Journal of Experimental Biology - Latest Issue

• Dehydration alters sprint speed capacity more than maximal endurance in a terrestrial lizard

  ABSTRACT

  The evolution of thermo-hydroregulation is determined by a cost–benefit balance, which in terrestrial ectotherms depends on the relationship between temperature, hydration status and maximal performance capacities. Earlier studies in amphibians uncovered deleterious effects of dehydration on a range of locomotor tasks and suggested that dehydration might further constrain the benefits of thermoregulation by decreasing tolerance to extreme temperatures. Hydric performance curves have been little investigated so far in dry-skin ectotherms, such as reptiles. Further, whether dehydration differently alters locomotor performance at low versus high temperatures in these organisms remains unresolved. Here, we manipulated drinking water availability over 10 days and quantified the hydric dependence of maximum running speed at different body temperatures as well as effects on endurance capacity in the lizard Zootoca vivipara. We further assessed whether performance decline could be explained by a loss of body condition, specifically hindlimb muscle loss. Lizards provided with limited drinking water declined significantly in condition and had much higher plasma osmolality, indicating sharp physiological dehydration. Despite that, we found only modest effects of dehydration on sprint speed, even at high body temperatures, and no obvious effects on endurance. Individual mass loss was non-linearly but weakly correlated with a decrease in endurance capacity. Sprint speed decreased with hindlimb muscle loss, and we found a slight reduction of the thermal performance breadth in the most dehydrated lizards. These results suggest that locomotor performance is primarily influenced by body temperature and secondarily by hydration state and only from a high dehydration threshold.

• Equivalent laws of pectoral fin propulsion parameters of cownose ray based on kinematic and hydrodynamic analysis

  ABSTRACT

  Batoids achieve remarkable swimming efficiency through adaptive speed modulation. While previous studies have preliminarily linked pectoral fin kinematics to swimming speed in cownose rays (Rhinoptera javanica), the dynamic relationship between fin motion patterns and propulsive performance has remained unclear. By integrating kinematic analysis with hydrodynamic experiments, this study establishes a consistent framework that reveals their unique propulsion mechanism. Kinetically, we found that fin velocity exhibits a linear relationship with swimming speed via coordinated amplitude–frequency modulation. The Strouhal number (St) decreases with increasing speed, with most values falling within the optimal range of 0.2–0.4. A bio-inspired robot successfully replicated the figure-of-eight motion of biological pectoral fins. Hydrodynamic experiments demonstrated that the fins generate comparable instantaneous thrust during both upstroke and downstroke, with thrust in each half-stroke following a unimodal pattern – increasing to a peak before declining. A parameter equivalence law was identified: when the product of frequency and amplitude (fA) is held constant, different kinematic combinations yield consistent mean thrust, and thrust shows a significant positive correlation with fA. This confirms that the rays dynamically regulate swimming speed through fin velocity while maintaining high efficiency across conditions. These findings not only advance the understanding of cownose ray propulsion but also provide a theoretical basis for motion control in bio-inspired underwater robots.

• Neck muscle twitch properties are associated with constraint on drum speed in woodpeckers, but not drum length

  ABSTRACT

  Animal displays are often limited by the properties of the muscles that generate them. Here, using in situ muscle stimulation, we investigated the twitch properties of the longus colli ventralis (LCv), a primary muscle used to protract the head and neck during territorial drumming displays in woodpeckers. Specifically, we tested LCv twitch kinetics and endurance in a manner that simulates drum speed (beats s⁻¹) and length (total beats), two signal features that can evolve independently of each other. We identified a maximum muscle contraction rate that may represent a physiological constraint relevant to drumming speed, but no relevant constraint on the repetition of contractions that might affect drum length. This suggests that twitch properties may differentially affect display components. Broadly, our findings highlight how certain display features may freely diversify independent of others owing to physiological limits, while pointing to the way complex signals can evolve under partial performance constraints.

• Dehydration impacts lizard speed, but not as much as heat 

• Biosynthesis of long-chain omega-3 fatty acids by the nestlings of a generalist seabird

  ABSTRACT

  Docosahexaenoic acid (DHA), a long-chain omega-3 fatty acid (n3-LCPUFA), is an integral component of vertebrate brains. Vertebrates maintain their DHA levels through biosynthesis using alpha-linolenic acid (ALA; omega-3 precursor) or by consuming preformed DHA and other n3-LCPUFAs which abound in the natural diets of marine predators. Yet, numerous marine predators, including generalist seabirds, now exploit anthropogenic resources potentially deficient in n3-LCPUFAs. Whether they can offset such deficiency by bioconverting ALA into DHA remains unknown. Here, we tested whether chicks of the ring-billed gull (Larus delawarensis), a generalist seabird thriving in cities, can biosynthesize n3-LCPUFAs, including DHA, from ALA. We brought into captivity 12 hatchlings from an urban colony and 12 from a natural colony. Nine hatchlings per colony were gavaged 490 μl of ALA-rich flaxseed oil daily for 3 days. The control groups (N=3 urban hatchlings, 3 natural hatchlings) received an omega-3-free caloric equivalent in place of the ALA supplement. All chicks received an omega-3-free diet throughout captivity (72 h). We also attempted to follow ALA's potential bioconversion into n3-LCPUFAs using an oral ¹³C₁-enriched ALA tracer. Unfortunately, compound-specific isotope analyses of brain and liver tissue failed to detect any ¹³C enrichment. Nevertheless, the flaxseed oil supplementation study provided evidence of some ALA bioconversion. Compared with controls, supplemented chicks from both colonies accumulated more of all ALA derivates in their tissues except for DHA. We demonstrate for the first time that a seabird shows incomplete omega-3 bioconversion abilities, leaving them potentially vulnerable to deficiencies associated with urban foraging and shifting marine ecosystems.