Truffles in the sky: the impact of stochastic and deterministic drivers on Rhizopogon communities of the Madrean Sky Island Archipelago

The Madrean Sky Islands Archipelago (MSIA) comprises mountain “islands” whose Pine-Oak forests appear in stark contrast to the surrounding “sea” of Sonoran Desert vegetation. Rhizopogon (Boletales) consists of obligate ectomycorrhizal (EcM) symbionts that form truffle sporocarps and associate exclusively with Pinaceae. The objectives of this project were to describe the diversity of species of Rhizopogon across the MSIA and to characterize whether community structure is determined by host diversity, island identity, geographic distance, or some interaction among these factors. We selected nine islands, two sites were sampled per island: one site dominated by Pinus species and the other by Pseudotsuga menziesii var. glauca. Rhizopogon diversity was characterized from sporocarps and from bioassay-based EcM root tips derived from P. muricata, Ps. menziesii var. menziesii, and Ps. menziesii var. glauca seedlings inoculated with soil samples collected along transects established at each site. The ITS rDNA fungal barcode was amplified, and sequences were used in community analyses. Twenty-one 99% OTUs in the genus Rhizopogon were identified across nine sky islands. While differential host association with Pinus and Pseudotsuga is a significant driver of community composition, our results supported a stronger island effect. Furthermore, Rhizopogon communities associated within hosts are characterized by random phylogenetic structures across sky islands and are not structured by geographic distance. These results are consistent with a strong isolation effect involving historical habitat fragmentation of sky islands in response to past climate changes, and that both niche partitioning and stochastic demographic processes function in shaping Rhizopogon communities of the MSIA.

Climate Refugia for Pinus Spp. In Topographic and Bioclimatic Environments of the Madrean Sky Islands of México and the United States

ContextRefugia are island-like habitats that are linked to environmental stability. Where topography acts as a deterministic control, microrefugia may continue to function as habitat under reduced rates of climate change. Continental island ecosystems provide propitious settings for identifying patterns of refugia at multiple scales and applying that knowledge to conservation. Objectives Our main objective was to identify microrefugia for pines where habitats are defined by topographic heterogeneity. Secondary aims were to describe climatic variation within microrefugia and examine how species’ response to seasonal climate alters spatial predictions of microrefugia. Methods We investigated how topography forms microrefugia in the Madrean sky islands, located in the borderlands of México and the United States. Our design incorporated pine species presence and absence field observations (P. strobiformis, P. engelmannii and P. chihuahuana, P. arizonica and P. discolor), modeled in relation to terrain, bioclimatic and remote sensing predictors. Results Terrain ruggedness, slope position and aspect defined microrefugia for pines within specific elevation ranges. Some species had narrow habitat preferences (e.g., P. chihuahuana); others exhibited a broader range of tolerance (e.g., P. arizonica). Hotspots of microrefugia were either limited to northern islands or occurred across central or southern latitudes. Response to seasonal climates shifted distributions of hotspots for species with open canopy structure and where regular fires occur. ConclusionsPine habitats with greater climate stability may provide holdouts and stepping-stones critical to species persistence with future change. Networks of refugia provide a promising focus for conservation, restoration, and fire management across a diverse, binational region.

A new species of Aphonopelma (Araneae: Mygalomorphae: Theraphosidae) from the Madrean pine-oak woodlands of northeastern Sonora, Mexico

The tarantula spider genus Aphonopelma Pocock, 1901 has received considerable attention in recent years but the group’s diversity remains poorly understood in Mexico, particularly in the pine-oak woodlands of the Sierra Madre Occidental and associated Madrean “Sky Islands”. A pair of tarantulas discovered from an unsampled region in the Sierra de Bacadéhuachi (the westernmost range of the Sierra Madre Occidental) in northeastern Sonora was found to be closely related to four species from the Madrean “Sky Islands” in Arizona and New Mexico. An integrative approach for delimiting species (incorporating data from molecular phylogenetics, morphology, distributions, and breeding periods) suggests that the specimens from Sierra de Bacadéhuachi belong to an undescribed species that is herein named Aphonopelma bacadehuachi sp. nov. This new species adds to our knowledge of an increasingly diverse assemblage of Aphonopelma from the Madrean Pine-Oak Woodlands Hotspot. Collaborations between Mexican and American researchers are needed to accelerate discovery and description of the group’s remaining diversity, particularly in light of the many threats facing the ecoregion including habitat degradation and climate change.

Evolution of Scaphinotus petersi (Coleoptera: Carabidae) and the role of climate and geography in the Madrean sky islands of southeastern Arizona, USA

Geographically isolated environments such as the conifer forests atop the Madrean “sky islands” in southeastern Arizona provide natural laboratories for studying factors involved in speciation and origins of biodiversity. Using molecular and geospatial analyses, we examine beetle population phylogeny, regional climate records, and the Quaternary paleobiogeography of forests to evaluate four hypothetical scenarios regarding the current geographic and population genetic patterns of Scaphinotus petersi. Scaphinotus petersi is a large, flightless beetle that resides in the Madrean conifer forests above ~ 1900 m asl. Our results do not support the current hypothesis that S. petersi populations found on seven separate mountain ranges are genetically distinct and separated as temperatures warmed after the Last Glacial Maximum (LGM). Rather, we show that only some of the ranges hold genetically distinct populations, and the timing of separation among the populations does not appear to coincide with specific climatic events such as warming trends. In addition, we show that predicted changes to the climate of the Madrean sky islands may result in the disappearance of S. petersi from some of the lower ranges by the end of this century.