Internodes as Storage Organs

Plants utilise many parts of themselves for food storage, which are often used as crops in agriculture: stem tubers in potatoes, leaf petioles in celery, leaves in onions, roots in carrots and turnips. These examples have been artificially modified by breeding for maximum storage, but considerable examples exist naturally, as anyone who has tried to remove the impressive tap roots of a dandelion (Taraxacum officinale) from flower beds will testify.

Silver weed, Argentine anserina

Large roots, leaves and stems are obvious candidates for storage. Yet plants often use less obvious structures, often to great benefit. Silverweed (Argentina anserina) is a very common plant of many habitats, from hegderow to sand dunes, so common that it can become a troubelsome weed in cultivated soil. It can spread quite rapidly using stolons, producing new plants or ramets at then end of each stolon. While the obvious purposes of the stolon internode between clones are to space out the plants and transport resources, it has been shown that the internodes act as storage organs (1). Juvenile, unrooted ramets were cut from stolons with and without the preceding internode. All ramets with the internode survived, while only 37% of those without did. Internodes that were left attached also decreased in dry weight over time, showing their use as storage organs.

References:

1. Stuefer and Huber, 1999. Ecology Letters 2 pp. 135-139

Ant Moth Bee!: Batesian Mimicry in the Curant Clearwing Moth

Currant Clearwing Moth, Synanthedon tipuliformis

First sights can often be deceiving. The Currant Clearwing Moth (Synanthedon tipuliformis) may not look it, but it is a moth. True, the name is a give-away, but in appearance it superficially has little in common with its lepidopteran cousins. While not quite the “Ant Moth Bee” amalgam of the title (with apologies to Captain Beefheart's Ant Man Bee), it does bear an uncanny resemblance to wasps. Along with other members of the Sesiidae family the wings are clear and scaleless, and much reduced in size when compared to other lepidopterans. As a result the body seems a lot larger but most strikingly of all they bear colourful, banded abdomens (1). 

Currant Clearwing Moth, Synanthedon tipuliformis

S. tipuliformis has therefore evolved a form of Batesian mimicry, when a relatively harmless species (S. tipuliformis) mimics the appearance of a relatively dangerous one (a number fo similarly banded stinging wasps) (2). The resemblance is quite accurate and within a habitat the moth is quite rare when compared to its wasp models, so that it is not often observed.

Currant Clearwing Moth, Synanthedon tipuliformis

S. tipuliformis larvae feed on a variety of soft fruit stems (e.g. black and red currant, gooseberry) and quite destructive, causing significant losses to yields (3). Eurasian in origin, it has now spread to the Americas and Australia. Control of the moth is by the very novel use of baited traps. Synthetic lures of S. tipuliformis sex pheremones attract the moths to traps that capture them for disposal (4).

Currant Clearwing Moth, Synanthedon tipuliformis

References:

1. Resh and Cardé (eds) 2009. Encyclopedia of Insects pp. 576-577
2. Resh and Cardé (eds) 2009. Encyclopedia of Insects pp. 634-635
3. Scözs et al., 1985. Entomologia Experimentalis et Applicata 39 pp. 131-133
4. Suckling et al., 2005. Journal of Chemical Ecology 31pp. 393-406

Fierce Nosey

Garden Grass-veneer, Chrysoteuchia culmella

One of the most common moths encountered in Ireland, and in Europe as a whole, this time of year is the Garden Grass-veneer, Chrysoteuchia culmella. A small, buff coloured moth with a metallic fringe on its forewings, it's most striking features are its almost piercing blue eyes and its prominent “nose”. This is in fact a modified mouth part, a distinctive feature of all Pyraloidea moths, the Snout Moths (1). Flying at night, the adults are usually seen in the day time, flying ponderously when disturbed from the grass stems that they rest on. The young feed on a variety of grass species, and have been implicated in significant damage to grasslands (2).

Garden Grass-veneer, Chrysoteuchia culmella

References:

1. Reaka-Kudla and Wilson, 1997. Biodiversity 2 (Ed. Solis) pp. 231-232
2. Gomboc et al., 1994. Zbornik Biotehniske fakultete Univerze v Ljubljani 63 pp. 213-221

Roadside Antimicrobials

Greater Stitchwort, Stellaria holostea

The search for novel plant compounds with beneficial medicinal properties in the last century or so has tended to focus on tropical and sub-tropical areas (1). Yet some very useful species exist right on our door steps. Take for example a plant that is entering the last throws of its yearly blooming, the Greater Stitchwort, Stellaria holostea. Commonly seen in hedgerows and roadside verges, this perennial, native to Ireland and Europe, produces delicately petaled white flowers on weak stems that grow up to 60 cm in length (2). A survey of native plants in Scotland for antimicrobial activity (1) showed methanol extracts from seeds of S. holostea had inhibitive effects on Pesudomonas aeruginosa, a major opportunistic pathogen in in intensive care patients, burn victims, organ transplant recipients, and cystic fibrosis patients (3).

Greater Stitchwort, Stellaria holostea

References:

1. Sarker et al., 2002. Journal of Ethnopharmacology 83 pp. 73-77
2. Phillips, 1982. Wildflowers of Great Britain
3. Oriol et al., 1996. International Journal of Antimicrobial Agents 7 pp. 65-68

Mind the Children

Common Pill Woodlouse, Armadillidum vulagre

While some people might say rolling up in a ball smacks of inner insecurities, for the pill woodlouse, Armadillidum vulgare, it is an essential survival response. It is such a distinguishing feature of this isopod that it lends it both its common and scientific names (Armadillidum from the latin armare, “to arm”).  Native to the peripheral Mediterranean, A. vulgare now has a worldwide distribution, extending its range into Europe after the last ice-age and into America and Asia due to human activities. It is mostly found in gardens and other cultivated areas (1).

Common Pill Woodlouse, Armadillidum vulagre showing brood pouch

Sexual activity in A. vulgare is photoperiod dependent. Long days trigger the breeding cycle, while shorter days result in sexual rest (2). Like most isopods, A. vulgare lays its eggs into a brood pouch or marsupium, where the young hatch before being released (1). The number of young carried per clutch by A. vulgare is one of the highest of all terrestrial isopods (3).

Common Pill Woodlouse, Armadillidum vulagre

References:

1. Juchault et al., Acta Oecologica 19 pp. 367-375
2. Mocquard et al., 2001. Comptes Rendus de l’Académie des Sciences - Series III - Sciences de la Vie 324 pp. 701-707
3. Lawlor, 1976. Evolution 30 pp. 777-785

Looks Like a Spider

Drassodes cupreus

Spiders live in a very three dimensional world. The web spinning and hunting techniques employed by various species requires excellent visual awareness of their surroundings. It is remarkable therefore that this is achieved with simple eyes (1). Unlike some other arthropods, spiders do not have compound eyes, yet these simple eyes are ranked as the best eyes among the arthropods, with a visual acuity to rival primates (2).

Eyes of Drassodes cupreus

Spiders possess four pairs of eyes in all, that are grouped in two pairs: a single pair of principle eyes and three pairs of secondary eyes (1).

Drassodes cupreus

In a species of ground spider, Drassodes cupreus, one of a pair of these secondary eyes does not form images at all. It uses a built in polarization filter in the eyes to determine the direction of skylight polarization. Amazingly, D. cupreus uses this as a compass, allowing it to find its way back to its nest after foraging (3).

References:

1. O'Carroll et al., 2001. The Journal of Experimental Biology 204 pp. 2481–2490
2. Land, 1985. Neurobiology of Arachnids (ed. F. G. Barth), pp. 53–78
3. O'Carroll et al., 1999. Nature 401 pp. 470-473

Knowing Your E. coli

Escherichia coli on Tryptic Soy Agar

The recent outbreak of Escherichia coli poisoning in Germany is a stark reminder of the pathogenicity of certain strains of this bacterium. Most commonly found as a faculative organism in the human gastrointestinal tract, pathogenic strains of E. coli can cause a variety of diarrheal diseases in humans as well as being a major source of urinary tract infections. The strains that cause diarrheal diseases are generally divided into 6 pathotypes (1), the relationships between which are neatly illustrated below, after Donnenberg (2002) (2).

Pathotypes of Escherichia coli, after Donnenberg, 2002

The most closely associated of the six are Enteropathogenic E. coli (EPEC), Enterohaemorrhagic E. coli (EHEC) and the Verocytoxigenic E. coli (VTEC). EPEC attaches to the gut lining, altering it in the process which leads to bloody diarrhea. VTEC produces verocytotoxins (also called Shiga toxins) which disrupt protein synthesis in host cells and cause diarrhea. EHEC possess the attachment ability of EPEC and the toxin producing capacities of VTEC, and as such can be seen as a subset of the two (1). The most infamous EPEC strain (and possible the most infamous E. coli strain) is E. coli O157:H7. Most commonly associated with raw beef, this strain causes haemolytic uraemic syndrome (which results in renal failure) as well as other illnesses which can often lead to death. The “O157:H7” moniker refers to the specific O- and H- antigen proteins expressed by the bacterium.

Of the other pathotypes, Enterotoxigenic E. coli (ETEC) is a major cause of traveler's diarrhea worldwide, producing toxins upon colonisation of the gut. Enteroinvasive E. coli (EIEC) invades host cells in the epithelial layer of the gut, spreading from cell to cell and causing a mild form of dysentery. Enteroaggregative E. coli (EAggEC, or EAEC) causes persistent diarrhea, and acts by aggregating on the gut wall and producing a toxin. Diffusely Adherent E. coli is most commonly associated with urinary tract infections, however it has been suggested to have a role as a causative agent of diarrhea.

All of the above pathotypes enter the body by the faecal-oral route, most often through water contaminated with faeces. Some pathotypes, most notably the VTEC, are associated with ruminant animals, with cattle being historically their main reservoir (1).

According to the Center for Disease Control in the US, the outbreak in Germany was caused by the strain E. coli O104:H4, a VTEC type strain, but one that also shows virulence characteristics of EAggEC pathotypes (3).

References:

1. O'Sullivan et al., 2007. Methods for Detection and Molecular Characterisation of Pathogenic E. coli, ISBN 1 84170 506 3
2. Donnenberg, 2002. Escherichia coli: Virulence Mechanisms of a Versatile Pathogen
3. http://www.cdc.gov/ecoli/2011/ecoliO104/

Small Little Green Shiny Fellas

In the back garden of a West Cork home my brother pointed out to me the presence of a most beautiful beetle walking around on some dock plants. It was no smaller than the nail on my baby finger and had a green iridescence with which I was truly delighted. The insects turned out to be a pair of female Green Dock Beetles (Gastrophysa viridula).  

Gastrophysa viridula on a dock leaf

Belonging to the Order Coleoptera [Beetles], they reside in the Family Chrysomelidae which is a taxon with an enormous profusion of highly specialised herbivorous species. There are nearly 40,000 species in this taxon and most are phytophagous (plant-feeders). Some species although having specialised on a narrow range of plant species, that is choosing only to eat a few different types or even just one, have not yet entered any type of evolutionary dead-end. In fact they are able to switch to new host species if required; for example if the predation pressure on an ancestral host plant becomes too much. For a herbivore to do this it needs to contend with many different factors including locating the new plant, utilising its nutrients and dealing with its defensive mechanisms. All these abilities are conferred by  the pheno- and genotypic plasticity of the herbivore and indeed the plant. Other important herbivorous taxon such as the Lepidoptera (moths and butterflies) have different ecological niches for the larvae and adult stages but not so with the Chrysomelidae and so they need to choose a host plant suitable for egg deposition, larvae and adults. It is therefore beneficial to the insect to take note of the change of host plant quality throughout time and season and also to account for previous oviposition and feeding that has taken place. As one can see the demands on a herbivorous insect for successful choice and subsequent utilisation of a host plant are immense. The perceptive abilities for location of the host plant and the insects digestive abilities to gain adequate nutrients - when plant is encountered the beetles will be required to efficiently digest the plant material and cope with the plant toxins - as well as contending with herbivores and carnivores already present, all come into play during host choice. One must not forget too that phytopathogens are known to alter the attractiveness of the plants. (1)

Our leaf beetle, Gastrophysa virudula, fed and oviposited less on dock plants (Rumex obtusifolius) which were infected by the rust fungus Uromyces rumicis than it did in healthy plants in laboratory environments. The alteration in nitrogen contents were observed in rust-infected dock plants and were not fed on by G. viridula. The diseased plants also contained higher levels of calcium oxalate but whether these cues caused the reduced feeding is yet unclear. (1 & 2)

Beetles reared on infected dock leaves had greater larval mortality and slower development. Fecundity was also reduced and regarding oviposition few larvae survived from eggs laid on rusted leaves in the field. (2)

Having said all this I am glad to report that no such rust fungus was evident on the leaves shown in the pictures. Our fellas were happy out!!!

Note the distended black abdomen which is evident on the female species when ready for oviposition (3) and in fact is a type of sexual dimorphism. The following picture [different location] shows this dimorphism with the smaller beetle being the male:

Sexual Dimorphism in Green Dock Beetle

And so we went our separate ways and the beetles had their dock leaves and I my coffee and pizza and custard and what not.It's funny what you'll find in a garden and exciting to know that multitudes of life cycles are turning around every single second on this earth. For them it is a matter of survival and for us merely a more than trifling curiosity. Still it was great to see them.

Later,

Ken.


1. Fernandez and Hilker, Host plant location by Chrysomelidae, Basic and Applied Ecology, Volume 8, Issue 2, 1 March 2007, Pages 97-116


2. Hatcher, Paul, Ayres and Whittaker, The effect of foliar disease (rust) on the development of Gastrophysa viridula
(Coleoptera: Chrysomelidae). Ecological Entomology, 19, November 1994, Pages 349–360

3. Insectoid.Info, Green Dock Beetle, http://www.insectoid.info/beetles/leaf-beetle/green-dock-beetle/