Intraspecific life history variation in the introduced range of Cynoglossum officinale

Abstract

All organisms must allocate resources to reproduce and survive. The study of intraspecific life history variation can provide insight into how different selective pressures, such as herbivory or climate, can favor different life history strategies and constrain others depending on which life stages are most vulnerable to the selective pressures. I examined how variation in herbivory and climate influences variation in the flowering size of plants and the occurrence of semelparity versus iteroparity at sites across part of the introduced range of an invasive plant, houndstongue (Cynoglossum officinale, Boraginaceae). Houndstongue is a short-lived semelparous perennial in its native range. In its introduced range, a previous study documented increased rates of iteroparity and a higher threshold flowering size compared to the native range. I hypothesized that the recent introduction of a specialist biocontrol root-boring insect (Mogulones crucifer) would decrease threshold flowering size, and reduce the proportion of iteroparous plants in the introduced range at sites with the weevil present. I surveyed 24 sites across the northwestern United States to quantify the frequency of semelparity versus iteroparity and to estimate abundance of M. crucifer. I found that the proportion of iteroparous plants varied across sites and that winter precipitation and weevil presence best explained this variation. Sites with greater precipitation and no weevils had a higher frequency of iteroparity. I used demographic data collected from six sites to estimate threshold flowering size. Sites with a higher attack rate by weevils had a lower threshold flowering size than those with a lower attack rate. The variation in frequency of flowering and threshold flowering size that I documented in North American houndstongue populations and the relationships between this variation and herbivory and climate provide evidence for how selective pressures shape the life histories of invasive plants.

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