Thursday, December 27, 2012

A Mayfly in December

It has been a a mild winter here in Ireland, especially considering the arctic conditions of two and three years ago. It is therefore not unusual to see a few strange phenological events occurring, such as plants in full flower and moths on the wing. One of the oddest, yet most delightful that I have seen recently is most certainly an adult mayfly, on the wing, not eleven days ago some 17 km from Cork city. It was odd because, as the name suggests, mayflies tend to emerge around May. Yet the emergence period for some species can from March to October. Still, seeing one a little over a week from Christmas was a little peculiar.

This sighting is also of interest as it brings to mind the recently published Red List of Irish Ephemoptera (1), detailing a check-list of the Irish species and their conservation status. Ireland is home to 33 species of mayfly, quite a low number in comparison to that of mainland Europe (350 species, (2)). However, even this relatively low number of species contributes greatly to their associated aquatic habitats. Mayflies spend the majority of their life in nymphal form (in some cases up to three years), and the feeding of these nymphs contributes greatly to the cycling and availability of nutrients in aquatic habitats (3). Such feeding can also greatly contribute to the cleansing of water systems and help maintain their integrity. On emergence from the nymphal stage the mayfly, uniquely in the insect world, passes through two terrestrail adult stages: the winged subimago and the winged and sexually mature imago. The life of these two stages is quite short in comparison to the nymphs (little more than a couple of hours in some stages), but large scale, synchronous emergence of adults results in significant movement of nitrogen and phosphorus from aquatic to terrestrial environments (3).

Check-list of Irish Mayflies. Key: CR = Critically Endangered, EN = Endangered, VU = Vulnerable, NT = Near Threatened, lc = least concern dd = deficient data.
SpeciesConservation Status
Siphlonurus armatusCR
Baetis atrebatinusEN
Ephemerella notataEN
Rhithrogena germanicaVU
Procloeon bifidumVU
Leptophlebia marginataVU
Kageronia fuscogriseaNT
Ameletus inopinatusNT
Baetis fuscatusdd
Alainites (Baetis) muticuslc
Baetis rhodanilc
Baetis scambuslc
Baetis vernuslc
Caenis horarialc
Caenis luctuosalc
Caenis macruralc
Caenis rivulorumlc
Centroptilum luteolumlc
Cloeon dipterumlc
Cloeon similelc
Ecdyonurus disparlc
Ecdyonurus insignislc
Ecdyonurus torrentislc
Ecdyonurus venosuslc
Electrogena lateralislc
Ephemera danicalc
Heptagenia sulphurealc
Leptophlebia vespertinalc
Paraleptophlebia cinctalc
Rhithrogena semicoloratalc
Serratella ignitalc
Siphlonurus alternatuslc
Siphlonurus lacustrislc

In Ireland, six species of mayfly are listed as critically endangered, with two more near threatened (1). All of these species have restricted distributions and it is unfortunately unsurprising that they are classed as such. The are species found in streams and rivers, which points to the increased pressures of pollution that these habitats have had, and unfortunately continue to have (1).

  1. Kelly-Quinn and Regan, 2012. Ireland Red List No. 7: Mayflies (Ephemeroptera). National Parks and Wildlife Service, Department of Arts, Heritage and the Gaeltacht, Dublin, Ireland
  2. Brittain, Michel Sartori, 2009. Encyclopedia of Insects pp. 328-334
  3. Burian, 2009. Encyclopedia of Inland Waters pp. 299-314

Wednesday, December 26, 2012

A Winter-time Orange

Yellow Brain Fungus, Tremella mesenterica
Trees denuned of their leaves can make for many a forlorn vista at this time of the year, but they do provide the opportunity to spot some strange fruit indeed. Arboreal fungi that would otherwise remain obscured are quite visible among the bare branches. One of the most obvious is the shocking-orange coloured Yellow Brain Fungus (Tremella mesenterica). For all the world looking like somebodies discarded worryingly luminous bubblegum, T. mesenterica is (like all members of the Tremella genus) an obligate parasite of other fungi. In Ireland it is most commonly encountered on Gorse (Ulex spp.), where its host is most commonly found growing, fungi of the genus Peniophora. Indeed, T. mesenterica is often found growing on the upper part of a Gorse branch with the Peniophora species producing fruiting bodies on the underneath of the branch (1).
Yellow Brain Fungus, Tremella mesenterica
T. mensenterica's almost cartoonish colour belies an organism that has shown itself to have a number of surprising and useful applications. For example, fruiting bodies of the fungus fed to rats with diabetes have been shown to have a significant effect on the disorder (2). It also posses extracellular polysaccharides that have been shown to have immunomodulatory properties and thus may have potential in anti-tumor and anti-inflammatory treatments (3). Specifically, it has been shown to surpress the production of hormones (human chorionic gonadotropin) associated with tumor cells and therefore may have a role in the chemotherapeutic treatment of certain forms of cancer in the future (4).
  1. Roberts, 1995. Mycologist 9 pp. 110-114
  2. Hui-Chen et al., 2006. Life Sciences 78 pp. 1957-1966
  3. Nan-Yin et al., 2006. Food Chemistry 99 pp. 92-97
  4. Yen-Wen et al., 2006. Life Sciences 79 pp. 584-590

Tuesday, December 25, 2012

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).
  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

Tuesday, December 11, 2012

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.
  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.