Journal of Experimental Biology最新文献

Many animals communicate using call and response signals, but the evolutionary origins of this type of communication are largely unknown. In most cricket species, males sing and females walk or fly to calling males. In the tribe Lebinthini, however, males produce calls that trigger a vibrational reply from females, and males use the substrate vibrations to find the responding female. Here we assess two hypotheses regarding the behavioral origin of this multimodal duet in the Lebinthini. We conducted playback experiments and measured behavioral and neuronal responses in multiple related cricket species to assess whether the precursor to the lebinthine duet was 1) a startle response to high-frequency sound, or 2) elaboration of a preexisting courtship behavior. We found behavioral similarities between the vibrational response of Lebinthini females and the acoustic startle behavior in other gryllid crickets. Specifically, the amplitude of the vibrational reply increases with male song amplitude in Lebinthini, and the magnitude of vibrations produced by two gryllid species when startled with ultrasound also correlates with the stimulus amplitude. Like in-flight startle behavior, the startle vibrations produced by perched crickets are suppressed when low-frequency sound is played simultaneously. We also observed courtship behavior in four gryllid species and found few instances of female vibration. Vibrational signals observed in Gryllus pennsylvanicus females were not correlated with male calls and occurred more frequently in pairs that did not mate after courtship. Combined, accumulating evidence supports the hypothesis that the lebinthine duet more likely evolved from a startle precursor than courtship behavior.

Understanding and monitoring wildlife behavior is crucial in ecology and biomechanics, yet challenging due to the limitations of current methods. To address this issue, we introduce WildPose, a novel long-range motion capture system specifically tailored for free-ranging wildlife observation. This system combines an electronically controllable zoom-lens camera with a LiDAR to capture both 2D videos and 3D point cloud data, thereby allowing researchers to observe high-fidelity animal morphometrics, behavior and interactions in a completely remote manner. Field trials conducted in Kgalagadi Transfrontier Park (South Africa) have successfully demonstrated WildPose's ability to quantify morphological features of different species, accurately track the 3D movements of a springbok herd over time, and observe the respiratory patterns of a distant lion. By facilitating non-intrusive, long-range 3D data collection, WildPose marks a significant complementary technique in ecological and biomechanical studies, offering new possibilities for conservation efforts and animal welfare, and enriching the prospects for interdisciplinary research.

Efficient navigation is crucial for the reproductive success of many migratory species, often driven by competing pressures to conserve energy and reduce predation risk. Little is known about how non-homing species achieve this balance. We show that sea lamprey (Petromyzon marinus), an ancient extant vertebrate, uses persistent patterns in hydro-geomorphology to quickly and efficiently navigate through complex ecosystems. Hydrodynamic flow models coupled with bathymetric mapping and fine scale acoustic telemetry revealed movement paths that tracked thalweg scour channels promoting rapid and efficient upstream migration, suggesting the existence of a bathymetric highway system. Near-substrate swimming along this path resulted in a median of 5.8% energy savings while also promoting improved safety from nocturnally active predators. We hypothesize sea lampreys use a novel mechanism, hydrostatic pressure guided rheotaxis, to achieve this navigation. It is likely this tactic relies on sensory information from the animal's primitive lateral line and perhaps the inner ear. Insights from this study can be used to redesign conservation practices to achieve improved control where the animal is invasive and improved fish passage within its native range.

We investigated the extracellular and intracellular digestion of bivalves employing magnetic resonance imaging (MRI). Ruditapes philippinarum clams and Mytilus galloprovincialis mussels were incubated in seawater containing a contrast reagent (GdDTPA) at 20°C. The digestive systems, from the esophagus to the rectum, were visualized at a high signal intensity by the T1-weighted MRI. The crystalline style of the clam was also identified, which turned counterclockwise when viewed from a ventral-posterior position at a rate of 16 rpm. Determined using the T1 relaxation rate, the uptake and excretion rates of the GdDTPA in the mussel's digestive glands were 2.9 and 0.25 d-1, respectively, indicating that the intracellular digestion in the gland acinar cells is slower than the extracellular digestion. These results demonstrate that MRI with contrast reagents is useful to study the activity of digestive system in the bivalves, and this technique can likely be applied to the study of other invertebrates.

Nondimensional groups of measured quantities enable comparison between measurements of animals under different conditions and comparison between species. One of the most used such group is the Reynolds number, which compares inertial and viscous contributions to forces on swimming animals. This group includes two quantities that are chosen by the researcher: a typical length and speed. Choosing these parameters will affect the numerical value of the Reynolds number, defining the state of the fluid flow. For example: by choosing fish body length as opposed to propulsive fin chord, results may vary by an order of magnitude with consequences for analysis and hydrodynamic regimes. Here we suggest a standardized sets of lengths and speeds to be used for aquatic animal locomotion to enable confident utilization of data from different sources. This framework aims to improve comparative studies within the field.

The allatostatin (AST) family of neuropeptides are widespread in arthropods. The multitude of structures and pleiotropic actions reflect the tremendous morphological, physiological and behavioral diversity of the phylum. Regarding the AST-C (with C-terminal PISCF motif) peptides, crustaceans commonly express three (AST-C, -CC, -CCC) that have likely arisen by gene duplication. However, we know little regarding their physiologically relevant actions. Here we functionally characterize the cognate receptor for AST-C and AST-CC, determine tissue expression and comprehensively examine the localization of AST mRNA and peptide. We also measured peptide release, circulating titers and performed bioassays to investigate possible roles. AST-C and -CC activate a single receptor (AST-CRd), but this, and other candidate receptors were not activated by AST-CCC. Whole mount in-situ hybridization (ISH) and hybridization chain reaction (HCR) FISH complemented neuropeptide immunolocalization strategies and revealed extensive expression of AST-Cs in the central nervous system. AST-C or -CCC expressing neurons were found in the cerebral ganglia, but AST-CC expression was never observed. Of note, we infer that AST-C and -CC are co-expressed in every neuron expressing crustacean cardioactive peptide (CCAP) and bursicon (BURS); all four peptides are released from the pericardial organs during a brief period coinciding with completion of emergence. In contrast to other studies, none of the AST-C peptides exhibited any effect on ecdysteroid synthesis or cardiac activity. However, expression of the AST-C receptor on hemocytes suggests a tantalizing glimpse of possible functions in immune modulation following ecdysis, at a time when crustaceans are vulnerable to pathogens.

Decapod crustaceans regulate molting through steroid molting hormones, ecdysteroids, synthesized by the molting gland (Y-organ, YO). Molt-inhibiting hormone (MIH), a neuropeptide synthesized and secreted by the eyestalk ganglia, negatively regulates YO ecdysteroidogenesis. MIH signaling is mediated by cyclic nucleotide second messengers. cGMP-dependent protein kinase (PKG) is the presumed effector of MIH signaling by inhibiting mechanistic Target of Rapamycin Complex 1 (mTORC1)-dependent ecdysteroidogenesis. Phylogenetic analysis of PKG contiguous sequences in CrusTome as well as 35 additional species in NCBI RefSeq, identified 206 PKG1 sequences in 108 species and 59 PKG2 sequences in 53 species. These included four PKG1α splice variants in the N-terminal region that were unique to decapods, as well as PKG1β and PKG2 homologs. In vitro assays using YOs from the blackback land crab (Gecarcinus lateralis) and green shore crab (Carcinus maenas) determined the effects of MIH±PKG inhibitors on ecdysteroid secretion. A general PKG inhibitor, Rp-8-Br-PET-cGMPS, countered the effects of MIH, as ecdysteroid secretion increased in PKG-inhibited YOs compared to C. maenas YOs incubated with MIH alone. By contrast, a PKG2-specific inhibitor, AP-C5 (4-[4-(1H-Imidazol-1-yl)phenyl]-N-2-propyn-1-yl-2-pyrimidinamine), enhanced the effects of MIH, as ecdysteroid secretion decreased in G. lateralis and C. maenas YOs incubated with AP-C5 and MIH compared to YOs incubated with MIH alone. These data suggest that both PKG1 and PKG2 are activated by MIH, but have opposing effects on mTORC1-dependent ecdysteroidogenesis. A model is proposed in which the dominant role of PKG1 is countered by PKG2, resulting in low ecdysteroid production by the basal YO during intermolt.

Peripheral arterial chemoreceptors monitor the levels of arterial blood gases and adjust ventilation and perfusion to meet metabolic demands. These chemoreceptors are present in all vertebrates studied to date but have not been described fully in reptiles other than turtles. The goals of this study were to 1) identify functional chemosensory areas in the South American rattlesnake (Crotalus durissus) 2) determine the neurochemical content of putative chemosensory cells in these areas and 3) determine the role each area plays in ventilatory and cardiovascular control. To this end, rattlesnakes were instrumented with transonic flow probes, arterial catheters, and subcutaneous impedance electrodes to measure shunt fraction, heart rate, blood pressure and ventilation, respectively. The catheters were placed at three putative chemosensory sites, the bases of the aortic arch, pulmonary artery, as well as at the carotid bifurcation, for site specific activation with sodium cyanide (NaCN, 0.5mg/0.1ml). These same sites were subsequently examined using immunohistochemical markers for acetylcholine, tyrosine hydroxylase (TH, the rate limiting enzyme in catecholamine synthesis) and serotonin, to identify putative oxygen-sensing cells. All three sites were chemosensory and stimulating each led to cardiovascular (shunt fraction and heart rate) and respiratory adjustments although not in an identical fashion. All three chemosensory areas contained cells positive for serotonin (5-HT), however, cells positive for vesicular acetylcholine transporter (VAChT) were found only in the aorta and pulmonary artery. We found no labeling for TH at any site.

Cross-protection occurs when exposure to one stressor confers heightened tolerance against a different stressor. Alternatively, exposure to one stressor could result in reduced tolerance against other stressors. Although cross-protection has been documented in a wide range of taxa at juvenile and adult life stages, whether early developmental exposure to a stressor confers cross-protection or reduced tolerance to other stressors later in life through developmental plasticity remains largely unexplored. In this study, we examined whether altered temperature during embryonic development results in developmental plasticity in upper thermal tolerance or hypoxia tolerance using a small topminnow, Fundulus heteroclitus, and examined potential underlying molecular mechanisms. We incubated embryos at one of two ecologically relevant temperatures (20 °C or 26 °C) until hatch. Once hatched, fish were raised at a common temperature of 20 °C for one year, and tolerance was assessed in both juveniles (6 months) and early adults (1 year). Developmental temperature had no significant effect on thermal tolerance (CTmax) in juvenile fish, or on the transcript abundance of thermal-tolerance related genes (constitutive heat shock proteins, hsc70, hsp90b). In contrast, reduced developmental temperature decreased hypoxia tolerance but increased transcript levels of the hypoxia inducible factor hif1α in juvenile fish but the effects were less evident in older fish. Overall, we found no indication of developmental plasticity for thermal tolerance, but there was evidence of negative impacts of lower developmental temperature on hypoxia tolerance in juveniles associated with changes in gene expression, providing evidence of developmental plasticity across stressors and levels of organization.

Coastal deoxygenation poses a critical threat to tropical coral reefs. Dissolved oxygen (DO) depletion can cause hypoxia-induced stress and mortality for scleractinian corals. Coral hypoxic responses are species-specific and likely modulated by the duration and severity of low-DO conditions, although the physiological mechanisms driving hypoxia tolerance are not fully understood. In this study, the Caribbean corals Acropora cervicornis, Porites astreoides, and Siderastrea siderea were exposed to either severe (1.5 mg L-1 DO) or moderate (3.5 mg L-1 DO) deoxygenation or a control treatment (6 mg L-1 DO). All corals survived 2 weeks of deoxygenation but exhibited sublethal changes to coral metabolism after 1- and 2-week exposures, compared to controls. Maximum quantum yield (Fv/Fm) was suppressed after 1 week in both deoxygenation treatments in A. cervicornis, and after 2 weeks in S. siderea and P. astreoides exposed to severe or moderate treatments, respectively. Respiration rates were lower than controls in A. cervicornis and S. siderea after 1 and 2 weeks of severe deoxygenation. The reduced respiration of P. astreoides after 1 week of moderate deoxygenation returned to control levels in week 2. Overall coral metabolic budgets, assessed by ratios of gross photosynthesis to respiration (Pg:R), were more autotrophic, or photosynthesis-dominant, after 1 week of severe deoxygenation in S. siderea and P. astreoides, while Pg:R was not significantly different in A. cervicornis between treatments. These results reveal that some corals shift their metabolism to tolerate low-oxygen conditions and avoid bleaching or mortality, indicating that metabolic plasticity is an important aspect of coral resistance to deoxygenation.