CE02 - Terre vivante

Microbial competition in mutualistic interactions with ticks – MICROM

Submission summary

Microbial life has a pervasive influence on macro-organisms. Many microbes are essential for their development, immunity and nutrition. These mutualistic interactions have facilitated the adaptation of major eukaryotic lineages to specialized niches, altering ecosystems and biodiversity. Indeed, arthropods often carry maternally inherited bacteria that are required for diet-niche exploitation. Some major arthropod lineages of economical, medical or veterinary interests only exist thanks to these mutualistic symbioses. These interactions have led to highly co-evolved relationships that are traditionally envisioned as stable cooperative associations. However, these mutualistic relationships are much more dynamic than previously thought: replacement of ancestral symbionts by non-coevolved symbionts are common. The MICROM project examines this unexpected dynamic in ticks: the aim is to determine the factors that influence the evolution of a little-known tick-symbiont mutualism.

In the MICROM project, we will explore how mutualistic relationships are built, maintained, and extinguished by conflict-ridden interaction using ticks as ideal biological models. Ticks exclusively feed on blood but this is a nutritionally unbalanced diet: To avoid nutritional deficiency, all ticks harbor symbionts producing B vitamins. This B vitamin supplementation by symbionts is critical for their growth, reproduction and survival, but the origin of these symbionts vary substantially between tick taxa. Recent phylogenetic reconstructions found evidence for symbiont replacements during the radiation of ticks, with recent, and probably ongoing, invasions by foreign symbionts and subsequent extinctions of ancestral B vitamin provisioning symbionts.

We propose to test the hypothesis that hosts and symbionts can enter into an evolutionary spiral that leads to the evolution of developmental dependence beyond the original benefits of the symbiosis and to irreversible codependence and associated risks. We notably conjecture that competition between symbionts with similar metabolic capabilities is a central force in the dynamics of mutualistic symbiotic interactions. We will examine these mechanisms through a comparative approach between ticks (and tick cells) either naturally infected by their co-evolved symbionts or artificially co-infected with foreign symbionts. The characterization of phenotypes and competitive outcomes, along with extensive genomics and transcriptomics, will reveal the mechanisms destabilizing co-evolved mutualistic interactions. Notably, we will investigate on a series of outstanding points on (1) evolutionary convergence in mutualistic symbionts at both phenotypic and genomic levels; (2) evolutionary processes driving the emergence of novel mutualisitic symbioses through the extinction of ancestral symbionts; (3) how degradation of symbiont genomic content favors a competitive, albeit non co-evolved, symbiont. Beyond its fundamental importance in evolutionary ecology, understanding how ticks adapt to a blood feeding lifestyle is essential to understand the biology of these major disease vectors and, possibly, to develop novel control strategies.

Project coordination

Olivier DURON (Maladies Infectieuses et Vecteurs : Ecologie, Génétique, Evolution et Contrôle)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

EBI Ecologie et biologie des interactions
MIVEGEC Maladies Infectieuses et Vecteurs : Ecologie, Génétique, Evolution et Contrôle
LBBE BIOMÉTRIE ET BIOLOGIE EVOLUTIVE

Help of the ANR 512,447 euros
Beginning and duration of the scientific project: October 2021 - 48 Months

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