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Effect of heavy metal toxicity on calanoid copepods: experimental approach
|Authors: ||Esther Uzoma Kadiene|
|Contributors: ||NTOU:Institute of Marine Biology|
Cadmium, Toxicity, Calanoid copepod, Sex;Life history traits;Bio-accumulation;Oral intake of water;Transcriptome;Multigeneration
|Issue Date: ||2020-07-03T08:34:08Z
|Abstract: ||在日漸嚴重的環境污染之下，越來越多的研究開始關注橈足類生物生態的未來。本研究將探討影響哲水蚤橈足類金屬毒性的生物因子。 首先，探究鎘金屬（cadmium）毒性對不同性別和生殖狀態的兩種橈足類哲水蚤的影響。這兩種哲水蚤橈足類分別為生長於溫帶地區（法國塞納河口）的Eurytemora affinis（Poppe 1880），以及亞熱帶地區（台灣淡水河口）的安氏偽鏢水蚤（Pseudodiaptomus annandalei, Sewell 1919）。研究結果顯示，兩物種對鎘金屬毒性，各有不同的敏感度，且皆明顯和該個體的性別和生殖狀態相關。此外，本研究更進一步使用P. annandalei作為範本物種，來探究鎘金屬毒性對橈足類生物生活史特徵的影響。結果顯示，鎘金屬毒性也和橈足類的發育階段相關，並對其生長、生殖和壽命有負面影響。 為了瞭解對鎘金屬毒性敏感度的性別差異，本研究進行了有關生物累積的實驗。在自然環境中，橈足類可能直接經由水或間接因食物攝取，而造成體內金屬含量累積。先前的實驗檢驗了兩種途徑的金屬攝入，初步得出橈足類經食物攝取（微藻類）的金屬攝入速率。在不同鹽分濃度和溫度條件下，將路氏巴夫藻（Diacronema lutheri）和鎘金屬接觸，以探究微藻類累積鎘金屬的情況。結果顯示，高溫低鹽的環境會影響藻類的鎘金屬攝入。接著藉由水和食物兩種路徑，使P. annandalei接觸鎘金屬，根據前述實驗結果，可以得知P. annandalei從水直接攝入的鎘金屬含量，明顯高於藉由食物攝入的量。 關於橈足類由水攝入的鎘金屬量高於經食物攝入的量，學者提出了相關假設，認為是因為橈足類由口腔攝入水分的緣故，才使得水成為比食物攝取更重要的金屬生物累積路徑。該假設的驗證方式，為將橈足類暴露於染色的介質中，置於顯微鏡下觀察，可以看到染色的介質經由口腔進入臟器中。該生物累積實驗，證實了橈足類經由口腔攝入水分的論點。 將P. annandalei橈足類暴露於鎘金屬中，進行轉錄組學檢驗和其性別特異差異表達的分子研究，結果顯示該物種面對鎘金屬毒素時，有明顯的性別差異。該研究並探討雌性個體相較雄性個體，對鎘金屬毒素敏感度較低的原因。此外，多世代連續暴露於鎘金屬中，可能使P. annandalei發展出適應性，尤其在雌性個體中的可能性更高。儘管橈足類可以發展出適應有毒化學物質的機制，水中不斷升高的金屬濃度，再加上世代間由母體轉移的金屬含量，都增加了橈足類體內金屬含量的濃度。長期暴露於金屬毒素中，會降低物種的適應度，並危及橈足類的族群結構。 本研究顯示，範本物種的死亡率、生活史特徵、分子反應，可以作為環境風險評估的重要生物指標。|
As a result of growing concern in the face of increasing environmental pollutants, several studies were carried out on copepod ecology. This thesis focused on biotic factors that affect metal toxicity of calanoid copepods. Firstly, cadmium (Cd) toxicity between two copepods in the order; Calanoida; Eurytemora affinis (Poppe 1880) from a temperate region (Seine Estuary, France) and Pseudodiaptomus annandalei (Sewell 1919) from a subtropical region (Danshuei Estuary, Taiwan), were determined based on their sex and reproductive states. Results from this investigation revealed that both copepods have different levels of sensitivity to cadmium toxicity and also, their sensitivity to cadmium was significantly dependent on their sex and reproductive states. In addition, an investigation of cadmium toxicity on copepod life history traits was made using P. annandalei as a model species. Cd showed negative effects on growth, reproduction and lifespan of this copepod species. The results revealed further that Cd toxicity was also dependent on the developmental stages of the copepods. To understand the reason for sex-specific sensitivity to cadmium, an investigation on the bioaccumulation of Cd was carried out. In the natural environments, copepods could bio accumulate metals either directly from the water or indirectly from consumed diets. Before, both routes of metal uptake were tested, some preliminary test was carried out on the rate at which copepod diet (microalgae) were accumulating Cd. Microalgae accumulation of Cd was tested by exposing Diacronema lutheri to Cd under different conditions (salinity and temperature). At the end, it was observed that increased temperature and low salinity influenced the uptake of Cd in the algae. P. annandalei was then exposed to Cd in water and through their diets, using information from above results. This investigation revealed that P. annandalei uptake of Cd was significantly more from water than from the diets. A hypothesis was developed based on why copepod uptake of Cd from water was higher than from dietary Cd exposure. It was assumed that metal uptake from water is a more important route in the bioaccumulation of metals than through diet route because of oral intake. This hypothesis was tested by exposing copepods to a dyed medium. By the aid of a microscope, the dyed medium was observed to have entered inside the gut of the copepod through the mouth opening. Oral intake of water by copepods was confirmed by a bioaccumulation test. A molecular study on the transcriptomic assay and sex-specific differential expression of P. annandalei exposed to Cd was carried out. The results showed that P. annandalei responded to Cd toxicity in a sex-specific manner and that females were less sensitive to Cd than male copepods. Moreover, multigenerational exposure of P. annandalei to Cd showed a possible development of adaptation, particularly in female copepods. Although, copepods could develop adaptive mechanisms to tolerate toxic chemicals, an increasing concentration of metals in the aquatic environment in addition to maternal transfers of metals over several generations could increase metal concentrations in copepods. A long term exposure could reduce their fitness, thereby compromising copepod population structure. This study showed that mortality, life history traits and molecular responses of model copepod species can provide important bio-indicators for environmental risk assessments.
|Appears in Collections:||[海洋生物研究所] 博碩士論文|
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