Structure and analysis of nanobody binding to the human ASIC1a ion channel

ASIC1a is a proton-gated sodium channel involved in modulation of pain, fear, addiction, and ischemia-induced neuronal injury. We report isolation and characterization of alpaca-derived nanobodies (Nbs) that specifically target human ASIC1a. Cryo-electron microscopy of the human ASIC1a channel at pH 7.4 in complex with one of these, Nb.C1, yielded a structure at 2.9 Å resolution. It is revealed that Nb.C1 binds to a site overlapping with that of the Texas coral snake toxin (MitTx1) and the black mamba venom Mambalgin-1; however, the Nb.C1-binding site does not overlap with that of the inhibitory tarantula toxin psalmotoxin-1 (PcTx1). Fusion of Nb.C1 with PcTx1 in a single polypeptide markedly enhances the potency of PcTx1, whereas competition of Nb.C1 and MitTx1 for binding reduces channel activation by the toxin. Thus, Nb.C1 is a molecular tool for biochemical and structural studies of hASIC1a; a potential antidote to the pain-inducing component of coral snake bite; and a candidate to potentiate PcTx1-mediated inhibition of hASIC1a in vivo for therapeutic applications.

Black-bellied Coral Snake Sinomicrurus nigriventer (Wall, 1908) (Elapidae): an extended distribution in the western Himalaya, India

The Black-bellied Coral Snake Sinomicrurus nigriventer (Wall, 1908) was recently elevated to specific status from Himachal Pradesh where it was also known historically. We present here two individual observations of S. nigriventer from Uttarakhand State of India that constitute the first state record of the species increasing the distribution range ~105 km towards east in the western Himalaya.

Predator-Based Selection And The Impact of Edge Sympatry On Components of Coral Snake Mimicry

Mimicry is a vivid example of how predator-driven selection can impact phenotypic diversity, which itself can be influenced by the presence (sympatry) or absence (allopatry) of a dangerous model. However, the impact of sympatry and allopatry on predation on mimicry systems at fine spatial scales (e.g., edge sympatry, allopatry) is not well understood. We used a clay replica study in a montane tropical site in Honduras to test the impact of edge sympatry on 1) overall attack rates, 2) the fitness benefit of mimetic coloration, 3) predation on specific mimetic signal components, and 4) temporal variation in predator-based selection on mimicry components. Unlike previous research, we found that mimetic phenotypes received significantly more attacks than cryptic replicas in edge sympatry, suggesting that mimetic phenotypes might not confer a fitness benefit in areas of edge sympatry. Additionally, we documented temporal variation in predator-based selection, as the impacts of allopatry on predatory attacks varied among years. Our results imply that the effect of sympatry and allopatry on predator-based selection in mimicry systems may be more complex than previously thought for species-rich assemblies of coral snakes and their mimics in the montane tropics.

Morphological and Molecular Evidence Reveals the First Record of the Coral Snake Micrurus filiformis (Serpentes: Elapidae) as Prey of the Piranha Pygocentrus cariba (Teleostei: Serrasalmidae)

Coral snakes of the genus Micrurus have been recorded as prey of rapacious birds, some mammals and other snakes, but so far not as prey of fishes. The black spotted piranha, Pygocentrus cariba, is an opportunistic predator that feeds mainly on fishes, occasionally on other vertebrates, but has so far not been reported to prey on snakes. Herein, based on morphological and molecular data (mitochondrial 16S fragment), we report the first case of predation of P. cariba on the coral snake Micrurus filiformis. Additionally, we briefly discuss the significance of this new finding for the diet of P. cariba and comment on the systematics and distribution of M. filiformis.

Genetic mechanisms and correlational selection structure trait variation in a coral snake mimic

Covariation among traits shapes both phenotypic evolution and ecological interactions across space and time. However, rampant geographical variation in the strength and direction of such correlations can be particularly difficult to explain through generalized mechanisms. By integrating population genomics, surveys of natural history collections and spatially explicit analyses, we tested multiple drivers of trait correlations in a coral snake mimic that exhibits remarkable polymorphism in mimetic and non-mimetic colour traits. We found that although such traits co-occur extensively across space, correlations were best explained by a mixture of genetic architecture and correlational selection, rather than by any single mechanism. Our findings suggest that spatially complex trait distributions may be driven more by the simple interaction between multiple processes than by complex variation in one mechanism alone. These interactions are particularly important in mimicry systems, which frequently generate striking geographical variation and genetic correlations among colour pattern traits.