Parallel evolution in sympatric, hybridizing species: performance ofColiasbutterflies on their introduced host plants

Abstract

Shared ancestry and introgression can contribute to genetic similarity between hybridizing species, and it is generally difficult to disentangle these causes. However, shared ancestry plays a more limited role in traits that have recently undergone parallel directional selection in the two species, permitting the role of introgression to be better understood. The butterflies Colias eurytheme (Boisduval) and Colias philodice (Godart) (Lepidoptera, Pieridae) are native to North America and have shifted their host ranges in parallel onto several introduced weedy and agricultural legumes. These butterflies hybridize at moderate rates throughout their range, and there is a strong possibility that they could be sharing host-associated adaptations. We split families of each species among nine introduced, prospective hosts and measured survivorship, larval duration, pupal weight, and a new variable, effective daily growth rate (DGR), analogous to a compound daily interest rate in economics. We found strong effects of host, sex, and family (species), but negligible effects of the host*species interaction that would indicate species-specific differences in performance on different hosts. We found speciesspecific life-history differences: C. eurytheme matured significantly later and reached a significantly larger body size than C. philodice while growing at the same DGR. Protandry was strong, and males, in addition to pupating sooner than females, grew significantly faster than females as measured by DGR. We measured broad-sense heritabilities and genetic correlations for host-associated performance variables. Most pairwise comparisons of performance among hosts and most pairwise comparisons between performance variables showed positive genetic correlations, except survivorship where little heritability was found. Nevertheless, a factorial multivariate analysis of variance of G-matrices showed highly significant species, host, and host*species interactions, suggesting differentially evolving genetic architectures underlying host adaptation in these two species, despite the small differences in overall performance. At least some of the genes affecting host performance in Colias are likely to be in the small, species-diagnostic regions and not shared via introgression between these hybridizing species. For biologists interested in the evolutionary ecology of their host associations, including applied biologists managing their agricultural pest potential, C. eurytheme and C. philodice are most usefully studied as if they were a single polymorphic species wherever they co-exist. In studying species that hybridize readily with a sympatric congener, it may often be necessary to include the second species in the experimental design.

Impacts of climate warming on hybrid zone movement: Geographically diffuse and biologically porous “species borders”

“…comm.) has been difficult to partition or categorize, and remains academically unsettled (Dethier, 1954;Fox & Morrow, 1981;Denno & McClure, 1983;Diehl & Bush, 1984;Cobb & Whitham, 1993;Harrison, 1998;Howard & Berlocher, 1998;Mopper & Strauss, 1998;Berlocher & Feder, 2002;Dres & Mallet, 2002;Scriber, 2002b;Sperling, 2003;Porter & Levin, 2007;Tilmon, 2008). New molecular genomic techniques have given some insight and elicited considerable excitement Fig.…”

“…comm.) has been difficult to partition or categorize, and remains academically unsettled (Dethier, 1954; Fox & Morrow, 1981; Denno & McClure, 1983; Diehl & Bush, 1984; Cobb & Whitham, 1993; Harrison, 1998; Howard & Berlocher, 1998; Mopper & Strauss, 1998; Berlocher & Feder, 2002; Dres & Mallet, 2002; Scriber, 2002b; Sperling, 2003; Porter & Levin, 2007; Tilmon, 2008). New molecular genomic techniques have given some insight and elicited considerable excitement about finding the genetic basis of ecological divergence and speciation (Wu, 2001; Hey, 2006; Putnam et al , 2007; Gompert et al , 2008; Nosil et al , 2009a, 2009b; Via, 2009; Kane et al , 2009; Maroja et al , 2009a).…”

Integrating ancient patterns and current dynamics of insect–plant interactions: Taxonomic and geographic variation in herbivore specialization

“…comm.) has been difficult to partition or categorize, and remains academically unsettled (Dethier, 1954; Fox & Morrow, 1981; Jaenike, 1990; Denno & McClure, 1983; Diehl & Bush, 1984; Luebke et al , 1988; Cobb & Whitham, 1993; Harrison, 1998; Howard & Berlocher, 1998; Mopper & Strauss, 1998; Berlocher & Feder, 2002; Dres & Mallet, 2002; Scriber, 2002b; Sperling, 2003; Porter & Levin, 2007; Abrahamson & Blair, 2008; Tilmon, 2008). While of great ecological and evolutionary interest, the correlation between the oviposition preference and the larval performance on different hosts has been variable for several reasons (Wiklund, 1975; Thompson, 1988; Agosta, 2006; Craig & Itami, 2008; Friberg & Wiklund, 2009; but see Berenbaum & Feeny, 2008).…”

Molecular evidence for hybridization in Colias (Lepidoptera: Pieridae): are Colias hybrids really hybrids?

“…The phylogenetic relationships among C. eurytheme, C. eriphyle, and C. philodice are poorly understood. The species have undergone parallel evolution, and their traits are similar in many respects (Porter and Levin ). Putative hybrids occur between C. eurytheme and C. philodice in the eastern United States (Gerould ) and between C. eurytheme and C. eriphyle in the west (Taylor ).…”