Local adaptation in a plant herbivore interaction depends on the spatial scale

Abstract

Local adaptation has central importance in the understanding of co-evolution, maintenance of sexual reproduction, and speciation. We investigated local adaptation in the alkaloid-bearing legume Crotalaria pallida and its seed predator, the arctiid moth Utetheisa ornatrix, at different spatial scales. When we studied three populations from south-east Brazil (150 km apart), we did not find evidence of local adaptation, although we did find interpopulational differences in herbivore performance, and a significant interaction between herbivore sex and plant population. These results indicate that both moth and plant populations are differentiated at the regional scale. In a comparison of populations from Brazil and Florida, the herbivore showed local adaptation to its host plant; for both moth populations, the pupae were heavier when the larvae ate the sympatric than the allopatric host population. We discuss the scale dependence of our results and the possible causes for the lack of local adaptation at the regional scale, even in the presence of plant and moth differentiation. The results obtained demonstrate the importance of studying co-evolution and local adaptation at different geographical scales.

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

“…Nitrogen content varied at the continental scale, the same scale on which adaptation was observed. However, this trait is unlikely to be the main driver trait because larval consumption of seeds from Florida and Brazil did not differ [18]. Finally, trichomes are also unlikely to be the main driver of local adaptation patterns because, in the laboratory tests, leaves were offered only during the first two days, and larval mortality during this period was similar in the two plant populations [18].…”

“…However, this trait is unlikely to be the main driver trait because larval consumption of seeds from Florida and Brazil did not differ [18]. Finally, trichomes are also unlikely to be the main driver of local adaptation patterns because, in the laboratory tests, leaves were offered only during the first two days, and larval mortality during this period was similar in the two plant populations [18]. Therefore, the patterns of adaptation observed at the continental scale may be driven by another resistance trait not yet measured (possible candidate traits include isoflavonoids, non-protein amino acids and proteinase inhibitors [28]–[32]), or, more likely, by the emerging property of the synergistic effect of several of these traits [27].…”

“…In 2006, we started the plants in April and collected the samples in October. Although the conditions of the greenhouses differed between the countries, we have evidence showing that any such difference did not affect our results [18]. For the EFNs experiment, we used a set of plants grown in the Brazilian greenhouse in 2005.…”

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

“…Divergent natural selection can be experienced continentally, regionally, locally and within single populations (Scriber, 2002a; Thompson, 2005; Eckert et al , 2008; Cogni & Futuyma, 2009; Laine, 2009). The “abundant center hypothesis” suggests abundant populations exist in the center of a species range but decline near range edges (Sagarin & Gaines, 2002; Gaston, 2003; Sagarin et al , 2006; Hellmann et al , 2008; but see Eckert et al , 2008).…”

“…Local adaptations for insect–plant interactions create coevolutionary/or geographic mosaics that depend on the spatial scale (see Thompson, 1994, 2005; Bossart & Scriber, 1999; Scriber, 2002a, 2002b; Cogni & Futuyma, 2009) and also with their interaction with the abiotic environment (Scriber & Lederhouse, 1992; Laine, 2008, 2009). In Florida, the generalist P. glaucus species feeds only on sweet bay of the Magnoliaceae and shows higher survival and faster growth rates than other P. glaucus populations (but not higher efficiencies; Scriber, 1986a).…”