Wildlife Australia - Spring 2017

REGENERATION AND PARTHENOGENESIS

How do you know whether a worm is male or female? The simple answer is: it’s both.

Worms are hermaphrodites that produce both sperm and eggs. Two worms may

inseminate each other by rubbing together the swollen, ring-like structures, known

plurally as ‘clitella’, that encircle each body near the head and contain both male and

female sex openings called gonopores. Sperm is shared, but an egg is also released by

ovaries and grows in a cocoon-like sac in the clitellum. However, some, such as those

in the genus Amynthas, are able to self-fertilise to produce female offspring using

parthenogenesis – the original ‘virgin birth’. Parthenogenesis isn’t the only incredible feat

earthworms are capable of: amazing powers of regeneration mean they can regrow or

replicate sections of the body, depending on the level and location of the damage.

Left: A lumbricidae earthworm showing the prominent clitellum. Photo: Michael Linnenbach [CC]

garnered the club a ‘Special Prize for the Promotion of Science’
in the 1992 Eureka Science Awards, which must have pleased
participants. The survey results were published in a paper in Soil
Biology & Biochemistry and subsequent studies used EWDU as a
model (for example, earthworm surveys in Wales and Canada).
The data also enabled the publication of a simple key to some
of Australia’s most common earthworm species, especially
useful in populated southern regions. Longer term, Earthworms
Downunder helped biologists determine which species were
influential in Australia, thus directing research priorities. It also
revealed that invasive species, especially those in the European
Lumbricidae family, had colonised huge tracts of Australian soil
within a short time frame. Humans must have greatly assisted
their dispersal, as earthworms are unlikely to travel far on
their own. Earthworms may be accidentally transported large
distances in soil along with potted plants. The cocoons that
contain their eggs – often just the size of a cereal grain – can
sometimes also be carried from one place to another in soil
clods attached to tractor tyres.
We now know that some agricultural soils in Australia lack
earthworms altogether; others are dominated by native species,
yet others by invasive species, and many have combinations of
both. Since EWDU, further benefits have been demonstrated,
such as the burial of top-dressed lime, by vertically burrowing
species, deep into the soil to offset soil acidity – a major throttle
for plant production – and the transfer of key nutrients such as
nitrogen from decomposing plant litter to cereal plants. EWDU
helped demonstrate that the exotic deep-burrowing Aporrectodea
longa, which markedly benefits agricultural soil structure and
function, is essentially confined to Tasmania, thus clarifying
geographic patchiness in our soil fauna. A ‘healthy’ earthworm
community generally features a mix of vertical and horizontal
burrowing species, yet this information indicated that vertical
burrowers were lacking in most agricultural fields in southern
mainland Australia.

Although the Earthworms Downunder project produced great
outcomes, we still need to know much more about the basic
biology and function of native earthworm species, especially in
native ecosystems, and the extent to which invasive and native
species compete, perhaps driving soil processes in different
directions. What are the implications for the restoration of native
ecosystems if exotic soil fauna dominate targeted sites? We
know that invasive European earthworms are currently causing
significant disturbances to the floristics within North American
forests. To protect our beneficial soil invertebrates (and the
vertebrate species that depend on healthy soils, which includes
humans), we need to better recognise which of these creatures
must be controlled and which deserve nurturing – and where.
Further enlisting the help of everyday Australians in their own
backyards might be key to helping us do that.

The green earthworm (Allolobophora

chlorotica), is now widespread in Australia and

has two colour morphs: green and pink.

Photo: Gilles San Martin [CC]

Deep-burrowing species such as

Aporrectodea longa are beneficial

for soils, so are often ‘seeded’

into pastures. Photo: Geoff Baker

THE OTHER 99%

Allolobophora chlorotica takes on a decidedly

green pigmentation in moist soils.

Photo: Maximilian Paradiz

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