Ancestral Reconstruction of Diet and Fang Condition in the Lamprophiidae: Implications for the Evolution of Venom Systems in Snakes

Paedomorphosis and retention of juvenile diet lead speciation in a group of Neotropical snakes (Colubroides-Philodryadini)

Dipsadidae is one of the largest clades of extant reptiles, showing an impressive morphological and ecological diversity. Despite this fact, the developmental processes behind its diversity are still largely unknown. In this study, we used 3D reconstructions based on micro-CT data and geometric morphometrics to evaluate the skull morphology of Philodryas agassizii, a small, surface-dwelling dipsadid that consume spiders. Adult individuals of P. agassizii exhibit a cranial morphology frequently observed in juveniles of other surface-dwelling colubroideans, represented in our analysis by its close relative Philodryas patagoniensis. Large orbits, gibbous neurocranial roof and a relatively short jaw complex are features present in juveniles of the latter species. Furthermore, we performed an extensive survey about diet of P. patagoniensis in which we detected an ontogenetic dietary shift, indicating that arthropods are more frequently consumed by juveniles of this dietary generalist. Thus, we infer that P. agassizzii retained not only the ancestral juvenile skull morphology but also dietary preferences. This study reveals that morphological changes driven by heterochronic changes, specifically paedomorphosis, influenced the retention of ancestral life history traits in P. agassizii, and therefore promoted cladogenesis. In this way, we obtained first evidence that heterochronic processes lead speciation in the snake megadiverse clade Dipsadidae.

The Non-Dereliction in Evolution: Trophic Specialisation Drives Convergence in the Radiation of Red Devil Spiders (Araneae: Dysderidae) in the Canary Islands

Natural selection plays a key role in deterministic evolution, as clearly illustrated by the multiple cases of repeated evolution of ecomorphological characters observed in adaptive radiations. Unlike most spiders, Dysdera species display a high variability of cheliceral morphologies, which has been suggested to reflect different levels of specialization to feed on isopods. In this study, we integrate geometric morphometrics and experimental trials with a fully resolved phylogeny of the highly diverse endemic species from the Canary Islands to 1) quantitatively delimit the different cheliceral morphotypes present in the archipelago, 2) test their association with trophic specialization, as reported for continental species, 3) reconstruct the evolution of these ecomorphs throughout the diversification of the group, 4) test the hypothesis of convergent evolution of the different morphotypes, and 5) examine whether specialization constitutes a case of evolutionary irreversibility in this group. We show the existence of 9 cheliceral morphotypes and uncovered their significance for trophic ecology. Further, we demonstrate that similar ecomorphs evolved multiple times in the archipelago, providing a novel study system to explain how convergent evolution and irreversibility due to specialization may be combined to shape phenotypic diversification in adaptive radiations.

Evolution of the rostral scale and mimicry in the genus Xenodon Boie, 1826 (Serpentes: Dipsadidae: Xenodontinae)

Snakes are a stimulating life form from an evolutionary perspective. Despite the basic morphological body shape (limbless, with a tubular body), these vertebrates are extremely diverse. The Neotropical region is one of the most diverse regions for snakes in the world, with >650 known species. Within this great diversity, the genus Xenodon includes 12 species with interesting adaptations to terrestrial and semi-fossorial habitats. Members of this genus are mostly diurnal and terrestrial, feed mainly on anurans and exhibit Batesian mimicry of venomous snakes of the genera Bothrops or Micrurus. Here, through phylogenetic analysis and ancestral state estimation, we explore the evolution of the rostral scale and mimicry within the genus Xenodon. Our results suggest that the ancestral lineage of Xenodon had a rounded rostral scale and exhibited Bothrops mimicry. The evolution of the rostral scale in Xenodon might be related to abiotic factors, as an adaptation for open and forested habitats, and mimicry is likely to be related to biotic factors, as a defensive strategy resembling those of venomous snakes.

Repeated dietary shifts in elapid snakes (Squamata: Elapidae) revealed by ancestral state reconstruction

Identifying the traits of ancestral organisms can reveal patterns and drivers of organismal diversification. Unfortunately, reconstructing complex multistate traits (such as diet) remains challenging. Adopting a ‘reconstruct, then aggregate’ approach in a maximum likelihood framework, we reconstructed ancestral diets for 298 species of elapid snakes. We tested whether different prey types were correlated with one another, tested for one-way contingency between prey type pairs, and examined the relationship between snake body size and dietary composition. We demonstrate that the evolution of diet was characterized by niche conservation punctuated by repeated dietary shifts. The ancestor of elapids most likely fed on reptiles and possibly amphibians, with deviations from this ancestral diet occurring repeatedly due to shifts into marine environments and changes in body size. Moreover, we demonstrate important patterns of prey use, including one-way dependency—most obviously the inclusion of eggs being dependent on a diet that already included the producers of those eggs. Despite imperfect dietary data, our approach produced a robust overview of dietary evolution. Given the paucity of natural history information for many organisms, our approach has the potential to increase the number of lineages to which ancestral state reconstructions of multistate traits can be robustly applied.