The Holly and the Ivy... and the Ivy

The two leaf forms of ivy (Hedera helix), cordate (left) and palmate (right)

Its Christmas time, and all around the house... people have placed a variety of plants to add to create a festive spirit about. Poinsettias have become quite popular in this part of the world (and make a convenient, low risk present for neighbours), but the traditional Christmas trees and garlands of holly and ivy are still the most popular. All three of these now Christian traditions arose from older traditions (1): ivy (Hedera helix) in particular was considered a sybol of female fertility because of its late flowering period (September to November) and production of berries (around this time of the year) (2). Although it can be quite an invasive pest in some parts of the world, these two facts make it an important source of nectar and pollen for insects in late autumn/early winter and an equally important source of food for birds later in the year in its native range.

However, one of the most striking features of holly is that two distinct, different leaf shapes will be seen on the one plant - a five lobed, palmate form and a cordate form that shows little to no lobing. The lobed leaf is found on the climbing, juvenile stems of the plant, with the cordate form on the flowering stems. This is known as heteroblasty, a phenomenon that is found in many plant species, but that is most famously illustrated in ivy. It was first described by Karl Goebel in 1898, who noted that as plants grow they add new modules (stem with attached leaf) which show gradual changes of form in most cases (3). However in some species, such as ivy, the changes are more dramatic. The reasons for this are still unclear but defence against herbivory and nutrient and water supply differences have been suggested as causes (3). Indeed, Ivy has been shown to produce palmate leaves in low light conditions and cordate leaves in high light (4).
 

References:

1. Miles, 2008. Christmas in Ritual and Tradition, Christian and Pagan p. 275
2. Phillips, 1977. Wild Flowers of Britain p. 172
3. Zotz et al., 2011. Botannical Reviews 77 pp. 109–151
4. Rogler and Hackett, 1975. Physiologia Plantarum 34 pp. 141–147

Hiding Out With The Cuttlefish

Common Cuttlefish (Sepia officinalis)

The ability of cephalopods to vary their colour has been known since antiquity and while most species can achieve impressive colour changes, few can match the common cuttlefish (Sepia officinalis) for sheer dramatic quality. This is in part due to the size (1.5 mm in diameter) and density (50 per square mm) of the chromatophores (1), the neurally controlled colour bearing organs that can change the pigmentation and hence appearance of the animal with incredible detail. However in part it is, as the chromatophores are just one movement in the symphony that makes each animals body pattern.

Body pattern change is used in feeding feeding, avoiding predators and communication, and is therefore an integral part of S. officinalis life history. Its most striking aspect are the chromatophores, organs that are unique in the animal kingdom to cephalopods. Body pattern is controlled in a hierarchical fashion in S. officinalis: behaviour will dictate body pattern and hence organ response. Body pattern is constructed using four components, such as coloration of which chromatophores play a part. However, they are aided by organs such as leucophores which scatter light of all waveslengths and iridiphores, which produce interference colours when viewed from certain angles, often giving pink and iridescent greens and blues (1). The other three components are textural (the smoothness or papillation of the skin), postural (the orientation of the body parts) and locomotor (the action of the animal, e.g. resting, burying, scuttling, etc.). These components are themselves divided into units which are in turn divided into elements, such as the previously mentioned chromatophores. This complex hierarchy of organisation allows for the wide variety of body shapes observed in S. officinalis.
 

Such an intricate response mechanism is under tight control of the central nervous system and is driven by visual stimuli. Environmental cues taken in by the eye and transferred to the optic lobe where information is processed and transferred to the lateral basal lobe which will control motor response (1). Amazingly, these neural areas are already well developed upon hatching in S. officinalis and newly emerged cuttlefish are immediately able to conceal themselves from predators (2). They use strategies such as colour resemblence, disruptive coloration, obliterative shading, shadow elimination, disguise and adaptive behaviour to avoid becoming a meal from fish such as the Comber (Serranus cabrilla).
 

Human ability to distinguish symmetrical objects easily and quickly lead to the assumption that the use of these behaviours would be greatly enhanced by the use of asymmetrical patterns. However, it has been demonstrated that in cryptic behaviour, S. officinalis will exhibit a high degree of bilateral symmetry (3). This seems counter-intuitive: symmetrical objects would stick out much more obviously in a random, asymmetrical environment. Yet S. officinalis is notoriously difficult to spot in its native environment. This may be due to a number of factors (3). Predators of S. officinalis may not use symmetry as a visual clue. Also the orientation of the axis of symmetry is important, as unless the axis is horizontal or vertical, symmetry becomes less apparent to the viewer. Alternatively, symmetry may play a vital role in concealment. By highlighting a symmetrical pattern on its body, S. officinalis may be taking the emphasis off its own body shape, making it seem just an interesting but inedible artifact to its predators.

References:

1. Hanlon and Messenger, 1998. Cephalod Behaviour pp. 31-46
2. Langridge, 2006. Proceedings of the Royal Society Series B 273 pp. 959-967
3. Hanlon and J. B. Messenger, 1988. Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 320 pp. 437-487

Cuttlefish picture taken at Galway Atlantiquaria, Salthill, Co. Galway.

First Irish Record for the Southern Oak Bush Cricket

Ireland is home to 12 species of breeding orthopterans (grasshoppers and crickets), with five of these being classed as crickets or bush crickets (1). It is only in the last thirty five years that three of these have been recorded, with Pholidoptera griseoaptera, the Dark Bush Cricket, being first recorded as 1983 (2). This trend may be due to the lack of attention that Irish orthopterans have been paid in the past, or may be a phenomenon that has been seen in European dragonflies, that of the spread of certain species from the center of mainland Europe to its peripheries.

Female Southern Oak Bush Cricket, Meconema meridionale

This is most evident in the case of the Southern Oak Bush Cricket, Meconema meridionale. This species was thought to be an exclusively Southern European species, but has extended its range and during the 1990's was to be found in France, Holland and Belgium (3). In 2001 it had reached Britain (4), being discovered in three localities in England from where it has steadily spread. This introduction was though to have been via imported horticultural material and given the strong trade links between Britain and Ireland it is assumed it can only be a short time before M. meridionale reaches Irish shores. And so it has proved to be. On the 9th of November last, I spotted a female adult M. meridionale on a limestone pillar at the entrance to a building on the Western Road in Cork city. The weather at that point had been unseasonably warm and when I first saw it I assumed it was the closely related (and Irish native) the Oak Bush Cricket (Meconema thallasinium), a species often seen close to houses and other buildings. However this individual was lacking in the distinctive long, green wings associated with M. thallasinium and was in fact brachypterous (having abnormally small wings). This is the distinguishing feature of the otherwise almost identical M. meridionale. This may be an errant traveling individual, but the species recent range expansion points to the discovery of a breeding population in Ireland being a very distinct possibility in the not too distant future.

References:

1. Haes and Harding, 1997. Atlas of grasshoppers, crickets and allied insects in Britain and Ireland
2. O'Connor and O'Connor, 1985. Entomologists' Gazette 36 pp. 229-232
   Maclean, 2010. Silent Summer: The State of Wildlife in Britain and Ireland p. 533
   Hawkins, 2001. British Journal of Entomology and Natural History 14 pp. 207-213

Hold On

Common Limpet, Patella vulgata

Probably the most familiar intertidal organism on western European coastlines is the Common Limpet, Patella vulgata. Its conical shell can often be seen in enormous numbers on rocky shore of all degrees of wave action, and numbers are maintained by the relatively long life of certain individuals. Where conditions promote slow growth, some individuals can live up to 17 years of age (1). For a sedate looking animal, often encountered encrusted with algae and barnacles, they are voracious feeders. Although they have been reported to consume a wide variety of micororganisms (2), algae of the intertidal zone is the food of choice. And what a choice; P. vulagata feeds a plethora of different species, including Fucus spp., Ulva spp. and red encrusting algae (1). This is all facilitated by the iron and silica hardened teeth on the radula, which rasp the algae with incredible efficiency. In situations where P. vulagata have been artificially removed form shorelines, Ulva spp. have quickly covered the rocks.

Common Limpet Home Scar

A rocky shore is not for the faint of heart, with waves action dislodging anything not firmly attaced to its surface. Organisms need to be firmly attached to the rock, and P. vulgata is truly a master at this. Depending on where the animal is to be found on the rock face, the shell height will vary. Those at high shore levels have tall shells with a small shell length, while individuals at a low shore levels have shorter but longer shells, which keeps them closer to the rock (1). P. vulgata attaches to their substrate by using a combination of suction and glue like adhesion (3). The specific mode of attachment is dependant on their location at the time. At high tide, when P. vulgata is at its most active feeding, suction is employed. This involves decreasing the pressure under the foot of the animal which forms a tight seal with the substrate. At low tide, when foraging does not occur due to the increase risk of predation, P. vulgata employs a glue-like secretion from its foot which creates a seal that is stronger than that created by suction, however it is more permanent and does not allow movement for foraging. At rest, P. vulgata also employs a home scar, a depression created in the substrate by chemical action and abrasion by the shell of the animal. This is returned to after each foraging excursion as it increases the adhesion power significantly (4).

References:

1. Fish and Fish, 2011. A Student's Guide to the Seashore pp. 205-206
2. Jenkins and Hartnol, 2001. Journal of Experimental Marine Biology and Ecology 30 pp. 123-139
3. Smith, 1992. Journal of Experimental Marine Biology and Ecology 1600 pp. 205-220
4. Smith, 1991. Journal of Experimental Biology 161 pp. 151-169

Punk Moth

Pale Tussock Moth Larva, Calliteara pudibunda

With its bleached-blonde mohawk, running halfway down its yellow and black body and a shocking-red spike of tail hair, the larvae of the Pale Tussock Moth (Calliteara pudibunda) is nothing if not an attentions seeker. Yet its wildly flamboyant appearance serves an important role for the caterpillar. Its long body hairs will cause irritation upon handling, and in some cases can cause severe damage to human skin (1). It is therefore avoided by most predators, a fate that the less hirsute adults are unfortunate to avoid, being food for a variety of birds. It is found throughout Europe, and is most common in the south and west of Ireland (2).

Pale Tussock Moth Larva, Calliteara pudibunda

C. pudibunda is a polyhpagous insect, feeding on a range of plants including including hops, birch, elm, flowering cherry, hazel, hornbeam, oak, poplar, pussy willow and walnut (3). Beech is a particular favourite and large numbers have been known to occur that put immense stress on commercial beech plantations. Commercial, monocultural forests such as these are remarkable only for their lack of invertebrate biodiversity due to their lack of floral diversity (4), so lack of competition is partly responsible for such outbreaks. However, the introduction of only a small number of other tree species has been shown to reduce the numbers of C. pudibunda significantly (5). Chemical volatiles emitted from Norway Spruce grown in co-culture with beech will mask the signals that attract egg laying females to the host beech trees. Such inhibition has lead to a 25% reduction in numbers of C. pudibunda in commercial forests.

References:

1. Backshall, 2007. Venom: Poisonous Animals in the Natural World p 49
2. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 112
3. Alford, 2012. Pests of Ornamental Trees, Shrubs and Flowers p. 320
4. Christensen and Jens Emborg, 1996. Forest Ecology and Management 85 pp. 47-51
5. Heiermann and Schütz, 2008. Forest Ecology and Management 255 p. 1161-1166

Blog Awards Ireland Finals

From left to right: Sally from Register 365, John from 21stcenturynaturalist (me), Nicola from The Sequin Cinderella and Steve from Register 365.

 A great night was had by all at the finals of the Blog Awards Ireland on Saturday the 13th last in the Osprey Hotel in Naas. Unfortunately 21stcenturynaturalist didn't take home any prizes, but the Science/Education awards went to the truly excellent Science Calling!, a most deserved winner. Congratulations to Maria Delaney on a blog that always excites and educates me.

Foreground, from left to right:  Nicola from The Sequin Cinderella, John from 21stcenturynaturalist (me), and Steve from Register 365.

Best Blog was awarded to Wise Words, while Best Blog Post (presented by the wonderful people at Register 365) went to Head Rambles for "A friendship of a lifetime". A full list of winners is available here.

Oxtongue in the City

Bristly Oxtongue, Picris echioides

Urban, and for that matter suburban, landscapes are often thought of as ever changing, ever moving. The commonly held opinion is that building works, cleaning and development in such areas make dynamic habitats that only the most adaptable and durable organisms can make anything close to a permanent home in. Rural habitats, which seem to experience less human interference other than agriculture, should be far more suitable for a larger range of organisms. And generally these two statements can be held to be broadly true. However, as always, there are a few delightful anomalies.

Bristly Oxtongue, Picris echioides

Bristly Oxtongue (Picris echioides) is a large and often quite branched annual or biennial of dry, disturbed ground (1). A common plant in southern England and Wales (2), it is of rare and local occurence in Ireland, being found only with any frequency in the South and South-East (1), and is considered to be nationally rare (3). Such low frequency may be explained by its status as an introduced species, being a native of the Mediterranean (4). P. echioides certainly earns its common name, Bristly Oxtongue as it is is covered in bristles arising from small white blisters all over the plant. In the past the leaves were boiled and eaten (2), possible for medical reasons as there is anecdotal evidence that it has an effect on stomach complaints (5). There may be some truth in this, as the aerial parts of the plant contains sesquiterpene lactones, some of which are seemingly unique to P. echioides (6). Its flowers, which from a distance resemble a number of other yellow Asteracea, reveal upon inspection the most wonderfully delicate sepals.

Bristly Oxtongue, Picris echioides

As it is such a scarce plant, it was with great surprise that I received most welcome correspondnace from one Mr. Pat Dunne of Cork city outlining not one, but two locations for this flower in the city. The first is on the docks of the river Lee, near to the city center. At once this area was a very busy access point for the various industries within the city, but with their disappearance or relocation the docks have become less used and this undisturbed habitat has seemingly proved ideal for P. echioides. Similarly, the second site (located in the city suburb of Ballyphehane) is a small section of waste ground in a now disused factory. While this site was in the past tended when the factory was operational, this no longer seems to be the case, which is, again, a boon for the plant. So while cities as a whole may be never ceasing monuments to progress, there are parts of them that remain refreshingly static and a refuge for wonderful organisms.

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 252
2. Philips, 1977. Wild Flowers of Britain p. 94
3. O'Mahony, 2009. Wild Flowers of Cork City and County p. 73
4. Preston et al., 2002. New Atlas of the British and Irish Flora p. 928
5. Hooper, 1817. A New Medical Dictionary p. 629
6. Marco et al., 1992. Phytochemistry 31 pp. 2163-2164