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In the late 1940s, Rio Grande Sucker Pantosteus plebeius was reported in tributaries of the Gila River in the Colorado Basin and presumed to be introduced because of its absence in mid-19th century surveys. We assayed genetic variation at ten microsatellite loci and two mtDNA genes (cyt b and ND4) to test the hypothesis of human-mediated introduction into the Gila within the last century. Phylogeographic analysis indicated that Gila River populations shared recent common ancestry with populations in the Mimbres River. Using approximate Bayesian computation (ABC), we rejected the hypothesis that Rio Grande Sucker was introduced to the upper Gila River within the last century. Rather, we hypothesize an older (∼4000 years before present) headwater capture event that facilitated transfer of fishes from the Mimbres to Sapillo Creek in the Gila Basin. From there, suckers dispersed to the San Francisco River and became established in upland stream habitats. Rio Grande Sucker exhibits low levels (<10%) of introgression with Desert Sucker but maintains species cohesion in the Gila Basin. We conclude that Rio Grande Sucker is native to the Gila Basin, and that these populations harbor unique diversity that could play an important role in species conservation. More generally, rigorous testing for human-mediated translocation is a difficult analytical problem, but a definitive means to do so is essential to fully understand the biogeography of freshwater fishes of the American Southwest.
Horned lizards, Phrynosoma spp., and harvester ants, Pogonomyrmex spp., could be in a predator–prey arms race in which the lizards are specialists that feed on harvester ants, and ants have highly toxic venom and other defenses to help deter predacious horned lizards. All 23 examined species of harvester ants possess venoms that are highly lethal to mice, but the venoms of the tested ant species were nearly inactive toward horned lizards. Blood plasma of Phrynosoma cornutum contains a factor (or factors) that neutralizes the ability of harvester ant venom to kill mice, but does not neutralize the venoms of honeybees, a rattlesnake, Russell's viper, or a cobra. A species of harvester ant present only in southern South America was used to test the predictions that the lethality of harvester ant venom evolved in response to predation pressure from horned lizards, and that horned lizard plasma does not neutralize the lethality of this species of harvester ant. This ant species did not overlap in range with horned lizards, which have a range from Guatemala to Canada. Not only was the venom of the South American ant species the most lethal of all tested harvester ant venoms, the venom's lethal activity was neutralized by horned lizard plasma. These results indicate that horned lizards responded to the lethality of their invertebrate prey's venom, but that the harvester ant venom lethality did not evolve in response to predation pressures by present day horned lizards.
Internal implantation of radio-transmitters is the preferred attachment technique for snakes, but the high costs and invasive nature of the surgery make a functional alternative desirable. Attaching radio-transmitters externally can be a cost-effective alternative to surgical implantation. External transmitter attachment site and methodology depend on the unique morphology of a given study species, making external adherence impractical for most snake species. Rattlesnake rattles are unique morphological features that can serve as an attachment site for external radiotransmitters. From 2011 to present, we have been attaching transmitters to the rattles of Eastern Diamondback Rattlesnakes (Crotalus adamanteus; EDB) using thread and epoxy. We calculated average monitoring duration using radio-telemetry data collected from 49 adult EDBs telemetered from 2014 to 2017 in coastal South Carolina. On average, we monitored EDBs for 189±78 days with 14 EDBs monitored >240 days and 3 EDBs monitored >300 days. External transmitter attachment is a viable alternative to surgical implantation, providing a noninvasive approach to monitoring rattlesnakes.