Protocol for Nuestro Sueño: A randomized trial of a couples-based intervention to improve PAP adherence and sleep health among Hispanic patients beginning positive airway pressure (PAP) and their part

Lichens are widely used by various groups of invertebrates as a habitat or food source. Smaller animals (e.g., tardigrades, nematodes, mites, and springtails) primarily find refuge in lichens but also have been observed to feed on them. Larger animals (e.g., snails, beetles, and butterfly larvae), on the other hand, only tend to consume them. Animal grazing activity can have both positive and negative consequences for lichens. Positive effects include, for example, the spreading of lichen propagules carried on the bodies of small invertebrates and their deposition together with feces. Grazing can induce sturdier lichen growth, which in turn can reduce the risk of damage by wind or other external forces. Coincidentally, the consumption of photobiont cells and physical damage to the lichen tissue caused by feeding often lead to a visible deterioration of lichens, making the negative effects obvious. Lichens have evolved defence mechanisms against invertebrate grazing, such as low concentrations of essential elements reducing food quality, or high concentrations of secondary metabolites. They produce a large array of different secondary metabolites, sometimes called lichen substances. Depending on their location in the thallus, lichen substances have been attributed different roles: secondary metabolites occurring mainly in the outer layers of lichens, such as the upper cortex and photobiont layer (e.g. parietin and usnic acid), are hypothesized to protect lichens against solar radiation while compounds produced deeper in the thallus, in the medulla (e.g. vulpinic and pinastric acid) have been suggested to have protective antiherbivore activity. Yet, the role of lichen secondary metabolites in interactions with invertebrates remains ambiguous; some provide protection against specific grazers, but not against all herbivores. Several studies have demonstrated defensive effects of certain secondary metabolites (e.g. atranorin, lecanoric acid) against grazing invertebrates, especially gastropods. Reutimann and Scheidegger showed that oribatid mites were repelled by fumarprotocetraric acid from the lichen , but at the same time they were attracted by other secondary metabolites, namely atranorin and norstictic acid, from . While controlled feeding experiments of mites and lichens are scarce, lichen-mite interactions have regularly been documented and shown to be manifold. Oribatid mites are frequently associated with lichens and use them as habitat and food source but also as breeding ground. There are numerous accounts of mite infestations harming lichens, and some authors even consider oribatid mites the chief pests of lichens. That said, the consequences of lichen-mite interactions are rarely obvious, with one notable exception: , with its characteristic red spots on the thallus, is perhaps the most striking example of an infestation of a lichen with mites. The red color is caused by rhodocladonic acid, a lichen substance commonly occurring in the genus ; however, it is usually restricted only to the reproductive structures. Furthermore, the substance is also known from other lichens (e.g. ). Rhodocladonic acid production in , originally identified as , was suggested to be a result of grazing mites. Recently, we confirmed that the presence of mites correlates with the red coloration, however, not with externally feeding adults, but rather endophagous tunnelling juvenile mites that seem to use tunnels as shelters to complete their development. Various authors, suggested an antiherbivorous effect of rhodocladonic acid, which should protect the lichen from excessive grazing. However, studies providing a possible explanation for the ecological role of rhodocladonic acid in are currently lacking. Notably, other morphologically and ecologically similar species occupying the same habitats and being similarly exposed to grazing mites do not produce this red pigment. In this study, we selected two ecologically similar, yet chemically distinct species ( and ) alongside to evaluate whether variation in secondary chemistry affects mite grazing. Previous research has shown that the oribatid mite communities associated with these three lichens are largely identical, even across broader geographic scales. While the mites do not appear to discriminate between these lichens in terms of suitable habitat, it remains unclear whether they do so when the lichens are the only available food source. To address this question, we used these three species as a potential food source, and conducted food choice experiments with adult individuals of and , which are the most frequently found mite species in these lichens in Europe. Specifically, we aimed to test (1) Do mites distinguish between different lichen species they encounter regularly in their natural habitat? (2) Does the occurrence of certain lichen substances (barbatic, fumarprotocetraic, rhodocladonic acids) influence their feeding behaviour? Answering these questions allows