COS 145-2 - Defense and floral trait trade-offs in Solanum carolinense across a latitudinal gradient

Abstract: Plants have evolved multiple defense strategies to minimize the damage of herbivory. Past studies have demonstrated that producing these defenses is costly and can reduce growth or reproductive output, or in some cases change reproductive strategy. However, for plant species with broad geographic distributions, numerous environmental factors can vary across the species distribution that may alter resource allocation to different types of defenses or to reproductive traits (i.e., floral traits). The tradeoffs between defenses and floral traits might be negligible in favorable environmental conditions, but tradeoffs could increase in stressful environmental conditions. A major unresolved question, therefore, is how allocation to suites of plant defense traits (i.e., syndromes) and floral traits change across latitudinal gradients. Here we collected data from 25 Solanum carolinense populations growing across a 29-44° latitudinal gradient in the eastern United States. We measured different plant functional traits including spines, trichomes, total glycoalkaloids, male:hermaphroditic flower ratio, corolla diameter, and stamen length and compared how they change across a latitudinal gradient. We found that plants in northern populations had higher amounts of chemical defenses such as glycoalkaloids, whereas southern populations had more physical defenses such as spines. Additionally, southern populations had higher male:hermaphroditic floral ratios, smaller flowers, and larger stamens. This shows that populations with more defended plants invest less maternally, showing a tradeoff between constitutive defenses and floral investment. Thus, favorable environmental conditions such as higher temperatures in the south favor more costly defenses but change the reproductive strategy of plants.