Inbreeding alters volatile signalling phenotypes and influences tri‐trophic interactions in horsenettle (Solanum carolinense L.)

Abstract

The ecological consequences of inter-individual variation in plant volatile emissions remain largely unexplored. We examined the effects of inbreeding on constitutive and herbivore-induced volatile emissions in horsenettle (Solanum carolinense L.) and on the composition of the insect community attracted to herbivore-damaged and undamaged plants in the field. Inbred plants exhibited higher constitutive emissions, but weaker induction of volatiles following herbivory. Moreover, many individual compounds previously implicated in the recruitment of predators and parasitoids (e.g. terpenes) were induced relatively weakly (or not at all) in inbred plants. In trapping experiments, undamaged inbred plants attracted greater numbers of generalist insect herbivores than undamaged outcrossed plants. But inbred plants recruited fewer herbivore natural enemies (predators and parasitoids) when damaged. Taken together, these findings suggest that inbreeding depression negatively impacts the overall pattern of volatile emissions - increasing the apparency of undamaged plants to herbivores, while reducing the recruitment of predatory insects to herbivore-damaged plants.

Preference for outbred host plants and positive effects of inbreeding on egg survival in a specialist herbivore

“…In contrast to our results, damaged outbred horsenettle plants (Solanum carolinense) were more effective than inbred plants in attracting predatory hymenopterans, the natural enemies of the herbivores [26]. This difference was accounted for by the stronger induction of volatiles in the outbred plants relative to inbred plants [26]. It may be that the egg deposition as such does not alter the emission of volatile compounds or other cues used by predators and parasitoids in V. hirundinaria.…”

Inbreeding in horsenettle (Solanum carolinense) alters night-time volatile emissions that guide oviposition byManduca sextamoths

“…Our previous work on horsenettle has documented significant effects of inbreeding on plant defences against insect herbivores, including alteration of constitutive and induced volatile emissions and the plant -insect interactions they mediate [16]. For example, we observed higher levels of constitutive volatile emissions from inbred plants (relative to outbred plants) under field conditions, which appeared to mediate increased recruitment of insect herbivores.…”

“…Collections occurred on four successive nights, with one inbred and one outbred plant from each family represented each night, and were conducted in a greenhouse with no supplemental lighting using a push -pull collection system (Analytical Research Systems, Gainesville, FL, USA (see [16] for full description). Each volatile trap collected headspace volatiles for a maximum of 4 h (to prevent break-through loss of small molecular weight compounds) from 22.00 to 02.00 (trap 1) and 02.00 to 06.00 (trap 2).…”

“…Thus, constitutive plant volatile emissions can provide host-location cues for insect herbivores that may convey information about plant identity and ecologically relevant aspects of the plant phenotype. It is reasonable to assume that such interactions frequently entail the exploitation by herbivores of emissions that serve no adaptive signalling function for the plant but rather derive as byproducts of plants' normal physiological activities [5,15,16]. However, it is also possible that constitutive emissions may in some cases play an active signalling function.…”

Inbreeding compromises host plant defense gene expression and improves herbivore survival

“…18 In addition to the pivotal role that JA plays in plant direct chemical defense, JA is also involved in the synthesis of plant volatiles, a major element of indirect defense. Previous field trials, using M. sexta damaged horsenettle plants, showed that inbreeding curtails the plant's production of key terpenoid volatiles 24 -this negatively impacts the plant's ability to attract predators and/or parasitoids. Furthermore, JA is the main signaling molecule for plant structural defense induction (e.g.…”