Evolution Of Insects
The most recent understanding of the evolution of insects is based on studies of the following branches of science: molecular biology, insect morphology, paleontology, insect taxonomy, evolution, embryology, bioinformatics and scientific computing. It is estimated that the class of insects originated on Earth about 480 million years ago, in the Ordovician, at about the same time terrestrial plants appeared.[1] Insects evolved from a group of crustaceans.[2] The first insects were land bound, but about 400 million years ago in the Devonian period one lineage of insects evolved flight, the first animals to do so.[1] The oldest definitive insect fossil, Rhyniognatha hirsti, is estimated to be407 to 396 million years old. Global climate conditions changed several times during the history of Earth, and along with it the diversity of insects. The Pterygotes (winged insects) underwent a major radiation in the Carboniferous (356 to 299 million years ago) while the Endopterygota (insects that go through different life stages withmetamorphosis) underwent another major radiation in the Permian (299 to 252 million years ago).
Most extant orders of insects developed during the Permian period. Many of the early groups became extinct during the mass extinction at the Permo-Triassic boundary, the largest extinction event in the history of the Earth, around 252 million years ago.[3] The survivors of this event evolved in the Triassic (252 to 201 million years ago) to what are essentially the modern insect orders that persist to this day. Most modern insectfamilies appeared in the Jurassic (201 to 145 million years ago).
In an important example of co-evolution, a number of highly successful insect groups — especially the Hymenoptera (wasps, bees and ants) and Lepidoptera (butterflies) as well as many types of Diptera (flies) and Coleoptera (beetles) — evolved in conjunction with flowering plants during the Cretaceous (145 to 66 million years ago).[4]
Many modern insect genera developed during the Cenozoic that began about 66 million years ago; insects from this period onwards frequently became preserved in amber, often in perfect condition. Such specimens are easily compared with modern species, and most of them are members of extant genera.
The Permian (299 to 252 million years ago) was a relatively short time period, during which all the Earth's major land masses were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"), and the Paleo-Tethys Ocean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink.[9]:400 At the end of the Permian, the biggest mass extinction in history occurred, collectively called the Permian–Triassic extinction event: 30% of all insect species became extinct; this is one of three known mass insect extinctions in Earth's history.[17]
The Triassic (252 to 201 million years ago) was a period when arid and semiarid savannas developed and when the first mammals, dinosaurs, and pterosaurs also appeared. During the Triassic, almost all the Earth's land mass was still concentrated into Pangaea. From the east a vast gulf entered Pangaea, the Tethys sea. The remaining shores were surrounded by the world-ocean known as Panthalassa. The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated.[17] The climate of the Triassic was generally hot and dry, forming typical red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole; in fact, the polar regions were apparently moist and temperate, a climate suitable for reptile-like creatures. Pangaea's large size limited the moderating effect of the global ocean; its continental climate was highly seasonal, with very hot summers and cold winters. It probably had strong, cross-equatorial monsoons
The Cretaceous (145 to 66 million years ago) had much of the same insect fauna as the Jurassic until much later on. During the Cretaceous, the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Oceanwidened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies. Though Gondwana was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged.[39] The Berriasian epoch showed a cooling trend that had been seen in the last epoch of the Jurassic. There is evidence that snowfalls were common in the higher latitudes and the tropics became wetter than during the Triassic and Jurassic.[40] Glaciation was however restricted to alpine glaciers on some high-latitude mountains, though seasonal snow may have existed farther south. Rafting by ice of stones into marine environments occurred during much of the Cretaceous but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia
The Paleogene (66 to 23 million years ago) comprises the first part of the Cenozoic, which during this time the continents assumed their modern shapes. The fragments of Gondwana (South America, Africa, India and Australia) began to drift northwards. The collision of India with the Eurasian landmass led to the folding and formation of the Himalayas. Similarly, the Alps were folded in Central Europe by the collision of the African plate with Europe. A land bridge between North America and South America did not yet exist. The Atlantic Ocean continued to widen during the Paleogene. In the North, the last land bridge between North America and Europe broke up during the Eocene. Climate during the Paleogene was warm and tropical as most time during the Mesozoic. The climate in the beginning was drier and cooler than in the preceding Cretaceous, but the temperature strongly increased during the Eocene and subtropical vegetation spread up to Greenland and Patagonia. The climate near the poles was cool temperate, in Europe, North America, Australia and the southern part of South America warm temperate. Near the equator there was tropical climate, flanked by hot and arid zones in the north and the south. In the Oligocene, global cooling started. Antarctica was covered by an ice sheet and subsequently, sea levels dropped. Except an intermittent warm period during the late Oligocene, global cooling continued and finally led to the Pleistocene ice age
During the Neogene (23 to 0 million years ago), the continents assumed the positions they are in today. The South American continent drifted to the west towards the subduction zone in the Pacific, during this process the Andes were folded. During the Pliocene (5 million years ago) the land bridge between South America and North America was formed, and the fauna exchange started. The formation of this land bridge also affected global climate. The Indian subcontinent continued its collision with Asia, but added a westward movement as well, leading to the folding of the Caucasus. The folding of the Himalaya continues until today. The collision of Africa with Europe and the rise of the lithosphere under the Alborán Sea (westernmost Mediterranean) lead to the separation of the Mediterranean from the Atlantic Ocean. During this period, that lasted 600,000 years (6 to 5.3 million years ago), the Mediterranean desiccated nearly completely (Messinian salinity crisis). Only at the end of this period the desiccated basin was flooded through a narrow canal near Gibraltar, according to today's view quickly, but without catastrophic effects.[17] The Neogene was a period of global cooling, which finally led to the Pleistocene ice age. At the beginning of the Miocene, temperatures in the northern hemisphere initially were still temperate. However, by the formation of the land bridge between South America and North America, the warm ocean current was cut off and the polar caps cooled down dramatically. During the Gelasian period ice sheets began to form both in the Arctic and Antarctic region. This marked the starting point of a new ice age which continues until today, with glacial cycles and intermittent warmer periods (interglacials). During the glacials the continental glaciers pushed to the 40th parallel in some regions and covered major parts of North America, Europe and Siberia. Each glacial advance tied up large volumes of water and the sea levels dropped globally by around 100 m. During the interglacials, the sea level rose again and coastal flooding was common during this time
A report in November 2014 unambiguously places the insects in one clade, with the remipedes as the nearest sister clade.[50] This study resolved insect phylogeny of all extant insect orders, and provides "a robust phylogenetic backbone tree and reliable time estimates of insect evolution."[50] Finding strong support for the closest living relatives of the hexapods had proven challenging due to convergent adaptations in a number of arthropod groups for living on land.[51]
A phylogenetic tree of the arthropods and related groups[52]
Fossils[edit]
Insect fossils are not merely impressions, but also appear in many other forms; While wings are indeed a common insect fossil, they do not readily decay or digest, which is why birds and spiders typically leave the wings after devouring the rest of an insect. Terrestrial vertebrates are almost always preserved just as bony remains (or inorganic casts thereof), the original bone usually having been replaced by the mineral apatite. Occasionally, mummified or frozen vertebrates are found, but their age is usually no more than several thousand years. Fossils of insects, in contrast, are preserved as three-dimensional, permineralized, and charcoalified replicas; and as inclusions in amber and even within some minerals. There is also abundant fossil evidence for the behavior of extinct insects, including feeding damage on fossil vegetation and in wood, fecal pellets, and nests in fossil soils. Dinosaur behavior, by contrast, is recorded mostly as footprints and coprolites.
The insect fossil record extends back some 400 million years to the lower Devonian, while the Pterygotes (winged insects) underwent a major radiation in the Carboniferous. The Endopterygota underwent another major radiation in the Permian. Survivors of the mass extinction at the P-T boundary evolved in the Triassic to what are essentially the modern Insecta Orders that persist to modern times. Most modern insect families appeared in the Jurassic, and further diversity probably in genera occurred in the Cretaceous. By the Tertiary, there existed many of what are still modern genera; hence, most insects in amber are, indeed, members of extant genera. Insects diversified in only about 100 million years into essentially modern forms.The Carboniferous (359 to 299 million years ago) is famous for its wet, warm climates and extensive swamps of mosses, ferns, horsetails, and calamites.[9] Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as Permo-Carboniferous in age. The cooling and drying of the climate led to the Carboniferous Rainforest Collapse (CRC). Tropical rain forests fragmented and then were eventually devastated by climate change.[12]
Remains of insects are scattered throughout the coal deposits, particularly of wings from cockroaches (Blattodea);[13] two deposits in particular are from Mazon Creek, Illinois and Commentry, France.[14] The earliest winged insects are from this time period (Pterygota), including the aforementioned Blattodea, Caloneurodea, primitive stem-group Ephemeropterans, Orthoptera, Palaeodictyopteroidea.[9]:399 In 1940 (in Noble County, Oklahoma), a fossil of Meganeuropsis americana represented the largest complete insect wing ever found.[15] Juvenile insects are also known from the Carboniferous Period.
The Permian (299 to 252 million years ago) was a relatively short time period, during which all the Earth's major land masses were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"), and the Paleo-Tethys Ocean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink.[9]:400 At the end of the Permian, the biggest mass extinction in history occurred, collectively called the Permian–Triassic extinction event: 30% of all insect species became extinct; this is one of three known mass insect extinctions in Earth's history.[17]
2007 study based on DNA of living beetles and maps of likely beetle evolution indicated that beetles may have originated during the Lower Permian, up to 299 million years ago.[18]In 2009, a fossil beetle was described from the Pennsylvanian of Mazon Creek, Illinois, pushing the origin of the beetles to an earlier date, 318 to 299 million years ago.[19] Fossils from this time have been found in Asia and Europe, for instance in the red slate fossil beds of Niedermoschel near Mainz, Germany.[20] Further fossils have been found in Obora, Czech Republic and Tshekarda in the Ural mountains, Russia.
The Triassic (252 to 201 million years ago) was a period when arid and semiarid savannas developed and when the first mammals, dinosaurs, and pterosaurs also appeared. During the Triassic, almost all the Earth's land mass was still concentrated into Pangaea. From the east a vast gulf entered Pangaea, the Tethys sea. The remaining shores were surrounded by the world-ocean known as Panthalassa. The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated.[17] The climate of the Triassic was generally hot and dry, forming typical red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole; in fact, the polar regions were apparently moist and temperate, a climate suitable for reptile-like creatures. Pangaea's large size limited the moderating effect of the global ocean; its continental climate was highly seasonal, with very hot summers and cold winters. It probably had strong, cross-equatorial monsoons
The Paleogene (66 to 23 million years ago) comprises the first part of the Cenozoic, which during this time the continents assumed their modern shapes. The fragments of Gondwana (South America, Africa, India and Australia) began to drift northwards. The collision of India with the Eurasian landmass led to the folding and formation of the Himalayas. Similarly, the Alps were folded in Central Europe by the collision of the African plate with Europe. A land bridge between North America and South America did not yet exist. The Atlantic Ocean continued to widen during the Paleogene. In the North, the last land bridge between North America and Europe broke up during the Eocene. Climate during the Paleogene was warm and tropical as most time during the Mesozoic. The climate in the beginning was drier and cooler than in the preceding Cretaceous, but the temperature strongly increased during the Eocene and subtropical vegetation spread up to Greenland and Patagonia. The climate near the poles was cool temperate, in Europe, North America, Australia and the southern part of South America warm temperate. Near the equator there was tropical climate, flanked by hot and arid zones in the north and the south. In the Oligocene, global cooling started. Antarctica was covered by an ice sheet and subsequently, sea levels dropped. Except an intermittent warm period during the late Oligocene, global cooling continued and finally led to the Pleistocene ice ageDuring the Neogene (23 to 0 million years ago), the continents assumed the positions they are in today. The South American continent drifted to the west towards the subduction zone in the Pacific, during this process the Andes were folded. During the Pliocene (5 million years ago) the land bridge between South America and North America was formed, and the fauna exchange started. The formation of this land bridge also affected global climate. The Indian subcontinent continued its collision with Asia, but added a westward movement as well, leading to the folding of the Caucasus. The folding of the Himalaya continues until today. The collision of Africa with Europe and the rise of the lithosphere under the Alborán Sea (westernmost Mediterranean) lead to the separation of the Mediterranean from the Atlantic Ocean. During this period, that lasted 600,000 years (6 to 5.3 million years ago), the Mediterranean desiccated nearly completely (Messinian salinity crisis). Only at the end of this period the desiccated basin was flooded through a narrow canal near Gibraltar, according to today's view quickly, but without catastrophic effects.[17] The Neogene was a period of global cooling, which finally led to the Pleistocene ice age. At the beginning of the Miocene, temperatures in the northern hemisphere initially were still temperate. However, by the formation of the land bridge between South America and North America, the warm ocean current was cut off and the polar caps cooled down dramatically. During the Gelasian period ice sheets began to form both in the Arctic and Antarctic region. This marked the starting point of a new ice age which continues until today, with glacial cycles and intermittent warmer periods (interglacials). During the glacials the continental glaciers pushed to the 40th parallel in some regions and covered major parts of North America, Europe and Siberia. Each glacial advance tied up large volumes of water and the sea levels dropped globally by around 100 m. During the interglacials, the sea level rose again and coastal flooding was common during this timeA report in November 2014 unambiguously places the insects in one clade, with the remipedes as the nearest sister clade.[50] This study resolved insect phylogeny of all extant insect orders, and provides "a robust phylogenetic backbone tree and reliable time estimates of insect evolution."[50] Finding strong support for the closest living relatives of the hexapods had proven challenging due to convergent adaptations in a number of arthropod groups for living on land.[51]
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In 2008, researchers at Tufts University uncovered what they believe is the world's oldest known full-body impression of a primitive flying insect, a 300 million-year-old specimen from the Carboniferous Period.[53] The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, from the 396 million year old Rhynie chert. It may have superficially resembled a modern-day silverfish insect.nsects are prey for a variety of organisms, including terrestrial vertebrates
. The earliest vertebrates on land existed 350 million years agoand were large amphibious piscivores, through gradual evolutionary change, insectivory was the next diet type to evolve.[12] Insects were among the earliest terrestrial herbivores and acted as major selection agents on plants.[4] Plants evolved chemical defenses against this herbivory and the insects in turn evolved mechanisms to deal with plant toxins. Many insects make use of these toxins to protect themselves from their predators. Such insects often advertise their toxicity using warning colors.[4] This successful evolutionary pattern has also been utilized by mimics. Over time, this has led to complex groups of coevolved species. Conversely, some interactions between plants and insects, like pollination, are beneficial to both organisms. Coevolution has led to the development of very specific mutualisms in such systems.
Taxonomy[edit]
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| Cladogram of living insect groups,[55] with numbers of species in each group.[56] Note thatApterygota, Palaeoptera and Exopterygota are possibly paraphyletic groups. | |||||||||||||||||||
Traditional morphology-based or appearance-based systematics has usually given Hexapoda the rank of superclass,[59] and identified four groups within it: insects (Ectognatha), springtails (Collembola), Protura and Diplura, the latter three being grouped together as Entognatha on the basis of internalized mouth parts. Supraordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data. A recent theory is that Hexapoda is polyphyletic (where the last common ancestor was not a member of the group), with the entognath classes having separate evolutionary histories from Insecta.[60] Many of the traditional appearance-based taxa have been shown to be paraphyletic, so rather than using ranks like subclass, superorder and infraorder, it has proved better to use monophyletic groupings (in which the last common ancestor is a member of the group). The following represents the best supported monophyletic groupings for the Ins
Origin of insect flight[edit]
The origin of insect flight remains obscure, since the earliest winged insects currently known appear to have been capable fliers. Some extinct insects (e.g. the Palaeodictyoptera) had an additional pair of winglets attached to the first segment of the thorax, for a total of three pairs.
The wings themselves are sometimes said to be highly modified (tracheal) gills.[citation needed] And there is no doubt that the tracheal gills of the mayfly nymph in many species look like wings.[citation needed] By comparing a well-developed pair of gill blades in the naiads and a reduced pair of hind wings on the adults, it is not hard to imagine that the mayfly gills (tergaliae) and insect wings have a common origin, and newer research also supports this.[citation needed] The tergaliae are not found in any other order of insects, and they have evolved in different directions with time. In some nymphs/naiads the most anterior pair has become sclerotized and works as a gill cover for the rest of the gills. Others can form a large sucker, be used for swimming or modified into other shapes. But it doesn't have to mean that these structures were originally gills.
Theories[edit]
When the first forests arose on Earth, new niches for terrestrial animals were created. Spore-feeders and others who depended on plants and/or the animals living around them would have to adapt too to make use of them. In a world with no flying animals, it would probably just be a matter of time before some arthropods who were living in the trees evolved paired structures with muscle attachments from their exoskeleton and used them for gliding, one pair on each segment. Further evolution in this direction would give bigger gliding structures on their thorax and gradually smaller ones on their abdomen. Their bodies would have become stiffer while thysanurans, which didn't evolve flight, kept their flexible abdomen.
Nice topic...quite informative!
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