Optimizing development time in a seasonal environment: The 'ups and downs' of clinal variation.

This paper explores the problem of adapting development time to changes in the length of time conditions are favourable for growth and reproduction ('season length'). It is shown that systematic changes in season length along some gradient such as latitude can generate either simple clines in development time or 'saw-tooth' clines. The relationship between development time and body size gives rise to a corresponding variation in body size. The generation of a 'saw-tooth' cline does not require sharp environmental changes. Both types of clinal variation are observed in insects.