A male Ranitomeya variabilis poison frog carrying his tadpole. Image credit: Marie-Therese Fischer (CC BY 4.0)
The first microbes that animals encounter after birth can impact their health and development for life. In many species, these microbes are passed from parent to offspring during close contact or while caring for the young – a process known as vertical transmission. While this has been well studied in mammals, we know much less about how, or even if, microbes are passed from parent to offspring in amphibians.
Amphibians rely on healthy skin to breathe and regulate water and salt levels, and skin-dwelling microbes also help protect them from infections. Many tropical frogs also display striking forms of parental care. For example, many poison frog parents carry their newly hatched tadpoles from land to small pools of water on their backs. This journey can take hours or even days, creating a perfect opportunity for microbes to transfer from parent to offspring through skin-to-skin contact.
Despite this, it remains unclear how parental care in frogs influences the composition of microbes in their offspring. To find out more, Fischer et al. explored when and how poison frog tadpoles acquire their skin microbes. First, the researchers examined whether frog embryos are exposed to microbes while still developing inside the egg. Then they tested whether physical contact during transport – when the parent carries the tadpole – actually passes microbes to the tadpole, and whether those microbes remain on the tadpole’s skin as it grows.
To answer these questions, Fischer et al. combined lab experiments with field research. Using DNA sequencing to study the bacteria living on tadpole skin, Fischer et al. found that most microbes begin colonizing only after the tadpoles hatch from their egg membranes, just before they are carried to water by a parent. In laboratory experiments, tadpoles picked up microbes through direct contact with the skin of the parent carrying them. In wild frogs, it was found that while microbes do transfer, only a few persisted on the tadpoles’ skin over time.
These findings are important for understanding how microbial communities are formed and how parental care shapes this process. For frogs, skin microbes provide a crucial defense against deadly diseases such as chytrid fungus. By understanding how and when amphibians acquire beneficial microbes, we can help protect the habitats and behaviors that support this process and better conserve vulnerable species.
