Growth rate and life span in Drosophila V. The effect of prolongation of the period of growth on the total duration of life (J.H. Northrop, 1917)--revisited.

Sixty-eight years ago Northrop observed a constant life span in Drosophila after a progressive increase of the duration of development of the flies achieved by using a yeastless nutrient medium to which he added yeast with a progressively increasing delay. This evidence against the more recent concept of an increased life span following an experimentally decreased developmental rate has generally been ignored due, presumably, to the imprecise methodology employed by Northrop at a time that Drosophila research was just commencing. We describe here a study that aimed at re-examining and extending Northrop's work by developing the flies in either a yeastless or a lightly yeasted medium. While in a yeastless medium development of flies was virtually arrested until yeast was added, in the yeasted medium a slow growth of the larvae was possible before yeast was added. With another method, larval growth rate was reduced over the entire developmental period by adding a relatively low amount of yeast in four portions and with various delays between portions (the first portion being added without delay). Our study confirmed the "Northrop-effect", i.e. the absence of an effect on life span from increased duration of development by a virtual arrest of growth of the larvae for a number of days. Further, it showed that manipulation of growth rate by portioning the yeast amount did not unequivocally support the concept that a lower growth rate leads to an increased life span.