The evolution of fruit color: phylogeny, abiotic factors and the role of mutualists

?果實顏色的演化:系統(tǒng)發(fā)育、非生物因素及共生者的作用

The adaptive significance of fruit color has been investigated for over a century. While color can fulfill various functions, the most commonly tested hypothesis is that it has evolved to increase fruit visual conspicuousness and thus promote detection and consumption by seed dispersing animals. However, fruit color is a complex trait which is subjected to various constraints and selection pressures. As a result, the effect of animal selection on fruit colour are often difficult to identify, and several studies have failed to detect it. Here, we employ an integrative approach to examine what drives variation in fruit color.

水果顏色的適應性研究已有一個多世紀的歷史。雖然顏色可以完成多種功能，但最常見的假設是，它已經(jīng)進化到增加水果的視覺顯著性，從而促進傳播種子的動物的發(fā)現(xiàn)和消費。然而，水果的顏色是一個復雜的性狀，它受到各種各樣的限制和選擇壓力。因此，動物對水果顏色的選擇的影響往往很難識別，一些研究未能發(fā)現(xiàn)它。在這里，我們采用一種綜合的方法來研究是什么導致了水果顏色的變化。

We quantified the colour of ripe fruit and mature leaves of 97 tropical plant species from three study sites in Madagascar and Uganda. We used phylogenetically controlled models to estimate the roles of phylogeny, abiotic factors, and dispersal mode on fruit color variation. Our results show that, independent of phylogeny and leaf coloration, mammal dispersed fruits are greener than bird dispersed fruits, while the latter are redder than the former. In addition, fruit color does not correlate with leaf colour in the visible spectrum, but fruit reflection in the ultraviolet area of the spectrum is strongly correlated with leaf reflectance, emphasizing the role of abiotic factors in determining fruit color. These results demonstrate that fruit color is affected by both animal sensory ecology and abiotic factors and highlight the importance of an integrative approach which controls for the relevant confounding factors.

我們對馬達加斯加和烏干達三個研究地點的97種熱帶植物的成熟果實和成熟葉片的顏色進行了量化。我們使用系統(tǒng)遺傳學控制的模型來估計系統(tǒng)發(fā)育、非生物因素和分散模式對果實顏色變化的作用。結(jié)果表明，在不受系統(tǒng)發(fā)育和葉色影響的情況下，哺乳動物果實比鳥類果實更綠，鳥類果實比哺乳動物果實更紅。此外，在可見光譜中，果實顏色與葉片顏色無關(guān)，但光譜中紫外區(qū)域的果實反射與葉片反射率密切相關(guān)，強調(diào)了非生物因素在決定果實顏色中的作用。這些結(jié)果表明，水果的顏色受動物感官生態(tài)和非生物因素的影響，并強調(diào)了控制相關(guān)混雜因素的綜合方法的重要性。

Understanding the origin and adaptive significance of fruit color has been a lively source of debate for over a century. While less varied than flower color globally, fruit color diversity is nonetheless extensive, spanning and surpassing the human capacity to detect it. Fruit color diversity has been attributed to phylogenetic constraints, environmental constraints, and protection from antagonists. Yet the oldest, best documented, and most contentious hypothesis for why fruit color is so diverse centres on its role in attracting seed dispersing mutualists. The disperser hypothesis posits that the colour of fleshy fruits evolved to maximise visual detection by specific animal mutualists to facilitate seed dispersal.

了解水果顏色的起源和適應的意義是一個多世紀以來爭論的一個活躍的來源。雖然水果的顏色在全球范圍內(nèi)不如花的顏色那么多樣化，但水果的顏色多樣性是廣泛的，跨越并超過了人類對其的探測能力。果實顏色的多樣性是由于系統(tǒng)發(fā)育的限制、環(huán)境的限制以及對拮抗物的保護。然而，關(guān)于水果顏色為何如此多樣化的最古老、記載最充分、爭議最大的假說，集中在它在吸引相互分散的種子方面所起的作用上。散布者假說假設，肉質(zhì)水果的顏色進化是為了讓特定的動物互惠主義者能夠最大限度地觀察到，從而促進種子的散布。

The finding that fruit and leaf reflectance in only the UV part of the spectrum are correlated may indicate the importance of solar radiation in fruit colour, at least across certain parts of the spectrum. While solar radiation is required to maintain plant function, excess light absorption can be damaging, and even fatal, to plant tissues，

發(fā)現(xiàn)只有光譜的紫外部分的水果和葉子的反射率是相關(guān)的，這可能表明太陽輻射對水果顏色的重要性，至少在光譜的某些部分。雖然維持植物的功能需要太陽輻射，但過量的光吸收對植物組織是有害的，甚至是致命的，這可能導致使用植物色素作為光保護膜。

Absorption at certain spectra, particularly in the ultraviolet, can result in photoinhibition and photodamage – reduced photosynthetic efficiency and cell damage. Plants have mechanisms to detect and respond to variation in ambient light, and to attenuate harmful solar radiation via investment incompounds.Plant UV reflectance may also function to reduce water loss in plant parts. Experimentally, UV reflectance has been found to increase likelihood of ripening, and responsive to both solar radiation and edaphic factors in temperate, agricultural systems.

某些光譜的吸收，特別是在紫外線下的吸收，會導致光抑制和光損傷——降低光合效率和細胞損傷。植物具有探測和響應環(huán)境光變化的機制，并通過對化合物的投資來減弱有害的太陽輻射。植物的紫外反射率也可以減少植物部分的水分流失。實驗發(fā)現(xiàn)，在溫帶農(nóng)業(yè)系統(tǒng)中，紫外線反射率增加了成熟的可能性，并且對太陽輻射和土壤因子都有反應。

In conclusion, our results confirm that fruit colour is largely independent of phylogeny and that it is affected by both abiotic factors and interaction with seed-dispersing animals. They join several recent studies which demonstrated the malleability of fruits to frugivore sensory and feeding ecology. Yet they also highlight the importance of the multivariate approach which recognises that fruit color is shaped by multidirectional selection pressures, and that only by considering them in concert can the effect of each be isolated and understood.

綜上所述，我們的研究結(jié)果證實，果實顏色在很大程度上與系統(tǒng)發(fā)育無關(guān)，并且受非生物因素和與種子分散動物相互作用的影響。他們加入了最近的幾項研究，這些研究表明，水果具有可塑性，可以在感官和飼養(yǎng)生態(tài)方面產(chǎn)生果味。然而，他們也強調(diào)了多元方法的重要性，這種方法認識到水果的顏色是由多方位的選擇壓力形成的，只有把它們結(jié)合起來考慮，才能孤立和理解每種顏色的影響。