Chemical communication in mating shore crabs Carcinus maenas

Locating and evaluating a suitable partner for mating is one of the most important events in any sexually reproducing organism. To achieve this, an animal must be able to locate its partner over both long and short distances, and finally evoke the proper mating behaviour. This is made possible by use of conspecific signals picked up by one or several sensory systems, the most well investigated being visual, acoustic, tactile and olfactory. This thesis presents evidence that the shore crab Carcinus maenas utilize pheromones and other chemical signals for mating. Briefly, I have studied male and female responses to odours and urine from both sexes in long-range, near-range and at contact range. Males are attracted to female urine pheromones. When concentration and spatial scale are varied, the same chemicals (urine) evoke a chain of different behaviours. At close distance and high concentrations pairing-related behaviours are evoked, and search-related behaviours and display are abandoned. Conversely, low concentrations on longer distances show more search and display and no pairing behaviour. Response variability plays a significant role in modifying behaviour in this species. I have shown that much of this can be attributed to a novel primer pheromone, which increases male receptivity to the female pheromone. Female moult stage also affects male responses at contact-range, but not at near-range. Male status also affect his search, but not pairing behaviour. The female pheromone has due to the lack of long-range properties not been able to explain how males locate females over a distance. Instead, present evidence suggested that the pattern may be reversed, with females of the right moult stage locateing males over long distances. The females are able to discriminate between male and female odour and search preferentially for males. The pheromone in male urine evokes several pairing-specific behaviours in females, similar to the case of males and female pheromones. As a final step in linking pheromone communication to the lek mating system, we show that females are able to identify male status by odour, and preferentially search for the dominant male. Females previously exposed to a fight between the dominant and subordinate male also showed higher preference for the dominant, than females that were unfamiliar with the males. This dissertation shows that chemical communication during the mating period is of utmost significance for a marine species, the shore crab. Apart from this I have shown that complex behavioural chains can be evoked by the same cue, presented at different spatial context and concentration. I have also shown how important it is to know the mating system of the species to be able to identify the steps where pheromones and other chemical signals affect behaviour such as search and choice of a partner

Copper reduced mating behaviour in male shore crabs (Carcinus maenas (L.))

Many crustaceans use pheromones to find mates and induce mating behaviours. If pollutants impair the ability to detect chemosensory cues and respond to pheromone signals, they could profoundly affect mating. In a series of laboratory experiments, the effect of copper (0, 0.1 or 0.5 mg Cu(II) per litre for 5 days) on specific components of the mating behaviour of male shore crab Carcinus maenas was investigated, as well as differences in sensitivity between red and green colour morphs. The results show that copper exposure clearly altered the response of C. maenas males to a pheromone stimulus (pre-moult female urine) presented alone, together with a dummy female (a sponge injected with pre-moult female urine) or with a real female. Crabs exposed to the highest copper treatment took more than twice as long to initiate search activity after pheromone introduction and their search behaviour was less directed. When offered a dummy female, male crabs showed decreased pheromone discrimination in both copper treatments. Stroking was the only mating behaviour significantly affected, with a 90% reduction in red crabs in the highest copper treatment. Additionally, crabs of the highest copper treatment more often pinched the dummy female (non-mating behaviour). Finally, male crabs exposed to copper more often pinched pre-moult females and it took about three times longer to establish cradle-carrying. Thus, copper affects the ability of males to detect female pheromones, perform specific mating behaviours and to form pairs. (c) 2006 Elsevier B.V. All rights reserved

Primer and short-range releaser pheromone properties of premolt female urine from the shore crab Carcinus maenas

The European shore crab Carcinus maenas is considered to rely on a female pheromone when mating. Evidence, however, is scarce on how the urine pheromone in itself affects males. We investigated male primer and releaser responses to female pheromones with methods that minimized effects from females, delivering female urine either as a pump-generated plume or deposited on a polyurethane sponge. We delivered the pheromone at different concentrations in far, near, and close/contact range to get a picture of how distance affects behavioral response. Our results show that substances in premolt female urine (PMU) function as primer and potent short-range releaser pheromones. Based on the olfactometer and sponge tests, we conclude that PMU stimulus in itself is sufficient to elicit increased search and mating-specific behaviors such as posing, posing search, cradle carrying, and stroking. Pheromone concentrations do not seem to be important for attenuating search and posing as long as the level is above a certain threshold concentration. Instead, pheromone levels seem to play a role in male acceptance of females, recruiting more males to respond, and generating better responses with increasing concentration