Earthworms Flashcards
How long have earthworms been studied for and why are they interesting or important?
Earthworms have been studied for several centuries, and their significance in scientific research has grown over time. The interest in earthworms can be traced back to the 17th century, but it gained momentum in the 19th century with the pioneering work of Charles Darwin.
Here are some reasons why earthworms are interesting and important:
Soil Health and Fertility: Earthworms play a crucial role in maintaining soil health and fertility. They burrow through the soil, creating channels that improve aeration and water infiltration. Their castings (excrement) are rich in nutrients, enhancing soil fertility. This makes them important for agriculture.
Ecological Engineers: Earthworms are considered “ecosystem engineers” because they modify their environment. Their burrowing activities influence soil structure, nutrient cycling, and microbial activity. This, in turn, has broader ecological implications for the habitats they inhabit.
Charles Darwin’s Research: Charles Darwin conducted extensive studies on earthworms and even wrote a book titled “The Formation of Vegetable Mould through the Action of Worms” in 1881. Darwin recognized the significance of earthworms in soil formation and nutrient cycling.
Indicator Species: Earthworms are sensitive to changes in their environment. The presence or absence of certain earthworm species can be indicative of soil quality and environmental conditions. Monitoring earthworm populations can be a useful tool in assessing the health of ecosystems.
Waste Decomposition: Earthworms are excellent decomposers. They break down organic matter, such as dead plant material, and accelerate the decomposition process. This contributes to the recycling of nutrients in ecosystems.
Biological Studies: Earthworms are also studied for their physiology, anatomy, and behavior. They are used as model organisms for understanding various biological processes, including reproduction, regeneration, and responses to environmental stimuli.
Sustainable Agriculture: The positive impact of earthworms on soil health has led to increased interest in their role in sustainable agriculture. Some farming practices aim to promote earthworm populations to enhance soil structure and fertility.
Bioindicators: As sensitive organisms, earthworms are used as bioindicators of soil pollution. Changes in their populations or behavior can indicate the presence of contaminants, making them valuable tools in environmental monitoring.
What did Darwin consider?
-Importance in pedogenesis (earthworms grind and mix soil and organic matter in their guts)
-understood their importance in burial of surface litter
-their role in humification
-their role in burial of archaeological remains
-their contribution to soil fertility (rather than as pests)
-whether earthworms are intelligent
“their sexual passion is strong enough to overcome for a time their dread of light”
“the perception of vibration, seems much the most highly developed”
Soils: a biotic frontier!
Soils are a ‘biotic frontier’ like deep sea vents and tropical forest canopies
Dominant macrofauna in soils = earthworms
Significant role in pedogenesis
Ingest 2-30X body weight per day
Physical, chemical and microbiological properties of soils affected by earthworms
Earthworm ecosystem services
*Soil formation
earthworm mucus binds to minerals and helps form organic part of the soil
Mineral weathering
Humus formation
Burial of surface matter
*Soil structure
Compaction & loosening
Particle size (aggregate) distribution
*Water regulation
Soil porosity
Surface roughness
Effect on bulk density
*Nutrient cycling
N mineralization
*Primary production
increased mineralization
modification soil porosity
biocontrol of pests and pathogens
stimulate microbial activity
What are Anecic?
Anecic species are the largest species of earthworms in the UK and they form vertical burrows
What is an Endogeic earthworm?
Endogeic earthworms live in and feed on the soil. They make horizontal burrows through the soil to move around and to feed and they will reuse these burrows to a certain extent. Endogeic earthworms are often pale colours, grey, pale pink, green or blue. Some can burrow very deeply in the soil.
What are Epigeic?
Epigeic earthworms live on the surface of the soil in leaf litter. These species tend not to make burrows but live in and feed on the leaf litter. (tiger worms red-stripy worms)
Describe feeding ecology
dead plants and mineral components (sandy components enhance gizzard action)
detritivores versus geophages
detritivores – epigeics and anecics
geophages – endogeics
may possess gut symbionts, but may also contain regular soil bacteria rather than gut-specific microbiome
significant level of food selection by particular specieslitterbag experiments
may ingest many nematodes
may eat living roots
Microhabitat searches
deadwood
dung
leaf litter
compost
hedgerows
Earthworm sampling – how?
Mustard sampling using a mustard solution
Onion extract sampling
Soil pit sampling
Earthworm identification
Only readily identify adults
Lack of taxonomic expertise
Molecular tools need labs, money and bioinformatics skills
Need to examine clitellum and tubercula pubertatis
Internal morphology
prostomium
clitellum
Part of the head
The clitellum is a thickened glandular and non-segmented section of the body wall near the head in earthworms and leeches, that secretes a viscid sac in which eggs are stored.
tubercula pubertatis
is a glandular thickening on the clitellum (or. saddle) of adult earthworms.
Earthworms: DNA barcoding potential
Taxonomy, biogeography, community ecology – impossible without reliable i.d.
Possibly many cryptic species – evidence for highly divergent lineages even in well-known species like Lumbricus terrestris
Between spp divergences exceed 15% at COI!
What’s DNA barcoding?
DNA barcoding is a method of specimen identification using short, standardized segments of DNA. Every species has its own barcode, just as every person has their own fingerprint.
Worms are much more diverse than it seems morphologically.
