Where does male-to-male aggression compromise cooperation?

We discuss how the diverse nature of aggression and cooperation can be understood if we focus our attention on where aggression reaches a compromise with non-aggression and/or cooperation in response to the relatedness between interactors. First we address whether Hamiltons rule explains the variation in male-to-male aggressiveness. Next we show that the variation in aggression and cooperation known in males of social spider mites (Saito, Evolution 49:413–417, 1995) can be explained by the change in relatedness (i.e. inclusive fitness) and effect of cooperative defence (synergistic effect). Then we learn that there is a sufficient condition of cooperation, which is determined primarily by two factors: the relatedness and synergistic effect of males. Furthermore, we expect that there is a condition where the aggression between males varies, depending upon how close the values of relatedness are to those of the sufficient condition of cooperation

Nest size variation reflecting anti-predator strategies in social spider mites of Stigmaeopsis (Acari: Tetranychidae)

The social spider mites (Acari: Tetranychidae) of Stigmaeopsis weave dense nests on the underside of host leaves. Four species occur on the leaves of bamboo in Japan: Stigmaeopsis longus, S. celarius, S. takahashii and S. saharai. We initially reconfirmed the occurrence of distinct variation in nest size among the species. Based on the hypothesis that this variation plays a role in protecting the spider mites from predators, we looked at the behavior of the natural enemies that occur on the host plants along with members of Stigmaeopsis. We found considerable variation in the ability of nests to protect the spider mite eggs. The smallest nests protected the eggs against 3 predators, whereas the largest nests protected the eggs only against one predator species. In other words, decreases in nest size increased egg defense. Thus we concluded that nest size variation reflects a strategy for reducing predation

Influence of Addition of Nickel on the Thermal Expansion, Rigidity Modulus and Its Temperature Coefficient of the Alloys of Cobalt, Iron and Chromium, Especially of Co-Elinvar. II : Additions of 30 and 40 per cent of Nickel

The influence of additions of 30 and 40 per cent of nickel on the thermal expansion in the range from 10 to 50°, rigidity modulus at 20°and its temperature coefficient in the range from 20 to 50°of the alloys of cobalt, iron and chromium was studied. The relations between those properties and the concentrations of nickel-added alloys were almost similar qualitatively to those in the case of the ternary alloys of cobalt, iron and chromium, that is, there were two groups of alloys, one showing a positive temperature coefficient of rigidity modulus and the other a negative. And it has been found that the content of cobalt at the composition showing the smallest value of the coefficient of thermal expansion and the largest positive maximum of the temperature coefficient of rigidity modulus decreases with the increase of nickel content and finally reaches zero at the composition of invar in the binary system of nickel and iron, while the content of chromium does not change until that of nickel reaches about 15 per cent, then gradually decreases and becomes zero at the composition of about 30 per cent of nickel and the rest of iron. In the case of addition of 30 per cent of nickel, the smallest thermal expansion coefficient was 1.87×10^, while in the case of addition of 40 per cent, it was 0.54×10^. The largest positive values of the temperature coefficient of rigidity modulus in the corresponding cases were respectively +76.4×10^ and +81.0×10^. The largest and smallest values of rigidity modulus in the case of addition of 30 per cent of nickel were 7.84×10^kg/cm^2 and 4.55×10^kg/cm^2, and in the case of 40 per cent of nickel they were respectively 8.96×10^kg/cm^2 and 4.69×10^kg/cm^2