Varying Herbivore Population Structure Correlates with Lack of Local Adaptation in a Geographic Variable Plant-Herbivore Interaction

Local adaptation of parasites to their hosts due to coevolution is a central prediction of many theories in evolutionary biology. However, empirical studies looking for parasite local adaptation show great variation in outcomes, and the reasons for such variation are largely unknown. In a previous study, we showed adaptive differentiation in the arctiid moth Utetheisa ornatrix to its host plant, the pyrrolizidine alkaloid-bearing legume Crotalaria pallida, at the continental scale, but found no differentiation at the regional scale. In the present study, we sampled the same sites to investigate factors that may contribute to the lack of differentiation at the regional scale. We performed field observations that show that specialist and non-specialist polyphagous herbivore incidence varies among populations at both scales. With a series of common-garden experiments we show that some plant traits that may affect herbivory (pyrrolizidine alkaloids and extrafloral nectaries) vary at the regional scale, while other traits (trichomes and nitrogen content) just vary at the continental scale. These results, combined with our previous evidence for plant population differentiation based on larval performance on fresh fruits, suggest that U. ornatrix is subjected to divergent selection even at the regional scale. Finally, with a microsatellite study we investigated population structure of U. ornatrix. We found that population structure is not stable over time: we found population differentiation at the regional scale in the first year of sampling, but not in the second year. Unstable population structure of the herbivore is the most likely cause of the lack of regional adaptation

Lectins from seeds of Crotalaria pallida (smooth rattlebox)

A lectin from the seeds of Crotalaria pallida (CPL), with an apparent molecular mass of 30 kDa, determined by SDS-polyacrylamide gel electrophoresis, showed human type A and B erythrocytes agglutination activity, which is inhibited by raffinose and galactose. The lectin requirement for divalent cation was demonstrated with EDTA/EGTA blocking hemagglutination activity. Although the N-terminal amino acid sequence of CPL is identical to another lectin from Crotalaria striata, which is taxonomically synonymous to Crotalaria pallida, these lectins differ in amino acid composition and hemagglutination properties. (C) 2002 Published by Elsevier Science Ltd.60544144