Wednesday, June 30, 2010

The Pygmy Shrew

The pygmy shrew (Sorex minutus) the smallest mammal in UK & Ireland favours hedgerows, field borders and woodlands. It continually searches for insects, snails and spiders and its tails is two-thirds that of its body length, 6cm. Yes, 6cm! (Complete British Wildlife, P. Skerry, HarperCollinsPublishers Ltd., 1997).

Pygmy shrew (Sorex minutus)

I found the dead animal back in April, on a pathway high in a woods in Hebden Bridge. I am not the one who is holding it mind you. I let a braver soul take this honour.

Note the size

Sorex minutus is a small (2.9-5.0 g) endotherm at the theoretical size limit for continuous endothermy and like other soricine shrews, stays active throughout the winter. But the pygmy shrew is more restricted in the range of behavioural and morphological strategies that may be used to conserve energy in winter compared to most rodent species. The strategy of short-term daily torpor as a means of reducing overall energy use is common among most winter-active homeotherms but not so for members of the soricine subfamily. One morphological strategy that is used by soricine shrews is an active winter regression in skeleton and internal organ mass, which also reduces total energy expenditure. Behaviourally, winter acclimatized S. minutus maintain a significantly lower RMR (Resting Meatabolic Rate) than other seasonal cohorts. McDevitt and Andrews suggest that the overwintering strategy of S. minutus is one of minimising energy expenditure wherever possible, by reducing mass and RMR, and by demonstrating an increasing reliance on behavioural thermoregulation. (Regina McDevitt, J. F. Andrews, Seasonal variation in the metabolic rate of the Pygmy shrew, Sorex minutus: Can resting metabolic rate be measured in post-absorptive shrews?, Journal of Thermal Biology, Volume 20, Issue 3, June 1995, Pages 255-261).

Although this fellow made it through the winter it looks like his luck ran out.

On a totally unrelated topic, I visited Sylvia Platt's grave that day too.



Monday, June 28, 2010

Passing Time with The Passerines

A guest post by Ken.

We are all familiar with the European Robin (Erithacus rubecula), that little friendly fellow at the end of the garden who is always quite out of reach and usually the first bird one has pointed out to as a child. A hard guy to catch but a bold fellow at that. However, in the New World they have their own robin. The American Robin.

So as I was taking a walk recently in Provo, Utah I spotted a bird which appeared to have an orange breast. I thought he was almost like our blackbird (Turdus merula) but a friend informed me later that he was, in fact, called the American Robin (Turdus migratorius).

Today I will discuss both.

Although both birds have orange breasts (the term 'redbreast' is associated usually with the robin and whilst it is an orange colour, this was considered red in the British Isles as 'orange' was not used until the introduction of the fruit of the same name), and both are passerine birds of the Order Passeriformes, the similarity ends there.

The European Robin has grey to brown upper parts and a white belly. It is a member of the Muscicapidae family or 'The Old World flycatchers'. It is found throughout Europe as far south as North Africa and as far east as West Siberia. It is approximately 13cm in length and weighs around 20g.

European Robin (Erithacus rubecula)

Male robins defending their feeding territory in winter do so aggressively but have low levels of testosterone, while males who defend a breeding territory in spring will have higher levels of testosterone. During both phases, song is an integrated part of territorial defense. Schwabl and Kriner suggest that the components of male robin song that are sung year-round as “keep out” signals are independent of testosterone, while the production of components that signal sexual information to females depends on testosterone, possibly augmenting the incorporation into and/or production of sexual components of the song. (Hubert Schwabl, Eva Kriner, Territorial aggression and song of male European robins (Erithacus rubecula) in autumn and spring: Effects of antiandrogen treatment, Hormones and Behavior, Volume 25, Issue 2, June 1991, Pages 180-194).

The American Robin is around the same length as our common blackbird (Turdus merula) at 23-28cm but is lighter at 77grams. It has a black head with white eye arcs and supercilia as well as a white belly. The back is usually brown in colour and the breast is orange although can appear slightly pink.

American Robin (Turdus migratorius)

It is a ubiquitous species in North America which has adapted to urbanization. The American robin and the grey catbird (Dumetella carolinensis) were the only species that remained present as the proportion of the land covered by houses went from 5% to 85%. The suburban environment, compared to woodland and farmland, is characterized by the presence of large patches of short grass, which are ideal for foraging throughout the breeding season. Morneal et al. found that American robins potentially can have a large clutch size and very high rates of reproductive success in suburban settings and that the breeding season seems to be of greater length in suburbs than in more rural areas. They suggest that suburbs may offer a greater variety and abundance of food and foraging sites due to the presence of more bare soil and areas where vegetation is kept short throughout the breeding season. Watering of lawns also mimics precipitation and favours the ascent of earthworms towards the litter. (Francois Morneau, Claire Lepine, Robert Decarie, Marc-Andre Villard, Jean-Luc DesGranges, Reproduction of American robin (Turdus migratorius) in a suburban environment, Landscape and Urban Planning, Volume 32, Issue 1, April 1995, Pages 55-62).

So there you have it. Robins. Both old world and new.



Thursday, June 24, 2010

Vampire Plants?

Common Broomrape, Orobranche minor

Broomrapes (Genus: Orobranche, Family Orobanchaceae) are holoparasitic plants that depend wholly on their hosts for nutrition (Young et al., 1999 Annals of the Missouri Botanical Garden 86 pp. 876–893). Agriculturally they are a major pest of fava bean, chickpea, lentil, tomato, potato, tobacco and sunflower, to name but a few, in East Africa, the Mediterranean region and the Middle East (Takeuchi et al., 1998 Phytochemistry 49 pp. 1967-1973).

They lack chlorophyll and germinate in response to stimulants present in the root exudates of the host plant (Joel et al., Physiologia Plantarum 120 pp. 328 - 337). The fact that broomrapes are totally dependent on their hosts for water, nutrients and reduced carbon, and the fact that they have lost photsynthetic function, indicates eerie parallels with the sun-hating vampire of Stoker's Dracula.

So, is it true that the broomrapes need no light? It has been shown that the photosynthetic genes have been eliminated from broomrape plastid genomes, meaning these plastids can never develop to mature chloroplasts and the plants can never photosynthesise (dePamphilis and Palmer, 1990 Nature 348 pp. 337–339). However, Kobayashi et al. (2005, Plant Physiology and Biochemistry 43 pp. 499-502) showed that a homologue of a cryptochrome gene (OmCRY1) in Common Broomrape (Orobranche minor) was expressed in higher amounts in plants grown in the dark than in the plants grown under natural daylight. Cryptochrome are blue-light photoreceptors that regulate factors such as the circadian clock in higher plants. This work shows that, although they are non-photosynthetic, broomrapes still use light to control non-photosynthetic functions.

Sexual Dimorphism in St. Mark's Fly

St. Mark's Fly (Bibio marci) is so called because of its appearance around St. Mark's Day, the 25th of April. This makes them an important pollinator of fruit trees and other crops. They fly in an odd manner with their legs dangling under the body (Chinery, 1997 Collins Gem Insects pp. 189). Sexual dimorphism is quite pronounced in B. marci, with the male have much larger eyes than the female. Males use their specialised eyes to detect and catch females on the wing (Zeil, 1983 Journal of Comparative Physiology 150 pp. 379-393)

Male Bibio marci

Female Bibio marci

Mating of Bibio mari

A Selection of Shield Bugs

Shield bugs are members of the superfamily Pentatomoidea of the bug order (Hemiptera). Pentatomoids are generally larger than other Hemipterans, with most having five segmented antennae. They are predominantly herbivorous and are often brightly coloured (Schaefer, 2009 "Prosorrhyncha: Heteroptera and Coleorrhyncha" in Encyclopedia of Insects pp. 839-855).

Sloe Bug, Dolycoris baccarum

Hawthorn Shield Bug, Acanthosoma haemorrhoidale

Green Shield Bug, Palomena prasina

Squash Bug, Coreus marginatus

Krek-Krek-Krek of the Moorhen

Adult Moorhen, Gallinula chloropus

Moorhens (Gallinula chloropus) are widely distributed throughout Ireland and are found in a wide range of wetlands. They are omnivorous and have a strong vegetarian inflence, with grazing accounting for 75% of time feeding (Pollack and O'Halloran, 1995 Biology and Environment: Proceedings of the Royal Irish Academy 95B pp. 59-64). Swimming with a jerky, head bobbing motion, they can often be heard in flight at night (Hayman and Hume, 2002 The Birdwatcher's Pocket Guide to Britain and Europe pp. 91).

Two Juveniles

The Trials of the Azure Damselfly

The Azure Damselfly, Coenagrion puella

Darwin, in The Descent of Man (1871), stated the development of a character under sexual selection may be limited by an opposing force of natural selection. This is beautifully illustrated in a study by Banks and Thompson (1985, Animal Behaviour 33 pp. 1175-1183) on mating habits in the Azure Damselfly, Coenagrion puella.

C. puella is a medium sized damselfly with a body length of 23-30 mm. It is sexually dimorphic, the males being larger than the females and have less black marking on the abdomen. They are associated with slow moving water areas although individuals may be found well away from water in suitable areas such as wet meadows (Gibbons, 1999 Insects of Britain and Ireland pp. 21). Males distinguish females from other similar species (C. pulchellum, and to a lesser extent Enallagma cyathigera) mainly by color, color pattern, body shape, and flight style. Males will pursue and attempt to grasp any female that comes within sight, and if successful in achieving tandem, will attempt immediately to initiate copulation (Tennessen, 2009 “Odonata: Dragonflies and Damselflies” in Encyclopedia of Insects pp. 721-729). This occurs when the male clasps the female's prothorax with his anal appendages. The female then curls her abdomen upwards to bring her genitalia into contact with the male's accessory genitalia under his second abdominal segment.

Banks and Thompson found that a male's mating success is determined, not by size, but by the number of days it spends at a breeding site, which is in turn determined by the life span of the male. They also found that weather conditions had a major effect on mating success as C. puella only engages in reproductive activity on warm, sunny days. This evidence illustrates that variance in male reproductive success is neither evidence for sexual selection, nor a measure of its intensity.

The Azure Damselfly, Coenagrion puella

Wednesday, June 9, 2010

Just Sometimes, Variety Can Kill You

Spiders are generalist feeders, predating on a wide variety of animals. This is especially true for the Lycosid (wolf) spiders, who employ a sit and wait strategy in pursuit of prey. This reduces their ability to be selective in feeding. Toft and Wise (1999, Oecologia 119 pp. 191 – 197) have shown that prey of similar morphology and behaviour can have wildly different effects on wolf spider health. Spiders fed the collembolan Tomocerus bidentatus showed excellent growth rates, while those fed on an alternate collembolan, Folsomia candida, had lower survial rates than spiders who were starved.

Similar results were reported by Oelbermann and Scheu (2002 Basic Applied Ecology 3 pp. 285 – 291) in a study on Pardosa lugubris.

Pardosa lugubris

P. lugubris is a common wolf spider, found widespread on leaf litter and beneath vegetation. They are most visable in early to mid summer when the female can be seen bearing a cocoon of eggs attached to the spinnerets at the tips of the abdomen (see picture above and below). After the brood hatches they remain on the mother's opisthosoma, attached to the spiny, knobbed hairs that are peculiar to adult female Lycosids for 3 to 6 days before dispersing (Rovner et al., 1973 Science 182 pp. 1153 – 1155).

Pardosa lugubris

Oelbermann and Scheu found that P. lugubris was unable to recognize and refuse detrimental prey species (such as F. candida) in mixed diets. The presence of these toxic or low quality prey species can counteract the perceived benefits of mixed diets (e.g. good fatty acid and amino acid intake) for such generalist predators. This has implications in the use of generalist predators as biological control agents, as the presence of toxic prey species would negate any effect on target prey species.

Tuesday, June 1, 2010

The Biter Bit

Coralline alga

Or at least covered over. The picture above seems to show a limpet (Patella vulgata) completely covered with an encrusting corraline alga, on which it feeds. However revenge isn't what it used to be as the alga is actually growing on an empty shell. Yet the picture does illustrate the often tenacious growing habits of corraline algae.

Corralines are red algae that encase their cells in calcium carbonate, which increases resistance to damage and herbivory, but reduces photosynthetic capacity. However there are reports of animals grazing almost exclusively on corralines, e.g. the limpet Acmaea testudinalis grazing on Clathromorphum circumscriptum (Steneck, 1982 Ecology 63 pp. 507-522). They have two distinct morphological habits: erect (as can be seen in Corallina officinalis below) and encrusting.

Corallina officinalis

The encrusting species grow as radiating sheet-like patches over hard substrata such as shells (above) but more frequently on rocks. The coralline growing on the rock in the picture below is quite bleached, a result of photoinhibition (Littler, 1973 Journal of Experimental Marine Biology and Ecology 11 pp. 103–120).

Encrusting coralline alga on red sandstone rock in an intertidal rock pool

Corallines dominate the surfaces of subtidal zones in the North Western Atlantic (Adey and Macintyre, 1973 The Geological Society of America Bulletin 84 pp. 883-904). They are also common, if secondary, components of coral reefs (Riding et al., 1991 Sedimentology 38 pp. 799–818).