Genetic shift in photoperiodic response correlated with global warming

Abstract

To date, all altered patterns of seasonal interactions observed in insects, birds, amphibians, and plants associated with global warming during the latter half of the 20th century are explicable as variable expressions of plastic phenotypes. Over the last 30 years, the genetically controlled photoperiodic response of the pitcher-plant mosquito, Wyeomyia smithii, has shifted toward shorter, more southern daylengths as growing seasons have become longer. This shift is detectable over a time interval as short as 5 years. Faster evolutionary response has occurred in northern populations where selection is stronger and genetic variation is greater than in southern populations. W. smithii represents an example of actual genetic differentiation of a seasonality trait that is consistent with an adaptive evolutionary response to recent global warming.

Figure 1

Localities at 30–50°N latitude from which W. smithii were collected from S. purpurea (Inset) from the overwintering generation in 1972, 1988, 1993, and 1996. For each pie diagram, a blackened quadrant indicates a year that larvae were collected at that locality.

Figure 2

Critical photoperiods of W. smithii collected during the overwintering generation from 1972 to 1996 determined from static (1972, 1996) or changing (1988, 1993) photoperiods. Analysis of covariance (Table 1) indicated significantly steeper slopes for the earlier year in each comparison, meaning that shifts toward shorter critical photoperiods (more southern phenotypes) increased with latitude.