Wednesday, December 14, 2011

Not Quite an Insect

Campodea spp.
Even though there are only four species present in Ireland (all from the genus Campodea (1)), diplurans are often observed in soils, where they are perfectly adapted to life there feeding on live prey and decaying organic matter amongst the leaf litter. With their lack of eyes, lack of pigment, long tapered bodies and long antennae they resemble miniature centipedes, but their six legs on their three segmented thorax tell another story. Diplurans are hexapods, and while often placed in the class Insecta, they should really be seen as insects' closests relative (2). While sharing many features with insects (body divided into head, thorax and abdomen, three pairs of walking legs, and a segmented abdomen devoid of legs), they are distinguished from insects by having antennae devoid of a chordotonal sensory organ in the pedicel and by the lack of an appendicular ovipositor and of a median unpaired caudal filament (2). Often referred to as 'two pronged bristletails', this name is derived from presence of only one pair of caudal appendages, the cerci. There are about 1000 species of diplurans described present throughout the planet in all but the harshest areas (deserts, polar regions and areas above 3500 metres). Three major lineages exist: Campodeoidea, Projapygoidea, and Japygoidea (3).

  1. Ferriss et al., 2009. Irish Biodiversity: a taxonomic inventory of fauna
  2. Kock, 2009. Encyclopedia of Insects (Second Edition) pp. 281-283
  3. Luan et al., 2004. Pedobiologia 48 pp. 453-459

Saturday, December 3, 2011

What's In A Song?

Technically speaking, birds make two sounds: a call and a song. The call is relatively short and somewhat muted and is used for basic contact or in times of alarm, whereas the song  is a much elaborate and intricate affair and is associated with courtship and mating. Birdsong consists of sequences of smaller discrete units called elements. Groups of elements are combined into intermediate units called syllables, which in turn combine to make songs. If these units, elements and syllables, exist throughout an entire species they are called universal categories (1). 
Male (top) and female Chaffinch (Fringilla coelebs)
The song of the Chaffinch (Fringilla coelebs) is a wonderfully bubbly affair, especially when compared with the simple “pink” that is its call (2). Its song consists of an initial trill of several repeated syllable phrases, followed by a “flourish,” which typically consists of a short phrase of high-pitch elements and one long buzzy element (3). It has been shown that male Chaffinches assess songs differently from females based on the relative length of the trill and the flourish, showing that the differences in the two parts represents a communicative relevance (4). Analysis of Chaffinch song with a dynamic time-warping algorithm showed that the syllables were linked to certain positions within the song and were not randomly distributed (2). This lends further credence to the theory that birdsong has parallels with human language.

  1. Lachlan et al., 2010. Journal of Comparative Psychology  124 pp. 92-108
  2. Sterry, 2004. Collins Guide to Irish Wildlife
  3. Thorpe, 1954. Nature 173 p 465
  4. Leitão et al., 2006.  Animal Behaviour 71 pp. 1289-1296.

Friday, December 2, 2011

Sniffing Out a Meal

Figwort Weevil, Cionus scrophulariae
The wonderfully patterned Figwort Weevil (Cionus scrophulariae) is a fairly common but shy animal in Ireland that can be found on plants of the family Scrophulariaceae. The larvae may also be seen here, covered with a shiny, sticky substance. This is a diffuse peritrophic membrane that acts as a deterent to any potential predators (1). Production of this membrane in the posterior mid-gut stops once the larva has stopped feeding and a new, ribbon-type structures begin to be made which are used to construct cocoons.
Figwort, Scrophularia nodosa
The weevil's main food source is the Figwort (Scrophularia nodosa) from where it gets its name. Figwort is an excellent coloniser, but mainly of waste ground and populations are therefore often scattered across an area. C. scrophulariae can find these populations using odors from Figwort. The larger the patch size of Figwort plants, the stronger the odor and the higher the density of  C. scrophulariae individuals associated with them (2).

  1. Tristram, 1978. Journal of Insect Physiology 24 pp. 391-398
  2. Anderson and Hambäck, 2011. Athropod-Plant Interactions 5 pp. 269-277

Thursday, December 1, 2011

Local Evolution in the Large White Butterfly

Large White Butterfly Larva, Pieris brassicae, feeding
The bane of any gardener attempting to grow a few tasty brassicas, the larvae of the Large White Butterfly (Pieris brassicae) is a rapacious feeder. Reports in the past of 100% crop loss (1) may have been reduced but globally the loss to its main 18 food plants runs to 1% of total yield (2). Such heavy damage by this widespread, Palaerartic species is due to the practice of females laying batches of eggs, as opposed to its close relatives who tend to lay eggs singly (3). The results can be devastating to behold, with plant leaves reduced to skeletal forms.
Large White Butterfly Adult, Pieris brassicae
Like many other insect species, P. brassicae undergoes diapause in response to short photoperiods which serves to outlast periods with unsuitable conditions such as low temperature and low food supplies (4). However, one population of P. brassicae in Andalusia in southern Spain has evolved an additional response to long photoperiods (3). This summer diapause (or aestivation), which is only found in this Spanish population, last three months and represents something of  a major evolutionary novelty, because it cannot have evolved via a gradual transformation of the ancestral photoperiodic response in which only short day-lengths induced diapause. Its role is unclear as the butterfly loses three generations by undergoing aestivation. It has been shown that the attack rate of its main parasitoid, Cotesia glomerata is reduced as a result of aestivation, thus increasing survival rate of the larvae (5).
Large White Butterfly Larvae, Pieris brassicae
  1. Cansdale, 1876. Entomologist 8-9 p. 257
  2. Feltwell, 1978. Journal of Research on the Lepidoptera 17 pp. 218-225
  3. Held and Speith, 1999. Journal of Insect Physiology 45 pp. 587-598
  4. Beck, 1980. Insect Photoperiodism
  5. Pörschmann and Spieth, 2011. Entomological Science 14 pp. 31–36