The 1993 film Jurassic Park
speculated that Dinosaur DNA might be extracted from blood preserved inside
Mosquitoes, Culcidae, trapped in amber during the Mesozoic. Needless to say
this is highly improbable for a number of reasons, most notably that fossils
preserved in amber, while retaining physical shape, are known to be chemically
altered during the preservation process. A less obvious flaw in this story is
that Mosquitoes do not typically favour woodland environments, and are
therefore rather rare as fossils preserved in amber, though a number of Biting
Midges, Ceratopogonidae, are known from amber, and some of these have been
found in association with preserved Trypanosome parasites, which are spread by
blood-sucking Insects, implying that these fossil Midges were blood-feeders.
The Kishenehn Formation comprises
finely bedded shales laid down in anoxic conditions at the bottom of a lake
about 46 million years ago. These shales have produced a number of very well
preserved Mosquitoes, which have been assigned to two species, Culiseta kishenehn and Culiseta lemniscata, both interpreted to
be small Bird-feeding species. One of these appears to be a blood-engorged
female (only female Mosquitoes suck blood, and then only before producing
eggs), which Greenwalt et al. chose
for testing for haemoglobin derived products. This specimen was well enough
preserved to assign it to the genus Culiseta
but not to a specific species, though the abdomen region was well preservesd.
Culiseta species (Diptera:
Culicidae), a blood-engorged female from the Middle Eocene Kishenehn Formation
of northwestern Montana. Note the distended and opaque dark-coloured abdomen.
Scale Bar is 2 mm. Greenwalt et al. (2015).
The most obvious indicator of
haemoglobin is iron; however iron is a very common element in fossil
preservation, particularly is fossils such as those from the Kishenehn
Formation which were preserved in anoxic waters, where sulphur-iron Bacteria
typically play a role in preservation. In order to establish whether the
engorged female Mosquito contained more iron than would be expected, Greenwalt et al. also tested a male Mosquito from
the same formation (male Mosquitoes do not suck blood). Samples of material
from the abdomens of both specimens were tested for iron with mass
spectrometry, revealing that the female did indeed contain raised levels of
iron, suggesting the presence of haemoglobin derived chemicals.
Culiseta species (Diptera:
Culicidae), a male from the Middle Eocene Kishenehn Formation of northwestern
Montana. The white dots indicate the areas of that were analysed. Scale Bar is 2
mm. Greenwalt et al. (2015).
Next Greenwalt et al. tested the specimens for porphyrins,
a group of proteins from which haemoglobin molecules are constructed, and which
it breaks back down to as it decays. These could be used to definitively
indicate the presence of vertebrate blood in the Mosquito at the time of death.
Porphyrins are not exclusively produced by vertebrates; chlorophyll is composed
of porphyrins as are the haemocyanin molecules used to transport oxygen in some
invertebrates (but not Mosquitoes), and many microorganisms also use
porphyrins. However no known organism produces porphyrins in any appreciable
quantities in an anoxic environment, so any porphyrins found in the specimens
are likely to have got there before the Mosquitoes died.
Using time-of-flight secondary
ion mass spectrometry Greenwalt et al. were
able to detect haemoglobin-derived porphyrin molecules in the female Mosquito,
but not the male, suggesting that this specimen was indeed gorged with
vertebrate blood at the time of death. This is the first detection of blood
derived chemicals in a blood-feeding Insect known in the fossil record.
See also…
Winter Crane Flies (Trichoceridae) are large True Flies (Diptera) with a (slightly erroneous) reputation for being tolerant of cold conditions. In fact a few species are capable of remaining active in winter, with some even mating and laying eggs beneath snow cover, but other members of the group are no more tolerant of...
Non-biting Midges (Chironomidae) are small Flies closely related to the Biting Midges, Solitary Midges and Blackflies. They closely resemble Mosquitoes, but despite their appearance and relationships, they are quite harmless, lacking biting mouthparts. It was...
Mosquitoes are small Flies notorious for their habit of sucking blood. Only the females do this, the males...
