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

The frequency and duration of environmental stressors, such as heat waves and drought, will continue to grow due to ongoing climate change, thereby increasing the likelihood that organisms will experience stressors consecutively. Exposure to one stressor can improve or impair future tolerance to the same stressor (i.e., hardening or softening, respectively), or enhance or reduce future tolerance to a different stressor (i.e., cross-protection or cross-susceptibility, respectively). Understanding whether stress improves or impairs animals’ abilities to withstand future stressors is critical for determining the physiological sensitivity of animals to ongoing climate change. Here, we used a factorial design with the variable field cricket (Gryllus lineaticeps) to evaluate whether prior heat or desiccation stress influenced subsequent heat or dessication tolerance. Given the potential energetic costs of hardening and cross-protection, we further examined whether resource (food) acquisition promoted hardening and cross-susceptibility. Prior heat exposure reduced future heat tolerance (i.e., softening), and prior exposure to both heat and desiccation reduced future desiccation tolerance (i.e., softening and cross-susceptibility), potentially due to terminal reproductive investment. Further, resource acquisition (amount of body mass gained) did not influence stress tolerance because individuals that acquired more resources were not more likely to exhibit benefits (rather than costs) to their future stress tolerance. In sum, our results suggest the increasing frequency of climate-related stressors may pose a significant physiological risk to some animals.

Chemotaxis is the biologically intrinsic navigation towards or away from chemical stimuli. It is a crucial behavioral response for animals when interacting with their environment and a tool for locating sustenance, hosts, and other vital environmental signals. Prior research has predominantly concentrated on the chemotactic behaviors of free-living and entomopathogenic nematodes in response to volatile soil constituents. The present work conducts for the first time the chemotaxis assay of Syphacia obvelata (Nematoda: Oxyuridae) parasitizing the vertebrate cecum as an experimental model for detecting this behavior in parasitic nematodes. We tested two mouse biological samples, namely urine, and serum, as odorants to study the in vitro chemotactic behavior of S. obvelata. The experiments were conducted in triplicate groups of twenty-two worms for gradient dilutions between 10^-0, 10^-1, 10^-3, and 10^-5ml, using a semi-solid formula of agar (Brenner 1974; Stiernagle. 2006) as a nutrient surface medium for cultivation. The chemotaxis chamber and photography system were applied according to Hirotsu et al. 2015 with some modification to be convenient with the current experiment. The chemotaxis index is computed along with the cultivated worms’ mean number attracted toward or repulsed away from the odorants. The control groups included ten worms with an ablated olfactory sense organ (amphid) that was targeted using a 785 nm picosecond pulsed laser with a power of 10 mW and a confocal Raman microscope. dose-dependent chemotactic response to both urine and serum, with diluted concentrations (10⁻⁵) acting as attractants and undiluted forms acting as repellents. There is also a time-dependent enhancement of chemotaxis, with stronger positive responses at 60 min for both stimuli. Unexpectedly, the high concentration of anal gland secretion consistently repels worms, with stronger repulsion over time. This study advances our knowledge of the sensory mechanisms of Oxyuridae, life cycle navigation, and parameters that promote retro-infection. It also provides the first insight into the chemotactic behavior of these creatures. It also highlights the potential of laser microsurgery as a precise tool for investigating complex sensory systems in minute organisms.

Serotonin (5-HT) induces sperm hyper-motility in bivalves. This process has been suggested to be associated with K⁺ efflux due to higher concentrations of K⁺ ions in testicular fluid compared to that of seawater. This hypothesis was supported by inhibition of 5-HT–induced sperm hyper-motility in artificial seawater (ASW) containing high extracellular K⁺ ions or in the presence of a voltage-dependent K⁺ channel blocker (4-AP). Here, we studied changes of sperm membrane potential to elucidate 5-HT–induced sperm hyper-motility signaling in Pacific oyster (Crassostrea gigas). Sperm motility was partially initiated (48.34 ± 7.80%) in ASW, and decreased at 5 min post-activation (p < 0.05). In the presence of 10^–5 M 5-HT, sperm motility was recorded 81.63 ± 3.55%, which remained unchanged within 60 min post-activation. After sperm activation in ASW with or without 5-HT, fluorescence intensity of membrane potential-sensitive fluorescent (DiSC₃(5)) was decreased to lower than that of the resting stage, indicating membrane hyperpolarization. Induction of membrane hyperpolarization, using valinomycin or in K⁺-free ASW (KF-ASW) could not trigger sperm hyper-motility, suggesting that hyperpolarization itself did not induce sperm hyper-motility. Next, we showed that membrane hyperpolarization was due to K⁺ efflux. The fluorescence intensity of DiSC₃(5) was increased in ASW or KF-ASW containing 4-AP, suggesting membrane depolarization due to inhibition of K⁺ efflux. The valinomycin–induced membrane hyperpolarization was changed to depolarization by subsequent additions of KCl, suggesting that changes in the electrochemical gradient of K⁺ ions resulted in the retention of intracellular K⁺ ions. Observed membrane depolarization in the presence of 4-AP or high K⁺ ions was associated with inhibition of 5-HT–induced sperm hyper-motility. Taken together, this study shows that 5-HT–induced sperm hyper-motility was associated with membrane hyperpolarization due to K⁺ efflux.

Movement is a key driver of population dynamics. Movement ability and propensity often vary among populations and individuals. These differences may be particularly strong in aquatic species, where the ability to move within a site is not necessarily correlated to the ability to move between sites. In periods of range expansion, these differences can lead to non-equilibrium dynamics, whereby more mobile phenotypes arrange themselves spatially. This can be even more pronounced when dispersal success is nonrandom with respect to a heritable trait, thus acting as an agent of selection. This process—dubbed spatial sorting—can be particularly pronounced in non-native species, often hastening the speed of invasion spread. However, before spatial sorting occurring, there must first be individual differences in traits that confer greater movement success. Recently, a high-density breeding and expanding population of the non-native pipid frog, Xenopus tropicalis, in west-central Florida, offering a great opportunity to test whether movement success is predicted by individual differences in morphology or locomotor capacity. To test this, we compared the morphology, maximal exertion capacity, and jumping performance of movers and residents. We found that relative to residents, movers had longer hindlimbs, wider ilia, and traveled for greater time intervals before reaching exhaustion. These results suggest functional morphological and physiological traits are important in determining inter-site movement success.

The ecophysiological profiles of decapods adapted to estuarine and freshwater environments are remarkably diverse, likely reflecting independent colonization processes. There are no clear patterns in the energy expenditure associated with inhabiting these environments or general physiological processes, such as nitrogenous waste production, water regulation, or responses to salinity changes. We compared energy expenditure, measured as oxygen consumption, total ammonia production, and muscle water content in two euryhaline shrimp species of the genus Palaemon: the estuarine P. macrodactylus and the freshwater P. argentinus, under normal conditions and after exposure to salinity changes over periods ranging from 6 hours to 3 weeks. We also assessed the behavior of both species along a salinity gradient to understand if behaviorally mediated salinity selection may play a role in tuning the energy balance. The oxygen consumption profiles differed between species, both under normal conditions and in response to salinity changes. The freshwater species exhibited lower and stable oxygen consumption. Both species tended to eliminate more ammonia immediately after being transferred from a concentrated to a more diluted condition. While the estuarine species maintained effective water content regulation, the freshwater species experienced immediate dehydration at high salinity and failed to recover over the long term. Freshwater species actively selected low salinity water, whereas the other showed no clear salinity preference. The results suggest that the observed differences in energy expenditure and volume regulation between species are related to full adaptation to freshwater. Behavior may act reinforcing the divergence.

The South American plains vizcacha, Lagostomus maximus, is recognized as the mammalian species with the highest ovulation rate which can reach as many as 800 ova. This remarkable polyovulation phenomenon was first reported in the 1970s and has remained unchanged in its findings ever since. We conducted an extensive re-evaluation of ovulation in L. maximus by examining natural ovulation, ovulation induced through the administration of exogenous hormones and autologous seminal plasma, while also categorizing the morphological characteristics and maturation stages of the released ova. Our results confirm L. maximus as the foremost polyovulatory mammalian species, albeit with a mean of 154 ± 87, ranging from 29 to 326 oocytes per oestrous cycle. We observed the concurrent presence of spontaneous ovulation, serving as a mechanism to eliminate defective oocytes, alongside induced ovulation, referred to as “euovulation,” that promotes the release of cumulus-oocyte complexes suitable for fertilization. In addition, we provide evidence for the involvement of seminal plasma in the process of induced ovulation and show that the “pseudovulation” phenomenon occurring at mid-gestation, which contributes to the formation of secondary corpora lutea, does not entail the release of oocytes into the oviducts. Our analysis also revealed the presence of spontaneous parthenogenetic oocyte activation and subsequent development, which occurred both during oocyte release in the ovulatory phase and within unruptured follicles in the ovary.

Culex pipiens (Cx. pipiens) are ubiquitous vectors of public health pathogens responsible for numerous human diseases. Consequently, their management is imperative. So, this study aimed to assess the susceptibility of third instar larvae of Cx. pipiens to distinct concentrations of jujube oil, LC₅₀ and LC₉₀ were determined. Also, the developmental duration of immatures, percentage of emerged adults, and the physiological responses at the sublethal concentration were recorded. GC–MS analysis was carried out to characterize the fractions of the jujube oil. Additionally, bioinformatics analysis was utilized. The results showed that the third instar larvae were susceptible to jujube oil, with larval mortality escalating in correlation with increased oil concentration and exposure time. Sublethal exposure to the oil significantly prolonged the larval developmental duration from 11 days of control to 15 days of treated. Conversely, the percentage of the emerged adults were decreased from 88.89% in the control to 17.78%in the treated. The data also indicated that the treatment of the larvae with the sublethal concentration significantly decreased the activities of acetylcholinesterase, glutathione S transferase, arginine kinase, cytochrome P450, and ecdysone. Conversely, the titers of catalase and 3-hydroxykynurenine were increased. The GC–MS analysis identified 9-Octadecenoic acid, methyl ester, (E)-, Octadecanoic acid, methyl ester and Hexadecanoic acid, methyl ester as predominant components. Bioinformatics assessments indicated ecdysone, juvenile hormone, and tryptophan oxygenase showed the lowest binding affinity scores. In sum, this study supports the potential of jujube oil as an effective alternative botanical agent for control of Cx. pipiens larvae.