Ducks can be Cuckoos too

When it comes to reproduction

Ducks are a remarkable family of birds (the Anatidae). They swim, they dive, they fly, their young are adorable and the males, known as drakes can be exceptionally pretty. Last but not least, expertly prepared they taste exceptionally good and that is one reason, why duck shooters are out to bag them. And that is also the reason why the New Zealand Duck Shooters’ Association had supported my student Dale Towers with a grant to study acceptability and design of nesting boxes by New Zealand Blue Ducks. Few people who accuse hunters and anglers of being cruel to animals seem not to know that people like duck shooters, hunters and anglers are usually excellent conservationists, who care and make sure that the animals they love (to shoot or hook) will still be around in the future. And come to think of it, what is more acceptable: to hunt and shoot an animal, which during its evolution got used to being attacked by predators? Or to befriend an animal, make it trust its owner, and then send it to the slaughterhouse?

Anyway, Dr Towers, noticed several things: experienced older ducks arrive early and choose their nest box in the centre of a cluster of boxes; that’s the safest place. Younger less experienced individuals have to make do with nest boxes at the periphery, where attacks by predators are more likely and the effects of bad weather, for example, strong wind can be more severe. He also noticed that the ducks frequently visit nest boxes that are not their own and quickly deposit an egg in another duck’s nest, if they find it unoccupied. Dale found that out of 10 eggs in a nest there could have been as many as six that were not laid by the nest owner, but by a different individual. And yet, these “other eggs” were not recognized or at least they were not removed, but brooded by the nest owner irrespective of the eggs’ origin that it was incubating. Did the nest owner not notice whose eggs she was sitting on or did it not matter at all?

Laying eggs into different nests can benefit the layer in several ways: The ‘brood parasite’ may not have found a suitable nest itself or should it experience a failed clutch of its own eggs, then having some of its eggs brooded elsewhere, the effort of laying the eggs was not wasted and offspring with the egg layer’s genetic material will be generated after all. It also means, of course, that ducklings from one clutch are not all brothers and sisters, but genetically mixed. That could perhaps prevent inbreeding. There is, however, a problem for the duck that sneaks in to lay an egg into the nest of another duck: it takes a bit of time and while the ‘brood parasite’ lays its egg in somebody else’s nest, it cannot guard its own nest and thus may herself be “parasitized” by another individual. Real cuckoo birds, of course, never have a nest of their own and invariably must choose a host for their own egg. However, while in the case of ducklings no fights ensue between the unequal siblings, in the cuckoo’s case the fate of its unrelated nestmates is sealed: they’ll be pushed out of the nest to die or may even be eaten by the young cuckoo.

What I really like about this blog’s title, is its tongue-in-cheek double meaning: yes, the female duck does behave like a cuckoo, when she lays her eggs in another nest, but the owner of the nest, also a duck, is “a real cuckoo” not to notice that she’s not sitting on only her own eggs, but brooding those of another individual (in English the word cuckoo is often used to mean “a stupid individual”).

© Dr V.B. Meyer-Rochow and, 2020.
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 with appropriate and specific direction to the original content. 

Stinging and Injection Devices of Animals

Cases of convergent evolution

What qualifies as a sting and what had better be called a bite is not always clear and most people say they’ve been bitten by a mosquito while some refer to the “bite” as a “sting”. If the sharply pointed end of a structure is pushed into the tissue of another individual, I think we should call it a sting  –  and stinging animals abound. The stinging devices in animals are amazingly diverse and although we tend to think immediately of the defensive stings of bees and wasps, stinging is also used to deposit, for example in female parasitic wasps, their eggs into caterpillar or spider hosts on whose tissue the larval baby wasps can feed. Injecting venom can be the fastest way to immobilise prey and some stinging animals like, for example the fish-eating slowly moving cone shells or some spiders and snakes that inject venom into their victims, make use of their stinging devices in this way. To obtain oxygen under water without having to come up to the surface, the larvae of the mosquito Mansonia spp. impale the air-containing cavities in the stems of underwater plants with their syringe-like “stinging” syphons.

Venomous snakes, depending on the species, have two ways of delivering the venom to their victims. In those with venom glands connected with teeth at the back of the mouth, the teeth are not hollow, but possess a narrow groove on their inner side, in which the venom runs along. More dangerous are the hollow front teeth of some snakes. These teeth are normally folded up and tucked away under the roof of the mouth when not used, but when needed they point forward to strike the prey and to deliver the venom through tiny pores at their tips. The bite is carried out with a considerable force and the venom is forced from its storage glands into the wound of the victim. A rather similar method is employed by spiders, which also inject venom through a canal inside their two oral appendages, known as chelicerae. The chelicerae have very pointy tips with a hole at the end and the venom stems from the glands at the base of the chelicerae or from deeper in the head. How a droplet of the liquid venom can be pressed through the very narrow tube in the hollow chelicerae and then leave through the tiny pore at the end is something for scientists interested in fluid mechanics and involves some knowledge of the viscosity of the venomous liquid. In most web-building spiders the two chelicerae work like pincers, but in the often much bigger mygalomorph spiders the chelicerae work in parallel striking prey like 2 axes from above.

Similar fluid mechanical problems would apply to the venom delivery of wasp and bee stingers, for they resemble hypodermic needles. The honey bee stinger is barbed (a bit like that totally unrelated stinger of the stingray) and stays in the flesh of a stung human, leading to the death of the bee, but continues to pump venom by itself for some minutes. Wasp stingers and those of some powerfully venomous ants like the Australian bull ant are smooth and can be used repeatedly. Giant centipedes are feared because of their strong mandibles, sometimes referred to as ‘fangs’, which possess a canal through which a venom can be injected into a bitten individual. However, stingers delivering a potent venom that can kill are known not from centipedes, but scorpions. The most dangerous stinging animals in the sea are probably the already mentioned cone shells with their single hollow chitin tooth connected to a venom bulb, further the so-called stone fishes and some others with venomous fin rays as well as stingrays (the death of Steve Irwin comes to mind). The only “stinging mammal” is the male platypus with its venomous and hollow hind leg spurs. But who’d want to pet or even have a chance to pet a platypus?

© Dr V.B. Meyer-Rochow and, 2020.
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 with appropriate and specific direction to the original content. 

biology zoology blog benno meyer wrinkle

“Wrinkle-wrinkle, au revoir”

How I wonder what you are

I have recently been reading about wrinkles. Not because I am worried about my wrinkles (I actually think wrinkles can make a face look more interesting than if it was “as smooth as a baby’s bottom”), but because so many people here in East Asia seem terrified of getting wrinkles and avoid an exposure to direct sunlight through face masks, parasols, summer hats, lotions, creams, etc. The scientific literature on wrinkles includes information on skin structure and function, biochemical and physiological reasons to develop wrinkles, but I couldn’t find anything about perhaps the most obvious reason: you get older, you shrink!  As we age, our height diminishes. During the time I passed university examination I was 184 cm tall; now I am 181 cm tall. People who have spent some time in the space station circling around our planet Earth under zero gravity conditions reverse that trend and are a little bit taller when they return to Earth. An apple that ages shrinks and becomes wrinkly. And humans  – how about us?

Wrinkles consist of more or less deep furrows and bulges and they usually develop along locations of microlines in the skin. The latter form a polygonal network of fine lines easily visible on the outer skin layer (the epidermis) with a magnifying glass. Under the epidermis lie the dermis and hypodermis with their stabilizing connective tissue component proteins collagen for structural integrity and elastin for flexibility and plasticity. And, not to forget, there is hyaluronic acid in the skin with its multiple functions. All the skin layers are associated with underlying lymphatic vessels along with perilymphatic and subcutaneous fat tissue, known as panniculus adiposus and p. carnosus. What is most damaging and a cause of the skin to age is oxidative stress, in other words free oxygen radicals. These radicals are highly reactive and may be produced by the breakdown of double-bond fatty acids following an exposure to UV-radiation. There are, of course, ways the skin tries to protect itself: a higher sebaceous gland density of the skin is correlated with shallower wrinkles, but as the pillars of the skin (like collagen and hyaluronic acid) slowly diminish and the skin becomes drier the decline in skin cell renewal of older people can only be slowed down with a nutrition that is rich in vitamins and anti-oxidants.

What matters also are the genetic factors and how rapidly a person ages. In addition, smoking and heat are often mentioned as wrinkle-promoting, and so is lack of sleep; in fact, anything that causes skin to become dehydrated. However, there is one cause that is related to facial expressions.  Grooves on the forehead during thinking, or wrinkles during laughter, or the vertical lines between your eyes during squinting to see more clearly: such lines can become permanently visible as expressive wrinkles. There is generally not terribly much that an ageing person can do to avoid getting wrinkles, but there is one dog breed (the “Shar-pei”), in which the wrinkles disappear with age. For other and much bigger animals with wrinkled skins, the wrinkles can actually be an advantage as they can hold moisture that can then evaporate from a larger surface area and in this way lead to the cooling of the wrinkled individual. This suggestion has often been advanced to explain the folds and wrinkles of the skins of elephants and rhinoceroses. However, fact is that any animal (other than a Shar-pei dog) develops wrinkles as it ages, especially around the joints. But because animals are covered in fur we tend to overlook their wrinkles  -with one exception: the beautiful, pain-free naked mole rats. Their incredibly wrinkled bodies help these subterranean, naked rodents to turn around in their narrow tunnels and navigate corners with ease.

To return to my earlier statement that we shrink as we age and that space travellers are taller when returning to Earth: my hypothesis is that they would not only be slightly taller but also less wrinkled (provided they got enough sleep and had good vitamin-rich food while at the space station). In any case: Every wrinkle has a story to tell and as for me, there will be a lot more stories when I’m older.

© Dr V.B. Meyer-Rochow and, 2020.
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 with appropriate and specific direction to the original content.