RESUMO
Connectivity of coral reef fish populations relies on successful dispersal of a pelagic larval phase. Pelagic larvae must exhibit high swimming abilities to overcome ocean and reef currents, but once settling onto the reef, larvae transition to endure habitats that become hypoxic at night. Therefore, coral reef fish larvae must rapidly and dramatically shift their physiology over a short period of time. Taking an integrative, physiological approach, using swimming respirometry, and examining hypoxia tolerance and transcriptomics, we show that larvae of cinnamon anemonefish (Amphiprion melanopus) rapidly transition between "physiological extremes" at the end of their larval phase. Daily measurements of swimming larval anemonefish over their entire early development show that they initially have very high mass-specific oxygen uptake rates. However, oxygen uptake rates decrease midway through the larval phase. This occurs in conjunction with a switch in haemoglobin gene expression and increased expression of myoglobin, cytoglobin, and neuroglobin, which may all contribute to the observed increase in hypoxia tolerance. Our findings indicate that critical ontogenetic changes in the gene expression of oxygen-binding proteins may underpin the physiological mechanisms needed for successful larval recruitment to reefs.
Assuntos
Recifes de Corais , Perciformes , Animais , Larva/genética , Transcriptoma , Peixes/fisiologia , Perciformes/fisiologia , Hipóxia/genética , OxigênioRESUMO
Ultraviolet radiation (UVR) is a pervasive factor that has shaped the evolution of life on Earth. Ambient levels of UVR mediate key biological functions but can also cause severe lethal and sublethal effects in a wide range of organisms. Furthermore, UVR is a powerful modulator of the effects of other environmental factors on organismal physiology, such as temperature, disease, toxicology and pH, among others. This is critically important in the context of global change, where understanding the effects of multiple stressors is a key challenge for experimental biologists. Ecological physiologists rarely afford UVR discussion or include UVR in experimental design, even when it is directly relevant to their study system. In this Commentary, we provide a guide for experimental biologists to better understand if, when, and how UVR can be integrated into experimental designs to improve the ecological realism of their experiments.
Assuntos
Raios Ultravioleta , Animais , Estresse Fisiológico , Projetos de PesquisaRESUMO
Mangrove habitats can serve as nursery areas for sharks and rays. Such environments can be thermally dynamic and extreme; yet, the physiological and behavioural mechanisms sharks and rays use to exploit such habitats are understudied. This study aimed to define the thermal niche of juvenile mangrove whiprays, Urogymnus granulatus. First, temperature tolerance limits were determined via the critical thermal maximum (CTMax) and minimum (CTMin) of mangrove whiprays at summer acclimation temperatures (28 °C), which were 17.5 °C and 39.9 °C, respectively. Then, maximum and routine oxygen uptake rates (MO2max and MO2routine, respectively), post-exercise oxygen debt, and recovery were estimated at current (28 °C) and heatwave (32 °C) temperatures, revealing moderate temperature sensitivities (i.e., Q10) of 2.4 (MO2max) and 1.6 (MO2routine), but opposing effects on post-exercise oxygen uptake. Finally, body temperatures (Tb) of mangrove whiprays were recorded using external temperature loggers, and environmental temperatures (Te) were recorded using stationary temperature loggers moored in three habitat zones (mangrove, reef flat, and reef crest). As expected, environmental temperatures varied between sites depending on depth. Individual mangrove whiprays presented significantly lower Tb relative to Te during the hottest times of the day. Electivity analysis showed tagged individuals selected temperatures from 24.0 to 37.0 °C in habitats that ranged from 21.1 to 43.5 °C. These data demonstrate that mangrove whiprays employ thermotaxic behaviours and a thermally insensitive aerobic metabolism to thrive in thermally dynamic and extreme habitats. Tropical nursery areas may, therefore, offer important thermal refugia for young rays. However, these tropical nursery areas could become threatened by mangrove and coral habitat loss, and climate change.
RESUMO
Ultraviolet radiation (UVR) from the sun is a natural daytime stressor for vertebrates in both terrestrial and aquatic ecosystems. UVR effects on the physiology of vertebrates manifest at the cellular level, but have bottom-up effects at the tissue level and on whole-animal performance and behaviours. Climate change and habitat loss (i.e. loss of shelter from UVR) could interact with and exacerbate the genotoxic and cytotoxic impacts of UVR on vertebrates. Therefore, it is important to understand the range and magnitude of effects that UVR can have on a diversity of physiological metrics, and how these may be shaped by taxa, life stage or geographical range in the major vertebrate groups. Using a meta-analytical approach, we used 895 observations from 47 different vertebrate species (fish, amphibian, reptile and bird), and 51 physiological metrics (i.e. cellular, tissue and whole-animal metrics), across 73 independent studies, to elucidate the general patterns of UVR effects on vertebrate physiology. We found that while UVR's impacts on vertebrates are generally negative, fish and amphibians were the most susceptible taxa, adult and larvae were the most susceptible life stages, and animals inhabiting temperate and tropical latitudes were the most susceptible to UVR stress. This information is critical to further our understanding of the adaptive capacity of vulnerable taxon to UVR stress, and the wide-spread sublethal physiological effects of UVR on vertebrates, such as DNA damage and cellular stress, which may translate up to impaired growth and locomotor performance. These impairments to individual fitness highlighted by our study may potentially cause disruptions at the ecosystem scale, especially if the effects of this pervasive diurnal stressor are exacerbated by climate change and reduced refuge due to habitat loss and degradation. Therefore, conservation of habitats that provide refuge to UVR stress will be critical to mitigate stress from this pervasive daytime stressor.
Assuntos
Ecossistema , Raios Ultravioleta , Animais , Raios Ultravioleta/efeitos adversos , Vertebrados/fisiologia , AnfíbiosRESUMO
In fishes, swimming performance is considered an important metric to measure fitness, dispersal and migratory abilities. The swimming performance of individual larval fishes is often integrated into models to make inferences on how environmental parameters affect population-level dynamics (e.g. connectivity). However, little information exists regarding how experimental protocols affect the swimming performance of marine fish larvae. In addition, the technical setups used to measure larval fish swimming performance often lack automation and accurate control of water quality parameters and flow velocity. In this study, we automated the control of multi-lane swimming chambers for small fishes by developing an open-source algorithm. This automation allowed us to execute repeatable flow scenarios and reduce operator interference and inaccuracies in flow velocity typically associated with manual control. Furthermore, we made structural modifications to a prior design to reduce the areas of lower flow velocity. We then validated the flow dynamics of the new chambers using computational fluid dynamics and particle-tracking software. The algorithm provided an accurate alignment between the set and measured flow velocities and we used it to test whether faster critical swimming speed (U crit) protocols (i.e. shorter time intervals and higher velocity increments) would increase U crit of early life stages of two tropical fish species [4-10-mm standard length (SL)]. The U crit of barramundi (Lates calcarifer) and cinnamon anemonefish (Amphiprion melanopus) increased linearly with fish length, but in cinnamon anemonefish, U crit started to decrease upon metamorphosis. Swimming protocols using longer time intervals (more than 2.5 times increase) negatively affected U crit in cinnamon anemonefish but not in barramundi. These species-specific differences in swimming performance highlight the importance of testing suitable U crit protocols prior to experimentation. The automated control of flow velocity will create more accurate and repeatable data on swimming performance of larval fishes. Integrating refined measurements into individual-based models will support future research on the effects of environmental change.
RESUMO
The most utilized method to measure swimming performance of fishes has been the critical swimming speed (UCrit) test. In this test, the fish is forced to swim against an incrementally increasing flow of water until fatigue. Before the water velocity is increased, the fish swims at the water velocity for a specific, pre-arranged time interval. The magnitude of the velocity increments and the time interval for each swimming period can vary across studies making the comparison between and within species difficult. This issue has been acknowledged in the literature, however, little empirical evidence exists that tests the importance of velocity and time increments on swimming performance in fish. A practical application for fish performance is through the design of fishways that enable fish to bypass anthropogenic structures (e.g. dams) that block migration routes, which is one of the causes of world-wide decline in sturgeon populations. While fishways will improve sturgeon conservation, they need to be specifically designed to accommodate the swimming capabilities specific for sturgeons, and it is possible that current swimming methodologies have under-estimated the swimming performance of sturgeons. The present study assessed the UCrit of shortnose sturgeon using modified UCrit to determine the importance of velocity increment (5 and 10 cm s-1) and time (5, 15 and 30 min) intervals on swimming performance. UCrit was found to be influenced by both time interval and water velocity. UCrit was generally lower in sturgeon when they were swum using 5cm s-1 compared with 10 cm s-1 increments. Velocity increment influences the UCrit more than time interval. Overall, researchers must consider the impacts of using particular swimming criteria when designing their experiments.