Quantitative measure of fitness in tri-trophic interactions and its influence on diet breadth of insect herbivores

Herbivore-plant interactions should be studied using a tri-trophic approach, but we lack a quantitative measure of the combined effect of top-down and bottom-up forces on herbivore fitness. We propose the combination of the bi-trophic fitness slopes as a tri-trophic fitness measure. We use the relationship between fitness associated with top-down and bottom-up forces and the frequency of host plant use to calculate the top-down and bottom-up fitness slopes, which we then combine to obtain three possible directions of tri-trophic slopes. A positive tri-trophic slope indicates that herbivores have overall greater tri-trophic fitness on the more frequently used hosts. A null tri-trophic fitness slope indicates that herbivores have similar fitness on all host plants. A negative tri-trophic slope indicates that herbivores have generally lower fitness on the more frequently used hosts. We tested the explanation power of our method using data from the literature that tested herbivore host shifts and experimentally using a generalist herbivore with variable diet breadth across populations. We found that in host shifts, herbivores have higher tri-trophic fitness on the novel host, while in generalist populations, herbivores use most frequently the best host available. We present applications in other research areas and consider the limitations of our approach. Our approach is a first step towards a comprehensive model of multiple selective forces acting on the evolution of interactions.

Global change and the importance of fire for the ecology and evolution of insects

Climate change is drastically altering global fire regimes, which may affect the structure and function of insect communities. Insect responses to fire are strongly tied to fire history, plant responses, and changes in species interactions. Many insects already possess adaptive traits to survive fire or benefit from post-fire resources, which may result in community composition shifting toward habitat and dietary generalists as well as species with high dispersal abilities. However, predicting community-level resilience of insects is inherently challenging due to the high degree of spatiotemporal and historical heterogeneity of fires, diversity of insect life histories, and potential interactions with other global change drivers. Future work should incorporate experimental approaches that specifically consider spatiotemporal variability and regional fire history in order to integrate eco-evolutionary processes in understanding insect responses to fire.

Complex community and evolutionary responses to habitat fragmentation and habitat edges: what can we learn from insect science?

Habitat fragmentation is the primary factor leading to species extinction worldwide and understanding how species respond to habitat edges is critical for understanding the effects of fragmentation on insect diversity in both natural and managed landscapes. Most studies on insect responses to the habitat edge focus on bottom-up changes in resources. Only a few recent studies have examined multi-trophic responses to habitat edges; the results of these studies highlight the problem that we lack a conceptual framework to understand the complex results observed when a single species' response to an edge 'cascades' throughout the food web in ways that are currently not predictable. Recent research from insect systems suggests that habitat edge responses cascade both up and down multi-trophic foodwebs and these altered species interactions may affect evolutionary processes. Future studies that investigate the effects of habitat edges on both ecological and evolutionary dynamics can help to fill these knowledge gaps and we suggest that insects, with short generation times, present an ideal opportunity to do so.

Trade-offs in host choice of an herbivorous insect based on parasitism and larval performance

Herbivore diet breadth is predicted to evolve in response to both bottom-up and top-down selective pressures, including host plant abundance, quality and natural enemy pressure. As the relative importance and strength of interactions change over an herbivore's geographic range, local patterns of host plant use should change in response, altering local diet breadths. Fall webworm (Hyphantria cunea) is a widespread, polyphagous moth species that feeds on hundreds of plant species worldwide. Populations of fall webworm in Colorado remain polyphagous, but their diet breadth is restricted compared to other populations and thus present an ideal opportunity to test the ecological drivers of host use by a polyphagous herbivore. We investigated how host abundance, larval performance, and parasitism affect host use for fall webworm to test how these selective pressures may act individually or in concert, as well as the role of any trade-offs among fitness components, to explain diet breadth and host use. We found that host abundance was a significant predictor of host use, which suggests a selective pressure to reduce search time for oviposition sites by adult females. We also detected an important trade-off between bottom-up and top-down selective pressures: higher quality host plants also had a greater proportion of larval mortality due to parasitism. Local patterns of host plant abundance appear to narrow the set of hosts used by fall webworms in Colorado, while the trade-off between host quality and risk of parasitism helps explain the maintenance of a generalized feeding strategy within this restricted set of hosts.

Enemy-free space for parasitoids

Natural enemies often cause significant levels of mortality for their prey and thus can be important agents of natural selection. It follows, then, that selection should favor traits that enable organisms to escape from their natural enemies into "enemy-free space" (EFS). Natural selection for EFS was originally proposed as a general force in structuring ecological communities, but more recently has become conceptually narrow and is typically only invoked when studying the evolutionary ecology of host plant use by specialized insect herbivores. By confining the application of EFS to specialist herbivores, its potential value to community and evolutionary ecology has been marginalized. As a first step toward exploring the potential explanatory power of EFS in structuring ecological niches of higher trophic-level organisms, we consider host use by parasitoids. Here, we present three distinct mechanisms from our studies of caterpillar host-parasitoid interactions suggesting that parasitoids may be under selection to exploit traits of their hosts and the plants on which those hosts feed to garner EFS for their developing offspring. The neglect of EFS as a top-down selective force on host use by parasitoids may be a serious limitation to basic and applied ecology, given the great diversity of parasitoids and their significance in controlling herbivore populations in both natural and managed ecosystems. Parasitoids and other mesopredators represent excellent candidates for further developments of EFS theory and testing of its broader importance.

Intraplant movement of generalist slug caterpillars (Limacodidae: Lepidoptera): effects of host plant and light environment

Insect herbivores frequently move about on their host plants to obtain food, avoid enemies and competitors, and cope with changing environmental conditions. Although numerous plant traits influence the movement of specialist herbivores, few studies have examined movement responses of generalist herbivores to the variable ecological conditions associated with feeding and living on an array of host plants. We tested whether the movement patterns of two generalist caterpillars (Euclea delphinii Boisduval and Acharia stimulea Clemens, Limacodidae) differed on six different host tree species over 10 d. Because these tree species vary in the range of light environments in which they commonly grow, we also compared the movement responses of E. delphinii caterpillars to two contrasting light environments, sun and shade. For both caterpillar species, multiple measures of movement varied significantly among host tree species. In early censuses, movement rates and distances were highest on red oak and black cherry and lowest on white oak. Site fidelity was greatest on white oak and lowest on black cherry. Movement of both caterpillar species varied inversely with mean predator density on five of the six host trees. Other ecological predictors (e.g., leaf size and the density of other herbivores) were unrelated to movement. Light environment altered behavior such that caterpillars in the shade moved and fed more often, and moved greater distances, than caterpillars in the sun. Although the mechanism(s) promoting or inhibiting movement under these different conditions requires further study, the consequences of increased movement for caterpillar development and mortality from natural enemies are discussed.

Facilitative effects of group feeding on performance of the saddleback caterpillar (Lepidoptera: Limacodidae)

Gregarious feeding by insect herbivores is a widely observed, yet poorly understood, behavioral adaptation. Previous research has tested the importance of group feeding for predator deterrence, noting the ubiquity of aposematism among group-feeding insects, but few studies have examined the role of feeding facilitation for aggregates of insect herbivores. We tested the hypothesis that group feeding has facilitative effects on performance of the saddleback caterpillar, Acharia stimulea Clemens, a generalist herbivore of deciduous trees. In an understory forest setting, we reared caterpillars alone or in groups on two different host plants, white oak (Quercus alba L.) and American beech (Fagus grandifolia Ehrlich), and recorded multiple measures of insect performance during regular field censuses. As predicted, A. stimulea caterpillars feeding in groups on white oak had increased relative growth rates compared with caterpillars feeding alone, and the magnitude of this facilitative effect varied among censuses, conferring benefits both early and late in development. By contrast, no facilitative effects of group feeding were detected on beech, suggesting that the benefits of facilitative feeding may be host specific. On both hosts, caterpillar development time was slightly faster for group-feeding cohorts compared with their solitary counterparts. Because early instar caterpillars are particularly vulnerable to predation and parasitism, even modest increases in growth rates and reductions in development time may decrease exposure time to enemies during these vulnerable stages. On both hosts, group feeding also reduced the trade-off between individual development time and cocoon mass, suggesting that feeding efficiency is improved in group feeders relative to solitary caterpillars.

Health-related quality of life and functional outcomes following nerve transfers for traumatic upper brachial plexus injuries

We report the patient-scored Health-Related Quality of Life (HRQoL) and functional outcomes of a cohort of 21 consecutive patients undergoing nerve transfer surgery for traumatic upper brachial plexus injuries. Outcomes were assessed using the British Medical Research Council power grading system, Short-Form 36, Disability of Arm, Shoulder and Hand questionnaire, and Pain Visual Analogue Scale (PVAS). The mean age of our cohort was 29.8 years (range 18-53 years), with a mean follow-up period of 42.9 months. At follow-up, elbow flexion ≥ M3 strength was achieved in 17/21 patients. Shoulder abduction ≥ M3 was achieved in 14/19 patients. External rotation ≥ M3 strength was achieved in 11/15 patients. Delayed surgical repair correlated negatively with HRQoL outcomes. Higher injury severity scores and smoking were associated with higher PVAS scores. These findings provide key prognostic information for patients and peripheral nerve surgeons embarking upon this intensive pathway to potential recovery.

Nutrient presses and pulses differentially impact plants, herbivores, detritivores and their natural enemies

Anthropogenic nutrient inputs into native ecosystems cause fluctuations in resources that normally limit plant growth, which has important consequences for associated food webs. Such inputs from agricultural and urban habitats into nearby natural systems are increasing globally and can be highly variable, spanning the range from sporadic to continuous. Despite the global increase in anthropogenically-derived nutrient inputs into native ecosystems, the consequences of variation in subsidy duration on native plants and their associated food webs are poorly known. Specifically, while some studies have examined the effects of nutrient subsidies on native ecosystems for a single year (a nutrient pulse), repeated introductions of nutrients across multiple years (a nutrient press) better reflect the persistent nature of anthropogenic nutrient enrichment. We therefore contrasted the effects of a one-year nutrient pulse with a four-year nutrient press on arthropod consumers in two salt marshes. Salt marshes represent an ideal system to address the differential impacts of nutrient pulses and presses on ecosystem and community dynamics because human development and other anthropogenic activities lead to recurrent introductions of nutrients into these natural systems. We found that plant biomass and %N as well as arthropod density fell after the nutrient pulse ended but remained elevated throughout the nutrient press. Notably, higher trophic levels responded more strongly than lower trophic levels to fertilization, and the predator/prey ratio increased each year of the nutrient press, demonstrating that food web responses to anthropogenic nutrient enrichment can take years to fully manifest themselves. Vegetation at the two marshes also exhibited an apparent tradeoff between increasing %N and biomass in response to fertilization. Our research emphasizes the need for long-term, spatially diverse studies of nutrient enrichment in order to understand how variation in the duration of anthropogenic nutrient subsidies affects native ecosystems.

Health-related quality of life, surgical and aesthetic outcomes following microvascular free flap reconstructions: an 8-year institutional review

INTRODUCTION

Microvascular free flap reconstruction has revolutionised the reconstruction of complex defects of traumatic, oncological, congenital and infectious aetiologies. Complications of microvascular free flap procedures impact negatively on patient post-operative course and outcome.

METHODS

We performed a retrospective analysis of 102 consecutive patients undergoing 108 free flap procedures at a tertiary referral centre over an 8-year period. Logistic regression analysis was used to identify factors predictive of free flap complications. Health-related quality of life (HRQoL) and aesthetic outcomes were assessed using the Short Form 36 questionnaire and a satisfaction visual analogue scale respectively.

RESULTS

In total, 108 free tissue transfers were performed; 23% were fasciocutaneous free flaps, 69% musculocutaneous and 8% osteoseptocutaneous. The overall flap success rate was 92.6%. Over a third of patients (34.3%) had flap-related complications ranging from minor wound dehiscence to total flap loss. ASA (American Society of Anesthesiologists) grade ≥2 (OR: 16.9, 95% CI: 15.3-18.1, p<0.009), history of smoking (OR: 6.1, 95% CI: 5.5-7.2, p<0.049), body mass index ≥25 kg/m(2) (OR: 21.3, 95% CI: 20.8-22.1, p<0.003), low albumin (odds ratio [OR]: 2.2, 95% confidence interval [CI]: 1.2-3.9, p<0.003) and peripheral vascular disease (OR: 6.9, 95% CI: 5.9-7.5, p<0.036) were identified as factors independently predictive of free flap complications.

CONCLUSIONS

Patients undergoing uncomplicated free flap surgery and those reporting superior post-operative flap aesthesis have higher HRQoL scores. Microvascular free tissue transfer has revolutionised our approach to the reconstruction of complex defects, providing a safe, reliable procedure to restore functionality and quality of life for patients.

Image-guided transnasal cryoablation of a recurrent nasal adenocarcinoma in a dog

An eight-year-old female spayed Airedale terrier with rapid recurrence of a nasal adenocarcinoma following image-guided intensity-modulated radiation therapy was treated with transnasal, image-guided cryotherapy. Ice ball size and location were monitored real-time with computed tomography-fluoroscopy to verify that the entire tumour was enveloped in ice. Serial computed tomography scans demonstrated reduction in and subsequent resolution of the primary tumour volume corresponding visually with the ice ball imaged during the ablation procedure. Re-imaging demonstrated focallysis of the cribriform plate following ablation that spontaneously resolved by 13 months. While mild chronic nasal discharge developed following cryoablation, no other clinical signs of local nasal neoplasia were present. Twenty-one months after nasal tumour cryoablation the dog was euthanased as a result of acute haemoabdomen. Image-guided cryotherapy may warrant further investigation for the management of focal residual or recurrent tumours in dogs, especially in regions where critical structures preclude surgical intervention.

Winter predation of diapausing cocoons of slug caterpillars (Lepidoptera: Limacodidae)

Predators exert strong top-down pressure on herbivorous insects, but research on how predators affect herbivore fitness often focuses on the more active juvenile and adult life stages while ignoring the pupal or cocoon life stage. Few studies have investigated predation of lepidopteran pupae or cocoons and even fewer have investigated species that are not forest pests. Here we present a study on overwinter survival for two moth species in the family Limacodidae, a group of polyphagous species found in deciduous forests. We placed cocoons of the saddleback caterpillar, Acharia stimulea (Clemens), and the spiny oak-slug caterpillar, Euclea delphinii (Boisduval), in the field under saplings of six different tree species and monitored predation and survival. This is the first study to examine predation rate among different host plants within a site. We found that cocoon predation was fairly high and differed significantly between limacodid species (29% for A. stimulea vs. 22% for E. delphinii). Predation rate did not differ among the six host plant species that we tested and also did not vary annually. Through phenotypic selection analyses, we found that cocoon mass affected both the likelihood of predation and overwinter survival; larger cocoons were less likely to be depredated and more likely to successfully emerge the following year. Overall our results indicate that cocoon predation is an important source of mortality for these two limacodid species and that there may be positive selection for greater cocoon mass for both limacodid species.

Sympathetic control of heart rate in nNOS knockout mice

Inhibition of neuronal nitric oxide synthase (nNOS) in cardiac postganglionic sympathetic neurons leads to enhanced cardiac sympathetic responsiveness in normal animals, as well as in animal models of cardiovascular diseases. We used isolated atria from mice with selective genetic disruption of nNOS (nNOS(-/-)) and their wild-type littermates (WT) to investigate whether sympathetic heart rate (HR) responses were dependent on nNOS. Immunohistochemistry was initially used to determine the presence of nNOS in sympathetic [tyrosine hydroxylase (TH) immunoreactive] nerve terminals in the mouse sinoatrial node (SAN). After this, the effects of postganglionic sympathetic nerve stimulation (1-10 Hz) and bath-applied norepinephrine (NE; 10(-8)-10(-4) mol/l) on HR were examined in atria from nNOS(-/-) and WT mice. In the SAN region of WT mice, TH and nNOS immunoreactivity was virtually never colocalized in nerve fibers. nNOS(-/-) atria showed significantly reduced HR responses to sympathetic nerve activation and NE (P < 0.05). Similarly, the positive chronotropic response to the adenylate cyclase activator forskolin (10(-7)-10(-5) mol/l) was attenuated in nNOS(-/-) atria (P < 0.05). Constitutive NOS inhibition with L-nitroarginine (0.1 mmol/l) did not affect the sympathetic HR responses in nNOS(-/-) and WT atria. The paucity of nNOS in the sympathetic innervation of the mouse SAN, in addition to the attenuated HR responses to neuronal and applied NE, indicates that presynaptic sympathetic neuronal NO does not modulate neuronal NE release and SAN pacemaking in this species. It appears that genetic deletion of nNOS results in the inhibition of adrenergic-adenylate cyclase signaling within SAN myocytes.

Backyard burning

This study was undertaken to determine whether changes had occurred in the numbers of burns that could be related to backyard burning subsequent to the introduction of the council tax throughout Eire for the collection of household refuse. Numbers of patients admitted to our unit who had sustained burns by burning rubbish were recorded prospectively over a period of 12 months. A random control group was taken as three years prior to this and results found by retrospective chart review. Between January and November 2005, 168 patients were admitted to the National Burns Unit, St James's Hospital Dublin, Ireland. Nineteen of these patients sustained flame burns from backyard burning. One hundred and seventy patients were admitted in the comparative period of 2002; Seven of these from backyard burning. The total number of inpatient days for these patients in 2005 (255) was significantly more than in 2002 (68) (p=0.024). The numbers in our study show a marked increase in the number of patients sustaining burns in this manner, and appear to correlate with the introduction of bin charges by a number of county councils around the country last year. This study demonstrates that the introduction of legislation can have an unforeseen adverse affect on the population if not introduced in correlation with appropriate public education. While the introduction of waste charges represents a very necessary move forward in waste disposal in Ireland, public awareness campaigns should be implemented to prevent further such injuries from occurring.