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/