 10 sub-themes which, characterised participants’ experiences. Coping and resilience was impacted upon via formal methods of support including management, debriefing and referral to outside agencies. Alongside this, more informal methods aided resilience. Informal methods included peer support, support from family and friends and the use of humour. Uniquely, this study uncovered how detachment is used to manage emotions. The study has implications for the services need to support the emotional needs of paramedics