A fellow biology-nerd friend of mine (Hi you-know-who-you-are-Herr-Doktor) has asked me to write, quote: “more science for dummies, please!” I’m not so sure about it, though. It seems that all I do is dumb science. I don’t need to write about it. Oh wait… I’m getting it all wrong – it’d be writing about science for dummies and not about dumb science for… Okay, let’s start again.
Science for dummies. How should I tackle it? In my limited understanding of the terminology, it’d be a translation of a biological event described in a stuck-up “I studied biology for 10 years” scientific language to “I didn’t even take biology in high school” or “High school? Are you kidding me?!” language. More or less correct, right? Okay, I can do that. As a treat, I’ll throw a paragraph about usefulness of translated science in our everyday lives. (And by the way, I don’t take back writing about dumb science. It’d be a topic for another very long, frustrating, and R-rated writing experience.)
“Scaling of swim speed in breath-hold divers”
In a paper in Journal of Animal Ecology, Watanabe et al. presented strong evidence in support of a fine-tuned adaptation of breath-hold divers enabling them to dive, swim, and forage for long periods. They examined the scaling relationship of swim speed in free-ranging air-breathing diving animals: diving birds, mammals and turtles (37 species; mass range, 0·5–90 000 kg) with phylogenetically informed statistical methods and derived the theoretical prediction for the allometric exponent under the cost of transport (COT) hypothesis by constructing a biomechanical model.
Using the largest dataset currently available and phylogenetically informed statistical method, they asserted that the absolute swim speed of diving animals increases with body mass. Furthermore, residuals about the scaling line showed that endotherms (birds and mammals) swam faster than ectotherms (turtles) for their size, suggesting that metabolic power production limits swim speed. However, among endotherms, birds swam much faster than mammals for their size for currently unclear reasons. This might be explained by an abrupt change in drag associated with the flow transition with a Reynolds number just below ∼3 × 105, the lower limit of turbulent flow.
Importantly, some uncertainties in the biomechanical model and a large variation of swim speed around the scaling line among and within classes remain unexplained. Authors found some potential constraints, i.e. COT minimization, metabolic power production and Reynolds number. Nevertheless, swim speed is a complex behavioral trait, where many factors interact (e.g. mechanical, morphological, physiological and ecological factors). Therefore, further theoretical and experimental work is required to better understand underlying complexities in the choice of swim speed.
“Whales are so big so they can swim faster. Or maybe not.”
A group of scientists from Japan collected swim speeds of air-breathing (i.e., they need to hold their breath while underwater) diving animals ranging from small seabirds, through sea turtles, to the largest marine mammals, blue whales (no fish included in the study, but they have gills and breath underwater). Then, the scientists performed complicated calculations based on statistical methods and made some predictions based on a model they created. Afterwards, they concluded that the bigger the animal the faster swimmer it is. It basically means that whales are so big so they can swim faster.
There’s no so tiny problem though. The model kind of collapses since small seabirds swim actually faster than much bigger mammals… Yeah… Much ado about nothing… Authors admit themselves that more factors need to be considered for their size vs. speed swimming calculations, such as mechanical (one would imagine, for example, that water resistance created by big whales is a bit different than by tiny little birds), morphological and physiological (comparing birds to turtles to whales can’t be that straightforward, after all), and bunch of other factors that may matter but the scientists have no clue about them at the moment. It doesn’t seem like the scientists have much clue about anything they published…
All in all, the model of size vs, speed is incorrect, at least at this stage. More work is required to resolve the burning question how the size of animals that need to hold their breath underwater relates to their swimming speed. And after all these studies, we still don’t know why whales are so big. Darn it!
ANYTHING USEFUL FOR Homo sapiens?
Unless some scientist will study whether big fat air-breathing Homo sapiens divers are faster swimmers than the skinny ones. Many factors would have to be taken into account. To name the few: lung capacity (the ability to hold breath under water isn’t spread equally; some can stay underwater for barely a minute, which would be difficult to collect data), mechanics (for example, hairy vs. bold individuals that would surely create different water resistance), and whether the study subjects can swim in the first place – please, that’s the most important variable. Then, we could re-visit this useless but somewhat entertaining topic.
“Self-recognition and Ca2+-dependent carbohydrate-carbohydrate cell adhesion provide clues to the Cambrian explosion.”
Fernàndez-Busquets et al. in Molecular Biology and Evolution proposed that two coinciding innovations were required for the Cambrian explosion of life, which marked a generalized acceleration in metazoan evolution. Firstly, allorecognition was likely to have evolved to prevent the negative effects of chimerism, for example, germ-cell parasitism or the introduction of deleterious mutations from fusion with genetically different individuals. Secondly, the calcium increase in Cambrian oceans resulted in significantly longer dissociation times of cell adhesion molecules, which increased the polyvalent binding forces between the calcium-dependent molecules. This allowed the integrity of genetically uniform animals, facilitating genetic constitutions to remain within the metazoan individual and be passed down inheritance lines.
In presented studies, the authors utilized sponges, namely Microciona prolifera, the oldest extant Precambrian metazoan phylum. Dissociated sponge cells have the capacity to species-specifically sort out and re-aggregate through calcium-dependent multivalent carbohydrate–carbohydrate interactions of the g200 glycan found on extracellular proteoglycans, termed aggregation factors. Single molecule force spectroscopy analysis of g200–g200 binding indicated that calcium affects the lifetime (+Ca/−Ca: 680 s/3 s) and bond reaction length (+Ca/−Ca: 3.47 Å/2.27 Å). Calculation of mean g200 dissociation times in low and high calcium within the theoretical framework of a cooperative binding model indicated the nonlinear and divergent characteristics leading to either disaggregated cells or stable multicellular assemblies, respectively. The researchers claim that this fundamental phenomenon can explain a switch from weak to strong adhesion between primitive metazoan cells caused by the well-documented rise in ocean calcium levels at the end of Precambrian time.
Recent evidence places the appearance of sponges during the Cryogenian period, >635 Ma whereas the major bursts in animal diversification took place in the next and last Precambrian period, the Ediacaran. The body plans characteristic of modern phyla are thought to have evolved gradually after the time of the Cambrian explosion, in an accelerated evolution of the lineages that had already started to diverge earlier. According to current estimates, oceanic calcium rose from very low levels around 2 mM to reach approximately 10 mM at the Precambrian–Cambrian boundary system and continued increasing up to concentrations that were higher in early Cambrian oceans than they are at present. Thus, with the presented data, the effect proposed by the authors for calcium-dependent cell adhesion on the evolution of early metazoans would have been mainly exerted during the Precambrian diversification phase.
“Way before the evolutionary appearance of apes and humans – there were sponges.”
A group of scientists from different places in Europe and US set to resolve the mystery of one of the most relevant episodes in the history of life on Earth: how come there was such an accelerated evolution in the majority of animal group of organisms in the Cambrian era, lasting from 542 to 488 million years ago? Simple: because there was more calcium in the oceans at that time. Thanks to calcium, one cell (let’s define cells as building blocks in an animal body) could better recognize the other right-fitting one vs. you-don’t-belong-here one and form a uniform organism. That was the beginning of multi-cellular organisms, i.e. the ones consisting of more than one cell (forgive me if I’m a bit annoying with my definitions; it’s science for dummies after all…). All animals are multi-cellular (that’s including us, humans, obviously). Well, there’s an exception – there’s always one – since some aquatic parasites are one-cell animals. Anyway, the ability to form and maintain such a wonderful multi-cellular life form was passed on and voilà!, the evolution could move on to form more and more complex creatures.
The most valid animal model to study all these wonders? Sponges. Yes, sponges are animals and not plants. In fact, they’re the oldest and the simplest living multi-cellular animals on Earth. They were there, at the very beginning of evolution. And they’re still here. How cool is that?! Forget apes. We needed sponges way before that to be able to evolve into anything resembling an organized and functioning more-than-one-cell creature.
Sponges have one remarkable ability that makes them a technically perfect model for these kinds of studies. When one cuts different species of sponges into pieces, squeezes remains through the mesh into the water to get single cells, lets them mix for a while in seawater with calcium, one can then see cells from one sponge species finding one another and specifically reforming a pre-cut parent sponge. A bit brutal process but indeed amazing. So, the researchers cut lots of sponges into pieces, or precisely lots of individual sponges from one species, got their single cells and isolated specific molecules from the surface of these cells (and gave them some scientific names). Then, they showed that these molecules mediate those specific interactions when cells recognize one another, and it all of course depends on the amount of calcium in seawater. The authors used a very fancy instrument, called atomic force microscope, to measure those interactions. I have used it myself in thepast but I’ll refrain from explaining how it works – it’d get a bit too scientific for this section.
In the last summary paragraph, the authors describe the timeline to connect the amount of calcium in oceans, the appearance of sponges, and the evolutionary explosion of animal life in the Cambrian. Sponges appeared long before the Cambrian period, around 850 to 635 million years ago. The major increase in animal diversity took place just before the Cambrian. The evolution of the body plan, which characterizes modern more-than-one-cell animal beings, started just after the Cambrian. The amount of calcium in oceans was on the rise till it reached unspecified, but higher than present, values in the early Cambrian… Let’s take a breather… Tough one to crack… So, anything significant for the evolutionary explosion of life studied here happened before the Cambrian, right? The animals physically connected to modern beings started evolving after the Cambrian, right? So can we just stop bragging about the Cambrian???!!!
ANYTHING USEFUL FOR Homo sapiens?
Yeap. Two things. Two pieces of knowledge. It could be more but the knowledge about evolutionary importance of calcium is insignificant (we’ll just keep on taking it for our bones) and I’m simply not dealing with the Cambrian issue anymore.
Knowledge number one: Sponges are not only animals but also they’re the oldest metazoans on Earth! Number two: Although cut into pieces, smashed and mixed with some other stuff that doesn’t belong, little tiny sponge cells can find themselves and re-grow to the original organism! Remember “Terminator 2: Judgment Day”? One of the last scenes when T-1000 Terminator is frozen, blown to pieces by “Arnold Terminator”, then the pieces melt, slide to one another, and the Terminator is reformed. Sponges can do that too!!!!
This knowledge could have an impact on couple of situations. Depending on the state of nerd-iness, sense and quality of humor, the amount of alcohol consumed (not enough vs. too much) of both sides involved in the scenario, one could try to impress somebody with the information at the party or any other social event. Remember though, many factors, including the mentioned ones, will impact the outcome of that attempt.
While the first scenario have a potential to be funny, the second one is just grim. I wonder how the person using natural sea sponges will feel like when taking a bath next time… Using a once-upon-a-time-alive-but-now-dead-and-dried animal for scrubbing… So rude.
Maybe all this will have an impact on the existence of sponges. “No cutting. No drying. Learn some respect, people! We’re your ancestors!”