FIGURE 4.

Potential transgenerational impacts of environmental exposures. Top: Heuristic depiction of fly development in an unperturbed landscape (left) and in a landscape modified by exposure to a strong environmental stress (right). The flow in a modified canal leads to characteristic modifications in somatic tissues of the fly and/or its germline and/or its microbiome. Bottom: Illustration of a few possible scenarios of development in subsequent offspring of exposed ancestors. Scenario (1): if the parental change in the environment does not modify the genome or the epigenetic state of the fertilized egg and, in addition, the microbiome is either unperturbed or fully restored (“no memory,” most left panel), the offspring may follow the regular trajectory in an unperturbed landscape. Scenarios (2 and 3): if the initial state of the fertilized egg and/or the microbiome associated with the egg are modified following the parental exposure (“memory”), the development of the offspring may differ from their parents even if the external environmental reverts to normal already during the parental generation. In these cases, alteration in offspring development might reflect localization to a different canal in the original or in a modified landscape (scenarios 2 and 3, left trajectory), or localization to a canal that has been modified by the impact of having modifications in the fertilized egg and/or the microbiome (scenario 3, right trajectory). Scenarios (4 and 5): if the external environmental stress persists beyond the parental generation it may again lead to changes in the entry point and shape of the canal (“no accumulation,” scenario 4) as well as further modify the entry point and shape (“accumulation,” scenario 5).