The Sex Reversal Pattern of Scarus ghobban and Scarus rivulatus (Family Scaridae, Teleost)
| Autor: | Yi-Ta Shao, 邵奕達 |
|---|---|
| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 Most male individuals of all species of the genus Scarus which were reversed from females, are called “secondary males”. However, a few individuals of “primary males” would have male’s reproductive ability, but never process sex reversal in their lifespan, and keeping female’s outlook (initial phase). Because parrotfishes have these two kinds of males existing in the same species, they belong to “diandry” protogynous hermaphroditisms. Previous studies suggested that the mechanisms that cause primary male might be due to social effect or genetic control. In our experiments, Blue barred parrotfish (Scarus ghobban) and rivulated parrotfish (Scarus rivulatus) were used to study the sex reversal model of parrotfish and the possible reasons that cause the juveniles develop to be primary males. This study including three major parts: (1) the relationship between body size and sexual types of two species. (2) the comparison of the tissue structures of the testes in both male types by histological observation. (3) the possible karyotypes difference, i.e. the genetic differences between primary and secondary male. This study shown that the body size of blue barred parrotfish (initial phase: 100-475 mm; terminal phase: 275-525 mm) were larger than rivulated parrotfish (initial phase: 126-270 mm; terminal phase: 246-350 mm), and there was a wider overlap zone between both color phases in Blue Barred parrotfish (S. ghobban: 47.2%, then S. rivulatus: 10.7%). Histological results showed that no matter primary or secondary males, they all had classical lobular testes. But, by contrast of the pure testis tissue of primary male, there were many mature or atric oocytes that remained in the testis of secondary male. Additionally, a few secondary males of the blue barred parrotfish were discovered whose process of sex reversal occurred earlier or faster than that for normal secondary males. Histological evidence further suggested that these individuals had never had a female reproductive function. Furthermore, these males which had no difference with other secondary males was found on the chromosome level. In our study, a heteromorphic chromosome was observed between primary males and secondary males of the rivulated parrotfish (Scarus rivulatus), which could prove that being a primary male is predetermined by a genetic factor. Based on the ecological interactive diversity of the two species, a preliminary hypothesis was put forth to explain those phenomena. Due to the spawning tactics used, the proportion of primary males in rivulated parrotfish populations is much higher than that in blue-barred parrotfish populations. On the other hand, the appearance of premature males was suggested to be a way of supplying sperm which was lacking in the population of the blue-barred parrotfish. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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