Category Archives: Evolution

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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Friday Fellow: Elegant sunburst lichen

by Piter Kehoma Boll

Bipolar and Alpine in distribution, occurring in both Arctic and Antarctic regions, as well as on the Alps and nearby temperate areas, the elegant sunburst lichen (Xanthoria elegans) is a beautiful and interesting creature. As all lichens, it is formed by a fungus associated with an alga.

An elegant sunburst lichen growing on a rock in the Alps. Photo by flickr user Björn S...*

An elegant sunburst lichen growing on a rock in the Alps. Photo by flickr user Björn S…*

The elegant sunburst lichen grows on rocks and usually has a circular form and a red or orange color. Growing very slowly, at a rate of about 0.5 mm per year, they are useful to estimate the age of a rock face by a technique called lichenometry. By knowing the growth rate of a lichen, one can assume the lichen’s age by its diameter and so determine the minimal time that the rock has ben exposed, as a lichen cannot grow on a rock if it is not there yet, right? This growth rate is not that regular among all populations. Lichens growing closer to the poles usually grow quickly because they seem to have higher metabolic rates to help them survive in the colder climates.

Beside its use to determine the age of a rock surface, the elegant sunburst lichen is a model organism in experiments related to resistance to the extreme environments of outer space. It has showed the ability to survive and recover from exposures to vacuum, UV radiation, cosmic rays and varying temperatures for as long as 18 months!

Maybe when we finally reach a new inhabitable planet, we will find out that the elegant sunburst lichen had arrived centuries before us!

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References:

Murtagh, G. J.; Dyer, P. S.; Furneaux, P. A.; Critteden, P. D. 2002. Molecular and physiological diversity in the bipolar lichen-forming fungus Xanthoria elegans. Mycological Research, 106(11): 1277–1286. DOI: 10.1017/S0953756202006615

Wikipedia. Xanthoria elegans. Available at: < https://en.wikipedia.org/wiki/Xanthoria_elegans >. Access on June 30, 2016.

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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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Friday Fellow: Darwin’s Orchid

by Piter Kehoma Boll

Orchids comprise one of the most numerous families of plants, so it is more than time to have an orchid Friday Fellow. And what could be a better choice than the Darwin’s orchid, Angraecum sesquipedale?

Native from Madagascar, the Darwin’s orchid has nice star-like white flowers with a waxy appearance that are produced in the wild from June to September. It is an epiphytic orchid, growing on trees, and its roots may reach several meters in length around the tree trunks.

The white waxy flowers of the Darwin's orchid. Notice the long spurs hanging from the flowers.

The white waxy flowers of the Darwin’s orchid. Notice the long spurs hanging from the flowers. Photo by Wilfred Duckitt*.

The most distinct feature of this species is the presence of a very long spur, a tube up to 43 cm long that contains the nectar. The epithet “sesquipedale” is given after that feature, meaning “one and a half foot long” in Latin, referring to the length from the end of the spur to the tip of the dorsal sepal. After examining several flowers, the naturalist Charles Darwin predicted the existence of a pollinator with a proboscis that was long enough to reach the nectar at the end of the spur. Later, Alfred Wallace noticed that the Morgan’s sphix moth (Xanthopan morganii), found in East Africa, had a proboscis almost long enough to reach the nectar and suggested that naturalists should look for similar species in Madagascar. In fact, some time later, specimens of the Morgan’s sphinx moth with a very long proboscis, long enough to reach the end of the spur, were found in Madagascar, confirming Darwin’s prediction. Unfortunately it happened only after Darwin’s death, so that he never became aware of the discovery…

Currently there are many cultivars and hybrids of the Darwin’s orchid all around the world.

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References:

Nilsson, L. A. 1988. The evolution of flowers with deep corolla tubes. Nature, 333: 147-149. DOI: 10.1038/334147a0

Wikipedia. Angraecum sesquipedale. Availabe at: < https://en.wikipedia.org/wiki/Angraecum_sesquipedale >. Access on June 18, 2016.

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Biological fight: Should we bring mammoths back?

by Piter Kehoma Boll

Everybody knows the amazing large animals that are found in Africa and Southeast Asia. Elephants, giraffes, rhinos, hippos, horses, lions, tigers… such large creatures, mostly mammals, are usually called megafauna, the “large fauna”.

Mammals as big as the African bush elephant once roamed the Americas. Photo by flickr user nickmandel2006*.

Mammals as big as the African bush elephant once roamed the Americas. Photo by flickr user nickmandel2006*.

The Americas once had an astonishing megafauna too, full of mastodons, mammoths, giant sloths, giant armadillos and sabertooth tigers. Nowadays it is restricted to some bears and jaguars. What happened to the rest of them? Well, most went extinct at the end of the Pleistocene, around 11,ooo years ago.

South America once had mammals as big as an African bush elephant. Picture by Dmitry Bogdanov** (dibgd.deviantart.com)

South America once had mammals as big as an African bush elephant, such as the giant sloth. Picture by Dmitry Bogdanov** (dibgd.deviantart.com)

As humans already inhabited the Americas by this time, it was always speculated if humans had something to do with their extinction. It is true that nowadays hundreds, thousands of species are endangered due to human activities, so it is easy to think that humans are the best explanation for their extinction, but 10 thousands years ago the number of humans on the planet was thousands of times smaller than today and our technology was still very primitive, so it is unlikely that we could hunt a species to extinction by that period… if we were working alone.

No, I’m not talking about humans cooperating with aliens! Our sidekick was the famous climate change. Periods of extreme warming during the pleistocene seem to have had a strong impact on the populations of many large mammals and, with the aid of humans hunting them down and spreading like an invasive species, the poor giants perished.

Le Mammouth by Paul Jamin

Le Mammouth by Paul Jamin

This happened more than 10 thousand years ago, TEN THOUSAND YEARS.

In Africa, elephants and large carnivores are well known for their importance in structuring communities, especially due to their trophic interactions that shape other populations. The extinct American megafauna most likely had the same impact on the ecosystem. As a result, suggestions to restore this extinct megafauna has been proposed, either by cloning some of the extinct species or, more plausibly, by introduced extant species with a similar ecological role.

Svenning et al. (2015) review the subject and argue in favor of the reintroduction of megafauna to restore ecological roles lost in the Pleistocene, an idea called “Pleistocene rewilding” or “trophic rewilding”, as they prefer. They present some maps showing the current distribution of large mammals and their historical distribution in the Pleistocene, which they call “natural”. They also propose some species to be introduced to substitute the ones extinct, including replacements for species extinct as long as 30 thousand years ago. Now is this a good idea? They think it is and one of the examples used is the reintroduction of wolves in the Yellowstone National Park. But wolves were not extinct for millenia there, neither are they a different species that would replace the role of an extinct one.

A wolf pack in Yellowstone National Park

A wolf pack in Yellowstone National Park

Rubenstein & Rubenstein (2016) criticized the idea, arguing that we should focus on protecting the remaining ecosystems and not trying to restore those that were corrupted thousands of years ago. They also argue that using similar species may have unintended consequences. Svenning et al. answered that this is mere opinion and that a systematic research program on trophic rewilding should be developed. The reintroduction of horses in the New World and its non-catastrophic consequences is another point used to respond to the critiques.

So what’s your opinion? Should we bring mammoths, mastodonts, giant sloths and sabertooth tigers back? Should we introduce elephants and lions in the Americas to play the role that mastodonts and smilodonts had?

My opinion is no. The idea may seem beautiful, but I think it is actually fantastic, too fabulous and sensational. Horses may have come back to the Americas without bringing destruction, but we cannot be sure with anything, even with several theoretical and small-scale studies. We all know how often introducing species goes wrong, very wrong. Look at poor Australia and Hawaii, for instance. Furthermore, those giant mammals went extinct TEN THOUSAND YEARS AGO. Certainly ecosystems have adapted to their extinction. Life always finds a way. There are worse threats to those ecosystems to be addressed, such as their eminent destruction to build more cities and raise more cattle and crops.

Get over it. Mammoths are gone. Let’s try to save the elephants instead, but without bringing them to the Brazilian cerrado. They don’t belong there. They belong in the African savannah.

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References:

Rubenstein, D. R.; Rubenstein, D. I. From Pleistocene to trophic rewilding: A wolf in sheep’s clothing. PNAS, 113(1): E1. DOI: 10.1073/pnas.1521757113

Svenning, J-C.; Pedersen, P. B. M.; Donlan, C. J.; Ejrnæs, R.; Faurby, S.; Galetti, M.; Hansen, D. M.; Sandel, B.; Sandom, C. J.; Terborgh, J. W.; Vera, F. W. M. 2016. Science for a wilder Anthropocene: Synthesis and future directions for trophic rewilding research. PNAS, 113(4): 898-906. DOI: 10.1073/pnas.150255611

Svenning, J-C.; Pedersen, P. B. M.; Donlan, C. J.; Ejrnæs, R.; Faurby, S.; Galetti, M.; Hansen, D. M.; Sandel, B.; Sandom, C. J.; Terborgh, J. W.; Vera, F. W. M. 2016. Time to move on from ideological debates on rewilding. PNAS, 113(1): E2-E3. DOI: 10.1073/pnas.1521891113

Wade, L. 2016. Giant jaguars, colossal bears done in by deadly combo of humans and heat. Science News. DOI: 10.1126/science.aag0623

Wade, L. 2016. Humans spread through South America like an invasive species. Science News. DOI: 10.1126/science.aaf9881

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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: Blue whale

by Piter Kehoma Boll

We’ve talked about the cutest and the leggiest, so now it’s time to introduce the largest, at once.

I think most of us know already that the largest animal ever is our beloved blue whale, Balaenoptera musculus. It can reach 30 m in length and weigh more than 180 tonnes. It’s really big, but probably not as big as many people think. There are some popular legends, like that the heart of a blue whale is the saze of a car or that a human could swim inside its aorta, which are not actually true.

It's almost impossible to find a good photo of the entire body of a blue whale. Afterall, it's huge and lives underwater!

It’s almost impossible to find a good photo of the entire body of a blue whale. Afterall, it’s huge and lives underwater!

But what else can we say about the blue whale? It is a rorqual, a name used to designate whales in the family Balaenopteridae and, as all of them, its main and almost exclusive food is krill, a small crustacean very abundant in all oceans. And krill needs to be abundant in order to provide the thousands of tonnes that all whales in the oceans need to eat every day. A single blue whale eats up to 40 million krill in a day, which equals to roughly 3.5 tonnes. A blue whale calf (young) is born measuring around 7 m in length and drinks around 500 liters of milk per day!

Blue whales were abundant in nearly all oceans until the beginning of the 20th century, when they started to be hunted and were almost extinct. Nowadays, the real population size is hard to estimate, but may encompass as few as 5,000 specimens, much less than the estimated hundreds of thousands in the 19th century. Due to such a drastic reduction in the population, the blue whale is currently listed as “endangered” in IUCN’s Red List.

But let's see a blue whale in all of its blueness.

But let’s see a blue whale in all of its blueness.

Occasionally, blue whales can hybridize with fin whales (Balaenoptera physalus) and perhaps even with humpback whales (Megaptera novaeangliae), a species classified in a different genus! Some recent genetic analyses, however, indicate that the Balaenoptera genus is polyphyletic and the blue whale may become known as Rorqualus musculus.

Different from other whales, blue whales usually live alone or in pairs, but never form groups, even though they may sometimes gather in places with high concentrations of food.

Like other cetaceans, especially other baleen whales, the blue whale sings. The song, however, is not as complex and dynamic as the ones produced by the related humpback whale. An intriguing fact that was recently discovered is that the frequency of the blue whale song is getting lower and lower at least since the 1960s. There is no good hypothesis to explain this phenomenon yet, but several ones have been proposed, such as the increase in background noise due to human activities or the increase in population density due to the decrease in whaling.

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References:

Hassanin, A.; Delsuc, F.; Ropiquet, A.; Hammer, C.; van Vuuren, B. J.; Matthee, C.; Ruiz-Garcia, M.; Catzeflis, F.; Areskoug, V.; Nguyen, T. T.; Couloux, A. 2012. Patter and timing of diversification of Cetartiodactyla (Mammalia, Laurasiatheria), as revealed by a comprehensive analysis of mitochondrial genomes.  Comptes Rendus Biologies, 335: 32-50.

Mellinger, D. K.; Clark, C. W. 2003. Blue whale (Balaenoptera musculus) sounds from the North Atlantic. Journal of the Acoustical Society of America, 114(2): 1108-1119.

Wikipedia. Blue whale. Available at: <https://en.wikipedia.org/wiki/Blue_whale&gt;. Access on January 27, 2016.

 

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