A Pine in Distress: How Infection by Different Pathogenic Fungi Affect Lodgepole Pine Chemical Defenses.

In North America, lodgepole pine is frequently subjected to attacks by various biotic agents that compromise its ability to defend against subsequent attacks by insect herbivores. We investigated whether infections of lodgepole pine by different pathogenic fungal species have varying effects on its defense chemistry. We selected two common pathogens, Atropellis canker, Atropellis piniphila, and western gall rust, Endocronartium harknessii, affecting mature lodgepole pine trees in western Canada. We also included three ophiostomatoid fungi Grosmannia clavigera, Ophiostoma montium, and Leptographium longiclavatum associated with the mountain pine beetle (Dendroctonus ponderosae), because they are commonly used to investigate induced defenses of host trees of bark beetles. We collected phloem samples from lodgepole pines infected with the rust or the canker and healthy lodgepole pines in the same stand. We also inoculated mature lodgepole pines with the three fungal symbionts and collected phloem samples 2 weeks later when the defense chemistry was at its highest level. Different fungal species differentially altered the terpene chemistry of lodgepole pine trees. E. harknessii and the fungal symbionts altered the terpene chemistry in a similar pattern while trees responded to the infection by the A. piniphila differently. Our study highlights the importance of considering specific biotic stress agents in tree susceptibility or resistance to the subsequent attacks by insect herbivores, such as mountain pine beetle.

Bark Beetles Utilize Ophiostomatoid Fungi to Circumvent Host Tree Defenses.

Bark beetles maintain symbiotic associations with a diversity of microbial organisms, including ophiostomatoid fungi. Studies have frequently reported the role of ophiostomatoid fungi in bark beetle biology, but how fungal symbionts interact with host chemical defenses over time is needed. We first investigated how inoculations by three fungal symbionts of mountain pine beetle affect the terpene chemistry of live lodgepole pine trees. We then conducted a complimentary laboratory experiment specifically measuring the host metabolite degradation by fungi and collected the fungal organic volatiles following inoculations with the same fungal species on lodgepole pine logs. In both experiments, we analyzed the infected tissues for their terpene chemistry. Additionally, we conducted an olfactometer assay to determine whether adult beetles respond to the volatile organic chemicals emitted from each of the three fungal species. We found that all fungi upregulated terpenes as early as two weeks after inoculations. Similarly, oxygenated monoterpene concentrations also increased by several folds (only in logs). A large majority of beetles tested showed a strong attraction to two fungal species, whereas the other fungus repelled the beetles. Together this study shows that fungal symbionts can alter host defense chemistry, assist beetles in overcoming metabolite toxicity, and provide possible chemical cues for bark beetle attraction.

Recruitment of the serratus anterior as an accessory muscle of ventilation during graded exercise.

The role of the serratus anterior (SA) as an accessory muscle of ventilation and its physiologic significance under exercising conditions remains unclear. Recent investigations have utilized the measurement of SA as an analog for respiratory muscle oxygenation. The purpose of this investigation was to examine the action of the serratus anterior via surface electromyography (EMG) and near infrared spectroscopy (NIRS) during exercise while controlling for muscular effort not related to ventilation. Nine healthy volunteers (age = 24.4 +/- 0.5 years, VO2max = 3.416 +/- 0.35 l min(-1); VEpeak = 127.5 +/- 13.1 l min(-1); TVpeak = 2.844 +/- 0.226 l) completed a graded exercise test to volitional exhaustion on a cycle ergometer. The subjects' arms were folded and relaxed at the abdomen to minimize muscular effort resulting from scapular stabilization during pushing/forward flexion of the arms associated with cycle ergometry. VO2 and V were monitored breath-by-breath throughout exercise. EMG was recorded over the right SA, and a near infrared probe was placed over the left SA. No significant differences were observed throughout the graded exercise test for tissue oxygenation (StO2) (n = 6, F[1.532, 7.661] = 0.895, P > 0.05, eta2 = 0.15) or EMG (n = 9, F[1.594, 12.75] = 3.067, P > 0.05, eta2 = 0.27). Although the recruitment of the SA has been postulated to aid in ventilation in various postures and disease states, it is concluded that it shows little muscular effort in healthy subjects during upright cycling. Additional research is needed to conclude the pertinence of utilizing StO2 of the SA as an analog for respiratory muscle oxygenation.