14Desert communities word-wide are used as natural laboratories for the study of convergent 15 evolution, yet inferences drawn from such studies are necessarily indirect. Here, we brought 16 desert organisms together (rodents and vipers) from two deserts (Mojave and Negev). Both 17 predators and prey in the Mojave have adaptations that give them competitive advantage 18 compared to their middle-eastern counterparts. Heteromyid rodents, kangaroo rats and pocket 19 mice, have fur-lined cheek pouches that allow the rodents to carry larger loads under predation 20 risk compared to gerbilline rodents. Sidewinder rattlesnakes have heat-sensing pits, allowing 21 them to hunt better on moonless nights when their Negev sidewinding counterpart, the Saharan 22 horned vipers, are visually impaired. In behavioral-assays, we used giving-up density (GUD) to 23 gage how each species of rodent perceived risk posed by known and novel snakes. We repeated 24 this for the same set of rodents at first encounter and again two months later following intensive 25 "natural" exposure to both snake species. Pre-exposure, all rodents identified their evolutionarily 26 familiar snake as a greater risk than the novel one. However, post-exposure all identified the 27 heat-sensing sidewinder rattlesnake as a greater risk. The heteromyids were more likely to avoid 28 encounters with, and discern the behavioral difference among, snakes than their gerbilline 29 counterparts. 30 31 34Deserts, and desert rodents in particular, provide a model system for studying parallel and 35 convergent evolution. Deserts around the world form at least five evolutionarily independent 36 laboratories of adaptation, ecology, and evolution [1][2][3][4][5][6]. Shared environmental conditions of 37 temperature, precipitation, and aridity force evolutionary processes in a manner that results in 38 similar adaptations in species that fill similar ecological roles. Not only do species converge, but 39 communities may too [7][8][9][10]. A good example of this can be studied in desert dunes of the 40 Mojave and of the Negev deserts. In both of these systems we find an array of plants that drop 41 their seeds onto the sand (creating a seed bank); a variety of rodent species feed on these seeds 42 [11][12][13]; and medium-sized sidewinding vipers feed on the rodents [14,15]. 43The Mojave and Negev deserts of North America and the Middle East, respectively, 44 possess rodents with similar ecologies [5,7,13,16,17]. These rodents are nocturnal, semi-45 fossorial, seed-eating, and seed caching. However, the heteromyid rodents of the Mojave may 46 have a constraint breaking adaptation compared to their convergent counterparts in the Negev, 47 the gerbilline rodents. A constraint-breaking adaptation is a game-changing evolutionary 48 adaptation that alters, relaxes or eliminates tradeoffs and confers a competitive advantage to its 49 holder over those lacking the trait as defined by Rosenzweig and McCord [18]. The heteromyids 50 have external fur lined cheek pouches that allow...

Desert communities world-wide are used as natural laboratories for the study of convergent evolution, yet inferences drawn from such studies are necessarily indirect. Here, we brought desert organisms together (rodents and vipers) from two deserts (Mojave and Negev). Both predators and prey in the Mojave have adaptations that give them competitive advantage compared to their middle-eastern counterparts. Heteromyid rodents of the Mojave, kangaroo rats and pocket mice, have fur-lined cheek pouches that allow them to carry larger loads of seeds under predation risk compared to gerbilline rodents of the Negev Deserts. Sidewinder rattlesnakes have heat-sensing pits, allowing them to hunt better on moonless nights when their Negev sidewinding counterpart, the Saharan horned vipers, are visually impaired. In behavioral-assays, we used giving-up density (GUD) to gauge how each species of rodent perceived risk posed by known and novel snakes. We repeated this for the same set of rodents at first encounter and again two months later following intensive “natural” exposure to both snake species. Pre-exposure, all rodents identified their evolutionarily familiar snake as a greater risk than the novel one. However, post-exposure all identified the heat-sensing sidewinder rattlesnake as a greater risk. The heteromyids were more likely to avoid encounters with, and discern the behavioral difference among, snakes than their gerbilline counterparts.

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