Functional significance of an unusual chela dimorphism in a marine decapod: specialization as a weapon?

The squat lobster Munida rugosa has an unusual chela dimorphism exhibited mainly by large males. Some individuals have 'arched' chelae in which there is a gap between the dactylus and the pollex when closed, and others have a 'straight' morphology in which the dactylus and pollex oppose along most of their length. Geometric morphometric analysis indicated that, compared with males, the arched morphology does not develop fully in females, so further investigation was confined to males. In males, the distal part of the chela was similar in both the forms and seemed to be adapted to hold and shred prey items. Both morphologies had a major cylindrical tooth on the inner proximal part of the dactylus, but the arched morphology had a higher and wider propodus, a greater major tooth-pollex distance and a greater force generation than the straight morphology. The findings suggest that the arched chela morphology in M. rugosa is a sexually selected trait adapted to inflict puncture wounds on opponents during agonistic interactions. The arched morphology, therefore, appears to have evolved in males by means of sexual selection because it enhanced the function of the chela as a weapon, while retaining functionality for feeding.

Bioenergetic modelling of the marine phase of Atlantic salmon (Salmo salar L.).

A bioenergetic model of marine phase, wild Atlantic salmon was constructed to investigate the potential effects on post-smolt growth of predicted changes in oceanic conditions. Short-term estimates of growth in weight were similar to measurements in captivity and simulated growth varied with water temperature and swimming speed as expected. Longer-term estimates of growth in length were less than that achieved by wild salmon, particularly with constant swimming assumed. The model was sensitive to parameters relating to maximum daily food consumption, respiration and the relationships between body energy content, length and weight. Some of the sensitive parameters were based on substantive information on Atlantic salmon and their realistic ranges are likely to be much narrower than those tested. However, other parameter values were based on scant data, farmed Atlantic salmon or other salmonid species, and are therefore less certain and indicate where future empirical research should be focussed.