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| Articles about Iguanas |
| Lluvia de iguanas | | 2008-01-05 17:40:00 | | La inusual caÃda de la temperatura sufrida esta semana en Miami (Florida, EE.UU.) provocó un fenómeno sorprendente en los parques que bordean la ciudad: una lluvia de iguanas que caÃan de los árboles, sobre cuyas ramas, paralizadas por el frÃo, habÃan quedado catalépticas.En los parques Bill Baggs y Crandon de Key Biscaine, al sur de Miami, los transeúntes vieron, boquiabiertos, a las iguanas aplastarse contra el suelo, como si estuvieran muertas. Pero no lo estaban. Los agentes municipales las recogÃan y las ponÃan bajo el sol para que se calentaran y revivieran.La iguana tropical es un reptil de sangre frÃa que necesita una temperatura superior a 23 ºC, y se siente mucho más a gusto cuando el termómetro alcanza los 35 ºC. Pero el miércoles y el jueves, el mercurio descendió a 4 o 5 ºC en algunas zonas de Florida.“Con temperaturas inferiores a 15 ºC, las iguanas empiezan a tener problemas para moverse; pero si bajan a 5 ºC, se quedan totalmente paralizadasâ€, explicó Perran Ross, experto del departamento de Vida Silvestre de la universidad de Florida.Por eso, cuando hace mucho frÃo, su cuerpo entra en reposo y únicamente su corazón sigue latiendo. Es cuando se caen de los árboles en los que se habÃan refugiado.“Algunas no consiguen superar el shock y mueren. Otras logran calentar su cuerpo bajo el solâ€, señaló P. Ross.Las iguanas tropicales no son originarias del sur de Florida, pero fueron introducidas desde México, América central y América latina. | | By: los irracionales | | |
| | Body Size, Performance and Fitness in Galapagos Marine Iguanas | | 2007-01-16 06:12:48 | | Integrative and Comparative Biology 2003 43(3):376-386; doi:10.1093/icb/43.3.376Martin Wikelski and L. Michael RomeroComplex organismal traits such as body size are influenced by innumerable selective pressures, making the prediction of evolutionary trajectories for those traits difficult. A potentially powerful way to predict fitness in natural systems is to study the composite response of individuals in terms of performance measures, such as foraging or reproductive performance. Once key performance measures are identified in this top-down approach, we can determine the underlying physiological mechanisms and gain predictive power over long-term evolutionary processes. Here we use marine iguanas as a model system where body size differs by more than one order of magnitude between island populations. We identified foraging efficiency as the main performance measure that constrains body size. Mechanistically, foraging performance is determined by food pasture height and the thermal environment, influencing intake and digestion. Stress hormones may be a flexible way of influencing an individual's response to low-food situations that may be caused by high population density, famines, or anthropogenic disturbances like oil spills. Reproductive performance, on the other hand, increases with body size and is mediated by higher survival of larger hatchlings from larger females and increased mating success of larger males. Reproductive performance of males may be adjusted via plastic hormonal feedback mechanisms that allow individuals to assess their social rank annually within the current population size structure. When integrated, these data suggest that reproductive performance favors increased body size (influenced by reproductive hormones), with an overall limit imposed by foraging performance (influenced by stress hormones). Based on our mechanistic understanding of individual performances we predicted an evolutionary increase in maximum body size caused by global w | | By: Evolution Research - Main Blog | | |
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