Discovery of a new tarantula species from the Madrean Sky Islands and the first documented instance of syntopy between two montane endemics (Araneae, Theraphosidae, Aphonopelma): a case of prior mistaken identity

The Chiricahua Mountains in southeastern Arizona are renowned for their exceptional biodiversity and high levels of endemism. Morphological, genomic, behavioral, and distributional data were used to report the discovery of a remarkable new tarantula species from this range. <i>Aphonopelmajacobii</i> <b>sp. nov.</b> inhabits high-elevation mixed conifer forests in these mountains, but also co-occurs and shares its breeding period with <i>A.chiricahua</i>-a related member of the <i>Marxi</i> species group-in mid-elevation Madrean evergreen oak and pine-oak woodlands. This marks the first documented case of syntopy between two montane endemics in the Madrean Archipelago and adds to our knowledge of this threatened region's unmatched tarantula diversity in the United States. An emended diagnosis and redescription for <i>A.chiricahua</i> are also provided based on several newly acquired and accurately identified specimens. Phylogenetic analyses of mitochondrial and genomic-scale data reveal that <i>A.jacobii</i> <b>sp. nov.</b> is more closely related to <i>A.marxi</i>, a species primarily distributed on the Colorado Plateau, than to <i>A.chiricahua</i> or the other Madrean Sky Island taxa. These data provide the evolutionary framework for better understanding the region's complex biogeographic history (e.g., biotic assembly of the Chiricahua Mountains) and conservation of these spiders.