Background/Question/Methods Microbiomes are now broadly known to provide numerous benefits to their hosts, from immunity and digestion to reproductive success. The vertical transmission of beneficial microbes from parents to offspring has been observed in multiple species, both oviparous and viviparous. Vertical transmission of microbes has also been linked to improved offspring success, for example by protecting eggs from pathogens in the absence of direct parental care post-oviposition. Infection with pathogenic soil fungi is strongly associated with the mortality of soil-incubated eggs, but may be ameliorated by the transmission of beneficial microbes. To determine whether 1) maternal microbes are deposited on eggs during oviposition via the cloaca, and 2) whether they have an antifungal effect that increases hatching success, we conducted direct challenges between dissected or oviposited eggs from the striped plateau lizard (Sceloporus virgatus) and fungi isolated from failed S. virgatus eggs. Unique fungal and bacterial morphs were also isolated from eggs midway through incubation using a culture-based approach in order to identify potential pathogenic fungi and antifungal bacteria. Direct challenges were carried out between individual strains of bacteria and fungi to assess the antifungal capabilities of bacteria isolated from the S. virgatus eggshell microbiome. Results/Conclusions Dissected eggs (which had no contact with the cloaca) had significantly lower hatch success, and hatchlings from dissected eggs were significantly smaller and lighter than those from oviposited eggs, indicating that some element of oviposition is key for hatchling success. The results of sequencing indicate that at least one genus of bacteria (Enterobacter sp.) is found both in the cloacae of females and on eggshells, suggesting that vertical transmission occurs and may be partially responsible for increased hatch success in oviposited eggs. Three fungi were found to dominate the eggshell community of both dissected and oviposited eggs exposed to a “cocktail” of different fungal strains, suggesting that they may be responsible for egg mortality in this species. At least two of these species of fungi have known pathogenic effects in other reptiles, as well as the capability to produce antibacterial and antifungal metabolites. These results suggest an antagonistic relationship between fungi and bacteria on S. virgatus eggshells, and support our hypothesis that bacteria transmitted during oviposition may improve hatch success in this species. These findings suggest that vertical transmission of beneficial microbes may serve as a form of parental care and occur via a novel pathway, contact with the cloaca.
