Developmental Symbiosis as Protection
Embryos often do not have the time to form an immune system before they encounter pathogenic microbes. Developmental symbioses can protect the embryo against such predation.
How Do Symbionts Get Together?
How are developmental symbioses established? Mechanisms of external transfer (from the environment), horizontal transfer (from other members of the species), and vertical transfer (in the oocytes) have been documented.