Do Microbiota in the Soil Affect Embryonic Development and Immunocompetence in Hatchling Reptiles?

Gregory P Brown,Richard Shine

doi:10.3389/fevo.2021.780456

Abstract

Reptile eggs develop in intimate association with microbiota in the soil, raising the possibility that embryogenesis may be affected by shifts in soil microbiota caused by anthropogenic disturbance, translocation of eggs for conservation purposes, or laboratory incubation in sterile media. To test this idea we incubated eggs of keelback snakes (Tropidonophis mairii, Colubridae) in untreated versus autoclaved soil, and injected lipopolysaccharide (LPS) into the egg to induce an immune response in the embryo. Neither treatment modified hatching success, water uptake, incubation period, or white-blood-cell profiles, but both treatments affected hatchling size. Eggs incubated on autoclaved soil produced smaller hatchlings than did eggs on untreated soil, suggesting that heat and/or pressure treatment decrease the soil’s suitability for incubation. Injection of LPS reduced hatchling size, suggesting that the presence of pathogen cues disrupts embryogenesis, possibly by initiating immune reactions unassociated with white-blood-cell profiles. Smaller neonates had higher ratios of heterophils to leucocytes, consistent with higher stress in smaller snakes, or body-size effects on investment into different types of immune cells. Microbiota in the incubation medium thus can affect viability-relevant phenotypic traits of hatchling reptiles. We need further studies to explore the complex mechanisms and impacts of environmental conditions on reptilian embryogenesis.

Highlights

The embryos of most species of oviparous reptiles spend the majority of their total developmental period outside the mother’s body, in external nests (e.g., Shine, 1983)
Because any null result from such a study may be due to lack of penetration of the shell by local micro-organisms, we ran another study in which we directly introduced lipopolysaccharide (LPS, a component of bacterial cell walls) into the egg to stimulate an immune response by the embryo
Autoclaving the incubation substrate had no significant effect on any white blood cell (WBC) measures (Table 2)

Summary

INTRODUCTION

The embryos of most species of oviparous reptiles spend the majority of their total developmental period (typically, the latter two-thirds) outside the mother’s body, in external nests (e.g., Shine, 1983). Because any null result from such a study may be due to lack of penetration of the shell by local micro-organisms, we ran another study in which we directly introduced lipopolysaccharide (LPS, a component of bacterial cell walls) into the egg to stimulate an immune response by the embryo. This second experiment allowed us to assess the effects of chemically signaling the presence of pathogenic microbiota without introducing any confounding deleterious affects (such as propagation) that would arise from introducing harmful bacteria. We predicted that the presence of microbiota (or their chemical cues) could impose developmental costs on embryos that would be manifested in altered morphological or immunological measures

MATERIALS AND METHODS

Findings

RESULTS