Neanthes acuminata Ehlers (1868) is a monogamous coastal polychaete with male parental care and a high level of sexual selection. We measured the level of prezygotic isolation among allopatric populations of N. acuminata; from the East and West Coast of the USA, a population from Hawaii, and a laboratory culture originating from Los Angeles, CA. All populations were found to preferably mate with members of their own population. Individuals from populations from Atlantic vs. Pacific Ocean failed to pair and to mate, either during the 10 min or 48 hr experiments. Instead, individuals showed high levels of aggressive behavior. Experiments measuring the levels of interpopulation aggression, established that individuals can recognize and discriminate among different populations of N. acuminata on the basis of olfactory cues. Aggressive behavior was induced by exposure of animals to seawater "conditioned" by individuals from the other populations, thus demonstrating the role of olfaction in the detection of "home" populations. The aggressive display was stronger upon exposure to seawater conditioned with "unrelated" populations and especially between Pacific and Atlantic populations.
The syntheses of two side chain liquid crystal polymers, a polyacrylate and a polymethacrylate, are reported. In each of the polymers the liquid-crystalline side group carries an asymmetric carbon atom, thereby making some of the liquid crystal phases formed by the polymers optically active and chiral. For the chiral polyacrylate smectic A and chiral ferroelectric smectic C phases are observed, however for the chiral polymethacrylate a cholesteric phase is detected above the smectic A phase. It is found that the smectic A to cholesteric phase transition is mediated by the formation of an intermediary twisted smectic A phase. This intermediary phase is a liquid-crystalline analogue of the Abrikosov flux phase found in Type I1 superconductors.
IntroductionRenn and Lubensky showed theoretically [l] that when an optically active liquid crystal undergoes a transition from the smectic to the cholesteric (chiral nematic) state, the phase change can be mediated by the formation of an intermediary twist grain boundary phase. On heating, the layered structure of the smectic A phase breaks down to give the helical orientational arrangement of the molecules in the cholesteric phase. Under certain circumstances, for example where the layer ordering is weak and/or the chirality is strong, the transition can take place via an intermediary phase where the layer structure is retained, but with a helical ordering of the molecules imposed in the same plane as the layers. These two structural features are, however, incompatible with each other. This problem is resolved by the formation of a periodic array of defects which allow for the generation of a helical structure Thus, the structure of the intermediary frustrated twisted smectic A phase is one where the molecules are arranged randomly in layers with their long axes perpendicular to the layer planes. A helix is formed in the plane of the layers by the small rotation, in the same direction, of small blocks of the smectic phase. The rotation between blocks is allowed by the formation of screw dislocations. As the overall structure is helical the distribution of the defects is periodic, thereby forming a lattice (see figure 1). The screw dislocations form grain boundaries and hence this intermediary phase is called a twist grain boundary phase [l]. The physics of the incorporation of screw dislocations into the structure of the smectic A phase is similar to that for the penetration of a magnetic field into the superconducting phase of a Type I1 superconductor in order to produce an Abrikosov flux phase [2]. Thus, the twisted grain boundary phase has also been called the liquidcrystalline analogue of the Abrikosov flux phase [3].
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