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Animal biologists have recently focused on individual variation in behavioral traits and have found that individuals of many species have personalities. These are defined as consistent intraspecific differences in behaviors that are repeatable across different situations and stable over time. When animals sense danger, some individuals will alert neighbors with alarm calls and both calling and responding vary consistently among individuals. Plants, including sagebrush, emit volatile cues when they are attacked by herbivores and neighbors perceive these cues and reduce their own damage. We experimentally transferred volatiles between pairs of sagebrush plants to evaluate whether individuals showed consistent variation in their effectiveness as emitters and as receivers of cues, measured in terms of reduced herbivore damage. We found that 64% of the variance in chewing damage to branches over the growing season was attributable to the identity of the individual receiving the cues. This variation could have been caused by inherent differences in the plants as well as by differences in the environments where they grew and their histories. We found that 5% of the variance in chewing damage was attributable to the identity of the emitter that provided the cue. This fraction of variation was statistically significant and could not be attributed to the environmental conditions of the receiver. Effective receivers were also relatively effective emitters, indicating consistency across different situations. Pairs of receivers and emitters that were effective communicators in 2018 were again relatively effective in 2019, indicating consistency over time. These results suggest that plants have repeatable individual personalities with respect to alarm calls.

Grasses are major agricultural products worldwide and they are critical to ecosystem function in many terrestrial habitats. Despite their global importance, we know relatively little about their defenses against herbivory. Grasses tend to be tolerant of leaf loss because their valuable meristems are located underground, out of reach for above ground herbivores. Many grasses have unidirectional leaf hairs, prickles, and spines that make moving up the leaf blade easy, but make moving down, toward the meristem, difficult. We tested the hypothesis that unidirectional grass hairs direct small arthropod herbivores away from the meristems. In a field survey of the distribution of herbivore damage, we found that leaf tips received five times more damage than leaf bases for Avena barbata. Early-instar grasshoppers fed three times as often on leaf tops as on leaf bases of pubescent individuals in a common garden laboratory experiment. This effect was not observed for glabrous individuals where grasshoppers damaged leaf bases as often as leaf tops. A common generalist caterpillar, Heliothus virescens, was more than twice as likely to turn in the direction of the hairs, away from the meristems, when it encountered pubescent leaves of A. barbata. However, larger caterpillars of the generalist feeder Arctia virginalis showed no directional bias when they encountered pubescent leaves. In common garden experiments, selection on pubescence was weak and inconsistent over space and time. Under some circumstances, individuals of A. barbata with pubescent leaves were more likely to produce seeds than were individuals with fewer hairs. The surveys, behavioral experiments with small insects, and estimates of lifetime reproduction all support the hypothesis that unidirectional leaf hairs on A. barbata, and perhaps other grasses, serve as an unstudied defense that direct small herbivores away from the meristems.

Edge responses have been studied for decades and form a critical component of our understanding of how organisms respond to landscape structure and habitat fragmentation. Until recently, however, the lack of a general, conceptual framework has made it difficult to make sense of the patterns and variability reported in the edge literature. We present a test of an edge effects model which predicts that organisms should avoid edges with less-preferred habitat, show increased abundance near edges with preferred habitat or habitat containing complementary resources, and show no response to edges with similar-quality habitat that offers only supplementary resources. We tested the predictions of this model against observations of the edge responses of 15 butterfly species at 12 different edge types within a complex, desert riparian landscape. Observations matched model predictions more than would be expected by chance for the 211 species/edge combinations tested over 3 years of study. In cases where positive or negative edge responses were predicted, observed responses matched those predictions 70% of the time. While the model tends to underpredict neutral results, it was rare that an observed edge response contradicted that predicted by the model. This study also supported the two primary ecological mechanisms underlying the model, although not equally. We detected a positive relationship between habitat preferences and the slope of the observed edge response, suggesting that this basic life history trait underlies edge effects and influences their magnitude. Empirical evidence also suggested the presence of complementary resources underlies positive edge responses, but only when completely confined to the adjacent habitat. This multi-species test of a general edge effects model at multiple edge types shows that resource-based mechanisms can explain many edge responses and that a modest knowledge of life history attributes and resource availability is sufficient for predicting and understanding many edge responses in complex landscapes. [ABSTRACT FROM AUTHOR]

Genetic variation among plants can influence host choice and larval performance in insect herbivores. Ploidy (cytotype) variation is a particularly dramatic form of plant genetic variation, and where diploid and polyploid cytotypes of a species occur in sympatry, they may provide herbivores with choices that are distinguished by profound and genome-wide genetic differences. We tested for non-random attack by five gallmaking insect herbivores on diploid, tetraploid, and hexaploid cytotypes of the goldenrod Solidago altissima L., working in seven midwestern US populations where the ploidies co-occur on spatial scales relevant to insect host choice. For four of the five herbivores, attack was non-random with respect to ploidy at one or more sites. Ploidy effects on attack were complex: the ploidy subjected to highest attack varied both across herbivores within sites and (for most herbivores) across sites within herbivores. Ploidy effects on attack will alter rates of encounter between insect herbivores—either increasing or decreasing the likelihood of two herbivores sharing a host plant ramet, compared with the case with no effects of ploidy. Plant ploidy variation appears likely to have a major impact on insect community organization, and perhaps on plant–herbivore coevolution, but that impact is likely to be spatially heterogeneous. [ABSTRACT FROM AUTHOR]

Timing of arrival at a resource often determines an individual’s reproductive success. Tree-killing bark beetles can reproduce in healthy trees by attacking in adequate numbers to overcome host defences that could otherwise be lethal. This process is mediated by aggregation and antiaggregation pheromones. Beetles that arrive early in such a “mass attack” must contend with undiminished tree defences, and produce enough pheromones to attract more beetles, but have a head start on gallery construction and egg-laying. Beetles that arrive late may be impeded by competition and diminishing availability of phloem, but should experience fewer costs associated with pheromone production and battling tree defences. We investigated relationships between timing of arrival, body size, pheromone production and fitness in the southern pine beetle, Dendroctonus frontalis. In field experiments, we captured beetles that arrived early (pioneers) and late on slash pine trees, Pinus elliottii, and measured pheromone amounts in their hindguts. We marked gallery entrances of beetles as they landed on a tree and measured their reproductive success after the attack terminated. We found no difference in body size or pheromone amounts between early and late arrivers. Most beetles arrived at the middle of the attack sequence, and excavated longer galleries per day than early arrivers. The number of offspring produced per day by beetles that established galleries midway through mass attack was higher than those that arrived early or very late in the sequence. Our results suggest that beetles do not exhibit adaptive phenotypic plasticity in pre-landing pheromone production, depending on the extent of previous colonisation of a host. Rather, it appears that stabilising selection favours beetles that attack in the middle of the sequence, and contributes to attack synchrony. Synchronous attack on trees is essential before population booms characteristic of tree-killing bark beetles can occur in nature. [ABSTRACT FROM AUTHOR]