Signaling aggression.

From psychological and sociological standpoints, aggression is regarded as intentional behavior aimed at inflicting pain and manifested by hostility and attacking behaviors. In contrast, biologists define aggression as behavior associated with attack or escalation toward attack, omitting any stipulation about intentions and goals. Certain animal signals are strongly associated with escalation toward attack and have the same function as physical attack in intimidating opponents and winning contests, and ethologists therefore consider them an integral part of aggressive behavior. Aggressive signals have been molded by evolution to make them ever more effective in mediating interactions between the contestants. Early theoretical analyses of aggressive signaling suggested that signals could never be honest about fighting ability or aggressive intentions because weak individuals would exaggerate such signals whenever they were effective in influencing the behavior of opponents. More recent game theory models, however, demonstrate that given the right costs and constraints, aggressive signals are both reliable about strength and intentions and effective in influencing contest outcomes. Here, we review the role of signaling in lieu of physical violence, considering threat displays from an ethological perspective as an adaptive outcome of evolutionary selection pressures. Fighting prowess is conveyed by performance signals whose production is constrained by physical ability and thus limited to just some individuals, whereas aggressive intent is encoded in strategic signals that all signalers are able to produce. We illustrate recent advances in the study of aggressive signaling with case studies of charismatic taxa that employ a range of sensory modalities, viz. visual and chemical signaling in cephalopod behavior, and indicators of aggressive intent in the territorial calls of songbirds.

Identification and expression of amphioxus beta-microseminoprotein (MSP)-like gene encoding an ancient and rapidly evolving protein in chordates.

The cDNA encoding beta-microseminoprotein-like (beta-MSPL) was identified from the gut cDNA library of amphioxus. It contains a 336 bp open reading frame corresponding to a deduced protein of 111 amino acids and has eight cysteines conserved and located at the same positions as those in the vertebrate beta-MSPs. At amino acid level, it shares 12-20% similarity to the vertebrate beta-MSPs, and seems lacking the signal peptide at the N-terminus. This not only confirms that beta-MSP is a rapidly evolving protein during phylogeny, but also provides further data on the degree of diversity between species of this protein. RT-PCR and Northern blotting show that amphioxus beta-MSPL is expressed in all tissues examined, suggesting that beta-MSPL plays a fundamental role. However, in situ hybridization reveals that positive hybridization signals were present in all blastomeres of the embryos from 4-cell to gastrula stages, while its expression is restricted exclusively to notochord, somites and primitive gut in neurulae and larvae, and disappears in the ectoderm including the neural tube differentiated from the ectoderm. This suggests that beta-MSPL is possibly involved in the differentiation of ectoderm during embryonic development of cephalochordate amphioxus though it is ubiquitously expressed in embryos prior to gastrula stage and in the adult animal.