Allozyme variability in central, peripheral and isolated populations of the scarce heath (Coenonympha hero: Lepidoptera, Nymphalidae); implications for conservation

Genetic drift tends to lower geneticvariability in peripheral and isolatedpopulations. These populations also tend todiverge from more central populations if thedegree of isolation is high enough. Theseprocesses could have opposite effects on thevalue of the respective populations in thespecies conservation context. On the basis ofallozyme polymorphism data, we compare geneticvariability and differentiation between core,peripheral and isolated populations of thescarce heath, a butterfly endangered inNorthern and Central Europe. Genetic variationwas lowest in populations that were bothperipheral and isolated(P = 16.5%, Hobs = 0.017),and highest in the central populations(P = 35%,Hobs = 0.052). However, overall variability waslow also in the core area compared to that ofclosely related butterfly species. Theperipheral region was more differentiated fromthe other regions than the isolated region(F_PC = 0.118, F_PI = 0.257,F_IC = 0.068). This study indicated thatisolation in combination with marginality havecaused an erosion of the gene pool. Theobserved patterns may be caused both by thecontemporary population structure of thespecies, as well as by the colonisationhistory. Both genetic and ecological evidencesuggests that the species is likely to followthe stepping-stone model of dispersal.     

Phenotypic plasticity in a generalist insect herbivore with the combined use of direct and indirect cues

Ultimate causes of phenotypic plasticity in visual appearance are frequently related to increasing the degree of crypsis in a way specific to the environment. The cues used to elicit such plastic responses may be both direct (i.e. straightforward background matching) as well as indirect. In the latter case, cues other than the visual signals from of the environment are used to predict the phenotype best corresponding to the particular situation. On the basis of a series of laboratory experiments we show that the remarkable variability in the visual appearance of the larvae of the geometrid moth Ematurga atomaria, though genetically based in part, involves a substantial environmental component. Using multiple correspondence analysis, we transformed the multidimensional variation in colour and pattern into two dimensions interpretable as patterning and darkness. Plastic changes in the darkness of the larvae were elicited by direct cues: the larvae were darker when reared on dark host‐plants. Host‐specific degree of patterning was also induced in absolute darkness which indicates the use of an indirect cue. This was unexpected because the study species is broadly polyphagous, and thus not likely to have evolved adaptations specific to particular host‐plant species. Indeed, the larvae of E. atomaria originating from geographic populations using different host‐plants showed analogous plastic responses which indicates that the link between the indirect cue and visual appearance of the host needs not to be specific to plant species. In an additional experiment, we showed that surface roughness is a likely candidate to serve as the proximate cue for determination of some pattern elements, a case not reported for insect larvae earlier.     

Why is body size more variable in stressful conditions: an analysis of a potential proximate mechanism

Patterns of variability in quantitative traits across environmental gradients have received relatively little attention in evolutionary ecology. A recent meta-analysis showed that relative phenotypic variability in body size tends to decrease with improving environmental conditions. This pattern was explained by introducing the concept of upper threshold size to a general optimality model of individual growth but alternative explanations certainly exist. In particular, it is frequently observed in insects that variability in individual growth rates decreases with improving environmental conditions. Here we explore the effect of this phenomenon on environment-specific variability in adult sizes. A quantitative model shows that relative variability in adult sizes is independent of environmental quality if absolute variability in growth rates remains constant across the gradient of environmental quality. Deviations from this borderline case are definitely realistic in both directions. Both negative and positive relationships between relative variability of body size and environmental quality can thus be predicted to arise as a consequence of environment-specific variability in growth rates. The variability itself can be both genetic or environmental in its nature. We present empirical data which support both the assumptions and conclusions of our model-based analysis, as well as emphasize the advantages of controlled experiments for understanding the proximate sources of phenotypic variance.