So nat’ralists observe, a flea
Hath smaller fleas that on him prey;
And these have smaller fleas to bite ’em.
And so proceeds Ad infinitum
From On Poetry: A Rhapsody by Jonathan Swift
I’ve said ‘weird and wonderful’ in this blog perhaps far too many times but over billions of years evolution has led to so many incredible things in nature that I never cease to be amazed. And here again I found myself the other week reading a story that just blew my mind! If I say upfront that the story is about parasitic wasps, most people will probably not get too excited about it. Neither parasites nor wasps are the first things that even I would associate with being wonderful. Weird maybe, but wonderful??? But do bear with me here for a moment and I hope I can convince you otherwise.
You know, I sometimes think that animals are just walking colonies of multiple kinds of cells that evolved to live in a symbiotic relationship with one another. Seriously, it is highly unlikely that we would be able to survive without all the viruses and bacteria that live in and on us. We need these little microorganisms for all sorts of things from immune system development to nutrient acquisition. Moreover, increasing amount of evidence shows that our microbiome and virome are an essential part of who we are, and perhaps humans would be a very different species today if some of these animal-microbe interactions would have not occurred during the course of evolution.
Changing the environment one lives in may require significant changes in animal’s morphology and behaviour. This is especially the case if we are talking about such drastic change as a switch from living on land to living in or on water. Some 200 million years ago ancestral species of a group of semi-aquatic bugs, known as Gerromorpha, had made such transition and over time, evolved traits allowing them to live on the surface of water. One of many new challenges facing animals living on water is being exposed to predators not only from above but also from below. Insects within the infraorder Gerromorpha have adapted their leg morphology to both be able to glide on the surface of water and escape the water-dwelling predators. The more ancestral-like species of Gerromorpha have midlegs which are shorter than hindlegs and move in a similar pattern like the closely related terrestrial species, whereas the more derived species, e.g. water striders, have longer midlegs and move with rowing-like leg motions. It is quite difficult to identify the exact genetic factors which determine development of adaptive such traits because these traits are often a result of both genetic and epigenetic modifications as well as are usually not a single gene determined. However, a recent study by a research group from The Institute of Functional Genomics of Lyon has been able to find a link between the morphology of water strider’s legs, an anti-predator response and the genes involved.
Hummingbirds have incredibly high metabolic rates. Their hearts can beat more than 1000 times per minute, they inhale more than 200 times per minute and their oxygen consumption during flight can be 10 times grater than that of an elite marathon runner. Clearly all this work requires a lot of energy, which the hummingbirds get by feeding on nectar and consuming more than their own weight of it each day. As quick and efficient acquisition of nectar is essential for hummingbird’s survival their tongues have shape that allows to preform its function perfectly. The tongue of a humming bird consists of two rods and each rod has many hook shaped hairs (called lamella or lamellae for plural) attached to it (figure 1 and video 1).
Carnivorous plants have always captured people’s imagination: the Krynoids in Dr. WHO, Cleopatra in Addams Family, Snargaluff in Harry Potter… to name but a few. And perhaps the excitement isn’t that surprising considering that typical plants for most of us are but a picture in the background of our daily lives.
There are many different ways, each perhaps more ingenious than the last one that carnivorous plants have evolved to catch their prey. The infamous Venus flytrap uses small electrical currents, that are induced by an insect brushing against the tiny hairs on its trap, to snap close its “jaws”; bladderwort uses vacuum to suck its victim into a tiny cell that will end up being its final resting place. Perhaps, compared to these exotic examples, the pitcher plats with their puddles of liquid to drown the insect in don’t seem as exciting but, as ever, the looks may be deceiving. Pitchers often have distinct colorations to attract insects, they secrete nectar on the rims of their pitfalls to lure the poor creatures for a “free meal”. When an insect attempts to land on the rim it turns out that the rim is made up of tiny downward pointing scales and is covered with liquid which makes the landing platform very slippery and by the time the mistake can be registered the insect is already falling down into its doom. At the bottom of each pitfall a pool is liquid solution, which consists of various digestive enzymes and bacteria, that will eventually and inevitably digest the insect leaving the plant to absorb all of its nutrients.
Interestingly, some pitcher plants are better at catching the insects than others and indeed, some pitchers grow in areas that have far too few suitable insects to make the carnivorous life-style a sustainable one. So how do they survive? Well, it turns out that what may be one’s grave can be another’s home. Namely, a type of pitcher plant called Nepenthes rafflesiana elongate, which grows in the jungles of Borneo, has evolved special characteristics to accommodate the living of Hardwicke’s woolly bat inside it. The pitcher of Nepenthes r. e. is larger and longer than some closely related species and the level of digestive liquid at the bottom of the plant is usually significantly reduced. Indeed, in some cases pitchers have been found that are large enough to comfortably accommodate inside a mother and its juvenile baby bat. In addition, the slender shape and a special lignified girdle of the pitchers allow the bats to settle head first inside the trap without slipping down to the bottom.
One may wonder what’s the benefit for the plant to have a bat living inside it if it blocks the insects from being lured into the traps. It turns out that the plants benefit from its inhabitants by being used as lavatories! The faeces of bats are rich in nutrients such as nitrogen, which can be absorbed by the plant to be used in its own metabolism. In addition, some pitcher plants are also pollinated by the bats. Bats are actually not the only animals that make use of pitcher plants, a similar mutualistic relationship between tree shrews and another species of pitcher plant, Nepenthes lowii, also exist (those interested see here).
It turns out, that not only the shapes some pitfall traps are especially accommodating for the bats to live in, but also the trap has special reflective properties to make it easy to find. Bats use echolocation to track and catch insects they feed on, however, this ability has also been adapted to find the suitable pitchers for nesting. Recently, it has been shown that the back walls of the pitchers that have mutualistic relationships with bats, also have significantly better acoustic signal reflection compared to those that don’t. Consequently, in the cluttered jungles the echolocation signal is more likely to come back from pitchers that are suited for roosting making them easier to find.
Grafe, T. Ulmar, et al. “A novel resource–service mutualism between bats and pitcher plants.” Biology Letters 7.3 (2011): 436-439.
Schöner, Michael G., et al. “Bats Are Acoustically Attracted to Mutualistic Carnivorous Plants.” Current Biology (2015).
Leaf-cutter ants are absolutely fascinating little creatures. Found in North and South America, their colonies can contain up to 5 million ants and the queen of the colony can lay almost 30,000 eggs every day. These tiny workers have substantial impact on the ecological communities they live in: mixing the soil, selectively choosing which plants leaves to cut and which seeds to carry significantly modifies the environment they live in. And it is not for decorative purposes that they work so hard to bring those leaves back to their colonies (one piece of a leaf can weight up to 50 times the ant’s weight!). Leaf-cutter ants also belong to a group of fungus-growing ants, which, as their name implies, spend their time and resources on culturing fungi (process called fungiculture). Fungiculture has originated 50 million years ago and is an example of symbiosis, a mutually beneficial interaction between two or more organisms. Leaf-cutters bring the leaves back to the colony which provides a constant source of nutrition for their ‘fungal garden’ (this is the actual term used for the specialised space in the colony where the fungus is cultivated). As an added value the ants also take care of the fungal garden by cleaning it from any invading parasites as well as facilitating fungal spore dispersal. In return, ants eat the fungus, which is their primary food source (so it’s almost like a personal ant veggie garden). Continue reading →
A propagation of behaviours between individuals is known as “social contagion”. This is just a fancy term that includes a range of things from information spread between users of the media to flocking behaviour in birds. However, while measuring the rate and direction of information spread is reasonably straightforward, how various forms of contagious behaviour are initiated and what social interactions act as clues for the spread of particular behaviour in nature is not well understood. Over the years many different hypotheses have been proposed to explain the workings of social contagion in different animals; from suggestion of communication via telepathy in flocking birds to, a more reasonable sounding, changes in water pressure caused by sudden movements in schooling fish. One strategy of studying social contagion in animals is to create models of networks between individuals in the group, where each individual is connected to another one by one or more strings of information that can act as social clues to help to decide what behaviour to adopt.
Considering it is Easter I though it would be very appropriate to write something on an egg-related topic and, as a personal bonus, to mix some viruses in as well ☺ .
I suppose most of us are used to seeing eggs that have either white or brown shells. However, those are just the types that are sold in supermarkets, but people who grow different types of chickens will note that sometimes the eggshells can be blue or green as well. Were do all these colours come from? Eggshell colours are determined by the pigments that are secreted when eggs develop in uterus of a hen. Pigment protoporphyrin, for example, is derived from blood haemoglobin and contributes to brown eggshell coloration. By contrast, blue eggs predominantly have billiverdin pigment in their shells. Billiverdin is a component of bile salts and acts as an antioxidant, which is why it has been proposed that blue egg coloration could act as a signal of female genetic fitness (figure 1).
We spend almost 30 years of our lives asleep, however, we still have limited understanding about the function of sleep. Scientists and philosophers have been trying to understand why animals need sleep for more than 2000 years. In his book “On Sleep and Sleeplessness”, Aristotle wrote:
“With regard to sleep and waking, we must consider what they are: whether they are peculiar to soul or to body, or common to both; and if common, to what part of soul or body they appertain: further, from what cause it arises that they are attributes of animals, and whether all animals share in them both, or some partake of the one only, others of the other only, or some partake of neither and some of both”