Eastern Indigo Snakes Exhibit an Innate Response to Pit Viper Scent and an Ontogenetic Shift in Their Response to Mouse Scent

Heterospecific eavesdropping on disturbance cues of a treefrog

Alarm signals and cues are crucial to animal survival and vary greatly across species. Eavesdropping on heterospecific alarm signals and cues can provide eavesdroppers with information about potential threats. In addition to acoustic alarm signals, evidence has accumulated that chemical alarm cues and disturbance cues can also play a role in alerting conspecifics to potential danger in adult anurans (frogs and toads). However, there is very little known about whether disturbance cues are exploited by heterospecifics. In the present study, we conducted a binary choice experiment and a prey chemical discrimination experiment, respectively, to test the responses of a sympatric anuran species (red webbed treefrogs, Rhacophorus rhodopus) and a sympatric predator species (Chinese green tree vipers, Trimeresurus stejnegeri) to disturbance odors emitted by serrate-legged small treefrogs (Kurixalus odontotarsus). In the binary choice experiment, we found that the presence of disturbance odors did not significantly trigger the avoidance behavior of R. rhodopus. In the prey chemical discrimination experiment, compared with odors from undisturbed K. odontotarsus (control odors) and odorless control, T. stejnegeri showed a significantly higher tongue-flick rate in response to disturbance odors. This result implies that disturbance odor cues of K. odontotarsus can be exploited by eavesdropping predators to detect prey. Our study provides partial evidence for heterospecific eavesdropping on disturbance cues and has an important implication for understanding heterospecific eavesdropping on chemical cues of adult anurans.

Captivity Affects Head Morphology and Allometry in Headstarted Garter Snakes, Thamnophis sirtalis

In response to the growing number of amphibian and reptiles species in decline, many conservation managers have implemented captive breeding and headstarting programs in an effort to restore these populations. However, many of these programs suffer from low survival success, and it is often unclear as to why some individuals do not survive after reintroduction. Here I document changes to head morphology in the eastern garter snake, Thamnophis sirtalis, in response to time spent in captivity. Thamnophis raised on three diet treatments all differed in head size from wild individuals, and head size differed between the three treatments. Overall, head size was smaller in all three diet treatments than in wild snakes, potentially limiting the available prey for the captive garter snakes. Allometric patterns of growth in head size were also different for each diet treatment. Several potential implications of these changes in morphology are discussed, and what these changes may mean for other species that are part of headstarting and reintroduction programs.

Ontogeny of strike performance in ball pythons (Python regius): a three-year longitudinal study

The rapid strike of snakes has long been of interest in terms of mechanical performance. Recently, several nonvenomous taxa have been found to strike with the same incredible strike velocity and acceleration as the high-performing vipers. However, little is known regarding how these patterns change through ontogeny. Here I present ontogenetic strike data on ten ball pythons (Python regius) over a three year time period, from birth to sexual maturity. I found that performance declined rapidly over the first 18 months in nearly all kinematic measures. This puts the adult data out of the currently developing trend of high performance being maintained across the diversity of snakes. The underlying cause of the decline in performance is unclear, but there are several avenues of behavior, morphology, biomechanics, and ecology to be investigated.

Serum-based inhibition of pitviper venom by eastern indigo snakes (Drymarchon couperi)

When organisms possess chemical defenses, their predators may eventually evolve resistance to their toxins. Eastern indigo snakes (Drymarchon couperi; EIS) prey on pitvipers and are suspected to possess physiological resistance to their venom. In this study, we formally investigated this hypothesis using microassays that measured the ability of EIS blood sera to inhibit (A) hemolytic and (B) snake venom metalloproteinase (SVMP) activity of copperhead (Agkistrodon contortrix) venom. To serve as controls, we also tested the inhibitory ability of sera from house mice (Mus musculus) and checkered gartersnakes (Thamnophis marcianus), a snake that does not feed on pitvipers. Sera from both EIS and gartersnakes inhibited over 60% of SVMP activity, while only EIS sera also inhibited venom hemolytic activity (78%). Our results demonstrate that EIS serum is indeed capable of inhibiting two of the primary classes of toxins found in copperhead venom, providing the first empirical evidence suggesting that EIS possess physiological resistance to venom upon injection. Because we documented resistance to hemolytic components of pitviper venom within EIS but not gartersnakes, we speculate this resistance may be driven by selection from feeding on pitvipers while resistance to SVMP may be relatively widespread among snakes.

Summary: We confirm eastern indigo snakes possess a physiological resistance to pitviper venom and speculate that venom resistance in snakes may be a product of antagonistic interactions and phylogenetically conserved traits.