Hello, my name is Lars Vilhelmsen. I work with insects and I am responsible for part of the insect collection at the Natural History Museum of Denmark. Insects are the dominant element in the terrestrial faunas today, both with regard to number of individuals and biomass. Colonies of some social insects like ants and termites may contain millions of individuals and combined may constitute up to one third of animal biomass in some tropical rainforests. I will present some of the possible key events in insect evolution that made it possible for them to expand their diversity. Today, more than one million insects have been described. They are by far the most species rich group of organisms on the planet. Together with their close relatives, the spiders, mites, millipedes and some other groups, they dominate the terrestrial ecosystems today. In this chart, we see representatives of major groups of organisms in a landscape, scaled to a size reflecting the proportion they make up of the diversity. Notice that the fly, representing insects, in the upper right corner is the largest and the mite in the lower left corner representing non-insect arthropods is also very large. How did insects arise and evolve to reach their current status on the planet? There can be little doubt that the common ancestor of the hexapods or insects living today was a terrestrial animal, but ultimately, they must have evolved from marine arthropods. Currently, no such close fossil relatives to the hexapods have been identified with certainty. In 2003, the Devonian marine fossil Devonohexapodus of approx. 390 million years age was described. It was interpreted as having a head with one pair of antennae, a thorax with six elongate legs and a long abdomen comprising at least 35 segments with a pair of shorter appendages each. Especially the three pairs of longer legs indicates that Devonohexapodus is related to hexapods as the presence of a thorax with three segments with a pair of legs each is perhaps the most important feature defining hexapods. Hexapod literally means "six legs". However, there are other features in Devonohexapodus that do not resemble hexapods. Especially the mouthparts that are usually observed in hexapods cannot be identified in Devonohexapodus. Eventually, by comparing with additional material of an already described marine arthropod, called Wingertshellicus, it turns out that many of the features in Devonohexapodus indicating hexapod affinities have been misinterpreted. For example, the appendages identified as thoracic legs in Devonohexpodus are really attached to the head, and there is no differentiated thorax as such. It seems the Devonohexapodus specimen is just an aberrantly preserved specimen of Wingertshellicus, a taxon not considered to be closely related to hexapods. Even if early fossil hexapod relatives have not been identified, there is increasing evidence that the closest living relatives of the hexapods are among the Crustacea, and that the hexapods arise from within the Crustacea. A possible close living relative of the Hexapoda might be the Remipedia, a small group of cave-dwelling crustaceans. Remipedians have a long trunk with unspecialized paired limbs down the side. Among the first undoubted hexapods that appear in the fossil record in the Devonian is the 400 million year old Rhyniella from the Rhynie Chert in Scotland. It can be identified as a springtail, a very common group today, especially in soils. Rhyniella occurs in the same formation as some of the earliest simple land plants and might have been feeding from them. Another interesting fossil from the Rhynie Chert is Rhyniognatha. This is not a complete body fossil. Rhyniognatha mostly consists of the mandibles, the first and usually largest and toughest of the mouthparts in insects. The mandibles in Rhyniognatha have prominent teeth and are attached to the head capsule by two separate articulation points, indicated by the red arrows. The two articulation points are an important character shared by all true insects, but not with springtails and a few other early hexapod groups. The double articulation allows insects to have a much stronger bite than those with only a single articulation. This is important when chewing for example tough plant material. Having biting mouthparts is ancestral for the insects. The mandibles chew the food and the other mouthparts, the maxillae and the labium, help manipulate and moisten the food. This is still how the majority of insects process their food. However, the mouthparts are one of the parts of the insect body that is most frequently modified. This has allowed insects to exploit many different food sources. A modification that has occurred repeatedly within the evolution of insects is the development of sucking mouthparts. This is a specialization to imbibe liquid food, whether from plants or animals. Examples of insects with sucking mouthparts are most butterflies and moths, which suck nectar from flowers, aphids, which suck fluid directly from the vascular system of the plant, and mosquitoes, which suck blood from vertebrates. The sucking is done with a proboscis, which has been formed independently in a number of insect groups. Which of the mouthparts are included in the proboscis varies from group to group. The most complicated proboscis is found in Diptera, that is, flies and mosquitoes, and Hemiptera, that is, bugs and aphids. In these groups, the proboscis is formed from all or most of the mouthparts. In contrast, butterflies and moths have a much simpler proboscis, formed by a small subunit of the maxillae, with the rest of the mouthparts being mostly reduced. The plasticity of insect mouthparts has probably facilitated rapid adaptation and radiation on different kinds of food. Now you know the basics of how insects handle food. In the next video, we will look at how insects evolved the flight
