Abstract
The relationships among animal form, function and performance are complex, and vary across environments. Therefore, it can be difficult to identify morphological and/or physiological traits responsible for enhancing performance in a given habitat. In fishes, differences in swimming performance across water flow gradients are related to morphological variation among and within species. However, physiological traits related to performance have been less well studied. We experimentally reared juvenile damselfish, Acanthochromis polyacanthus, under different water flow regimes to test 1) whether aspects of swimming physiology and morphology show plastic responses to water flow, 2) whether trait divergence correlates with swimming performance and 3) whether flow environment relates to performance differences observed in wild fish. We found that maximum metabolic rate, aerobic scope and blood haematocrit were higher in wave-reared fish compared to fish reared in low water flow. However, pectoral fin shape, which tends to correlate with sustained swimming performance, did not differ between rearing treatments or collection sites. Maximum metabolic rate was the best overall predictor of individual swimming performance; fin shape and fish total length were 3.3 and 3.7 times less likely than maximum metabolic rate to explain differences in critical swimming speed. Performance differences induced in fish reared in different flow environments were less pronounced than in wild fish but similar in direction. Our results suggest that exposure to water motion induces plastic physiological changes which enhance swimming performance in A. polyacanthus. Thus, functional relationships between fish morphology and performance across flow habitats should also consider differences in physiology.
Highlights
What drives performance differences among individuals and species? This fundamental question has fascinated researchers for decades [1,2,3,4,5,6]
In fishes that use their pectoral fins to generate thrust (median-paired fin (MPF) labriform swimmers), the distribution of species and individuals across water flow gradients is strongly related to the biomechanical relationship between pectoral fin shape and swimming performance [20,21]: tapered fins tend to be faster steady swimmers, whereas rounded fins tend to be optimized for manoeuvring in low-flow habitats [20,22,23,24]
We explored the relationships among organismal form, performance and the environment by studying intraspecific trait variation related to water flow habitat in a labriform-swimming coral reef fish, Acanthochromis polyacanthus, a planktivorous damselfish (Pomacentridae) in the Coral Sea and Great Barrier Reef (GBR)
Summary
What drives performance differences among individuals and species? This fundamental question has fascinated researchers for decades [1,2,3,4,5,6]. In fishes that use their pectoral fins to generate thrust (median-paired fin (MPF) labriform swimmers), the distribution of species and individuals across water flow gradients is strongly related to the biomechanical relationship between pectoral fin shape and swimming performance [20,21]: tapered fins tend to be faster steady swimmers (i.e. straight-line swimming at a constant velocity), whereas rounded fins tend to be optimized for manoeuvring in low-flow habitats [20,22,23,24] This functional relationship appears useful for predicting patterns of species assemblages and ecology based on measured morphological traits [6]. Physiological traits such as increased aerobic capacity and blood oxygen carrying capacity are more complex to measure in swimming fishes, but may well contribute to observed performance differences
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