Chemical Defenses of Arthropods


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The estimates of arthropods based on both methodologies resulted in a total of 6, arthropods caught through pitfall trapping and 6, arthropods through stomach contents analysis, distributed among 27 categories of the Phylum Arthropoda. The pitfall traps were less efficient than the analysis of stomach contents to estimate low motility and aggregated arthropods, and the second technique was less efficient than the first to estimate abundances of animals bearing chemical defenses and flying or jumping arthropods.

These results proposes a less biased estimate taking into account the best estimates of each technique.

We compared both the composition of the community and the environmental variables among landscape components based on a permutation procedure. Then we generated one axis of direct ordination for the communities from the 12 sampling unities using the NMDS technique and tested the hypothesis that it depends on the main reduced axes through a PCA of environmental variables using a multiple regression test.

We found a significant difference in the composition of the community and in the environmental variables of M and R compared to E, but no difference among the first two. There was a significant regression between one of the reduced axis of the environmental variables PCA1 and the ordination axis of community composition NMDS. An autocorrelation test found no significant association between distance among sampling unities and their differences in composition.

Orders like Coleoptera, Isoptera, Acari and Hymenoptera seemed to be associated mainly to the reference forest, whereas Isopoda, Opiliones, Araneae, Lepidoptera and Chilopoda were mostly related to the eucalypt monoculture. Out of the 27 arthropods categories found, 19 were used by the local herpetofauna. The diet composed mainly of itens from the Phylum Arthropoda, was classified in Hexapoda, Aracnida, Miriapoda and Crustacea. Ants, termites, crikets, spiders and acari were the itens that most contributed to the whole of the diets.

It was possible to identify a guild of frogs and lizards concentrating on the consuption of ants. Especialy in the case of frogs where all species, but one, showed positive eletivity for this item. When patches are consumed without creating a hole, this is referred to as window feeding,because it usually results in translucent window-like patches across the leaf.

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Piercing and sucking is a form of herbivory found in many arthropods with mouthparts modified to pierce plant tissues and suck nutritious fluids from the leaf veins or stems. This leaves a distinct damage mark or series of piercing sites on the plant. Here, the different parts of the mouth have been transformed into a proboscis specialized for piercing and sucking plant fluids Fig.

Boring into plant tissues creates holes in the plant, in which the animal can live Figs 5F, 6A and 8. Typically, borings occur in the woody tissues of plants Fig. Many borers also consume living cambial tissues, which are responsible for the growth of stems and roots; this can severely damage the host plant.

Borings are produced by a wide range of arthropod groups, including oribatid mites and beetle larvae. Sometimes, borings containing coprolites are preserved in mineralized wood Fig. Seed predation , the behaviour of consuming seeds, has a long fossil record. Fossil seeds may have a chewed hole in the husk, indicating either that an arthropod bored its way into the seed, or that a larva chewed its way out. Fossils of the seed Trigonocarpus Fig. Galling is a form of herbivory in which the insect induces a growth on the plant that acts as a microhabitat and food source, usually for the larvae Fig.

The adult insect or larva injects chemicals into the plant, which stimulate abnormal cell division. Often, the internal tissues of a gall become enriched with starch and other nutrients, which feed the growing insect. The gall protects the insect from predation.

Galls take many forms, and can be recognized in fossils as swollen outgrowths on the surface or around the base of a leaf.

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Figure 2G shows an image of a parasitic wasp using its ovipositor — a long, piercing, egg-laying tube — to deposit eggs inside the larvae of another insect that has already developed inside a gall on the underside of an oak leaf. Endophytic oviposition is the practice of laying eggs inside plants Fig. A range of insects use their ovipositor to insert the eggs inside plant tissues, affording them some protection and often depositing them close to a food source.

Oviposition scars can be recognized on fossil leaves and stems, sometimes as a series of small holes along the leaf midrib or plant stem Fig. Leaf mining , in which insect larvae tunnel through leaf tissues Figs 6F and 9B , first appeared in the earliest Triassic period million to million years ago; Fig.

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Following endophytic oviposition described above , the hatched larvae feed on the most nutritious tissues of the leaves between the outer layers of waxy cuticle; this has the advantage of ensuring that they are not exposed to predators. The patterns developed by different leaf miners can be quite distinct, and so leaf mines are readily recognizable in well-preserved compression fossils Fig.

Some plants have evolved to avoid leaf miners by developing leaf patterns that fool adult insects into thinking that the leaves have already been fed on. Pollination is a mutually beneficial interaction, in which an animal transports pollen between the reproductive structures of different plants, and is rewarded with nutrition — either consuming a portion of the pollen, or drinking nectar provided by the plant.

Pollination may have begun with arthropods feeding directly on spores sporivory or pollen pollenivory , and accidentally dispersing them. If a proportion of the spores or pollen could survive digestion, or became entrapped in the hairs and carapace of the arthropod, then sporivory and pollenivory may have become beneficial to the plant. Spores and pollen are common components of fossilized arthropod coprolites Fig.

True pollination can be identified in fossils by the shape and structure of fossil insect mouthparts and through the presence of plant structures such as nectaries and flowers. Conrad Labandeira, a palaeontologist specializing in arthropod—plant interactions, described four distinct phases in the historical development of arthropod herbivory Fig.

The first phase consists exclusively of feeding, boring and piercing or sucking on external foliage. The second phase includes the development of oviposition, galling and seed predation. Phase three involves the development of leaf mining in the earliest Triassic. The fourth phase began in the Early Cretaceous and continues to the present, and includes the expansion of species-specific relationships between insect herbivores and their flowering-plant hosts. This means that considerable time was required for arthropods to develop adaptations for exploiting these new plant resources.

Some of the earliest evidence of arthropods interacting with plants comes in the form of coprolites from Silurian around million to million years rocks in the Welsh borderlands and Gotland in Sweden. These coprolites contain a variety of spores and other plant fragments, which were probably produced by detritivores living among the earliest terrestrial plant communities. Detritivorous arthropods that are thought to have been present in terrestrial ecosystems at this time include myriapods such as millipedes and mites; other modern arthropod detritivores such as terrestrial isopods woodlice did not reach the land until much later.

Coprolites containing plant spores are particularly common in these deposits; however, this might reflect preservational biases, because the material that makes up the walls of plant spores and pollen is extremely durable and lends itself to fossilization. Our most complete glimpse into the early world of arthropod—plant interactions comes from a remarkable rock deposit from the Early Devonian period around million years ago : the Rhynie Chert.

This famous site in Aberdeenshire, Scotland, preserves the remains of entire ecosystems of plants, arthropods and other animals, many of which have been exquisitely fossilized in three dimensions, including cellular details of plant tissues. The organisms were living in an environment populated with volcanically charged hot springs, similar to Yellowstone National Park today.

When the mineral-rich volcanic waters spilled out from hot pools, they entombed the surrounding plants and animals in silica. Over time, as the sediments were buried, this silica turned to chert, an extremely stable and hard glass-like rock, in which the remains of this ecosystem were preserved Fig. When thin sections of the Rhynie Chert and nearby Windyfield chert are studied under the microscope, evidence of a number of different arthropod—plant interactions can be observed, including a range of coprolites, body fossils of arthropods sometimes including gut contents and lesions in the plant stems where the arthropods had pierced into the xylem tissues.

The Rhynie Chert also contains some of the earliest evidence of the interactions between non-arthropod invertebrates and plants, in the form of exquisitely preserved nematode worms infesting the plant Aglaophyton major. The palaeoecosystem preserved at Rhynie exhibits several trophic levels and significant numbers of predatory arthropods. This level of complexity could suggest that the terrestrial ecosystem had been developing for a long time before the Early Devonian, but had not been preserved in the fossil record. By the Carboniferous period, arthropod—plant interactions had become more varied.

Our information on Carboniferous arthropod—plant interactions is more detailed than that for other time periods, in part because the fossils are buried in rocks that have long been dug up to extract coal in Europe and North America, and also because of the abundance of coal balls that preserve plant debris with exceptional cellular detail. In addition to this, nodules of the iron-based mineral siderite from sediments of this age contain excellent fossils of many terrestrial arthropods that inhabited lowland forests. One fossil that has been the subject of much attention is Psaronius Fig.

Detailed studies of the fossilized tissues of this plant have revealed traces of arthropod damage, as well as coprolites associated with all organs of the tree fern. This indicates that a variety of different arthropods were reliant on this plant. A similar range of interactions has been identified in the fossilized remains of the Glossopteris plant from deposits of Permian age around million to million years ago.

Glossopteris grew in Permian wetlands of the Southern Hemisphere and was a very different plant to Psaronius ; despite these differences, a similar guild of herbivores and detritivores was apparently present in both. Throughout the Mesozoic era around million to 66 million years ago , arthropod—plant interactions became increasingly sophisticated. The first definitive fossils of leaf-mining appear in sediments from the earliest Triassic. It saw the first occurrence in the fossil record of the Lepidoptera butterflies and moths , which later became major consumers and pollinators of many plants.

Finally, fossil scorpionflies from the Jurassic have mouthparts that indicate that they probably fed on nectar-like substances, and therefore probably acted as pollinators. Some of the earliest plant—insect pollinator relationships may have been developed in this group. The radiation of angiosperms in the Cretaceous period ranks among the most significant changes ever in the terrestrial biosphere. The complex suite of interactions between angiosperms and their insect pollinators and herbivores generated a hyperdiversity of species that radiated throughout the Cretaceous and into the Cenozoic era from around 66 million years ago to the present.

The rise of angiosperms occurred in tandem with a diversification of specialized pollination agents in insects, and also the origins of the social insects wasps, ants, bees, termites and some aphids , many of which are known from fossils occurring in amber Figs 2D and 7F,G,H. Remarkably preserved charcoalified fossils from the Early Cretaceous of Portugal have revealed the structure of some of the earliest flowers; the diversity of such floral structures increased during the Cretaceous Fig.

Within this geological era, the Paleocene — Eocene boundary was a particularly interesting period for insect—plant interactions. An interval of significant climatic change, the Palaeocene—Eocene Thermal Maximum 56 million years ago marks the beginning of the Eocene, with multiple lines of evidence from studies of geochemistry, fossils and sediments pointing to a period of rapid global warming sparked by an abrupt increase in the concentration of greenhouse gases in the atmosphere. Significantly, plant fossils from the earliest Eocene are distinguished by an increased abundance of instances and types of herbivory-related damage Fig.

This intensification of herbivory was possibly driven by the increased concentrations of atmospheric carbon dioxide, which reduced the nutritional value of the plant material. This meant that larger volumes of plant tissue had to be consumed to obtain the required nutrition. Throughout history, plants have responded to arthropod herbivores by evolving defences. Among the most widely used are chemical defences such as toxins that are concentrated in the plant tissues or exuded onto the plant surface to poison or otherwise deter herbivores. Plants have even developed complex chemical-based defences that attract predators of the insect herbivores.

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The evolution of such defences cannot be inferred easily from the fossil record; however, some specific damage types can at least indicate the presence of chemical anti-herbivory defences Fig. Plants also deter arthropod herbivores by increasing the amount of indigestible materials in their tissues, such as lignin and silica, which can wear down arthropod mandibles.

Mechanical defences can include structures such as thorns, which discourage browsing by mammals or other large herbivores; smaller spines or even hairs can help to deter arthropods Fig. Trichomes are small hairs or protrusions that are found on many parts of fossil and living plants, and can function as mechanical defences Fig. In the extreme cases of carnivorous plants such as sundews Fig. Some plants use mimicry to deceive would-be herbivores: passion flowers, for example, produce small growths that resemble butterfly eggs to dupe female butterflies into thinking that eggs have already been deposited and the plant would be an unsuitable site for their young.

Such structures are potentially identifiable in fossil plants.

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Plants are not just food sources and hosts for arthropods. They have harnessed insects as their pollination couriers, and many plants are totally reliant on species-specific pollinators for their reproduction. These insects are in turn completely dependent on their plant partners for nutrition. Mimicry is also an important interaction between the two groups; insects often resemble leaves, twigs and other organs of a plant as camouflage to avoid predators Fig.

Conversely, some plants have evolved to resemble insects: for example, bee orchids resemble female bees in colour, shape and scent, tricking male bees to land on them and carry their pollen Fig. Fossil examples of mimicry include remarkable specimens of Jurassic scorpionflies from China that closely resemble fossilized Ginkgo tree leaves in the same deposits, and Jurassic lacewings with wings resembling pinnate leaves.

The fossil record of arthropod—plant interactions can help us to answer some important questions on the processes that govern the formation of new species. In , the entomologist and demographer Paul R. Ehrlich and the botanist and environmentalist Peter H. Raven proposed a model of coevolution that went some way to explaining the high species diversity seen in herbivorous insects Fig.

In time, insect herbivores evolve counter-adaptations to these defences in an arms race that allows the insects to radiate and exploit these new host-plant resources. There is some evidence to support this model, because plant groups that have convergently evolved certain chemical defences often contain more species than groups that have not, and herbivorous clades of insects are usually more diverse than their non-herbivorous sister clades.

The fossil record could help us to further investigate such evolutionary processes.


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If the escape and radiate model is accurate, then after plant radiations in the fossil record we would expect to find a stepwise radiation of herbivorous insects. Fossils can give us data on the first occurrence of certain features, and calibration points for comparing the evolution of plants and insects. If very specific types of feeding damage can be found on certain fossil plants, for example, this could help us to identify when particular feeding strategies evolved. By studying coprolites and arthropod damage, we can reconstruct patterns and changes in herbivory, and identify arthropod functional feeding groups even without body fossils.

Coprolites and gut contents might also help palaeontologists to reconstruct ancient food webs, giving us a much richer picture of what ancient ecosystems were like. The fossil record of arthropod—plant interactions is an invaluable resource that can be used to better understand the history of life on land, and how the complex web of modern biodiversity arose. Behrensmeyer, A. Terrestrial ecosystems through time.

University of Chicago Press, Chicago. Cleal, C.

Chemical Defenses of Arthropods Chemical Defenses of Arthropods
Chemical Defenses of Arthropods Chemical Defenses of Arthropods
Chemical Defenses of Arthropods Chemical Defenses of Arthropods
Chemical Defenses of Arthropods Chemical Defenses of Arthropods
Chemical Defenses of Arthropods Chemical Defenses of Arthropods
Chemical Defenses of Arthropods Chemical Defenses of Arthropods

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