Tag Archives: coevolution

Don’t let the web bugs bite

by Piter Kehoma Boll

If you think spiders are scary creatures, today you will learn that they are scared too. But what could scary a spider? Well, a web bug!

We usually think of spider webs as an astonishing evolutionary achievement of this group of arachnids and a very efficient way to capture prey without having to pursue them. Webs are sticky, resistant, and only spiders themselves can move freely through them. The only problem is that this is not true.

emesaya_feeding

A thread-legged assassin bug (Emesaya sp.) feeding on a spider after invading the spider’s web in the Western Ghats, India. Photo by Vipin Baliga.*

A group of bugs that conquered the spider world are the so-called thread-legged assassin bugs, which comprise the subfamily Emesinae of the assassin bugs (family Reduviidae). As the name implies, the assassin bugs are a group of true bugs (suborder Heteroptera) that are expert killers of other creatures.

During their evolution, the thread-legged assassin bugs seem to have acquired a special taste for spiders and throughout the world they are usually associated with these eight-legged predators. In many cases, such as the one seen in the picture above, the bugs prey on the spiders, having developed the ability to move through the webs. They usually produce vibrations on the web that attract the spiders. Those, thinking that they caught a prey, are lured directly to their death in the legs and proboscis of the terrible bug.

Some thread-legged assassin bugs have, however, found another way to harass spiders: by stealing their food. In the latter scenario, the bugs usually wait close to or on the spider’s web and, when an insect is caught, they steal it from the spider by ripping it off the web. This kind of behavior is called kleptoparasitism, which means “parasitism by stealing”.

But how can spiders avoid this bug nightmare?

Until recently, it was thought that spiders were safe inside caves. Although emesinid bugs do occurr in caves, their association with spiders seemed to be weaker or non-existent there. But new findings are revealing that they pursue our arachnid fellows even to the deepest abysses of Earth.

The earliest cave-dwelling thread-legged assassin bug known to prey on spiders is Bagauda cavernicola, from India. Its spider-eating habits are known since the first decades of the 20th century.

The second species, Phasmatocoris labyrinthicus, was found almost a century later, in 2013, in Arizona, USA. More than only preying on spiders, such as the species Eidmanella pallida that lives in the same cave, P. labyrinthicus seem to have developed the ability to manipulate abandoned spiderwebs and use them to detect and capture prey for their own consumption. Only a single instance of such a behavior has been recorded and the species’s behavior needs further studies.

phasmatocoris_labyrinthicus_eating

Phasmatocoris labyrinthicus feeding on the spider Eidmanella pallida in the Kartchner Caverns, Arizona, USA. Photo extracted from Bape, 2013.

Now, only 3 years later, there are new evidences of more thread-legged assassin bugs molesting spiders in caves. And this time the observations were made in Minas Gerais, Brazil. One individual of the bug species Emesa mourei was seen standing on the web of a recluse spider (Loxosceles similis) while the spider was at the web’s edge. Another specimen of E. mourei was seen feeding on a fly near the web of a pholcid (cellar spider). The fly and the legs of the bug had vestiges of silk, indicating that the bug stole the fly from the spider. Another bug species, Phasmatocoris sp., was observed on a web of the cellar spider Mesabolivar aff. tandilicus. If this species of Phasmatocoris manipulates spider webs the same way that P. labyrinthicus seems to do is something yet to be investigated.

emesa_mourei_eating

Nymph of Emesa mourei feeding on a fly that it apparently stole from a pholcid spider in the cave Lapa Arco da Lapa, Minas Gerais, Brazil. Photo by Leonardo P. A. Resende, extracted from Resende et al., 2016.

With three different and very distant records of thread-legged assassin bugs associated with spiders in caves, it is clear that the poor arachnids cannot get rid of those bugs even if they run down into the bowels of the Earth.

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ResearchBlogging.orgReferences:

PAPE, R. (2013). Description and Ecology of A New Cavernicolous, Arachnophilous Thread-legged Bug (Hemiptera: Reduviidae: Emesini) from Kartchner Caverns, Cochise County, Arizona Zootaxa, 3670 (2) DOI: 10.11646/zootaxa.3670.2.2

Resende, L., Zepon, T., Bichuette, M., Pape, R., & Gil-Santana, H. (2016). Associations between Emesinae heteropterans and spiders in limestone caves of Minas Gerais, southeastern Brazil Neotropical Biology and Conservation, 11 (3) DOI: 10.4013/nbc.2016.113.01

Wignall, A., & Taylor, P. (2010). Predatory behaviour of an araneophagic assassin bug Journal of Ethology, 28 (3), 437-445 DOI: 10.1007/s10164-009-0202-8

Wygodzinsky, P. W. 1966. A monograph of the Emesinae (Reduviidae, Hemiptera). Bulletin of the American Museum of Natural History, 133:1-614.

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This work is licensed under a Creative Commons Attribution-NonCommerical-NoDerivs 2.0 Generic License.

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Friday Fellow: Darwin’s Orchid

by Piter Kehoma Boll

Orchids comprise one of the most numerous families of plants, so it is more than time to have an orchid Friday Fellow. And what could be a better choice than the Darwin’s orchid, Angraecum sesquipedale?

Native from Madagascar, the Darwin’s orchid has nice star-like white flowers with a waxy appearance that are produced in the wild from June to September. It is an epiphytic orchid, growing on trees, and its roots may reach several meters in length around the tree trunks.

The white waxy flowers of the Darwin's orchid. Notice the long spurs hanging from the flowers.

The white waxy flowers of the Darwin’s orchid. Notice the long spurs hanging from the flowers. Photo by Wilfred Duckitt*.

The most distinct feature of this species is the presence of a very long spur, a tube up to 43 cm long that contains the nectar. The epithet “sesquipedale” is given after that feature, meaning “one and a half foot long” in Latin, referring to the length from the end of the spur to the tip of the dorsal sepal. After examining several flowers, the naturalist Charles Darwin predicted the existence of a pollinator with a proboscis that was long enough to reach the nectar at the end of the spur. Later, Alfred Wallace noticed that the Morgan’s sphix moth (Xanthopan morganii), found in East Africa, had a proboscis almost long enough to reach the nectar and suggested that naturalists should look for similar species in Madagascar. In fact, some time later, specimens of the Morgan’s sphinx moth with a very long proboscis, long enough to reach the end of the spur, were found in Madagascar, confirming Darwin’s prediction. Unfortunately it happened only after Darwin’s death, so that he never became aware of the discovery…

Currently there are many cultivars and hybrids of the Darwin’s orchid all around the world.

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References:

Nilsson, L. A. 1988. The evolution of flowers with deep corolla tubes. Nature, 333: 147-149. DOI: 10.1038/334147a0

Wikipedia. Angraecum sesquipedale. Availabe at: < https://en.wikipedia.org/wiki/Angraecum_sesquipedale >. Access on June 18, 2016.

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*Creative Commons License
This work is licensed under a Creative Commons Attribution 2.0 Generic License.

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Friday Fellow: Giant Tube Worm

by Piter Kehoma Boll

Giant tube worms Riftia pachyptila. Photo extrected from planeterde.de

Giant tube worms Riftia pachyptila. Photo extracted from planeterde.de

ResearchBlogging.org Let’s dive deep into the ocean and talk about this awesome animal, the giant tube worm Riftia pachyptila. Initially classified in a separate phylum, Vestimentifera, today it is included in a family of Annelids called Sibloginidae. Its common name comes from the fact that it can reach a length of 2.4 meters, quite big for a worm.

Endemic to deep-sea hydrothermal areas in the Pacific ocean, these worms are adapted to tolerate the high temperatures, pressure and levels of hydrogen sulfide in their environments. With their body protected by a chitin tube which can reach 3 meters in length, the only part exposed is a red structure, the branchial plume, highly vascularized ad rich in a hemoglobin complex of high molecular mass.

Below the plume lies the vestimentum, a muscular region which hosts the brain and the heart and is responsible for the extension and withdrawal of the plume. The name of the old phylum comprising this species, Vestimentifera, refers to this structure.

Follwing the vestimentum is the trunk and after it the opisthosome, which anchors the animal to the tube.

The plume is used to carry oxygen, carbon dioxide and sulfides into the animal’s body, which, however, lacks a mouth and gut.

A worm out of its tube. Photo extracted from spineless.ucsd.edu

A worm out of its tube. Photo extracted from spineless.ucsd.edu

To achieve nutrients, the giant tube worms host an endosymbiotic chemolithoautotrophic γ-Proteobacterium inside the trophosome, a richly vascularized organ in the trunk that constitutes a specific morphological adaptation to house the symbiotic bacteria. The sulfides are transported by the worm from the environment to the symbionts, which possess a sulfur oxidizing respiratory system and so can produce metabolic energy for themselves and for the worm.

The association between the giant tube worm and its chemoautrophic bacteria was the first of this kind to be described more than 30 years ago by Cavanaugh et al. and is currently the best studied one, but many questions about the details of this relationship, including the achievement of the bacteria by young worms, are yet to be fully answered.

Since the worm lacks a digestive system, its nutrition is entirely dependent on its symbiotic bacteria and all the anatomic adaptations designed to allow this association makes this a very good example of coevolution and make us think that there are no limits for life to adapt itself.

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References:

Lopez-Garcia, P., Gaill, F., & Moreira, D. (2002). Wide bacterial diversity associated with tubes of the vent worm Riftia pachyptila. Environmental Microbiology, 4 (4), 204-215 DOI: 10.1046/j.1462-2920.2002.00286.x

Minic, Z., & Hervé, G. 2004. Biochemical and enzymological aspects of the symbiosis between the deep-sea tubeworm Riftia pachyptila and its bacterial endosymbiont. European Journal of Biochemistry, 271 (15), 3093-3102 DOI: 10.1111/j.1432-1033.2004.04248.x

Stewart FJ, & Cavanaugh CM 2006. Symbiosis of thioautotrophic bacteria with Riftia pachyptila. Progress in molecular and subcellular biology, 41, 197-225 PMID: 16623395

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