biology zoology blog benno meyer rochow parasites

Advantages of Handicaps and Entertaining Parasites: such situations do exist

Situations in which it can be an advantage to possess a handicap do exist and not just for men who want to avoid having to serve in the army, or girls with big breasts who can’t run or jump well but may get a movie contract, or individuals who exaggerate a condition in order to be selected to participate in the Paralympics. When visiting the Apatani in Arunachal Pradesh (India), the explanation given to me why their women used to have large holes with a piece of wood in the alae of their noses (the wings of the nose), I was told that it was to make them look ugly, unattractive. That must have been a handicap, but whether true or not, women with such nose perforations would have been less likely to be stolen or kidnapped by marauding tribes than women with more beautiful noses. Nowadays younger women no longer follow that practice.

A better example (also involving humans) are people, especially in tropical Africa that suffered from an anaemic condition caused by mutated blood cells that did not have the typical disc-like shapes but resembled a crescent or sickle. Although people suffering from sickle cell anaemia as the condition is called have a life expectancy of between 40 and 50 years (which is certainly not an advantage), they do, however, have the advantage of not getting ill with malaria: the organism causing malaria like Plasmodium spp. cannot use the abnormal red blood cells of people suffering from sickle cell anaemia. This advantage led to an increased number of people carrying the sickle cell gene in their genome and explains why sickle cell anaemia sufferers are much more common in African rather than European populations.

However, irrespective of whether African or European, parasitic worms can be present in both of them and although generally disliked, some of the gut parasites can indeed be beneficial. First of all, it’s been known that a single tapeworm residing in a person’s gut tries to prevent other tapeworms to settle there as well and entertaining one rather than a whole crowd is certainly the better option. Modern research credits certain parasitic helminths (so-called flukes) and nematodes (= round worms) with assisting the immune system of their human host. It is claimed that human hosts harbouring parasitic worms such as those mentioned above are less frequently later in life to develop atopic disorders like for example Crohn’s bowel disease, asthma, allergic urticaria, etc. than people not playing hosts to the parasitic worms.

In animals it easy to understand that an abnormal honey bee that cannot sting or has an abnormal stinging apparatus has an advantage, because “normal” honey bees lose their lives when they sting someone: their barbed stinging dart stays in the flesh of the victim and pulls out the gut of the departing bee, actually disemboweling the poor bee. An interesting example of a handicap that turns out a blessing is that of some male fish of a variety of species. These supposedly male fish lack some of the masculine traits, are weaker, avoid fights and overall can be so effeminate that they are not being chased out of a truly male male’s territory, but are tolerated. Individuals such as these, by being handicapped for not being strong and aggressive like real males, can sneak up to female fish and mate with them secretly and without being discovered by the masculine males. A somewhat similar situation would be male crickets unable to sing and attract females. However, the non-singer if placed not too far from a singer can intercept an approaching female, thereby avoiding the danger of being detected by a parasitic fly that finds its host by its host’s sound.

A most peculiar case is that of the parasitic Cymothoa exigua, which attaches itself to its host fish’s tongue and causes the tongue to atrophy (decrease in size until it has all but disappeared). This parasitic isopod then replaces the lost fish tongue with its own body, so that the fish can use the parasite as if it were its own normal tongue. If this may be a borderline between parasitism turning into symbiosis, my last example is even more problematic. Plant growth on top of a Papua Niugini weevil’s wing covers must impair the beetle’s movements (a disadvantage), but being more difficult to be seen has to be an advantage for the weevil and so the awkward epiphytic growth on the back of the beetle turns out to be beneficial in the end.

© Dr V.B. Meyer-Rochow and, 2020.
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