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Evolutionary Biology of Parasitism
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
Another factor potentially driving host speciation, one that has not yet received the full attention it deserves, is the involvement of symbionts. As we have noted throughout this book, symbionts are a ubiquitous feature of organismal life and are bound to influence all aspects of the biology of their hosts. In some cases, these symbionts dramatically alter their host’s reproductive biology, so much so they are considered reproductive parasites. Consider bacteria of the genus Wolbachia that infect many arthropods and nematodes, with species of fruit flies (Drosophila) being commonly studied model hosts. Wolbachia is discussed in other contexts in this book as well, including as targets for the treatment of filarial worms that carry Wolbachia symbionts, or in their role in affecting the ability of mosquitoes to vector diseases like dengue or malaria (Chapter 9). In the present context as reproductive parasites, these bacteria are vertically transmitted in the host female’s gametes and can cause cytoplasmic incompatibility (CI). CI is when sperm and eggs are unable to collaborate to form a viable progeny. For instance, sterility can result if a male host infected with Wolbachia copulates with an uninfected female (or is infected with a different strain of Wolbachia). Her offspring suffer 100% embryonic mortality. By killing the offspring of females lacking the Wolbachia causing CI, females who do carry CI will be favored, and thus CI-causing Wolbachia will spread relentlessly in the population.
The Diseases – Malaria, Filariasis and Dengue
Published in Jacques Derek Charlwood, The Ecology of Malaria Vectors, 2019
Wolbachia is a bacterium that affects a large number of arthropods. It has been estimated that between 20% and 70% of insect species are infected. A number of mechanisms have evolved to enhance its transmission. In some insects, the number of males produced is reduced (because it is only eggs that transfer the bacterium). In mosquitoes, due to a phenomenon known as cytoplasmic incompatibility infected males are unable to fertilise uninfected females, which then lay sterile eggs (Figure 12.17) because the cycle of mitotic division of the parental chromosomes in the first few divisions are out of sync and so division fails and the egg dies.
Evolutionary Biology of Parasitism
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2015
Eric S. Loker, Bruce V. Hofkin
Another factor potentially driving host speciation, one that has not yet received the full attention it deserves, is the involvement of symbionts. As we have noted throughout this book, symbionts are a ubiquitous feature of organismal life and are bound to influence all aspects of the biology of their hosts. In some cases, these symbionts dramatically alter their host’s reproductive biology, so much so they are considered reproductive parasites. Consider for a moment a-proteobacteria of the genus Wolbachia that infect many arthropods and nematodes, with species of fruit flies (Drosophila) being commonly studied model hosts. These bacteria are vertically transmitted in the host female’s gametes. In some instances they cause cytoplasmic incompatibility (CI). In this case, sterility can result if a male host that is infected with Wolbachia copulates with a female who is uninfected (or is infected with a different strain of Wolbachia). The offspring suffer 100% embryonic mortality. By killing the offspring of females lacking the Wolbachia causing CI, females who do carry CI will be favored, and thus CI-causing Wolbachia will spread relentlessly in the population.
Wolbachia-Virus interactions and arbovirus control through population replacement in mosquitoes
Published in Pathogens and Global Health, 2023
Thomas H Ant, Maria Vittoria Mancini, Cameron J McNamara, Stephanie M Rainey, Steven P Sinkins
Wolbachia pipientis are alphaproteobacteria found in many arthropod species and some nematodes [1]. As obligate endosymbionts, Wolbachia are transmitted from mother to offspring in the egg cytoplasm during oogenesis. Wolbachia-host interactions often combine elements of parasitism and mutualism: in some instances, they provision a host with nutrients [2], enhance germline stem cell proliferation and thereby increase host fecundity [3], and can have a potent capacity to protect hosts from some pathogens (see Table 1). Many strains also induce one of several forms of reproductive manipulation, facilitating their invasion and maintenance in host populations [47,107–110]. Cytoplasmic incompatibility (CI) is one such manipulation, and results from a sperm modification that causes infertility when a Wolbachia-carrying male mates with a Wolbachia-free female or with a female carrying a reciprocally incompatible Wolbachia strain, but can be rescued by a female carrying the same or otherwise compatible Wolbachia strain. Because CI results in a relative reproductive advantage for Wolbachia-carrying females, CI-inducing Wolbachia strains can often maintain very high population infection frequencies. The fitness advantage for Wolbachia-carriers generated by CI is frequency dependent and is highest when a Wolbachia strain is close to fixation, while at very low frequencies the population-level effects of CI are negligible. This results in a threshold frequency above which there is spread and below which Wolbachia is lost; the threshold depends on CI penetrance, efficiency of maternal transmission, and fitness effects. Phenotypes that improve the spread of a Wolbachia strain are expected to be selected for; mathematical models suggest that pathogen protection can significantly lower the frequency thresholds required for Wolbachia invasion [111].
wsp-based analysis of Wolbachia strains associated with Phlebotomus papatasi and P. sergenti (Diptera: Psychodidae) main cutaneous leishmaniasis vectors, introduction of a new subgroup wSerg
Published in Pathogens and Global Health, 2018
Fateh Karimian, Hassan Vatandoost, Yavar Rassi, Naseh Maleki-Ravasan, Nayyereh Choubdar, Mona Koosha, Kourosh Arzamani, Eslam Moradi-Asl, Arshad Veysi, Hamzeh Alipour, Manouchehr Shirani, Mohammad Ali Oshaghi
Although, in general, each sand fly species like P.sergenti or other insect species seemingly harbors a single Wolbachia subgroup within a single Supergroup, P.papatasi and some other insect species including sand flies, fruit flies, beetles, wasps and mosquitoes present a polyphyletic species [45–49]. For examples, Wolbachia endosymbionts (wLcy and wLev) occurred in the population of Lutzomyia c. cayennensis [30], Aedes albopictus presented two divergent Wolbachia groups A and B (wAlbA and wAlbB) [46,50], and D.simulans grants five different Wolbachia variants [51] including wMel, wRiv, and wHaw of Supergroup A and wAu, and wMa of Supergroup B [29,52]. Parvizi, Bordbar [53] found two Wolbachia strains in sand flies, one strain (Turk 07, accession KC576916) in the two sister taxa of P.mongolensis and P.caucasicus and another strains in P.papatasi (Turk 54, accession EU780683). They concluded that one species of sand fly can be infected with different Wolbachia strains and that different species of sand flies can be infected with a common strain. The presence of two or more Wolbachia strains in a single species may be explained by either shared ancestral origin or interspecific hybridization (horizontal transmission) between two closely species that led to introgression of a different Wolbachia strain [47,54–58]. One strain of Wolbachia in particular (designated Adm) appears to have undergone extensive ‘recent’ horizontal transmission. Mechanisms of intertaxon transmission are unknown, although there is indirect evidence for exchange between parasitoids and their host insects [47]. The two Wolbachia subgroups (wSerg and wPip) were found simultaneously in the TUMS/SPH lab and Ardabil strains of P.papatasi. Wolbachia multiple infection in a population with identical ecological region has been already reported in some insects [52]. Cytoplasmic Incompatibility (CI) is a known phenomenon happening in crosses between males Wolbachia infected and uninfected females or females infected with other type of Wolbachia, resulted in intense decrease in the amount of viable eggs produced. However, different level of CI intensity has been observed between host species. For example, CI is fully expressed in D. simulans but is fully or partially permissive in D. melanogaster [51]. These authors concluded that host factors are involved in the control of CI. In another study by James, Dean [52] the dynamics associated with double and single Wolbachia infections in D. simulans was investigated. They showed that the CI is higher when a singly infected male is mated with a female carrying the other strain (1.00–0.30) in comparison with an uninfected female (0.33–0.08), suggesting that both sexes (male and female) fund to the expression of CI. They suggested that either the DNA of these bacterial isolates have diverged from a shared ancestral ones, host genetic factors has led to lessening in the CI phenotype, or some Wolbachia may display different levels of incompatibility.