樊曉麗，林植華，胡雄光，雷煥宗，李　香

麗水學院生態(tài)學院, 麗水　323000

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卵胎生入侵種食蚊魚的兩性異形和雌性繁殖輸出

樊曉麗，林植華*，胡雄光，雷煥宗，李香

麗水學院生態(tài)學院, 麗水323000

摘要:檢測了卵胎生入侵種食蚊魚(Gambusia affinis)繁殖期個體大小和形態(tài)特征的兩性異形以及雌性繁殖輸出。結果表明，繁殖期，雌性個體的數(shù)量顯著大于雄性個體，雌性個體的體長顯著大于雄性個體，食蚊魚屬于偏向雌性的兩性異形。以體長為協(xié)變量的One-way ANCOVA及后續(xù)的Tukey′s檢驗顯示，特定體長食蚊魚的雌性個體的頭寬、眼間距、體寬和體重均顯著大于雄性個體；頭長和尾鰭長的兩性間差異不顯著。6個形態(tài)特征變量的主成分分析(Eigenvalue ≥ 1)發(fā)現(xiàn)，前2 個主成分共解釋65.1%的變異。頭寬、眼間距、體寬和體重在第一主成分有較高的正負載系數(shù)(解釋45.4%變異)，頭長在第二主成分有較高的負負載系數(shù)(解釋19.7%變異)。食蚊魚的繁殖輸出與母體個體大小的線性回歸顯示，窩仔數(shù)和窩仔重均與母體體長、體重呈顯著的正相關；食蚊魚的繁殖輸出與母體局部特征的線性回歸顯示，窩仔數(shù)和窩仔重均與母體頭寬、眼間距和體寬呈顯著的正相關。窩仔數(shù)與后代個體的平均體長呈顯著的正相關、與后代個體的平均體重相關不顯著，后代個體大小與數(shù)量不發(fā)生權衡。食蚊魚繁殖期的性別比例、個體大小和局部形態(tài)特征的兩性異形受生育力選擇、性選擇、生態(tài)位分化、食物競爭等多種選擇壓力的作用，也有利于該物種種群擴張和快速入侵。

關鍵詞：食蚊魚；卵胎生；兩性異形；性別比例；繁殖輸出

食蚊魚(Gambusiaaffinis)是原產于北美洲大西洋沿岸低洼地和溝渠等的一種暖水性(25—30℃)營卵胎生的小型硬骨魚類，隸屬于鳉形目(Cyprinodontiformes)，食蚊魚屬(Gambusia)[19]。在繁殖期，性成熟雄性個體的臀鰭特化形成交配器，卵子在雌性體內受精并發(fā)育成仔魚產出[20- 21]，一尾雌魚能同時貯存多個雄性個體的精子發(fā)生多批次產仔，產出仔魚能夠自由游動和攝食[22- 24]。1927 年食蚊魚被引入我國[25]，目前普遍存在于在中國長江以南地區(qū)的水體中[26]，甚至出現(xiàn)在云南高原湖泊中[27]。全球范圍來看，該物種已擴散到全球溫帶和熱帶地區(qū)(除南極洲以外)[28- 29]。大量研究表明，入侵種食蚊魚通過競爭和捕食等機制對當?shù)赝林N和生物多樣性產生了嚴重影響[30- 34]。因此，食蚊魚已經(jīng)被納入由世界自然保護聯(lián)盟公布的全球100種最具威脅的外來入侵種名單[35]。

本文以食蚊魚為材料，檢測繁殖期形態(tài)特征的兩性異形，利用其卵胎生的特點實現(xiàn)雌性繁殖特征的有效收集，探討該物種兩性異形的形成原因，以及食蚊魚的全球入侵和擴散的相關機制。

1材料與方法

1.1實驗動物的采集與形態(tài)測定

2014年3月5日—10日，11：00—13:00，從浙江省麗水學院持久性池塘(28°27′N，119°53′E)的水面表層用聚乙烯加工的手撈網(wǎng)(網(wǎng)目3 mm × 3 mm)捕獲食蚊魚(N=92)，帶回兩棲爬行動物實驗室，混養(yǎng)在25℃人工氣侯室內的塑料箱(70 cm× 50 cm× 40 cm)中，箱內放置一些金魚藻(Ceratophyllumdemersum)。

用Sartorius分析天平分別稱取成魚的體重(±0.001 g, 雌魚為產前體重)，用Sony DSC-T100數(shù)碼相機記錄親魚形態(tài)，用ImageJ 1.44p軟件測定親魚的體長(從吻端到尾椎終端的距離)、頭長(由吻端到鰓蓋骨后緣的水平距離)、頭寬(眼眶后緣處頭部的水平寬度)、眼間距(左右兩側眼背緣之間的最小距離)、體寬(背鰭起始處左右兩側身體之間的距離)以及尾鰭長(尾鰭起始處到尾鰭末端的距離)(± 0.01 mm)。記錄性別，臀鰭的第3、4、5鰭條延長特化形成具有固著小勾、感覺小棘和輸精管溝的交配器(也稱生殖足)的個體為雄魚[20]，軀干兩側具有黑色胎斑的個體為雌魚[36]。

1.2雌性繁殖輸出

懷仔雌魚單獨飼養(yǎng)在透明塑料碗(直徑約150 mm)內，水深120 mm，放置一定數(shù)量金魚藻，碗口蓋1 mm網(wǎng)眼的防逃網(wǎng)罩，每天定量喂食魚飼料。仔魚一旦產出，記錄產仔數(shù)，隨機挑出10條仔魚記錄其體長、體重，同時稱取雌魚產后體重(±0.001 g)。實驗結束后，實驗動物放回原先捕獲水體。

1.3數(shù)據(jù)分析

所有數(shù)據(jù)的統(tǒng)計分析用Statistica 統(tǒng)計軟件包完成。數(shù)據(jù)在作進一步統(tǒng)計分析前檢驗其正態(tài)性(Kolmogorov-Smirnov test)和方差同質性(F-max test)。經(jīng)檢驗，部分形態(tài)學數(shù)據(jù)經(jīng)ln轉換后符合參數(shù)統(tǒng)計條件。用線性回歸、方差分析(One-way ANOVA)、協(xié)方差分析(One-way ANCOVA)、主成分分析等處理和比較相應的數(shù)據(jù)，比較矯正平均值前檢驗斜率的均一性。文中涉及的非參數(shù)統(tǒng)計為G-檢驗。描述性統(tǒng)計值用平均值 ± 標準誤(范圍)表示，顯著性水平設置為α=0.05。

圖1　食蚊魚雌雄個體體長的頻數(shù)分布圖　Fig.1　Body length frequency distributions of female and male mosquitofish, G. affinis

2結果

2.1個體大小和局部形態(tài)特征的兩性異形

共采集食蚊魚92尾，雌性62尾，均有產仔行為，雄性30尾，均有延長具勾的臀鰭，雌性個體的數(shù)量顯著大于雄性個體(G-檢驗，G=11.37，df=1，P<0.001)。記錄了其中38尾雌性個體完整的形態(tài)和繁殖特征，該數(shù)據(jù)用于形態(tài)特征的比較和分析，食蚊魚雌雄形態(tài)特征的描述性統(tǒng)計見表1。數(shù)據(jù)經(jīng)ln轉換后，符合參數(shù)統(tǒng)計的條件。One-way ANOVA顯示，雌性個體的體長顯著大于雄性個體(圖1，表1)，最小的雌性個體大于最大的雄性個體；以體長為協(xié)變量的One-way ANCOVA及后續(xù)的Tukey′s 檢驗顯示，特定體長食蚊魚的雌性個體的頭寬、眼間距、體寬和體重均顯著大于雄性個體(allP<0.001，圖2，表2)；頭長和尾鰭長的兩性間差異不顯著(表1)。6個形態(tài)特征變量的主成分分析(Eigenvalue ≥ 1)發(fā)現(xiàn)，前2 個主成分共解釋65.1%的變異(表3)。頭寬、眼間距、體寬和體重在第一主成分有較高的正負載系數(shù)(解釋45.4%變異)，頭長在第二主成分有較高的負負載系數(shù)(解釋19.7%變異)。

表1　食蚊魚形態(tài)特征的描述性統(tǒng)計值

表中數(shù)據(jù)用平均值±標準誤(范圍)表示;表中顯示One-way ANOVA(體長)或ANCOVA(其余形態(tài)變量以體長為協(xié)變量)的F值和顯著性水平(數(shù)據(jù)經(jīng)ln轉換);F：成年雌體；M：成年雄體

圖2　以體長為自變量的食蚊魚頭寬、眼間距、體寬和體重的回歸剩余值(數(shù)據(jù)經(jīng)ln轉換)Fig.2　Mean values (± SE) for regression residuals of head width, interorbital width, body width and body mass against body length of G. affinis圖中數(shù)值表示兩性間回歸剩余值的差值

形態(tài)變量Morphologicalvariables平均值Mean標準誤Standarderror最小值Minimum最大值Maximum體長Bodylength/mm35.660.71028.3347.62產仔后體重Postpartumbodymass/mg503.9833.243233.201107.20窩仔重Littermass/mg151.8210.82557.60393.20窩仔數(shù)Littersize21.211.3031047仔魚平均體長Meanlitterbodylength/mm7.010.0806.128.23仔魚平均體重Meanlitterbodymass/mg7.230.3013.9010.94

2.2雌體繁殖輸出

食蚊魚的繁殖輸出與母體個體大小的線性回歸顯示(圖3)，窩仔數(shù)與母體體長(F1, 36=28.24,P<0.0001)、體重(F1, 36=39.94,P<0.0001)呈顯著的正相關；窩仔重與親本的體長(F1, 36=56.60,P<0.0001)、體重(F1, 36=92.31,P<0.0001)呈顯著的正相關。

食蚊魚的繁殖輸出與母體局部特征的線性回歸顯示(圖4)，窩仔數(shù)與母體頭寬(F1, 36=15.32,P<0.0001)、眼間距(F1, 36=18.64,P<0.001)和體寬(F1, 36=21.80,P<0.0001)呈顯著正相關；窩仔重與母體頭寬(F1, 36=35.56,P<0.0001)、眼間距(F1, 36=28.88,P<0.001)和體寬(F1, 36=48.09,P<0.0001)呈顯著正相關。

窩仔數(shù)與后代個體的平均體長呈顯著的正相關(r2=0.11,F1, 36=4.45,P<0.042, 圖5)、與后代個體的平均體重相關不顯著(r2=0.01,F1, 36=0.39,P=0.536)。

表36個成體形態(tài)特征變量的主成分分析的負載系數(shù)

Table 3Loading of the first two axes of a principal component analysis on six adult morphological variables

形態(tài)變量Morphologicalvariables負載系數(shù)FactorloadingPC1PC2頭長Headlength-0.005-0.967頭寬Headwidth0.756-0.357眼間距Interorbitalwidth0.758-0.319體寬Bodywidth0.7970.044尾鰭長Caudalfinlength0.5880.115體重Bodymass0.7730.005解釋變異Varianceexplained45.4%19.7%

用變量與體長的回歸剩余值去除大小差異的影響，對每個主成分有主要貢獻的變量用黑體注明

圖3　食蚊魚的繁殖輸出與母體個體大小的相關性Fig.3　Correlation between female body size and reproductive output of G. affinis

圖4　食蚊魚的繁殖輸出與母體局部特征的相關性Fig.4　Correlation between local features and reproductive output of G. affinis

圖5　食蚊魚窩仔數(shù)與仔魚平均體長的相關性　Fig.5　Correlation between litter size and mean litter body length of G. affinis

3討論

繁殖期食蚊魚性別比例偏離1∶1，雌性個體顯著多于雄性個體，這與已有結果一致[20]，雄性個體一旦完成授精后就從種群中消失，這可能是完成繁殖后，給雌性個體留下更多的環(huán)境資源和空間[22]，有利于雌性個體提高后代的數(shù)量和成活率，可能是造成該物種種群擴張和快速入侵的原因之一。

魚類普遍存在的個體大小的兩性異形，主要受生育力選擇、性選擇、生態(tài)位分化、食物競爭等多種選擇壓力的作用[5, 14, 16, 37- 39]。食蚊魚的雌性個體顯著大于雄性(表1，圖1)，首先與食蚊魚的攝食和生長的性別分化有關，食蚊魚在6 日齡臀鰭開始分化時，雄魚的攝食量和生長速度開始低于雌魚，且隨著日齡的增加差異加大[40]，雄性個體在性成熟后生長便接近于停滯[25]，此階段將身體主要能量用在對雌魚的爭奪及交配行為上[25, 41- 44]。其次，食蚊魚在生長發(fā)育、性成熟和能量分配等應對策略上的性別差異在一定程度上促進了生態(tài)位的分化、減少了種內的資源競爭，使種群內的雌魚有更多機會獲得生長發(fā)育所需的食物資源，這也為其生態(tài)入侵提供了有利的條件[1, 40, 45]。再次，食蚊魚的繁殖輸出(窩仔數(shù)與窩仔重)均與雌體大小(體長和體重)呈顯著的正相關(圖3)，這一結果與已有研究[20]的實驗結果相吻合，也類似于卵胎生密點麻蜥(Eremiasmultiocellata)[46]和蝘蜓(Sphenomorphusindicus)[47]等動物的情況。據(jù)此可以推斷：(1)食蚊魚增大繁殖輸出的主要途徑是增加窩仔數(shù)及相應的窩仔重；(2)當食物可得性和雌體貯能狀況不成為限制因素時，雌體大小是繁殖輸出的主要決定因子。這也意味著雌性親魚個體越大，產下后代仔魚也越多(或質量越好)，這正如先前報道的許多其他魚類一樣[5, 48- 50]。故生育力選擇是促使食蚊魚大個體雌性形成的選擇壓力。

在本研究中，特定體長的食蚊魚雌性個體的頭寬與眼間距均顯著大于雄性個體(表1，圖2)。雌性個體擁有較寬頭部和眼間距有利于雌性個體獲取更多的食物資源來滿足繁殖期連續(xù)多次產仔的能量需求，配偶競爭中更多的受精機會[51]。母體內的胚胎發(fā)育過程中重量和體積的增加，使得腹腔空間成為增加繁殖輸出的限制因子[47]。食蚊魚雌性個體的體寬顯著大于雄性個體(表1，圖2)，因而形成較大的腹腔容量，雌性個體通過局部特征的擴大來增加腹腔容量，提高懷仔量，從而增加雌性個體的繁殖輸出，這同時也反映了生育力選擇對局部特征兩性異形的影響[7- 8]。食蚊魚繁殖輸出(窩仔數(shù)與窩仔重)也與雌體的頭寬、眼間距和體寬這3個局部形態(tài)特征呈顯著的正相關(圖4)，進一步證實了食蚊魚局部形態(tài)特征與雌性個體繁殖特征的相關性。

初產仔魚個體大小通常直接影響到它的存活、生長速度、競爭能力等一系列的適合度，故它被認為是卵胎生(或胎生)生物生活史特征的一個重要參數(shù)[52- 55]。在本研究中，食蚊魚的窩仔數(shù)與初產仔魚個體大小呈顯著正相關(圖5)，這表明雌體食蚊魚生育力的提高，并不以減少后代的個體大小為代價，即卵胎生食蚊魚的后代個體大小與數(shù)量之間不發(fā)生權衡，這也是食蚊魚種群擴張和快速入侵的一個優(yōu)勢。

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Sexual dimorphism and female reproductive outputs of the ovoviviparous and invasive mosquitofishGambusiaaffinis

FAN Xiaoli, LIN Zhihua*, HU Xiongguang, LEI Huanzong, LI Xiang

CollegeofEcology,LishuiUniversity,Lishui323000,China

Abstract：In this study, we measured the sexual dimorphism in body size and six other mophometrical variables along with the individual fecundity in females of ovoviviparous and invasive mosquitofish Gambusia affinis, collected in Lishui (Zhejiang, eastern China), during the reproductive season. The results showed that the number of adult females was more than that of the males during the breeding season, and the body length of adult females was significantly longer than that of adult males. Therefore, G. affinis is a species with highly female-biased sexual size dimorphism. One-way analysis of variance with body length as a covariate showed significantly higher (P<0.0001) head width, interorbital width, body width, and body mass for G. affinis females than males, while no significant sexual differences were identified based on the head length or caudal fin length. A principal component analysis resolved two components (with Eigenvalues ≥ 1) from six morphometrical variables, accounting for 65.1% of variation in the original data. The first component (45.4% variance explained) had high positive loading for size-free values of head width, interorbital width, body width, and body mass; and the second component (19.7% variance explained) had high negative loading for the size-free value of head length. Analysis of unary linear regression showed that the reproductive outputs (including brood size and mass) of G. affinis positively correlated with the female body length, body mass, head width, interorbital width, and body width. Brood size positively correlated with the average body length of offspring, but there was no correlation between the brood size and the average body mass. No trade-off was identified between the size and number of offspring. Sexual dimorphism in sex ratio, body size, and local characteristics of G. affinis was influenced by a variety of selection pressure parameters, including fecundity selection, sexual selection, niche differentiation, and food competition during the breeding season. Sexual dimorphism also contributed to population expansion and rapid invasion of the species. Our results have provided some basic data for further studies on the evolution mechanisms of fish sexual dimorphism.

Key Words:Gambusia affinis; ovoviviparity; sexual dimorphism; sex ratio; reproductive outputs

基金項目:國家自然科學基金項目(31270443); 浙江省大學生科技創(chuàng)新活動計劃(2013R429025)

收稿日期:2014- 12- 03; 網(wǎng)絡出版日期:2015- 08- 26

*通訊作者

Corresponding author.E-mail: zhlin1015@126.com

DOI:10.5846/stxb201412032399

樊曉麗，林植華，胡雄光，雷煥宗，李香.卵胎生入侵種食蚊魚的兩性異形和雌性繁殖輸出.生態(tài)學報,2016,36(9):2497- 2504.

Fan X L, Lin Z H, Hu X G, Lei H Z, Li X.Sexual dimorphism and female reproductive outputs of the ovoviviparous and invasive mosquitofishGambusiaaffinis.Acta Ecologica Sinica,2016,36(9):2497- 2504.