Distribution of Endosymbiotic Reproductive Manipulators Reflects Invasion Process and Not Reproductive System Polymorphism in the Little Fire Ant Wasmannia auropunctata

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Endosymbiotic reproductive manipulators may have drastic effects on the ecological and evolutionary dynamics of their hosts. The prevalence of these endosymbionts reflects both their ability to manipulate their hosts and the history of the host populations. The little fire ant Wasmannia auropunctata displays a polymorphism in both its reproductive system (sexual versus clonal populations) and the invasive status of its populations (associated to a habitat shift). We first screened for the presence of a diverse array of reproductive parasites in sexual and clonal populations of W. auropunctata, as a means to investigate the role of endosymbionts in reproductive phenotypes. Wolbachia was the only symbiont found and we then focused on its worldwide distribution and diversity in natural populations of W. auropunctata. Using a multilocus scheme, we further characterized the Wolbachia strains present in these populations. We found that almost all the native sexual populations and only a few clonal populations are infected by Wolbachia. The presence of similar Wolbachia strains in both sexual and clonal populations indicates that they are probably not the cause of the reproductive system polymorphism. The observed pattern seems rather associated to the invasion process of W. auropunctata. In particular, the observed loss of Wolbachia in clonal populations, that recurrently emerged from sexual populations, likely resulted from natural heat treatment and/or relaxed selection during the shift in habitat associated to the invasion process. PDF

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Symbiontes et arthropodes – quelles implications pour la lutte biologique?

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Une version vulgarisée (en français AFS_01_13_F_Aebi et en allemand AFS_02_13_D_Aebi) d’un article paru dans le Journal of Applied Ecology, publiée dans Recherche Agronomique Suisse.

Zindel R, Gottlieb Y, Aebi A. (2011) Arthropod symbiosis, a neglected parameter in pest and disease control programs. Journal of Applied Ecology 48: 864–872

Gut microbiome rules what a mite can eat. New paper in The FASEB Journal

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The biology of many arthropods can only be understood when their associated microbiome is considered. The nutritional requirements of the bulb mite Rhizoglyphus robini Claparede (Acari: Astigmata: Acaridae) in the laboratory have been shown to be very easily satisfied, and in the field the mites prefer fungus-infected over uninfected plants. To test whether symbiotic bacteria facilitate the survival of R. robini on a nutritionally-unbalanced diet, we investigated the composition of its microbiome. Using 454 pyrosequencing of 16S rRNA gene fragments, three genera were found to dominate the bacterial community: Myroides  (41.4%), Serratia  (11.4%) and Alcaligenes  (4.5%); the latter two are known to include chitinase producing species. Laboratory experiments demonstrated that mite fecundity is significantly higher (2 times) on fungus than on controls (sterilized potato dextrose agar and filter paper). Also, when mite homogenate was applied to a chitin layer, the halo produced through degradation was clearly visible while the saline control did not produce a halo. We thus concluded that R. robini utilizes fungal chitin, at least to a certain extent, as a food source with the help of its associated bacteria. This information supports the general concept of multigenome organisms and the involvement of bacteria in the mite’s nutritional ecology.

Renate Zindel, Maya Ofek, Dror Minz, Eric Palevsky, Einat Zchori-Fein, and Alexandre Aebi (2013) The role of the bacterial community in the nutritional ecology of the bulb mite Rhizoglyphus robini (Acari: Astigmata: Acaridae) FASEB J fj.12-216242; published ahead of print January 10, 2013, doi:10.1096/fj.12-216242 available here

A new hypothesis to understand Honeybee colony losses?

Picture: Mario Waldburger

Honeybees, through their role as pollinators, provide a crucial ecosystem service to natural flora and agriculture worldwide. Parasites and pathogens represent an increasing threat to honeybees. Colony collapse disorder (CCD) in the USA and other types of colony losses in other parts of the world are characterized by unexplained decrease of adult population leading to colony death. Although scientists do not fully understand the causes of these losses, current knowledge suggests that these are multifactorial and that the interactions between weakening agents such as pathogens and parasites may play a key role in this phenomenon. To date, a factor not taken into account in this project, is the presence and role of endosymbionts associated with arthropods. In addition to their ability to manipulate the reproduction strategy of their hosts, there is increasing evidence that endosymbionts confer pathogen (e.g. virus) resistance to their host to improve their spread in order to invade their host’s population.

Aebi A and Neumann P (2011) Endosymbionts as a key to understand honey bee colony losses? Trends in Ecology and Evolution doi:10.1016/j.tree.2011.06.008

Arthropod symbioses: a neglected parameter in pest- and disease-control programmes

1. Arthropods are important players in biological control as pests, control agents and transmitters of invertebrate diseases. Arthropods are frequently infected with one or several micro-organisms, serving as micro-ecosystems in which multiple interactions can take place. These micro-organisms include disease agents and symbiotic micro-organisms. The latter are usually vertically transmitted and can have a broad spectrum of effects on their hosts, ranging from reproductive manipulations to protection against natural enemies. These interactions may directly or indirectly alter the biology of many arthropods in agriculturally, medically and ecologically relevant ecosystems.

2. Symbiotic micro-organism-induced reproductive manipulations such as cytoplasmic incompatibility and parthenogenesis induction can substantially affect the rearing of biological control agents. Many insects, and recently also mites and nematodes, have been found to be infected, displaying a wide range of effects. We discuss examples of arthropod-micro-organism interactions and effects,
which could have consequences for the practical application of arthropods in biological control.

3. Symbiotic micro-organisms can also be involved in host protection against natural enemies such as parasitoids, pathogenic bacteria, fungi and viruses.

4. Symbiotic bacteria can influence the vectorial capacity of disease-vectoring arthropods and may be very helpful in decreasing the transmission of disease agents.

5. Synthesis and applications. The effect of micro-organisms on the outcome of biological control programmes is usually not considered in risk assessments and failure analyses. This review emphasizes
the importance of endosymbiotic micro-organisms in comprehensive biological control programmes and provides recommendations on how to recognize, avoid or benefit from these influential tenants.

Zindel R, Gottlieb Y, Aebi A. (2011) Arthropod symbiosis, a neglected parameter in pest and disease control programs. Journal of Applied Ecology DOI: 10.1111/j.1365-2664.2011.01984.x