Abstract

The small spotted catshark, Scyliorhinus canicula is becoming a model species for the investigation of the olfactory system and is an important morphological link in early vertebrate phylogeny.

Catsharks are known to sexually segregate and previous observations of the pre-copulatory behaviour of Scyliorhinus canicula have suggested that they use sex pheromones as olfactory signals. They also exhibit some existing sexual dimorphisms to head and tooth morphology.

This study examined the olfactory system of male and female catsharks and assessed whether any sexual dimorphisms existed as well as examined whether any left-right asymmetries existed to the paired structures within each gender.

The olfactory organs of males were significantly heavier than those of females. Males had significantly larger olfactory lamella in both length depth and surface area than females. Males also had longer secondary folds to their lamella than females. Females had significantly larger total brains than males but there was no significant difference in weight.

The total abundance of crypt cells was higher in male olfactory organs than females although there is some controversy in the existing literature over their possible function.

Females showed no differences between their left-right asymmetries. The olfactory nare openings, lamella lengths, depths and surface area were all larger on the right side of males than the left. This could suggest possible klinotaxy in the olfactory organs of males.

Of all the features recorded in this study both sexual and asymmetric dimorphisms were limited to those features related to olfaction. The possible reasons for these dimorphisms are discussed in this study but ultimately more information is needed on the use of odorants for reproduction in elasmobranchs.

Additional Notes

Supervisor: Dr Colin Waring

Course: Master of Philosophy - MPhil

Date Deposited: 2017-05-08

URI/permalink: https://library.port.ac.uk/dissert/dis12867.html