Impact of attack by Gnorimoschema gallmakers on their ancestral and novel Solidago hosts

Abstract

Interactions between insect herbivores and host plants can involve herbivorehost pairs that are evolutionarily ancient or only recently associated. Novel herbivore-host species pairs are continually being formed via host shifts, dispersal, and increasingly via anthropogenic introductions. Conceptual models of enemy-victim coevolution (specifically, the evolution of plant tolerance and of insect virulence) suggest that the impact of an herbivore on its novel host should, at least at first, be more intense than its impact on its ancestral host. We tested this hypothesis for the specialist gallmaking caterpillar Gnorimoschema gallaesolidaginis (Lepidoptera: Gelechiidae) on its ancestral and novel hosts, Solidago altissima and S. gigantea. We measured aboveground ramet mass for paired attacked and unattacked ramets of each species at two sites (Fredericton, NB, and Toronto, ON, Canada), and also measured allocation of tissue mass to stems, leaves, and flowers in galled and ungalled ramets. G. gallaesolidaginis attack reduced ramet growth considerably more on S. gigantea, the novel host, consistent with the coevolutionary hypothesis. We were unable to detect reallocation of tissues in galled ramets as a mechanism for tolerance, and found no intraspecific difference in the impact of gallmaking on allocation patterns. Herbivore host shifts between alternative native hosts will provide an excellent opportunity to understand the evolutionary history of novel herbivore-host associations, particularly (as in the Solidago system) when multiple insect herbivores have host-shifted across the same plant pair.

Invasion success of a scarab beetle within its native range: host range expansion versus host-shift

“…Heard & Kitts (2012) suggested that host-shifts can be followed by host-associated differentiations that can result in the evolution of new biotypes of specialist races, or so-called host-races (Diehl & Bush, 1984; Drès & Mallet, 2002). Over the last decades, numerous examples of host-race formation in insects have been described.…”

“…Even though the ecological host-shift theory appears to conform to this case study, the slight variation in terms of weight gain between the two populations, following the artificial host-shift on clover suggests that some level of evolutionary change has occurred for the population collected from exotic pastures. Heard & Kitts (2012) suggested that host-shifts can be followed by host-associated differentiations that can result in the evolution of new biotypes of specialist races, or so-called host-races ( Diehl & Bush, 1984 ; Drès & Mallet, 2002 ). Over the last decades, numerous examples of host-race formation in insects have been described.…”

Synergistic and additive effects of drought stress and simulated herbivory on two goldenrods, Solidago altissima and S. gigantea

“…These species both experience frequent herbivory and periodic episodes of drought. These closely related and ecologically similar species are a widely used model system for studies of plant-insect interactions (e.g., Abrahamson and Weis 1997;Heard and Kitts 2012;Williams and Avakian 2015), plant invasions (e.g., Sakata et al 2015;Szymura and Szymura 2016), life history evolution (e.g., Schmid et al 1995;Hafdahl and Craig 2014), and other issues in evolutionary ecology. We examined the impact of drought stress and early-season clipping on different plant structures (both aboveground and belowground) and on patterns of resource allocation among them.…”

Use of Host-Plant Trait Space by Phytophagous Insects during Host-Associated Differentiation: The Gape-and-Pinch Model

“…Because attack rates for most Solidago herbivores are low, achieving powerful hypothesis tests for any herbivore will entail marking very large numbers of ramets-especially since ramet selection must be done before attack begins to avoid distortions of attack-space measurements if trait values change under herbivore attack. In Solidago, for instance, ramet biomass and height are often reduced by herbivory [91][92][93]. I am currently expanding on the illustrative study with the goal of securing larger sample sizes for the herbivores studied here and acceptable sample sizes for many more herbivores.…”