1. Although there is a great deal of theoretical and empirical data about the life history responses of time constraints in organisms, little is known about the latitude-compensating mechanism that enables northern populations' developmental rates to compensate for latitude. To investigate the importance of photoperiod on development, offspring of the obligatory univoltine damselfly Lestes sponsa from two populations at different latitudes (53°N and 63°N) were raised in a common laboratory environment at both northern and southern photoperiods that corresponded to the sites of collection.
2. Egg development time was shorter under northern photoperiod regimes for both populations. However, the northern latitude population showed a higher phenotypic plasticity response to photoperiod compared with the southern latitude population, suggesting a genetic difference in egg development time in response to photoperiod.
3. Larvae from both latitudes expressed shorter larval development time and faster growth rates under northern photoperiod regimes. There was no difference in phenotypic plastic response between northern and southern latitude populations with regard to development time.
4. Data on field collected adults showed that adult sizes decreased with an increase in latitude. This adult size difference was a genetically fixed trait, as the same size difference between populations was also found when larvae were reared in the laboratory.
5. The results suggest phenotypic plasticity responses in life history traits to photoperiod, but also genetic differences between north and south latitude populations in response to photoperiod, which indicates the presence of a latitudinal compensating mechanism that is triggered by a photoperiod.