Accessing cryptic diversity in Neotropical rattlesnakes (Serpentes: Viperidae: Crotalus) with the description of two new species

Abstract

Members of the Crotalus durissus species complex are widely distributed from Mexico to Argentina in areas with mainly seasonally dry tropical deciduous forest. Although four species (C. culminatus, C. durissus, C. simus and C. tzabcan) are currently recognized, species limits remain to be tested. Previous genetic studies suggest that C. durissus and C. simus may be paraphyletic and that at least one cryptic species may be present. We analyzed 2596 bp of DNA sequence data from three mitochondrial and one nuclear gene to infer phylogenetic relationships in the Neotropical rattlesnakes. We also examined museum and wild specimens as well as captive animals to analyze morphological characters. Our results suggest that the current taxonomy of the Crotalus durissus species complex does not reflect evolutionary history. We found strong support for five independent lineages within Crotalus simus (sensu lato), with genetic and morphological evidence for three previously recognized taxa and two new species, as well as three major lineages within C. durissus that each represent species hypothesis to be tested with additional evidence. We also found support to retain C. totonacus in the Crotalus molossus species complex. We suggest conservative taxonomic changes to the complex and related species, but more evidence is needed (e.g., morphology, ecology and venom composition) to clarify relationships among species.

A Clot Twist: Extreme Variation in Coagulotoxicity Mechanisms in Mexican Neotropical Rattlesnake Venoms

“…A logical explanation is that Antivipmyn R does not include C. culminatus venom in its immunizing mixture, relying on venom from adult C. simus specimens instead (112). C. simus has been recently split into C. ehecatl and C. mictlantecuhtli throughout most of its Mexican range (26), which is likely to affect antivenom manufacturing in turn. To our knowledge, no snake antivenom is produced using venom from juvenile individuals, and this is due to practical constraints of lower venom yields from smaller snakes.…”

“…From a phylogenetic point of view, C. culminatus is consistently retrieved as an early divergence from the rest of the C. durissus complex (18,26). Therefore, the true procoagulant venom phenotype observed in this species might have evolved independently or represented the ancestral state for this clade.…”

“…Therefore, the true procoagulant venom phenotype observed in this species might have evolved independently or represented the ancestral state for this clade. The latter possibility was investigated by testing the venom of C. molossus, part of the sister clade to the C. durissus complex alongside C. basiliscus, C. ornatus, and C. totonacus (26,27). However, our thromboelastography and factor activation results revealed only a weakly pseudo-procoagulant venom action for the nominate subspecies C. m. molossus and distinctly anticoagulant patterns for a C. m. oaxacus representative, which greatly degraded fibrinogen to a point where addition of thrombin was unable to form a clot.…”

“…Among the most iconic and medically significant rattlesnake species in Mexico are the Neotropical rattlesnakes: Crotalus culminatus, C. ehecatl, C. mictlantecuhtli, C. simus, and C. tzabcan. These species are part of the Crotalus durissus complex, which also includes the eponymous species C. durissus alongside C. vegrandis (22,25,26) and is in turn included in the C. durissus group with a sister clade comprising C. basiliscus, C. molossus, C. ornatus, and C. totonacus [ (22,27), Figure 1]. These medium-to large-bodied rattlesnakes range from the southwestern United States (C. molossus) to northern Argentina (C. durissus), where they are responsible for a considerable number of serious envenoming cases (14,15,(28)(29)(30)(31)(32).…”

Neotropical Rattlesnake (Crotalus simus) Venom Pharmacokinetics in Lymph and Blood Using an Ovine Model

“…Its venom is used in the hyperimmunization of horses to produce antivenom in Mexico [4]. The organisms formerly classified as C. simus that are distributed in the state of Veracruz have recently been proposed to be a new species (C. mictlantecuhtli) [5], but for the purpose of consistency with prior reports we will refer to them here using the traditional taxonomy.…”