摘要

鸚哥魚屬(Scarus)的所有魚種，大部分的雄性個體都是經歷性轉變所形成的次生雄魚；然而也有，少部分的個體並不會經歷此種過程，甚至還保有性轉換前的雌性外表，都具有雄性的生殖能力，這類的雄魚被稱之為〝原生雄魚〞(primary male)；因此，鸚哥魚類被稱為具雙雄性(diandry)的雌性先熟物種(protogynous)。研究指出形成原生雄魚的原因可能是社會行為或遺傳因素使然。本研究以台灣海域常見的藍點鸚哥魚(Scarus ghobban)及雜紋鸚哥魚(Scarus rivulatus)為對象，探討鸚哥魚的性轉換模式及形成原生性雄魚之原因；研究分三部分進行：(1) 紀錄體長大小與性別的關係。(2) 以組織學的觀察比較原生與次生雄魚之間精巢組織的異同。(3) 比較由稚魚直接分化而來的原生雄魚與經歷性轉換的次生雄魚之染色體核型的差別。本研究的採樣中藍點鸚哥魚的體型(初期型:100-475公厘；終期型:275-525公厘)普遍大於雜紋鸚哥魚 (初期型:126-270公厘；終期型:246-350公厘)，且形態之間在體型上具有較高的重疊率(S. ghobban:47.2%；S. rivulatus:10.7%)。 組織學的觀察發現不論原生或次生雄魚都具有典型壺腹狀(lobuar)的精巢。 但是，相對於原生雄魚純粹的精巢組織；次生性雄魚的精巢中殘存著許多成熟或退化的卵粒。 此外，在藍點鸚哥魚組織學的結果中發現有些次生雄魚所經歷的性轉變發生的比其他正常的次生性雄魚快，亦不曾具有雌性生殖的能力。 這類的雄魚與一般次生雄魚之間並不存在染色體的差異。 本研究還發現雜紋鸚哥魚之原生雄魚與次生雄魚(secondary male)之間有異型的染色體(heteromorphic chromosome)，此可以證明原生性雄魚是具有遺傳性的。 此外，本研究提出了一個初步的理論以解釋所觀察到的現象。 其中，原生雄魚的比例之所以會在雜紋鸚哥魚的族群中較高，推測是與雜紋鸚哥魚的產卵模式(群聚生殖)有關。 另一方面，藍點鸚哥魚中早熟雄魚的出現，可能是為了補充族群中，隨著終期型個體(terminal phase)的減少而缺乏的精子。

Abstract

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.

目錄

授權書………………………………………………………………………………….i
論文口試委員審定書…………………………………………………………………ii
謝辭…………………………………………………………………………………...iii
中文摘要……………………………………………………………………………...iv
英文摘要………………………………………………………………………………v
目錄………………………………………………………………………………......vii
1. 前言………………………………………………………………………………...1
2. 材料與方法………………………………………………………………………...6
2.1實驗物種…………………………………………………………………….6
2.2生殖腺組織觀察…………………………………………………………….6
2.3染色體觀察………………………………………………………………….7
3. 結果……………………………………………………………………………….10
3.1採樣狀況…………………………………………………………………...10
3.2雌性生殖能力與成熟……………………………………………………...10
3.3生殖腺組織觀察……………………………………………………………11
3.4細胞遺傳學實驗…………………………………………………………...13
4. 討論……………………………………………………………………………….16
4.1非同步成熟………………………………………………………………...16
4.2性轉換……………………………………………………………………...17
4.3原生雄魚與早熟雄魚……………………………………………………...19
4.4染色體差異………………………………………………………………...20
4.5〝偽雌〞雄魚………………………………………………………………20
4.6早熟雄魚出現的可能意義………………………………………………...22
4.7原生雄魚和次生雄魚之染色體差異……………………………...………23
4.8性別轉換和體型與性別組成狀態之關係………………………………...24
5. 結論……………………………………………………………………………….25
6. 參考文獻………………………………………………………………………….26
7. 圖表……………………………………………………………………………….34
8. 附錄……………………………………………………………………………….56

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