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 assessed 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) an elaboration of a pre-existing 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 from courtship behavior.

Ultrasonic cavitation noise from fast vessels overlaps spectrally with echolocation clicks of toothed whales and therefore has the potential to degrade echolocation performance through auditory masking of returning echoes. Here, we tested that hypothesis by exposing two trained echolocating porpoises carrying DTAGs to two different levels of decidecade noise centered on 2 kHz (non-masking) and 125 kHz (masking) during an active target discrimination task. We found no click level adjustments or effects on discrimination performance in trials with non-masking noise or low-level masking noise. However, when exposed to high-level masking noise of 113±3 dB re. 1 µPa root mean square (RMS), the porpoises increased their mean click source levels by 7-17 dB. Despite this Lombard response of 0.2-0.5 dBsignal/dBnoise, and longer time and more clicks used by the porpoises to perform the task in noise, both animals were still significantly poorer at discriminating the targets (64-85% success rate) than in the other treatments (94-100%), thus demonstrating adverse masking effects. When the porpoises were offered spatial release from masking by relocating the noise source off-axis relative to the animal-to-target axis, echolocation performance was regained. We conclude that moderate levels of high-frequency noise, such as from cavitating vessel propellers several hundred meters from a vessel, can mask porpoise echolocation in a way that cannot be fully compensated for. As biosonar is vital for foraging and navigation around hazards such as gillnets for porpoises and other toothed whales, this study highlights that masking effects should be considered in impact assessments of cavitating vessels around echolocating toothed whales.

Humans expend more energy walking on uneven terrain, but the amount varies across terrains. Few experimental characterizations exist, each describing terrain qualitatively without any relation to others or to flat ground. This precludes mechanistic explanation of the energy costs. Here, we show that energy costs vary smoothly and approximately quadratically as a function of terrain amplitude. We tested this with healthy adults (N=10) walking on synthetic uneven terrain with random step heights of parametrically controlled maximum amplitude (four conditions 0-0.045 m) and at four walking speeds (0.8-1.4 m s-1). Both net metabolic rate and the rate of positive work increased approximately with amplitude squared and speed cubed (R2=0.74, 0.82, respectively), as predicted by a simple walking model. The model requires work to redirect the body center of mass velocity between successive arcs described by pendulum-like legs, at proportional metabolic cost. Humans performed most of the greater work with terrain amplitude early in the single stance phase, and with speed later in stance during push-off. Work and energy rates changed with approximately linear proportionality, with a ratio or delta efficiency of 49.5% (R2=0.68). The efficiency was high enough to suggest substantial work performed passively by elastic tendon and not only by active muscle. Simple kinematic measures such as mid-swing foot clearance also increased with terrain amplitude (R2=0.65), possibly costing energy as well. Nevertheless, most of the metabolic cost of walking faster or on more uneven terrain can be explained mechanistically by the work performed.

Plainfin midshipman fish (Porichthys notatus) exhibit seasonal auditory plasticity that enhances their reproductive success. During the summer, type I male midshipman acoustically court females and both the males and females exhibit increased auditory sensitivity during this period. The enhanced auditory sensitivity is associated with increased density of sensory hair cells in the saccule but not the utricle, suggesting that different mechanisms underlie physiological plasticity in distinct inner ear regions. To better understand how shifts in hair cell number occur within auditory tissues, we examined cell turnover across breeding states and sexes in midshipman fish. We found that reproductive type I males exhibited less saccular cell proliferation than non-reproductive males without a change in cell death, indicating a net loss of saccular cells during the breeding season. By contrast, saccular cell proliferation increased in summer females, with no seasonal changes in other inner ear epithelia. Collectively, our data reveal that multiple mechanisms are likely to contribute to seasonal auditory plasticity within a single species, potentially within the ear of an individual animal.

Beaks of granivorous songbirds are adapted to dehusk seeds fast and efficiently. This is reflected in the large variety of beak shapes and sizes among species specialized in different seed types. Generally, larger beaks improve the dehusking of larger seeds by transmitting and withstanding higher bite forces. Meanwhile, smaller beaks are better suited for processing smaller seeds by allowing faster beak movements and better seed handling dexterity. These patterns are presumably the result of a trade-off between force and velocity inherent to lever systems. Because beak shape also varies among individuals of the same species, we investigated whether beak shape relates to variation in feeding performance and beak kinematics in the domestic canary (Serinus canaria). We analysed beak morphology of 87 individuals through both traditional size measurements and 3D-landmark analysis to capture metrics such as beak depth, length, width and curvature. We related these metrics of morphology to data on feeding performance and beak kinematics during feeding on smaller canary seeds and larger, tougher hemp seeds. We found that individuals with larger absolute beak depths were faster at dehusking the large seeds. Even though individuals with shallow or long beaks displayed higher beak opening-closing frequencies, this did not result in a significantly shorter processing time of the smaller seeds. Our data are therefore in line with the presence of a force-velocity trade-off within a species, but without a velocity-related drawback of beak-size adaptations for increased bite force on the handling performance of a smaller and easier-to-crack seed.

Breath-holding foraging implies different adaptations to limit oxygen (O2) depletion and maximize foraging time. Physiological adjustments can be mediated through O2 consumption, driven by muscle mitochondria, which can also produce reactive oxygen species during reoxygenation. Southern elephant seals spend months foraging at sea, diving for up to 1 h. Pups transition abruptly to aquatic life after a post-weaning period, during which they fast and progressively increase their activity, making this period critical for the development of an adaptive response to oxygen restriction and oxidative stress. We compared the functional capacity of a swimming muscle in 5 recently weaned and 6 adult female southern elephant seals. High-resolution respirometry was employed to examine muscle mitochondrial respiratory capacity and differences in protein and gene expression of the main regulatory pathways were determined using LC-MS/MS and RT-qPCR, respectively. Oxidative damage was measured in the plasma. We found that juveniles have higher mitochondrial coupling efficiency compared with adults, probably as a response to growth and significant physical activity reported during the post-weaning period. There were no differences in oxidative damage, but adults had a higher level of antioxidant defenses. Both hypoxia and oxidative response pathways appeared less activated in juveniles. This study highlights the differences in muscle metabolism and the likely adaptive response to hypoxia and oxidative stress between juvenile and adult south elephant seals. It also suggests that early constraints such as fasting, physical activity and short-term low O2 partial pressure exposure could contribute to immediate and long-term responses and help to acclimatize juveniles to aquatic life.

Although hormones are vital to an organism's ability to respond to environmental stressors, they can be directly altered by the environment and impact reproductive behavior. For example, in some fishes, aquatic hypoxia (low dissolved oxygen) inhibits the aromatase enzyme that converts testosterone to estradiol. Here, we examined the effects of short-term aromatase inhibition on reproductive behavior in male Pseudocrenilabrus multicolor, a widespread African cichlid, from one normoxic river population and one hypoxic swamp population. We further tested the response of females to treated and untreated males. We predicted that aromatase inhibition would decrease courtship and competitive behaviors, but the swamp population would be less affected given generational exposure to hypoxia. Specifically, we compared competition and courtship behavior of males treated with a short-term exposure to an aromatase inhibitor with control fish from the two populations. We found that both courtship and competitive behaviors were affected by the interaction between treatment and population. River fish performed fewer courtship and competitive behaviors under the aromatase inhibition treatment while the behavior of swamp males was unaffected. Additionally, we found that females from the swamp population preferred males from the aromatase inhibition treatment and river females preferred control males. While we found behavioral effects of short-term aromatase inhibition, we did not find any effects on male nuptial coloration. Overall, these results indicate that the effects of short-term aromatase inhibition on behavior could depend on local adaptation in response to hypoxia.

Animals that overwinter in temperate climates must prevent or repair damage to their cells to survive winter, but we know little about how they protect cellular structure at the cytoskeletal level. Both chilling (no ice formation) and freezing (ice formation) are hypothesized to cause substantial challenges to cell structure and the cytoskeleton. The spring field cricket Gryllus veletis becomes freeze tolerant following a 6-week acclimation to fall-like conditions, during which they differentially express multiple cytoskeleton-related genes. We tested the hypothesis that G. veletis alter their cytoskeleton during acclimation to support maintenance of cytoskeletal structure during freezing and thawing. We used immunocytochemistry and confocal microscopy to characterize changes in microfilaments (F-actin, a polymer of G-actin) and microtubules (a polymer of α- and β-tubulin) in three tissues. While we saw no effect of acclimation on microtubules, crickets increased the abundance of microfilaments in fat body and Malpighian tubules. When we chilled or froze these freeze-tolerant crickets, there was no apparent damage to the actin or tubulin cytoskeleton in fat body, but there was decreased cytoskeleton abundance in Malpighian tubules. When we froze freeze-intolerant (unacclimated) crickets, microfilament abundance decreased in fat body tissue, while microfilaments were unaffected by chilling to the same subzero temperature. Our study shows that freeze-tolerant crickets are able to prevent or rapidly repair ice-induced damage to the actin cytoskeleton in fat body, likely due to preparatory changes in advance of freezing - i.e., during acclimation. We suggest future directions examining the mechanisms that underlie these structural changes.

The shells of turtles serve as protection, yet shell shape and natural history widely vary among turtles. Here we identify the mechanical behavior that provides marine turtles, species characterized with fusiform shells, with biomechanical strength and resilience. The multi-layered carapacial bone structure seemingly serves a protective role for the muscles, nerves and viscera it houses. What are the shell's material properties that provide protection? Most previous work focused on non-marine turtles that differ in natural history and shell morphology from marine species. We measured carapacial mechanical behavior of green turtle (Chelonia mydas), loggerhead (Caretta caretta), and Kemp's ridleys (Lepidochelys kempii) across a range of body sizes in juvenile, subadult and adults. Carapace samples were tested using quasi-static compression to quantify stiffness (Young's modulus), yield strength, and toughness. The mechanical characteristics of marine turtle shells are grossly akin to that of other turtles and driven by the bone's sandwich structure. Yet, the material properties indicate that marine turtle shells are less stiff and strong than those of their freshwater and terrestrial counterparts. We hypothesize that increased flexibility of the shell may reflect tradeoffs for life that includes experiencing pressures from diving somewhat deeply, in marine environments. Shell material properties also differed among species and ontogenetically. Green turtles had the stiffest, strongest, and toughest shells while loggerhead carapaces were the most compliant. Stiffness and yield strength showed positive relationships with body size which were most pronounced in green turtles and Kemp's ridleys. Phylogenetic histories and ecological differences likely drive this interspecific variation.

Adolescence is a sensitive period because it is associated with the ontogeny of key neurological, physiological, and behavioural systems. These systems can be permanently altered by social disruption during adolescence and therefore impair individuals' ability to cope with their environment later in life. We tested on captive zebra finches (Taeniopygia guttata) if pair disruption during emancipation affects the family social structure with potential consequences on the nutritional status, personality and corticosterone stress response of juveniles. We experimentally manipulated the social environment of 22 families during emancipation by replacing fathers with unfamiliar males (experimental families) or not (control families) and monitored the prevalence of affiliative, agonistic and sexual interactions between family members. We assessed offspring growth, timing of nutritional independence, body condition as well as five personality traits and corticosterone stress response to isolation. While we observed more agonistic and sexual behaviours in experimental families, we also observed more affiliative behaviours between experimental siblings and more maternal provisioning of the experimental juveniles. Among all the traits we tested, we only found a sex-dependent effect of the experimental treatment on spatial neophobia, suggesting that pair disruption may have long-term consequences on females' ability to cope with new environments. However, our findings suggest overall that emancipation is a less sensitive phase to social environment in comparison to the prenatal and early postnatal periods and that nutritional and social buffers may mitigate the lasting impacts of pair disruption on adolescent behavioural and stress response profiles in altricial species such as the zebra finch.