Additional Cases of Progenesis with a
Similar Ecological Basis

In my cursory examination of an immense and unfamiliar literature, I have been impressed with the common association of facultative progenesis and r selection for the exploitation of ephemeral and superabundant resources. The progenetic phase can be switched off by an automatic response to crowding or dwindling resources. Mobile forms are then produced for the discovery of new resources, although the development of complex sensorimotor systems requires a longer generation time, often with an increased number of molts. This pattern arises again and again in completely unrelated groups, including the following:

1. The mite Siteroptes graminum is also a fungal feeder (Rack, 1972). When food is superabundant, it becomes sexually mature at an early stage (Fig. 53). Moreover, the progenetics are "born" sexually mature since larval stages develop in the mother's body. As resources

Fig. 53. Progenesis in the mite Siteroptes graminum. A sexually
mature female with one male and four females growing within
her body. (From Rack, 1972.)