Ontogenetic and geographic venom variation in the Great Basin Rattlesnake, Crotalus oreganus lutosus

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  Ontogenetic and geographic venom variation in the Great Basin Rattlesnake, Crotalus oreganus lutosus Abstract Venom composition among the species of the Western Rattlesnake clade is often quite variable, depending on several factors such as geographic location and ontogeny. Venom composition not only affects the ability of a snake to acquire prey efficiently, but it can also significantly impact snakebite symptomology. Currently, there has been limited characterization of the venom from the Great Basin Rattlesnake ( Crotalus oreganus lutosus ), a lineage that is broadly distributed in the intermontane western United States. In this study we sample 67 individual Great Basin Rattlesnakes collected in Idaho, Utah, California, and Arizona. We find evidence for substantial ontogenetic and geographic variation in venom composition. Of the six toxin families assessed, all showed ontogenetic shifts to varying extents, with some trends differing from those observed in other rattlesnake sp...

Small Brains: Body Shape Constrains Tissue Allocation to the Central Nervous System in Ant-Mimicking Spiders

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Small Brains: Body Shape Constrains Tissue Allocation to the Central Nervous System in Ant-Mimicking Spiders

ABSTRACT

In Batesian mimicry, mimetic traits are not always as convincing as predicted by theory—in fact, inaccurate mimicry with only a superficial model resemblance is common and taxonomically widespread. The “selection trade-offs hypothesis” proposes a life-history trade-off between accurate mimetic traits and one or more vital biological functions. Here, using an accurate myrmecomorphic (ant-mimicking) jumping spider species, Myrmarachne smaragdina, we investigate how myrmecomorphic modifications to the body shape impact the internal anatomy in a way that could be functionally limiting. Specifically, via x-ray micro-computed tomography (microCT), we quantify how the spider's constricted prosoma, which emulates the head and thorax of ants, impacts the size of the central nervous system (CNS) and the venom glands. Although, relative to their whole-body mass, we found no significant difference in venom gland volume, the CNS of the ant-mimicking jumping spider was significantly smaller when compared with a relatively closely related non-mimic jumping spider, indicating that some trade-off between mimic accuracy and size of neural anatomy, as articulated by the “selection trade-offs hypothesis,” is a possibility. Our explorative evidence enables and encourages broader investigation of how variable mimic accuracy impacts the neuroanatomy in ant mimics as a direct test of the “selection trade-offs hypothesis.”

J. Kelly, M. B., Penna-Gonçalves, V., Willmott, N. J., McLean, D. J., Black, J. R., Wolff, J. O., & Herberstein, M. E. (2024). Small Brains: Body Shape Constrains Tissue Allocation to the Central Nervous System in Ant-Mimicking Spiders. Journal of Comparative Neurology, 532(11), e25680. https://doi.org/10.1002/cne.25680