The use of the major chelae by reproductive male crayfish (Orconectes rusticus) for discrimination of female odours

Abstract

The major chelae have been found to be important structures used for breeding and reproduction in crustaceans; however their role in the detection of conspecific sex odours is unknown. We implemented a behavioural bioassay to test whether male reproductive (form I) and nonreproductive (form II) crayfish (Orconectes rusticus) use their major chelae to detect reproductive female odours. We videotaped and analysed the behavioural reactions of form I and form II males to four different odour treatments: reproductive female-conditioned water, male-conditioned water, filtered fish homogenate (food odour; positive control), and water (negative control) delivered from an air stone (N = 20 per treatment). In addition, all males were under two sensory conditions: intact or blocked chelae. Chelae were chemosensory-blocked by coating their dorsal surface with super glue. Normalized odour source handling time was measured, along with time spent handling the odour source between differing groups of sensory appendages: major chelae/first walking legs and maxillipeds/first walking legs. Our results indicate that both form I and II, intact and blocked, male crayfish significantly handled the odour source after a food stimulus was introduced. These results indicate the efficacy of the behavioural assay and sensory-blocks. Only intact form I males handled the odour source significantly when a reproductive female odour was delivered. Sensory-blocking of the chelae of form I males eliminated this difference. Intact and blocked form II males showed no differences when presented with reproductive female odours. Intact form I male crayfish spent more time handling the reproductive female-conditioned water source with their major chelae/first walking legs than those crayfish exposed to food odours. These results strongly suggest that the major chelae contain necessary chemosensory structures needed for female odour source recognition.