Developmental biology and alternative life styles

Synopsis

Sexual differentiation is a paradigm case illustrating the potential of an animal to express alternative life styles. In this paper the morphogenesis of the male and female patterns are reviewed, especially in relation to the morphogenesis of the genital ducts. The stepwise events of morphogenesis are followed in terms of the cells as building blocks and attention is given to the plasticity of morphogenesis in this system. The suggestion is made that if the morphogenesis of this system is so plastic, then one could expect the inevitability of particular morphological and physiological arrangements becoming fixed following selection, as possibly seen, for example, in the diversity of species-specific variations found amongst the genitalia of insects. Following the discussion on the cellular strategies for the construction of the male and female ducts, the next part of this paper examines the underlying genetic structure upon which sexual dimorphism is based. The third theme poses the question as to whether there is an ontogenetic memory of past adaptations within the embryo which could be used to accelerate the rate of adaptation of a species to a new environmental challenge. In addressing this problem the example of the globin genes and globins, as well as of melanization, is considered, especially in relation to the fact that genes come in pieces.