Effects of salinity on life history traits of amphibians

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Presentation transcript:

Effects of salinity on life history traits of amphibians Reporter: Wan-Tso Hsu Advisor: Dr. Yeong-Choy Kam 各位老師,各位同學午安。 我今天要為各位報告的是「鹽度對兩棲類生活史特徵的影響」 我是報告者徐菀佐 我的指導老師是關永才教授

Contents Amphibian life history traits Effect of salinity The adaptation to salinity 我的演講將分成以下三部分進行: 第一部分要跟大家介紹兩棲類有趣的生活史特徵 第二部分跟大家介紹鹽度會對兩棲類的生活史特徵產生哪些影響 第三部分將為大家介紹兩棲類對鹽度的適應

Contents Amphibian life history traits Effect of salinity The adaptation to salinity 首先是兩棲類的生活史特徵

Amphibians have a complex life history 兩棲類是一種生活史比較複雜的生物, 從卵,到幼體,到變態為成體,會經過多個不同的生活史時期, 而生活環境也會隨著齡期而從轉換, 由水中生活而到陸上生活

Traits at metamorphosis are very important to future fitness Postmetamorphic life stage could be affected by an associated trait from premetamorphic life stage experiencing a different habitats. “The time of larval period and weight at metamorphosis can be predict adult amphibian’s survival and success of mating.” (Deban & Marks, 2002. Relyea & Hoverman, 2003) 其中最重要的生活史階段便是變態的過程, 因為他們在同一個生命週期內可能處在不同的環境裡, 變態後特徵的表現往往會受到變態前特徵的影響。 因為成體的存活率及生殖成功率,可以由蝌蚪期的長短以及變態時的體型大小,來加以預測 所以由水中到陸上的變態的過程是相當重要的生活史特徵 (Smith & Gill, 1978)

Adults can escape the extreme environment, but larvae can not. 再加上變態後的成體有較強大的行動力可以逃離激烈變化或有害的環境, 但變態前的幼體卻不能, 因此從蝌蚪到小蛙的這一段變態的過程, 是兩棲類生活史中最特別的地方。 http://www.tooter4kids.com/Frogs/life_cycle_of_frogs.htm

Environmental factors influencing life history traits Food Temperature pH Predators Density 而在這個生活史過程中,會受到許多不同環境壓力的影響: 例如環境食物量充不充足, 環境溫度是否過高或過低, 環境PH值變動會否過於劇烈, 當環境中有捕食者時, 或是當群集的密度太高時,都會對他們的生活史特徵產生影響。 (Newman, 1992)

Environmental factors influencing life history traits Salinity 而鹽度也是一個水中環境最常遇到的問題, 有時是因為降雨量減少造成的水池乾涸,水位的降低會導致水中離子濃度提高, 或是臨海地區的海水漲潮,都可能增加環境中的鹽度。 (Gomez-Mestre & Tejedo, 2005)

In a high salinity environment Salt : Na, Cl, K, Ca … 這時在池中的幼體由於表皮具有高度的通透性, 若環境鹽度較體內為高,離子非常容易藉由表皮進入體內, 當然,要維持體內滲透壓的恆定也就更不容易了。 Permeable skin makes ionic balance difficult

Contents Amphibian life history traits Effect of salinity The adaptation to salinity 因此鹽度對兩棲類水中的生活史特徵, 便可能造成許多不同方面的影響

Contents Amphibian life history traits Effect of salinity Survival Development and growth Metamorphosis The adaptation to salinity 我將就存活率、生長發育、以及變態 三部分來討論鹽度對其水中生活史特徵可能造成的影響

Contents Amphibian life history traits Effect of salinity Survival Development and growth Metamorphosis The adaptation to salinity 首先是存活率

Survival in different salinities Litoria ewingii http://www.frogsaustralia.net.au/frogs/display.cfm?frog_id=151 在Chinathamby於2006年做的實驗中,以偶而會遭遇到鹽度環境的澳洲棕背樹蛙為對象, 將其蝌蚪至於淡水以及不同鹽度下的半淡鹹水中,觀察其存活率, 發現當環境鹽度在5.6ppt前是沒有差異的,但是超過5.6ppt後,其存活率便會快速下降,甚至低於50% (Chinathamby et al 2006)

48-hr survivorship of tadpoles Rana limnocharis 而巫奇勳在最近幾年對於台灣的澤蛙實驗中, 針對不同地區族群在各個鹽度下48小時的存活率作觀察, 發現除蘭嶼族群外,綠島.國姓鄉等其他族群則無法在鹽度超過11ppt的環境中生存。 由此可見兩棲類對環境鹽度的耐受有其限度,且通常不高, 而耐受程度會隨著不同物種甚至同一物種在不同地區族群而有所不同 (Wu, Unpublished)

Contents Amphibian life history traits Effect of salinity Survival Development and growth Metamorphosis The adaptation to salinity 接下來讓我們來看看鹽度對生長發育的影響

Ionic concentration in different salinities 0ppt 6ppt 8ppt P Na(μmol) 3.86 ± 0.18 4.30 ± 0.17 5.07 ± 0.18 <0.001 Cl (μmol) 5.20 ± 0.20 5.89 ± 0.19 6.74 ± 0.20 0.04 Increase as salinity rises 在2003年,Gomez等人將西班牙當地所產黃條背蟾蜍的蝌蚪至於不同鹽度中, 發現隨著環境鹽度以及滲透壓的升高,其體內的離子濃度也會跟著上升, 其中以鈉離子和氯離子的濃度提升最為顯著 Bufo calamita http://www.herpetofauna.at/amphibien/bufo_calamita.php (Gomez-Mestre & Tejedo, 2003)

Glucose and protein concentration in different salinities 0ppt 6ppt 8ppt P Glucose (μmol) 0.55 ± 0.4 0.43 ± 0.5 0.36 ± 0.4 0.012 Proteins (mg) 0.92 ± 0.5 0.60 ± 0.4 0.6 ± 0.5 <0.01 Decrease as salinity rises Spend a lot of energy in osmoregulation Lower metabolic rate in saline water 但同樣環境鹽度升高,蝌蚪體內葡萄糖和蛋白質的濃度卻反而下降, 由於兩棲類高度滲透的體表容易使離子由體外進入體內, 因此作者推測在高鹽度的環境中, 可能蝌蚪為了調節體內離子濃度和滲透壓,需耗費大量的能量, 造成我們看到葡萄糖和蛋白質的濃度顯著下降的現象 (Gomez-Mestre & Tejedo, 2003)

Development in different salinities 0 ppt b b 6 ppt 而這樣耗費能量的結果,便可能使生長發育分配到的能量減少, 而使得生長發育的速度減緩。 這是黃條背蟾蜍蝌蚪在不同鹽度下孵化後第20天的發育情況, 恆軸是不同鹽度,縱軸是發育期數, 可以看見當環境鹽度提高時,發育的速率明顯下降 8 ppt (Gomez-Mestre & Tejedo, 2003)

Larval period in different salinities b b a 相對的,在較高鹽度的環境中, 從孵化到變態的蝌蚪期就會被顯著的拉長 0 ppt 6 ppt 8 ppt (Gomez-Mestre & Tejedo, 2003)

Tadpole growth in different salinities Rana limnocharis Weight (g) 在巫奇勳的澤蛙蝌蚪實驗中, 生長速率也會隨著環境鹽度的升高而減緩, 恆軸是時間點,縱軸是體重, 可以明顯的看見高鹽度者的生長停滯不前 Time (weeks) (Wu, Unpublished)

Tadpole development in different salinities Rana limnocharis 而在蝌蚪發育的情況也相當類似, 這個圖表顯示了澤蛙蝌蚪在7ppt以下的發育狀況正常且相似, 但當環境鹽度到達9ppt時,發育的速率就相對的減緩許多 (Wu, Unpublished)

Contents Amphibian life history traits Effect of salinity Survival Development and growth Metamorphosis The adaptation to salinity 最後來看鹽度對變態的影響

Thyroid hormone is important to metamorphosis Thyroid gland 對兩棲類變態最重要的體內調控賀爾蒙, 是甲狀腺素

Thyroid hormone T3 in different salinities T3 decrease as salinity rise at Gosner 38 and 42 在Gomez等人對黃條背蟾蜍蝌蚪的實驗中, 可以看見在變態前最關鍵的齡期,第38期時, 影響蝌蚪變態最顯著的甲狀腺荷爾蒙T3, 在蝌蚪體內的濃度會隨著鹽度的上升而下降, 而變態為足以離開水面的小蛙是為第42期,也有相同的趨勢。 (Gomez-Mestre & Tejedo, 2003)

Thyroid hormone T4 in different salinities T4 increase as salinity rise at Gosner 38 and 42 而合成T3的先驅產物T4的濃度則隨環境鹽度升高而升高, 作者推測可能是因為環境鹽度的升高,發生抑制而無法作用合成T3, 正因為環境鹽度經由滲透進入蝌蚪體內後, 往往會對體內酵素及荷爾蒙產生明顯的影響, 顯然鹽度對蝌蚪的變態過程也會有所改變 (Gomez-Mestre & Tejedo, 2003)

Metamorphic time & mass in different salinities B b c b b a b a a a a * 以澳洲的棕背樹蛙蝌蚪為例, A圖是在不同鹽度下從孵化到變態所需的時間,B圖則是變態時的體重, 可以發現當環境鹽度到達蝌蚪本身無法調控的濃度時, 變態時間便拉得很長,而變態體型則相對的較小, 但在4.2ppt的環境鹽度以內,則可以發現變態時間卻隨鹽度增加而減少 (Chinathamby et al 2006)

Metamorphic time & mass in different salinities Size 巫奇勳對澤蛙蝌蚪的實驗,則更明顯的驗證了這樣的模式, 在可以存活的極限鹽度9ppt,變態時間長且變態體型小, 7ppt以下的變態時間則隨著鹽度的減少而拉長,體型也相對的較大 (Wu, Unpublish)

When is the best time for metamorphosis ? MAX Size Low salinity MIN 我們一般預測高鹽環境下的蝌蚪變態所需要的時間不但比淡水環境下的蝌蚪來得長, 體型也相對的會比較小,而淡水環境下的蝌蚪則市長得有快又大 High salinity Time

When is the best time for metamorphosis ? MAX MIN

Metamorphic size and time are plastic to amphibian larvae MAX Low salinity Size plasticity MIN 但變態是一種相當複雜的生活史過程, 會受到諸多因素的影響,因此我們往往可以看到另一種有趣的趨式 就是當環境鹽度昇高但尚可忍受時,鹽水族群變態的時間點反而比淡水族群來得早, 因為他們可能在生長到最小的可變態體型時就趕緊變態,以求儘早脫離鹽水的環境, 而淡水族群則安心的長到最大體型才變態,以便在上到陸地後取得生存及生殖的優勢 這就是一種表型可塑性的表現, 藉由變態時間以及變態體型的可塑性來增加蝌蚪存活下來的機會, 避免在變態為小蛙前就被淘汰掉 high salinity Extreme high salinity Time

Metamorphic time & mass in different salinities Size 因此可見低鹽度的情況下,變態所需的時間反而比較長, 而變態體型也就可以長到最大再變態, (Wu, Unpublish)

Benefit and cost of plasticity Plasticity helps to avoid rapid change in environmental conditions. But small adult amphibians may not survive better or have lower reproductive succees in the future. 當然,這是必須要付出代價的,雖然表型可塑性可以幫助幼體儘早脫離劇烈的環境, 但提前變態的小體型成體,可能會在往後的存活以及繁殖中失敗。 無論如何,表型可塑性可以讓族群在短時間內應付環境變異, 但是如果族群長時間被困在這樣不利於自己生長發育的高鹽環境中(按) (Semlitsh, R.D. 1987)

When a population is restricted at a brackish habitat

Contents Amphibian life history traits Effect of salinity The adaptation to salinity 那麼有沒有可能高鹽族群, 藉由天澤直接適應高鹽度環境會更好?? 如此一來便可以避免表型可塑的代價

How to test plasticity or adaptation “Distinction between genetic variation and environmentally induced phenotypic variation is best made using reciprocal transplant experiments.” 要測試一個族群是否對環境的變異有基因上的適應, 最好的方法便是利用移地實驗以及common garden (Reznick and Travis 1996)

Transplant experiments Fresh water population Saline water population 實驗設計便是將兩地的族群分別置於相對的環境中, 藉由觀察表型特徵的改變與否, 來判斷族群本身是否已經有基因上的變化來適應不同的環境。 Fresh Saline

Three outcomes Population  genetic basis salinity survival high low Saline water population high 其實驗結果會呈現三種形式,以鹽度與存活率的圖表為例, 第一種是當族群只能適應原本生活環境的鹽度時, 顯然存活率的差異來自於族群遺傳上根本的不同, 與鹽度處理無關 low Fresh water population salinity low high

Three outcomes Environment  phenotypic plasticity survival salinity Saline water population high Fresh water population 第二種則是兩個族群的存活率對鹽度的處理都產生相同的結果, 存活率的差異與環境鹽度有關,與族群本身無關, 表示族群並未適應高鹽度的環境, 能夠存活只是因為表型可塑性造成的,而沒有基因上的適應 low salinity low high

Three outcomes Interaction  Local adaptation survival salinity high Saline water population 第三種便是其間有所交互關係,鹽度有所影響,而族群間也有所差異, 表示對於環境的不同,族群開始有基因上的分歧, 也就是有適應的開始,稱為Local adaptation Fresh water population low salinity low high (Alonso et al. 2001)

Local adaptation of an anuran amphibian to osmotically stressful environments Fresh water population Saline water population 實驗設計便是將兩地的族群分別置於相對的環境中, 藉由觀察表型特徵的改變與否, 來判斷族群本身是否已經有基因上的變化來適應不同的環境。 Fresh Saline (Gomez-Mestre & Tejedo, 2003)

Embryonic survival Fresh 6 ppt 8 ppt 他採取四個生於不同鹽度環境的族群, 其中三個是淡水族群,一個是鹽水族群, 再將他們個別放置於淡水與鹽水的環境中, 本圖表顯示實驗將四個族群的胚胎置於三個鹽度中時, 高鹽度顯著的增加淡水族群的死亡率,而對鹽水族群影響不顯著 Fresh 6 ppt 8 ppt

Embryonic survival Fresh 1 Fresh 2 Fresh 3 Saline Fresh 6 ppt 8 ppt CV=80.9 CV=132.1 Fresh 1 Fresh 2 CV=90 這個圖表延續上一張圖表的數據,恆軸是鹽度,縱軸是存活率, 每一個點代表同一族群內採自不同窩卵的胚胎, 顯示出淡水族群在鹽水環境中的存活率有極高的歧異度,有的鹽耐受度高有的鹽耐受度低, 而鹽水族群則存活率接近,作者推測可能是因為鹽水族群已經經過了天澤的淘汰, 族群可能已經開始有基因上一致性的改變 CV=37.6 Fresh 3 Saline Fresh 6 ppt 8 ppt Fresh 6 ppt 8 ppt

Larval survival Fresh Saline Saline P = 0.943 P = 0.09 P < 0.001 而對蝌蚪的實驗中,縱軸表示存活率, 恆軸表示3個淡水族群以及一個鹽水族群的移地放置, P值表示族群間的存活率差異是否達顯著, 結果顯示,鹽水環境造成4個族群的存活率都顯著的下降, 而族群間的鹽耐受存活率也有所差異, 同樣顯示了鹽水族群對鹽度環境有較好的耐受度 Fresh Saline Saline

Larval survival fresh brackish fresh brackish Fresh 2 Fresh 1 Fresh 3 本圖表同樣將同一族群內不同的窩卵個體存活率分隔出來, 恆軸是淡水與鹽水,縱軸是存活率, 淡水族群的蝌蚪在鹽水中的耐受存活率歧異度比鹽水族群來得高, 同樣顯示了鹽水族群可能經過了天澤的選擇 Fresh 3 Saline

Salinity–population interaction  Local adaptation survival Saline water population high 因此本實驗結果顯示,環境鹽度與族群的遺傳其間有所交互關係, 也就是說鹽度對存活有所影響,而族群間的遺傳也有所差異, 表示對於環境的不同,族群開始有基因上的分歧, 也就是有適應的開始,稱為Local adaptation Fresh water population low salinity low high

Summary Water salinity represents an environmental stress for many species of amphibians High salinity decrease larval survival Metamorphic time and size of amphibian larvae are plastic in different salinities 最後綜合以上所論, 高鹽對兩棲類幼體而言是一種環境壓力 高鹽環境會降低存活率

Summary Larvae at a low salinity will metamorphose at the maximum size. Larvae at a extreme high salinity will metamorphose at later at a minimum size. Larvae at a high salinity will metamorphose earliest at a smaller size 高鹽會延長蝌蚪期並延緩變態時間 高鹽會減低變態時的的體重

Summary When population migration is restricted, selection under extreme habitats lead to local adaptation. Results of transplant experiments showed population–salinity interactions, suggesting local adaptation in R. calamita. 若鹽水族群相較於淡水族群,有較高的鹽耐受度, 但是在淡水中的存活情況沒有差異的話, 表示對於鹽耐受存活率,其族群與鹽度之間有交互關係 顯示這個物種對於鹽度適應有了基因上的分歧,是為Local adaptation 最後,若是無法自高鹽度的環境中逃離, 則物種將傾向local adaptation 更甚於表型可塑性。

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Development Adult amphibians increase in their osmotic concentration urine retention accumulation of electrolytes enhanced urea synthesis (Gordon 1962; McBean and Goldstein 1970)

Orchid Island: As salinity increased, size at metamorphosis decreased Time Size In Orchid Island population The time at metamorphosis was significantly different between freshwater and 3 ppt SW treatments, But there was no significant difference among the other treatments, The size of metamorphosis was larger in the freshwater treatments, as salinity increased, the size at metamorphosis decreased. (Wu, Unpublish)

Plasticity Environmental heterogeneity tends to increase the phenotypic plasticity of traits, with phenotypes optimized to the particular conditions on each environment. (Rawson and Hilbish 1991; Sultan and Spencer 2002)

Plasticity When gene is affected by variation of environments, genotype will lead to multiple phenotypes Life history Metamorphic size and time behavior physiology (Miner et al. 2005)

High salinity tolerant species Rana cancrivora Xenopus laevis Bufo viridis http://www.froghome.idv.tw/html/class_1/rana_cancrivora.html http://www.britannica.com/eb/art/print?id=4886&articleTypeId=0 600 800 1000 http://www.hlasek.com/bufo_viridis_da1531.html

Adaptation “Different phenotypes among populations can be considered adaptive if they have a genetic basis, and they confer fitness advantage in a given environment.” (Endler 1986; Sinervo and Basolo 1996)

Wilbur and Collin’s model W > b yes W > b+c no yes dW Wdt no no > g yes Additional growth Initiate metamorphosis