Posible invasión de un nicho alimentario nuevo y microevolución en una especie mexicana de serpiente

Este ensayo trata los determinantes de la dieta en serpientes y en particular se discute un fenómeno único entre las 29 especies del género Thamnophis: la ingestión de acociles por T. melanogaster como posible invasión del género dentro de un nicho alimentario nuevo. Se plantea la oportunidad de estudiar aspectos del proceso de entrada como la microevolución de la conducta y la morfología de la dentición y cráneo asociada a la incorporación de una nueva presa en la dieta. Finalmente se discute la posibilidad de la acocilofagia como un carácter conductual ancestral que ahora sólo permanece como una conducta homóloga.Este ensayo trata los determinantes de la dieta en serpientes y en particular se discute un fenómeno único entre las 29 especies del género Thamnophis: la ingestión de acociles por T. melanogaster como posible invasión del género dentro de un nicho alimentario nuevo. Se plantea la oportunidad de estudiar aspectos del proceso de entrada como la microevolución de la conducta y la morfología de la dentición y cráneo asociada a la incorporación de una nueva presa en la dieta. Finalmente se discute la posibilidad de la acocilofagia como un carácter conductual ancestral que ahora sólo permanece como una conducta homóloga

SPEA MULTIPLICATA (Mexican Spadefoot). PREDATION

El documento (pdf) incluye dos paginas, la portada de la revista y el texto de la nota cientifica que solo son 4 parrafos, es solo una cuartillawe document a new predator-prey interaction between a neonate Mexican Dusky Rattlesnake (Crotalus triseriatus) and a toad Spea multiplicata.CONACY

MORTALIDAD INTENCIONAL DE PLESTIODON COPEI (SCINCIDAE) CAUSADA POR HUMANOS.

Artículo científicoIn México, several species of lizards are popularly considered as venomous species because they have bright colors, therefore they are susceptible to being intentionally killed. In this note we report an intentional mortality of a gravid female of Plestiodon copei for being considered as a venomous lizard, mainly for its tail coloration. This type of activity has a negative impact on the populations of P. copei, therefore it is necessary to highlight to the local residents that it is not a venomous species

Morphological convergence in a Mexican garter snake associated with the ingestion of a novel prey

Morphological convergence is expected when organisms which differ in phenotype experience similar functional demands, which lead to similar associations between resource utilization and performance. To consume prey with hard exoskeletons, snakes require either specialized head morphology, or to deal with them when they are vulnerable, for example, during molting. Such attributes may in turn reduce the efficiency with which they prey on soft-bodied, slippery animals such as fish. Snakes which consume a range of prey may present intermediate morphology, such as that of Thamnophiine (Natricinae), which may be classified morphometrically across the soft–hard prey dietary boundary. In this study, we compared the dentition and head structure of populations of Thamnophis melanogaster that have entered the arthropod–crustacean (crayfish)-eating niche and those that have not, and tested for convergence between the former and two distantly related crayfish specialists of the genus Regina (R. septemvittata and R. grahamii). As a control, we included the congener T. eques. Multivariate analysis of jaw length, head length, head width, and number of maxillary teeth yielded three significant canonical variables that together explained 98.8% of the variance in the size-corrected morphological data. The first canonical variable significantly discriminated between the three species. The results show that head dimensions and number of teeth of the two Regina species are more similar to those of crayfish-eating T. melanogaster than to non-crayfish- eating snakes or of T. eques. It is unclear how particular head proportions or teeth number facilitates capture of crayfish, but our results and the rarity of soft crayfish ingestion by T. melanogaster may reflect the novelty of this niche expansion, and are consistent with the hypothesis that some populations of T. melanogaster have converged in their head morphology with the two soft crayfish-eating Regina species, although we cannot rule out the possibility of a morphological pre-adaptation to ingest crayfish.Universidad Autónoma del Estado de México: 2865/2010 and 2663/201

SEXUAL SIZE DIMORPHISM, DIET, AND REPRODUCTION IN THE MEXICAN GARTER SNAKE, THAMNOPHIS EQUES

Although adult T. eques females had a longer SVL and HL than males, the sexes did not differ in their diet, and we found that larger females had more offspring. These results suggest that sexual size dimorphism in natural populations of T. eques may be determined by fecundity selection rather than by the ecological factors associated with the spectrum of available prey sizes. The lack of intersexual differences in the slope of the regression between HL and SVL, and the upward shift in the intercept of the regression line for females together with the shift along the common slope toward larger females (data for larger females do not overlap with the data for larger males), showed that the larger heads of the females are probably an outcome of their larger bodies (SVL) and not of the allometric relationship between these traits.In this study we examined diet, reproduction, and sexual dimorphism in body size of adult Thamnophis eques. We measured 307 adult snakes within the hydrologic system of High Lerma. Prey was obtained by forced regurgitation when snakes were collected, and gravid females were housed in the laboratory until parturition. Females had a longer snout-vent length and shorter tails than males, but there was no difference in total length between the two sexes. We found no evidence to support the hypothesis that sexual dimorphism is due to differences in prey size for this species because the sexes did not differ in the type and mass of prey they consumed; however, the size of gravid females was positively related to the number, but not size and weight, of their offspring. Our results suggested that sexual size dimorphism in natural populations of T. eques may be determined by fecundity selection rather than the ecological factors associated with the spectrum of available prey sizes. We also discuss possible reasons why the sexes did not differ in total lengthUniversidad Autónoma del Estado de México 2077/2005U, 2365/2006, 2865/2010U Consejo Nacional de Ciencia y Tecnología (33710)

Mecanismos proximos determinantes de la ecologia de culebras simpatricas del valle de toluca

El estudio de la ecología poblacional en las especies silvestres provee explicaciones adaptativas respecto al origen y diversidad de los modos y ciclos de vida y es una herramienta para entender los mecanismos y los efectos de la selección natural sobre la dinámica de las poblaciones. Los organismos están sujetos a las condiciones del medio en que habitan, por lo que se ha propuesto que algunas características de su ciclo de vida deben haber evolucionado como respuestas adaptativas a su hábitat (Stearns 1992). Los organismos administran e invierten sus recursos hacia sus diferentes actividades (por ejemplo el forrajeo, la reproducción, el crecimiento), en base al balance entre los costos y beneficios implicados y que determinan la expresión de su ecología en particular (Caswell 1989)

Visual Detection of Speckles in the Fish Xenotoca variata by the Predatory Snake Thamnophis melanogaster in Water of Different Turbidity

The results of this study suggest that speckles on male X. variata are visual signals to potential predators such as the snake T. melanogaster. However, speckles are not a determining factor; snakes display a higher frequency of predatory behavior toward the fish, but their predatory behavior is influenced by water turbidity. Turbidity is considered a constraint that affects foraging in aquatic predators such as the snake T. melanogaster because it is involved in the visual identification of potential prey and capture success. Further experiments are needed to test the direct influence of snake predation on variation in sexual traits, such as the number of speckles on the flanks of male X. variata. Therefore, natural selection caused by predation may constrain the development of sexually dimorphic traits in X. variata, as suggested by other studies showing that male secondary sexual traits often increase the risk of predationSemi-aquatic snakes integrate visual and chemical stimuli, and prey detection and capture success are therefore linked to the display of visual predatory behavior. The snake Thamnophis melanogaster responds preferentially to individuals of the fish Xenotoca variata with a greater number of bright, colorful spots (lateral speckles) compared with those with a smaller number; however, water turbidity can reduce underwater visibility and effect the vulnerability of fish. In this study, we tested whether the presence of iridescent speckles on the flanks of male X. variata interacted with water turbidity to modify the predatory behavior displayed by the snake T. melanogaster.We predicted that in an experimental laboratory test, the snakes would increase the frequency of their predatory behavior to the extent that the water turbidity decreases. The snakes were tested at six different levels of water turbidity, in combination with three categories of male fish (with few, a median number of, or many speckles). The results showed that in a pool with high or zero turbidity, the number of speckles is not a determining factor in the deployment of the predatory behavior of the snake T. melanogaster toward X. variata. Our findings suggest that snakes can view the fish at intermediate percentages of turbidity, but the number of speckles in male X. variata is irrelevant as an interspecific visual signal in environments with insufficient luminosity. The successful capture of aquatic prey is influenced by integration between chemical and visual signals, according to environmental factors that may influence the recognition of individual traits.Universidad Autónoma del Estado de México (2865/2010, 2663/2013, 3589/2013S

Temporal stability of an endemic Mexican treefrog

Changes in abundance and distribution of the three H. eximia age-sex categories, are related to seasonal variations in temperature and precipitation during the year. The ability of H. eximia to persist is constrained by human-induced habitat alterations of the temperate forest habitat in the CentralMexican Plateau. Small frog species, such as H. eximia, may be strongly disadvantaged by habitat fragmentation. The CentralMexican Plateau contains a major metropolitan area and 44.7% of this area is used for agriculture (CONAPO, 2010). This presents the possibility of a reduction in the suitability of existing habitat patches (i.e., fragments) which may affect both local and landscape-level pond-breeding amphibian population dynamics. Only temperate forest habitat seems to be suitable for H. eximia, therefore, conservation efforts should be directed to areas where suitable ecological variables are present and especially where human encroachment affects tree microhabitat. Most of what we know about this endemic treefrog comes from occasional captures of active animals. New studies are needed to better understand how the stability of a population of frogs relates to areas that are degraded by human land-use. For example, mark–recapture studies can elucidate terrestrial habitat requirements for local populations, genetic approaches may be used to infer gene flow, and to estimate dispersal and immigration. These types of studies will provide crucial information about the relative impact of land use on effective population size and reproductive success of local populationsThe demographic characteristics of an amphibian population fluctuate independently over time, mainly in response to the temporal variation of environmental factors, especially precipitation and temperature. These temporal fluctuations may contribute to the size of an amphibian population and could be used to determine the current conservation status of a species. During a five year (2004–2008) period, we studied the relative abundance, sex ratio, and age-sex structure of a population of metamorphosed individuals of the endemic treefrog Hyla eximia in CentralMexico. We also studied the species’ relationship with climatic variables such as temperature and precipitation.We found an interannual constant abundance during the study period. However, interannual differences were observed in the population structure by age-sex category (males, females, or juveniles), with decreased abundance of males and juveniles during the rainy months (August–November). The annual abundance of H. eximia was positively correlated with rainfall, but negatively with monthly temperature.We found the sex ratio was male-biased (2:1), except for year 2008. Also, differences in snout-vent length (SVL) were found between years, suggesting changes in recruitment of new individuals.We conclude that variations in abundance, and frequencies by age-sex category, of H. eximia are related to seasonal variations in temperature and precipitation characteristics of temperate zones. However, this temporal stability may suggest that anurans have an unusual capacity to persist even in the face of human-induced habitat change.Universidad Aut ´onoma del Estado de Mexico (2663/2013, 3589/2013SF)

El uso de señales aposemáticas en serpientes: Contra advertencia no hay engaño

The use of aposematic defense mechanisms by venomous predators is often overlooked. In this article, we make an exhaustive literature review to make known in an accessible language, the key aspects and theoretical concepts that lead to the evolution of aposematism, its diversity in snakes through several examples is also presented. In ecological terms, aposematism is an anti-predatory mechanism in which preys use various types of signals to warn potential predators, their danger and/or non-palatability due to the presence of a secondary defense mechanism. Its success will depend not only on factors and characteristics related to the organisms involved, but also on a third-party presence, including those who wish to benefit from this system.El uso de mecanismos de defensa aposemáticos por depredadores venenosos es ignorado frecuentemente. Por este motivo, se realiza una exhaustiva revisión bibliográfica para dar a conocer en un lenguaje accesible los conceptos teóricos clave que conducen la evolución del aposematismo, y se presenta su diversidad en serpientes a través de varios ejemplos. En términos ecológicos, el aposematismo es un mecanismo antipredatorio en el que las presas utilizan diversos tipos de señales para advertir a potenciales depredadores de su peligrosidad o no palatabilidad debido a la presencia de un mecanismo secundario de defensa. Su éxito dependerá no sólo de factores y características relacionados con los organismos involucrados, sino también de la presencia de terceros, que incluyen los que pretendan beneficiarse de este sistemaCONACY

Congenital feeding response to a novel prey in a Mexican gartersnake.

Articulo de investigación científica publicado en revista indizadaIn this study, we explored chemosensory, ingestive and prey-catching responses of neonate Mexican Black-bellied Gartersnakes (Thamnophis melanogaster) to crayfish (Cambarellus montezumae). By comparing snakes from a recently discovered crayfisheating population and a typical non-crayfish-eating population, we asked which behavioral components change as a species enlarges its feeding niche. In the crayfisheating population chemosensory responsiveness to crayfish was not enhanced but its heritability was higher. Neonates of both populations showed similar preference for freshly-molted versus unmolted crayfish, and whereas the tendency to ingest both crayfish stages remained stable between ages 15 and 90 days in the non-crayfisheating population, in the crayfish-eating population it actually decreased. Techniques to catch and manipulate molted crayfish were similar in the two populations. We discuss the possibility that there is no increase in the behavioral response to eat crayfish by the neonates of the crayfish-eating populations, possibly due to the absence of ecological and spatial isolation between the two T. melanogaster populations. The crayfish ingestion in some population of T. melanogaster can be explained by environmental differences between populations, or by recent origin of crayfish ingestion in T. melanogaster.Universidad Autónoma del Estado de México (3589/2013SF, 4047/2016SF, 4865/2019SF)