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The highest species richness and ecological diversity of extant snakes are in the tropics, primarily in South Asia and Central and South America. Tropical Africa has relatively lower richness and less diversity, but the evolution of tropical herpetofaunas, and the factors governing diversification through time at continental scales are poorly understood due to an understudied fossil record. The ecologies and geographic distributions of aniliid and uropeltoid snakes are examples. Modern species constitute either a grade or clade of fossorial, primarily wet forest taxa from South America and South Asia. Their distributions have historically been interpreted as Gondwanan vicariance following the isolation of Africa in the Early Cretaceous, but a definitive fossil record for these snakes is depauperate. Field research in the early Miocene (approx. 19 Mya) Tinderet sequence of western Kenya has produced precloacal vertebrae of an aniliid snake from multiple localities. Specimens possess vertebral apomorphies shared with extant South American Anilius scytale, including the morphology of the neural spine and prezygapophyseal angle. Combined with additional fossils from the Eocene of North Africa and Middle Miocene of Kenya, the Tinderet records demonstrate an unambiguous past record of an extant neotropical snake lineage in Africa and falsify previous vicariance hypotheses. Recent stable isotopic and palynological studies of Neogene eastern African fossil localities have indicated heterogenous environments, including C4 grasses and wood- to scrubland, associated with vertebrate faunas. Comparing climate parameters of habitats for extant Anilius and uropeltoid snakes as ecological analogues to the Tinderet snake with modern ecosystems equivalent to those reconstructed for the eastern African early Miocene demonstrates only limited overlap in precipitation and temperature values. This discord indicates either greater environmental heterogeneity than reconstructed for the early Miocene of eastern Africa, or a greater range of habitat variability in aniliid snakes than observed in extant Anilius.
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Urates of colubroid snakes are different from those of boids and pythonids
Abstract Uricotelic species, such as squamate reptiles, birds and insects, effectively eliminate nitrogen as uric acid in a solid form commonly called urates. Observations made over a decade suggested that the voided urates produced by colubroids (modern snake species) exhibit remarkable differences from those of boids and pythons (ancient snake species). Here, we compare the urates generated by eight captive snake species fed the same diet. Although all fresh urates were wet at the time of excretion, those produced by modern snakes dried to a powdery solid, whereas those of ancient species dried to a rock-hard mass that was tightly adherent to surfaces. Powder X-ray diffraction and infrared spectroscopy analyses performed on voided urates produced by five modern and three ancient snakes confirmed their underlying chemical and structural differences. Urates excreted by ancient snakes were amorphous uric acid, whereas urates from modern snakes consisted primarily of ammonium acid urate, with some uric acid dihydrate. These compositional differences indicate that snakes have more than one mechanism to manage nitrogenous waste. Why different species use different nitrogen-handling pathways is not yet known, but the answer might be related to key differences in metabolism, physiology or, in the case of ancient snakes, the potential use of urates in social communication.
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- Award ID(s):
- 2004435
- PAR ID:
- 10269326
- Date Published:
- Journal Name:
- Biological Journal of the Linnean Society
- Volume:
- 133
- Issue:
- 3
- ISSN:
- 0024-4066
- Page Range / eLocation ID:
- 910 to 919
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The highest species richness and ecological diversity of extant snakes are in the tropics, primarily in South Asia and Central and South America. Tropical Africa has relatively lower richness and less diversity, but the evolution of tropical herpetofaunas, and the factors governing diversification through time at continental scales are poorly understood due to an understudied fossil record. The ecologies and geographic distributions of aniliid and uropeltoid snakes are examples. Modern species constitute either a grade or clade of fossorial, primarily wet forest taxa from South America and South Asia. Their distributions have historically been interpreted as Gondwanan vicariance following the isolation of Africa in the Early Cretaceous, but a definitive fossil record for these snakes is depauperate. Field research in the early Miocene (approx. 19 Mya) Tinderet sequence of western Kenya has produced precloacal vertebrae of an aniliid snake from multiple localities. Specimens possess vertebral apomorphies shared with extant South American Anilius scytale, including the morphology of the neural spine and prezygapophyseal angle. Combined with additional fossils from the Eocene of North Africa, the Tinderet records demonstrate an unambiguous past record of an extant neotropical snake lineage in Africa and falsify previous vicariance hypotheses. Recent stable isotopic and palynological studies of Neogene eastern African fossil localities have indicated heterogenous environments, including C4 grasses and wood- to scrubland, associated with vertebrate faunas. Comparing climate parameters of habitats for extant Anilius and uropeltoid snakes as ecological analogues to the Tinderet snake with modern ecosystems equivalent to those reconstructed for the eastern African early Miocene demonstrates only limited overlap in precipitation and temperature values. This discord indicates either greater environmental heterogeneity than reconstructed for the early Miocene of eastern Africa, or a greater range of habitat variability in aniliid snakes than observed in extant Anilius.more » « less
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null (Ed.)The gastrointestinal tract (GIT) of vertebrates contains a series of organs beginning with the mouth and ending with the anus or cloacal opening. Each organ represents a unique environment for resident microorganisms. Due to their simple digestive anatomy, snakes are good models for studying microbiome variation along the GIT. Cloacal sampling captures the majority of the microbial diversity found in the GIT of snakes—yet little is known about the oral microbiota of snakes. Most research on the snake mouth and gut microbiota are limited to studies of a single species or captive-bred individuals. It therefore remains unclear how a host’s life history, diet, or evolutionary history correlate with differences in the microbial composition within the mouths and guts of wild snakes. We sampled the mouth and gut microbial communities from three species of Asian venomous snakes and utilized 16S rRNA microbial inventories to test if host phylogenetic and ecological differences correlate with distinct microbial compositions within the two body sites. These species occupy three disparate habitat types: marine, semi-arboreal, and arboreal, our results suggest that the diversity of snake mouth and gut microbial communities correlate with differences in both host ecology and phylogeny.more » « less
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Abstract Meiotic recombination in vertebrates is concentrated in hotspots throughout the genome. The location and stability of hotspots have been linked to the presence or absence of PRDM9, leading to two primary models for hotspot evolution derived from mammals and birds. Species with PRDM9-directed recombination have rapid turnover of hotspots concentrated in intergenic regions (i.e., mammals), whereas hotspots in species lacking PRDM9 are concentrated in functional regions and have greater stability over time (i.e., birds). Snakes possess PRDM9, yet virtually nothing is known about snake recombination. Here, we examine the recombination landscape and test hypotheses about the roles of PRDM9 in rattlesnakes. We find substantial variation in recombination rate within and among snake chromosomes, and positive correlations between recombination rate and gene density, GC content, and genetic diversity. Like mammals, snakes appear to have a functional and active PRDM9, but rather than being directed away from genes, snake hotspots are concentrated in promoters and functional regions—a pattern previously associated only with species that lack a functional PRDM9. Snakes therefore provide a unique example of recombination landscapes in which PRDM9 is functional, yet recombination hotspots are associated with functional genic regions—a combination of features that defy existing paradigms for recombination landscapes in vertebrates. Our findings also provide evidence that high recombination rates are a shared feature of vertebrate microchromosomes. Our results challenge previous assumptions about the adaptive role of PRDM9 and highlight the diversity of recombination landscape features among vertebrate lineages.more » « less
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Abstract Background The explosive radiation and diversification of the advanced snakes (superfamily Colubroidea) was associated with changes in all aspects of the shared venom system. Morphological changes included the partitioning of the mixed ancestral glands into two discrete glands devoted for production of venom or mucous respectively, as well as changes in the location, size and structural elements of the venom-delivering teeth. Evidence also exists for homology among venom gland toxins expressed across the advanced snakes. However, despite the evolutionary novelty of snake venoms, in-depth toxin molecular evolutionary history reconstructions have been mostly limited to those types present in only two front-fanged snake families, Elapidae and Viperidae. To have a broader understanding of toxins shared among extant snakes, here we first sequenced the transcriptomes of eight taxonomically diverse rear-fanged species and four key viperid species and analysed major toxin types shared across the advanced snakes. Results Transcriptomes were constructed for the following families and species: Colubridae - Helicops leopardinus , Heterodon nasicus , Rhabdophis subminiatus ; Homalopsidae – Homalopsis buccata ; Lamprophiidae - Malpolon monspessulanus , Psammophis schokari , Psammophis subtaeniatus , Rhamphiophis oxyrhynchus ; and Viperidae – Bitis atropos , Pseudocerastes urarachnoides , Tropidolaeumus subannulatus , Vipera transcaucasiana . These sequences were combined with those from available databases of other species in order to facilitate a robust reconstruction of the molecular evolutionary history of the key toxin classes present in the venom of the last common ancestor of the advanced snakes, and thus present across the full diversity of colubroid snake venoms. In addition to differential rates of evolution in toxin classes between the snake lineages, these analyses revealed multiple instances of previously unknown instances of structural and functional convergences. Structural convergences included: the evolution of new cysteines to form heteromeric complexes, such as within kunitz peptides (the beta-bungarotoxin trait evolving on at least two occasions) and within SVMP enzymes (the P-IIId trait evolving on at least three occasions); and the C-terminal tail evolving on two separate occasions within the C-type natriuretic peptides, to create structural and functional analogues of the ANP/BNP tailed condition. Also shown was that the de novo evolution of new post-translationally liberated toxin families within the natriuretic peptide gene propeptide region occurred on at least five occasions, with novel functions ranging from induction of hypotension to post-synaptic neurotoxicity. Functional convergences included the following: multiple occasions of SVMP neofunctionalised in procoagulant venoms into activators of the clotting factors prothrombin and Factor X; multiple instances in procoagulant venoms where kunitz peptides were neofunctionalised into inhibitors of the clot destroying enzyme plasmin, thereby prolonging the half-life of the clots formed by the clotting activating enzymatic toxins; and multiple occasions of kunitz peptides neofunctionalised into neurotoxins acting on presynaptic targets, including twice just within Bungarus venoms. Conclusions We found novel convergences in both structural and functional evolution of snake toxins. These results provide a detailed roadmap for future work to elucidate predator–prey evolutionary arms races, ascertain differential clinical pathologies, as well as documenting rich biodiscovery resources for lead compounds in the drug design and discovery pipeline.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/biolinnean/blab052
