Defense suppression benefits herbivores that have a monopoly on their feeding site but can backfire within natural communities

Background: Plants have inducible defenses to combat attacking organisms. Hence, some herbivores have adapted to suppress these defenses. Suppression of plant defenses has been shown to benefit herbivores by boosting their growth and reproductive performance. Results: We observed in field-grown tomatoes that spider mites (Tetranychus urticae) establish larger colonies on plants already infested with the tomato russet mite (Aculops lycopersici). Using laboratory assays, we observed that spider mites have a much higher reproductive performance on russet mite-infested plants, similar to their performance on the jasmonic acid (JA)-biosynthesis mutant def-1. Hence, we tested if russet mites suppress JA-responses thereby facilitating spider mites. We found that russet mites manipulate defenses: they induce those mediated by salicylic acid (SA) but suppress those mediated by JA which would otherwise hinder growth. This suppression of JA-defenses occurs downstream of JA-accumulation and is independent from its natural antagonist SA. In contrast, spider mites induced both JA- and SA-responses while plants infested with the two mite species together display strongly reduced JA-responses, yet a doubled SA-response. The spider mite-induced JA-response in the presence of russet mites was restored on transgenic tomatoes unable to accumulate SA (nahG), but russet mites alone still did not induce JA-responses on nahG plants. Thus, indirect facilitation of spider mites by russet mites depends on the antagonistic action of SA on JA while suppression of JA-defenses by russet mites does not. Furthermore, russet mite-induced SA-responses inhibited secondary infection by Pseudomonas syringae (Pst) while not affecting the mite itself. Finally, while facilitating spider mites, russet mites experience reduced population growth. Conclusion: Our results show that the benefits of suppressing plant defenses may diminish within communities with natural competitors. We show that suppression of defenses via the JA-SA antagonism can be a consequence, rather than the cause, of a primary suppression event and that its overall effect is determined by the presence of competing herbivores and the distinct palette of defenses these induce. Thus, whether or not host-defense manipulation improves a herbivore inverted question marks fitness depends on interactions with other herbivores via induced-host defenses, implicating bidirectional causation of community structure of herbivores sharing a plant

Induced plant-defenses suppress herbivore reproduction but also constrain predation of their offspring

Inducible anti-herbivore defenses in plants are predominantly regulated by jasmonic acid (JA). On tomato plants, most genotypes of the herbivorous generalist spider mite Tetranychus urticae induce JA defenses and perform poorly on it, whereas the Solanaceae specialist Tetranychus evansi, who suppresses JA defenses, performs well on it. We asked to which extent these spider mites and the predatory mite Phytoseiulus longipes preying on these spider mites eggs are affected by induced JA-defenses. By artificially inducing the JA-response of the tomato JA-biosynthesis mutant def-1 using exogenous JA and isoleucine (Ile), we first established the relationship between endogenous JA-Ile-levels and the reproductive performance of spider mites. For both mite species we observed that they produced more eggs when levels of JA-Ile were low. Subsequently, we allowed predatory mites to prey on spider mite-eggs derived from wild-type tomato plants, def-1 and JA-Ile-treated def-1 and observed that they preferred, and consumed more, eggs produced on tomato plants with weak JA defenses. However, predatory mite oviposition was similar across treatments. Our results show that induced JA-responses negatively affect spider mite performance, but positively affect the survival of their offspring by constraining egg-predation

Clinical Studies into the Causes of Idiopathic Macular Telangiectasia Type 2: Sleep Apnoea and Macular Telangiectasia: The SAMTel Project

Purpose: To assess the prevalence of Obstructive Sleep Apnoea (OSA) in a population with Macular Telangiectasia Type 2 (MacTel) and how OSA impacts on MacTel progression. Methods: In this case-control study participants completed a questionnaire which incorporated the Berlin Questionnaire (BQ) and questions regarding anthropometric data and medical history. A subset was sequentially selected to undertake overnight sleep analysis using the ResMed ApneaLink™. Using data acquired from the Busselton Population and Medical Research Foundation participants were case-matched based on age, sex and body mass index (BMI) along with, where possible, the presence of hypertension and diabetes. Results: There were 57 (30 ApneaLink) MacTel and 183 controls, respectively. There was no difference in self-reported sleep disordered breathing outcomes between the cohorts using the BQ (p=0.95). Analysis of key indices from ApneaLink recordings found that those with an Apnoea – Hypopnoea Index (AHI) and Oxygen Desaturation Index (ODI) > 5 episodes per hour had a more advanced stage of MacTel (AHI p = 0.05, ODI p = 0.03). 2 year MacTel disease progression rates were unremarkable. Conclusion: Patients with MacTel have a high prevalence of OSA which appears to result in a more advanced form of the disease