左圖的這只飛蠅是一個(gè)謎。
按道理說,，它應(yīng)當(dāng)進(jìn)化出像黃蜂一樣的外表,，就像右圖看到的一樣，從而能夠更好地避開那些饑餓的小鳥,。
但是許多食蚜蠅科的成員（圖中的這兩只都是）卻僅僅是依稀相似于那種帶刺的昆蟲,。
科學(xué)家曾推斷，這些不精確的模仿是因?yàn)樗鼈冊(cè)谕瑫r(shí)拷貝多個(gè)物種的外貌,，或者人類所看到的這些缺陷是鳥兒無法辨識(shí)的,。
為了驗(yàn)證這些以及其他解釋，研究人員分析了38種食蚜蠅,，以及10種蜜蜂和黃蜂,。
在對(duì)昆蟲的身體尺寸及顏色，還有它們的豐度及糊弄人類和鳥類的本事進(jìn)行了統(tǒng)計(jì)學(xué)分析之后,，研究人員放棄了大多數(shù)已有的解釋,。
實(shí)際上，加拿大卡爾頓大學(xué)的昆蟲學(xué)家Heather D.Penney和同事在3月21日出版的《自然》雜志上報(bào)告說,，答案歸根結(jié)底為昆蟲的大小——大的食蚜蠅有最棒的模擬,，而小的、像家蠅大小的食蚜蠅則最差,。
研究小組推斷,，由于鳥類傾向于吃掉那些最大的飛蠅，因此小的飛蠅僅僅是因?yàn)槿狈ψ銐虻膲毫Χ鵁o法進(jìn)化出完美的偽裝,。（生物谷 bioon.com）
doi:10.1038/nature10961
PMC:
PMID:
A comparative analysis of the evolution of imperfect mimicry
Heather D. Penney, Christopher Hassal,Jeffrey H. Skevington,Kevin R. Abbott,，Thomas N. Sherratt
Although exceptional examples of adaptation are frequently celebrated, some outcomes of natural selection seem far from perfect. For example, many hoverflies (Diptera: Syrphidae) are harmless (Batesian1) mimics of stinging Hymenoptera2. However, although some hoverfly species are considered excellent mimics, other species bear only a superficial resemblance to their models3 and it is unclear why this is so. To evaluate hypotheses that have been put forward to explain interspecific variation in the mimetic fidelity of Palearctic Syrphidae we use a comparative approach. We show that the most plausible explanation is that predators impose less selection for mimetic fidelity on smaller hoverfly species because they are less profitable prey items. In particular, our findings, in combination with previous results, allow us to reject several key hypotheses for imperfect mimicry: first, human ratings of mimetic fidelity are positively correlated with both morphometric measures and avian rankings, indicating that variation in mimetic fidelity is not simply an illusion based on human perception4; second, no species of syrphid maps out in multidimensional space as being intermediate in appearance between several different hymenopteran model species, as the multimodel hypothesis5 requires; and third, we find no evidence for a negative relationship between mimetic fidelity and abundance, which calls into question the kin-selection6 hypothesis. By contrast, a strong positive relationship between mimetic fidelity and body size supports the relaxed-selection hypothesis7, 8, suggesting that reduced predation pressure on less profitable prey species limits the selection for mimetic perfection.
