Beyond Janzen's Hypothesis: How Amphibians That Climb Tropical Mountains Respond to Climate Variation.

Janzen's hypothesis (JH) posits that low thermal variation selects for narrow physiological tolerances, and thus small species distributional ranges and high species turnover along tropical elevational gradients. Although this hypothesis has been intensely revisited, it does not explain how many tropical species may exhibit broad distributions, encompassing altitudinal gradients. Moreover, the physiological responses of tropical species remain largely unknown, limiting our understanding on how they respond to climate variation. To fill these knowledge gaps, we tested a major component of JH, the climate variability hypothesis (CVH), which predicts broader thermal tolerance breadth (Tbr = CTmax - CTmin) with broader temperature variation. Specifically, we sampled populations of five amphibian species distributed in two mountain ranges in Brazil's Atlantic Forest to test how CTmin and CTmax vary along elevational gradients. Since both thermal and water balance traits are pivotal to the evolutionary history of amphibians, we also measured rates of dehydration and rehydration and their relations with thermal tolerances. We found that broader temperature variation with increasing altitude did not always lead to broader Tbr, since changes in CTmin and CTmax were species-specific. In addition, we found that water balance did not show consistent variation with altitude, also with low correlations between hydric and thermal traits. While we also found that highland populations are at lower risk of thermal stress than lowland counterparts, both are living far from their upper thermal limits. As a consequence of intraspecific variation in physiological traits and spatial variation in climate along altitude, responses to climate variation in tropical amphibian species were context-dependent and heterogeneous. Together with recent studies showing thermal tolerances of some tropical amphibians comparable to temperate taxa, our findings highlight that several responses to climate variation in tropical species may not conform to predictions made by either the CVH or other important hypotheses concerning physiological variation. This reinforces the need to overcome geographical bias in physiological data to improve predictions of climate change impacts on biodiversity. (Portuguese abstract) Resumo A Hipótese de Janzen (JH) postula que a baixa variação térmica seleciona tolerâncias fisiológicas estreitas e, portanto, amplitudes restritas de distribuição das espécies e alta substituição de espécies ao longo de gradientes altitudinais tropicais. Embora intensamente revisitada, essa hipótese não explica como espécies tropicais podem exibir amplas distribuições geográficas, abrangendo gradientes altitudinais. Além disso, as respostas fisiológicas das espécies tropicais permanecem amplamente desconhecidas, limitando nossa compreensão sobre como elas respondem à variação climática. Para preencher essas lacunas de conhecimento, testamos um componente importante da JH, a Hipótese de Variabilidade Climática (CVH), que prevê uma maior amplitude de tolerância térmica (Tbr = CTmax - CTmin) quando a variação da temperatura ambiental é mais ampla. Especificamente, amostramos populações de cinco espécies de anfíbios distribuídas em duas cadeias montanhosas na Mata Atlântica do Brasil para testar como CTmin e CTmax variam ao longo de gradientes de altitude. Dado que parâmetros térmicos e do balanço hídrico são fundamentais para a história evolutiva dos anfíbios, também medimos as taxas de desidratação e reidratação e suas relações com as tolerâncias térmicas. Encontramos que uma variação de temperatura ambiental mais ampla com o aumento da altitude nem sempre conduz a uma Tbr mais ampla, uma vez que as mudanças em CTmin e CTmax foram espécie-específicas. Além disso, encontramos que o balanço hídrico não apresentou variação consistente com a mudança de altitude, e que as correlações entre parâmetros hídricos e térmicos foram baixas. Embora populações das maiores altitudes apresentaram menor risco de estresse térmico do que populações da mesma espécie em altitudes menores, ambas estão vivendo longe de seus limites térmicos superiores. Em consequência da variação intraespecífica em parâmetros fisiológicos e variação espacial no clima ao longo da altitude, as respostas à variação climática em espécies de anfíbios tropicais foram contexto-dependentes e heterogêneas. Juntamente com estudos recentes indicando tolerâncias térmicas de alguns anfíbios tropicais comparáveis a de táxons temperados, nossas descobertas destacam que várias respostas à variação climática em espécies tropicais podem não estar de acordo com as previsões feitas pela CVH ou outras hipóteses importantes sobre a variação fisiológica. Isso reforça a necessidade de superar o viés geográfico em dados fisiológicos para aperfeiçoar previsões dos impactos das mudanças climáticas sobre a biodiversidade. (Spanish abstract) Resumen La hipótesis de Janzen (JH) postula que la baja variación térmica selecciona tolerancias fisiológicas estrechas y, por lo tanto, rangos de distribución de especies restringidos con alta rotación de especies a lo largo de gradientes de elevación tropicales. Aunque esta hipótesis ha sido intensamente discutida, no explica cómo várias especies tropicales pueden exhibir distribuciones amplias, abarcando gradientes altitudinales. Además, las respuestas fisiológicas de las especies tropicales siguen siendo bastante desconocidas, lo que limita la comprensión de cómo responden a la variación climática. Para llenar estos vacíos de conocimiento, examinamos un componente importante de JH, la Hipótesis de Variabilidad Climática (CVH), que predice mayor amplitud de tolerancia térmica (Tbr = CTmax - CTmin) cuando la variación de temperatura es más amplia. Específicamente, tomamos muestras de poblaciones de cinco especies de anfibios distribuidas en dos cadenas montañosas en el Bosque Atlántico de Brasil para verificar cómo CTmin y CTmax varían a lo largo de este gradiente de elevación. Dado que los rasgos de equilibrio térmico y hídrico son fundamentales para la historia evolutiva de los anfibios, también medimos las tasas de deshidratación y rehidratación y sus relaciones con las tolerancias térmicas. Encontramos que una variación de temperatura más amplia con el aumento de la altitud no siempre conduce a una Tbr más amplia, ya que los cambios en CTmin y CTmax son específicos de la especie. Además, encontramos que el balance hídrico no muestra variación consistente con la altitud, con bajas correlaciones también entre los rasgos hídricos y térmicos. Si bien las poblaciones de las tierras altas tienen un menor riesgo de estrés térmico que las contrapartes de las tierras bajas, ambas se encuentran lejos de sus límites térmicos superiores. Como consecuencia de la variación intraespecífica en los rasgos fisiológicos y la variación espacial en el clima a lo largo de la altitud, las respuestas a la variación climática en las especies de anfibios tropicales fueron dependientes del contexto y heterogéneas. Junto con estudios recientes que muestran tolerancias térmicas de algunos anfibios tropicales comparables a los taxones de zonas templadas, nuestros hallazgos resaltan que varias respuestas a la variación climática en especies tropicales pueden no ajustarse a las predicciones hechas por el CVH u otras hipótesis importantes sobre la variación fisiológica. Esto refuerza la necesidad de superar el sesgo geográfico en los datos fisiológicos para mejorar las predicciones de los impactos del cambio climático en la biodiversidad.

Atividade muscular durante a marcha após acidente vascular encefálico / Muscle activity during gait following stroke

OBJECTIVE: To compare muscle activity and joint moments in the lower extremities during walking between subjects with stroke and control subjects. METHOD: We compared fifteen healthy volunteers and fifteen stroke patients, with the same age gender and weight data had been compared by electromyography. The system of signals acquisition used consisted of five pairs of electrodes of surface, beyond one electrogoniometer on the axis articulate of rotation of the joint of the ankle in study. RESULTS: Onset times with respect to heel-strike for the medial gluteus, tibialis anterior, soleus, rectus femoris and medial hamstring muscles were significantly earlier during the gait cycle in subjects with stroke than in control subjects. The cessation times of soleus, tibialis anterior, rectus femoris, and medial hamstring muscles were significantly prolonged in subjects with stroke. CONCLUSION: Subjects with stroke showed more co-contractions of agonist and antagonist muscles at the ankle and knee joints during stance phase. These gait changes and co-contractions may allow subjects with stroke to adopt a safer, more stable gait pattern to compensate for diminished sensory information from the ankle.

OBJETIVO: Buscar parâmetros da marcha de pacientes após ter sofrido acidente vascular encefálico (AVE) com hemiparesia. MÉTODO: Comparados 15 voluntários pós-AVE e 15 voluntários saudáveis com a mesma idade, gênero e peso. A comparação foi feita por eletromiografia utilizando cinco pares de eletrodos de superfície do lado comprometido (espástico) e um eletrogoniômetro sobre o eixo articular de rotação da articulação do tornozelo em estudo. RESULTADOS: O início da atividade eletromiográfica, a partir da fase de apoio, para os músculos glúteo medial, reto femoral, tibial anterior, sóleo, e porção medial dos isquiotibiais foi significantemente ativados anteriormente durante o ciclo da marcha nos voluntários pós-AVE. O final da atividade eletromiográfica para os músculos reto femoral, tibial anterior, sóleo, e porção medial dos isquiotibiais foi significantemente prolongado nos voluntários pós-AVE. Voluntários pós-AVE demonstraram também mais co-ativação dos músculos agonistas e antagonistas da articulação do tornozelo e joelho durante a fase de balanceio. CONCLUSÃO: Essas alterações e co-contrações musculares da marcha permitem que os voluntários pós-AVE adotem um padrão de marcha mais seguro e mais estável para compensar a diminuição da informação sensorial da articulação do tornozelo.

The ventilatory response to environmental hypercarbia in the South American rattlesnake, Crotalus durissus.

To study the effects of environmental hypercarbia on ventilation in snakes, particularly the anomalous hyperpnea that is seen when CO(2) is removed from inspired gas mixtures (post-hypercapnic hyperpnea), gas mixtures of varying concentrations of CO(2) were administered to South American rattlesnakes, Crotalus durissus, breathing through an intact respiratory system or via a tracheal cannula by-passing the upper airways. Exposure to environmental hypercarbia at increasing levels, up to 7% CO(2), produced a progressive decrease in breathing frequency and increase in tidal volume. The net result was that total ventilation increased modestly, up to 5% CO(2) and then declined slightly on 7% CO(2). On return to breathing air there was an immediate but transient increase in breathing frequency and a further increase in tidal volume that produced a marked overshoot in ventilation. The magnitude of this post-hypercapnic hyperpnea was proportional to the level of previously inspired CO(2). Administration of CO(2) to the lungs alone produced effects that were identical to administration to both lungs and upper airways and this effect was removed by vagotomy. Administration of CO(2) to the upper airways alone was without effect. Systemic injection of boluses of CO(2)-rich blood produced an immediate increase in both breathing frequency and tidal volume. These data indicate that the post-hypercapnic hyperpnea resulted from the removal of inhibitory inputs from pulmonary receptors and suggest that while the ventilatory response to environmental hypercarbia in this species is a result of conflicting inputs from different receptor groups, this does not include input from upper airway receptors.

Energetic and physiological correlates of prey handling and ingestion in lizards and snakes.

In this review, we summarize the energetic and physiological correlates of prey handling and ingestion in lizards and snakes. There were marked differences in the magnitude of aerobic metabolism during prey handling and ingestion between these two groups, although they show a similar pattern of variation as a function of relative prey mass. For lizards, the magnitude of aerobic metabolism during prey handling and ingestion also varied as a function of morphological specializations for a particular habitat, prey type, and behavior. For snakes, interspecific differences in aerobic metabolism during prey handling seem to be correlated with adaptations for prey capture (venom injection vs. constriction). During ingestion by snakes, differences in aerobic metabolism might be due to differences in cranial morphology, although allometric effects might be a potentially confounded effect. Anaerobic metabolism is used for prey handling and ingestion, but its relative contribution to total ATP production seems to be more pronounced in snakes than in lizards. The energetic costs of prey handling and ingestion are trivial for both groups and cannot be used to predict patterns of prey-size selection. For lizards, it seems that morphological and ecological factors set the constraints on prey handling and ingestion. For snakes, besides these two factors, the capacity of the cardio-respiratory system may also be an important factor constraining the capacity for prey handling and ingestion.

Evaporative water loss and oxygen uptake in two casque-headed tree frogs, Aparasphenodon brunoi and Corythomantis greeningi (Anura, Hylidae).

Evaporative water loss (EWL) and oxygen uptake (Vo2) was measured in two species of tree frogs with cranial co-ossification, Aparasphenodon brunoi and Corythomantis greeningi. Both species use their head to seal the entrance of bromeliads, tree holes or rocky crevices used as shelters. EWL was significantly reduced in sheltered individuals of both species as compared with those exposed nude to desiccation. EWL per unit area through the head surface was significantly lower than the body skin for A. brunoi but not for C. greeningi, EWL per unit surface area through C. greeningi body skin was about 50% that of A. brunoi, indicating a less permeable skin in the former species. The relationship between cranial coossification and EWL is discussed. Vo2 in A. brunoi was comparable with other anurans of similar size, whereas in C. greeningi, it was lower than predicted from body mass. Moreover, Vo2 in C. greeningi showed less sensitivity to temperature increase than in A. brunoi. C. greeningi occurs in a drier environment than A. brunoi, and this appears to be reflected in their EWL and Vo2 characteristics.