- Email: [email protected]
Measuring the bioenergetic cost of swimming in the field: a novative approach.
$24
Abstracts / Comparative Biochemistry and Physiology, Part B 126 (2000) SI-S108
PHYSIOLOGICAL VARIATION IN INSECTS: H I E R A R C H I C A L L E V E L S AND IMPLICATIONS FOR ECOLOGICAL DIVERSITY S.L. Chown Department o f Zoology & Entomology, University o f Pretoria, Pretoria 0002, South Africa Variation, and in particular regular pattern in that variation, forms the foundation for evolutionary physiology. Nonetheless, with the exception of seemingly good fits between the tolerances of animals, and the environments they live in, this variation is often not well explored. Indeed, there have been several recent calls for an expansion of research in this area. These have often been made in the context of an exploration of several assumptions, made by other disciplines, regarding both large and small-seale variation in animal physiologies. Here, I explore three examples of variation (both large- and small-scale) in a range of physiological traits in insects, and the consequences of this variation for physiological ecology and for a subject that has made several untested assumptions regarding animal physiological variation - mactoecology. First, building on work done by my graduate students and I, I show that at global, regional, and local scales, variation in insect upper lethal temperatures is far less variable than variation in lower lethal temperatures. This ultimately means that insects living at higher latitudes and altitudes tend to have a broader thermal tolerance range than those living in less variable environments. But this is not always the case. Not only does variation increase towards the poles, but variation in that variation does too. In addition, responses to low temperatures appear to be more sensitive to acclimation than do those to high tempmaures. Perhaps not surprisingly, these findings suggest that responses to high and low temperatures must be physiologically (and evolutionarily) deconpled. They also suggest that the physiological assumptions of the climatic variability hypothesis underlying Rapoport's rule may, in some instances, be correct. Second, I show that variation in upper and lower lethal limits, desiccation resistance and tolerance, and respiration rate is often partitioned at taxonomic levels well above that of the species. In other words, there has been considerable phylogenetic constraint in the evolution of the responses of insects to the environment. This finding might seem to suggest that several ideas regarding insect physiological adaptations have to be re-examined. However, because of the partitioning of massspecific variation mostly at the species level, and in light of the findings of recent comparisons of studies using raw and phylogentically corrected data, this may not necessarily be the case. Rather, these findings suggest that both approaches should be adopted where possible. Finally, I demonstrate that there is considerable intra-individual variation in the charaetedstics of insect discontinuous gas exchange cycles. This is perhaps well known to researchers in the field, but the implications thereof for arguments in favour of the adaptive nature of these regular cycles has not been sufficiently well explored.
MEASURING THE BIOENERGETIC COST OF SWIMMING IN THE FIELD: A N O V A T I V E APPROACH. G., Claireaux I and D.M., Webber 2 ICREMA, CNRS-IFREMER, BP 5, L ' H o u m e a u , France, 17137. 2Dalhousie University, Biology dept., Halifax, Canada, B 3 H 4J1. Better bioenergetic models of fish production systems require estimating the energy dissipated as activity metabolism. Early efforts to address this consideration have had limited success mainly because the methods tested could not be implemented at the spatial scale of natural field conditions. In this context we report the results of an experiment designed to verify the use of caudal peduncle differential pressure as a predictor of swimming speed in sea bass(Dicentrarchus labrax), both in the laborattty and in the field. Six individuals (0.180-0.226 kg) were instrumented with a miniature differential pressure sensor mounted on one side of the caudal peduncle and swum in a recircuiating ,,Brett style" respirometer. Differential pressure, tail beat frequency, tail beat amplitude and oxygen consumption (MO2) were highly correlated to swimming speed. Small changes in swimming speed of less than 0.05 m.s"t were readily detected as differences in tail beat pressure. We then designed an ultrasonic transmitter that sampled the taft pressure and output 10 millisecond acoustic pulses. The time between pulses was correlated to average and Max-Min pressure generated by the caudal peduncle. We introduced tagged sea bass (1.5 kg) into a tidal marsh pond (200 m2) and monitored their position and tail beat pressure each second for two weeks using a radio-acoustic buoy positioning system. Pressure was highly correlated to swimming speed calculated from positions, confirming that pressure as an indicator of caudal muscle power output can accurately predict activity patterns and swimming speeds of fish in nature.
Abstracts / Comparative Biochemistry and Physiology, Part B 126 (2000) SI-S108
PHYSIOLOGICAL VARIATION IN INSECTS: H I E R A R C H I C A L L E V E L S AND IMPLICATIONS FOR ECOLOGICAL DIVERSITY S.L. Chown Department o f Zoology & Entomology, University o f Pretoria, Pretoria 0002, South Africa Variation, and in particular regular pattern in that variation, forms the foundation for evolutionary physiology. Nonetheless, with the exception of seemingly good fits between the tolerances of animals, and the environments they live in, this variation is often not well explored. Indeed, there have been several recent calls for an expansion of research in this area. These have often been made in the context of an exploration of several assumptions, made by other disciplines, regarding both large and small-seale variation in animal physiologies. Here, I explore three examples of variation (both large- and small-scale) in a range of physiological traits in insects, and the consequences of this variation for physiological ecology and for a subject that has made several untested assumptions regarding animal physiological variation - mactoecology. First, building on work done by my graduate students and I, I show that at global, regional, and local scales, variation in insect upper lethal temperatures is far less variable than variation in lower lethal temperatures. This ultimately means that insects living at higher latitudes and altitudes tend to have a broader thermal tolerance range than those living in less variable environments. But this is not always the case. Not only does variation increase towards the poles, but variation in that variation does too. In addition, responses to low temperatures appear to be more sensitive to acclimation than do those to high tempmaures. Perhaps not surprisingly, these findings suggest that responses to high and low temperatures must be physiologically (and evolutionarily) deconpled. They also suggest that the physiological assumptions of the climatic variability hypothesis underlying Rapoport's rule may, in some instances, be correct. Second, I show that variation in upper and lower lethal limits, desiccation resistance and tolerance, and respiration rate is often partitioned at taxonomic levels well above that of the species. In other words, there has been considerable phylogenetic constraint in the evolution of the responses of insects to the environment. This finding might seem to suggest that several ideas regarding insect physiological adaptations have to be re-examined. However, because of the partitioning of massspecific variation mostly at the species level, and in light of the findings of recent comparisons of studies using raw and phylogentically corrected data, this may not necessarily be the case. Rather, these findings suggest that both approaches should be adopted where possible. Finally, I demonstrate that there is considerable intra-individual variation in the charaetedstics of insect discontinuous gas exchange cycles. This is perhaps well known to researchers in the field, but the implications thereof for arguments in favour of the adaptive nature of these regular cycles has not been sufficiently well explored.
MEASURING THE BIOENERGETIC COST OF SWIMMING IN THE FIELD: A N O V A T I V E APPROACH. G., Claireaux I and D.M., Webber 2 ICREMA, CNRS-IFREMER, BP 5, L ' H o u m e a u , France, 17137. 2Dalhousie University, Biology dept., Halifax, Canada, B 3 H 4J1. Better bioenergetic models of fish production systems require estimating the energy dissipated as activity metabolism. Early efforts to address this consideration have had limited success mainly because the methods tested could not be implemented at the spatial scale of natural field conditions. In this context we report the results of an experiment designed to verify the use of caudal peduncle differential pressure as a predictor of swimming speed in sea bass(Dicentrarchus labrax), both in the laborattty and in the field. Six individuals (0.180-0.226 kg) were instrumented with a miniature differential pressure sensor mounted on one side of the caudal peduncle and swum in a recircuiating ,,Brett style" respirometer. Differential pressure, tail beat frequency, tail beat amplitude and oxygen consumption (MO2) were highly correlated to swimming speed. Small changes in swimming speed of less than 0.05 m.s"t were readily detected as differences in tail beat pressure. We then designed an ultrasonic transmitter that sampled the taft pressure and output 10 millisecond acoustic pulses. The time between pulses was correlated to average and Max-Min pressure generated by the caudal peduncle. We introduced tagged sea bass (1.5 kg) into a tidal marsh pond (200 m2) and monitored their position and tail beat pressure each second for two weeks using a radio-acoustic buoy positioning system. Pressure was highly correlated to swimming speed calculated from positions, confirming that pressure as an indicator of caudal muscle power output can accurately predict activity patterns and swimming speeds of fish in nature.