Latitudinal and local geographic mosaics in host plant preferences as shaped by thermal units and voltinism in Papilio spp. (Lepidoptera)

Abstract

Abstract. Laboratory and field tests support the "voltinism-suitability hypothesis" of host selection at various latitudes as well as in local "cold pockets": The best hosts for rapid development will be selected by herbivorous insects under severe thermal constraints for completion of the generation before winter. Papilio canadensis and P. glaucus females do select the best hosts for rapid larval growth in Alaska and in southern Michigan, but not in northern Michigan and southern Ohio. In addition to latitudinal patterns, local host preferences of P. canadensis are described in relation to "phenological twisting" of leaf suitability for larval growth in cold pockets with "thermally constrained" growing season lengths. White ash leaves (Fraxinus americana) have the highest nutritional quality (relative to cherry, aspen, birch, and other local trees) throughout June and July for P. canadensis populations inside the cold pocket, but not outside. In all areas outside the cold pockets, even with bud-break occurring much later than other tree species, ash leaves rapidly decline in quality after mid-June and become one of the worse tree host species for larvae. This temperature-driven phenology difference creates a geographic mosaic in host plant suitability for herbivores. However, we also report here that the cold pocket of northern Michigan has basically disappeared since 1998. Implications of these changes are discussed in relation to volt inism and host plant selection.Various physiological and ecological adaptations to thermal unit constraints are evident with both species of naturally hybridizing butterflies (P. canadensis to the North and P. glaucus to the South). The rapid regional climate warming since 1998 in the Great Lakes region has allowed us to document some critical aspects of gene flow via analysis of independent "species-diagnostic" trait clines (including morphological, biochemical, and physiological characters). Narrower black bands on hind-wings, larger fore-wings, larval detoxification abilities for tulip tree leaves, behavioral preference of tulip tree leaves, and species-diagnostic allozymes such as PDG (x-linked) and HK (autosomal) provide evidence of these genodynamics. Laboratory hybridization studies (providing known reference groups) and field observations along the hybrid zone show that gene flow between P. glaucus and P. canadensis has recently been extensive across the historical hybrid zone.

Slow and fast development in ladybirds: occurrence, effects and significance

“…Variations in environmental factors, such as diet, temperature, and photoperiod (Ernsting and Issaks, 2000;Davidowitz et al, , 2005Plaistow et al, 2005) and the number of predators (Scriber, 2002;Röder et al, 2008;Chown and Gaston, 2010) are well known regulators of change in developmental rate. Such effects of environmental factors on development rate are well researched in a large number of organisms (e.g.…”

Evolution of insect‐plant relationships: chemical constraints, coadaptation, and concordance of insect/plant traits

“…However the recent few years (1996)(1997)(1998)(1999)(2000) have been much warmer than average, with 1998 the warmest year on record (Hughes, 2000), which has significantly affected the gene flow and trait cline patterns of these swallowtail butterflies across these colder areas of northern Michigan. These previously detectable geographic behavioral mosaics in local P. canadensis host preferences (shaped by local climatic cold pocket selective pressures during the 1980s and early 1990s) may have largely disappeared with the significant recent regional warming in northern Michigan (Giroux, 1998;Scriber, 2002b). It has been hypothesized that such thermal constraints from late spring and early fall freezes may be responsible for maintaining high frequencies of hybrid (introgressed) genotypes in giant silkmoths of the Hyalophora cecropia species group in California.…”

“…These regional climate changes appear to be altering the suite of 'diagnostic' population traits of the P. canadensis populations with an asymmetrical introgression northward across the hybrid zone (from Wisconsin in the West, throughout Michigan and New York to Vermont and Massachusetts in the East; Ording, 2001;Scriber, 2002b). This recent interspecific hybrid introgression includes morphological, behavioral, physiological detoxification, diapause, and molecular traits (see below).…”

“…Our own analysis of interspecific hybridization of Papilio glaucus and P. canadensis has shown that thermal units are resources themselves, affecting the quality of the 'habitat' for growth and reproduction (thereby locally selecting for certain host plant species of the highest nutritional quality; Scriber, 1996a). Recent surveys of species and hybrid 'diagnostic' morphological traits illustrate that trait clines are more precisely predicted by thermal unit accumulations (degree days) than by latitude or geographic distance, especially in mountainous areas with long steep river valleys as in New York State, Pennsylvania, and New England (Scriber, 2002b). These qualitative differences in intervening habitat quality, phytochemistry, and other environmental resources are also temporally variable, affecting the preference-performance relationships of herbivores (Cronin et al, 2001).…”

“…Since a 'true second generation' requires 2600-2800 F degree days it is likely that 'fractional voltinism' (with mortality of those failed attempts at a second generation exists in these areas of NY/VT; Scriber, 2002b). Morphological evidence from wing band patterns and diagnostic allozymes (Pgd-100 and Hk-100;Ording 2001;Scriber, 2002b) strongly suggest this geographically-widespread interspecific hybridization (northward movement of 'glaucus-like' traits) is a recent happening, perhaps enhanced by regional climate warming from 1998-present (Parmesan et al, 1999;Hughes, 2000;Scriber, 2002b).…”