Sex-change (or sequential hermaphroditism) is a phenomenon whereby an organism functions first as one sex, and then as the other in the later stage of its life. Sex change is an adaptation that has evolved to allow certain organisms to increase fitness through resource allocation of male and female functions in a single lifespan. Since the timing of sex change in an organism is critical to its reproductive output, the size or age at sex change is expected to be plastic in response to different environmental conditions. Social and environmental conditions usually convey the cues about the relative advantages of functioning as one sex or the other. Identifying the factors that influence the timing at sex change is important to understand the evolution of sex change in the life history. In order to elucidate how to optimize fitness through sex allocation in response to different environment, I studied the timing at sex change of Coralliophila violacea in different approach, including the age of individual, the compositions of social groups and the difference between two types of coral hosts in this thesis.
Firstly, I present a method to determine the age of this snail and its age at sex change. The growth striae on the operculum were studied and compared to the age estimated by the Gompertz growth function based on growth data obtained from mark-recapture experiments. There is a significant correlation between the number of striae on the operculum and the age estimated from the Gompertz growth function, and the relationship is 1:1. These results suggest that the number of striae on the operculum can be used as an age index, with each stria representing 1 year of age. The age of sex change of this snail, according to my estimates by both stria number and aperture-length inferences, occurs between 4 and 6 years old. Growth rates of the snails are negatively correlated to size. Furthermore, individuals undergoing sex-change grew faster than males and females.
This snail, Coralliophila violacea, forms snail patches on the surface of the massive coral, Porites spp. Secondly, the social factors were analyzed for the timing of this sedentary snail. These factors include the sex ratio, number of male and females, and the size of females in the snail patches, all of which could be important information in determining the timing of sex change. In this study only the size of the largest female could be significantly correlated with the size at sex change in a snail patch.
Finally, I survey the distribution, size and reproductive characteristics of the snail, Coralliophila violacea (Lamarck), which inhabits the surface of both the branching coral Porites nigrescens and the massive corals, P. lobata and P. lutea. Based on these results I examined the host effect on (1) population structure and (2) reproductive characteristics, including the size at sex change of symbionts.
On branching hosts, most snails were solitary, whereas on massive hosts, most had formed multiple-snail patches. Significantly smaller snails as well as proportionally more females were found on branching than on massive hosts. Furthermore, the fecundity of the females on the branching hosts was significantly lower than that on the massive hosts. The size at sex change (male to female) of the snails was smaller on the branching hosts than on massive hosts. Patch composition differences can partly explain the smaller size at sex change for snails on branching hosts; however, there was also evidence that host morphology had a significant effect on the timing of sex change.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0625107-163328 |
| Date | 25 June 2007 |
| Creators | Chen, Ming-Hui |
| Contributors | Chang-Feng Dai, Keryea Soong, Chao-Lun Chen, Min-Li Tsai, Ching-Fong Chang, Jin-Hua Cheng |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0625107-163328 |
| Rights | not_available, Copyright information available at source archive |
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