Lesbian Lizards of South America

Lesbian Lizards of South America

Some people may be disappointed that this is not some kind of sci-fi porn script but it is a pretty interesting occurrence (and it is completely true). This article will focus on sexual reproduction and the benefits and shortcomings of both asexual and sexual species. There is, unfortunately, a lot of background necessary before I get to the lesbian lizards so if that’s not your thing, skip down the second section “Species surviving without sex”. Although typically species exhibit two distinct sexes, certain organisms reproduce asexually. Offspring is produced from a single parent and therefore inherits genes from a sole donor. Such species are sometimes present as a single sex and have adapted to survive in this way. Both vertebrates and invertebrates have been observed to express forms of asexual reproduction naturally, however it is often unclear why certain organisms switch from sexual reproduction to asexuality.

Some sensual girl on girl lizard sex.

Sexual Reproduction

To put it very simply, sexual reproduction is the fusion of 2 gametes via fertilisation to form a zygote which will inevitably develop into the complete organism. There are many benefits to utilising the genetic makeup of 2 parents. First and foremost, it allows for genetic mixing and the purging of deleterious or harmful mutations within a population. Sexual reproduction will also increase the rate of adaptation to an ever changing environment as favourable traits are more likely to be passed on to offspring. However, relying on a mate is costly. The “2 fold-cost of sex” is a theory first outlined by John Maynard Smith and accurately states that when undergoing sexual reproduction, only half of your genetic material is being passed on and the overall genome of the offspring is being shared with another member of the population. There is also the risk of potentially breaking up favourable genetic combinations. Some “good genes” might not get passed on, potentially lowering the general fitness of offspring. Finally, finding a mate is in itself costly. Often, seeking a suitable partners requires significant investment of time and energy whilst also increasing the risk of predation and parasite transmission. Several species have such bizarre mating rituals that the male or female are harmed in the process, inhibiting future reproductive ability. So why bother? If the 2-fold cost of sex tells us anything, sexual reproduction is half as effective as asexual reproduction of passing on genes.

A very costly mating strategy. The male preying mantis sacrifices its own life for fecundity. In order to mate with the female, he allows her to literally eat him.

A diagram highlighting the 2-fold cost of sex. Reliance on a mate only allows half of the individuals genetic material to be passed to offspring. Asexual populations do not incur this cost and all genes passed on are the single parents. 

Species Surviving Without Sex - Lesbian Lizards, Bdelloid rotifers and many, many more.

It would appear that most animals utilise 2 parents and sex to produce offspring. We do it, as do dogs, cats, horses, lions, tigers, rabbits etc. etc. However, more animals than you think have scrapped the ‘popular’ system. In my opinion, the best example of this is the Whiptail Lizard (Cnemidophorus). They originated from hybridisations of sexually reproducing species and have since adapted to life without males. Females can produce full clones of themselves through a modified form of meiosis. The female’s germ cells undergo premeiotic doubling so that 2 consecutive division cycles in the meiosis process result in a diploid, instead of a haploid genome. The females in this population have actually been observed to mimic sex acts, as if mating was occurring between a male and female, but with no actual sex taking place, just to get the hormones pumping. I have included a link below to show exactly what I mean because I can’t mention lizard girl on girl action without some kind of video.

http://www.bbc.co.uk/programmes/p006v48r

Obligate parthenogenesis is the process whereby organisms reproduce exclusively asexually, like the whiptail lizard, who have no other option but to do so. The most documented, historic example is bdelloid rotifers. These microscopic organisms have been present for millions of years and yet, not one male has ever been documented. On the other, more adaptive side of asexual reproduction, is the facultative parthenogens. These animals are generally sexually reproducing, but can switch to asexual reproduction when extreme conditions make it necessary. The Komodo dragon, hammerhead shark and blacktip shark are prominent vertebrate examples of this phenomenon. Other creatures capable of parthenogenic reproduction are several snail species, many flatworms, water fleas, some crayfish, honey bees, parasitic wasps as well as at least 20 fish, 25 lizard, 1 snake, frog and salamander species.

Looking for a mate? Doesn't matter, she can reproduce without one!

Disadvantages of Single Sex Reproduction

Although reproducing asexually removes the expenditure associated with finding a mate, copulating and all the other risks involved, sexual reproduction is a much more beneficial mechanism of reproduction. If an organism lives in a changeable environment, it is easy for an individual to fall prey to its own ecosystem. For example, if new predators are introduced, it would be difficult to adapt a form of defence or camouflage; or say the climate changes it may be difficult for the individual to moderate its body temperature effectively. Also with asexual organisms, harmful mutations become “trapped” within a population as there is no genetic mixing/heterozygosity to remove them. Of course this is an issue that can occur in sexually reproducing organisms but it is less likely that these harmful traits will be passed on to subsequent generations (Unless inbreeding is involved – see http://www.stannagescience.blogspot.com.au/2015/01/inbreeding.html for more information). Accumulation of deleterious mutations is known as "Muller's Ratchet".

Conclusion

In many instances, eliminating one gender has proved successful but it is not without its added risks. To conclude, there is not one correct way of survival in regards to reproduction, it is a matter of adaptation to extreme circumstances as well as avoiding the accumulation of harmful mutations within a population. Success stories from either side provide evidence they can co-exist and bdelloid rotifers have shown you can survive exclusively without mating for millions of years! Although they don’t lead a particularly exciting life.

I have done my best to reel this post in as it was quickly becoming a full blown essay. If I haven’t been clear on any areas I can expand on some points and provide more colourful examples!

Cheers!

Simple Science Shorts #2

Science shorts 2

I made several promises that I would continue to write this blog after I left to go travelling. I had every intention of chilling in some internet café in Asia, having coffee and typing away but of course, at no stage did that actually happen. I have been lazy, and I intend on changing that now. Without diving straight into a full post on a specific topic I will try to piece together an easy to write, easy to read set of explanations for day to day occurrences or subjects that I have thought about over the past week. Ease myself back into it!

I like this picture. Its even relevant to the first section of this blog. DO NOT GIVE CHOCOLATE TO PUPPIES.

Why is chocolate toxic to dogs?

It is fairly wide known to anyone that owns a dog, not to give it chocolate. I was curious as to the specific reason for this however as it would be interesting if the particular substance that causes this toxicity is present in other things that could come into contact with dogs. It turns out that the poisonous substance contained within chocolate is theobromine, a xanthine alkaloid. Not only is this substance lethal to dogs, it is also poisonous to us, albeit in significantly larger doses. The lethal dose (LD₅₀) of theobromine in dogs is ~300mg/Kg body mass whereas in humans, LD₅₀ = ~1000mg/Kg. Take into account the significantly larger body weight of people and it is obvious how little chocolate is needed to poison a dog (and obviously it would take much less chocolate to kill a Chihuahua than a Great Dane). Theobromine increases metabolic rate, cardiovascular activity and neural activity which can result in cardiac arrest, hyperventilation and seizures in canines. This becomes fatal when the chemical pushes the body to function far beyond its capabilities resulting in permanent damage. Theobromine is found in chocolate because it is produced by the cocoa plant. This means that it can also be traced in coffee (and other caffienated beverages), cocoa powder as well as in tea leaves so again, avoid letting your dog come into contact with anything associated with cocoa plants!

One thing that is also very peculiar is that cats actually have a lower theobromine LD₅₀ than dogs. However, they do not possess the necessary receptors on their tongues to taste sweetness, and are therefore at a lower risk of ever experiencing theobromine poisoning.

The moral of this section is don't risk giving chocolate to a dog, even a small amount can be deadly. Think of the puppies.

Goosebumps

Hot dogs or legs?

Everyone at some stage has experienced Goosebumps. These small bumps on your skin and erect hairs arise from exposure to cold temperatures or even experiencing strong emotions such as fear, arousal or euphoria. Goosebumps, termed medically as “horripilation”, is innervated from the sympathetic branch of the autonomic nervous system and facilitated via contraction of arrector pili muscles attached to the hair follicles. This involuntary contraction responds to a variety of stresses for a number of reasons. The primary function is considered to be for insulation. Air becomes trapped between the erect hairs which enables the individual to retain heat. However, this trait has underwent expatation and is therefore not exclusively developed for heat retention. The sympathetic nervous system is synonymous with the ‘fight or flight’ response. There are strong hypotheses to suggest that under stressful situations, the contraction of the arrector pili muscles is being utilised to make the individual appear bigger and therefore more intimidating to a potential predator (such is the case in the porcupine raising its spines). It seems however that this trait has become a vestigial response to humans. This means that it has lost its original function. Humans no longer have much body hair to provide much added warmth, nor enough to increase body size a noticeable amount.

Interestingly, the colloquial name “Goosebumps” derives from the appearance of the bumps under a microscope. Evidently, they look very similar to the head and bill of a goose.

A simple representation of the effect of the arrector pili muscles causing a lump in the skin and erection of hair.

When Tanning Stops and Sunburn Begins

Showcasing melanogenesis in response to UVB radiation.

Everyone I know is different. Some people cannot get a tan if they pay for it; other turn golden brown looking out the window; and some people burn watching Thomas cook adverts. Why does the sun affect our skin so differently and what sort of damage is it actually doing to us? As with everything good in life, it is harming us in some way. Melanin pigmentation of the skin protects the body by absorbing solar radiation to a certain extent. The direct cause of tanning is exposure to UV rays from the sun (UVA, UVB or a combination of both) which results signalling to increase protection. The first mechanisms involved, is UVA radiation causing oxidative stress to melanin already present in your skin, resulting in oxidisation and rapid darkening of the skin tone. The second phase is triggered by UVB radiation which initiates melanogenisis (production of melanin). This is the body’s reaction to direct and indirect DNA damage within the skin and the increase of melanin present causes the skin colour to darken. Although the redness of sunburn appears to be the damaged consequence of exposure to UVB radiation, it is actually your body’s photoprotection response. By preventing UV protons from disrupting chemical bonds, melanin inhibits both direct and indirect alternation of DNA and the production of harmful free radicals. The damage of sunburn is mainly the formation of a thymine dimer which triggers several defence mechanisms like melanogenisis as well as apoptosis to kill and remove irreparably damaged cells and an inflammation process. Inflammation produces prostanoids and bradykinin which increase sensitivity to heat (making showering with sunburn particularly unpleasant) and also results in the overproduction of CXCL5 protein, activating nerve fibres, causing pain.

At some stage I intend on covering skin cancer associated with severe sunburn but that will require a post in itself.

There was going to be another section in this blog about allergies however it became very clear early on that this topic is much too large for a "shorts" post. I will make a full post on allergies sometime soon!

As always, feedback and ideas for other topics are very welcome.

Cheers!

Inbreeding

I have recently got into watching Game of Thrones so I thought there is no topic more appropriate than the wonders of inbreeding. Many people have heard the rumours that having offspring with blood relatives results in children with physical and mental defects, however there has never really been an explanation as to why that is the case. This article will outline the genetic reasoning behind these abnormalities (despite my hatred of studying genetics).

What is inbreeding?

Inbreeding is defined as the mating or breeding of individuals with a close genetic relationship (brother and sister, father and daughter etc). The problem lies with recessive genes. Whilst we all carry either beneficial or neutral genes, we also possess a selection of deleterious, recessive genes that have the potential to negatively impact our health. These recessive genes generally remain inactive as they are the recessive form of the gene and are never expressed in the presence of the harmless, dominant gene. If the recessive gene is not expressed, an individual will be a carrier of a potentially harmful genetic condition rather than a sufferer. Family members have a higher probability of carrying the same recessive, gene leading to its expression. The homozygosity of intrafamily-produced offspring means that they are at increased risk of being affected by recessive or deleterious traits which in turn leads to a decreased biological fitness.

Here is an example of a recessive gene being passed from parents to offspring. The second generation are only carrying the gene without experiencing any decrease in biological fitness. When the brother and sister snake then have a baby, the 3rd generation was passed matching recessive alleles which expresses the maladaptive gene. That red snake probably has an extra head, spinal bifida, cystic fibrosis or perhaps it is just red despite being from a black family.

The probability and severity of developing such disorders is increased the closer the genetic relationship between the biological parents (i.e. a brother and sister’s offspring has a much higher likelihood of congenital birth defects than a girl and her mother’s brother). This is because the closer the biological relationship, there is an increase of pairings of deleterious alleles which produce disorders. As the predominance of these deleterious, recessive alleles are rare in populations, it is highly unlikely that two unrelated parents will carry the same allele but close relatives share a large number of alleles, which increases the chance of one becoming dominant and therefore detrimental.

Is it exclusive to humans?

In the animal kingdom, inbreeding is more commonplace. Firstly there isn’t as much stigma to mating with a cousin when you are an elephant seal but also because often when a population becomes isolated, they do not have an option to breed with non-family. Animals also experience the negative impact of maladaptive homozygosity such is the example of the Isle Royale Wolves. As the population of wolves is isolated on an island, malformations are “stuck” in the population. In the recently published, annual report of the wolves, it was noted that the predation rate on the island has decreased significantly. It has been suggested that this is a result of ongoing inbreeding of the pack (Isle Royale is currently the longest running study of predator/prey interaction due to the observation of wolves and moose that crossed onto the island via an ice bridge. The study is currently in its 57^th year). Abnormalities such as too many bones in the vertebral column and vulnerable immune systems have been noted and are showing signs of spreading and unfortunately, there is no opportunity for genetic relief as “foreign” wolves cannot be naturally introduced to the island.

This is a comparison of a normal wolf vertebrae compared to one taken from an Isle Royale wolf. Note the slight size difference as well as the obvious deformity.

Benefits of Inbreeding

Of course, eliminating genetic diversity can be beneficial. Inbreeding produces uniform and predictable offspring. This is commonly seen in the pure-breeding of animals to ensure desirable traits are maintained and when an undesirable trait appears, selective mating is used to eliminate that particular mutation. Also, the primary issue with inbreeding is the doubling up of deleterious recessive alleles. On the contrary, inbreeding also doubles up advantageous “good genes”, keeping them within a population. 

Blood alcohol, what is your limit?

As you should all know, the legal limit for drinking alcohol and driving was lowered in Scotland on December 5^th.  From now on, a blood alcohol concentration of 50mg/100mls blood is considered over the legal limit (down from 80mg/100mls). Personally it made me realise that I did not fully understand the initial drink drive limit. Before it was commonly accepted to have a single pint or glass of wine and still be perfectly acceptable to drive however this 30mg reduction seems to have made all the difference. This article I will look at how your body processes alcohol and at what stage it becomes legal and safe to operate a vehicle.

An example of when it is not ok to drive soon.

Alcohol in your blood

The more I have looked into this topic the more complicated I have found it. Primarily due to the fact that there are many determining factors from the strength and volume of drink, to the size and weight of the drinker. Not to mention this persons particular tolerance to alcohol. Also a lot of research was conducted in America where they measure both blood alcohol content in different units but also have different serving volumes of alcohol. To put it simply, blood alcohol content is the blood ethanol concentration. In the case of Britain, it is expressed in mg/ml.

Without properly calibrated equipment, it is very difficult to provide an accurate reading of blood alcohol content. There are several “calculators” available online that give you an estimation so I tested to see what effect a small amount of alcohol can have on your body. The test provided the following result: As a 75kg male, if I consumed 2 pints and was tested one hour afterwards, my blood alcohol content would be 57mg/100ml, over the legal limit. Not only that, it would take in excess of 4 hours for that alcohol to completely leave my system. Obviously these online calculators must be taken with a pinch of salt but it shows how little alcohol it takes to be over the limit and also how long it remains in your system for.

Alcohol absorption, distribution and elimination. It takes longer than you might think.

Another major cause for concern is people driving after a drinking the night before. Many of us assume that after a few hours’ sleep, all the alcohol in our system will be gone. This however is not the case. Alcohol is absorbed through the GI tract: rapidly in the small and large intestine (due to its large surface area) but also slowly within the stomach itself. Post-absorption, alcohol is passed via the hepatic portal vein to the liver before entering the bloodstream. Alcohol has a high affinity for water and is therefore transported in the blood throughout the body. Once absorption is complete, an equilibrium occurs such that the blood at all points within the body contains approximately the same concentration of alcohol.

From the bloodstream, alcohol must be removed by a combination of metabolism, excretion and evaporation. The predominance of alcohol removal is via liver metabolism. Alcohol dehydrogenase converts ethanol into acetaldehyde (If you remember a previous blog on hangovers you will be familiar with this and if you haven’t read it, read it now! http://www.stannagescience.blogspot.co.uk/2014/08/the-hangover.html). A healthy individual will metabolise alcohol at a fairly consistent rate. Several factors however will influence the rate in which alcohol is metabolised. Rate of elimination tends to be higher when blood alcohol concentration is very high (potentially as the body considers the levels of toxins as a serious threat and invests more metabolic energy to remove it). Also, chronic alcoholics may actually be able to metabolise alcohol significantly quicker due to increased tolerance. The body’s ability to metabolise alcohol quickly diminishes with age, meaning older people take longer to process the same amount of alcohol as a younger person.

In terms of how long alcohol stays in your bloodstream, it is very difficult to predict. As stated before, there are many contributing factors to the speed of alcohol metabolism and as a result, will vary from person to person how quickly it is eliminated. If you consider a normal, healthy liver. It will metabolise alcohol at a constant rate – approximately 1 gram per hour for every 10kg of bodyweight. This is around 1 unit per hour post-consumption.

It is important to note that there is nothing that you can do to speed up the metabolism and therefore the elimination of alcohol in your system. Having a cup of coffee or a cold shower may make you feel more sober and alert but it has in no way reduced your blood alcohol concentration. When it comes to driving, it really is not worth the risk.

Even drinking plenty of water does not reduce the blood alcohol concentration, even if it does make you feel better.

I found a plethora of fairly average blood alcohol concentration calculators but I found this is one considers more factors and provides more information so I would recommend having a play on this: http://www.alcoholhelpcenter.net/program/BAC_Standalone.aspx

(units are in g/100ml so multiply by 100 to get the UK standard measurement of mg/100ml)