<簡介>2009年在PNAS上有兩篇文章對於幼蟲是否由有爪動物門（Onychophora；天鵝絨蟲，櫛蠶）經過基因體的雜交演化而來發表了正反兩方的意見。
Williamson反對達爾文認為幼蟲與其成蟲演化自單一祖先的假說，而主張會進行變態的動物之幼蟲基礎形態來自與成體不同的支系；亦即幼蟲的出現是由 成蟲與親緣關係遙遠的動物類群透過有性生殖的結合、發生基因體的雜交轉變而來，然後融合了來自兩個支系的雙重基因體生物，則在時間上依序表現兩組基因體。 起初可能是一個外觀如幼蟲之物種的卵被他種生物的精子授精，然後孵化為幼蟲狀，之後發生變態、再表現另一親代基因體之性狀，形成新的一種生物。此生物接下 來繼續演 化，造成新的動物支系出現。所謂的“Caterpillars”係指具有胸足與腹足之幼蟲形狀的動物，例如鱗翅目、鞘翅目與長翅目的幼蟲。甲蟲、蜂和蠅等 蛆狀的幼蟲由喪失“足”這個特徵的幼蟲演化而來。Williamson認為幼蟲的器官在蛹期被拆解然後重新裝配組合，這種非直接的發育形式（變態）並非僅 是由累積隨機突變、然後受到天擇壓力選汰而產生的結果，而是經由他所提出的基因體雜交理論演化而來。Williamson認為有爪動物門之成員應該是幼蟲 與其蛆狀外觀後裔的演化來源，並提出一個分子生物學的研究計畫，希望基因體學家進行實驗以驗證他的假說。在他的假設中，應該會有2組基因會在具蛆狀幼蟲形 態的所有昆蟲中找到：(i)有爪動物門決定幼蟲狀外觀之蛋白質的編碼序列 與(ii)隨後決定成蟲蛋白質的昆蟲基因。
Williamson反對達爾文認為幼蟲與其成蟲演化自單一祖先的假說，而主張會進行變態的動物之幼蟲基礎形態來自與成體不同的支系；亦即幼蟲的出現是由 成蟲與親緣關係遙遠的動物類群透過有性生殖的結合、發生基因體的雜交轉變而來，然後融合了來自兩個支系的雙重基因體生物，則在時間上依序表現兩組基因體。 起初可能是一個外觀如幼蟲之物種的卵被他種生物的精子授精，然後孵化為幼蟲狀，之後發生變態、再表現另一親代基因體之性狀，形成新的一種生物。此生物接下 來繼續演 化，造成新的動物支系出現。所謂的“Caterpillars”係指具有胸足與腹足之幼蟲形狀的動物，例如鱗翅目、鞘翅目與長翅目的幼蟲。甲蟲、蜂和蠅等 蛆狀的幼蟲由喪失“足”這個特徵的幼蟲演化而來。Williamson認為幼蟲的器官在蛹期被拆解然後重新裝配組合，這種非直接的發育形式（變態）並非僅 是由累積隨機突變、然後受到天擇壓力選汰而產生的結果，而是經由他所提出的基因體雜交理論演化而來。Williamson認為有爪動物門之成員應該是幼蟲 與其蛆狀外觀後裔的演化來源，並提出一個分子生物學的研究計畫，希望基因體學家進行實驗以驗證他的假說。在他的假設中，應該會有2組基因會在具蛆狀幼蟲形 態的所有昆蟲中找到：(i)有爪動物門決定幼蟲狀外觀之蛋白質的編碼序列 與(ii)隨後決定成蟲蛋白質的昆蟲基因。
幾個月後，Harta 與 Grosbergb在PNAS上發表了反駁Williamson的文章，他們認為動物生活史中特殊幼蟲形態的演化與喪失在不同的生活史階段與主要動物類群 之間產生複雜的相似或差異的樣式。其中一個相似的例子就是有爪動物門（Onychophora；天鵝絨蟲，櫛蠶）與某些昆蟲的幼蟲形態。他們認為 Williamson先前在PNAS上發表的看法ー櫛蠶的祖先透過雜交的方式造成昆蟲幼蟲形態的起源，而證據可由現生種櫛蠶、具有以及不具有幼蟲形態的昆 蟲之基因型來比對ー是驚人且無根據的。Williamson已經根據他的假說提出一系列的臆測，並催促基因體學家去測試。因此，他們利用文獻中已有的資料 去證明他的預測是錯誤的，親緣關係遙遠的的動物類群間的雜交無法解釋整體的形態與生活史的演化樣式，且動物的基因與基因體資料提供推翻櫛蠶與特定昆蟲之間 雜交或幼蟲形態轉移的強烈證據。這些證據包括：（1）寄生甲殼類的根頭目藤壺之基因體很小、且不須要從甲殼類身上獲取基因體。（2）完全變態類昆蟲比不具 幼蟲形態的昆蟲所擁有的基因體更小。（3）完全變態類昆蟲的基因比不具幼蟲形態的昆蟲者還要少，且也不須要從櫛蠶身上獲得基因。（4）完全變態類昆蟲並不 具有類似經由雜交而從櫛蠶身上獲得的基因體。（5）有爪動物門的基因體比完全變態類昆蟲還大，且亦並未和昆蟲雜交。
綜合以上兩篇， Williamson提出了神話故事般非常具有創意的假設，也提供了可測試的假說，然後由Harta 與 Grosbergb進行基因體上的比對提出證據反駁，雖然看似正反雙方的意見辯論，但也不能不算是一種科學研究上的合作討論。
文獻來源（1）：DI Williamson. 2009. Caterpillars evolved from onychophorans by hybridogenesis. PNAS.
Abstract
I reject the Darwinian assumption that larvae and their adults evolved from a single common ancestor. Rather I posit that, in animals that metamorphose, the basic types of larvae originated as adults of different lineages, i.e., larvae were transferred when, through hybridization, their genomes were acquired by distantly related animals. “Caterpillars,” the name for eruciforms with thoracic and abdominal legs, are larvae of lepidopterans, hymenopterans, and mecopterans (scorpionflies). Grubs and maggots, including the larvae of beetles, bees, and flies, evolved from caterpillars by loss of legs. Caterpillar larval organs are dismantled and reconstructed in the pupal phase. Such indirect developmental patterns (metamorphoses) did not originate solely by accumulation of random mutations followed by natural selection; rather they are fully consistent with my concept of evolution by hybridogenesis. Members of the phylum Onychophora (velvet worms) are proposed as the evolutionary source of caterpillars and their grub or maggot descendants. I present a molecular biological research proposal to test my thesis. By my hypothesis 2 recognizable sets of genes are detectable in the genomes of all insects with caterpillar grub- or maggot-like larvae: (i) onychophoran genes that code for proteins determining larval morphology/physiology and (ii) sequentially expressed insect genes that code for adult proteins. The genomes of insects and other animals that, by contrast, entirely lack larvae comprise recognizable sets of genes from single animal common ancestors.
文獻來源（2）：MW Hart and RK Grosberg. 2009. Caterpillars did not evolve from onychophorans by hybridogenesis. PNAS.
Abstract
The evolution and loss of distinctive larval forms in animal life cycles have produced complex patterns of similarity and difference among life-history stages and major animal lineages. One example of this similarity is the morphological forms of Onychophora (velvet worms) and the caterpillar-like larvae of some insects. Williamson [(2009) Proc Natl Acad Sci USA 106:15786–15790] has made the astonishing and unfounded claim that the ancestors of the velvet worms directly gave rise to insect caterpillars via hybridization and that evidence of this ancient “larval transfer” could be found in comparisons among the genomes of extantextant onychophorans, insects with larvae, and insects without larvae. Williamson has made a series of predictions arising from his hypothesis and urged genomicists to test them. Here, we use data already in the literature to show these predictions to be false. Hybridogenesis between distantly related animals does not explain patterns of morphological and life-history evolution in general, and the genes and genomes of animals provide strong evidence against hybridization or larval transfer between a velvet worm and an insect in particular.
綜合以上兩篇， Williamson提出了神話故事般非常具有創意的假設，也提供了可測試的假說，然後由Harta 與 Grosbergb進行基因體上的比對提出證據反駁，雖然看似正反雙方的意見辯論，但也不能不算是一種科學研究上的合作討論。
文獻來源（1）：DI Williamson. 2009. Caterpillars evolved from onychophorans by hybridogenesis. PNAS.
Abstract
I reject the Darwinian assumption that larvae and their adults evolved from a single common ancestor. Rather I posit that, in animals that metamorphose, the basic types of larvae originated as adults of different lineages, i.e., larvae were transferred when, through hybridization, their genomes were acquired by distantly related animals. “Caterpillars,” the name for eruciforms with thoracic and abdominal legs, are larvae of lepidopterans, hymenopterans, and mecopterans (scorpionflies). Grubs and maggots, including the larvae of beetles, bees, and flies, evolved from caterpillars by loss of legs. Caterpillar larval organs are dismantled and reconstructed in the pupal phase. Such indirect developmental patterns (metamorphoses) did not originate solely by accumulation of random mutations followed by natural selection; rather they are fully consistent with my concept of evolution by hybridogenesis. Members of the phylum Onychophora (velvet worms) are proposed as the evolutionary source of caterpillars and their grub or maggot descendants. I present a molecular biological research proposal to test my thesis. By my hypothesis 2 recognizable sets of genes are detectable in the genomes of all insects with caterpillar grub- or maggot-like larvae: (i) onychophoran genes that code for proteins determining larval morphology/physiology and (ii) sequentially expressed insect genes that code for adult proteins. The genomes of insects and other animals that, by contrast, entirely lack larvae comprise recognizable sets of genes from single animal common ancestors.
文獻來源（2）：MW Hart and RK Grosberg. 2009. Caterpillars did not evolve from onychophorans by hybridogenesis. PNAS.
Abstract
The evolution and loss of distinctive larval forms in animal life cycles have produced complex patterns of similarity and difference among life-history stages and major animal lineages. One example of this similarity is the morphological forms of Onychophora (velvet worms) and the caterpillar-like larvae of some insects. Williamson [(2009) Proc Natl Acad Sci USA 106:15786–15790] has made the astonishing and unfounded claim that the ancestors of the velvet worms directly gave rise to insect caterpillars via hybridization and that evidence of this ancient “larval transfer” could be found in comparisons among the genomes of extantextant onychophorans, insects with larvae, and insects without larvae. Williamson has made a series of predictions arising from his hypothesis and urged genomicists to test them. Here, we use data already in the literature to show these predictions to be false. Hybridogenesis between distantly related animals does not explain patterns of morphological and life-history evolution in general, and the genes and genomes of animals provide strong evidence against hybridization or larval transfer between a velvet worm and an insect in particular.
沒有留言:
張貼留言