夏繼剛 陳 梅 肖 靜 付世建

(重慶師范大學(xué)進(jìn)化生理與行為學(xué)實(shí)驗(yàn)室, 重慶市動(dòng)物生物學(xué)重點(diǎn)實(shí)驗(yàn)室, 重慶 401331)

秦嶺細(xì)鱗鮭代謝及低氧耐受能力對溫度馴化的響應(yīng)

夏繼剛 陳 梅 肖 靜 付世建

(重慶師范大學(xué)進(jìn)化生理與行為學(xué)實(shí)驗(yàn)室, 重慶市動(dòng)物生物學(xué)重點(diǎn)實(shí)驗(yàn)室, 重慶 401331)

為考察秦嶺細(xì)鱗鮭(Brachymystax lenok tsinlingensis)代謝及低氧耐受能力對溫度馴化的響應(yīng), 將實(shí)驗(yàn)魚于6℃、12℃和18℃下馴化4周后, 采用密閉式呼吸代謝測定儀對其靜止代謝率(Resting metabolic rate, RMR)和臨界氧壓(Critical oxygen press, Pcrit)等參數(shù)進(jìn)行測定。結(jié)果發(fā)現(xiàn), RMR隨馴化溫度升高而升高, 在6—12℃、12—18℃溫度內(nèi), RMR的Q10值分別為2.59和2.77, 表明該物種對溫度的敏感性較高; Pcrit值隨馴化溫度升高而升高且與RMR顯著正相關(guān), 在馴化溫度范圍內(nèi)(6—18℃), Pcrit提升了76.2%。研究結(jié)果提示: 秦嶺細(xì)鱗鮭應(yīng)對低氧環(huán)境的生理可塑性較差, 在高溫下RMR增加可能是導(dǎo)致其低氧耐受能力降低的內(nèi)在機(jī)制之一。

秦嶺細(xì)鱗鮭; 溫度馴化; 靜止代謝率; 低氧耐受; 溫度系數(shù)

溫度對動(dòng)物生理功能和生態(tài)學(xué)過程的影響是動(dòng)物生理生態(tài)學(xué)領(lǐng)域的核心問題[1,2]。在全球氣候變化、局域極端氣候頻繁發(fā)生的背景下, 物種的適合度與進(jìn)化進(jìn)程受到影響, 那些生境特殊、處于臨界分布狀態(tài)的物種對溫度的響應(yīng)備受科學(xué)界關(guān)注[3—5]。

秦嶺細(xì)鱗鮭(Brachymystax lenok tsinlingensis),俗稱“梅花魚”, 是目前世界上分布最南端的幾種鮭科魚類之一[6,7], 為第四紀(jì)冰川時(shí)期自北方南移的殘留物種, 是典型的陸封型冷水性山麓魚類, 其地域分布范圍狹窄、生境特殊、主要分布于秦嶺山系海拔1200—2300 m的山澗溪流及深水潭中[8]。調(diào)查研究發(fā)現(xiàn), 秦嶺細(xì)鱗鮭對生境水溫有嚴(yán)格要求,易受全球氣候變化和人為活動(dòng)的影響, 近20年來,其種群數(shù)量減少, 且生存海拔已經(jīng)提升了200—300 m[9,10]。鑒于該物種的特殊性及其生境的易損性, 我國政府已將其作為國家Ⅱ級重點(diǎn)保護(hù)水生野生動(dòng)物, 列入《中國瀕危動(dòng)物紅皮書》, 并于2009年成立了秦嶺細(xì)鱗鮭國家級自然保護(hù)區(qū)。然而, 對秦嶺細(xì)鱗鮭的研究工作相對滯后, 相關(guān)研究也僅限于形態(tài)、發(fā)育、基因組學(xué)等方面[7,10,11]。特別地,盡管水溫是決定該物種生存與分布的關(guān)鍵因子, 其熱生理學(xué)方面的研究卻鮮見報(bào)道。

一般來說, 溫度升高會導(dǎo)致魚類的靜止代謝率(Resting metabolic rate, RMR)提高, 致使魚體對溶解氧的需求加大; 然而水體的溶氧水平卻隨著溫度的升高而降低, 導(dǎo)致魚類攝氧難度加大, 對魚類的低氧耐受(Hypoxia tolerance)能力提出了嚴(yán)峻挑戰(zhàn)[12—14]。那么, 溫度變化將對魚類的低氧耐受能力造成何種影響呢?對此, 目前科學(xué)界尚無普適性的結(jié)論[15,16]。本文探究了秦嶺細(xì)鱗鮭幼魚代謝及低氧耐受能力對溫度馴化的響應(yīng), 旨在為該物種的保護(hù)生理學(xué)研究提供理論依據(jù)。

1 材料與方法

1.1 實(shí)驗(yàn)動(dòng)物

經(jīng)批準(zhǔn), 實(shí)驗(yàn)用秦嶺細(xì)鱗鮭幼魚采自太白湑水河珍稀水生生物國家級自然保護(hù)區(qū)(33°744′N, 107° 460′E), 被帶回實(shí)驗(yàn)室后, 于360 L自凈化循環(huán)控溫系統(tǒng)馴養(yǎng)適應(yīng)3周。馴養(yǎng)條件如下: 實(shí)驗(yàn)用水為充分曝氣脫氯并經(jīng)過活性炭過濾的自來水, 水溫(13.5±0.5)℃ (與采樣點(diǎn)的溫度接近), 溶解氧＞9 mg/L, 氨氮濃度＜0.01 mg/L; 每天早晨投喂黃粉蟲(Tenebrio molitor)幼蟲至飽足。

1.2 代謝水平及耐低氧能力測定

在溫度馴化結(jié)束后, 將實(shí)驗(yàn)魚禁食48h, 采用密閉式呼吸代謝測定儀[17]對其代謝水平及耐低氧能力進(jìn)行測定?？紤]到不同溫度馴化下實(shí)驗(yàn)魚代謝水平的差異, 為了能在相近的時(shí)間內(nèi)完成測定(避免暴露時(shí)間不同對實(shí)驗(yàn)魚可能帶來的影響), 根據(jù)預(yù)實(shí)驗(yàn)的研究結(jié)果, 本實(shí)驗(yàn)對各溫度馴化組(6℃、12℃和18℃)的測定分別采用體積為360、600和900 mL的呼吸室。呼吸室外以黑色遮光材料貼附,避免外界干擾。實(shí)驗(yàn)時(shí), 將實(shí)驗(yàn)魚輕移至呼吸室中,并使其在呼吸室中適應(yīng)12h以消除轉(zhuǎn)移脅迫, 用紗網(wǎng)封閉端口, 防止實(shí)驗(yàn)魚游出但同時(shí)又能實(shí)現(xiàn)呼吸室內(nèi)外水體交換; 測定時(shí), 將呼吸室端口加蓋密封并使用溶氧儀(HQ30, Hach Company, Loveland, CO, USA)連續(xù)監(jiān)測呼吸室內(nèi)溶氧水平的變化, 每2min記錄一次溶氧值, 直至水體溶氧值不再下降為止。適應(yīng)期間和測定過程中, 呼吸室內(nèi)的溫度均與測試魚前期的馴化溫度相同。各溫度馴化處理組的測試樣本量為n=8。

MO2實(shí)驗(yàn)魚呼吸耗氧率(Oxygen consumption rate, )的計(jì)算公式如下:

MO2=(DOkˉDOk+1)V/(t×m0.75)

式中, DOk和DOk+1分別為測定時(shí)間點(diǎn)k及k+1時(shí)刻呼吸室內(nèi)的溶氧水平(mg/L); V (L)為呼吸室體積與實(shí)驗(yàn)魚體積的差值; t (h)為時(shí)間點(diǎn)k與k+1的時(shí)間間隔; m (kg)為實(shí)驗(yàn)魚的體重。為消除體重對代謝率測定的影響, 將實(shí)驗(yàn)魚體重標(biāo)準(zhǔn)化為1 kg, 0.75為體重校正指數(shù)[18,19]。

臨界氧壓(Critical oxygen press, Pcrit)為魚類能夠維持基本生理功能的最低環(huán)境氧壓, 該指標(biāo)通常被用來評價(jià)魚類的低氧耐受能力。根據(jù)呼吸室內(nèi)水體DO與實(shí)驗(yàn)魚的關(guān)系, 采用“雙線法(Twosegmented straight lines)”求出[mg O2/(kg·h)]變化的Pcrit(mg/L)[20]。將Pcrit值出現(xiàn)以前, 所測得MO2的平均值作為實(shí)驗(yàn)魚的RMR。

1.3 數(shù)據(jù)處理

應(yīng)用軟件SPSS for Windows 16.0 (SPSS Inc., USA)對數(shù)據(jù)進(jìn)行統(tǒng)計(jì)分析。首先對實(shí)驗(yàn)數(shù)據(jù)進(jìn)行正態(tài)性和方差齊性檢驗(yàn)。采用單因素方差分析(ANOVA)和Tukey's HSD法檢驗(yàn)差異顯著性, 用“雙線法”分析求出Pcrit, 用線性回歸分析檢測Pcrit與RMR的關(guān)系。各組數(shù)據(jù)均以平均值±標(biāo)準(zhǔn)誤表示,顯著性水平設(shè)在P＜0.05。

4)為了減少對一般敏感負(fù)荷和敏感負(fù)荷的影響，希望將短時(shí)停電控制為瞬間中斷的停電事件，所以重合閘時(shí)間不應(yīng)超過3 s，建議整定為2.5 s較為合適。

2 結(jié)果

2.1 對馴化溫度和環(huán)境溶氧的響應(yīng)

2

在6℃、12℃和18℃馴化下秦嶺細(xì)鱗鮭幼魚

對環(huán)境溶氧的響應(yīng)模式見圖 1。從圖中可以看出秦嶺細(xì)鱗鮭幼魚為“氧調(diào)節(jié)型”魚類, 其代謝水平在一定的溶氧范圍內(nèi)維持相對穩(wěn)定的水平, 直到環(huán)境溶氧濃度下降到某一臨界值(圖中雙線的交叉點(diǎn))時(shí), 代謝水平才隨著環(huán)境溶氧的下降而下降。

圖 1 不同溫度馴化下秦嶺細(xì)鱗鮭幼魚代謝水平對環(huán)境溶氧的響應(yīng)Fig. 1 The oxygen consumption rateof juvenile Brachymystax lenok tsinlingensis under different acclimation temperatures and dissolved oxygen levels

溫度馴化對實(shí)驗(yàn)魚RMR影響顯著(F=43.2, P＜0.001)。RMR隨馴化溫度的增加而升高(圖 2)。與6℃馴化組相比, 18℃馴化導(dǎo)致實(shí)驗(yàn)魚的RMR提升了226.6%。

圖 2 溫度馴化對秦嶺細(xì)鱗鮭幼魚靜止代謝率(RMR)的影響Fig. 2 Effects of temperature acclimation on the resting metabolic rate (RMR) in juvenile Brachymystax lenok tsinlingensis上標(biāo)字母不同表示數(shù)值間差異顯著(P＜0.05); 數(shù)值以平均值±標(biāo)準(zhǔn)誤表示(n=8); 下同Values with different superscript letters denote statistically significant differences (P＜0.05) among groups; Values are presented as mean±SEM (n=8); the same applies below

2.2 Pcrit對馴化溫度的響應(yīng)及其與RMR的關(guān)系

溫度馴化對實(shí)驗(yàn)魚Pcrit影響顯著(F=10.0, P= 0.001)。Pcrit隨馴化溫度的增加而升高(圖 3)。與6℃馴化組相比, 18℃馴化導(dǎo)致實(shí)驗(yàn)魚的Pcrit提升了76.2%。線性回歸分析檢測結(jié)果表明, 在各馴化溫度下, Pcrit與RMR均顯著正相關(guān)(P＜0.05) (圖 4)。

圖 3 溫度馴化對秦嶺細(xì)鱗鮭幼魚臨界氧壓(Pcrit)的影響Fig. 3 Effects of temperature acclimation on the critical oxygen press (Pcrit) in juvenile Brachymystax lenok tsinlingensis

圖 4 秦嶺細(xì)鱗鮭幼魚臨界氧壓(Pcrit)與靜止代謝率(RMR)的關(guān)系Fig. 4 The relationships between critical oxygen press (Pcrit) and resting metabolic rate (RMR) in juvenile Brachymystax lenok tsinlingensis

2.3 溫度系數(shù)Q10

馴化溫度從6℃增加到12℃, RMR和Pcrit的Q10值分別為2.59和1.68; 馴化溫度從12℃增加到18℃, RMR和Pcrit的Q10值分別為2.77和1.53(表 1)。

表 1 秦嶺細(xì)鱗鮭幼魚臨界氧壓(Pcrit)與靜止代謝率(RMR)的Q10值Tab. 1 The Q10of critical oxygen press (Pcrit) and resting metabolic rate (RMR) in juvenile Brachymystax lenok tsinlingensis

3 討論

全球升溫給鮭科魚類的生存帶來了巨大挑戰(zhàn)[12,21,22]。秦嶺細(xì)鱗鮭作為世界上分布最南端的鮭科魚類之一, 故而可能更易受到溫度變化的影響。本研究結(jié)果表明, 溫度馴化對秦嶺細(xì)鱗鮭幼魚代謝水平及其低氧耐受能力均影響顯著。

溫度通過影響魚體內(nèi)多種代謝酶的活性進(jìn)而影響其代謝水平[23]。RMR是魚體在空腹、靜止?fàn)顟B(tài)下的代謝水平, 反映了機(jī)體運(yùn)行基本生理功能的維持能量消耗。魚類RMR隨溫度升高而升高的現(xiàn)象已在很多研究中被證實(shí)[22,24]; 然而, 由于各個(gè)物種溫度敏感性的不同, 其RMR對溫度響應(yīng)的程度往往存在差異性。例如, 鯽(Carassius carassius)、鳊(Parabramis pekinensis)等廣溫性鯉科魚類RMR的Q10值往往較小(一般小于2)[16,25], 而冷水性鮭科魚類RMR的Q10值往往較大(一般大于2)[22,24]。本研究發(fā)現(xiàn), 在6—12℃、12—18℃溫度范圍內(nèi), 秦嶺細(xì)鱗鮭幼魚RMR的Q10值分別為2.59和2.77(表 1), 表明該物種對溫度的敏感性較高, 研究結(jié)果分別與Eliason等[24]對紅大馬哈魚(Oncorhynchus nerka)、Remen等[26]對大西洋鮭(Salmo salar)以及Kelly等[22]對湖紅點(diǎn)鮭(Salvelinus namaycush)的研究結(jié)果相近。

Pcrit值反映了魚類在環(huán)境溶氧水平下降時(shí)獲取氧氣維持其基本生理功能的能力, Pcrit值越低的魚類低氧耐受能力越強(qiáng)[27]。那么, 魚類低氧耐受能力對溫度的響應(yīng)模式如何呢?研究發(fā)現(xiàn), 虹鱒(Salmogairdneri)的Pcrit值隨溫度升高而升高[15], 鯽的Pcrit值不受溫度影響[16], 鳊的Pcrit值隨溫度升高而降低[25]。事實(shí)上, 由于不同種類應(yīng)對低氧環(huán)境策略及其可塑性的不同[28], 魚類低氧耐受能力對溫度的響應(yīng)模式往往呈現(xiàn)出差異性。一般認(rèn)為, 由于溫度增加會引起魚體代謝水平升高, 導(dǎo)致機(jī)體的需氧量增加, 進(jìn)而導(dǎo)致機(jī)體的低氧耐受能力降低[14]; 然而, 在一定程度的升溫范圍內(nèi), 某些魚類也可能通過一系列的生理生化調(diào)節(jié)途徑來改善生理機(jī)能(例如, 血液循環(huán)加快、血紅蛋白氧親和力提高、代謝酶活性改變、鰓呼吸面積增大、心跳和呼吸頻率增加等),提高機(jī)體的攝氧能力[27,29], 故而使機(jī)體有可能維持甚至增加其低氧耐受能力。本研究發(fā)現(xiàn), 在高溫馴化下秦嶺細(xì)鱗鮭幼魚的低氧耐受能力顯著降低(Pcrit值顯著升高), 在馴化溫度范圍內(nèi)(6—18℃), 實(shí)驗(yàn)魚的Pcrit提升了76.2%; 此外, 通過對RMR和Pcrit的回歸分析, 發(fā)現(xiàn)各個(gè)溫度馴化處理下的實(shí)驗(yàn)魚Pcrit與RMR均顯著正相關(guān)(圖 4)?；谝陨戏治? 我們推測: 秦嶺細(xì)鱗鮭幼魚應(yīng)對低氧環(huán)境的生理可塑性較差, 高溫下RMR增加是導(dǎo)致該物種低氧耐受能力降低的內(nèi)在機(jī)制之一。

致謝:

感謝陜西師范大學(xué)生命科學(xué)學(xué)院梁剛副教授在野外采樣過程中給予的大力支持和幫助!

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THE METABOLISM AND HYPOXIA TOLERANCE OF BRACHYMYSTAX LENOK TSINLINGENSIS IN RELATION TO TEMPERATURE ACCLIMATION

XIA Ji-Gang, CHEN Mei, XIAO Jing and FU Shi-Jian
(Laboratory of Evolutionary Physiology and Behavior, Chongqing Key Laboratory of Animal Biology, Chongqing Normal University, Chongqing 401331, China)

Brachymystax lenok tsinlingensis, a second-class state-protected wild animal in the China Red Data Book of Endangered Animals, is generally regarded as one of the southernmost-distributed Salmonidae fish. Although temperature is critical for the survival and distribution of this species, information on its thermal physiology is extremely limited. In order to investigate the metabolism and hypoxia tolerance of B. lenok tsinlingensis in relation to temperature acclimation, fish were acclimated to the experimental temperature (6℃, 12℃, and 18℃) for 4 weeks, and sealed respirometers were used to determine the physiological parameters [e.g., resting metabolic rate (RMR) and critical oxygen press (Pcrit)]. Our results showed that the RMR increased with an increase in the acclimation temperature. The Q10of RMR at 6—12℃ and 12—18℃ were 2.59 and 2.77, respectively, suggesting that B. lenok tsinlingensis was of high sensitivity to temperature changes. The Pcritincreased with an increase in the acclimation temperature, and the values of Pcritincreased by 76.2% over the acclimation temperature range (6—18℃). Furthermore, significantly positive correlations were found between the Pcritand the RMR. Our findings indicate that B. lenok tsinlingensis evolves poor physiological plasticity in response to hypoxic environment, and that increasing RMR at high temperatures may have contributed to the decreased hypoxia tolerance in B. lenok tsinlingensis.

Brachymystax lenok tsinlingensis; Temperature acclimation; Resting metabolic rate (RMR); Hypoxia tolerance; Temperature coefficient (Q10)

Q175

A

1000-3207(2017)01-0201-05

10.7541/2017.25

2016-01-12;

2016-06-17

國家自然科學(xué)基金(31300340); 重慶師范大學(xué)青年拔尖人才培育計(jì)劃(14CSBJ08)資助 [Supported by the National Natural Science Foundation of China (31300340); Youth Top-notch Talent Cultivation Program of Chongqing Normal University (14CSB J08)]

夏繼剛(1980—), 男, 河南固始人; 博士, 副教授, 碩士生導(dǎo)師; 主要從事魚類環(huán)境生理與保護(hù)生態(tài)學(xué)研究。E-mail: jigang xia@163.com

付世建, E-mail: shijianfu9@hotmail.com