Plant polyploidy and non-uniform effects on insect herbivores

Abstract

Genomic duplication through polyploidy has played a central role in generating the biodiversity of £ower-ing plants. Nonetheless, how polyploidy shapes species interactions or the ecological dynamics of communities remains largely unknown. Here we provide evidence from a 4 year study demonstrating that the evolution of polyploidy has reshaped the interactions between a widespread plant and three species of phytophagous moths. Our results show that polyploidy has produced non-uniform e¡ects, with polyploids less attacked by one insect species, but signi¢cantly more attacked by two other species. These results suggest that the evolution of plant polyploidy may not generally confer uniform resistance to multiple species of insect herbivores. In the absence of such a uniform release, the extreme evolutionary success of polyploid plants is probably due to factors other than escape from herbivory. Together, these results suggest that a primary consequence of plant polyploidy may be to shape the ecological structure of plantî nsect interactions, thereby providing opportunities for diversi¢cation in both plant and insect taxa.

Selection for Phenotypic Divergence Between Diploid and Autotetraploid Heuchera Grossulariifolia

“…Perhaps more likely is the possibility that slight differences in the pollinator communities of the two ploidies observed at this site (Segraves and Thompson 1999) might exert different patterns of phenotypic selection that have little or nothing to do with the presence or absence of the other cytotype. Similarly, large differences in the community of floral parasites associated with each ploidy at this site Nuismer and Thompson 2001) might also lead to differing patterns of phenotypic selection that, again, have nothing to do with the other cytotype. Distinguishing between these various possible sources of divergent selection will be an important focus of future work.…”

“…Diploid and autotetraploid plants within this site are very well mixed spatially and show little evidence of microhabitat selection. In addition, although the two cytotypes are quite differentiated for some phenotypic traits, they do exhibit substantial overlap for several other potentially important traits, such as flowering phenology Nuismer and Thompson 2001). As a consequence, substantial scope exists for further phenotypic divergence to evolve.…”

“…Ploidy was determined through visual inspection of several key morphological traits (flower color, flower size, scape length, scape pubescence) that allow ploidy to be assigned rapidly and with a very high degree of accuracy Nuismer and Thompson 2001). Our initial plan was to use these same individuals throughout the three years of the study.…”

“…Plants growing at this site are regularly attacked by several species of insect parasite Nuismer and Thompson 2001) and are pollinated by multiple species of insect pollinator (Segraves and . More recent work has shown, however, that a single pollinator species, Bombus centralis, is responsible for the bulk of H. grossulariifolia pollination along the Salmon River (K. F. Merg and J. N. Thompson, unpubl.…”

Can enemy release explain the invasion success of the diploid Leucanthemum vulgare in North America?

“…Yet, in contrast to a generally larger plant size of polyploids (Ramsey and Ramsey 2014), the diploid L. vulgare produced more shoots and flower heads than the tetraploid L. ircutianum and our results suggest that the higher number of shoots of L. vulgare contributed to the higher attack rates of L. vulgare by D. stolidum and C. trisulcatus. Several field studies found differences in herbivore attack between closely related taxa differing in ploidy level (Thompson et al 1997;Nuismer and Thompson 2001;Münzbergová 2006;Arvanitis et al 2008;Halverson et al 2008;Arvanitis et al 2010;Richardson and Hanks 2011;Münzbergová et al 2015). However, depending on plant taxa, herbivore species or even the population examined, polyploid taxa were either less, more or equally attacked by herbivores than the closely related diploids.…”