How do
you feel about spiders? There are a lot of people who have arachnophobia. Personally,
I find them to be both fascinating and creepy. Hopefully with today’s post I
will increase your fascination of spiders by talking about the Eurasian diving
bell spider, Argyroneta
aquatica, which spends its life
underwater.
A.
aquatic have hydrophobic hairs on their
abdomen and the ventral side of the cephalothorax which help the spider trap
air at the surface of the water. They are also able to create an air-filled
bubble, called a “diving bell”, by forming webs on underwater vegetation. This
bell can act as a “physical gill” by taking up dissolved oxygen from the water
(Seymour & Hetz, 2011).
Besides spending its life
underwater the diving bell spider is different from other spiders because the
males are larger than the females. In many species the females are larger than
the males which mainly depend on variation in female size (Head, 1995). However,
in A.
aquatica males are larger than females
and have a more elongated body. The first legs and chelicerae were also longer
in males. These differences may benefit males because they are more mobile than
females and longer legs help the spiders dive while in the water (Schütz
& Taborsky, 2003). Different pressures may be
influencing the two sexes and causing them to have different body conditions
and shapes. If male spiders are more mobile than females predators may be a greater
risk to the survival of the male spiders. This could result in natural
selection occurring in which slower spiders will be preyed upon and spiders that
are able to travel through the water faster will have a higher fitness.
Here's a short video of the diving bell spider underwater:
References:
Head, G 1995, ‘Selection on fecundity and variation in
the degree of sexual size dimorphism among spider species (Class Araneae)’, Evolution, vol. 49, no. 4, pp. 776-781,
doi:10.2307/2410330.
Schütz, D, & Taborsky, M 2003, ‘Adaptations to an
aquatic life may be responsible for the reversed sexual size dimorphism in the
water spider, Argyroneta aquatica’, Evolutionary Ecology Research, vol. 5, pp.
105-117, <http://www.evolutionary-ecology.com/issues/v05n01/kkar1477.pdf>.
Seymour, RS, & Hetz, SK 2011, ‘The diving bell and the
spider: the physical gill of Argyroneta
aquatica’, The Journal of
Experimental Biology, vol. 214, pp. 2175-2181, doi:10.1242/jeb.056093.
