Modelling single nucleotide effects in phosphoglucose isomerase on dispersal in the Glanville fritillary butterfly: coupling of ecological and evolutionary dynamics

Dispersal comprises a complex life-history syndrome that influences the demographic dynamics of especially those species that live in fragmented landscapes, the structure of which may in turn be expected to impose selection on dispersal. We have constructed an individual-based evolutionary sexual model of dispersal for species occurring as metapopulations in habitat patch networks. The model assumes correlated random walk dispersal with edge-mediated behaviour (habitat selection) and spatially correlated stochastic local dynamics. The model is parametrized with extensive data for the Glanville fritillary butterfly. Based on empirical results for a single nucleotide polymorphism (SNP) in the phosphoglucose isomerase (Pgi) gene, we assume that dispersal rate in the landscape matrix, fecundity and survival are affected by a locus with two alleles, A and C, individuals with the C allele being more mobile. The model was successfully tested with two independent empirical datasets on spatial variation in Pgi allele frequency. First, at the level of local populations, the frequency of the C allele is the highest in newly established isolated populations and the lowest in old isolated populations. Second, at the level of sub-networks with dissimilar numbers and connectivities of patches, the frequency of C increases with decreasing network size and hence with decreasing average metapopulation size. The frequency of C is the highest in landscapes where local extinction risk is high and where there are abundant opportunities to establish new populations. Our results indicate that the strength of the coupling of the ecological and evolutionary dynamics depends on the spatial scale and is asymmetric, demographic dynamics having a greater immediate impact on genetic dynamics than vice versa

Functional ecological implications of intraspecific differences in wing melanization in Colias butterflies.

Variation in the degree of insect wing melanin affects thermoregulation, and is expected to be adapted to local environmental conditions, for example over an elevational gradient. The effects of melanization on flight activity and egg maturation rate were assessed in the closely related butterflies Colias philodice eriphyle and C. eurytheme using experimental manipulation of wing darkness and transplant experiments between high and low elevation sites. Experimental manipulation of wing darkness in C. p. eriphyle demonstrated that light males had reduced flight activity at high elevations, and darkened males had reduced flight activity at low elevations. In contrast, the transplant experiments revealed asymmetrical adaptation for male C. p. eriphyle. At high elevations darker, high-elevation males had higher flight activity than lighter, low-elevation males, but there was no difference between the two groups at low elevation. For females, melanization had no effect on flight activity. However, an increase in female C. eurytheme wing darkness led to a significantly higher egg maturation rate at cold ambient temperatures, which may increase female reproductive output under natural conditions. Therefore, dispersers moving down in elevation may be more successful than those moving up. © 2004 The Linnean Society of London