Avian blood parasites in an endangered columbid: Leucocytozoon marchouxi in the Mauritian Pink Pigeon Columba mayeri

There is increasing evidence that pathogens can play a significant role in species decline. This study of a complete free-living species reveals a cost of blood parasitism to an endangered host, the Pink Pigeon Columba mayeri, endemic to Mauritius. We investigated the prevalence and effect of infection of the blood parasite, Leucocytozoon marchouxi, in the free-living Pink Pigeon population. Overall, L. marchouxi infection prevalence detected was 18·3%. Juveniles were more likely to be infected than older birds and there was geographical variation in infection prevalence. Survival of birds infected with L. marchouxi was lower than that of uninfected birds to 90 days post-sampling. This study suggests that while common haematozoa are well tolerated in healthy adults, these parasites may have greater pathogenic potential in susceptible juveniles. The study is unusual given its completeness of species sampling (96%) within a short time-period, the accurate host age data, and its focus on blood parasites in a threatened bird species. Species for which long-term life-history data are available for every individual serve as valuable models for dissecting the contribution of particular pathogens to species decline

Quantitative differences in lipid raft components between murine CD4(+ )and CD8(+ )T cells

BACKGROUND: Lipid rafts have been shown to play a role in T cell maturation, activation as well as in the formation of immunological synapses in CD4(+ )helper and CD8(+ )cytotoxic T cells. However, the differential expression of lipid raft components between CD4(+ )and CD8(+ )T cells is still poorly defined. To examine this question, we analyzed the expression of GM1 in T cells from young and aged mice as well as the expression of the glycosylphosphatidylinositol (GPI)-linked protein Thy-1 and cholesterol in murine CD4(+ )and CD8(+ )T cell subpopulations. RESULTS: We found that CD4(+)CD8(- )and CD8(+)CD4(- )thymocytes at different stages of maturation display distinct GM1 surface expression. This phenomenon did not change with progressive aging, as these findings were consistent over the lifespan of the mouse. In the periphery, CD8(+ )T cells express significantly higher levels of GM1 than CD4(+ )T cells. In addition, we observed that GM1 levels increase over aging on CD8(+ )T cells but not in CD4(+ )T cells. We also verified that naïve (CD44(lo)) and memory (CD44(hi)) CD8(+ )T cells as well as naïve and memory CD4(+ )T cells express similar levels of GM1 on their surface. Furthermore, we found that CD8(+ )T cells express higher levels of the GPI-anchored cell surface protein Thy-1 associated with lipid raft domains as compared to CD4(+ )T cells. Finally, we observed higher levels of total cellular cholesterol in CD8(+ )T cells than CD4(+ )T cells. CONCLUSION: These results demonstrate heterogeneity of lipid raft components between CD4(+ )and CD8(+ )T cells in young and aged mice. Such differences in lipid raft composition may contribute to the differential CD4 and CD8 molecule signaling pathways as well as possibly to the effector responses mediated by these T cell subsets following TCR activation

Chromosome-level genome assembly for the Aldabra giant tortoise enables insights into the genetic health of a threatened population

The Aldabra giant tortoise (Aldabrachelys gigantea) is one of only two giant tortoise species left in the world. The species is endemic to Aldabra Atoll in Seychelles and is considered vulnerable due to its limited distribution and threats posed by climate change. Genomic resources for A. gigantea are lacking, hampering conservation efforts focused on both wild and ex-situ populations. A high-quality genome would also open avenues to investigate the genetic basis of the exceptionally long lifespan. Here, we produced the first chromosome-level de novo genome assembly of A. gigantea using PacBio High-Fidelity sequencing and high-throughput chromosome conformation capture (Hi-C). We produced a 2.37 Gbp assembly with a scaffold N50 of 148.6 Mbp and a resolution into 26 chromosomes. RNAseq-assisted gene model prediction identified 23,953 protein-coding genes and 1.1 Gbp of repetitive sequences. Synteny analyses among turtle genomes revealed high levels of chromosomal collinearity even among distantly related taxa. We also performed a low-coverage re-sequencing of 30 individuals from wild populations and two zoo individuals. Our genome-wide population structure analyses detected genetic population structure in the wild and identified the most likely origin of the zoo-housed individuals. The high-quality chromosome-level reference genome for A. gigantea is one of the most complete turtle genomes available. It is a powerful tool to assess the population structure in the wild population and reveal the geographic origins of ex-situ individuals relevant for genetic diversity management and rewilding efforts

Emerging Infectious Disease leads to Rapid Population Decline of Common British Birds

Emerging infectious diseases are increasingly cited as threats to wildlife, livestock and humans alike. They can threaten geographically isolated or critically endangered wildlife populations; however, relatively few studies have clearly demonstrated the extent to which emerging diseases can impact populations of common wildlife species. Here, we report the impact of an emerging protozoal disease on British populations of greenfinch Carduelis chloris and chaffinch Fringilla coelebs, two of the most common birds in Britain. Morphological and molecular analyses showed this to be due to Trichomonas gallinae. Trichomonosis emerged as a novel fatal disease of finches in Britain in 2005 and rapidly became epidemic within greenfinch, and to a lesser extent chaffinch, populations in 2006. By 2007, breeding populations of greenfinches and chaffinches in the geographic region of highest disease incidence had decreased by 35% and 21% respectively, representing mortality in excess of half a million birds. In contrast, declines were less pronounced or absent in these species in regions where the disease was found in intermediate or low incidence. Also, populations of dunnock Prunella modularis, which similarly feeds in gardens, but in which T. gallinae was rarely recorded, did not decline. This is the first trichomonosis epidemic reported in the scientific literature to negatively impact populations of free-ranging non-columbiform species, and such levels of mortality and decline due to an emerging infectious disease are unprecedented in British wild bird populations. This disease emergence event demonstrates the potential for a protozoan parasite to jump avian host taxonomic groups with dramatic effect over a short time period

The role of asymmetric interactions on the effect of habitat destruction in mutualistic networks

Plant-pollinator mutualistic networks are asymmetric in their interactions: specialist plants are pollinated by generalist animals, while generalist plants are pollinated by a broad involving specialists and generalists. It has been suggested that this asymmetric ---or disassortative--- assemblage could play an important role in determining the equal susceptibility of specialist and generalist plants under habitat destruction. At the core of the argument lies the observation that specialist plants, otherwise candidates to extinction, could cope with the disruption thanks to their interaction with generalist pollinators. We present a theoretical framework that supports this thesis. We analyze a dynamical model of a system of mutualistic plants and pollinators, subject to the destruction of their habitat. We analyze and compare two families of interaction topologies, ranging from highly assortative to highly disassortative ones, as well as real pollination networks. We found that several features observed in natural systems are predicted by the mathematical model. First, there is a tendency to increase the asymmetry of the network as a result of the extinctions. Second, an entropy measure of the differential susceptibility to extinction of specialist and generalist species show that they tend to balance when the network is disassortative. Finally, the disappearance of links in the network, as a result of extinctions, shows that specialist plants preserve more connections than the corresponding plants in an assortative system, enabling them to resist the disruption.Comment: 14 pages, 7 figure

Global patterns in island colonization during the Holocene

Analysis of the spatial and temporal structure of global island colonization allows us to frame the extent of insular human cultural diversity, model the impact of common environmental factors cross-culturally, and understand the contribution of island maritime societies to big historical processes. No such analysis has, however, been undertaken since the 1980s. In this paper we review and update global patterns in island colonization, synthesizing data from all the major island groups and theaters and undertaking quantitative and qualitative analysis of these data. We demonstrate the continued relevance of certain biogeographic and environmental factors in structuring how humans colonized islands during the Holocene. Our analysis also suggests the importance of other factors, some previously anticipated—such as culturally ingrained seafaring traditions and technological enhancement of dispersal capacity—but some not, such as the relationship between demographic growth and connectivity, differing trophic limitations impinging on colonizing farmers versus hunter-gatherer-foragers, and the constraining effects of latitude. We also connect colonization with continental dynamics: both the horizontal transmission of farming lifestyles earlier in the Holocene, and subsequent centrifugal processes associated with early state formation later in the Holocene.Bioarchaeolog

Seed dispersal by frugivores from forest remnants promotes the regeneration of adjacent invaded forests in an oceanic island

This is the final version. Available on open access from Wiley via the DOI in this recordForest remnants often act as refuges for native plant species within a degraded and highly fragmented forest matrix. Understanding whether these native patches can function as feeding grounds for frugivores and seed sources for native plant dispersal into the surrounding forest can provide critical information on ecosystem functions on a landscape scale and guidance on forest restoration. We used a large-scale natural system of eight granitic inselbergs in the Seychelles and recorded the identity and transport direction of seeds retrieved from the droppings of mist-netted birds across an invasion gradient. We found that inselberg forest remnants are important feeding areas for frugivores, acting as a source of native propagules to the surrounding invaded forests and potentially limiting the progression of non-native plant invasion. Two dominant non-native plant species (Cinnamomum verum and Clidemia hirta) were highly integrated into the frugivores' diets, competing with native plants for dispersal services. Despite the high non-native propagule pressure, the spill-over effect of native seeds into the invaded forest seemed to have a more durable positive effect on native plant recruitment fading out with distance to the inselberg edge. Our findings illustrate that remnant forest patches can generate positive spill-over of native seeds into degraded surrounding forests through directed seed transport by frugivores. This cross-boundary transport may slow down plant invasion and contribute to the recovery of adjacent degraded ecosystems. Forest remnants and avian frugivores therefore play a key role in the maintenance of native biodiversity and act as insurance for future restoration efforts.German Research Foundation (DFG)Portuguese Foundation for Science and Technolog

Chytrid Fungus (Batrachochytrium dendrobatidis) Undetected in the Two Orders of Seychelles Amphibians

Reports the first disease screening for chytrid Fungus (Batrachochytrium dendrobatidis) in amphibians across the Seychelles Archipelag

Low‐coverage reduced representation sequencing reveals subtle within‐island genetic structure in Aldabra giant tortoises

This is the final version. Available on open access from Wiley via the DOI in this recordData availability statement: The sequencing data that support the findings of this study are available at the NCBI Sequence Read Archive with the accession numbers SRX10954672–SRX10954704.Aldabrachelys gigantea (Aldabra giant tortoise) is one of only two giant tortoise species left in the world and survives as a single wild population of over 100,000 individuals on Aldabra Atoll, Seychelles. Despite this large current population size, the species faces an uncertain future because of its extremely restricted distribution range and high vulnerability to the projected consequences of climate change. Captive-bred A. gigantea are increasingly used in rewilding programs across the region, where they are introduced to replace extinct giant tortoises in an attempt to functionally resurrect degraded island ecosystems. However, there has been little consideration of the current levels of genetic variation and differentiation within and among the islands on Aldabra. As previous microsatellite studies were inconclusive, we combined low-coverage and double-digest restriction-associated DNA (ddRAD) sequencing to analyze samples from 33 tortoises (11 from each main island). Using 5426 variant sites within the tortoise genome, we detected patterns of within-island population structure, but no differentiation between the islands. These unexpected results highlight the importance of using genome-wide genetic markers to capture higher-resolution genetic structure to inform future management plans, even in a seemingly panmictic population. We show that low-coverage ddRAD sequencing provides an affordable alternative approach to conservation genomic projects of non-model species with large genomes.Swiss Government Excellence Scholarship for PostdocsUniversity of ZürichSwiss National Science FoundationGeorges and Antoine Claraz Foundatio