Snails Are Eating My House

The Garden Snail, Helix aspersa

With spring approaching fast, thoughts turn to the garden, specifically what vegetables to plant. Lettuces are always a good bet, some nice butterhead and iceberg, as they always get used. The trick is to sow them in a staggered fashion, avoiding them all coming good at the same time and having to find a plethora of lettuce recipes. Thoughts of planting them though also induces mild panic at the prospect of controlling their mollusc pests. One of the greatest of these is the Garden Snail (Helix aspersa, synonym: Cornu aspersum), a generalist herbivore that will also attack other crops as well as ornamentals in the garden (1). With its marbled brown and black shell to maintain, H. aspersa needs to take in a diet rich in calcium and its preferred diet shows plants rich in this mineral (2). Analysis of faecal matter has shown one of the most popular of these to be stinging nettles (Urtica dioica), a plant with a high calcium levels (3).
Areas with poor soil condions results in plants with low calcium levels, so H. aspersa has turn to other sources. Remarkably in 1999 damage to the paint work on houses in parts of Britany in France were shown to be the result of H. aspersa's feeding action (4). Further investigation showed that snails presented with 16 different watercolour paints showed a preference for those with higher calcium content (5).

References:

1. Capinera, 2001. Handbook of Vegetable Pests p. 570
2. Chevalier et al., 2003. Malacologia 45 pp. 125-132
3. Chevalier et al., 2001. Comptes Rendus de l'Académie des Sciences - Series III - Sciences de la Vie 324 pp. 979-98
4. Chevalier and Charrier, 1999. Rapport de Contrat pour la SOGEFI p. 42
5. Charrier, 1999. Peintures, les escargots attaquent, que choisir pp. 46-47

Guillemots and the Climate Change Mistake

Its nearly February and the weather persists in being unseasonably mild. A cold snap is forecast in the next few days but, touch wood, it shouldn't go near matching the bitterness of our previous two Irish winters. The consequences of this warm weather, garden bulbs in full bloom, frogs spawning early, may bring delight to us in banishing the darkness of winter from our minds, but they also serve to remind us of the ever present problem of climate change. It is fact that birds are breeding and singing earlier, migrant birds are arriving earlier, butterflies are appearing earlier and plants are shooting earlier (1). This blog has reported on dragonfly species increasing their European range northward into Ireland. The effects of climate change on fish species in the oceans is one of the most worrying, due to its knock on effect on other associated species and on the consequences it holds for commercial fisheries. In the North Sea, cod, anglerfish and snake blenny have all shifted their ranges further northwards (2).
 

Common Guillemots, Uria aalge, during breeding season

However, there is a risk in attributing too much to climate change and not recognising the effect humans activity may have directly in changes to species distribution and behaviour. An example of this is the virtual extinction of the Common Guillemot (Uria aalge) in Atlantic Iberia. This wonderful, chocolate-brown coloured auk numbered c. 20,000 individuals in Atlantic Iberia in the first half of the 20th century, the largest population of any seabird in the area. By 2004 it was considered quasi-extinct, with no no breeding attempts recorded since 2003 (3). Such a dramatic decline was thought to be a result of climate change as the Iberian population was at the southern most limit of the species, and thus prone to extinction under natural conditions. A reexamination of the data from the extinction however, revealed that climate change was not to blame. The largest population crash occurred from 1960 to 1974, when annually there was a decline of 33.3%. This period saw good climate conditions and higher or sustained availability of pelagic prey fish, but also marked a rapid shift away from using vegetal based nets in commercial fishing to those constructed from synthetic materials (3). This points the finger directly at another human-mediated extinction. It also shows how easy it is to attribute much to climate change without assessing the role we have directly in the survival of other species.

References:

1. Walther et al., 2002. Nature 416 pp. 389-395
2. Perry et al., 2005. Science 308 pp. 1912-1915
3. Munilla et al., 2007. Biological Conservation 207 pp. 359-371

The Many Patterned Cuckoo-Spit Froghopper

Two Cuckoo-Spit Froghoppers, Philaenus spumarius, mating

Philaenus spumarius, the Cuckoo-Spit Froghopper, is one of the commonest bugs in Irish hedgerows and gardens, especially from June to August when the green-ish nymphs are quite conspicuous due to their habit of hiding in a mass of spit-like bubbles which shield them from predators (1). The adults remain well hidden though, thanks to their excellent camouflage. However the pattern of this camouflage is highly variable, so variable in fact that it has led to up to 50 different synonyms being used for P. spumarius (2).

Cuckoo-Spit Froghopper nymph

Polymorphism such as this is common in many other animal species and while the mechanisms controlling it has been much source of debate, it is accepted that control is genetically based on alleles of gene loci (3). Although P. spumarius is of holartic distribution, levels of polymorphism have been found to be highest in the Mediterranean, now thought to be the point of origin for the species (4). Here, polymorphism is selected for based on visual selection, specifically to avoid predators during the long obligatory period of aestivation that P. spumarius undergoes. Since vegetation on which the eggs are layed and development takes place soon vanishes in the harsh weather of the Mediterranean, individuals soon have to move to other hosts, various shrub and tree species. 

The Cuckoo-Spit Froghopper, Philaenus spumarius

However, in more northern parts of Europe, vegetation cover remains ever-green meaning movement is not needed and removing the visual selection for polymorphisms. Yet it does occurs in these areas too, most probably due to gene flow drift (4).

The Cuckoo-Spit Froghopper, Philaenus spumarius

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 132
2. Nast, 1972. Palaearctic Auchenorrhyncha (Homoptera), an annotated Checklist
3. Halkka and Halkka, 1990. Evolutionary Biology 24 pp 149-191
4. Drosopoulos et al., 2010. Zoosystematics and Evolution 86 pp. 125-128

Oysters Hitch a Ride

Common Saddle Oyster, Anomia ephippium

Unlike most other bivalves, the Common Saddle Oyster (Anomia ephippium) does not bury itself in the sand or mud of the sea bed. Instead they cement themselves to rocks or other hard substrates by chalky byssus threads that grow through a hole in the lower shell (1). They are experts at early colonisation of a substrate, and are often the among the first organisms to do so at a new location (2), something which is evident from the pictures included here, showing colonisation of an abandoned water drum by many A. ephippium individuals. So quick are they to colonise in fact, that smaller individuals can be seen growing on some of the larger ones. Unfortunately for them the drum had washed quite far up a beach and partially filled with sand, making a return to the water unlikely. Growing up to 6 cm across, younger, smaller individuals can appear almost translucent with older examples being white to pale brown in colour (1).

A water drum, washed up a a beach with Common Saddle Oyster, Anomia ephippium growing on the surface

 

References:

1. Challinor et al., 2003. A Beginner's Guide to Ireland's Seashore p. 123
2. Bramanti et al., 2003. Italian Journal of Zoology 70 pp. 175-178

Winter Feeding by the Goldfinch

Goldfinch, Carduelis carduelis

While some of the Irish population of Goldfinch (Carduelis carduelis) migrate in the winter, the majority are present all year round (1). The bulk of C. carduelis diet in the summer and autumn is comprised of seeds of various plants, various thistle species in particular (2). The unavailability of these in the spring and winter has resulted in C. carduelis being a common visitor to bird feeders in suburban gardens. However, as these are not the most reliable of food sources, C. carduelis relies on insects throughout the lean months to feed. At this time of the year it is common to see flocks of C. carduelis alighting on trees throughout the country to feed on insects present among the branches, as is evident in the picture below and above. Behaviour of the bird will change with the sizes of these flocks. Individual birds in larger flocks become less alert and consume up to 20% more food (3). However, travelling time to the nest feeding spot is also increased as is the likely hood of a larger flock attracting predators.

Goldfinch, Carduelis carduelis

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife
2. Glück, 1985. Ibis 127 pp. 421-429
3. Glück, 1987. Ethology 74 pp. 65-79

Lichen Photobionts

Photobionts in a lichen get a raw deal in the naming department. The algal or cyanobacterial partner in the relationship may do all the hard work of using light to make glucose but lichens are named after their fungal component This might seem an unfair outcome until one considers that there are c. 15, 000 fungal species described for lichens but only c. 100 photobiont species (1). So its not taxonomic snobbery, its a case of the fungal partner being the more distinguishing of the two. However, although they may not be distinguishing, I do feel that they are rather distinguished. Below are examples of genera of two of the more common photobionts isolated from their respective partners:- Trebouxia (an algae and termed a phycobiont) and Nostoc (a cyanobacteria and termed a cyanobiont). While many lichens have both phyco- and cyanobionts, one dominates and is termed the primary photobiont (2). 90% of lichens contain phycobionts, the remaining 10% having cyanobionts (1).

Trebouxia sp. (centre) isolated from Ramilia fraxinea

Nostoc sp. (chain of cells in centre) isolated from Collema cristatum

References:

1. Lücking et al., 2009. American Journal of Botany 96 pp. 1409-1418
2. Whelan, 2011. Lichens of Ireland pp. 4-5

Fighting Infection the Apine Way

Common Carder Bee, Bombus pascuorum

This is the time of the year for getting sick. That's not a statistic, its just personal experience. The cold and dark days mean we spend more time cooped up in close proximity to others: others who are sick. And so it spreads to us, whatever it may be, laying us low till our immune systems kick in and get us back on the road. Yet if being close to other, infected individuals is a risk of disease, it must be hell for bees. Take the Common Carder Bee, Bombus pascuorum. A eusocial bee, it nests on the ground in colonies of up to 200 individuals (1). Break out the cough syrup, bee sized spoons.
 

Common Carder Bee, Bombus pascuorum

However, B. pascuorum has a sophisticated defence system for dealing with infection. A tough, outer cuticle must first be breached by invaders (2). If they are successful in getting past this first line of defence, a complex interaction of innate humoral and cellular immune reactions are activated in both the bee's tissues and haemocoel (2). Probably the best characterised of these responses is the synthesis of antimicrobial peptides. B. pascuorum produces a defensin, an apidaecin, an abaecin and an N-terminally blocked molecule which provides the bee with antimicrobial activity against fungi, Gram-positive and Gram-negative bacteria (2).
 

Common Carder Bee, Bombus pascuorum

Such a sophisticated defence system does have its drawbacks. Parasitism of B. pascuorum by species of Conopid fly is common (3), but often the hosts show no obvious effect due to the action of the defensive system. Activation of this system is quite energy expensive and under limiting food conditions (which is increasingly becoming the norm for bee populations in Ireland and Europe as a whole(4)) leads to significant decrease in survival (5).

References:

1. Chinery, 2004. Collins Gem Insects p. 251
2. Rees et al., 1997. Insect Biochemistry and Molecular Biology 27 pp. 413-422
3. Moret et al., 2000. Science 290 p 1166-1167
4. Brown and Paxton, 2009.  Apidologie 40 pp. 410-416
5. Moore, 2002. Parasites and the Behaviour of Animals p. 209