The Cuckoo Flower

Cuckoo Flower, Cardamine pratensis

As May approaches, so the Cuckoo Flower (Cardamine pratensis) blossoms. This perennial of damp grassland and stream sides has the most wonderful blush-purple flowers atop a stem rising at most 55 cm from a basal rosette of leaves (1). C. pratensis is actually a species complex, comprising a group of species with marked karyological and morphological variation that cover its large range, from Asia, Europe, North Africa and North America (2).Being a plant often present in grazing areas, C. pratensis has the ability to regenerate readily from any damage caused. Adventitious buds on the leaves result in the creation of a 'bud bank' in areas (3). A bud bank is an accumulation of dormant buds in the soil which serves to as a source of plant asexual regeneration after disturbance. When used in concert with seed banks, bud banks of C. pratensis allow the survival and proliferation of populations of the plant.

References:

1. Phillips, 1977. Wild Flowers of Britain p. 18
2. Lihovál et al., 2003. Taxon 52 pp. 783-801
3. Klimešová and Klimš, 2007. Perspectives in Plant Ecology, Evolution and Systematics 8 pp. 115–129

The Problems with the Decline of the Bumble-Bee

Queen Red-Tailed Bumble-Bee, Bombus lapidarius

The decline in bee numbers in Europe over the past 60 years has been a source of concern for a number of reasons. As well as the obvious loss of biodiversity, there is also the problem of a decrease in associated wild plant species and a decrease in the yield of certain crops (1). Bumble bees are no exception to this decline. In Ireland, six of the twenty species recorded are classed as being endangered or vulnerable (2).

Irish Bumble-Bee Species and Their Conservation Status*+

Species	Status
Bombus distinguendus	EN
Bombus ruderarius	VU
Bombus sylvarum	EN
Bombus monticola	LC
Bombus lucorum	LC
Bombus magnus	DD
Bombus cryptarum	DD
Bombus terrestris	LC
Bombus pratorum	LC
Bombus hortorum	LC
Bombus jonellus	LC
Bombus pascuorum	LC
Bombus muscorum	NT
Bombus lapidarius	NT
Bombus barbutellus	EN
Bombus rupertris	EN
Bombus campestris	VU
Bombus bohemicus	NT
Bombus vestalis	NE

One of the possible reasons often cited for this decline is the strict dietary specialisation of certain species (3). Those species who rely on a smaller number of plant species for food should be more threatened. However, this hypothesis is not borne out in the case of the Red-Tailed Bumble Bee (Bombus lapidarius). In Britain, it is a ubiquitous species, yet it has a very narrow floral diet (4), which dismisses the idea that diet alone is the cause of declining bee numbers.

Queen Red-Tailed Bumble-Bee (Bombus lapidarius)

With its red-orange rump and jet black body, B. lapidarius is quite the attractive species. Females can be seen at this time of year looking for burrows under stones in which to build nests (5,6). Unfortunately, B. lapidarius is classed as near treathened in Ireland (2). This decline has come in parallel with a loss of its major habitats here, coastal dunes and unimproved grassland. However as the example above with regards to diet shows, the decline is most likely due to a combination of factors.

*Conservation Status Key: EN=Endangered; VU=Vulnerable; NT=Near Threatened; LC=Least concern; NE=Not evaluated; DD=Data deficient.
+Adapted from Fitzpatrick et al., 2007.

References:

1. Goulson et al., 2008. Annual Review of Entomology 53 pp. 191-208
2. Fitzpatrick et al., 2007. Conservation Biology 21 pp. 1324-1332
3. Goulson et al, 2009. Biodiversity and Conservation 17 pp. 3269-3288
4. Connop et al., 2010.  Biological Conservation 143 pp. 2739-2746
5. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 144
6. Chinery, 1997. Collins Gen Insects p. 250

The Stress of Being a Sparrow

One of the most commonly encountered birds in both town and country is the House Sparrow (Passer domesticus). They are particularly active at this time of year, its mating season (February to May), when individuals and small groups can be seen collecting nesting materials and feeding. Remarkably, P. domesticus has altered its ecology to live in close association with humans. This is thought to have occurred with the development of the first towns and cities, when animals such as horses filled the streets with their seed-rich droppings (1). Such adaptability has given it a vest range, covering most of Africa and Eurasia. Introduction to North America took place in the 1850s on the East Coast of the US: colonisation was so intense that it took only 50 years for P. domesticus to reach the Pacific coast (1). Due to its affinity for human habitation however, it tends to be only locally common in areas (2). The drab looking females contrast with the well marked males, who show contrasting grey, chestnut and black colours.
 

Male House Sparrow, Passer domesticus

As social birds, flocks of P. domesticus are subject to strict hierarchies, and it has been found that these hierarchies are maintained by the physiological state of the bird, namely their size (3). Birds of a large size tend towards dominant positions within the hierarchies, with smaller birds being subordinates. When these positions were altered experimentally, with smaller birds being installed as dominants and vice versa, it was found that both groups suffered increased stress (measured as corticosterone concentrations, energy expenditure and immune functions) as a result of their new positions (4). When the birds were then given a choice of social position they reverted to type, with smaller birds opting for subordinate positions and larger ones for dominance.

References:

1. Beletsky, 2006. Collins Birds of the World pp. 404-406
2. Sterry, 2009. Collins Complete Guide to Irish Wildlife p. 90
3. Goymann and Wingfield, 2004.  Animal Behaviour 67 pp. 591– 602.
4. Lindström et al., 2005. Hormones and Behavior 48 pp. 311 – 320

A Loveliness of Ladybirds*

A Loveliness of Seven-Spot Ladybirds, Coccinella septempunctata

The Seven-spot Ladybird (Coccinella septempunctata) is the most common species of ladybird present in Ireland, often quite abundant in areas. Adults are emerging, or have emerged, from hibernation at this time of year and will remain active until October (1). It is a species that is widespread throughout the palaearctic region, and its success is due to a high degree of ecological plasticity. It is a highly mobile beetle, and capable of thriving in a variety of different habitats (eurytophic). Its can also be considered polyphagous in its diet, with at least 24 species of aphid being counted as prey (2). Post emergence from hibernation, when aphid number are be quite low, C. septempunctata will feed on nectar and pollen from a variety of plants. Females can also suspend oviposition in the presence of already hatched larvae, which avoids any problems of cannibalism. When eggs are layed, an excess of offspring for the carrying capacity of local food resources often results, which allows C. septempunctata to take advantage of unpredicatably occuring aphid populations (2).
 

Evidence of eurytophy in Coccinella septempunctata: larvae on a sand-dune

While numbers of C. septempunctata remain high in Ireland, they may soon be under threat from the invasive Harlequin Ladybird (Harmonia axyridis) which can not only out-compete, but also feeds on C. septempunctata larvae. The breeding site for H. axyridis reported on this blog last year (but sighted in 2012) along with another from Co. Carlow are worrying developments.

*The title of this post comes from the collective noun for a group of ladybirds, a loveliness.

References:

1. Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 150
2. Hodek and Michaud, 2008. European Journal of Entomology p. 1-12

A Floral Attraction

A Drone Fly, Eristalis tenax

One of the first large insects to be conspicuous at this time of year is the family of hoverflies known as Drone Flies (Eristalis spp.). The availability of pollen and nectar from the newly emerged catkins of willow provide a bountiful supply of food for the flies, and as the number of plants in flower increases, so will their numbers. Their common name, Drone Flies, comes from their resemblance to bees, a form of Batesian mimicry that no doubt gives them some degree of predators. Their larvae employ no such disguise and are quite distinctive, possessing a long respiratory tube attached to their anal gills that enables respiration as they are buried in the mud and earning them the name 'Rat-Tailed Maggots' (1).

Eristalis tenax covered in Willow pollen after feeding

Yet, watching one of the most common of the Drone Flies currently in flight, Eristalis tenax, flit from flower to flower in search of food does beg the question how do they know where the food is. How do they know that a flower is a flower? The answer is a variety of olfactory and visual signalling structures used by plants to attract insects. E. tenax in particular is attracted to yellow flowers, or yellow spots on flowers, with light in the colour range of 510-600 nm (green/yellow light) releasing the extension of the proboscis (2). Flowers use guide lines to attract the flies from a distance, which are also most effective when yellow (3). Attraction to the yellow colour is due to the fact that this is the colour of pollen, food for E. tenax. This explains it eliciting a feeding reaction.

Identification of Eristalis spp. is notoriously difficult, so I was very grateful to Stuart Dunlop at the Donegal Wildlife blog for his tips on identifying E. tenax.

References:

1. Robinson, 2005. Handbook of Urban Insects and Arachnids p. 188
2. Lunau, 1995. Plant Systematic and Evolution 198 pp.  235–252
3. Dinkel and Lunau, 2001. Journal of Insect Physiology 47 pp. 1111–1118

Triumph in Shade

Opposite-Leaved Golden-Saxifrage, Chrysosplenium oppositifolium

Flowering at this time of the year locally along shady stream banks and woodland flushes, the Opposite-Leaved Golden-Saxifrage (Chrysosplenium oppositifolium) is a wonderful, almost ephemeral plant. Its delicate yellow-green flowers that lack petals are found on stems that will root to form often dense patches, rarely rising over 10 cm high (1). Thriving as it does in such wet but moreover shady conditions, C. oppositifolium is remarkably adapted to the problems associated with living in low levels of light. As a shade adapted plant, C. oppositifolium has developed thinner leaves than its light loving close relatives (other members of the Saxifragaceae, eg. Saxifraga spathularis). Thin leaves are prone to sugar leakage, which can lead to fatal fungal infections. C. oppositifolium counteracts this threat by using sedoheptulose as its principal soluble sugar (2). This, being a 7-carbon sugar, is not readily metabolised by fungi giving C. oppositifolium a distinct advantage.

References:

1. Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 208
2. Crawford, 2008. Plants at the Margin: Ecological Limits and Climate Change p. 256

A Model Plant

Thale Cress, Arabidopsis thaliana

An inconspicuous weed of waste ground and walls throughout Ireland, and indeed much of the northern hemisphere, Arabidopsis thaliana (Thale Cress) doesn't look much. With tiny white flowers on a long stem arising from a neat rosette of leaves, the whole plant rarely grows over 40 cm high (1). Yet its small size belies its enormous stature as a model plant in genetics. Research on Arabidopsis has resulted in priceless information a variety of plant mechanisms such as how flowers develop and how plants control their circidarian rhythms (2). In terms of publication in the scientific literature, Arabidopsis is by far and away the most thoroughly studied plant in the world: in 2008, for example, 3500 papers were published on the plant (3).

Thale Cress, Arabidopsis thaliana

But why is it such an important plant? Economically it has no value, either as a food stuff or as a raw material. Crucially, Arabidopsis possess features that make it very suitable for genetic research, namely a short generation time, a small physical size that limits the need for growth facilities and prolific seed production through self pollination. It has a small genome, just 157 megabase pairs in length with just 5 chromosomes making it ideal for gene mapping (3).

Thale Cress, Arabidopsis thaliana

Such seemingly suitability is really only part of the story however when explaining its enduring  popularity as a model organism. Tireless work by a number of individuals in experimentation and analysis of Arabidopsis has also help elevate it to the plant par excellence in genetic research. The first research carried out on Arabidopsis was by Friedrich Laibach who determined the correct chromosome number during his PhD research in 1907 and published a compelling argument for its case as a model for genetic studies in 1943 (3). The Hungarian botanist George Rédei, working in the United States, continued to work on the plant in the 1950's and it was a review published by him in 1975 (4) that lead researchers such as Chris Somerville, Elliot Meyerowitz, Maarten Koornneef and David Meinke to realise its potential as a genetic model. Through collaboration and conferences they, among others, helped establish a vibrant network and a critical mass of information that lead to Arabidopsis' currently importance.

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife
2. Reeves and Coupland, 2000. Current Opinion in Plant Biology 3 pp 37–42
3. Koornneef and Meinke, 2010. The Plant Journal  61 pp. 909–921
4. Rédei, 1975. Annual Review of Genetics 9 pp 111-127