Escape performance in the sub-Antarctic notothenioid fish <i>Eleginops maclovinus</i>

Fast-start performance associated with escape behaviour was investigated in the sub-Antarctic notothenioid Eleginops maclovinus from the Beagle Channel, Tierra del Fuego, Argentina (mean winter water temperature 4degreesC, mean summer water temperature 10degreesC). Fish acclimated to 8.5degreesC for 2 months were filmed at 2, 4, 6, 8 and 10degreesC. Escape responses were temperature dependent over the range of temperatures tested. Maximum length-specific velocity ((V) over cap (max)), maximum length-specific acceleration ((A) over cap (max)) and inertial power output (P-iner) increased significantly with temperature. Q(10) values for (V) over cap (max), (A) over cap (max) and P-iner were 1.90, 3.27 and 8.90, respectively. Non-dimensional curvature of the spine ((c) over cap) also varied significantly with temperature, but was higher at low temperatures. The values of (c) over cap were threefold lower than previously reported for Antarctic notothenioids and similar to the values for temperate species. The results indicate that the high values of observed during escape behaviour in Antarctic notothenioids are not a universal feature of the suborder. A greater flexion of the body during fast starts is therefore a promising candidate for a specialised feature of behaviour linked to low-temperature performance.</p

A comparative study of the effects of constructional elements on the mechanical behaviour of dragonfly wings

Although wings of insects show a large variation in morphology, they are all made from a network of irregular veins interconnected through membranous areas. Depending on their shape, size, and position, wing veins are usually divided into three different groups: longitudinal veins, cross-veins and ambient veins. The veins together with the membrane and some other elements such as spines, nodus and pterostigma can be considered as the wing’s “constructional elements”. In spite of rather extensive literature on dragonfly wing structure, the role of each of these elements in determining the wing’s function remains mostly unknown. As this question is difficult to answer in vivo using biomechanical experiments on actual wings, this study was undertaken to reveal the effects of the constructional elements on the mechanical behaviour of dragonfly wings by applying numerical simulations. An image processing technique was used to develop 12 finite element models of the insect wings with different constructional elements. The mechanical behaviour of these models was then simulated under normal and shear stresses due to tension, bending and torsion. A free vibration analysis was also performed to determine the resonant frequencies and the mode shapes of the models. For the first time, a quantitative comparison was carried out between the mechanical effects selectively caused by different elements. Our results suggest that the complex interactions of veins, membranes and corrugations may considerably affect the dynamic deformation of the insect wings during flight.113122