Title

An Interdisciplinary Investigation of the Role of Crayfish Major Chelae in the Discrimination of Conspecific Odours: from Morphology to Behaviour

Date of Award

2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Biological Sciences

First Advisor

Paul Moore

Abstract

This dissertation examines the use of the major chelae by male crayfish ( Orconectes rusticus) for discrimination and localization of female odours and links this behaviour with sensory setae morphology and distribution. First, a behavioural bioassay was implemented to test whether male reproductive (form I) and non-reproductive (form II) crayfish use their major chelae to detect and discriminate reproductive female odours. Behavioural reactions of male crayfish, with intact or sensory blocked chelae, were recorded to four different odour treatments: female-conditioned water, male-conditioned water, fish homogenate, and water (control). Intact form I males handled the female odour source significantly more (46.4 ± 17.0 seconds) than blocked and form II males. Next, the role of sensory information from the major chelae in the localization of reproductive female odours was examined. Behavioural reactions of intact and blocked form I male crayfish were analyzed in response to three different odour treatments: female-conditioned water, male-conditioned water, and water (control) delivered from one end of a test arena. Large-scale movements and chemosensory sampling behaviours were measured. Male crayfish with intact major chelae spent more time (45.4 ± 7.7 %) closer to the odour source when the reproductive female odour was delivered compared to all other odours. Also, intact male crayfish spent more time chelae waving (61 %) in response to female odours than blocked males. Lastly, a comparative and morphological analysis of setae found on the major chelae of form I and II male crayfish was performed. To accomplish this, scanning electron microscopy, a permeability assay, anterograde labelling, and acetylated tubulin (AT) immunocytochemistry were used. Results show that form I crayfish had more sensory setae pockets and individual smooth setae on their major chelae compared to form II males. Also, smooth setae contained a terminal pore, were crystal violet permeable, and contained anterogradly labelled DiI and AT positive nerve fibers. Conversely, plumose setae lacked a terminal pore, did not label with DiI, and were crystal violet and AT negative. Overall, these results suggest that the major chelae are important sensory structures needed for the localization and discrimination of female odours and may be important for reproductive behaviours such as mate recognition.