scholarly journals Phylogenetic analysis suggests joint control of transmission mode in a grass-endophyte symbiosis

2016 ◽  
Author(s):  
Alexandra Brown ◽  
Erol Akçay
Keyword(s):  
Phylogenetic Analysis ◽  
Vertical Transmission ◽  
Horizontal Transmission ◽  
Model System ◽  
Transmission Mode ◽  
Joint Control ◽  
Grass Endophyte ◽  
Host Phylogeny

AbstractHow symbionts are transmitted between hosts is key to determining whether symbioses evolve to be harmful or beneficial. Vertical transmission favors mutualistic symbionts, and horizontal transmission more virulent ones. Transmission mode evolution itself depends on whether the host or symbiont can respond to selection on transmission mode. When hosts control the transmission mode, vertical transmission should evolve under more restrictive circumstances than when symbionts are in control. We take a phylogenetic approach to determine whether the host, symbiont, or both control transmission mode using the pooid grass-epichloid endophyte symbiosis as a model system. This study is the first to investigate control of transmission mode evolution in a phylogenetic context. We find a signal of host phylogeny but only in conjunction with symbiont identity. This pattern suggests joint control of transmission mode by the host and symbiont. It also suggests that non-genetic or non-conserved symbiont traits may determine whether host traits lead to vertical or horizontal transmission.

scholarly journals Transmission mode is associated with environment type and taxa across bacteria-eukaryote symbioses

2018 ◽  
Author(s):  
Shelbi L Russell
Keyword(s):  
Vertical Transmission ◽  
Horizontal Transmission ◽  
Transmission Mode ◽  
Symbiotic Associations ◽  
Transmission Modes ◽  
Symbiont Transmission ◽  
Environment Type ◽  
Full Separation ◽  
Host Evolution ◽  
Host Tissues

AbstractSymbiotic associations between bacteria and eukaryotes exhibit a range of transmission strategies. Anecdotal observations suggest that symbionts of terrestrial hosts tend to be strictly vertically inherited through host tissues, whereas symbionts of marine hosts tend towards horizontal transmission. Aside from a few cursory investigations, the rates and distributions of transmission modes have not been investigated in depth across associations, despite the consequences for symbiont and host evolution. To address this empirically and estimate the rate of each mode, I compiled data from the literature and for associations between transmission mode and the environment, transmission route, symbiont function, and taxa involved in the symbiosis. Of the 441 analyzed symbioses, 50.1% were strictly vertically transmitted, 34.0% exhibited some form of mixed mode transmission, and 15.9% were strictly horizontally transmitted. Binning symbioses by their environment revealed a significant skew towards vertical transmission on land and horizontal transmission in aquatic environments, with mixed modes abundant in both. However, host and symbiont taxa were not randomly distributed, which prevented the full separation of these variables. Overall, the data suggest that many symbiotic taxa are capable of horizontal transmission and barriers exist that reduce the rate of these events. Thus, both the environment type and host/symbiont taxa combined influence symbiont transmission mode evolution.One sentence summaryThrough an intensive analysis of the literature on symbiosis transmission modes, estimated rates for each transmission mode were calculated, revealing bias for horizontal transmission in the ocean and vertical transmission on land.

scholarly journals Can Differences in Symbiont Transmission Mode Explain the Abundance and Distribution of Fungus-Growing Termites in West Africa?

2020 ◽  
Vol 8 ◽  
Author(s):  
Judith Korb ◽  
Simon Kolotchèlèma Silué ◽  
N'golo Abdoulaye Koné
Keyword(s):  
Vertical Transmission ◽  
National Parks ◽  
Horizontal Transmission ◽  
Species Abundance ◽  
Transmission Mode ◽  
Termite Species ◽  
Symbiont Transmission ◽  
Ecological Dominance ◽  
Study Sites ◽  
Abundance And Distribution

Fungus-growing termites (Isoptera: Macrotermitinae) dominate African savannah ecosystems where they play important roles in ecosystem functioning. Their ecological dominance in these ecosystems has been attributed to living in an ectosymbiosis with fungi of the genus Termitomyces (Lyophyllaceae). Evolutionary theory predicts that the transmission mode of a symbiont determines cooperation and conflict between host and symbiont with vertical transmission (co-transmission of host and symbiont offspring to the next generation) leading to less conflict than horizontal transmission (symbionts are acquired by the host from the environment). Thus, one can hypothesize associations with vertical transmission to be ecological more successful than those with horizontal transmission. We tested this by analyzing whether there is an association between transmission mode and fungus-growing termite species abundance and distribution in West-African savannah and forest ecosystems. We used data from a total of 78 study sites comprising protected National Parks as well as anthropogenically disturbed ecosystems, covering Benin, Côte d'Ivoire, and Togo. Our results showed that, in contrast to expectation, species with horizontal symbiont transmission were more common. We encountered more often species with horizontal than vertical transmission. This result might be due to the fact that only five out of the 25 identified fungus-growing termite species had vertical transmission. Yet, species with horizontal transmission also had higher relative abundances within study sites than those with vertical transmission. Thus, transmission mode is unlikely to explain abundance differences between fungus-growing termite species.

scholarly journals Evolution of symbiont transmission in conditional mutualisms in spatially and temporally variable environments

2020 ◽  
Author(s):  
Alexandra Brown ◽  
Erol Akçay
Keyword(s):  
Vertical Transmission ◽  
Horizontal Transmission ◽  
Environmental Variation ◽  
Transmission Mode ◽  
Trade Off ◽  
Symbiotic Relationships ◽  
Physiological Constraints ◽  
Fitness Effects ◽  
Variable Environments ◽  
Symbiont Transmission

AbstractSymbiotic relationships affect the fitness and organismal function of virtually all organisms. In many cases, the fitness effects of symbiosis may be beneficial or harmful depending on the environment. The hosts of such symbionts are favored to acquire them only when the symbiont is beneficial. However, it is not clear whether such selection favors vertical or horizontal transmission, both, or neither. To address this question, we model the evolution of transmission mode in a conditional mutualism experiencing spatial and temporal environmental variation. We find that when symbionts affect host lifespan, but not fecundity, horizontal transmission can contain them to beneficial environments. Vertical transmission can produce symbiont containment when the environmental state is synchronized across locations. We also find an emergent trade-off between horizontal and vertical transmission, suggesting that physiological constraints are not required for the evolution of limits on the total amount of transmission.

scholarly journals Evolution of transmission mode in conditional mutualisms with spatial variation in symbiont quality

2018 ◽  
Author(s):  
Alexandra Brown ◽  
Erol Akçay
Keyword(s):  
Environmental Factors ◽  
Spatial Variation ◽  
Vertical Transmission ◽  
Horizontal Transmission ◽  
Environmental Context ◽  
Transmission Mode ◽  
Costs And Benefits ◽  
Low Frequencies ◽  
High Frequencies ◽  
Conditional Effect

AbstractWhile some symbioses are always mutualistic or parasitic, others have costs and benefits that depend on environmental factors. The environmental context may itself vary in space, in some cases causing a symbiont to be a mutualist in one location and a parasite in another. Such spatially conditional mutualisms pose a dilemma for hosts, who might evolve (higher or lower) horizontal or vertical transmission to increase their chances of being infected only where the symbiont is beneficial. To determine how transmission in hosts might evolve, we modeled transmission evolution where the symbiont had a spatially conditional effect on either host lifespan or fecundity. We found that over ecological time, symbionts that affected lifespan but not fecundity led to high frequencies of infected hosts in areas where the symbiont was beneficial and low frequencies elsewhere. In response, hosts evolved increased horizontal transmission only when the symbiont affected lifespan. We also modeled transmission evolution in symbionts, which evolved high horizontal and vertical transmission, indicating a possible host-symbiont conflict over transmission mode. Our results suggest an eco-evolutionary feedback where the component of host fitness that a conditionally mutualistic symbiont influences affects its distribution in the population, and, through this, the transmission mode that evolves.

scholarly journals The emerging diversity of Rickettsia

2006 ◽  
Vol 273 (1598) ◽  
pp. 2097-2106 ◽  
Author(s):  
Steve J Perlman ◽  
Martha S Hunter ◽  
Einat Zchori-Fein
Keyword(s):  
Phylogenetic Analysis ◽  
Vertical Transmission ◽  
Human Disease ◽  
Spotted Fever ◽  
Rocky Mountain ◽  
Blood Feeding ◽  
Model System ◽  
Rocky Mountain Spotted Fever ◽  
Research Directions ◽  
Transmission Pathways

The best-known members of the bacterial genus Rickettsia are associates of blood-feeding arthropods that are pathogenic when transmitted to vertebrates. These species include the agents of acute human disease such as typhus and Rocky Mountain spotted fever. However, many other Rickettsia have been uncovered in recent surveys of bacteria associated with arthropods and other invertebrates; the hosts of these bacteria have no relationship with vertebrates. It is therefore perhaps more appropriate to consider Rickettsia as symbionts that are transmitted vertically in invertebrates, and secondarily as pathogens of vertebrates. In this review, we highlight the emerging diversity of Rickettsia species that are not associated with vertebrate pathogenicity. Phylogenetic analysis suggests multiple transitions between symbionts that are transmitted strictly vertically and those that exhibit mixed (horizontal and vertical) transmission. Rickettsia may thus be an excellent model system in which to study the evolution of transmission pathways. We also focus on the emergence of Rickettsia as a diverse reproductive manipulator of arthropods, similar to the closely related Wolbachia , including strains associated with male-killing, parthenogenesis, and effects on fertility. We emphasize some outstanding questions and potential research directions, and suggest ways in which the study of non-pathogenic Rickettsia can advance our understanding of their disease-causing relatives.

scholarly journals Simulated folivory increases vertical transmission of fungal endophytes that deter herbivores and alter tolerance to herbivory in Poa autumnalis

2020 ◽  
Vol 125 (6) ◽  
pp. 981-991 ◽  
Author(s):  
Pedro E Gundel ◽  
Prudence Sun ◽  
Nikki D Charlton ◽  
Carolyn A Young ◽  
Tom E X Miller ◽  
...  
Keyword(s):  
Vertical Transmission ◽  
Transmission Rate ◽  
Horizontal Transmission ◽  
Fungal Endophytes ◽  
Natural Populations ◽  
Plant Tolerance ◽  
Hyphal Density ◽  
Symbiotic Fungi ◽  
Symbiont Transmission ◽  
Fitness Benefits

Abstract Background and Aims The processes that maintain variation in the prevalence of symbioses within host populations are not well understood. While the fitness benefits of symbiosis have clearly been shown to drive changes in symbiont prevalence, the rate of transmission has been less well studied. Many grasses host symbiotic fungi (Epichloë spp.), which can be transmitted vertically to seeds or horizontally via spores. These symbionts may protect plants against herbivores by producing alkaloids or by increasing tolerance to damage. Therefore, herbivory may be a key ecological factor that alters symbiont prevalence within host populations by affecting either symbiont benefits to host fitness or the symbiont transmission rate. Here, we addressed the following questions: Does symbiont presence modulate plant tolerance to herbivory? Does folivory increase symbiont vertical transmission to seeds or hyphal density in seedlings? Do plants with symbiont horizontal transmission have lower rates of vertical transmission than plants lacking horizontal transmission? Methods We studied the grass Poa autumnalis and its symbiotic fungi in the genus Epichloë. We measured plant fitness (survival, growth, reproduction) and symbiont transmission to seeds following simulated folivory in a 3-year common garden experiment and surveyed natural populations that varied in mode of symbiont transmission. Key Results Poa autumnalis hosted two Epichloë taxa, an undescribed vertically transmitted Epichloë sp. PauTG-1 and E. typhina subsp. poae with both vertical and horizontal transmission. Simulated folivory reduced plant survival, but endophyte presence increased tolerance to damage and boosted fitness. Folivory increased vertical transmission and hyphal density within seedlings, suggesting induced protection for progeny of damaged plants. Across natural populations, the prevalence of vertical transmission did not correlate with symbiont prevalence or differ with mode of transmission. Conclusions Herbivory not only mediated the reproductive fitness benefits of symbiosis, but also promoted symbiosis prevalence by increasing vertical transmission of the fungus to the next generation. Our results reveal a new mechanism by which herbivores could influence the prevalence of microbial symbionts in host populations.

scholarly journals Evolution of early male-killing in horizontally transmitted parasites

2015 ◽  
Vol 282 (1818) ◽  
pp. 20152068 ◽  
Author(s):  
Veronika Bernhauerová ◽  
Luděk Berec ◽  
Daniel Maxin
Keyword(s):  
Empirical Evidence ◽  
Vertical Transmission ◽  
Bacterial Strain ◽  
Horizontal Transmission ◽  
Distinct Species ◽  
High Efficacy ◽  
Infected Male ◽  
Male Killing ◽  
Wide Range ◽  
Male Killer

Early male-killing (MK) bacteria are vertically transmitted reproductive parasites which kill male offspring that inherit them. Whereas their incidence is well documented, characteristics allowing originally non-MK bacteria to gradually evolve MK ability remain unclear. We show that horizontal transmission is a mechanism enabling vertically transmitted bacteria to evolve fully efficient MK under a wide range of host and parasite characteristics, especially when the efficacy of vertical transmission is high. We also show that an almost 100% vertically transmitted and 100% effective male-killer may evolve from a purely horizontally transmitted non-MK ancestor, and that a 100% efficient male-killer can form a stable coexistence only with a non-MK bacterial strain. Our findings are in line with the empirical evidence on current MK bacteria, explain their high efficacy in killing infected male embryos and their variability within and across insect taxa, and suggest that they may have evolved independently in phylogenetically distinct species.

scholarly journals Tissue Tropisms and Transstadial Transmission of a Rickettsia Endosymbiont in the Highland Midge, Culicoides impunctatus (Diptera: Ceratopogonidae)

2020 ◽  
Vol 86 (20) ◽  
Author(s):  
Jack Pilgrim ◽  
Stefanos Siozios ◽  
Matthew Baylis ◽  
Gregory D. D. Hurst
Keyword(s):  
Vertical Transmission ◽  
Fat Body ◽  
Germ Line ◽  
Horizontal Transmission ◽  
Follicle Cells ◽  
Biting Midges ◽  
Diverse Range ◽  
Suspensory Ligament ◽  
Transstadial Transmission ◽  
Tissue Tropisms

ABSTRACT Rickettsia is a genus of intracellular bacteria which can manipulate host reproduction and alter sensitivity to natural enemy attack in a diverse range of arthropods. The maintenance of Rickettsia endosymbionts in insect populations can be achieved through both vertical and horizontal transmission routes. For example, the presence of the symbiont in the follicle cells and salivary glands of Bemisia whiteflies allows Belli group Rickettsia transmission via the germ line and plants, respectively. However, the transmission routes of other Rickettsia bacteria, such as those in the Torix group of the genus, remain underexplored. Through fluorescence in situ hybridization (FISH) and transmission electron microscopy (TEM) screening, this study describes the pattern of Torix Rickettsia tissue tropisms in the highland midge, Culicoides impunctatus (Diptera: Ceratopogonidae). Of note is the high intensity of infection of the ovarian suspensory ligament, suggestive of a novel germ line targeting strategy. Additionally, localization of the symbiont in tissues of several developmental stages suggests transstadial transmission is a major route for ensuring maintenance of Rickettsia within C. impunctatus populations. Aside from providing insights into transmission strategies, the presence of Rickettsia bacteria in the fat body of larvae indicates potential host fitness and vector capacity impacts to be investigated in the future. IMPORTANCE Microbial symbionts of disease vectors have garnered recent attention due to their ability to alter vectorial capacity. Their consideration as a means of arbovirus control depends on symbiont vertical transmission, which leads to spread of the bacteria through a population. Previous work has identified a Rickettsia symbiont present in several species of biting midges (Culicoides spp.), which transmit bluetongue and Schmallenberg arboviruses. However, symbiont transmission strategies and host effects remain underexplored. In this study, we describe the presence of Rickettsia in the ovarian suspensory ligament of Culicoides impunctatus. Infection of this organ suggests the connective tissue surrounding developing eggs is important for ensuring vertical transmission of the symbiont in midges and possibly other insects. Additionally, our results indicate Rickettsia localization in the fat body of Culicoides impunctatus. As the arboviruses spread by midges often replicate in the fat body, this location implies possible symbiont-virus interactions to be further investigated.

scholarly journals Application of the Neospora Caninum IgG Avidity ELISA in Assessment of Chronic Reproductive Losses after an Outbreak of Neosporosis in a Herd of Beef Cattle

2003 ◽  
Vol 15 (1) ◽  
pp. 3-7 ◽  
Author(s):  
Camilla Björkman ◽  
Milton M. McAllister ◽  
Jenny Frössling ◽  
Katarina Näslund ◽  
Felicia Leung ◽  
...  
Keyword(s):  
Point Source ◽  
Pregnancy Rate ◽  
Vertical Transmission ◽  
Neospora Caninum ◽  
Horizontal Transmission ◽  
Beef Cows ◽  
Abortion Rate ◽  
Reproductive Effects ◽  
Igg Avidity ◽  
Beef Herd

Point-source infections are most likely the cause for Neospora caninum–induced abortion outbreaks in cattle, whereas an increased annual abortion rate may be a consequence of vertical transmission. The aims of the present study were to examine the reproductive effects of neosporosis in a beef herd for 3 years, after a point-source outbreak and to use IgG avidity serology to examine the chronicity of infections and patterns of transmission. During the study, 76–78% of animals were seropositive for N. caninum. The pregnancy rate varied from 88% to 94%, without any reduction in the pregnancy rate of seropositive cows compared with seronegative cows. The annual abortion rate was 2.5–5.5%, and all but 1 abortion occurred in seropositive dams. The efficiency of vertical transmission was estimated to be 85%. Several calves, born to seronegative dams, were seropositive at 6–13 months of age, indicating a 22% mean annual rate of horizontal transmission. The mean avidity in seropositive cows increased from 30 during the initial outbreak to 74 after 3 years. The mode of IgG avidity was 21–40 during the initial abortion outbreak, 41–60 after 1 year, and 61–80 after 2 and 3 years. The results reveal high annual rates of both vertical and horizontal transmission of N. caninum in a herd of beef cows and provide further validation on the ability of the N. caninum IgG avidity ELISA to accurately assess the chronicity of infection.

scholarly journals Viral hepatitis B and C in HIV-exposed South African infants

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Cynthia Tamandjou Tchuem ◽  
Mark Fredric Cotton ◽  
Etienne Nel ◽  
Richard Tedder ◽  
Wolfgang Preiser ◽  
...  
Keyword(s):  
South Africa ◽  
Hepatitis B ◽  
Vertical Transmission ◽  
Horizontal Transmission ◽  
Hbv Dna ◽  
Molecular Testing ◽  
Lamivudine Resistance ◽  
Hiv Exposed Infants ◽  
Hcv Antibody ◽  
Hiv Exposed

Abstract Background Whilst much attention is given to eliminating HIV mother-to-child transmission (MTCT), little has been done to ensure the same for hepatitis B virus (HBV) transmission. The introduction of HBV immunization at six weeks of age has reduced HBV horizontal transmission in South Africa. However, in order to eliminate HBV MTCT, further interventions are needed. The risk of hepatitis C virus (HCV) MTCT in HIV-infected (HIV+) African women is not yet well described. This study aimed to determine the rate of HBV and HCV vertical transmission in HIV-exposed infants in South Africa. Methods Serum samples from infants enrolled in an isoniazid prevention study (P1041) were screened for HBV and HCV serology markers; screening was performed on samples collected at approximately 60 weeks of age of the infants. HBV DNA was quantified in HBsAg positive samples and HBV strains characterized through gene sequencing. All HCV antibody samples with inconclusive results underwent molecular testing. Results Three of 821 infants were positive for both HBsAg and HBV DNA. All HBV strains belonged to HBV sub-genotype A1. The rtM204I mutation associated with lamivudine resistance was identified in one infant, a second infant harboured the double A1762T/G1764A BCP mutation. Phylogenetic analysis showed clustering between mother and infant viral genomic sequences. Twenty-one of 821 HIV-exposed infants tested had inconclusive HCV antibody results, none were HCV PCR positive. Conclusions This study suggests that HBV vertical transmission is likely to be occurring in HIV-exposed infants in South Africa.. A more robust strategy of HBV prevention, including birth dose vaccination, is required to eradicate HBV MTCT. HCV infection was not detected.

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