苦苣苔自發性自交提供潛在生殖保障

Autonomous selfing provides potential reproductive assurance in Conandron ramondioides (Gesneriaceae)

馬弘文(Hong-Wen Ma)

指導教授 ： 王俊能

國立臺灣大學/生命科學院/生態學與演化生物學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201703234

摘要

苦苣苔為一種多年生草本植物，棲息在中海拔森林底下陰暗潮濕的岩壁或溪邊石頭上。由觀察到自然狀況下的結實率高達78%以及套袋處理的花朵依舊能結實，顯示可能存在自發性自交(Autonomous selfing)的機制。同時也多次記錄到熊蜂(Bombus spp. )訪花，代表昆蟲傳粉可能頻繁發生。為了瞭解苦苣苔在自然情況下之生殖策略，我們比較從花苞時期即套袋處理(代表自發性自交)與自然控制組(代表昆蟲傳粉與自發性自交)花朵的結實率，能夠得知自發性自交的能力如何，由套袋處理與自然控制組所得到的種子數分別523.5與541.9個種子(兩者無顯著差異)，顯示自發性自交的結實能力和自然情況一樣好。我們也在開花第一天、第三天、第五天進行去雄套袋處理，以及不去雄套袋處理，藉此探討自發性自交發生的時間是否與異交競爭，結果為去雄處理時間越晚的花朵(代表自發性自交發生的時間越久)種子數越多，顯示自發性自交於昆蟲能傳粉的開花期間會持續發生，符合競爭自交(Competing selfing)的模式。接著比較去雄花朵(代表昆蟲傳粉; FE)與自然控制組 (FI) 花朵的結實率，並計算出生殖保障(RA= (FI - FE) / FI)，即可得知自交所提供的生殖保障程度，由去雄花朵與自然控制組花朵得到的結果分別為473與541.9個種子，並計算出生殖保障(RA)為0.13顯示自發性自交提供的生殖保障不高，代表自然狀況下生殖策略主要仍靠昆蟲傳粉為主。同時我們也進行人工自花與異花授粉，以種子數與種子萌發率當作適存度(Fitness)的指標，比較自交子代的適存度(Ws)是否明顯低於人工異交 (Wo)，並計算出苦苣苔近交衰敗的程度(δ =1- Ws/ Wo)為0.385，當δ小於0.5時代表此自發性自交產生子代的生殖代價不高。綜合結果，我認為苦苣苔演化出同時具有昆蟲傳粉與自發性自交的混合型生殖策略(Mixed breeding system)，幫助它生存在森林底下的潮濕且陰暗環境。在昆蟲充足的環境下，苦苣苔能藉由昆蟲傳粉很有效率產生的種子，如果缺乏昆蟲時，也能藉由結籽能力強的的自發性自交機制讓自花授粉，以確保生殖的成功。

關鍵字

苦苣苔 ； 自發性自交 ； 生殖保障 ； 近交衰敗 ； 混合型生殖系統

並列摘要

Conandron ramondioides is a perennial herb that survives in patches of high humidity habitat in dense shade forest. High fruit set (78%) under natural conditions and bagged flowers imply that autonomous selfing exists. We have observed that bumble bees visited flowers frequently, which indicates insect pollination in C. ramondioides. To determine the capacity of autonomous selfing, we compared the seed set from bagged (prevent insect but autonomous selfing) and intact (natural condition) flowers. The average seed number per fruit are 523 and 541.9, respectively, which suggests that C. ramondioides has well-developed capacity for autonomous selfing. To confirm whether autonomous selfing compete with insect pollination, we emasculated the bagged flowers at the first, third day, and the fifth day. The results show that autonomous selfing can continuously occur during anthesis. The seed sets of bagged flowers that emasculated at different days increased gradually, which indicates the mode of autonomous selfing is competing selfing. In order to measure reproductive assurance, we compared the seed set of emasculated flowers (only allow insect pollination; FE) and that of intact flowers (FI). The seed set was 473 and 541, respectively. Reproductive assurance was 0.13 (RA = (FI – FE) / FI), which indicates that autonomous selfing in C. ramondioides provides low level of reproductive assurance. The calculated inbreeding depression, based on the proportion of difference between artificial outcrossing and selfing in seed germination rate and seed numbers, is low (δ=0.385).
According to our pollination experiment, we conclude that C. ramondioides possesses a mixed breeding system. The well-developed capacity for competing autonomous selfing and low inbreeding depression allows C. ramondioides to survive even when pollinators are lacking.

並列關鍵字

Reproductive assurance ； Conandron ramondioides ； Autonomous selfing ； Inbreed depression ； Mixed breeding system

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