Parasites Archives - The Sciku Project

January 4, 2024January 18, 2024

Mistletoe by Sarah Das Gupta

sweet Christmas kisses
beneath the white mistletoe
secret memories
By Sarah Das Gupta

Mistletoe is a semi-parasitic plant which lives off the nutrients and water from the host plant. Birds often spread the seeds from tree to tree, especially blackcaps and the mistle thrush which explains why clumps of mistletoe are found near the tops of trees.

In UK mistletoe is found most commonly in the south-west Midlands, particularly in Herefordshire. It is almost unseen in Scotland, Ireland and the rest of Wales. When picked, it will last for 2 weeks in a cool place. It would appear the plant has no connection with toes. This seems to be a corruption of the old English ‘tan’, meaning ‘twig’.

There has been some decline in mistletoe as a result of the diminishing number of old orchards, the apple being the favourite host, together with poplar, lime and conifers.

Mistletoe played an important role in Nordic legend. Balder was killed by his blind brother, Hodr, who used the plant as a missile. The Druids also valued the plant for medicinal purposes. The association of the plant with Christmas is probably because the berries appear in December and the leaves remain green. There is some evidence that the Greek holiday, Kronia, was associated with mistletoe and kissing. Many different varieties of mistletoe exist with different coloured berries in other continents

Botanical name:	Viscum album
Popular names:	Mistletoe
Family:	Santalaceae
Origin:	Northern Europe
Flowering:	February-April
Habitat:	Branches of apple, conifer, hawthorn, lime, poplar etc.

Further reading:

‘A Little Book About Mistletoe’, Jonathan Briggs, 2013, CreateSpace Independent Publishing Platform.

‘Mistletoe Winter’, Roy Dennis, 2021, Saraband.

‘Blood and Mistletoe, History of the Druids in Britain’, Ronald Hutton, 2011, Yale University Press.

‘Mistletoe’, Royal Horticultural Society.

Author bio:

Sarah Das Gupta is a young 81 year old. Loves writing haiku and most forms of poetry. Is learning to walk after an accident. Main outside interests include equine sports. Lives near Cambridge, UK. Read other sciku by Sarah here: ‘Redundant Ergot‘, ‘Redundant Vets’, ‘Dog’s Mercury’, ‘Bird’s Foot Trefoil’ and ‘The Glastonbury Thorn’.

December 23, 2021December 23, 2021

Mistletoe

festive parasites
regulating virulence
to preserve their hosts

Mistletoe is a parasitic plant often found growing on hardwoods, such as apple trees. Whilst able to photosynthesize itself, the majority of a mistletoe plant’s water and nutrients are taken from its host, putting strain on the host plant.

The burden of parasitism can be particularly hard on the host when environmental conditions are tough, for instance during a drought. Research by Nabity et al. (2021), however, has shown that the desert mistletoe (Phoradendron californicum) is able to adjust the balance between autotrophy (the amount it obtains resources for itself through photosynthesis) and heterotrophy (the amount it takes resources from its host).

During dry periods the researchers found that desert mistletoe plants increased the amount of photosynthesis they performed, limiting the burden they place on their environmentally stressed host, the velvet mesquite (Prosopsis velutina). In this way mistletoe plants increase the chances of their host plants surviving the harsh environmental conditions and, as a result, increase their own chances of survival.

The researchers also demonstrated evidence of competition for xylem resources between mistletoe plants on the same host, some of the first evidence of intraspecific competition in parasites. The mistletoe plants are able to detect other mistletoe plants on the same host and can adjust their virulence accordingly. Possible ways that mistletoe could detect one another include via scent (chemical compounds released through a plant’s pores) or through chemical compounds traveling along the host’s xylem.

The research also suggests that levels of relatedness between mistletoe plants sharing the same host may even affect virulence. More research is needed to clarify this, however, and to investigate whether the plants can actually detect relatedness or whether mistletoe’s method of seed dispersal simply means that plants sharing the same host are likely to have higher levels of relatedness than mistletoe plants on separate hosts.

Further reading: http://dx.doi.org/10.1016/j.cub.2021.01.034

October 8, 2021October 8, 2021

Darwin’s Finches

islands diverging
beaks for seeds and bugs and blood
letters rearranged

Darwin’s finches are a group of 18 species of passerine birds found across the Galápagos Islands (hence their other name of Galápagos finches). The group are a poster child for Darwin’s theory of evolution by means of natural selection. During his voyage on the HMS Beagle he collected specimens from what later turned out to be 12 of the 18 species, although Darwin himself didn’t realise the significance at the time, not realising they were all types of finch (ornithologist John Gould corrected him about the species) and not recording which islands they came from (he was later able to correctly assign them based on the notes of others on the voyage).

As the finches colonised the islands and began to adapt to the varied habitats and food resources available, the different groups diverged from each other, resulting in the separate species we see today. The finches themselves have a huge variety of forms (likely leading to Darwin’s confusion), most notably in their beak shapes and sizes. Their beaks are highly specialised to the food sources available on the different islands, with different species feeding on nuts, seeds, flowers, nectar, leaves, cacti, and invertebrates (including insects, parasites, larvae and spiders).

Perhaps the strangest of all is the Vampire Ground Finch (Geospiza septentrionalis) which feeds on the blood of other birds such as blue-footed boobies and Nazca boobies. It’s theorised that this behaviour evolved from mutualistic behaviours where the finch would clean parasites from the plumage of larger birds. These days their sharp beaks are used to peck their victim’s skin until it starts bleeding and the finches feed on the blood. Their unpleasant behaviours don’t stop there, however, as they steal eggs and roll them into rocks to break the shells, and they’ll also eat guano – excrement from seabirds. Since fresh water is scarce on their home islands (Wolf Island and Darwin Island), they also feed on nectar from Galápagos prickly pear flowers.

Molecular studies of Darwin’s finches suggests that the timing and spatial expression of at least four genes are responsible for the differences in beak structure, alphabetic changes that led to anatomical changes: BMP4 (which encodes Bone morphogenetic protein 4), CaM (which encodes Calmodulin), ALX1 (which encodes ALX homeobox protein 1), and HMGA2 (which regulates the expression of other genes).

A note about the sciku: this sciku has been written using a scale and focussing structure – narrowing in from the vast islands to the beaks to the individual letters of DNA. Have you ever tried writing sciku with a focussing structure? If so, how did you get on? Let us know in the comments below!

Interested instances of evolution in action? Check out this sciku by Prof Matthew J. James on the classic example of evolution, the Peppered Moth: Dark Moths.

November 29, 2018November 29, 2018

Ensnared

Poor social spider.

Ensnared, building its own tomb.

Parasitoid wasp.

Parasitoid wasps are known to lay eggs on their victims which are then consumed by the hatching larvae. Some species will even paralyse their victim and place them in a nest to be eaten alive by their offspring. Yet behaviour observed by Fernandez-Fournier et al (2018) has revealed a wasp species that behaves even more disturbingly.

Adult Zatypota sp. wasps were found to target a species of social spider that lives in a colony web and rarely leaves it. The wasps lay their eggs on the abdomen of the spider and when the larvae hatches it attaches to the spider. The larvae influences the spider to then leave its colony and spin a cocoon web in which the spider then waits until the larvae finally kills it. Its meal consumed, the larvae then spins a pupal cocoon within the protection of the outer cocoon web and a few days later emerges as an adult.

The results reveal that the spider is manipulated into performing unusual behaviours, since such social spiders rarely leave their colony and the cocoon web is a complete different form of web. The infected spider makes its own tomb before being eaten alive within it.

Original research: http://dx.doi.org/10.1111/een.12698

November 7, 2018November 7, 2018

Domino effect

Domino effect.

Ocean-behaviour-hookworms

lead to seal pup deaths.

The web of life, food chains, ecological balance – there are a lot of terms that indicate how interlinked ecosystems are. A recent, tragic example of this is how a rise in ocean temperatures can indirectly result in increased seal pup death from hookworm infection.

Seguel et al (2018) found that sea temperatures influenced the survival of South American fur seal pups. Sea temperatures effect wind patterns and ocean currents, changing the abundance of nutrients and as a result fishes. Higher sea temperatures resulted in lower fish abundance, meaning that fur seal mothers needed to spend more time at sea feeding, consequentially spending less time with their pups. The reduced maternal care led to lower pup growth rates and a less effective immune system, making the fur seal pups more susceptible and less likely to successfully fight off hookworm infection.

Original research: http://dx.doi.org/10.7554/eLife.38432

January 10, 2018May 4, 2018

Equal rights for parasites by Donald A. Windsor

All over the Earth

Equal rights for parasites!

All life forms conserved!

Most of the species on Earth are parasites, so parasites are an
integral part of Earth’s biosphere. Parasites enable ecosystems to
function, mainly by preventing monocultures and generating
biodiversity. Therefore, it certainly seems prudent to conserve
parasites. Admittedly, parasites are not warm, fuzzy attractions and
even horrify most people. Consequently, conserving parasites is an
uphill battle. To cheer on supporters, I came up with the catchy
slogan, “Equal rights for parasites!”

Original research:

Windsor, Donald A. Equal rights for parasites. Perspectives in
Biology and Medicine 1997 Winter; 40(2): 222-229. https://doi.org/10.1353/pbm.1997.0011

Windsor, Donald A. Most of the species on Earth are parasites.
International Journal for Parasitology 1998 Dec; 28(12): 1939-1941. https://doi.org/10.1016/S0020-7519(98)00153-2

Windsor, Donald A. Parasites’ rights gaining ground. Nature 2017 December 21/28; 552(7685): 334. https://doi.org/10.1038/d41586-017-08873-3

Donald A. Windsor, a biologist with a multidisciplinary background, is
fascinated by the enormous impact parasites have on ecosystems. He
retired from industrial pharmaceutical research and development 23
years ago. He is currently affiliated with the Ronin Institute for
Independent Scholarship. His blog is:
http://www.parasitesdominate.blogspot.com/

Enjoyed this sciku? Check out Donald’s other sciku: Native American Dugout Canoe in Central New York.

August 25, 2017August 25, 2017

Hijacked ant

Little hijacked ant,

blade held in jagged pincers,

awaits her demise.

The lancet liver fluke is a parasite of devious means. As an adult it lives in the livers of ruminant animals, often cattle, but it has an ingenious method of getting from one liver to another. First, its eggs are excreted in its host’s faeces, which is then consumed by a snail. The larvae develop into juveniles in the snail’s digestive tract and are eventually themselves excreted.

This is where the ants come in. Ants use snail slime for moisture and so consume the juveniles. Once inside an ant the parasites cause it to climb a blade of grass and clamp its mandibles to the top. The ant will remain attached all night and then return to its normal behaviour during the day. The aim of the parasite is for the ant (and attached blade of grass) to be eaten by a grazing animal – the parasite is then back in its main host and the cycle starts again. Summarised in Tarry, 1969.

June 4, 2017October 25, 2017

Enemy within

Enemy within:

Trojan tapeworms plotting for

reckless behaviour.

Sticklebacks infected with a tapeworm behave in ways that appear to maximise the tapeworm’s transmission to a new host: swimming near the surface of the water and so increasing the risk of being eaten by birds. A study by Talarico et al (2017) suggests that this change in behaviour is down to the influence of the tapeworm itself rather than a “general, systematic impairment of infected sticklebacks”, although other recent studies have demonstrated that there may also be additional reasons for this behavioural change.

Original research: https://doi.org/10.1007/s00265-017-2265-9

Discussion of study: https://doi.org/10.1007/s00265-017-2272-x