Dr Meyer Rochow bio essay : "Hitching a ride"

Teeth

Something to chew on

Many years ago on a Caribbean Cruise I met a man who had made a fortune with artificial teeth or, to be more precise, with developing chemicals for colour nuances between snow white and yellowish brown. I learned from him that human teeth display hundreds of subtle hues and of course jacket crowns or dentures need to resemble the natural teeth of a person.

Teeth, as we all know, hold important clues for the criminologist, but also for the palaeontologist studying distribution and evolution of vertebrates. Teeth are extremely durable; they are useful for seizing and chewing food and consist of bonelike material called “dentine” capped with the even harder “enamel”. Teeth in mammals can be categorized as incisors (the front teeth), canines (the corner teeth), and molars (the grinding teeth further back), but dolphins seem to lack dental specializations. Apart from their biting and chewing function, teeth may have other roles to play. In humans speech without teeth becomes slurred and difficult to understand. Baring of the teeth has signal function not only in humans, but many species, e.g., dog, monkey, horse, etc. Teeth in mole rats are used as “digging tools” to excavate the subterranean tunnels these rodents live in and large visible teeth may be a sexual characteristic as, for example, in boars, musk deer etc. In the pig deer (Babyrousa babyrussa) of Sulawesi, canine tusks of the male actually grow upward through the flesh of the snout and, continuing to grow, may even penetrate the animal’s skull!

Teeth can also be formidable weapons in defence, even if useless for biting and chewing: the tusks of elephants and hippopotamuses come to mind. But while the up to 80 cm long and six kg heavy tusks of the hippos are anatomically canines, those of the elephant are incisors. Incidentally, the world’s first plastic (namely celluloid) was invented by John Hyatt in 1865 to protect elephants, whose tusks, i.e. the ivory, was used to manufacture billiard balls for the increasingly popular cue sports like snooker etc. Some of the most complicated teeth are not found in mammals, but in snakes and certain deep sea fishes. Some venomous serpents possess hollow teeth with a canal inside for injecting or spitting venom, while some deep-sea fish may sport hinged and dagger-like teeth of grotesque proportions. And talking about fishes, sharks actually carry teeth not only on their jaws but much smaller ones, yet nonetheless proper little teeth, all over their body. Birds do not normally have teeth, but very occasionally reports of birds with a couple of teeth have been published, which serves as a reminder that the birds’ ancestors were indeed reptiles – and they did have teeth.

Although most mammals have two generations of teeth (milk and adult teeth), the proverbially lazy sloth produces only one set. A single over one metre long tooth is the rule in the Arctic narwhale male and a few mammals like the Australian platypus and anteaters have no teeth at all when adult. However, how silly zoological nomenclature can sometimes be shows the example of the armadillos: classified as “Edentata” (toothless animals), they actually possess more teeth than many other mammalian species. And toothless humans? Well, they are being helped by my acquaintance from the Caribbean Cruise.

thirst ship sheep sailor evolution

Let’s embark on another ship with this story!


© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

animal-zoology-parasite-benno-meyer-rochow-science

Hitching a Ride

Animal Hitchhickers

I hadn’t seen any for a long time, but last weekend I even accepted one of them in my car: hitchhikers. However, chances are you go for a hike in the Papuan bush (or tropical jungle for that matter) and you will come across some evil animal hitch-hikers, waving their sucker-armed front ends of their wormy bodies at you: leeches, terrestrial blood-thirsty ones. They sit on wet leaves or stones next to jungle paths, frequented by humans and animals, and wait to hitch a ride (and a blood meal) from a host and when satiated drop off again at a different location. But not all terrestrial leeches feed on blood (there are many species that prefer to gobble up earthworms) and there are other less blood-thirsty animals that get around by hitching a ride.

Examine some of the older, weaker blowflies buzzing against the window pane in a desperate attempt to get out, and you may occasionally find one that carries one, two, or even more 1-2 mm long pseudoscorpions on its body. The world record, incidentally, is 15 such tiny creatures on a single fly. Pseudoscorpions resemble scorpions, but lack the “stinger” (the long tail filament) and are also often referred to as book scorpions. They use flies as a means of transport without harming them. Pseudoscorpions are small, have tiny legs, cannot hop or fly and in order to disperse need to find transport – and what could be better than a big and tired blowfly, whose attempts to brush off the hitchhikers usually come to nothing?

The same can be said for many species of tiny mites, which climb “aboard” bigger insects like beetles and large spiders to get around. Dung beetles are a favourite vehicle for the tortoise mite, because it loves dung, but is too small and slow to crawl by itself from one dung pad to another. For it and other dung inhabitants like a roundworm by the name of Pelodera sp., to attach themselves to dung beetles is the perfect choice before a cow pad dries up. Similarly, pollen or nectar loving mites whose life span vastly extends that of the flower they are feeding on, need to reach another fresher flower before the old one wilts and such a journey is best achieved by hanging on to a flower-visiting transport insect as a stowaway.

In the sea there are many more examples of species of animals using others for transport. Remoras are fish whose dorsal fin has become a sucker organ and although the remoras can swim very well, to cover greater distances (and to be nearer some food that remains uneaten by their hosts) they attach themselves with their sucker to the underside of large turtles and fish like sharks and manta rays for example. Since the remora fish do not feed on their hosts and do not critically impair the latter’s swimming performance, they -just like the aforementioned pseudoscorpions, mites and round worms- cannot be termed parasites. Hitchhikers that do not negatively affect their hosts are termed “phoretics” and how they get around is known as “phoresy”. Having explained that, it becomes obvious that the blood-sucking terrestrial leeches, referred to at the start, or fleas are not phoretics, but parasites, ectoparasites to be precise. However, even if phoretics can’t be called parasites, they too, like human hitchhikers, can sometimes become a bit of a nuisance and difficult to shake off again. So, the step from being a phoretic to being a parasite isn’t a very big one.


roundworms insect science biology

For real parasites, read this article about roundworms!

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

roundworms insect science biology

Wriggling to Success

Who could beat the roundworms?

When zoologists mention the term “successful” in connection with animal species, they mean something different from the success that a sportsperson, a business manager or a movie star might be talking about. A successful animal species or animal group, referred to as a “taxon”, is one that is widespread and has been able to exploit a variety of different habitats. Clearly, insects are very successful as a group, for they occur in virtually all terrestrial habitats. But the emphasis has to be on “terrestrial”, because there are almost no marine species, yet more than 70% of the Earth is covered by oceans!

One of the truly most successful animal groups are the roundworms, i.e. nematodes as they are known to the zoologist. All of them in contrast to, for example, the earthworm have an unsegmented round body and the vast majority of them are microscopically small, though Ascaris, the horse roundworm, can grow to pocket ruler length and the giant amongst the roundworms, which lives in the placenta of whales, may reach more than a metre in length.

Roundworms exist in and on the soil, in and on other animals as well as plants and I have recently found several species inside the gut of millipedes. Some species occur in the deep sea, others call the desert home; some thrive in vinegar and even in the soggy, circular beer coasters of Bavaria roundworms have been found. Humans, especially children, may be hosts of the pinworm Enterobius vermicularis (a rather harmless parasite), but hook worms, Trichinella species and the horrible Wucheria bancrofti, the latter causing a disfiguring disease known as ‘elephantiasis’, are roundworm species one had better not encounter.

Nematodes are champion survivors and some species may enter a state known as cryptobiosis, during which totally dry and extremely low temperatures can be tolerated. Under optimal conditions, however, they can be prolific reproducers. They possess, of course, muscles for their characteristic whip-like propulsive movements, a mouth, a gut, a nervous system etc., but unlike most animals their nerves don’t send projections to the muscles: the muscles instead have long outgrowths to contact the nervous system.

If that is not peculiar enough, roundworm bodies are made up of a precise number of cells, so that the researcher can determine exactly how many cells the entire animal and its organs consist of and, even better still, what each embryonic cell will differentiate into during the animal’s development. No wonder that such cell-constancy displaying species (and especially the tiny Caenorhabditis elegans) have become celebrated ‘laboratory pets’ for geneticists, who take an interest in unravelling the fundamental processes of cell fates. The worm’s main disadvantage is that its behavioural repertoire is rather limited and morphologically Caenorhabditis elegans and other roundworms also exhibit far fewer interesting features than, for instance, the hundreds of fruit fly mutants (another ‘pet animal’ of the molecular geneticists) that researchers have access to for study.

Final advice: if by chance you should have become a roundworm’s unwilling host some day, don’t panic, for even the most successful creep (worm or otherwise) can be defeated.


parasite manipulation biology science

For more reading about parasites : click for another story : “Parasitic manipulations”

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.