Sea Cucumbers

I never enjoy getting sick, especially if it’s a sickness like the flu in which vomiting is a normal occurrence.  It is one of the most unpleasant feelings I think I’ve experienced. If I could never vomit again I would be one of the happiest people alive. It’s easy to understand why I would hate to be a sea cucumber, which basically vomits as defence mechanism.The sea cucumber Holothuria forskali will expel Cuvierian tubules when they are irritated. These tubules will then lengthen, become sticky and immobilize organisms (Vandenspiegel et al., 2000) by entangling the predator. These tubules are connected to the small and large intestines in the posterior part of the animal. Not only do they entangle the predators but they are also toxic which is effective against non-specialist predators (Dyck et al., 2011).

Normally when an organism loses an organ it is unlikely to survive. However, after the sea cucumber expels these tubules they will regenerate. Regeneration occurs immediately when many tubules have been expelled, but if only a few tubules were expelled there is a short period before regeneration occurs. Even though the tubules are regenerated it takes five weeks for them to be totally regenerated (Vandenspiegel et al., 2000). This brings up the question as to whether or not it is worthwhile to expel these tubules. In most cases when an organism is being preyed upon there is a flight or fight response. In the case of the sea cucumber it can’t run away very quickly but it doesn’t have a traditional method of fighting either. It doesn’t have to expel all of its tubules at one moment and as long as it has some tubules to expel, the sea cucumber has a method of fighting predators. Since the tubules do regenerate it isn’t losing its ability to fight either.

Here's a video about the sea cucumber:

References:

Dyck, SV, Caulier, G, Todesco, M, Gerbaux, P, Fournier, I, Wisztorski, M & Flammang, P 2011, ‘The triterpene glycosides of Holothuria forskali: usefulness and efficiency as a chemical defense mechanism against predatory fish’, Journal of Experimental Biology, vol. 214, pp. 1347-1356, doi:10.1242/jeb.050930.

Vandenspiegel, D, Jangoux, M & Flammang, P 2000, ‘Maintaining the line of defense: regeneration of cuvierian tubules in the sea cucumber Holothuria forskali (Echinodermata, Holothuroidea)’, The Biological Bulletin, vol. 198, no. 1, pp. 34-49, < http://www.biolbull.org/content/198/1/34.short>.

Snapping Shrimp

Whenever I think about the ocean I picture a relaxing and quiet realm. There’s probably coral and the fish that live there. I don’t normally picture there being a species of shrimp that disturbs the silence.

The snapping shrimp (Alpheidae) has a large snapper claw that it can close rapidly and produce a loud snapping sound. The snapper claw has a plunger and socket, when the claw is closed rapidly the plunger is pushed into the socket causing water to be displaced. A fast water jet is created from the collapse of a cavitation bubble (Versluis et. al, 2000). Because cavitation bubbles collapse quickly shock waves are emitted (Lauterborn & Ohl, 1998). The shock waves created by the snapping shrimp can be used as a means of communication, defence, or predation (Versluis et. al, 2000).

Even though sensory hairs on the snapping claws are used for communication (Versluis et. al, 2000), it is thought that the evolution of this claw did not occur for intraspecific fighting but for predation. The nutritional advantage of individuals likely contributed to the original evolution of this claw (Collier & Stingl, 2013). The more efficient and powerful an individual’s claw is the more likely the individual is of obtaining food and therefore passing on genes to future generations. The sensors on the claws are helpful in determining the size of claws an opposing shrimp has and help the shrimp determine whether or not it should fight their opponent. However, some large-clawed individuals may try to use deceit to prevent fighting to the death because there is little advantage (Collier & Stingl, 2013). In most cases deceit isn’t a common behaviour because it has a high risk. Many times the cost of the deceitful action may be higher than the benefit and therefore harm an individual.

Watch the snapping shrimp in action:

References:

Collier, J & Stingl, M 2013, ‘Evolutionary Moral Realism’, Biological Theory, vol. 7, no. 3, pp. 218-226, doi:10.1007/s13752-012-0067-x.

Lauterborn, W & Ohl, CD 1998, ‘Cavitation bubble dynamics’, Ultrasonics Sonochemistry, vol. 4, no. 2, pp. 65-75, doi:10.1016/S1350-4177(97)00009-6.

Versluis, M, Schmitz, B, Heydt, A & Lohse, D 2000, ‘How snapping shrimp snap: through cavitating bubbles’, Science, vol. 289, no. 5487, pp. 2114-2117, doi:10.1126/science.289.5487.2114.

Underwater Spider

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.

Exploding Termites

Welcome to Exploring Rare Adaptations! As the title suggests, I will try to understand why different animals have the adaptations that they do. If you are curious about any strange adaptation an animal has and want me to investigate it for you let me know in the comments.

Today, I thought we would look at Neocapritemas taracua which is a species of termites that is capable of exploding and releasing a toxic substance. The older workers in a colony have a higher toxicity level than younger workers and are therefore more likely explode. The toxicity level of the termites is determined by a blue crystal which is embedded in the termite. As a worker ages the crystal increases in size. The crystals are produced by specialized glands called “crystal glands” which are located under the epidermal cell layer and in the anterior portion of the pouch (Šobotník et. al., 2014).

Is there another reason that older workers are more toxic than younger workers? Over time the mandibles of the workers wear out and cannot be renewed through moulting (Šobotník et al., 2012). This suggests that a form of kin selection may be occurring in this population. Kin selection is selection affected by how related individuals are to each other. Kin selection can also result in altruism which is an action that directly decreases the fitness of the one performing the actor and benefiting the recipient (Foster et al., 2005). In this case the older workers will protect the younger workers by attacking a predator. By provoking the predator the older worker’s pouch that contains the toxic substance will likely be ruptured. The toxic substance will cover the predator with a sticky incapacitating substance (Šobotník et al., 2014). The younger worker will be protected with the older workers suicidal defence.

Here’s a short video of how the termites will defend their colonies.

References:

Foster, KR, Wenseleers, T, & Ratnieks, FLW 2006, ‘Kin selection is the key to altruism’, Ecology and Evolution, vol. 21, no. 2, pp. 57-60, viewed 10 March 2016, doi:10.1016/j.tree.2005.11.020.

Šobotník, J, Bourguignon, T, Hanus, R, Demianová, Z, Pytelková, J, Mareš, M, Foltynová, P, Preisler, J, Krasulová, J, & Roisin, Y 2012, ‘Explosive backpacks in old termite workers’, Science, vol. 337, no. 6093, pp. 436, viewed 10 March 2016, doi:10.1126/science.1219129.

Šobotník, J, Kutalová, K, Vytisková, B, Roisin, Y, & Bourguignon, T 2014, ‘Age-dependent changes in ultrastructure of the defensive glands of Neocapritermes taracua workers’, Arthropod Structure & Development, vol. 43, no. 3, pp. 205-210, viewed 10 March 2016, doi:10.1016/j.asd.2014.02.003.