Tag Archives: evolution

How do new species form?

by Piter Kehoma Boll

A long, long time ago, I wrote two posts here about the definition of species, explaining briefly the most important horizontal and vertical species concepts. So we all agree that species exists, but how they emerge? How one species become two, or how one species become another?

The phenomenon by which it occurs is called speciation. Well, sort of… It all depends on how you define a species, actually (so be certain to have read the posts I mentioned above).

355px-simplified_sketch_of_a_speciation_event_-_journal-pone-0042970-g007

Model of a lineage splitting into two lineages that evolve independently and eventually become separated species. Extracted from Hawlitschek et al. (2012)*

Speciation is usually defined as the evolution of reproductive isolation, therefore it deals more with the concept of biological species, but also with the ecological concept and certainly needs some insights on the vertical concepts. If two populations are reproductively isolated, it means that the individuals of one of them are unable or unwilling to breed with those of the other. This usually arrives through genetic and ecological differences that lead to differences in behavior, morphology, physiology. And considering that, we can classify reproductive isolation into two groups: pre-zygotic and post-zygotic isolation.

In pre-zygotic isolation, the two species are reproductively isolated because they do not want or cannot mate and produce an zygote. This may happen simply because of different behaviors in which the two species occupy different places in the environment, mate at different times of the year or even because they are not sexually attracted to each other. There are several experiments using fruitflies that demonstrate how this may evolve pretty fast.

In the late 1980s, William R. Rice and George W. Salt separated individuals of Drosophila melanogaster depending on their preference for dark × light and wet × dry environments, allowing them to mate only with other specimens showing the same preferences. After several generations, the individuals of one group were unable to mate with those of other groups because of their strong habitat preferences, making them unlikely to interact. A similar experiment was performed by Diane Dodd using the species Drosophila pseudoobscura, in which one population was raised with starch as food and other with maltose as food. In this case, after several generations the flies showed a strong preference to mate with individuals of the same group and to reject those of the other group.

640px-drosophila_speciation_experiment-svg

Evolution of reproductive isolation in fruit flies of the species Drosophila pseudoobscura after several generations fed with different sugars.

Such speciation events are called ecological speciation and are also well-documented in the widl, especially regarding fish preferring different habitats, such as shallow × deep water or still × running water. Eventually the individuals will diverge into two groups that are ecologically isolated in the same environment and consequently become reproductively isolated as well.

Post-zygotic isolation is generally a more advanced form of isolation that indicates deep genetic divergences. This is more commonly associated with the notion of biological species and is based on the inability of the individuals of the two species to produce viable offspring. They may mate with each other and even produce a zygote, but this will be unable to developed into an embryo or the offspring will be sterile or otherwise unable to survive enough to breed. A classical example is the mule, the hybrid of a mare and a donkey that is usully sterile.

Equus

A mare, Equus ferus caballus (left), a donkey, Equus africanus asinus (right) and a mule (center). Photos by ‘Little Miss Muffit’ (flickr.com/people/42562654@N00)(mare), Adrian Pingstone (donkey) and Dario Urruty (mule).

In both forms of speciation mentioned above, reproductive isolation usually arises from the accumulation of small differences due to natural selection. This may be enhanced by two phenomena, pleiotropy and genetic hitchhiking.

Pleiotropy is the phenomen by which a single gene have influence over more than one phenotypic trait. For example, a gene that influences the shape of a bird’s bill may also make it change its diet and its song. Several human genetic diseases, such as phenylketonuria (PKU), are examples of pleiotropy.

579px-leghorn_frizzle_chicken

The frizzled trait in chickens, which makes the feather curl outward, also leads to delayed sexual maturity and decreased metabolism rate. Photo by flickr user Just chaos.*

Genetic hitchhiking, on the other hand, is the phenomenon by which a gene that is naturally selected carries neighbours genes that are in the same DNA chain with it. In fruitflies, for example, a gene that is linked to courtship behavior may be drawn with the gene linked to a digestive enzyme, so that flies that specialize in one kind of sugar have a different courtship behavior than others specialized in another sugar.

That’s all for now. In a future post, I’ll talk about the geographic and genetic variables in species formation.

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References and further reading:

Bolnick, D. I., Snowberg, L. K., Patenia, C., Stutz, W. E., Ingram, T. & Lau, O. L. 2009. Phenotype-dependent native habitat preference
facilitates divergence between parapatric lake and stream stickleback. Evolution, 63(8): 2004-2016.

Hendry, A. P.2009. Ecological speciation! Or the lack thereof? Canadian Journal of Fisheries and Aquatic Sciences, 66: 1383-1398.

Hoskin, C. J. & Higgie, M. 2010. Speciation via species interactions: the divergence of mating traits within species. Ecology Letters, 13: 409-420.

Maan, M. E., Hofker, K. D., van Alphen, J. J. M. & Seehausen, O. 2006. Sensory drive in cichlid speciation. The American Naturalist, 167(6):
947-954.

Nosil, P. 2008. A century of evolution: Ernst Mayr (1904-2005). Ernst Mayr and the integration of geographic and ecological factors in
speciation. Biological Journal of the Linnean Society, 95: 26-46.

Turelli, M., Barton, N. H. & Coyne, J. A. 2001. Theory and speciation. TRENDS in Ecology and Evolution, 16(7): 330-343.

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Friday Fellow: Gold-and-Brown Rove Beetle

ResearchBlogging.orgby Piter Kehoma Boll

It’s time for our next beetle. Today the fellow I chose is Ontholestes cingulatus or gold-and-brown rove beetle. Rove beetles are the second most numerous family of beetles after weevils. Their more remarkable feature is that their elythra are short, not covering the abdomen most of the time. I always say that they look like if they were wearing a little jacket. So if you find an elongate beetle with short jacket-like elythra, it is most likely a rove beetle.

The gold-and-brown rove beetle is found throughout North America and is a predator as most rove beetles. It is usually found near carrion and dung, but it is not a scavenger. What it does there is too prey on fly larvae feeding on the rotten material.

An adult showing the nice golden "tail". Photo by Bruce Marlin.*

An adult showing the nice golden “tail”. Photo by Bruce Marlin.*

The gold-and-brown rove beetle is 13–20 mm long and mostly brown, but the last abdominal segments, as well as the underside of the thorax, have a beautiful and shiny gold color.

The mating behavior of the gold-and-brown rove beetle is interesting. Usually the male stays around the female after copulating with her in order to guard her from other males. This behavior usually ends soon after the female has laid the eggs, since at this point the male can be sure that he is the father of the children. To perform this guarding behavior is costly for the male, as he could be using this time to copulate with another female. But as receptive females are kind of rare, it is more advantageous to assure the paternity of the offspring of at least one female than to risk losing everything.

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References:

Alcock, J. (1991). Adaptive mate-guarding by males of Ontholestes cingulatus (Coleoptera: Staphylinidae) Journal of Insect Behavior, 4 (6), 763-771 DOI: 10.1007/BF01052230

BugGuide. Species Ontholestes cingulatus – Gold-and-Brown Rove Beetle. Available at: < http://bugguide.net/node/view/9548 >. Access on August 1, 2016.

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Gender Conflict: Who’s the man in the relationship?

ResearchBlogging.orgby Piter Kehoma Boll

Everyone with some sort of knowledge on evolution have heard of sexual conflict, how males and females have different interests during reproduction, and sexual selection, i.e., how one sex can influence the evolution of the other.

Sexual organisms are almost always defined by the presence of two sexes: male and female. The male sex is the one that produces the smaller gamete (sexual cell) and the female sex is the one that produces the larger gamete. The male gamete is usually produced in large quantities, because as it is small, it is cheaper to produce. On the other hand, the female gamete is produced in small quantities, because its large size makes it an expensive gamete.

A classical image of a male gamete (sperm) reaching a female gamete (egg) during fertilization. See the astonishing difference in size.

A classical image of a male gamete (sperm) reaching a female gamete (egg) during fertilization. See the astonishing difference in size.

As one can clearly see, the female puts a lot more resources in the production of a single descendant than a male does. As a result, females are usually very choosy regarding who will have the honor to fertilize her eggs. Males need to prove that they are worth the paternity, and female choice, through generations, increase male features that they judge attractive. A classical example is the peacock.

The peacock is one of the most famous examples of how sexual selection can drive the evolution of dioecious species. Photo by Oliver Pohlmann.

The peacock is one of the most famous examples of how sexual selection can drive the evolution of dioecious species. Photo by Oliver Pohlmann.

There are a lot of exceptions, of course, most of them driven by the social environment of the species or due to a unusual natural environment which may increase male investment. But all of this stuff refers to dioeicious species, i.e., species in which male and females are separate organisms. But what happens if you are part of a hermaphroditic species, therefore being male and female at the same time? Do you simply mate with anyone? Is everyone versatile everytime they get laid?

Well, there is a lot of diversity in these organism, but all the principles of sexual conflict are still valid. Even if you are male and female at the same time, you still has the desire to fertilize as many eggs as possible with your cheap sperm while choosing carefully who is worth fertilizing your own eggs. The main problem is that anyone else wants the same.

- Come on, darling. Let me fertilize you. - Will you let me fertilize you too? Photo by Jangle1969, Wikimedia user.*

“Come on, darling. Let me fertilize you.”
“Will you let me fertilize you too?”
Photo by Jangle1969, Wikimedia user.*

Imagine that you are a hermaphrodite with a handful of expensive eggs and lots of cheap sperm. You are willing to mate and you go on a hunt. Eventually you find another individual with the same intentions. You look each other in the eyes, get closer and start a conversation. Let’s assume that you didn’t find the other one very attractive to be the father of your children, but you whan to be the father of their children.

“So, what are your preferences?” you ask.
“Right now, I wanna be the male” the other one answers.

“Damn!”, you think. Both of you want the same thing. You guys want to play the same sexual role, so there’s a conflict of interests, or, as it is called, a “gender conflict”. In this case, regarding sexual behavior in biology, the word gender refers to the role you play during sex. Who will be the man in the relationship?

In face of this conflict, this hermaphrodite’s dilemma, you both have to find a solution. There are four possible outcomes:

1. You insist on being the male and your partner agrees to play the female against their will. You win, the other one loses.
2. Your partner insists on being the male and you agree to play the female against your will. The other one wins, you lose.
3. Both of you insist on being the male. Sex doesn’t happen and both of you go home without having got laid.
4. Both of you agree to play both roles. Sex happens and you successully deliver your sperm, but is forced to accept the other guy’s sperm too.

The worst for you is not being able to deliver your sperm, as you wished. So 2 and 3 are the worst outcomes. 1 is the better outcome for you, but how will you convince your partner to be the loser? So, the best solution for everyone is 4. Both are neither fully happy nor fully frustrated.

Eartworms use the 69 position to exchange sperm. Photo by Beentree, Wikimedia user.*

Eartworms use the 69 position to exchange sperm. Photo by Beentree, Wikimedia user.*

But is this the end? Not necessarily. The most stable mating behavior in a population is indeed to agree to play both roles, but things can go on after you kiss your mate goodbye. Now you have to deal with post-copulatory selection.

You have had sex, you delivered your sperm, but received sperm in return. A low-quality sperm in your opinion. You won’t let that fertilize your eggs, will you? Of course not! So, as soon as your partner is out of sight, you simply spit the sperm out before it reaches your eggs! He will never know.

A pair of flatworms, Macrostomum sp., mating. See how the white one, at the end, bends over itself and sucks the other guy's sperm in order to get rid of them. Image extracted from Schärer et al. (2004) [see references].

A pair of flatworms, Macrostomum sp., mating. See how the white one, at the end, bends over itself and sucks the other guy’s sperm out of the female pore in order to get rid of it. Image extracted from Schärer et al. (2004) [see references].

So you cheated your partner! You agreed to receive their sperm in exchange of your own, but then you discarded it as soon as your partner went away. You rule! Right? But… wait! What if they did the same? What if your sperm was discarded too?

You cannot risk that. That would be worse than not having get laid at the first place, because you would have wasted energy and sperm for nothing! But how can you assure that the sperm remains where it is supposed to be?

One strategy is to include some stiff bristles on your sperm cells so that they stick  on the inner wall of the female cavity and cannot be removed. The sperm cells function like thorns or spines that go in easily but are very hard to be pulled back. That’s what some flatworms do.

Two strategies used by species of Macrostomum to force the partner to have your sperm. (A) A species in which two individuals share sperm but later may try to get rid of the partners sperm have evoled sperm cells with bristles that hold the sperm in the female cavity. (B) Other species have evolved a more aggressive behavior, in which they inject sperm in the partner using a sytlet (penis) with a sharp end able to pierce the body. In this case there is no need to have bristled sperm cells. Image extracted from Shärer et al. (2011) [see references].

Two strategies used by species of Macrostomum to force the partner to have your sperm. (A) A species in which two individuals share sperm, but later may try to get rid of the partner’s sperm, have evoled sperm cells with bristles that hold the sperm in the female cavity. (B) Other species have evolved a more aggressive behavior, in which they inject sperm in the partner using a stylet (penis) with a sharp end able to pierce the body. In this case there is no need to have bristled sperm cells.
Image extracted from Shärer et al. (2011) [see references].

Other species evolved a more aggressive approach. They armed their penises with a sharp point that pierces the partners body, forcing it to take the sperm. The sperm is injected in the partner’s tissues and swims towards the eggs.

Both strategies may look like wonderful solutions for the male, but remember that they are hermaphrodites, so that everything can be used against themselves! And that’s the big hermaphrodite’s dilemma, or the ultimate hermaphrodite’s paradox. They are constantly trying to outrun themselves.

Isn’t evolution amazing?

See also: Endosperm: the pivot of the sexual conflict in flowering plants.

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References and futher reading:

Anthes, N., Putz, A., & Michiels, N. (2006). Hermaphrodite sex role preferences: the role of partner body size, mating history and female fitness in the sea slug Chelidonura sandrana Behavioral Ecology and Sociobiology, 60 (3), 359-367 DOI: 10.1007/s00265-006-0173-5

Janicke, T., Marie-Orleach, L., De Mulder, K., Berezikov, E., Ladurner, P., Vizoso, D., & Schärer, L. (2013). SEX ALLOCATION ADJUSTMENT TO MATING GROUP SIZE IN A SIMULTANEOUS HERMAPHRODITE Evolution, 67 (11), 3233-3242 DOI: 10.1111/evo.12189

Leonard, J. (1990). The Hermaphrodite’s Dilemma Journal of Theoretical Biology, 147 (3), 361-371 DOI: 10.1016/S0022-5193(05)80493-X

Leonard, J., & Lukowiak, K. (1991). Sex and the simultaneous hermaphrodite: testing models of male-female conflict in a sea slug, Navanax intermis (Opisthobranchia) Animal Behaviour, 41 (2), 255-266 DOI: 10.1016/S0003-3472(05)80477-4

Marie-Orleach, L., Janicke, T., & Schärer, L. (2013). Effects of mating status on copulatory and postcopulatory behaviour in a simultaneous hermaphrodite Animal Behaviour, 85 (2), 453-461 DOI: 10.1016/j.anbehav.2012.12.007

Schärer, L., Joss, G., & Sandner, P. (2004). Mating behaviour of the marine turbellarian Macrostomum sp.: these worms suck Marine Biology, 145 (2) DOI: 10.1007/s00227-004-1314-x

Schärer, L., Littlewood, D., Waeschenbach, A., Yoshida, W., & Vizoso, D. (2011). Mating behavior and the evolution of sperm design Proceedings of the National Academy of Sciences, 108 (4), 1490-1495 DOI: 10.1073/pnas.1013892108

Schärer, L., Janicke, T., & Ramm, S. (2015). Sexual Conflict in Hermaphrodites Cold Spring Harbor Perspectives in Biology, 7 (1) DOI: 10.1101/cshperspect.a017673

Wethington, A., & Dillon, JR, R. (1996). Gender choice and gender conflict in a non-reciprocally mating simultaneous hermaphrodite, the freshwater snail,Physa Animal Behaviour, 51 (5), 1107-1118 DOI: 10.1006/anbe.1996.0112

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Biological fight: kites, mites, quite bright plights

ResearchBlogging.orgby Piter Kehoma Boll

A recently described fossil from the Silurian Herefordshire Lagerstätte in the United Kingdom has called much attention.

A photo of the fossil itself. Image by Briggs et al., extracted from news.nationalgeographic.com

A photo of the fossil itself. Image by Briggs et al., extracted from news.nationalgeographic.com

The appearance of the creature was build by scanning the rock and creating a 3D reconstruction of the fossil. It revealed that the animal, obviously and arthropod, had several smaller creatures attached by long threads, like kites. The species was named Aquilonifer spinosus, meaning “spiny kite-bearer”.

A 3D reconstruction of what Aquilonifer and its kites would have looked like. Image by Briggs et al. extracted from sci-news.com

A 3D reconstruction of what Aquilonifer and its kites would have looked like. Image by Briggs et al. extracted from sci-news.com

The authors (Briggs et al., 2016) thought about three possibilities to explain the unusual “kites”. They could be parasites, phoronts (i.e., hitchhikers), or babies. The idea of parasites was discarded because such long threads separating them from the host would have made it difficult to feed properly. They also considered it unlikely to be a case of phoronts, i.e., a species that uses the host as a mean to move from one site to another, because there were too many of them and the host most likely would have removed them by using the long antennae.

Artistic impression of Aquilonifer spinosus by Andrey Atuchin.

Artistic impression of Aquilonifer spinosus by Andrey Atuchin.

The remaining option is that the kites were offspring. The mother (or father) would have attached them to itself in order do carry them around in a unique mode of brood care. The authors compare it to several other arthropod groups in which some species carry their babies around during their first days. They also consider that the animal could have delayed its molting process to avoid discarding the babies with the exoskeleton.

But can we be sure that this is the case? The entomologist Ross Piper thinks differently. He compares the kites to uropodine mites, in which the juveniles (deutonymphs) attatch themselves to beetles by long stalks in order to be transported from one food source to another. As there are marine mites, that could be the case. He also points out that the kites are scattered through the body, which would make them unlikely to be offspring, as such a distribution would only hinder the parent’s mobility.

Briggs at al. responded to Piper’s critique arguing that marine mites have only recently evolved and that Aquilonifer is very different from a terrestrial beetle. It was most likely a bentonic species, crawling on the ocean’s floor, and not a swimmer, so that it would not be a very good dispersal agent.

What do you think of it? I find it difficult to choose one side. Piper’s comparison with mites is interesting, but only as a way to suggest a convergent evolution. I cannot see how the kites would have been really mites or even arachnids. Now the argument on the kites’ position on the body is a good point. No other group of animals carries their young attached to long stalks spread all over the body. Furthermore, how would the parent properly place the juveniles there? I can only see it as a plausible way if the host were the father and the mother crawled over him to stick the eggs in place. Additionally, couldn’t they be true phoronts  that were benefitial to the host? The little fellows could benefit by moving around on the big pal and reaching new food sources while giving protection or other advantage in return. And regarding the delay in molting, I cannot see any evidence that there was any delay. We don’t know how long the kites remained there and perhaps after molting they could simply leave their little houses and build new ones on the host’s new skeleton.

We may never know the truth, but we can keep exchanging ideas.

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References:

Briggs, D., Siveter, D., Siveter, D., Sutton, M., & Legg, D. (2016). Tiny individuals attached to a new Silurian arthropod suggest a unique mode of brood care Proceedings of the National Academy of Sciences, 113 (16), 4410-4415 DOI: 10.1073/pnas.1600489113

Briggs, D., Siveter, D., Siveter, D., Sutton, M., & Legg, D. (2016). Reply to Piper: Aquilonifer’s kites are not mitesProceedings of the National Academy of Sciences, 113 (24) DOI: 10.1073/pnas.1606265113

Piper, R. (2016). Offspring or phoronts? An alternative interpretation of the “kite-runner” fossil Proceedings of the National Academy of Sciences, 113 (24) DOI: 10.1073/pnas.1605909113

Switek, B. 2016. This bizarre creature flew its babies like kites. National Geographic News. Available at < http://news.nationalgeographic.com/2016/04/160404-bizarre-creature-flew-babies-kites-arthropod-fossils-science/ >. Access on July 07, 2016.

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Male dragonflies are not as violent as thought

ResearchBlogging.orgby Piter Kehoma Boll

Males and females are defined by their gametes. Males have tiny, usually mobile gametes, while females have very large gametes that usually do not move. This means that females produce less gametes, but put a lot of resources in each one, i.e., female gametes are expensive. On the other hand, male gametes are very cheap, small and produced in large quantities. As a result of these differences, males and females have different interests during sex.

As females produce more expensive and less numerous gametes, they tend to be very selective on who they let fertilize them. But males benefit from fertilizing every female gamete they find in their way. In other words, females want quality and males want quantity. This difference in interests is called sexual conflict and is a strong evolutionary force.

One evolutionary adaptation that has been seen as resulting from sexual conflict is the mating system in odonates (dragonflies and damselfies). During sex, the male dragonfly grasps the female neck using a grapsing apparatus at the end of its abdomen. The female is then induced to connect the tip of its abdomen to the second and third segments of the male’s abdomen, where sperm is stored. The couple than flies together in a heart-like formation.

Two dragonflies of the species Rhionaescna multicolor copulation. The male is the blue one, which is grasping the female's neck and making her touch the tip of her abdomen to his second and third abdominal segments, where sperm is stored. Photo by Eugene Zelenko.*

Two dragonflies of the species Rhionaeschna multicolor copulating. The male is the blue one, which is grasping the female’s neck and making her touch the tip of her abdomen to his second and third abdominal segments, where sperm is stored. Photo by Eugene Zelenko.

It was thought that the male grasping apparatus forced an unwilling female to copulate with him, suggesting that the organ evolved through sexual conflict. The fact that males usually grab females way before they accept to mate and continue to hold them for a long time after the mating has finished (preventing her from mating with other males) seem to be good evidence for this theory. If this is true, than the female would try to get rid of the male, selecting stronger and bigger grasping apparatuses in males, as those would be more efficient in holding the female and, as a result, would lead to more descendants.

A study published last year tested this hypothesis. Córdoba-Aguilar et al. (2015) evaluated the allometry (the proportional size of a structure with respect to body size) of the male grasping apparatus in several dragonfly species. If males forced females to copulate, a hyperallometric relationship should be expected.

What does that mean? Well, let’s try to explain it the simplest way. When you plot data on the size of a structure according to the size of the body as a whole on a graph, using values that lead to a linear relationship, you may have different results. The structure may increase in size in the same way as the body, in a 1:1 relationship. In this case, the line in the graph is said to have a slope equal to 1 and there is an isometric relationship of the structure to the body. If the slope is greater than one, this means that the structure grows faster than the body, having a hyperallometric relationship. If the slope is smaller than one (but greater than zero), the relationship is hypoallometric and the structure grows slower than the body.

allometry

The measurements of the grasping apparatus in dragonflies in general showed an isometric relationship. So, according to this approach, the structure did not evolve as a “weapon” to subdue females. But which other explanations may exist then? It could be used as a courtship tool, a way for the male to convince the female to mate with him. It could also be a way to avoid interspecific mating, as the grasping apparatus has a strong specificity in shape to the female neck of the same species. A male dragonfly cannnot grasp a female of other species because the grasping apparatus simply does not fit in the female’s neck.

Both alternative hypotheses for the evolution of the apparatus are possible, but further studies are needed to test them.

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References:

Chapman, T., Arnqvist, G., Bangham, J., & Rowe, L. (2003). Sexual conflict Trends in Ecology & Evolution, 18 (1), 41-47 DOI: 10.1016/S0169-5347(02)00004-6

Córdoba-Aguilar, A., Vrech, D., Rivas, M., Nava-Bolaños, A., González-Tokman, D., & González-Soriano, E. (2014). Allometry of Male Grasping Apparatus in Odonates Does Not Suggest Physical Coercion of Females Journal of Insect Behavior, 28 (1), 15-25 DOI: 10.1007/s10905-014-9477-x

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Friday Fellow: Taq

by Piter Kehoma Boll

It’s time for us to start to look at the tiny little creatures living with us in this world. We haven’t featured any bacterium yet, so here comes the first one, the magnificent Taq!

Taq stands for Thermus aquaticus, the bacterium’s scientific name. It was initially discovered in hot springs of the Yellowstone National Park, but certainly no one could guess how it would impact science as a whole.

The Great Fountain Geyser in Yellowstone National Park is located near the place where Taq was first found. Photo by Paul Kordwig.*

The Great Fountain Geyser in Yellowstone National Park is located near the place where Taq was first found. Photo by Paul Kordwig.*

Usually with a small rod shape less than 1 µm in diameter and up to 10 µm in length, Taq can also reach more than 200 µm in length when acquiring a filament shape. Living in hot springs all around the world, it thrives at about 70°C. It produces its own food via chemosynthesis by oxydizing inorganic elements in the environment, but it can also associate with some cyanobacteria living in the same habitat to obtain food from their photosynthesis.

Taq under the microscope. The scale corresponds to 1µm. Photo by Diane Montpetit.

Taq under the microscope. The scale corresponds to 1µm. Photo by Diane Montpetit.

But what impact did it have in science? Well, because it lives in such high temperatures, Taq’s proteins need higher temperatures to denature, so they are useful to perform biochemical processes in high temperatures, such as in DNA amplification.

PCR (polymerase chain reaction) is a process used for amplifying short segments of an organism’s DNA. It needs to be performed in high temperatures in order to denaturate the DNA chain so that the primers can align. Primers are very short modified DNA fragments that determinate the beginning and the end of the segments that one wants to amplify. Amplifying a DNA segment means producing a large amount of copies of that segment. The problem in earlier PCRs was that the high temperatures needed to denaturate the DNA also denature the enzyme that produces the copies, called DNA polymerase. As a result, there was a need to add enzyme after every cycle of thermal denaturation. The DNA polymerase of Taq, called Taq polymerase, can resist the high temperatures of denaturation, so that it needs to be added only once.

Thanks to Taq polymerase, DNA amplification has become a much more efficient process, accelerating researches in molecular biology.

Sometimes revolution beginns with the tiniest things.

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References:

Brock, T. D. 1997. The value of basic research: discovery of Thermus aquaticus and other extreme thermophiles. Genetics, 146(4): 1207-1210.

Wikipedia. Thermus aquaticus. Available at: <https://en.wikipedia.org/wiki/Thermus_aquaticus&gt;. Access on January 21, 2016.

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Biological fight: the case of artificial stimuli in behavior research

by Piter Kehoma Boll

ResearchBlogging.org The study of animal behavior is an important approach to understand several aspects on the ecology and the evolution of living beings, both from the analyzed animals themselves and the species with which they interact. For example, understanding how a bee recognizes a flower as a food source and how it approaches it may explain a lot about the physiology and the evolution of the flower and vice-versa, thus clarifying why such a combination of characters is the one that is found in the current population.

As with virtually any type of study in biology, a research may be done with sampling or experiments. By sampling you obtain non-manipulated information directly from the environment. You collect or observe a small sample of the whole and infer the general situation of the population based on it. On the other hand, in an experiment you manipulate the environment and watches how the organisms will react to the different stimuli presented to them and, from this, you develop your conclusion.

For example, if you want to know what a species of frog eats, you may find out by sampling, observing some frogs in the wild while they feed or capturing some and examining their stomach contents. You may also offer them different kinds of food, either in the environment or in the lab, and observe how the frogs reacts to each one.

Thus, in experiments you control the stimuli the species receives from the environment. This is the point where things start to get nasty. May the stimuli have artificial elements, i.e., elements that cannot be found by the animal in its habitat?

The opinions about it are divergent and recently led to a “formal fight” published in the journal Ethology:

On one side is a group of researchers from several universities around the world (Hauber et al., 2015) that defends the use of artificial stimuli to analyze behavior. They use as a model the studies on the rejection of eggs of parasitic birds by parasitized birds, a well-studied phenomenon.

First, let us contextualize this phenomenon briefly:

Several bird species, mainly cuckoos, do not incubate their own eggs. Instead of doing it, they lay them in the nests of birds of other species and hope that the poor creatures incubate and later feed the chicks as if they were their own. As a result, natural selection favors cuckoos whose eggs are more similar to the ones of the parasitized bird and also favors the parasitized birds that better distinguish their eggs from the ones of the intruders. It is a typical evolutionary race.

Find the intruder. The similarity between the egg of the parasite and the parasitized can vary greatly. Photos by wikipedia user Galawebdesign (left)* and by Grüner Flip (right).

Find the intruder. The similarity between the egg of the parasite and the parasitized can vary greatly. Photos by wikipedia user Galawebdesign (left)* and by Grüner Flip (right).

In experimental studies on egg rejection by parasitized birds, it is common to use artificial eggs that exaggerate features of natural eggs. This includes, for example, changing color and size in order to understand which is the most relevant for the bird to recognize the eggs as being yours or not. However, can we trust the results of such experiments using artificial elements?

Haubert et al. (2015) think that we can. Their arguments in favor of the use of such artificial stimuli are the following:

  1. Real eggs of the studied species are difficult to get in large quantities and could cause significant impacts over the populations if used. So, artificial eggs ensure the integrity of populations.
  2. It is difficult to get a set of natural eggs similar enough to allow the necessary repetitions to validate the test. After all, a result is only considered valid if it is recorded several times in face of the same stimulus. Artificial eggs allow identical copies and, thus, true repetitions.
  3. Natural eggs vary in several aspects at the same time, such as color, size, form, texture… In artificial eggs it is possible to control these aspects and allow only one to show free variation, so isolating the influence of each one during the recognition by the bird.
  4. A variation beyond the ones found in the wild may help to find populations with different degrees of perception of strange eggs and consequently where are the sites of higher selective pressure.
Original eggs of the parasitized species painted to exaggerate color features. Photos by István Zsoldos. Extracted from Moskát et al. 2010.

Original eggs of the parasitized species painted to exaggerate color features. Photos by István Zsoldos. Extracted from Moskát et al. 2010.

Not everyone looks so favorably to such an unrestrained use of artificial stimuli. Soon after the opinion of Hauber et al. we find the reply of David C. Lahti (2015) who faces all by himself the “artificialist” army. Lahti shows some aversion to such exaggerate use of artificial elements that many times are not used in a responsible manner.

Suggesting a more restrict use of artificial elements, he argues the following:

  1. Our perception of the environment is different from the one of the species we are studying. For instance, a bird sees a much wider range of colors than we do. When we paint an artificial egg black and white in order to simulate a natural black and white egg, we don’t know whether the bird really sees both eggs with the same colors. So, while we suppose that the eggs look similar by our perception, the reality from the bird’s point of view can be very different.
  2. When we try to create a set of artificial eggs that vary in only one aspect, such as the size of the spots on the shell, for instance, in order to control the influence of this stimulus only, we always end up including secondary stimuli that are not measured, such as the paint used to make the spots. If the birds shows a different response to eggs with small spots (natural ones) when compared to eggs with large spots (artificial ones), how can we know that the difference was not caused by the perception of the paint, either chemically or visually, by the animal? It would be necessary to perform tests that would discard this possibility, but it does not happen usually.
  3. Exaggerated artificial stimuli may go beyond the species’ range of recognition. An egg with a color too different from any color variation found in the environment could cause the bird not to see it as an egg, which would lead to problems in the interpretation of the results.

Concerning this last argument, Hauber et al. emphasize that is important to take care on a priori interpretations on the species behavior. That is to say, we cannot guess what the bird is thinking. The fact that the bird removes the parasite’s eggs from the nest or not does not mean that it is capable of recognize the egg as an intruder, or even as an egg. The way the bird interprets the stimulus is not as important as its response to it.

Therefore, we can conclude that artificial stimuli can be advantageous and in several circumstances they are the only available alternative. It is important, however, to take care with their use and try to be sure that secondary features, generally neglected, are not considered important by the animal.

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References:

Hauber, M.; Tong, L.; Bán, M.; Croston, R.; Grim, T.; Waterhouse, G.; Shawkey, M.; Barron, A.; & Moskát, C. 2015. The Value of Artificial Stimuli in Behavioral Research: Making the Case for Egg Rejection Studies in Avian Brood Parasitism Ethology, 121 (6), 521-528 DOI: 10.1111/eth.12359

Lahti, D. 2015. The Limits of Artificial Stimuli in Behavioral Research: The Umwelt Gamble Ethology, 121 (6), 529-537 DOI: 10.1111/eth.12361

Moskat, C.; Ban, M.; Szekely, T.; Komdeur, J.; Lucassen, R.; van Boheemen, L.; & Hauber, M. 2010. Discordancy or template-based recognition? Dissecting the cognitive basis of the rejection of foreign eggs in hosts of avian brood parasites Journal of Experimental Biology, 213 (11), 1976-1983 DOI: 10.1242/​jeb.040394

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