Temperature-dependent effects on mutualistic, antagonistic, and commensalistic interactions among insects, fungi and mites

The relative abundance and nature of associations between symbiotic species can be affected by abiotic conditions with consequences for population dynamics. We investigated the effects of temperature on the community of mites and fungi associated with the southern pine beetle, Dendroctonus frontalis, an important pest of pine forests in the southern United States. First, we determined whether the growth rates of mutualistic and antagonistic fungi associated with D. frontalis differed in their responses to temperature. Second, we tested the effects of temperature on the abundance of, and interactions among, fungi, mites and beetles within D. frontalis-infested trees. Fungi differed in their growth responses to temperature, resulting in changes in fungal-beetle associations. Mite species associated with D. frontalis also differed in their responses to temperature, resulting in different mite communities associated with bark beetle progeny. The effects of temperature on beetle reproduction could not be assessed because of high wood borer density, but inter-relations among surviving beetles, mites and fungi were altered by temperature. Results support the hypothesis that temperature can produce direct and indirect effects on the web of mutualistic and antagonistic relationships within the community of D. frontalis and their symbiotic mites and fungi. et al. 2005a, 2006). The inter-relations between bark beetles and symbionts (e.g., microbes and mites) may at times be significantly impacted by factors external to the interaction such as seasonal temperatures or changes in precipitation (Klepzig and Six 2004) that can drastically affect the population dynamics and the composition of species within a community. Variation in abiotic conditions may affect a community by altering the relative abundance of species and/or the strength of species interactions (Callaway and Walker 1997). Hofstetter et al. (2006) observed strong seasonal changes in the relative abundances of mites and fungi associated with D. frontalis, and Lombardero et al. (2000a, 2003) showed marked differences between D. frontalis and mites in their developmental sensitivity to temperature. Here, we quantified the effects of temperature on abundances and interactions between D. frontalis and its major fungal and mite associates. Specifically, we focused on the response of beetle-mutualistic fungi: Ceratocystiopsis ranaculosus Perry and Bridges, Entomocorticium sp. A; a beetle-antagonistic fungus: Ophiostoma minus (Hedgc.); and three genera of mites: Tarsonemus, Dendrolaelaps, and Trichouropoda to various temperatures, and assessed how potential differences in temperature-responses might affect community interactions. We experimentally manipulated the temperatures experienced by intact communities of D. frontalis and their symbionts within naturally infested trees. We hypothesized that fungal growth rates and abundances, as well as mite abundance within D. frontalis-infested trees are differentially affected by various temperatures. Autecological responses to temperature predict that increasing temperatures will lead to (1) higher mite loads on beetles (due to increased mite reproduction and population abundance; Lombardero et al. 2000b); (2) differing ratios of the mutualistic fungi: C. ranaculosus and E. sp. A (due to expected differences in individualistic temperature responses; Klepzig et al. 2001a); and (3) increased abundance of the antagonistic fungus O. minus (due to expected increased O. minus and mite growth rates with increasing temperature). We determined whether autecological responses to temperature match the observed abundances of species exposed to various temperatures.