Mosquito experiment concluded

It’s hard to see from the photo but when I checked my bucket after a week away, there were definitely a few mosquito larvae swimming around. There was also an impressive biofilm on the bottom of the bucket. It took less than a month for mosquitoes to breed in a newly formed pool of stagnant water. My son also noticed that a nearby flower pot with water only a few centimeters deep also had larvae. So the claims that mosquitos will breed in tiny amounts of stagnant water is true.IMG_3158

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Mosquito update

IMG_2917It’s been about two weeks since I first set out my bucket, although I had to move it to a less obtrusive location. Still no signs of mosquito larvae, although judging from my bite frequency even with mosquito repellant, mosquito activity is still high in my garden. I see the occasional insect trapped (they are not really floating since at their size water is highly viscous) in the surface and there is a nice collection of plant debris at the bottom. The water level seems a little bit higher. It has rained at least once every two days since my first post although it has also been very hot so the input seems mostly balanced by the evaporative loss. I’m starting to believe that mosquitos have their prefered gestation grounds that they perpetually use and only exploit new locales when necessary.

The mosquito experiment

This month, Baltimore, along with much of the mid-Atlantic has been inundated with rain.  It was already the rainiest July on record as of last week. My yard has also been infested with mosquitos this summer. It was a very wet early summer, then it was extremely hot and dry for two weeks before the most recent deluge. Supposedly, mosquitos will breed in any amount of stagnant water. I thus decided to do an experiment to see how long it takes for a mosquito to find a suitable pool of water and go through a life cycle.  I started this on a whim by putting out some buckets a week ago.  Unfortunately, I wasn’t serious at first and didn’t record the exact date but I think it was Friday, July 20, which was right before the epic rains started. Below is a photo of my two buckets.  As you can see, one is filled to the brim and it is a pretty big bucket.  I haven’t measured the height yet but it looks like it is around 30 cm.  You can see a presumably dead mosquito floating in the orange bucket.  On the bottom, along with plant debris, are what I believe to be egg sacks, which look like 1 cm long beads on a string. The eggs are on the bottom and not floating, which is what I thought they were supposed to do. Maybe they are failures but we will see. There are also some other smaller insects and ants floating or trapped in the surface of the water.  I don’t see any larvae yet. The water was pretty clear as of Thursday of last week so it took about a week for the mosquitos to find the water.  That gives you a time window for how long you have before you should empty out any trapped water.  I plan to run this experiment until the larvae pupate and then I’ll end it before they become full adults.IMG_2834.jpg

CO2 and the return of the dinosaurs

The dinosaurs lived during the Mesozoic Era, which was divided into the Triassic, Jurassic, and Cretaceous Periods. Many of the iconic dinosaurs that we know and love such as Tyrannosaurus rex and Triceratops lived at the end of the Cretaceous while others such as Stegosaurus and Apatosaurus (formerly known as Brontosaurus) lived 80 or so million years earlier in the Jurassic. I used to picture all the dinosaurs co-existing simultaneously but the time span separating Stegosaurus from T. rex is larger than that between T. rex and the present! Dinosaurs also weren’t the only creatures alive at that time, just the most dominant ones. Technically, the term dinosaur only applies to land-based reptiles with certain features. The avian reptiles, such as Pteranodon, or the marine ones, such as Plesiosaurs, resembled dinosaurs but were not classified as such. Aside from those dinosaur-like animals, there were also invertebrates, fish, sharks, and a class of animals called Synapsids, defined by an opening in the skull behind the eyes, from which all mammals are descended.

Synapsids were small marginal creatures during the Mesozoic but came to dominate the land after the dinosaurs went extinct at the end of the Cretaceous (the KT extinction event). The consensus theory is that a large asteroid or comet strike in the Yucatan set off fire storms, seismic events and a cloud that blocked sunlight for up to a year. This caused plants to die globally, which collapsed the food chain.The only survivors were creatures that could go deep underwater or bury underground and survive long periods with little or no food. Survivors of the KT extinction include some fish, small sharks, small crocodiles and other cold blooded reptiles, small bipedal theropod dinosaurs, of which T-Rex is a member, and small rodent-like synapsids.

If the KT extinction event was a transient perturbation then it is reasonable to expect that whatever it was that allowed dinosaurs to become dominant would remain and the surviving theropods would come to dominate again. But that is not what happened. Theropods did survive to become modern birds but aside from a few exceptions, most are small and almost all are avian. Instead, the Synapsids came to dominate and the largest creature to ever live, namely the Blue Whale, is a Synapsid. Now this could be purely due to random chance and if we played out the KT event over and over there would be some distribution where either Synapsids or dinosaurs become dominant. However, it could also be that global conditions after the Cretaceous changed to favour Synapsids over dinosaurs.

One possible change is the atmospheric level of carbon dioxide. CO2 levels were higher than they are today for much of the past 500 million years, even with the recent rapid increase. The levels were particularly high in the Triassic and Jurassic but began to decline during the Cretaceous (e.g. see here) and have continued to decrease until the industrial revolution when it turned upwards again. Average global temperatures were also higher in the Mesozoic. The only other time that C02 levels and global temperatures have been as low as they are now was in the Permian before the Great Dying. During the Permian, the ancestor to dinosaurs was a small insectivore that had the ability to run on two legs while the dominant creatures were none other than the Synapsids! So, mammal-like creatures were dominant before and after the dinosaurs when CO2 levels and temperatures were low.

Perhaps this is just a coincidence but there is one more interesting fact to this story and that is the amount of stored carbon (i.e. fossil fuels) has been very high twice over the past 500 million years – the Permian and now. It had been believed that the rise in CO2 at the end of the Permian was due to increased volcanism but a paper from 2014, (see here), speculated that a horizontal gene transfer event allowed an archaea microbe to become efficient in exploiting the buried carbon and this led to an exponential increase in methane and CO2 production. The active volcanos provided the necessary nickel to catalyze the reactions. Maybe it was simply a matter of time before some creature would find a way to exploit all the stored energy conveniently buried underground and release the carbon back into the atmosphere. The accompanying rise in temperatures and increased acidification of the oceans may also spell the end of this current reign of Synapsids and start a new era. While the smart (rich?) money seems to be on some sort of trans-human cyborg being the future, I am betting that some insignificant bird out there will be the progenitor of the next dominant age of dinosaurs.

Cecil and the hunter

Like many others, I was first outraged when I heard about the death of the beloved lion in Zimbabwe at the hands of a hunter from Minnesota. But I then quickly realized that I am in no position to judge the man. Over the past week, I have dined on salmon, chicken, pork, tuna, and beef. Just because I don’t go into the brush to kill an animal I consume doesn’t mean that I am not directly responsible for its demise. The only difference between me and a hunter is that I do not find any sport in the shooting of animals. There are nearly a hundred million cows at any given time in the US waiting to be slaughtered. Is the life of a cow not as valuable as that of a lion? It is no fault of the cow that she is not an iconic symbol like the lion. Fish are wild animals and we are hunting them to extinction. Tuna can live very long lives and are partially warm blooded. Sharks exhibit very complex behavior and have live births. I would suggest that the death of a big fish is no less tragic than the death of a big cat.

The unfortunate hunter paid a lot of money to go on what he thought was a legal hunt. The guides he hired may have misled him and broken the law but hunting lions in Zimbabwe is not a crime. Remember that this is a country that was near economic collapse just a decade ago and could use an infusion of hard currency. I have argued before that hunting may ironically be a way to preserve wildlife and habitat. The interests of hunters and environmentalists could be aligned. Regulated hunting could be an antidote to illegal poaching. If the hunter broke a law then he should be prosecuted. Otherwise, his choice of recreation is protected by the First Amendment of the US Constitution.

Ideas on CBC radio

 

One of the most intellectually stimulating radio shows (and podcasts) is Ideas with Paul Kennedy on CBC radio. It basically covers all topics. Many of the shows span several hour-long segments. One inspiring show I highly recommend is devoted to landscape architect Cornelia Hahn Oberlander. She was a pioneer in green and sustainable architecture. She is also still skiing at age 93!

Did microbes cause the Great Dying?

In one of my very first posts almost a decade ago, I wrote about the end-Permian extinction 250 million years ago, which was the greatest mass extinction thus far. In that post I covered research that had ruled out an asteroid impact and found evidence of global warming, possibly due to volcanos, as a cause. Now, a recent paper in PNAS proposes that a horizontal gene transfer event from bacteria to archaea may have been the main cause for the increase of methane and CO2. This paper is one of the best papers I have read in a long time, combining geological field work, mathematical modeling, biochemistry, metabolism, and evolutionary phylogenetic analysis to make a compelling argument for their hypothesis.

Their case hinges on several pieces of evidence. The first comes from well-dated carbon isotopic records from China.  The data shows a steep plunge in the isotopic ratio (i.e ratio between the less abundant but heavier carbon 13 and the lighter more abundant carbon 12) in the inorganic carbonate reservoir with a moderate increase in the organic reservoir. In the earth’s carbon cycle, the organic reservoir comes from the conversion of atmospheric CO2 into carbohydrates via photosynthesis, which prefers carbon 12 to carbon 13. Organic carbon is returned to inorganic form through oxidation by animals eating photosynthetic organisms or by the burning of stored carbon like trees or coal. A steep drop in the isotopic ratio means that there was an extra surge of carbon 12 into the inorganic reservoir. Using a mathematical model, the authors show that in order to explain the steep drop, the inorganic reservoir must have grown superexponentially (faster than exponential). This requires some runaway positive feedback loop that is difficult to explain by geological processes such as volcanic activity, but is something that life is really good at.

The increased methane would have been oxidized to CO2 by other microbes, which would have lowered the oxygen concentration. This would allow for more efficient fermentation and thus more acetate fuel for the archaea to make more methane. The authors showed in another simple mathematical model how this positive feedback loop could lead to superexponential growth. Methane and CO2 are both greenhouse gases and their increase would have caused significant global warming. Anaerobic methane oxidation could also lead to the release of poisonous hydrogen sulfide.

They then considered what microbe could have been responsible. They realized that during the late Permian, a lot of organic material was being deposited in the sediment. The organic reservoir (i.e. fossil fuels, methane hydrates, soil organic matter, peat, etc) was much larger back then than today, as if someone or something used it up at some point. One of the end products of fermentation of this matter would be acetate and that is something archaea like to eat and convert to methane. There are two types of archaea that can do this and one is much more efficient than the other at high acetate concentrations. This increased efficiency was also shown recently to have arisen by a horizontal gene transfer event from a bacterium. A phylogenetic analysis of all known archaea showed that the progenitor of the efficient methanogenic one likely arose 250 million years ago.

The final piece of evidence is that the archaea need nickel to make methane. The authors then looked at the nickel concentrations in their Chinese geological samples and found a sharp increase in nickel immediately before the steep drop in the isotopic ratio. They postulate that the source of the nickel was the massive Siberian volcano eruptions at that time (and previously proposed as the cause of the increased methane and CO2).

This scenario required the unlikely coincidence of several events –  lots of excess organic fuel, low oxygen (and sulfate), increased nickel, and a horizontal gene transfer event. If any of these were missing, the Great Dying may not have taken place. However, given that there have been only 5 mass extinctions, although we may be currently inducing the 6th, low probability events may be required for such calamitous events. This paper should also give us some pause about introducing genetically modified organisms into the environment. While most will probably be harmless, you never know when one will be the match that lights the fire.