Papadopoulos, Anthony (2007-05). An ecophysiological framework for the morphological evolution of bluegill sunfish. Doctoral Dissertation. Thesis uri icon

abstract

  • Body shape affects the capacity and efficiency of swimming in fishes, and places constraints on foraging and reproductive performance. Hence, fitness components, such as aerobic swimming capacity and efficiency, can be determined from analysis of swimming energetics using active respirometry. In particular, body shape adaptations, such as streamlining, aim at reducing hydrodynamic drag (resistance), thereby increasing swimming efficiency in the presence of water flow, which is a principal contributor to resistance for fish inhabiting rivers. For two populations of bluegill sunfish, one from the Brazos River and the other from Moelman's Slough (a Brazos River oxbow lake), the metabolic transport rate (MTR) was determined to evaluate differences in swimming efficiency. The standard cost of swimming (SCOS) was also determined to evaluate differences in swimming capacity, which represents the overall capacity of the skeletal muscles to generate mechanical power to overcome hydrodynamic resistance. The MTR and the SCOS describe holistic swimming performance, where the MTR specifies the hydrodynamic response due to swimming, and the SCOS specifies the physiologic response due to swimming. The differences in swimming performance are mainly attributed to factors affecting hydrodynamic resistance and could be predicted by morphology; because body shape, like water flow, is also a principal contributor to resistance. Multivariate body shape, from generalized Procrustes analysis, was used to assess the influence of multiple shape traits on swimming costs. This measure of shape related to swimming performance using partial least-squares analysis showed the two bluegill populations to be significantly different. The results were as follows: the shallow-bodied condition in bluegills was highly correlated with efficient swimming and low swimming capacities; whereas, deep-bodied bluegills were highly correlated with inefficient swimming and high swimming capacities. This is an empirical case of divergent natural selection. For convergence, however, the position of the caudal peduncle is consistent with optimal swimming speed (Um), which depends on standard metabolic rate (SMR), or metabolic maintenance. Bluegills with erect caudal peduncles have a high range of swimming speeds without suffering much cost of swimming ability compared to bluegills with prone caudal peduncles. The adaptive physiological response to high Um is due to a low SCOS because swimming efficiency is low and metabolic maintenance is high. In other words, bluegills that are inefficient swimmers and require a high energy intake cannot survive unless they gain the ability to increase their foraging capacity by thrust or metabolic power reduction. This is perhaps one of the most remarkable adaptive physiological responses due to the joint effects of shape and SMR.
  • Body shape affects the capacity and efficiency of swimming in fishes, and places
    constraints on foraging and reproductive performance. Hence, fitness components, such
    as aerobic swimming capacity and efficiency, can be determined from analysis of
    swimming energetics using active respirometry. In particular, body shape adaptations,
    such as streamlining, aim at reducing hydrodynamic drag (resistance), thereby increasing
    swimming efficiency in the presence of water flow, which is a principal contributor to
    resistance for fish inhabiting rivers. For two populations of bluegill sunfish, one from the
    Brazos River and the other from Moelman's Slough (a Brazos River oxbow lake), the
    metabolic transport rate (MTR) was determined to evaluate differences in swimming
    efficiency. The standard cost of swimming (SCOS) was also determined to evaluate
    differences in swimming capacity, which represents the overall capacity of the skeletal
    muscles to generate mechanical power to overcome hydrodynamic resistance. The MTR
    and the SCOS describe holistic swimming performance, where the MTR specifies the
    hydrodynamic response due to swimming, and the SCOS specifies the physiologic
    response due to swimming. The differences in swimming performance are mainly
    attributed to factors affecting hydrodynamic resistance and could be predicted by
    morphology; because body shape, like water flow, is also a principal contributor to
    resistance. Multivariate body shape, from generalized Procrustes analysis, was used to
    assess the influence of multiple shape traits on swimming costs. This measure of shape
    related to swimming performance using partial least-squares analysis showed the two bluegill populations to be significantly different. The results were as follows: the
    shallow-bodied condition in bluegills was highly correlated with efficient swimming and
    low swimming capacities; whereas, deep-bodied bluegills were highly correlated with
    inefficient swimming and high swimming capacities. This is an empirical case of
    divergent natural selection. For convergence, however, the position of the caudal
    peduncle is consistent with optimal swimming speed (Um), which depends on standard
    metabolic rate (SMR), or metabolic maintenance. Bluegills with erect caudal peduncles
    have a high range of swimming speeds without suffering much cost of swimming ability
    compared to bluegills with prone caudal peduncles. The adaptive physiological response
    to high Um is due to a low SCOS because swimming efficiency is low and metabolic
    maintenance is high. In other words, bluegills that are inefficient swimmers and require a
    high energy intake cannot survive unless they gain the ability to increase their foraging
    capacity by thrust or metabolic power reduction. This is perhaps one of the most
    remarkable adaptive physiological responses due to the joint effects of shape and SMR.

publication date

  • May 2007