Smart Mites

Parasitologists commonly observe species in which one sex is more heavily parasitized than the other. For example, territorial male impalas carry a much higher tick load than bachelor or female impalas (paper by Mooring and colleagues found here).  Territorial males spend less time grooming to remove ticks and instead spend their time watching for intruding males and wandering females.

Most of the explanations I’ve read for why one sex is more heavily burdened by parasites have focused on how host behavior, physiology and immune status influences their infection status. Few studies have examined if males or females have higher parasite loads because parasites are actively choosing one sex over another.

I was excited yesterday to come across this paper which examined whether or not parasitic mites are capable of preferentially infesting one sex. These researchers had previously observed that female bats from the genus Myotis are often infested with more mites than are males and so they decided to examine whether part of this pattern could be explained by the parasites “preferring” females.

Mites can not survive very long on their own and require a host for food and energy. It’s in the mite’s best interest to try to stay in areas of high bat density. This way they have plenty of other hosts when they reproduce and their offspring need to find a host of their own. It’s also a good idea to have other alternatives nearby in case the bat that the mite is currently living on falls ill and the mite needs to abandon ship.

If you’re like me, then when you imagine what bats you envision a cave wall with bats crammed in there nose to nose. The bats that roost in these large groups are females with their young. The males on the other hand, are loners. Instead of roosting with the group, they find a place to hunker down on their own. This means that, given a choice, mites should prefer to infest females who will surround themselves with other tasty bats over males encounter other bats far less frequently.

Researchers decided to test whether or not mites were capable of preferentially infecting females given a choice between both sexes. They placed a male and a female bat into an enclosed arena where their movements were limited and released a set number of mites into the enclosure. After keeping track of the mites’ choices, the researchers released the bats into an outdoor arena. Ten days later, the bats were recaptured and mite survival was quantified.

I know lots of people who don’t seem to know what’s good for them, but the mites seem to have it all figured out. The mites choose adult females significantly more often than they choose adult males AND their survival on female bats was much higher than on males.

The exact mechanism by which the mites differentiate between the sexes is unknown, but it’s likely that they’re using hormonal cues.

The more I learn about parasites the more amazed I am at how good they are at keeping themselves alive. This study showed that they’re capable of making good decisions when picking a host and I’ve discussed in a previous post how parasites are able to alter the behavior of hosts that they’ve successfully infected. I wouldn’t be surprised to find that the decisions made by parasites are driving differences in parasite loads between the sexes in lots of other species as well.

My Beef With Bottled Water

Some of the comments on my “Don’t Be a Sucker 101″ post accused me of assuming that most people buy bottled water because they wish to avoid the fluoride that is added to tap water. I’m sorry if I was unclear, but I was not making that assumption. I don’t give regular bottled water drinkers THAT much credit.

Here’s the problem.

Old man giardia

1) TAP WATER IS FINE IN MOST CASES. Tap water is regularly tested and local municipalties have to abide by super stringent water quality standards. Lots of research has gone into establishing these standards and confirming that the levels of compounds in the water are safe for human consumption.

According to a 4-year National Resource Defense Council report, bottled water companies frequently are not held to the same standards. For example, bottled water companies are not required to test for waterborne parasites like giardia (a parasite that looks like an old man and will give you a nasty case of diarrhea) while local water municipalaties are required to do so.

In fact, the same NRDC report that I mentioned above identified contamination (bacteria, arsenic and synthetic organic chemicals) in nearly 1/3 of the bottled waters that they tested. I tried to read the rebuttal argument to the NRDC report from Bottled Water Web (the “definitive bottled water site”), but only paying members are allowed to view the document.

2) LOTS OF BOTTLED WATER CAME FROM THE TAP TO BEGIN WITH. Between 25-40% of the bottled water found on shelves didn’t come from pristine mountain springs, but from the local water utility near bottled water production plants. On the plus side, this at least means that the water has met FDA standards…

For example, Coca-Cola’s Dasani and Pepsi’s Aquafina come from local water sources and pass the water through a few additional filters before marking it up 10,000% and sticking it on the shelves.

If you’ve examined the research and have decided that you personally believe the levels of certain compounds should be even lower than recommended, then fine. Go find a bottled water company that filters more of this compound out than local municipalities do. I am going to go out on a limb here and say that probably no more than 10% (I think this is a conservative estimate) of bottled water consumers have looked at the research and made an educated decision about buying their water.

3) BOTTLED WATER IS RIDICULOUSLY EXPENSIVE. I’m not convinced that tap water which is already totally safe for human consumption is worth a huge mark-up after being run through a few more filters. During my days in the food service industry (thank god those are over!) I remember selling bottled water to customers for $2.16. I would always offer to give them a glass of tap water, but many preferred the bottled water instead. I found this particularly amusing as we were selling Dasani, which I’ve already noted is simply refiltered tap water anyway. Anyway, if you consider that they could have gotten tap water for free then they’re essentially paying infinitely more for bottled water.

4) PACKAGING AND PROCESSING CAN INTRODUCE CONTAMINANTS. In the past, processing and packaging the tap water introduced bacteria, resulting in water that was less safe to consume than when it first left the faucet (references here and here). The last study that I read on this topic was published in 1998, so I’ll concede that the industry may have cleaned up its act by now. That doesn’t change the fact that the water has encountered a whole lot more surfaces and has had a lot more time to sit and culture bacteria than would water that came directly from the tap.

5) WASTE. This one is pretty obvious, so I won’t harp on it for long. You can probably imagine how much plastic is wasted in packaging bottled water, but lots of water is wasted as well. For example, producing 1 liter of bottled water requires the usage of 3 liters of water in the production process. Here are some other fun facts.

–

To be fair, there are certainly some cases where it may be smart to drink bottled water. For example, if you have a kidney condition and need to avoid fluoride, then researching which bottled water companies remove fluoride and then purchasing water from that company may be a good idea.

If you’re ever in an area where you know the tap water is contaminated or are outside of the US in countries where the tap water isn’t well regulated, then again it might be a good idea to drink bottled water.

To reiterate, if you live in a town in which the EPA’s yearly water quality report has informed you that you have high, unsafe contaminant levels in your drinking water, then I’m NOT talking about you. But you’re in the minority, so I’m talking about nearly everyone else.

There certainly are times when spending a lot of money on bottled water makes sense, but the majority of bottled water sales are purchased outside of these circumstances. Part of the taxes I pay go to ensuring the quality of the tap water I consume. As I live in a city that boasts no water quality problems, I stay away from bottled water as much as possible.

Epigenetics and delivery

In earlier posts I discussed how studies on rats have revealed that early life experiences modify the epigenome, which has long term consequences for stress responsiveness, reproductive behaviors, and obesity rates. It’s often difficult to do epigenetic studies on humans due to ethical concerns, but some pretty clever work has been done lately revealing that the results from the rat studies may be broadly applicable.

I found this article recently that describes a study comparing the methylation patterns of children delivered naturally to children delivered by C-section. They found that the section of the epigenome which codes for white blood cells is more heavily methylated in children born by C-section, perhaps because this procedure is more stressful for the child than natural birth.

We already know that children delivered by C-section are at a greater risk for diabetes, allergies and leukemia and the researchers who ran this study postulate that these greater risks may be the result of changes in methylation patterns during delivery.

It’s unclear whether the methylation patterns is caused by the procedure per se or by the mother’s stress over whatever complications are resulting in the need for a C-section in the first place. Further studies will be needed, but (as I mentioned in a previous post) some studies have already concluded that the fetus’ epigenome is altered when mothers are stressed out or depressed during gestation.

If researchers can convincingly make the claim that C-sections change methylation patterns (and therefore patterns of gene expression) in babies and that these changes in gene expression result in a greater risk for particular diseases, then perhaps we’ll see the trends in C-section rates reverse. At the moment, the percentage of deliveries that are done by C-section is steadily increasing worldwide.

I was under the impression that most C-sections were done when there were complications that put the mother and/or the baby at risk, but it looks like there are plenty of less serious reasons for why women get this procedure done. Some mothers elect to have C-sections so that they can “maintain vaginal tone” (i.e., they don’t want to become “loose”) or because they don’t want to experience the pain associated with childbirth.  Doctors are also inclined to perform C-sections at the slightest hint of a complication because this could save them from dealing with expensive malpractice suits.

I’d be interested in seeing if differences in the prevalence of particular diseases between countries could be correlated with country specific C-section rates. For example, Brazil has the highest rate of C-section delivery and I would be interested in finding out if they also have high rates of diabetes, allergies and leukemia as well.

Hopefully clever research will teach us more about the link between C-section, the epigenome and the risk of contracting particular diseases. If a clear link is found then we may see a big change in the way the public perceives non-emergency C-sections.

Don’t Be a Sucker 101

Bottled water sales are a sure sign that there are a lot of suckers out there. The world is full of people who can be talked into buying or believing almost anything, but who would make far better decisions if they had a very basic understanding of subjects like chemistry, logic, and statistics. I would love to see a course entitled “Don’t Be a Sucker 101″ taught as an after school program or as a college elective course. The course would cover these topics:

1) Ridiculously basic chemistry.

Concentration matters.

For example, there are currently a lot of people who think that fluoride is dangerous to human health, and there is even a group actively working to get officials to stop adding fluoride to our drinking water. For those who don’t know, fluoride is added to our drinking water because it decreases the rate of tooth decay. In fact, studies have shown that water defluoridation results in an 18-40% decrease in children’s cavities. For poor families who can’t afford good dental care, water fluoridation makes a big difference.

But the critics of fluoride have a point. It CAN be dangerous. The key point, however, is that it is only dangerous in high concentrations. Like many other compounds (e.g., niacin, Vitamin A, and copper), fluoride is beneficial to the human body at low concentrations but is toxic or even fatal at high concentrations. The levels at which we encounter fluoride in our day-to-day lives are typically within the healthy range.

2) Basic logic.

I think that this part is particularly important. Politicians and advertisers are constantly making illogical statements in an attempt to sway public opinion. Here are a few that I think people fall for pretty often:

Ignoratio elenchi. These are arguments that may be true, but are not relevant to the question at hand. For example, I’ve heard people argue that evolution can not be true because, if it were true, then life would have no meaning. The potential ethical implications of evolution are not relevant to the question of whether or not evolution is “true” and thus should not be included in arguments against evolution.

This type of logical fallacy seems particularly popular with politicians, who often avoid directly answering a question by diverting attention to an argument that they feel more comfortable making. If more people were watching out for ignoratio elenchi fallacies then perhaps we could hold more politicians accountable for answering the question they were actually asked.

Ad hominem. An ad hominem attack is when someone attempts to discredit a statement made by an opponent by attacking the person rather than addressing the claim. A good example of this can be found in a previous post, where the author tries to discredit the claims of a group of scientists by noting that these scientists once collaborated with a scientist who now has a bad reputation. They should have attacked the scientist’s methods and claims.

It definitely is important to take into consideration who is making a particular claim. If the person making the claim is an established liar, then you certainly want to take their arguments with a grain of salt. But if you’re arguing about the best way to deal with the financial crisis, for example, then the fact that your opponent smoked pot once in 10th grade probably isn’t relevant.

Appeal to authority. Check out my post on the worst advertisement ever for my favorite example. In essence, this type of argument hinges on the hope that the listener will believe a statement is true simply because it was made by a prominent figure. Lots of money is spent and poor decisions are made because people are more than willing to do what an authority figure directs them to do.

A particularly heinous way in which appeals to authority are used is in commercials with doctors to sell products. A doctor’s opinion on a particular product or procedure means nothing unless that doctor has conducted peer-reviewed research to back his opinion up. Unfortunately, many of us are quick to trust anything that comes out of a doctor’s mouth without carefully scrutinizing her statements.

3) Basic statistics.

People rarely question the statistics that they encounter on a day-to-day basis. For example, when you hear that 50% of people believe X, you should immediately ask yourself 1) What was the sample size on that poll? and 2) What sample population was polled (e.g., a call-in poll would have very different results if the viewers were calling in while watching Bill O’Reilly as opposed to Keith Olbermann)?

Many people also fail to put statistics into perspective. Hearing that 332 peopled died from swine flu sounds impressive, but it means nothing unless you also know how many people were infected total (and did not die) as well as information about the people that did die (e.g., were these 332 people immunocompromised or elderly?). I’m certainly not indicating that the swine flu or other emerging diseases should not attract our attention (or more importantly the attention of epidemiologists), but I do think that the publicity surrounding swine flu caused unnecessary hysteria in the United States.

Here is another good blog post on the misuse of statistics by creationists and AIDS denialists.

4) Home economics.

This course would cover the absolute basics, including what to expect when you get your first credit card, buy your first house, or take out your first loan. Who knows, maybe we could have avoided some of the current housing crisis if people understood what they were getting into.

–

Don’t Be a Sucker 101 wouldn’t even have to be a particularly long course. If the course met for 2 hour sessions once a week it could probably be done in a month’s time. Anyway, I’m looking forward to hearing about what you think belongs in a Don’t Be a Sucker course.