Selection Mosaic Exerted by Specialist and Generalist Herbivores on Chemical and Physical Defense of Datura stramonium

Abstract

Selection exerted by herbivores is a major force driving the evolution of plant defensive characters such as leaf trichomes or secondary metabolites. However, plant defense expression is highly variable among populations and identifying the sources of this variation remains a major challenge. Plant populations are often distributed across broad geographic ranges and are exposed to different herbivore communities, ranging from generalists (that feed on diverse plant species) to specialists (that feed on a restricted group of plants). We studied eight populations of the plant Datura stramonium usually eaten by specialist or generalist herbivores, in order to examine whether the pattern of phenotypic selection on secondary compounds (atropine and scopolamine) and a physical defense (trichome density) can explain geographic variation in these traits. Following co-evolutionary theory, we evaluated whether a more derived alkaloid (scopolamine) confers higher fitness benefits than its precursor (atropine), and whether this effect differs between specialist and generalist herbivores. Our results showed consistent directional selection in almost all populations and herbivores to reduce the concentration of atropine. The most derived alkaloid (scopolamine) was favored in only one of the populations, which is dominated by a generalist herbivore. In general, the patterns of selection support the existence of a selection mosaic and accounts for the positive correlation observed between atropine concentration and plant damage by herbivores recorded in previous studies.

Could alternative solanaceous hosts act as refuges for the tomato leafminer, Tuta absoluta?

“…Climatic variations (Agosta 2006), phenological and physiological state of the plants (Ayabe et al 2014), local selective pressures on plant traits (Castillo et al 2014), or the presence of plant endophytic symbionts and insect pathogens (Crawford et al 2010;Gurulingappa et al 2010) may also have an influence on host plant availability for the insects. Such variability in plant resource may have a significant impact on the spatiotemporal patterns of plant selection for female oviposition.…”

Selection on tropane alkaloids in native and non‐native populations of Datura stramonium

“…In the native range, scopolamine was positively selected in three populations. Previous evidence shows that this alkaloid is a component of resistance to herbivores of D. stramonium in its native range, though it does not account for all variation in resistance owing to spatial variation in the pressure exerted by specialist herbivores (see Castillo et al, 2014;Miranda-Pérez et al, 2016). For instance, the dietary specialist leaf beetle Lema trilineata daturaphila and the seed predator Trichobaris soror are absent in tropical, low altitude, locations of central Mexico (Castillo et al, 2014;J.…”

“…Alkaloids are toxic to animals, affecting enzymes and altering different physiological processes; some have strong effects on the nervous systems (Mithöfer & Boland, 2012). Studies have shown selection on one or two tropane alkaloids of D. stramonium when consumed by dietary specialist or generalist herbivores (Castillo et al, 2014;Miranda-Pérez et al, 2016;Shonle & Bergelson, 2000).…”

“…We used high-performance liquid chromatography (HPLC) to quantify the concentration of atropine and scopolamine in leaves of D. stramonium (El Bazaoui, Bellimam, & Soulaymani, 2011). The extraction method consisted of a series of acid-base reactions (see Castillo et al, 2013Castillo et al, , 2014. The samples were injected into a Waters Alliance 2695 HPLC device.…”

Plant Antiherbivore Defense in Diverse Environments

“…The secondary plant compound is more effective against herbivores specialist, but the precursor is still effective against generalist. Then, when there is a community of generalists, D. stramonium produces atropine [82].…”