An animal’s microbes not only help it to digest food, absorb nutrients and fight disease, they are also important during normal development. Researchers at Indiana University have shown that the collection of microbes passed from a beetle mother to her offspring (the maternal microbiome) is critically important for development of beetle larvae and their resistance to environmental challenges. The study, led by evolutionary developmental biologists, Daniel Schwab and Armin Moczek, focused on the dung beetle species, Onthophagus gazella.
In humans, a mother passes her microbiome to her child during passage through the birth canal and through physical contact such as hugging and kissing. In dung beetles, the mother passes on her microbiome by laying her egg on top of a fecal secretion, called a pedestal, which becomes the first food source of the hatched larva. This happens inside a buried ball of dung called a brood ball. When the microbiota of the pedestal and dung are removed, dung beetle larvae develop slower and don’t grow as big as their siblings raised in the presence of microbes. Microbiota are therefore important for the normal development of dung beetles.
Next, researchers showed that it was specifically the maternal microbiome, rather than the nutrients of the pedestal or other environmental bacteria, that was important for enhanced larval growth. To do this, they isolated microbes from pedestals and from soil in a pasture naturally inhabited by dung beetles. Eggs without pedestals were then hatched in the presence of only the maternal microbiome, soil microbiome or none at all. Larvae hatched with the maternal microbes grew faster and bigger than their siblings hatched in the presence of soil microbes or no microbes at all. This highlights the importance of the maternal microbiome over other sources of microbiota for development.
In the wild, dung beetle eggs and larvae are naturally exposed to varying environmental conditions, such as changes in moisture levels and temperature. When the researchers introduced these environmental challenges to the lab-reared beetles, they found that the beneficial effects of the maternal microbiome in development were further amplified. Under standard conditions, the microbiome only affected growth but didn’t affect larval survival; however, when dung beetle eggs were hatched in dry conditions (desiccation stress), the microbiome became very important for survival. Similarly, when the temperature fluctuated along a day-night rhythm, the importance of the maternal microbiome in maintaining larval growth rate was much enhanced.
This study shows that the maternal microbiome is important for dung beetle development and survival and becomes even more important under environmentally challenging conditions. The experiments fit with several other recent studies demonstrating that there is much more to inheritance than the transmission of genes, with parents frequently behaving in ways that pass key developmental resources on to their offspring.
For more detail, read the paper here:
Developmental and Ecological Benefits of the Maternally Transmitted Microbiota in a Dung Beetle.
Schwab DB, Riggs HE, Newton ILG, Moczek AP. 2016. Am Nat 188(6):679-692.
