Journal of Experimental Biology - Latest Issue

• Effects of high hydrostatic pressure on the mechanical performance and behavior of shallow-water jellyfish ( Aurelia aurita )

  ABSTRACT

  Hydrostatic pressure in the marine environment increases linearly with depth, and organisms at 1000 m experience pressures 100 times greater than those at sea surface level. Previous work has examined the effects of pressure on neuron and nervous system activity in some organisms, as well as the various biochemical adaptations of deep-water species. However, the effects of pressure on other biological tissues are not well understood. In this study, we took the shallow-water jellyfish Aurelia aurita and exposed it to pressures of up to 30 MPa (equivalent to 3000 m depth). We observed behavioral and kinematic changes that are likely due to mechanical effects of hydrostatic pressure on the swimming muscles and bell mesoglea. The pulsation rate of the bell was found to correlate with hydrostatic pressure, although the effect was small relative to the variability between individuals. Both the maximum contraction and relaxation rates of the bell were found to be significantly reduced at high pressure (30 MPa) relative to near-surface pressure (<1 MPa). The changes in pulse frequency and relaxation rate were both fully and immediately reversed upon release of pressure, but the change to contraction rate was not. Because bell contraction is controlled by muscle fibers and relaxation is controlled by elastic fibers in the mesoglea, the differential effects on contraction versus relaxation suggest that different tissues are affected differently by pressure. This opens the way for future work on how individual organisms can adapt to different environments.

• Beyond calcium: cross-bridge binding regulates titin's contribution to muscle force

  ABSTRACT

  Since the 1950s, muscle contraction has been explained by the sliding filament and cross-bridge theories involving actin and myosin. However, these theories do not account for certain muscle properties, such as residual force enhancement (rFE). The sarcomeric protein titin has been proposed to contribute to active force and rFE, but its role remains unclear. A leading hypothesis suggests that titin binds to actin, thereby shortening its spring-like segment, with calcium regulating this interaction. We investigated the roles of calcium and cross-bridge formation in titin mechanics by measuring the length of titin's PEVK region in sarcomeres during (i) passive stretch, (ii) active stretch with cross-bridge inhibition (via 2,3-butanedione monoxime, BDM) and (iii) active isometric contraction. PEVK lengths were similar for passive and cross-bridge-inhibited conditions but were longer for active contractions. Our results suggest that cross-bridge engagement, not calcium alone, modulates titin extensibility and passive force under physiological conditions.

• Extraordinary creatures: hagfishes

  Hagfishes are ancient jawless fishes that are found in all of the oceans, except around Antarctica, at depths between 100 and 1000 m, usually in coastal waters. The animals are extremely agile and can tie themselves in knots; they mainly scavenge on carcasses that fall from above. When attacked by large fish, such as sharks, hagfish instantaneously release an enormous quantity of slime, which clogs the attacker's gills, forcing them to release the hagfish almost unharmed. Douglas Fudge, Chapman University, USA, has been studying hagfish since 1997, working initially on the biomechanics of their slime, before investigating other aspects of their biology. Fudge has identified five new hagfish species and Eptatretus fudgei is named after him. He tells Journal of Experimental Biology about these extraordinary living fossils, how they are remarkable escapologists and how they survive shark attacks.

• ECR Spotlight – Dhairya Desai

  ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Dhairya Desai is an author on ‘ Beyond calcium: cross-bridge binding regulates titin's contribution to muscle force’, published in JEB. Dhairya is a Graduate Student (MSc) in the lab of Walter Herzog at the University of Calgary, Canada, investigating muscle contraction at the protein level, aiming to clarify force production and functional performance.

• Insulin-like peptide has antagonistic pleiotropic effects on male combat traits and survival traits in an armed beetle

  ABSTRACT

  The expression of sexually selected traits, such as exaggerated weapons and ornaments, often entails trade-offs against life-history traits. While phenotypic trade-offs are well documented, the underlying molecular physiological mechanisms remain largely unexplored. In this study, we investigated the potential role of an insulin-like peptide, ILP2, in mediating the trade-off between sexually selected combat traits and survival traits in the broad-horned flour beetle, Gnatocerus cornutus. RNA interference (RNAi)-mediated knockdown (KD) of ILP2 during larval stages resulted in a reduction in the development of mandibular horns and overall body size. Interestingly, ILP2 KD males had increased lipid storage and enhanced starvation tolerance, indicating a shift in resource allocation from sexually selected traits to survival traits. Behaviorally, ILP2 KD males showed decreased locomotor activity and reduced aggression, leading to lower combat success. These findings suggest that ILP2 functions as a key mediator in the allocation of resources between combat and survival traits, highlighting its pleiotropic effects on morphology, metabolism and behavior. Our study provides novel insights into the molecular physiological mechanisms underlying life-history trade-offs associated with sexually selected traits.