Sexually-transmitted nematode worms and dung beetle microbiomes

Researchers report that nematode worms found on dung beetles are transmitted from mothers to offspring and aid the development of beetle larvae. Dung beetles (Onthophagus taurus) transfer beneficial microbes to larval offspring in chambers called brood balls, which are composed of herbivore dung and consumed by larvae; the microbes help the larvae digest tough plant tissues found in dung. Cris Ledón-Rettig and colleagues tested whether nematode worms, often found in close contact with dung beetles, are similarly transferred between partners during sex and from mothers to offspring. Through field observations and manipulations of artificial brood chambers in which beetle larvae develop, the authors found that the nematode Diplogastrellus monhysteroides, which accumulates in the beetles' genitals, is transmitted during copulation and from mothers to offspring. The nematodes alter the membership of bacterial and fungal communities in brood balls, boosting the abundance of plant-digesting bacteria such as Dysgonomonas, Sphingobacterium, and Acinetobacter and reducing the levels of harmful bacteria such as Desulfovibrio, which produces toxic hydrogen sulfide. The nematode's combined effects likely benefit the beetle larvae, enabling the larvae to derive nutrition from an otherwise inaccessible plant diet. In contrast to previous studies, the findings lend support to the notion that nematode worms are neither freeloading parasites nor cohabiting commensals of dung beetles. Instead, nematode worms add to the maternal endowment that enhances the fitness of both parents and offspring, according to the authors.

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Article #18-09606: "Diplogastrellus nematodes are sexually transmitted mutualists that alter the bacterial and fungal communities of their beetle host," by Cris C Ledón-Rettig, Armin P Moczek, and Erik J. Ragsdale

MEDIA CONTACT: Cris Ledón-Rettig, Indiana University, Bloomington, IA; tel: 812-855-8821; e-mail: crisledo@indiana.edu

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