Evolutionary allometry and ecological correlates of fang length evolution in vipers

Traits for prey acquisition form the phenotypic interface of predator–prey interactions. In venomous predators, morphological variation in venom delivery apparatus like fangs and stingers may be optimized for dispatching prey. Here, we determine how a single dimension of venom injection systems evolves in response to variation in the size, climatic conditions and dietary ecology of viperid snakes. We measured fang length in more than 1900 museum specimens representing 199 viper species (55% of recognized species). We find both phylogenetic signal and within-clade variation in relative fang length across vipers suggesting both general taxonomic trends and potential adaptive divergence in fang length. We recover positive evolutionary allometry and little static allometry in fang length. Proportionally longer fangs have evolved in larger species, which may facilitate venom injection in more voluminous prey. Finally, we leverage climatic and diet data to assess the global correlates of fang length. We find that models of fang length evolution are improved through the inclusion of both temperature and diet, particularly the extent to which diets are mammal-heavy diets. These findings demonstrate how adaptive variation can emerge among components of complex prey capture systems.

Características para aquisição de presas formam a interface fenotípica das interações predador-presa. Em predadores venenosos, a variação morfológica no aparelho de entrega de veneno, como presas e ferrões, pode ser otimizada para despachar presas. Aqui, determinamos como uma única dimensão dos sistemas de injeção de veneno evolui em resposta à variação no tamanho, condições climáticas e ecologia alimentar de cobras viperídeos. Medimos o comprimento das presas em mais de 1.900 espécimes de museus representando 199 espécies de víboras (55% das espécies reconhecidas). Encontramos tanto o sinal filogenético quanto a variação dentro do clado no comprimento relativo das presas entre as víboras, sugerindo tendências taxonômicas gerais e potencial divergência adaptativa no comprimento das presas. Recuperamos alometria evolutiva positiva e pouca alometria estática no comprimento das presas. Presas proporcionalmente mais longas evoluíram em espécies maiores, o que pode facilitar a injeção de veneno em presas mais volumosas. Por fim, aproveitamos os dados climáticos e de dieta para avaliar os correlatos globais do comprimento das presas. Descobrimos que os modelos de evolução do comprimento das presas são melhorados através da inclusão de temperatura e dieta, particularmente na medida em que as dietas são dietas pesadas para mamíferos. Essas descobertas demonstram como a variação adaptativa pode surgir entre os componentes de sistemas complexos de captura de presas.

The systematics of Tachymenini (Serpentes, Dipsadidae): an updated classification based on molecular and morphological evidence

Despite the recent advances in the systematics of snakes, the diversity of several Neotropical groups of species remains poorly understood. The lack of studies focused on the phylogenetic relationship within most of the 20 tribes of Dipsadidae precludes a better understanding of the evolution of this diverse family. Here, we present a comprehensive phylogenetic analysis of Tachymenini, a heterogeneous tribe that comprises 36 viviparous species of dipsadids, grouped in seven genera based on morphological similarities. The tribe is widely distributed throughout South America presenting very distinctive phenotypes, habitats, and behaviours. The phylogenetic relationship among tachymenins is a well-recognized challenge regarding the systematics of the South American dipsadids. The similar morphotype of some generalist species, combined with the very derived morphology of some strict specialists, creates a complexity of traits that has prevented the comprehension of the systematics of the group. To address such a challenge, we combine molecular (six loci) and morphological (70 characters) datasets in an integrative phylogenetic approach. The resultant phylogenetic trees indicate, with strong support, that three of the seven current recognized genera (Tachymenis, Tomodon, and Thamnodynastes) are non-monophyletic and, consequently, we propose a new systematic arrangement for Tachymenini. We revalidate two genera, Dryophylax and Mesotes, and we describe three additional monotypic genera, Apographon gen. n., Tachymenoides gen. n., and Zonateres gen. n. to accommodate Tomodon orestes, Tachymenis affinis, and Thamnodynastes lanei, respectively. We also include Tomodon ocellatus and Pseudotomodon trigonatus in Tachymenis and describe a new genus, Galvarinus gen. n., to accommodate the Tachymenis chilensis species group. Furthermore, we also provide an evolutionary scenario for the speciation events based on a time-calibrated tree, commenting on the diversification and origin of the tribe, and on the probable existence of undescribed species of Mesotes and Dryophylax.

Notes on the hyperossified pumpkin toadlets of the genus Brachycephalus (Anura: Brachycephalidae) with the description of a new species

Four species of pumpkin toadlets are currently recognized by the extreme condition of hyperossification in the skull and vertebral column within the genus Brachycephalus. In addition to their larger body size, relative to other congeneric species, Brachycephalus darkside, Brachycephalus ephippium, Brachycephalus garbeanus, and Brachycephalus margaritatus share remarkable osteological features, such as the large paravertebral plates forming an ornamented dorsal bone shield, visible through the integument. We add to the current knowledge of this group by analyzing its diversity and describing a new hyperossified species from some important Atlantic Forest remnants in southeastern Brazil, including those bordering São Paulo, the largest and most populous city in South America. The new species is diagnosed by a combination of morphological, osteological, and bioacoustic characters, with further evidence of mtDNA sequences to confirm its distinction from the other congeners. The parotic and paravertebral bone plates externally bordered with a rough and pale contour can readily distinguish the new species from the other hyperossified species within Brachycephalus. The new species is widely distributed along the Serra do Mar mountain range, including the regionally named Serra de Paranapiacaba, in elevations from 700 to 1000 m above sea level (a.s.l.), in the central coast of the state of São Paulo, southeastern Brazil. We discuss valuable morphological characters within this group of species, reinforce the need for further studies, and highlight the relevance of protected areas for biodiversity conservation in metropolitan regions.

A new species of Thamnodynastes Wagler, 1830 from western Amazonia, with notes on morphology for members of the Thamnodynastes pallidus group (Serpentes, Dipsadidae, Tachymenini)

The genus Thamnodynastes is the most diverse within the tribe Tachymenini, with an extensive and complex taxonomic history. The brief descriptions and lack of robust diagnostic characters are the main sources for identification errors and for the difficulty to assess the diversity estimates of the genus. The Thamnodynastes pallidus group was briefly designated to encompass the most arboreal species of the genus, with thinner bodies and longer tails: T. pallidus, T. longicaudus, T. sertanejo, and a fourth undescribed species. After its designation, no other paper addressed this group and its morphological variation, especially for the hemipenis, is still undetermined. After the analysis of all species of Thamnodynastes we were able to corroborate the distinctiveness of the T. pallidus group and to accurately diagnose its fourth species from the western portion of the Amazonia lowlands. The new species is distinguishable from all congeners, except T. sertanejo, by the absence of ventral longitudinal stripes, 17/17/11 dorsal scale rows, and dorsal dark brown blotches on the anterior third of the body. The new species is distinguished from T. sertanejo by the higher number of subcaudals, lower number of ventrals, and smaller body and head sizes. We also provide additional diagnostic features for the Thamnodynastes pallidus group, including new data on hemipenial variation. Finally, we briefly discuss the defensive behavior and morphological characters associated with arboreality in members of the T. pallidus species group.