Observaciones sobre la dieta de Crotalus triseriatus (Serpiente de cascabel oscura mexicana)

Observations on the diet of Crotalus triseriatus (Mexican dusky rattlesnake) from central México are reported. We recovered the remains of 12 individual prey items from 11 different snakes. Prey included 7 rodents, 4 lizards and 1 salamander. These observations reinforce that C. triseriatus consumes a diverse diet and utilizes varied foraging strategies.Se registran observaciones sobre la dieta de Crotalus triseriatus (serpiente de cascabel oscura mexicana) en el centro de México. Recuperamos 12 diferentes presas provenientes de 11 serpientes. Las presas incluyen 7 roedores, 4 lagartijas y 1 salamandra. Nuestras observaciones sugieren que C. triseriatus tiene una dieta diversa y presenta hábitos alimenticios variados

Análise preliminar revela baixos níveis de diversidade na estrutura filogeográfica da cascavel mexicana Crotalus polystictus (Serpentes: Viperidae).

Se investigaron las relaciones matrilineales entre poblaciones de la serpiente de cascabel Mexicana cabeza de lanza  (Crotalus polystictus), esta especie se distribuye en valles que presentan elevaciones altas de la meseta del sur de México. Se analizó un fragmento mitocondrial de la ATPasa 8 y 6, los genes (589 pares de bases) revelaron bajos niveles de diversidad genética, con poco polimorfismo nucleótico entre la muestra geográfica analizada. La poca divergencia (1.0%) intraespecífica encontrada en los genes de la ATPasa 8 y 6 en C. polystictus contrastan con los fuertes porcentajes de divergencia (~1.0–14.1%) que han sido observados dentro de otros linajes de serpientes de cascabel mexicanas que habitan elevaciones altas. La variación intraespecífica es observadacomúnmente en especies de cascabel que se distribuyen en elevaciones menores y que presentan una distribución amplia (por ejemplo, C. tigris). Proponemos que la baja diversidad genética encontrada en C. polystictus comparada con la diversidad registrada en otras serpientes de cascabel que habitan elevaciones altas, se debe a diferencias ecológicas que han dado como resultado una respuesta evolutiva diferente en esta especie a los eventos climáticos del Pleistoceno. Nuestros resultados de una aparente baja diversidad genética en C. polystictus son un fuerte soporte para hacer un llamadoa la importancia de realizar iniciativas de conservación para proteger praderas con elevaciones altas en el centro de México.Foram investigadas as relações matrilineares entre as populações da cascavel mexicana Crotalus polystictus, uma espécie que habita vales de altitude do planalto do sul do México. Os genes (589 pares de bases) de um fragmento mitocondrial da ATPase 8 e 6 revelaram níveis relativamente baixos de diversidade genética, com poucos polimorfismos de nucleotídeos entre a amostra geográfica analisada. A baixa divergência da sequência intraespecífica (1.0%) encontrada nos genes da ATPase 8 e 6 de C. polystictus contrasta com asfortes divergências (~1.0–14.1%) observadas em outras linhagens de cascavel que habitam grandes altitudes, sendo que a variação intra-específica é observada comumente em espécies de cascavel que estão distribuídas em altitudes mais baixas e apresentam uma ampla distribuição (por exemplo, C.tigris). Propomos que a baixa diversidade genética encontrada em C. polystictus, comparada com a de outras cascavéis que habitam altitudes elevadas, pode refletir diferenças ecológicas que resultaram em uma resposta evolutiva diferente aos eventos climáticos do Pleistoceno. Nossos resultados deuma baixa diversidade genética aparente em C. polystictus destacam a importância de iniciativas de conservação para proteger os campos de altitude da região central do México.We investigated matrilineal relationships among populations of the Mexican lance-headed rattlesnake (Crotalus polystictus), a pitviper inhabiting high-elevation valleys of the densely populated southern Mexican Plateau. A fragment of the mitochondrial ATPase 8 and 6 genes (589 base pairs) revealed comparatively low levels of genetic diversity, with few nucleotide polymorphisms across the portion of the geographic distribution sampled. The shallow intraspecific sequence divergence (1.0%) in C. polystictus ATPase 8 and 6 genes contrasts with deepdivergences (~1.0–14.1%) observed within other montane rattlesnake lineages from the Mexican highlands, and is more typical of intraspecific variation observed in lowland rattlesnake species with similar distributional extents (e.g., C. tigris). We posit that the low genetic diversity in C. polystictus relative to that of other highland rattlesnakes may reflect ecological differences resulting in a different evolutionary response to Pleistocene climatic events. Our finding of apparently low genetic diversity in C. polystictus highlights the importance of conservation initiatives to protect high elevation grasslands in central Mexico

Venom Ontogeny in the Mexican Lance-Headed Rattlesnake (Crotalus polystictus)

As trophic adaptations, rattlesnake venoms can vary in composition depending on several intrinsic and extrinsic factors. Ontogenetic changes in venom composition have been documented for numerous species, but little is known of the potential age-related changes in many rattlesnake species found in México. In the current study, venom samples collected from adult and neonate Crotalus polystictus from Estado de México were subjected to enzymatic and electrophoretic analyses, toxicity assays (LD50), and MALDI-TOF mass spectrometry, and a pooled sample of adult venom was analyzed by shotgun proteomics. Electrophoretic profiles of adult males and females were quite similar, and only minor sex-based variation was noted. However, distinct differences were observed between venoms from adult females and their neonate offspring. Several prominent bands, including P-I and P-III snake venom metalloproteinases (SVMPs) and disintegrins (confirmed by MS/MS) were present in adult venoms and absent/greatly reduced in neonate venoms. Age-dependent differences in SVMP, kallikrein-like, phospholipase A2 (PLA2), and L-amino acid oxidase (LAAO) activity levels were confirmed by enzymatic activity assays, and like many other rattlesnake species, venoms from adult snakes have higher SVMP activity than neonate venoms. Conversely, PLA2 activity was approximately 2.5 X greater in venoms from neonates, likely contributing to the increased toxicity (neonate venom LD50 = 4.5 μg/g) towards non-Swiss albino mice when compared to adult venoms (LD50 = 5.5 μg/g). Thrombin-like (TLE) and phosphodiesterase activities did not vary significantly with age. A significant effect of sex (between adult male and adult female venoms) was also observed for SVMP, TLE, and LAAO activities. Analysis of pooled adult venom by LC-MS/MS identified 14 toxin protein families, dominated by bradykinin-inhibitory peptides, SVMPs (P-I, P-II and P-III), disintegrins, PLA2s, C-type-lectins, CRiSPs, serine proteinases, and LAAOs (96% of total venom proteins). Neonate and adult C. polystictus in this population consume almost exclusively mammals, suggesting that age-based differences in composition are related to physical differences in prey (e.g., surface-to-volume ratio differences) rather than taxonomic differences between prey. Venoms from adult C. polystictus fit a Type I pattern (high SVMP activity, lower toxicity), which is characteristic of many larger-bodied rattlesnakes of North America.Funding for this study was provided in part by the Colorado Office for Economic Development and International Trade (to SPM). Additional funds were provided by the UNC Office of Research

Ecología trófica de tres especies de serpientes de cascabel en México: Crotalus Aquilus, Crotalus Polystictus y Crotalus Willardi

El objetivo general de éste trabajo es aumentar el conocimiento que se tiene sobre la ecología de la alimentación en serpientes de cascabel de México mediante un robusto análisis de la dieta de tres especies, dos de ellas endémicas y que habitan el centro del país, Crotalus aquilus y Crotalus polystictus, y otra, Crotalus willardi, que habita el norte del país, en los estados de Chihuahua y Sonora. El conocimiento de la ecología trófica de estos tres crótalos es cuasi inexistente, con la excepción de estudios en las poblaciones de C. willardi de los Estados Unidos de América (US).Tesis Univ. Granada. Departamento de Zoologí

Data from: Sexual differences in head form and diet in a population of Mexican Lance-headed Rattlesnakes, Crotalus polystictus

Sexual dimorphism of phenotypic traits associated with resource use is common in animals, and may result from niche divergence between sexes. Snakes have become widely used in studies of the ecological basis of sexual dimorphism because they are gape-limited predators and their head morphology is likely to be a direct indicator of the size and shape of prey consumed. We examined sexual dimorphism of body size and head morphology, and sexual differences in diet in a population of Mexican lance-headed rattlesnakes, Crotalus polystictus, from the State of México, Mexico. Maximum snout–vent length of males was greater than that of females by 21%. Males had relatively larger heads, and differed from females in head shape after removing effects of head size. In addition, male rattlesnakes showed positive allometry in head shape: head width was amplified while snout length was truncated with increased head size. In contrast, our data did not provide clear evidence of allometry in head shape of females. Adults of both males and females ate predominately mice and voles; however, males also consumed a greater proportion of larger mammalian species, and fewer small prey species. The differences in diet correspond with dimorphism in head morphology, and provide evidence of intersexual niche divergence in our study population. However, because the sexes overlapped greatly in diet, we hypothesize that diet and head dimorphisms in C. polystictus are likely related to different selection pressures in each sex arising from preexisting body size differences rather than from character displacement for reducing intersexual competition

Shallow phylogeographic structure in the declining Mexican Lance-headed Rattlesnake, Crotalus polystictus (Serpentes: Viperidae)

We investigated matrilineal relationships among populations of the Mexican lance-headed rattlesnake (Crotalus polystictus), a pitviper inhabiting high-elevation valleys of the densely populated southernMexican Plateau. A fragment of the mitochondrial ATPase 8 and 6 genes (589 base pairs) revealed comparatively low levels of genetic diversity, with few nucleotide polymorphisms across the portion of the geographic distribution sampled. The shallow intraspecificsequence divergence (1.0%) in C. polystictus ATPase 8 and 6 genes contrasts with deep divergences (~1.0–14.1%) observed within other montane rattlesnake lineages from the Mexican highlands, and is more typical of intraspecific variation observed in lowland rattlesnake species with similar distributional extents (e.g., C. tigris). We posit that the low genetic diversity in C. polystictus relative to that of other highland rattlesnakes may reflect ecological differences resulting in a different evolutionary response to Pleistocene climatic events. Our finding of apparently low genetic diversity in C. polystictus highlights the importance of conservation initiatives to protect high elevation grasslands in central Mexico