最古老的蚊子化石帶來吸血驚愕

Recently Yahoo News on-line reported the following:

Oldest mosquito fossil comes with a bloodsucking surprise

Wed, December 6, 2023 at 12:20 a.m. GMT+8

By Will Dunham

WASHINGTON (Reuters) - Hundreds of thousands of people worldwide are killed annually by malaria and other diseases spread through the bite of mosquitoes, insects that date back to the age of dinosaurs. All of these bites are inflicted by females, which possess specialized mouth anatomy that their male counterparts lack.

But it has not always been that way. Researchers said they have discovered the oldest-known fossils of mosquitoes - two males entombed in pieces of amber dating to 130 million years ago during the Cretaceous Period and found near the town of Hammana in Lebanon. To their surprise, the male mosquitoes possessed elongated piercing-sucking mouthparts seen now only in females.

"Clearly they were hematophagous," meaning blood-eaters, said paleontologist Dany Azar of the Chinese Academy of Sciences' Nanjing Institute of Geology and Paleontology and Lebanese University, lead author of the study published this week in the journal Current Biology. "So this discovery is a major one in the evolutionary history of mosquitoes."

The two fossilized mosquitoes, both representing the same extinct species, are similar in size and appearance to modern mosquitoes, though the mouthparts used for obtaining blood are shorter than in today's female mosquitoes.

"Mosquitoes are the most notorious blood-feeders on humans and most terrestrial vertebrates, and they transmit a certain number of parasites and diseases to their hosts," Azar said.

"Only fertilized female mosquitoes will suck blood, because they need proteins to make their eggs develop. Males and unfertilized females will eat some nectar from plants. And some males do not feed at all," Azar added.

Some flying insects - tsetse flies, for instance - have hematophagous males. But not modern mosquitoes.

"Finding this behavior in the Cretaceous is quite surprising," said paleontologist and study co-author André Nel of the National Museum of Natural History of Paris.

The delicate anatomy of the two mosquitoes was beautifully preserved in the fossils. Both displayed exceptionally sharp and triangle-shaped jaw anatomy and an elongated structure with tooth-like projections.

The researchers said they suspect that mosquitoes evolved from insects that did not consume blood. They hypothesize that the mouthparts that became adapted for obtaining blood meals originally were used to pierce plants to get access to nutritious fluids.

Plant evolution may have played a role in the feeding divergence between male and female mosquitoes. At the time when these two mosquitoes became stuck in tree sap that eventually became amber, flowering plants were beginning to flourish for the first time on the Cretaceous landscape.

"In all hematophagous insects, we believe that hematophagy was a shift from plant liquid sucking to bloodsucking," Azar said.

The fact that these earliest-known mosquitoes are bloodsucking males, Azar added, "means that originally the first mosquitoes were all hematophagous - no matter whether they were males or females - and hematophagy was later lost in males, maybe due to the appearance of flowering plants, which are contemporaneous with the formation of Lebanese amber."

Plenty of animals were present to provide blood meals: dinosaurs, flying reptiles called pterosaurs, other reptiles, birds and mammals.

The researchers said while these are the oldest fossils, mosquitoes probably originated millions of years earlier. They noted that molecular evidence suggests mosquitoes arose during the Jurassic Period, which ran from about 200 million to 145 million years ago.

There are more than 3,500 species of mosquitoes worldwide, found everywhere except Antarctica. Some become disease vectors transmitting malaria, yellow fever, Zika fever, dengue and other diseases. According to the World Health Organization, more than 400,000 people die annually from malaria - a parasitic infection - mostly children under age 5.

"On the other side, mosquitoes help to purify the water in ponds, lakes and rivers," Nel said. "In general, an animal can be a problem but also can be helpful."

(Reporting by Will Dunham, Editing by Rosalba O'Brien)

華盛頓（路透社）—全世界每年有數十萬人死於瘧疾和其他透過蚊子叮咬傳播的疾病，這種昆蟲的歷史可以追溯到恐龍時代。 所有這些咬傷都是由雌性造成的，雌性擁有雄性同類所缺乏的特殊口腔解剖結構。

但情況並非總是如此。 研究人員表示，他們發現了已知最古老的蚊子化石 - 在黎巴嫩 Hammana 鎮附近發現的兩隻雄性蚊子化石，埋在可追溯到 1.3 億年前白堊紀的琥珀中。 令他們驚訝的是，雄性蚊子擁有細長的刺吸式口部構造，而這種口部構造現在只出現在雌性身上。

本週發表在《當代生物學》雜誌上的這項研究的主要作者、中國科學院南京地質古生物研究所和黎巴嫩大學的古生物學家 Dany Azar 說， “顯然它們是吸血的” ，即食血者。 “所以這一發現是蚊子進化史上的重大發現。”

這兩種蚊子化石均代表同一已滅絕物種，其大小和外觀與現代蚊子相似，但用於獲取血液的口部比今天的雌性蚊子短。

 Azar說： 「蚊子是人類和大多數陸生脊椎動物中最臭名昭著的吸血動物，它們會將一定數量的寄生蟲和疾病傳播給宿主」。

Azar 補充道: 「只有受精的雌性蚊子才會吸血，因為它們需要蛋白質來使卵發育。雄性和未受精的雌性蚊子會吃一些植物的花蜜。有些雄性根本不吃東西」。

有些飛行昆蟲 - 例如采采蠅 - 有吸血的雄性。 但現代蚊子不是。

巴黎國家自然歷史博物館的古生物學家和研究合著者 André Nel說: 「在白堊紀發現這種行為相當令人驚訝」。

兩隻蚊子精緻的解剖結構在化石中完美地保存着。 它們都顯示出異常鋒利的三角形下顎解剖結構以及帶有細長齒狀突起的結構。

研究人員表示，他們懷疑蚊子是從不吸食血液的昆蟲演化而來的。 他們推測，進化至可獲取血液作餐的口部構造, 最初是用來刺穿植物以獲得營養液的。

植物進化可能在雄性和雌性蚊子之間的攝食差異中發揮了作用。 當這兩隻蚊子被困在樹液中並最終變成琥珀時，在白堊紀景山水環境中, 開花植物第一次開始茂盛生長。

Azar說: 「在所有吸血昆蟲中，我們認為吸血行為是從吸取植物液體轉變到吸血的」。

Azar補充說，這些已知最早的蚊子是吸血雄性，「這意味著最初的第一批蚊子都是吸血的 - 無論它們是雄性還是雌性 - 後來雄性的吸血能力消失了，可能是因為開花植物的出現，與黎巴嫩琥珀的形成在同時代發生。”

許多提供血餐的動物都出現：恐龍、翼龍、其他爬行動物、鳥類和哺乳動物。

研究人員表示，雖然這些是最古老的化石，但蚊子可能先起源於數百萬年之前。 他們指出，分子證據顯示蚊子出現在侏羅紀時期，距今約 2 億至 1.45 億年前。

全世界有超過 3,500 種蚊子，除南極洲外，到處都有蚊子的蹤跡。 有些成為傳播瘧疾、黃熱病、寨卡熱、登革熱和其他疾病的疾病媒介。 據世界衛生組織稱，每年有超過 40 萬人死於瘧疾（一種寄生蟲感染），其中大多數是 5 歲以下的兒童。

Nel 說: 「另一方面，蚊子有助於淨化池塘、湖泊和河流中的水」; 「一般來說，動物可能會帶來問題，但也可能會帶來幫助」。

So, researchers have discovered that two male mosquitoes entombed in amber dating to 130 million years ago possessed elongated piercing-sucking mouthparts seen now only in females. This fact indicates that originally the first mosquitoes were all hematophagous - no matter whether they were males or females - and hematophagy was later lost in males, maybe due to the appearance of flowering plants on earth.