Anatomical observations on the ampullae of Lorenzini from selected skates and galeoid sharks of the Western North

The gross structure of the ampullae of Lorenzini and its distribution on the body of 40 species of skates (Rajoidei) and 5 species of sharks (Galeomorphii) were compared in an attempt to investigate correlations within this system to feeding mechanisms. Three general lines of morphological change are observed. A larger proportion of the ampullary pores are associated with the ventral surface of the dorsoventrally flattened skates than the more conically shaped sharks. The relative proportion of ventral pores is significantly reduced on those species inhabiting aphotic waters. Secondly, the more piscivorous rajoids possess an array of ventral pores which covers the majority of the body surface whereas those species feeding predominantly on infaunal invertebrates exhibit a comparatively reduced pattern which are primarily concentrated around the mouth. The density of these pores on the adult is inversely related to the collective mobility of each species\u27 prey items. Similarly, the relative density of pores on the sharks is reduced in both those species inhibiting pelagic waters and those exhibiting reduced prey selectivity. Lastly, the overall size of, and the number of alveoli associated with, each ampulla is directly related to the habitat depth of each skate species. The proposed effects of each of these modifications is discussed. The overall pore distribution appears compensatory for reduced visual input whereas relative densities (resolution) further reflect major differences in feeding strategies. Increased ampullary size and complexity suggest mechanisms for increased sensitivity and signal-to-noise ratios

Hydrodynamic Aspects of Shark Scales

The energetics of fish locomotion depends on a balance between thrust and drag. The interest stimulated by Gray\u27s Paradox , that is the seeming lack of sufficient power to overcome many of the estimated values of drag, has resulted in the delineation of a number of potential drag reducing mechanisms (Webb, 1975). Of particular interest is a variety of structural mechanisms, such as scombroid scale corselets (Walters, 1962) and scale ctenii (Burdak, 1969; Bone, 1972), which increase surface roughness and thereby alter boundary layer characteristics. Elasmobranch placoid scales, or dermal denticles, may perform such a function. Bone and Howarth (1966) have suggested that this type of scale reduces drag by creating turbulence in the boundary layer, thereby preventing its separation. More recently, Walsh and Weinstein (1978) have shown that surfaces composed of longitudinally arranged v-shaped grooves can significantly reduce drag through a reduction in the turbulent bursting activity. Placoid scales from a number of galeoid shark species exhibit this type of surface morphology and may therefore represent a potential drag reduction mechanism. More...

Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms

It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystemclimate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models.This is the publisher’s final pdf. The published article is copyrighted by New Phytologist Trust and can be found at: http://www.newphytologist.org/Keywords: Climate change, Temperature acclimation, Optimum temperature, Thermal optimality, Temperature adaptatio

Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms

• It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales.• Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms.• We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration.• Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystem–climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models