Salmon Lice, Lepeophtheirus salmonis, Exhibit Specific Chemotactic Responses to Semiochemicals Originating from the Salmonid, Salmo salar

Adult male salmon lice, Lepeophtheirus salmonis, displayed kinetic and rheotactic behavioral responses to seawater conditioned with the Atlantic salmon, Salmo salar. The kinetic response was initiated by a range of skin, mucus, and flesh preparations from salmon and from a nonsalmonid, the turbot Scophthalmus maximus. Kinesis was quantified by digitally recording the movement of individual lice and by measuring both speed and distance traveled. A directional response, measured in Y-tube assays, was seen in the presence of salmon-conditioned water, but not of turbot-conditioned water. Thus, there is strong evidence that chemical signals are used by salmon lice to mediate host-finding behavior. It is hypothesized that, although salmon lice are excited by the presence of fish-derived semiochemicals, there is a salmonid-specific signal that mediates their positive rheotactic response to a host.     

A critical body size for use of pheromones in mate location

Pheromones have demonstrated importance in mate location in many insect species. Because chemoreception is the most universal sense, it has been assumed that pheromones also are important in aquatic organisms, including bacteria, but few have been found. The physical limits on effective strategies for organisms to come into contact for mating were modeled with assumptions appropriate for organisms less than a millimeter in size in an open aquatic environment. One sex was assumed to be motile, while the other sex was passive or devoted energy to locomotion or to diffusible pheromone production. Assuming spherical organisms, random locomotion by the second sex at the same velocity as the first sex increases the chances of contact by a factor of 4/3 over being passive; this ratio is independent of size. For detection by contact, the effectiveness of searching increases with the third power of the radius of the organisms; for detection by pheromones, search effectiveness increases with the seventh power of the radius above a critical size. Diverting energy from motility to pheromone production is not productive for organisms smaller than the critical size, which corresponds to a radius of 1.8 times the square root of the diffusion coefficient of the pheromone times the threshold concentration for detection divided by the rate of pheromone production per unit volume of organism. Thus, pheromone production is very favorable for organisms much above the critical size, which appears to be between 0.2 and 5 mm in water. On the other hand, bacteria are probably too small to use diffusable pheromones for mate location; most protozoans and rotifers may also be too small.     

Sex recognition in the leopard gecko,Eublepharis macularius (Sauria: Gekkonidae) Possible mediation by skin-derived semiochemicals

Male leopard geckoes,Eublepharis macularius, rely on skin-derived semiochemicals to determine the sex of conspecifics. Males respond to other males with agonistic behavior while females elicit courtship behavior from males. While females were shedding, males responded to them with agonistic behavior. The same females were courted both before and after shedding. An initial survey of hexane-extracted skin lipids from male and female geckoes revealed fatty acids common to both sexes. Several steroid analogs of cholesterol were unique to males while long-chain methyl ketones were unique to females. Results are discussed in the context of skin lipids serving as pheromones in reptiles.     

Chemical mate recognition and release of male sexual behavior in polybiine wasp,Belonogaster petiolata (Degeer) (Hymenoptera: Vespidae)

The results of bioassays using freshly killed gynes ofBelonogaster petiolata (Degeer) and hexane extracts of their tagmata and abdominal glands provide evidence for the existence of chemical signals in the venom, thorax, and head of gynes that serve as mate recognition cues and releasers of copulatory behavior in conspecific males. Attraction of males to the source of the chemicals occurs over short distances (a few centimeters).