Journal of experimental zoology. Part A, Ecological and integrative physiology最新文献

Salinity can be an environmental stressor for anurans, as their highly permeable skin makes them prone to osmotic stress when exposed to saline conditions. However, certain anuran species have colonized areas near saltwater habitats, suggesting an ability to acclimate to saline conditions. Here, we evaluated physiological and behavioral responses to saline conditions in adult Cuban treefrogs (Osteopilus septentrionalis), an invasive anuran found throughout Florida. To examine their response to salinity, adult frogs were maintained in two treatments simulating a freshwater (0.5 ppt) or brackish (8.0 ppt) environment for 6 weeks. To assess their physiological response to this potential stressor, all frogs were submerged in a brackish solution to quantify individual weight change every 2 weeks. We found that frogs maintained in brackish solution lost more weight at Weeks 2 and 6 when compared to Week 0, suggesting that salinity may be an environmental stressor for Cuban treefrogs. Yet, the weight change at Week 4 was similar to the pre-exposure period, which may indicate that constant exposure to salinity may alter their physiological response to saline conditions. To supplement the physiological analyses, we investigated avoidance behavior toward saline conditions by offering individuals a choice between freshwater or brackish environments. Our results showed that Cuban treefrogs chose freshwater environments more frequently and may thus avoid saline ones. This study reveals that salinity may induce plastic and avoidance responses in Cuban treefrogs, potentially allowing them to expand their range into areas typically stressful for most anurans.

Slow and sustainable intermittent swimming has recently been described in several Centrarchid fishes, such as bluegill and largemouth bass. This swimming behavior involves short periods of body-caudal fin undulation alternating with variable periods of coasting. This aerobic muscle powered swimming appears to reduce energetic costs for slow, sustainable swimming, with fish employing a “fixed-gear” or constant tailbeat frequency and modulating swimming speed by altering the length of the coasting period. We asked if this swimming behavior was found in other fish species by examining volitional swimming by brook trout in a static swimming tank. Further, we employed muscle mechanics experiments to explore how intermittent swimming affects muscle power output in comparison to steady swimming behavior. Brook trout regularly employ an intermittent swimming form when allowed to swim volitionally, and consistently showed a tailbeat frequency of ~2 Hz. Coasting duration had a significant, inverse relationship to swimming speed. Across a range of slow, sustainable swimming speeds, tailbeat frequency increased modestly with speed. The duration of periods of coasting decreased significantly with increasing speed. Workloop experiments suggest that intermittent swimming reduces fatigue, allowing fish to maintain high power output for longer compared to continuous activity. This study expands the list of species that employ intermittent swimming, suggesting this behavior is a general feature of fishes.

Since 2000, a well-established population of the invasive oriental shrimp Palaemon macrodactylus has been present in fully marine conditions in the southwestern Atlantic Ocean (~38° S). To assess the physiological performance of this atypical population restricted to fully marine conditions, we conducted a laboratory experiment in which individuals were transferred from 35 ‰S (local seawater) to 2 ‰S; 5 ‰S; 10 ‰S; 20 ‰S; 50 ‰S and 60‰ for short (6 h), medium (48 h), and long (>504 h) acclimation periods. We measured the time course response of relevant parameters in the shrimp's hemolymph; activity of Na⁺, K⁺-ATPase (NKA), and V-H⁺-ATPase (VHA); and muscle water content. Shrimp showed great osmoregulatory plasticity, being able to survive for long periods between 5 ‰S and 50 ‰S, whereas no individual survived after transfer to either 2 ‰S or 60 ‰S. Shrimp hyper-regulated hemolymph osmolality at 5 ‰S and 10 ‰S, hypo-regulated at 35 ‰S and 50 ‰S, and isosmoticity was close to 20 ‰S. Compared to 35 ‰S, prolonged acclimation to 5 ‰S caused a decrease in hemolymph osmolality (~34%) along with sodium and chloride concentrations (~24%); the NKA and VHA activities decreased by ~52% and ~88%, respectively, while muscle water content was tightly regulated. Our results showed that the atypical population of P. macrodactylus studied here lives in a chronic hypo-osmo-ion regulatory state and suggest that fully marine conditions contribute to its poor performance at the lower limit of salinity tolerance (<5 ‰S).

Honey bees play a pivotal role in shaping ecosystems and sustaining human health as both pollinators and producers of health-promoting products. However, honey bee colony mortality is on the rise globally, driven by various factors, including parasites, pesticides, habitat loss, poor nutrition, and climate change. This has far-reaching consequences for the environment, economy, and human welfare. While efforts to address these issues are underway, the current progress in electron paramagnetic resonance (EPR) instrumentation affords using the immense potential of this magnetic resonance technique to study small samples such as honey bees. This paper presents the pioneering 2D in vivo EPR imaging experiment on a honey bee, revealing the ongoing redox-status of bees’ intestines. This way, by monitoring the spatio-temporal changes of the redox-active spin-probes’ EPR signal, it is possible to gain access to valuable information on the course of ongoing bees’ pathologies and the prospect of following-up on the efficiency of applied therapies. Employing a selection of diverse spin-probes could further reveal pH levels and oxygen concentrations in bee tissues, allowing a noninvasive assessment of bee physiology. This approach offers promising strategies for safeguarding pollinators and understanding their biology, fostering their well-being and ecological harmony.

Preparation for oxidative stress (POS) has been widely reported in animals under controlled laboratory conditions, but whether this phenomenon is visible in animals under natural conditions remains to be explored. Altitudinal gradients provide a good opportunity to address this question, since environmental conditions become more hostile with increasing altitude. Here, we investigated the levels of oxidative stress, oxidative damage, and antioxidant defenses in Chinese toads (Bufo gargarizans) along an altitudinal gradient (50 m, 1200 m, 2300 m, 3400 m above sea level). The results show that changing altitude led to a significantly lower ratio of oxidized to reduced glutathione in liver, with a higher value at 50 m. This ratio in muscle tissues did not differ significantly between altitudes of 50 m, 2300 m, and 3400 m. However, reduced glutathione content increased significantly along the altitude, with higher values in liver at 2300 m and higher values in skeletal muscle at 3400 m. Malondialdehyde (MDA) content in liver did not change significantly with increasing altitude. Brain and muscle tissues showed a higher MDA content at 50 m than the other three altitudes. The activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione-S-transferase, as well as total antioxidant capacity, also displayed tissue-specific upregulation in heart, skeletal muscle, and brain, but all of these antioxidant enzymes except for glutathione-S-transferase were significantly reduced in liver along the altitudinal gradient. In summary, environmental factors at higher altitude did not lead to higher levels of oxidative stress and oxidative damage in B. gargarizans, mainly due to stronger antioxidant defenses. This study corroborates the occurrence of POS in high-altitude toads living under field conditions and contributes to revealing the biochemical adaptations to extreme environments at higher altitude.

Sensing and acquiring dissolved oxygen is crucial for nearly all aquatic life. This may become even more vital as dissolved oxygen concentrations continue to decline in many aquatic environments. While certain phenotypes that enable fish to live in low oxygen have been characterized, adaptations that arise following sudden, drastic reductions in dissolved oxygen are relatively unknown. Here, we assessed the blind Mexican cavefish, Astyanax mexicanus, for alterations to gill morphology that may be adaptive for life in hypoxic caves. The Astyanax system provides the unique opportunity to compare gill morphology between stereotypical “surface” adapted morphotypes and obligate cave-dwelling conspecifics. While the surface environment is well-oxygenated, cavefish must cope with significantly reduced oxygen. We began by quantifying traditional morphological gill traits including filament number and length as well as lamellar density and height in surface fish and two distinct cave populations, Pachón and Tinaja. This enabled us to estimate total lamellar height, a proxy for gill surface area. We then used immunohistochemical staining to label 5-HT-positive neuroepithelial cells (NECs), which serve as key oxygen sensors in fish. We discovered an increase in gill surface area for both cavefish populations compared to surface, which may enable a higher capacity of oxygen acquisition. Additionally, we found more NECs in Pachón cavefish compared to both surface fish and Tinaja cavefish, suggesting certain selective pressures may be cave-specific. Collectively, this work provides evidence that cavefish have adapted to low oxygen conditions via alterations to gill morphology and oxygen sensing, and informs evolutionary mechanisms of rapid adaptation to dramatic, chronic hypoxia.

Thyroid hormones (THs) play important roles in growth, development, morphogenesis, reproduction, and so on. They are mainly meditated by binding to thyroid hormone receptors (TRs) in vertebrates. As important members of the nuclear receptor superfamily, TRs and their ligands are involved in many biological processes. To investigate the potential roles of TRs in the gonadal differentiation and sex change, we cloned and characterized the TRs genes in protogynous rice field eel (Monopterus albus). In this study, three types of TRs were obtained, which were TRαA, TRαB and TRβ, encoding preproproteins of 336-, 409- and 415-amino acids, respectively. Multiple alignments of the three putative TRs protein sequences showed they had a higher similarity. Tissue expression analysis showed that TRαA mainly expressed in the gonad, while TRαB and TRβ in the brain. During female-to-male sex reversal, the expression levels of all the three TRs showed a similar trend of increase followed by a decrease in the gonad. Intraperitoneal injection of triiodothyronine (T3) stimulated the expression of TRαA and TRαB, while it had no significant change on the expression of TRβ in the ovary. Gonadotropin-releasing hormone analogue (GnRHa) injection also significantly upregulated the expression levels of TRαA and TRαB after 6 h, while it had no significant effect on TRβ. These results demonstrated that TRs were involved in the gonadal differentiation and sex reversal, and TRα may play more important roles than TRβ in reproduction by the regulation of GnRHa in rice field eel.

The present study reports the results of an electrophysiological analysis of sleep in the East African root rat, Tachyoryctes splendens, belonging to the rodent subfamily Spalacinae. Telemetric electroencephalographic (EEG) and electromyographic recordings, with associated video recording, on three root rats over a continuous 72 h period (12 h light/12 h dark cycle) were analyzed. The analysis revealed that the East African root rat has a total sleep time (TST) of 8.9 h per day. Despite this relatively short total sleep time in comparison to fossorial rodents, nonrapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep states showed similar physiological signatures to that observed in other rodents and no unusual sleep states were observed. REM occupied 19.7% of TST, which is within the range observed in other rodents. The root rats were extremely active during the dark period, and appeared to spend much of the light period in quiet wake while maintaining vigilance (as determined from both EEG recordings and behavioral observation). These recordings were made under normocapnic environmental conditions, which contrasts with the hypercapnic environment of their natural burrows.

Flatworms are among the best studied animal models for regeneration; however, they also represent an emerging opportunity to investigate other biological processes as well. For instance, flatworms are nocturnal and sleep during the day, a state that is regulated by sleep/wake history and the action of the sleep-promoting neurotransmitter gamma-aminobutyric acid (or GABA). Sleep is widespread across the animal kingdom, where it serves many nonexclusive functions. Notably, sleep saves energy by reducing metabolic rate and by not doing something more energetically taxing. Whether the conservation of energy is apparent in sleeping flatworms is unclear. We measured the oxygen consumption rate (OCR) of flatworms dosed with either (1) GABA (n = 29) which makes flatworms inactive or (2) dopamine (n = 20) which stimulates flatworms to move, or (3) day and night neurotransmitter-free controls (n = 28 and 27, respectively). While OCR did not differ between the day and night, flatworms treated with GABA used less oxygen than those treated with dopamine, and less than the day-time control. Thus, GABA affected flatworm physiology, ostensibly by enforcing energy-conserving sleep. Evidence that dopamine increased metabolism was less strong. This work broadens our understanding of flatworm physiology and expands the phylogenetic applicability of energy conservation as a function of sleep.

Thermal performance curves (TPCs) provide a framework for understanding the effects of temperature on ectotherm performance and fitness. TPCs are often used to test hypotheses regarding local adaptation to temperature or to develop predictions for how organisms will respond to climate warming. However, for aquatic organisms such as fishes, most TPCs have been estimated for adult life stages, and little is known about the shape of TPCs or the potential for thermal adaptation at sensitive embryonic life stages. To examine how latitudinal gradients shape TPCs at early life stages in fishes, we used two populations of Fundulus heteroclitus that have been shown to exhibit latitudinal variation along the thermal cline as adults. We exposed embryos from both northern and southern populations and their reciprocal crosses to eight different temperatures (15°C, 18°C, 21°C, 24°C, 27°C, 30°C, 33°C, and 36°C) until hatch and examined the effects of developmental temperature on embryonic and larval traits (shape of TPCs, heart rate, and body size). We found that the pure southern embryos had a right-shifted TPC (higher thermal optimum (T_opt) for developmental rate, survival, and embryonic growth rate) whereas pure northern embryos had a vertically shifted TPC (higher maximum performance (P_max) for developmental rate). Differences across larval traits and cross-type were also found, such that northern crosses hatched faster and hatched at a smaller size compared to the pure southern population. Overall, these observed differences in embryonic and larval traits are consistent with patterns of both local adaptation and countergradient variation.