對(duì)于北極冬天的極夜,，馴鹿可能會(huì)用一種獨(dú)特的方式來應(yīng)對(duì)：極夜期間,，它們的眼睛變得對(duì)光更加敏感。
與很多脊椎動(dòng)物和大多數(shù)哺乳動(dòng)物（特別是那些在夜間活動(dòng)的動(dòng)物）一樣,，馴鹿眼睛的視網(wǎng)膜后方有一層可以反光的含蛋白質(zhì)組織,。該結(jié)構(gòu)被稱為反光膜，使眼睛的感光神經(jīng)元有第二次機(jī)會(huì)來檢測(cè)微觀條件下稀缺的光子,。（反光膜還會(huì)產(chǎn)生“眼耀”,，使黑暗中動(dòng)物的眼睛看起來似乎在發(fā)光。）在極晝的日子里,，馴鹿有著黃色的眼耀,。但是在極夜期間，反光膜反射的光呈現(xiàn)出明顯的藍(lán)色光澤,。
研究人員稱,，這是一種在其他哺乳動(dòng)物中未注意到的季節(jié)性變化。為了研究這種不尋常的顏色變化,，研究人員將一些馴鹿眼球帶入實(shí)驗(yàn)室,，并向其施加一些重量。在壓力下,，眼球幾乎立即改變了眼耀的顏色,。研究人員稱，這符合在野外各種季節(jié)里發(fā)生的情況,。冬天,，馴鹿的瞳孔不斷擴(kuò)張，增加了流體的壓力,，而這反過來減少了反光膜中膠原纖維的間距,，從而增加了眼中光的散射，將反射光改變成在黑暗中有優(yōu)勢(shì)的更短波長的光,。這些變化使馴鹿眼睛的感光性提高了100倍到1000倍,。
研究人員將報(bào)告發(fā)表在10月29日的英國《皇家學(xué)會(huì)學(xué)報(bào)B》上。他們認(rèn)為,，雖然這種構(gòu)造降低了生物的視覺敏感度,，但總體而言是一種折中方案,，通過幫助馴鹿在黑暗中更好地發(fā)現(xiàn)捕食者， 從而促進(jìn)馴鹿的生存,。(生物谷Bioon.com)
生物谷推薦的英文摘要
Proceedings of the Royal Society B doi: 10.1098/rspb.2013.2451
Shifting mirrors: adaptive changes in retinal reflections to winter darkness in Arctic reindeer
Karl-Arne Stokkan, Lars Folkow, Juliet Dukes, Magella Neveu, Chris Hogg, Sandra Siefken, Steven C. Dakin and Glen Jeffery
Arctic reindeer experience extreme changes in environmental light from continuous summer daylight to continuous winter darkness. Here, we show that they may have a unique mechanism to cope with winter darkness by changing the wavelength reflection from their tapetum lucidum (TL). In summer, it is golden with most light reflected back directly through the retina, whereas in winter it is deep blue with less light reflected out of the eye. The blue reflection in winter is associated with significantly increased retinal sensitivity compared with summer animals. The wavelength of reflection depends on TL collagen spacing, with reduced spacing resulting in shorter wavelengths, which we confirmed in summer and winter animals. Winter animals have significantly increased intra-ocular pressure, probably produced by permanent pupil dilation blocking ocular drainage. This may explain the collagen compression. The resulting shift to a blue reflection may scatter light through photoreceptors rather than directly reflecting it, resulting in elevated retinal sensitivity via increased photon capture. This is, to our knowledge, the first description of a retinal structural adaptation to seasonal changes in environmental light. Increased sensitivity occurs at the cost of reduced acuity, but may be an important adaptation in reindeer to detect moving predators in the dark Arctic winter.
