Constitutive and induced structural defenses in horsenettle were negatively affected by inbreeding. Reduced flower production and internode length on damaged plants compared to controls suggests that defense induction entails significant costs.

Plant volatiles serve as key foraging and oviposition cues for insect herbivores as well as their natural enemies, but little is known about how genetic variation within plant populations influences volatile-mediated interactions among plants and insects. Here, we explore how inbred and outbred plants from three maternal families of the native weed horsenettle (Solanum carolinense) vary in the emission of volatile organic compounds during the dark phase of the photoperiod, and the effects of this variation on the oviposition preferences of Manduca sexta moths, whose larvae are specialist herbivores of Solanaceae. Compared with inbred plants, outbred plants consistently released more total volatiles at night and more individual compounds-including some previously reported to repel moths and attract predators. Female moths overwhelmingly chose to lay eggs on inbred (versus outbred) plants, and this preference persisted when olfactory cues were presented in the absence of visual and contact cues. These results are consistent with our previous findings that inbred plants recruit more herbivores and suffer greater herbivory under field conditions. Furthermore, they suggest that constitutive volatiles released during the dark portion of the photoperiod can convey accurate information about plant defence status (and/or other aspects of host plant quality) to foraging herbivores.

No abstract

Premise of research. Angiosperms are commonly classified as self-incompatible or self-compatible. This dichotomy has influenced research on the ecological and demographic consequences of colonization because of the predicted benefits of self-compatibility for establishment at low density. Some individuals of self-incompatible species, however, exhibit partial self-incompatibility (PSI), meaning that they set variable amounts of seed following self-pollination. Here, we investigate genetic and environmental components of PSI in tristylous Lythrum salicaria as a context for understanding colonization and the floral morph structure of invasive populations. Methodology. We surveyed variation in PSI using experimental self-and cross-pollinations on plants (n p 338) grown under glasshouse conditions. We compared the stability in expression of PSI over 2 yr (n p 80), and by pollinating selected clones (n p 12) grown under wet and dry conditions. We compared the compatibility status of mid-styled parents (n p 14) and their selfed offspring to determine whether there was a genetic component to PSI and whether the expression of PSI, measured as fruit set after self-pollination, differed between segregating long-and mid-styled plants. Pivotal results. Approximately 34% of plants set seed following self-pollination. The mid-styled morph produced more fruit following self-pollination in comparison with the remaining morphs. An index of self-compatibility (ISC) exhibited significant repeatability for individual plants over two successive flowering seasons. There was no systematic influence of wet and dry growing conditions at flowering on PSI, but significant genetic differences among clones in overall expression of PSI were evident. A heritable component to PSI was confirmed by parentoffspring regression, and compatibility values were significantly higher in mid-versus long-styled progeny. Conclusions. Our study demonstrated a weak but significant genetic component to morph-specific variation in PSI. The capacity of the M-morph to set seed after selfing may enable individuals to found populations and contribute to the occurrence of dimorphic populations missing the short-styled morph in the invasive range of L. salicaria.

Sexual reproduction in heterostylous populations may be vulnerable to demographic conditions because of the small number of mating types in populations. Here, we investigate mating and fertility under natural and experimental conditions in tristylous Lythrum salicaria L., an invasive species that exhibits a wide range of floral morph ratios and demographic contexts. We grew 147 open-pollinated seed families from six populations with different morph structures to estimate intermorph mating (d). In a field experiment, we used progeny ratios from 47 spatially isolated individuals to estimate d, and measured the intensity of pollen limitation experienced by the morphs. The M- and S-morphs experienced high rates of d, regardless of population size or morph ratio. Estimates for the L-morph revealed low levels of intramorph mating in three dimorphic and two trimorphic populations, but near complete intramorph mating in a monomorphic population. Despite high levels of intermorph mating in the field experiment, the morphs experienced significant pollen limitation of fruit and seed set, but this did not differ in intensity among the morphs. Our field experiment demonstrates that although plant isolation was associated with pollen limitation of seed set, “long-distance” bee-mediated pollen flow served to maintain intermorph mating. Tristyly in L. salicaria is remarkably robust to the demographic variation associated with colonization.