: Amphibian populations have been declining worldwide and the exact mechanisms underlying these changes are not well understood. We examined environmentally induced phenotypic changes that may reflect ongoing stresses on individuals and therefore their ability to persist in increasingly changing landscapes. Specifically, we evaluated the contribution of habitat loss on the size, allometry, and levels of fluctuating asymmetry of Eleutherodactylus antillensis and E. coqui, 2 common species that are endemic to Puerto Rico. We x-rayed frogs collected at 9 sites that differed in the amount of forest cover and measured their snout-vent, radio-ulna, femur, and tibio-fibula lengths. E. antillensis and E. coqui were smaller in the highly disturbed (≤20% forest cover) than in the intermediately (20–70% forest cover) and little-disturbed (≥70% forest cover) landscapes. In E. antillensis but not in E. coqui, the slope and intercept of the curves relating snout-vent length with the length of the 3 bones differed with degree of forest cover, suggesting an effect of habitat loss on body shape. In E. antillensis and E. coqui, differences between right and left sides corresponded to true fluctuating asymmetry; however, only the radio-ulna length of E. coqui showed a trend toward an increase in fluctuating asymmetry with habitat loss. Because body size scales with a variety of physiological, life history, and ecological traits, conservation programs aimed at monitoring morphological changes in amphibians may help in understanding the mechanisms that contribute to their persistence in changing environments.




Resumen: Las poblaciones de anfibios han declinado mundialmente y los mecanismos subyacentes en estos cambios no son bien conocidos. Examinamos cambios fenotipicos inducidos ambientalmente que pueden reflejar el estres continuo sobre individuos y por lo tanto su habilidad para persistir en paisajes en cambio constante. Especificamente, evaluamos la contribucion de la perdida de habitat sobre el tamano, la alometria y los niveles de asimetria fluctuante de Eleutherodactylus antillensis y E. coqui, dos especies comunes endemicas a Puerto Rico. Tomamos radiografias a ranas recolectadas en 9 sitios que difieren en la cantidad de cobertura forestal y medimos sus longitudes hocico-cloaca, radio-ulna, femur y tibia-fibula. E. antillensis y E. coqui fueron mas pequenos en los paisajes muy perturbados (≤20% de cobertura forestal) que en los paisajes con perturbacion intermedia (20–70% de cobertura forestal) y que en los poco perturbados (≥70% de cobertura forestal). En E. antillensis pero no en E. coqui, la pendiente y la intercepcion de las curvas que relacionan la longitud hocico-cloaca con la longitud de los 3 huesos difirio con el grado de cobertura forestal, lo que sugiere un efecto de la perdida de habitat sobre la forma del cuerpo. En E. antillensis y E. coqui, las diferencias entre los flancos derecho e izquierdo correspondieron a una asimetria fluctuante real; sin embargo, solo la longitud del radio-ulna de E. coqui mostro una tendencia hacia el incremento de la asimetria fluctuante con la perdida de habitat. Debido a que el tamano corporal incrementa con una variedad de caracteristicas fisiologicas, de historia de vida y ecologicas, los programas de conservacion enfocados a monitorear los cambios morfologicos de anfibios pueden ayudar a entender los mecanismos que contribuyen a su persistencia en ambientes cambiantes.

The contribution of habitat loss to changes in body size, allometry, and bilateral asymmetry in two Eleutherodactylus frogs from Puerto Rico.

Dispersal distributions are often characterized by many individuals that stay close to their origin and large variation in the distances moved by those that leave. This variation in dispersal distance can strongly influence demographic, ecological, and evolutionary processes. However, a lack of data on the fitness and phenotype of individual dispersers has impeded research on the role of natural selection in maintaining variation in dispersal distance. Six years of spatially explicit capture-mark-recapture data showed that survival increased with dispersal distance in the stream salamander Gyrinophilus porphyriticus. To understand the evolutionary implications of this fitness response, we tested whether variation in dispersal distance has a phenotypic basis. We used photographs of marked individuals to measure head, trunk, and leg morphology. We then tested whether dispersal distances over the six-year study period were predicted by these traits. Dispersal distance was significantly related to leg morphology: individuals with relatively long forelimbs and short hindlimbs dispersed the farthest. These results support the hypothesis that positive fitness consequences maintain phenotypes enabling long-distance dispersal. More broadly, they suggest that natural selection can promote variation in dispersal distance and associated phenotypes, offering an alternative to the view that dispersal distance is driven by stochastic or landscape-specific mechanisms.

Can natural selection maintain long-distance dispersal? Insight from a stream salamander system

We report the development of a new quantitative method of assessing the effects of anthropogenic impacts on living beings; this method allows us to assess actual impacts and to travel backwards in time to assess impacts. In this method, we have crossed data on fluctuating asymmetry (FA, a measure of environmental or genetic stress), using Didelphis albiventris as a model, with geographical information systems data relating to environmental composition. Our results show that more impacted environments resulted in statistically higher levels of FA. Our method appears to be a useful and flexible conservation tool for assessing anthropogenic impacts.

/pdf/marsupials-from-space-fluctuating-asymmetry-geographical-4nuk36dfon.pdf

Marsupials from space : fluctuating asymmetry, geographical information systems and animal conservation

Habitat fragmentation has the potential to influence the development and thus the phenotype of organisms. The asymmetry of bilateral traits may be indicative of the extent to which developmental stability is compromised by the stressful conditions underlying fragmentation. Using an assemblage- and population-level approach, we explored asymmetry differences in tarsus and outermost tail feathers of birds inhabiting fragmented landscapes in the tropical Andes of Colombia. More than 2500 individuals of 185 species were mist-netted at nine forest sites representing continuous forest (> 1000 ha), medium- (70–110 ha), and small-sized (8–20 ha) fragments. Feathers showed true fluctuating asymmetry (FA), whereas tarsus presented a mixture of FA and directional asymmetry. Overall, asymmetry was lowest in continuous forest, and highest in small and medium fragments. These patterns remained unchanged when directionality and differences in species composition, abundance, and foraging tactics were considered. The population-level analyses showed a general trend of increased asymmetry variation in fragments, yet the responses were not always in the same direction. Increased asymmetry may represent an outcome of processes that contribute to the persistence of species in changing environments, and to the generation of phenotypic innovation, which suggests individual adjustments of development to deal with stress. This calls into question the deliberated application of FA as a biomonitoring tool for conservation. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 119–133. ADDITIONAL KEYWORDS: Andes – Colombia – developmental stability – directional asymmetry – feathers – fluctuating asymmetry – Neotropical birds – tarsus.

https://www.museum.lsu.edu/cuervo/pubs_files/Cuervo_RestrepoBJLS2007.pdf

Assemblage and population-level consequences of forest fragmentation on bilateral asymmetry in tropical montane birds

: Developmental instability, measured as fluctuating asymmetry (FA), is often used as a tool to measure stress and the overall quality of organisms. Under FA, it is assumed that control of symmetry during development is costly and that under stress the trajectory of development is disturbed, resulting in asymmetric morphologies. Amphibian emergent infectious diseases (EIDs), such as Ranavirus and chytrid fungus, have been involved in several mortality events, which makes them stressors and allows for the study of FA. We analyzed nine populations of green frogs (Rana clamitans) for the presence or absence of Ranavirus and chytrid fungus. Individuals were measured to determine levels of FA in seven traits under the hypothesis that FA is more likely to be observed in individuals infected by the pathogens. Significantly higher levels of FA were found in individuals with Ranavirus compared with uninfected individuals among all populations and all traits. We did not observe FA in individuals infected with chytrid fungus for any of the traits measured. Additionally, we observed a significant association between Ranavirus infection and levels of FA in both males and females, which may indicate this viral disease is likely to affect both sexes during development. Altogether, our results indicate that some EIDs may have far-reaching and nonlethal effects on individual development and populations harboring such diseases and that FA can be used as a conservation tool to identify populations subject to such a stress.




ResumenLa inestabilidad del desarrollo, medida como asimetria fluctuante (AF), a menudo se utiliza como una herramienta para medir estres y la calidad integral de los organismos. Bajo AF, se asume que el control de la simetria durante el desarrollo es costoso y que bajo estres se perturba la trayectoria del desarrollo, dando como resultado morfologias asimetricas. Las enfermedades infecciosas emergentes (EIE) en los anfibios, como Ranavirus y hongo chytridio, han sido involucradas en varios eventos de mortalidad, por lo que son factores estresantes y permiten el estudio de AF. Analizamos nueve poblaciones de ranas verdes (Rana clamitans) para la presencia o ausencia de Ranavirus y hongo chytridio. Los individuos fueron medidos para determinar los niveles de AF en siete atributos bajo la hipotesis de que es mas probable observar la AF en individuos infectados por los patogenos. Encontramos niveles de AF significativamente mayores en individuos con Ranavirus en comparacion con individuos no infectados entre todas las poblaciones y todos los atributos. No observamos AF en individuos infectados con el hongo chytridio para ninguna de los atributos medidos. Adicionalmente, observamos una asociacion significativa entre la infeccion por Ranavirus y los niveles de AF tanto en machos como hembras, lo cual puede indicar que es probable que esta enfermedad viral afecte a ambos sexos durante el desarrollo. En conjunto, nuestros resultados indican que algunas EIE pueden tener efectos de largo alcance y no letales sobre el desarrollo de individuos y poblaciones que hospedan tales enfermedades y que la AF puede ser utilizada como una herramienta de conservacion par identificar poblaciones sujetas a tal estres.

Effects of two amphibian pathogens on the developmental stability of green frogs.

We compared a range of anatomical features of northern leopard frogs (Rana pipiens Schreber) collected from areas where deformity rates were low (-2% in nonstressed regions) and high (-40% in the stressed region) to determine if one or more of these characters might be useful in detecting developmental stress Deformed individuals from the stressed region were significantly lighter than normal frogs both from the same region and from nonstressed regions Body length, head width, femur length, and forelimb length were also significantly shorter in deformed and normal individuals from the stressed region than in individuals from nonstressed regions Despite being smaller, deformed individuals had significantly larger pigment spots Fluctuating asymmetry in femur length, femur spot area, femur spot number, and tibio-fibula length was significantly greater in deformed frogs than in normal frogs from the stressed population and the nonstressed group Of these characters, however, only femur spot number

Differences in size, pigmentation, and fluctuating asymmetry in stressed and nonstressed northern leopard frogs (Rana pipiens)

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Differences in size, pigmentation, and fluctuating asymmetry in stressed and nonstressed northern leopard frogs (Rana pipiens)