Journal of Experimental Biology - Latest Issue

  • Past environments modulate response to fluctuating temperatures in a marine fish species, Sebastes fasciatus

    ABSTRACT
    Predicted ocean warming will impact the survival and structure of various marine organisms, in particular ectotherms. Phenotypic plasticity enables species to cope with environmental changes, providing a vital buffer for evolutionary adaptations. Yet, the dynamics and molecular mechanisms underpinning these plastic responses remain largely unexplored. Here, we assessed the impact of temperature acclimation on the capacity of organisms for thermal plasticity. We conducted a genome-wide transcriptomic analysis on the Acadian redfish, Sebastes fasciatus, exposed to four temperatures (2.5, 5.0, 7.5 and 10.0°C) over a long-term period (up to 10 months) followed on some individuals by a short-term temperature change (+2.5°C or −2.5°C for 24 h), simulating natural temperature variation the species could encounter. Our results showed a dynamic transcriptional response to temperature involving various gene functions. The rapid response to temperature shifts, coupled with the sustained expression of specific genes over an extended period, highlighted the capacity of this species for plasticity in response to temperature changes. We also detected a significant effect of the interaction between the long- and short-term temperature exposures on gene expression, highlighting the influence of the past environment on the response to short-term temperature changes. Specifically, fish acclimated to higher temperatures demonstrated an increased stress-related response to environmental fluctuations, as evidenced by both the shape of their reaction norms and the involvement of stress-related gene functions. This result suggests that temperature conditions predicted for the near future in the Northwest Atlantic will trigger reduced adaptive plasticity to environmental fluctuations, highlighting the vulnerability of this species to ocean warming.

  • Courtship vocalizations in male ducks: spectral composition and resonance of the syringeal bulla

    ABSTRACT
    Ducks display a unique and dramatic sexual dimorphism in their vocal organ, the syrinx. Males have a left-sided bulla that is not present in females and that has been long hypothesized to play a role in courtship vocalizations, though this connection has never been tested. The large, hollow morphology of the bulla and its proximity to the sound-producing vocal folds introduce the possibility that it may work as a Helmholtz resonator, which makes it possible to predict the resonance frequencies enhanced by this structure. We found that during early ontogeny, the distribution of energy across the harmonic spectrum of contact calls is not different between males and females. We then used microcomputed tomography (µCT) scans of duck syringes to estimate resonance frequencies of the bullae and compared these with spectral features of their vocalizations. This comparison overall supports the idea that the bulla resonance may specifically enhance aspects of courtship vocalizations, especially in species that have a tonal courtship whistle. This was further supported when we tested the frequencies produced when air was blown through 3D printed bullae. We also saw potential influence of the bulla in non-courtship vocalizations, which could be explored further with a greater understanding of the input of other vocal tract features that influence vocalization. We observed that, in general, excepting the common eider, bulla size shows a weak positive correlation with male bird body mass. This study provides support for the long-held hypothesis that the adult male duck bulla influences resonance frequencies, in particular in courtship vocalizations.

  • Dynamics of release and activity of select neuropeptides post-bloodmeal in the female mosquito, Aedes aegypti

    ABSTRACT
    Female Aedes aegypti secrete urine rapidly post-bloodmeal ingestion, with diuresis beginning immediately for removal of excess salts and water. This post-prandial diuresis includes a peak, post-peak and late phase, involving the combined actions of multiple hormones, including diuretic and anti-diuretic factors. Calcitonin-like diuretic hormone 31 (DH31) and kinin peptides stimulate diuresis through actions on their cognate receptors localized in the Malpighian ‘renal’ tubules (MTs). In contrast, the anti-diuretic neurohormone CAPA inhibits secretion by MTs stimulated by select diuretic hormones, including DH31. Although DH31 and kinin are critical in achieving post-prandial diuresis, and CAPA functions as an important anti-diuretic hormone, the kinetics of their release and haemolymph levels remain unknown. Here, using heterologously expressed receptors for A. aegypti DH31, CAPA and kinin, we investigated the titres of these hormones in the haemolymph of female mosquitoes at different time points after blood feeding. Haemolymph extracts from female mosquitoes contained levels of diuretic peptides, specifically kinin and DH31, that increased immediately post-bloodmeal, with levels peaking at 2 and 5 min, respectively, whereas DH31 levels remained elevated for 15 min. Comparatively, levels of CAPA peptides in the haemolymph steadily increased 15 min post-blood feeding, with levels peaking at 30 min. Synergistic actions were observed between DH31 and a kinin-like peptides on the MTs, providing a physiological context for the rapid release of these peptides into the female haemolymph. Altogether, these results demonstrate that DH31 and kinin are released immediately post-bloodmeal and, along with CAPA peptides, have a coordinative action on the MTs to maintain haemolymph homeostasis through regulation of primary urine secretion.

  • Olfactory detection of ursodeoxycholic acid (UDCA) in large yellow croaker ( Larimichthys crocea ): responses, pathways and receptor functions

    ABSTRACT
    Olfactory communication plays a critical role in fish behavior and physiology, particularly in environments where visual and auditory signals are constrained. Bile acids, dual-function molecules serving as digestive agents and olfactory signals, are potent olfactory cues in aquatic ecosystems. The present study investigated the role of ursodeoxycholic acid (UDCA) as an olfactory attractant in large yellow croaker (Larimichthys crocea), an endangered species. Electrophysiological recordings demonstrated that UDCA elicits strong, concentration-dependent olfactory responses with a detection threshold of 10−12 mol l−1. Behavioral assays revealed UDCA-induced attraction exceeding that of other structurally similar bile acids, demonstrating significantly higher potency (P<0.05). Transcriptome analysis and pharmacological treatments revealed functional associations in UDCA detection. V2R1 upregulation and PLC pathway engagement (day 3) preceded delayed induction of OR11A1, TAAR13C-10 and OR52L2 with cAMP signaling (day 7), suggesting phased receptor involvement. Functional receptor expression assays confirmed that V2R1 mediates UDCA-induced calcium signaling, whereas OR11A1, TAAR13C-10 and OR52L2 respond through cAMP signaling. The present study provides a comprehensive understanding of UDCA chemosensation, linking receptor function, signaling pathways and behavioral responses. These findings enhance our understanding of fish olfactory systems and offer potential applications for species conservation and sustainable fisheries management.

  • Navigating turbulence: the effects of eddy size on the swimming performance of walleye ( Sander vitreus ) larvae

    ABSTRACT
    Walleye (Sander vitreus) populations experience substantial interannual fluctuations driven largely by high rates of larval mortality. To investigate the potential mechanisms underlying recruitment in walleye larvae, we assessed the effect of turbulence on larval swimming performance in a recirculating flow chamber. We measured the critical swimming speeds (Ucrit) of larvae throughout their first 5 weeks of development in response to increasing levels of turbulence and varying eddy sizes, generated through controlled water flow and the use of grid turbulence. As early as the first week post hatch, larvae exhibited a rheotactic response, demonstrating the ability to resist and swim against turbulent flows to some extent. Measured Ucrit increased with larval total length (LT; or age), and was lower in the grid-turbulence treatment, in which both the turbulence and the size of eddies were constrained by the grid spacing. Conversely, the relative critical swimming speeds based on body length (Ucrit,rel) declined with LT; swimming performance declined significantly when the eddy diameter approached approximately two-thirds of the larvae's total length. This ratio declined with age in the no-grid treatment, but was relatively constant in the grid treatment. Our results suggest that the scale of turbulence, rather than the magnitude of turbulent energy, has a greater influence on swimming performance. These findings highlight the importance of considering eddy length scale when assessing the swimming performance of fish larvae. Additionally, the swimming parameters established in this study can inform more realistic larval dispersal models for walleye as well as fisheries management decisions.