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Parasite turnover zone at secondary contact: a new pattern in host-parasite population genetics

We introduce a new pattern of population genetic structure in a host-parasite system that can arise after secondary contact of previously isolated populations. Due to different generation time and therefore different tempo of molecular evolution the host and parasite populations reach different degrees of genetic differentiation during their separation (e.g. in refugia). Consequently, during the secondary contact the host populations are able to re-establish a single panmictic population across the area of contact, while the parasite populations stop their dispersal at the secondary contact zone and create a narrow hybrid zone. From the host's perspective, the parasite's hybrid zone functions on a microevolutionary scale as a "parasite turnover zone": while the hosts are passing from area A to area B, their parasites turn genetically from the area A genotypes to the area B genotypes. We demonstrate this novel pattern on a model composed of Apodemus mice and Polyplax lice by comparing maternally inherited markers (complete mitochondrial genomes, and complete genomes of vertically transmitted symbiont Legionella polyplacis) with SNPs derived from the louse genomic data. We discuss circumstances that may lead to this pattern and possible reasons why it has been overlooked in the studies on host parasite population genetics.

Data from: The many faced symbiotic snakelocks anemone (Anemonia viridis, Anthozoa): host and symbiont genetic differentiation among colour morphs

How can we explain morphological variations in a holobiont? The genetic determinism of phenotypes is not always obvious and could be circumstantial in complex organisms. In symbiotic cnidarians, it is known that morphology or colour can misrepresent a complex genetic and symbiotic diversity. Anemonia viridis is a symbiotic sea anemone from temperate seas. This species displays different colour morphs based on pigment content and lives in a wide geographical range. Here, we investigated whether colour morph differentiation correlated with host genetic diversity or associated symbiotic genetic diversity by using RAD-sequencing and symbiotic dinoflagellate typing of 140 sea anemones from the English Channel and the Mediterranean Sea. We did not observe genetic differentiation among colour morphs of A. viridis at the animal host or symbiont level, rejecting the hypothesis that A. viridis colour morphs correspond to species level differences. Interestingly, we however identified at least four independent animal host genetic lineages in A. viridis that differed in their associated symbiont populations. In conclusion, although the functional role of the different morphotypes of A. viridis remains to be determined, our approach provides new insights on the existence of cryptic species within A. viridis.

Data from: Fecundity compensation is dependent on the generalised stress response in a nematode host

Background: Fecundity compensation, increased offspring output following parasite exposure, is widely reported, but the underlying mechanisms remain unclear. General stress responses are linked to other indirect defences against parasites, and therefore may be responsible. We challenged strains of Caenorhabditis elegans (wild-type and mutants with compromised or strengthened stress responses) with Staphylococcus aureus. Results: In all strains except the compromised stress response mutant, we saw elevated offspring production if hosts survived initial parasite exposure. Conclusion: We infer that general stress responses are linked with fecundity compensation. These results may explain why trade-offs are not observed among parasite defence mechanisms.

Development and field evaluation of a motion sensor activated suction trap to study vector-host interactions

1. Researchers elucidating vectors of zoonotic diseases encounter problems with inefficient surveillance techniques leading to underestimation of the importance of some species, and the overestimation of the importance of others. Carbon dioxide-baited light traps are the most widely used traps for sampling vector groups. However aspirating directly from the hosts is the most accurate method to incriminate vectors. 2. A novel vector trapping system was developed, consisting of a suction trap, activated by a motion sensor, and controlled by a microcontroller, which activates automatically when host animals approach. The prototype was tested in two field experiments with ungulates and biting midges (Diptera: Ceratopogonidae) at a preserve in Florida. We measured the biting midge community collected at traps near and far from hosts and compared communities using diversity metrics and abundance curves. 3. Traps activated in the presence of host animals with 94% accuracy. Diversity and richness of Culicoides species differed between sensor and control traps with 11 species captured by control traps and 7 species by sensor traps. Vector species were captured in significantly greater numbers in sensor traps, while more non-vector species were caught in control traps. 4. Results confirm that vector species can be underrepresented in light trap collections, likely due to their tight associations with vertebrate hosts, a finding that should be taken into consideration when incriminating arbovirus vectors. Our novel trap system was a first attempt at solving the issue of collecting vector species from non-tame animals, effectively aspirating questing midges. Simple modifications of the system could be made to target other vector-host systems.

Community composition of arctic root-associated fungi mirrors host plant phylogeny

The number of plant species regarded as non-mycorrhizal increases at higher latitudes, and several plant species in the High-Arctic Archipelago Svalbard have been reported as non-mycorrhizal. We used the rRNA ITS2 and 18S gene markers to survey which fungi, as well as other micro-eukaryotes, were associated with roots of 31 arctic plant species not usually regarded as mycorrhizal in Svalbard. We assessed to what degree the root-associated fungi showed any host preference and whether the phylogeny of the plant hosts may mirror the composition of root-associated fungi. Fungal communities were largely structured according to host plant identity and to a less extent by environmental factors. We observed a positive relationship between the phylogenetic distance of host plants and the distance of fungal community composition between samples, indicating that the evolutionary history of the host plants plays a major role for which fungi colonize the plant roots. In contrast to the ITS2 marker, the 18S rRNA gene marker showed that chytrid fungi were prevalently associated with plant roots, together with a wide spectrum of amoeba-like protists and nematodes. Our study confirms that arbuscular mycorrhizal (AM) fungi are present also in arctic environments in low abundance.

opencc-zeroOct 2020View details →

Data from: Parasite infection leads to widespread glucocorticoid hormone increases in vertebrate hosts: a meta-analysis

1. Parasites and pathogens (hereafter parasites) commonly challenge organisms, but the extent to which their infections are physiologically stressful to hosts remains unclear. Importantly, vertebrate hormones, glucocorticoids (GCs), have been reported to increase, decrease, or show no alterations stemming from infections, challenging the generality of parasite-associated GC responses and motivating a search for important moderator variables. 2. We undertook the first meta-analysis of changes in vertebrate GCs following experimental infection with parasites, extracting 146 effect sizes from 42 studies involving 32 host and 32 parasite species to test for general patterns of GC following infection, as well as the influence of moderators. 3. Overall, infection increased GCs relative to preliminary or control levels when the single largest effect sizes from repeated measures studies were examined, suggesting that parasites of vertebrate hosts can be thought of generally as physiological stressors by elevating GCs. 4. When all effect sizes were included along with the moderator of sampling time post-infection (tPI), parasite infection still had a positive effect on host GCs. However, the strength of that effect did not relate consistently to tPI, illustrating temporal differences in GC changes during the course of infection among parasite taxa (e.g., arthropod versus bacterial infections). Other moderator variables examined did not influence GC responses. 5. Studies broadening the range of host and parasite taxa, and sampling during critical time windows, would aid in our understanding of variation in the host stress response and its consequences for fitness of both vertebrate hosts and their parasites. 25-Sep-2019

opencc-zeroOct 2020View details →

Contrasting effects of host tree isolation on population connectedness in two tropical epiphytic bromeliads

Premise of the study Conversion of primary forests to pastures is a major cause of habitat fragmentation in the tropics. Fragmentation is expected to impede gene flow for many plant species that are restricted to remaining forest fragments. Epiphytes may be especially vulnerable to this effect of forest fragmentation because they depend on host trees. However, trees that remain in pastures may enhance connectivity across the landscape for epiphyte species that can thrive on such trees. To investigate this possibility, we studied the genetic structures of two such species on isolated pasture trees and surrounding forest, in relation to their local abundances in different habitat types and aspects of their reproductive biology including pollen and seed dispersal agents, and looked for evidence of increased or diminished gene flow. Methods We used microsatellite markers to assess geographic patterns of genetic diversity and differentiation in two epiphytic bromeliads, Catopsis nitida and Werauhia tonduziana, in the Monteverde region of Costa Rica. Key results About 85% of the FST value for Catopsis nitida was found among pastures within regions, while for Weruahia tonduziana, about 80% of the FST value was contributed by differences between regions, indicating much more gene flow within regions, relative to C. nitida. Conclusions Although there was substantial genetic differentiation among epiphyte populations, those on isolated pasture trees were not substantially less diverse than those in adjacent forests, suggesting that pasture trees may serve as "stepping stones" that help these species maintain their genetic connectedness and diversity at larger geographic scales.

opencc-zeroOct 2020View details →

Data from: Vaginal host immune-microbiome interactions in a cohort of primarily African-American women who ultimately underwent spontaneous preterm birth or delivered at term

Background: Recent studies suggest that alterations in the vaginal microbiome allow for the assessment of the risk for spontaneous preterm birth (PTB), the leading cause of neonatal morbidity and mortality worldwide. However, the associations between the local immune response and the vaginal microbiome are still poorly understood. Herein, we characterize the vaginal host immune-microbiome interactions in women who ultimately underwent PTB and in those who delivered at term. Methods: Vaginal fluid samples from 52 pregnant women (of whom 18 underwent PTB and 34 delivered at term) were collected from 10-32 weeks in a case-control study. Concentrations of 33 immune mediators were determined using sensitive and specific immunoassays. The previously published 16S rRNA gene sequence and bacterial phylotype data of these subjects were utilized in this study. Linear mixed effects models were utilized to test associations between vaginal immune mediator concentrations and bacterial phylotype relative abundances. Results: 1) Specific immune mediators (β-defensins 2 and 3, IL-1β, CXCL10, CCL2, CCL3, SLPI, and VEGF) correlated with 18 different vaginal bacterial phylotypes in the overall study population; 2) vaginal concentrations of CXCL10, CCL2, CCL3, SLP1 and VEGF negatively correlated with non-Lactobacillus members of the vaginal microbiome; 3) vaginal concentrations of CXCL10 were negatively correlated with 15 bacterial phylotypes, most of which are typical members of Community State Type IV of the vaginal microbiome, such as Gardnerella vaginalis, Megasphaera sp. type 1, and Atopobium vaginae; 4) Gemella spp. were negatively correlated with vaginal concentrations of VEGF, CCL2, CCL3, SLPI, and CXCL10; 5) when comparing PTB cases to term controls, five soluble immune mediators (CCL26, CCL22 and CCL2, CXCL10 and IL-16), and especially CCL26, were negatively correlated with five typical members of Community State Type IV: Sneathia sanguinegens, Parvimonas micra, Veillonellaceae, BVAB2, and Gemella spp; and 6) Sneathia sanguinegens had stronger negative associations with all five soluble immune mediators (CCL26, CCL22 and CCL2, CXCL10 and IL-16) in PTB cases than in term controls. Conclusions: The assessment of vaginal host immune-microbiome interactions revealed that specific soluble immune mediators, mainly CXCL10, negatively correlated with typical members of Community State Type IV of the vaginal microbiome. In addition, this assessment particularly showed that Sneathia sanguinegens had stronger negative associations with different immune mediators, including CXCL10 and CCL26, in women who ultimately had a PTB compared to those who delivered at term. These findings provide insight into the vaginal host immune-microbiome interactions in normal and complicated pregnancies.

opencc-zeroDec 2019View details →

Data from: Comparative phylogeography of three host sea anemones in the Indo-Pacific

Aim The mutualistic relationship between anemones and anemonefishes is one of the most iconic examples of symbiosis. However, while anemonefishes have been extensively studied in terms of genetic connectivity, such information is lacking entirely for host sea anemones. Here, we provide the first information on the broad-scale population structure and phylogeographic patterns of three species of host sea anemone, Heteractis magnifica, Stichodactyla mertensii, and Entacmaea quadricolor. We evaluate if there is concordance in genetic structure across several distinct biogeographic areas within the Indo-Pacific region and to what extent the observed patterns may concur with those found for anemonefishes. Location Indo-Pacific, including the Red Sea. Taxon Heteractis magnifica, Stichodactyla mertensii, and Entacmaea quadricolor Methods Microsatellite markers and a combination of statistical methods includingBayesian clustering, Isolation by Distance (IBD), Analysis of Molecular Variance (AMOVA), and Principal Components Analysis (PCA) were used to determine population structure. The congruence among distance matrices method (CADM) was used to assess similarity in spatial genetic patterns among species. Results Significant population structure was identified in the three host anemone species. Each species is likely composed of at least two genetic clusters corresponding to two biogeographic regions, the Red Sea and the rest of the Indo-Pacific. Two of the three anemone species seem to be experiencing admixture where the two main clusters overlap (the Maldives). IBD analyses in the Red Sea revealed differences in gene flow among species, suggesting more limited dispersal potential for E. quadricolorthan forS. mertensiiand H. magnifica. Clonality is documented in S. mertensii for the first time. Main conclusions This research documents the genetic population structure for three ecologically important host sea anemones across the Indo-Pacific and provides valuable insights regarding their biogeography and evolution. Specifically, we found high levels of genetic divergence between populations across different biogeographic regions, suggesting different evolutionary lineages within species. At the same time, common geographic overlap of population structures suggests similar evolutionary histories among all three species. Interestingly, the observed patterns are congruent to some extent with structure reported for several anemonefish species, reflecting their close ecological association.

opencc-zeroNov 2020View details →

Cardinium localization during its parasitoid wasp host's development provides insights into cytoplasmic incompatibility

Arthropods harbor heritable intracellular symbionts that may manipulate host reproduction to favor symbiont transmission. In cytoplasmic incompatibility (CI), the symbiont sabotages the reproduction of infected males such that high levels of offspring mortality result when they mate with uninfected females. In crosses with infected males and infected females, however, (the "rescue" cross), normal numbers of offspring are produced. A common CI-inducing symbiont, Cardinium hertigii, causes variable levels of CI mortality in the parasitoid wasp, Encarsia suzannae. Previous work correlated CI-induced mortality with male development time in this system, although the timing of Cardinium CI-induction and the relationship between development time and CI mortality was not well understood. Here, using a combination of crosses, manipulation of development time, and fluorescence microscopy, we identify the localization and the timing of the CI-induction step in the Cardinium-E. suzannae system. Antibiotic treatment of adult Cardinium-infected males did not reduce the mortality associated with the CI phenotype, suggesting that CI-alteration occurs prior to adulthood. Our results suggest that the alteration step occurs during the pupal period, and is limited by the duration of pupal development: 1) Encarsia produces most sperm prior to adulthood, 2), FISH localization of Cardinium in testes showed an association with sperm nuclei throughout spermatogenesis but not with mature sperm and 3) two methods of prolonging the pupal period (cool temperatures and the juvenile hormone analog methoprene) both caused greater CI mortality, suggesting the degree of alteration is limited by the duration of the pupal stage. Based on these results, we compare two models for potential mechanisms of Cardinium sperm modification in the context of what is known about analogous mechanisms of Wolbachia, a more extensively studied CI-inducing symbiont.

opencc-zeroNov 2020View details →

Climate and host genotype jointly shape tree phenology, disease levels and insect attacks

One of the best known ecological consequences of climate change is the advancement of spring phenology. Yet, we lack insights into how changes in climate interact with intraspecific genetic variation in shaping spring and autumn phenology, and how such changes in phenology will translate into seasonal dynamics of tree-associated organisms. To elucidate the impact of warming and tree genotype on spring and autumn phenology, as well as the consequences for the population dynamics of a fungal pathogen (Erysiphe alphitoides) and plant-feeding insect (Tuberculatus annulatus), we conducted an active field heating experiment using grafts of five oak genotypes (Quercus robur). We found that experimental warming generally advanced oak bud burst in spring and delayed leaf senescence in autumn, while additional variation was explained by tree genotype and warming-by-genotype interactions. Warming or tree genotype did not affect disease levels at the beginning of the season, but shaped both disease levels and aphid density during the latter part of the season. Overall, our findings demonstrate that elevated temperature and genetic variation affect spring and autumn phenology, as well as the seasonal dynamics of higher trophic levels. Such effects may be either direct (i.e. temperature affecting tree phenology and attack independently) or indirect (as due to climate-induced changes in plant traits or the synchrony between trees and their attackers). To achieve a predictive understanding of the ecological responses and potential evolutionary changes of natural food webs in response to climate warming, we should merge the frameworks of global warming and community genetics.

FIGURES 377–380 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 377–380. Distribution of Mitrapsylla in Brazil: 377. M. hamata sp. nov. (square), holocalycis sp. nov. (circle), M. itacoatiara sp. nov. (triangle), M. itaparica (Crawford) (rhombus), M. longicauda Brown & Hodkinson (inverted triangle); 378. M. machaerii sp. nov. (triangle), M. megacerca Burckhardt & Queiroz (square), M. melanothorax sp. nov. (circle), M. ochra sp. nov. (rhombus), M. pallida sp. nov. (inverted triangle); 379. M. periandrae sp. nov. (triangle), M. pterodontis sp. nov. (rhombus), M. pterogynis sp. nov. (square), M. repens Burckhardt & Queiroz (circle), M. securigera sp. nov. (inverted triangle); 380. M. soror sp. nov. (square), M. truncata sp. nov. (inverted triangle), M. villosi sp. nov. (triangle), M. viridis Burckhardt & Queiroz (circle), M. xanthoptera sp. nov. (rhombus). For abbreviations of state names see Fig. 1.

FIGURES 363–372 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 363–372. Mitrapsylla spp., female subgenital plate, ventral view: 363. M. ochra sp. nov.; 364. M. pallida sp. nov.; 365. M. periandrae sp. nov.; 366. M. pterodontis sp. nov.; 367. M. pterogynis sp. nov.; 368. M. securigera sp. nov.; 369. M. soror sp. nov.; 370. M. truncata sp. nov.; 371. M. villosi sp. nov.; 372. M. xanthoptera sp. nov.

FIGURES 337–342 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 337–342. Mitrapsylla spp., female terminalia, lateral view: 337. M. pterogynis sp. nov.; 338. M. securigera sp. nov.; 339. M. soror sp. nov.; 340. M. truncata sp. nov.; 341. M. villosi sp. nov.; 342. M. xanthoptera sp. nov. Scale bar = 0.1 mm.

FIGURES 343–362 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 343–362. Mitrapsylla spp., female subgenital plate, ventral view: 343. M. aeschynomenis sp. nov.; 344. M. amazonica sp. nov.; 345. M. andirae sp. nov.; 346. M. aurantia sp. nov., 347. M. brevigenis sp. nov.; 348. M. cassiae sp. nov.; 349. M. ceplaciensis (White & Hodkinson); 350. M. clavata sp. nov.; 351. M. cubana Crawford; 352. M. cujabensis sp. nov.; 353. M. cuspidata sp. nov.; 354. M. didyma sp. nov.; 355. M. domahovskii sp. nov.; 356. M. halbertae sp. nov.; 357. M. hamata sp. nov.; 358. M. holocalycis sp. nov.; 359. M. itacoatiara sp. nov.; 360. M. itaparica (Crawford); 361. M. machaerii sp. nov.; 362. M. melanothorax sp. nov.

FIGURES 325–330 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 325–330. Mitrapsylla spp., female terminalia, lateral view: 325. M. domahovskii sp. nov.; 326. M. halbertae sp. nov.; 327. M. hamata sp. nov.; 328. M. holocalycis sp. nov.; 329. M. itacoatiara sp. nov.; 330. M. itaparica (Crawford). Scale bar = 0.1 mm.

FIGURES 331–336 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 331–336 Mitrapsylla spp., female terminalia, lateral view: 331. M. machaerii sp. nov.; 332. M. melanothorax sp. nov.; 333. M. ochra sp. nov.; 334. M. pallida sp. nov., 335. M. periandrae sp. nov.; 336. M. pterodontis sp. nov. Scale bar = 0.1 mm.

FIGURES 313–318 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 313–318. Mitrapsylla spp., female terminalia, lateral view: 313. M. aeschynomenis sp. nov.; 314. M. amazonica sp. nov.; 315. M. andirae sp. nov.; 316. M. aurantia sp. nov.; 317. M. brevigenis sp. nov.; 318. M. cassiae sp. nov. Scale bar = 0.1 mm.

FIGURES 265–273 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 265–273. Mitrapsylla spp., male terminalia, lateral view: 265, 268, 271: paramere, outer surface; 266, 269, 272: paramere, inner surface; 267, 270, 273: distal segment of aedeagus. 265‾267. M. pterogynis sp. nov.; 268‾270. M. securigera sp. nov.; 271‾273. M. soror sp. nov. Scale bar = 0.05 mm.

FIGURES 319–324 in Taxonomy and host-plant relationships of the psyllid genus Mitrapsylla (Hemiptera: Psylloidea: Psyllidae) in Brazil

FIGURES 319–324. Mitrapsylla spp., female terminalia, lateral view: 319. M. ceplaciensis (White & Hodkinson); 320. M. clavata sp. nov.; 321. M. cubana Crawford; 322. M. cujabensis sp. nov.; 323. M. cuspidata sp. nov.; 324. M. didyma sp. nov. Scale bar = 0.1 mm.