Sexually Transmitted Mutualist Nematodes Promote Host Growth Across Dung
Beetle Species
Abstract
Many symbionts are sexually transmitted and impact their host’s
development, ecology, and evolution. While the significance of symbionts
that cause sexually transmitted diseases (STDs) is relatively well
understood, the prevalence and potential significance of the sexual
transmission of beneficial symbionts remain elusive. Here, we study the
effects of sexually transmitted mutualist nematodes on their dung beetle
hosts. Symbiotic Diplogastrellus monhysteroides nematodes are present on
the genitalia of male and female Onthophagus beetles and are
horizontally transmitted during mating and vertically passed on to
offspring during oviposition. A previous study indicates that the
presence of nematodes benefits larval development and life history in a
single host species, Onthophagus taurus. However, Diplogastrellus
nematodes can be found in association with a variety of beetle species.
Here, we replicate these previous experiments, assess whether the
beneficial effects extend to other host species, and test whether
nematode-mediated effects differ between male and female hosts. Rearing
three distantly related dung beetle species with and without nematodes,
we find that the presence of nematodes benefits body size, but not
development time or survival across all three species. Likewise, we
found no difference in the benefit of nematodes to male compared to
female beetles. These findings highlight the role of sexually
transmitted mutualists in the evolution and ecology of dung beetles.
Furthermore, these results suggest a potential new avenue through which
environmental pollution with veterinary deworming agents may affect dung
beetles and their ecosystem services.