Category Archives: Behavior

Badass females are unpopular among praying mantids

by Piter Kehoma Boll

One of the most iconic representations of praying mantids is that of a female eating the male after (or during) sex, an unpleasant scenario that starts with a beheading before the poor male even finishes his job.

Mantismeal

Delicious male meal. Photo by Wikimedia user Classiccardinal.*

According to some studies, when the male is beheaded, he increases the pumping of semen into the female, thus increasing the chances of fecundation. This could make one think that being eaten is actually an advantage to the male, as it makes him have more offspring.

Several observations with different species show the opposite though. Males make everything they can to avoid being eaten by the female, as it allows them to copulate with additional females. But how can they escape from such a gruesome destiny?

It is known that hungry females are more eager to eat the partner than satiated ones. Well-fed females (fat ones) are also less likely to have a meal in bed than malnourished ones. Males can tell whether a female is hungry or malnourished and thus avoid those in such conditions. They like fat and fed females. But this is not the only thing that males take into account when choosing the appropriate mother for their children.

A study from 2015 by researchers of the University of Buenos Aires have shown that males of the species Parastagmatoptera tessellata, found in South America, also choose females based on their personality.

In a laboratory experiment, a male was put in a container where he could see two females, one aggressive and one non-aggressive. Another male was presented to both females (which were unable to see each other) and the aggressive female always attacked the male, while the non-aggressive one never did. After watching how each female behaved, the male received access to both and could choose his favorite one.

And guess what? The non-aggressive one was chosen most of the time. This means that males are not only able to tell whether they are likely to be eaten based on the female’s hunger and nutritional condition, but also by analyzing the behavior of the female towards other males.

See also:

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

Male dragonflies are not as violent as thought

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ResearchBlogging.orgReferences:

Lelito, J., & Brown, W. (2008). Mate attraction by females in a sexually cannibalistic praying mantis Behavioral Ecology and Sociobiology, 63 (2), 313-320 DOI: 10.1007/s00265-008-0663-8

Scardamaglia, R., Fosacheca, S., & Pompilio, L. (2015). Sexual conflict in a sexually cannibalistic praying mantid: males prefer low-risk over high-risk females Animal Behaviour, 99, 9-14 DOI: 10.1016/j.anbehav.2014.10.013

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Don’t let the web bugs bite

by Piter Kehoma Boll

If you think spiders are scary creatures, today you will learn that they are scared too. But what could scary a spider? Well, a web bug!

We usually think of spider webs as an astonishing evolutionary achievement of this group of arachnids and a very efficient way to capture prey without having to pursue them. Webs are sticky, resistant, and only spiders themselves can move freely through them. The only problem is that this is not true.

emesaya_feeding

A thread-legged assassin bug (Emesaya sp.) feeding on a spider after invading the spider’s web in the Western Ghats, India. Photo by Vipin Baliga.*

A group of bugs that conquered the spider world are the so-called thread-legged assassin bugs, which comprise the subfamily Emesinae of the assassin bugs (family Reduviidae). As the name implies, the assassin bugs are a group of true bugs (suborder Heteroptera) that are expert killers of other creatures.

During their evolution, the thread-legged assassin bugs seem to have acquired a special taste for spiders and throughout the world they are usually associated with this eight-legged predators. In many cases, such as the one seen in the picture above, the bugs prey on the spiders, having developed the ability to move through the webs. They usually produce vibrations on the web that attract the spiders. Those, thinking that they caught a prey, are lured directly to their death in the legs and proboscis of the terrible bug.

Some thread-legged assassin bugs have, however, found another way to harass spiders: by stealing their food. In the latter scenario, the bugs usually wait close to or on the spider’s web and, when an insect is caught, they steal it from the spider by ripping it off the web. This kind of behavior is called kleptoparasitism, which means “parasitism by stealing”.

But how can spiders avoid this bug nightmare?

Until recently, it was thought that spiders were safe inside caves. Although emesinid bugs do occurr in caves, their association with spiders seemed to be weaker or non-existent there. But new findings are revealing that they pursue our arachnid fellows even to the deepest abysses of Earth.

The earliest cave-dwelling thread-legged assassin bug known to prey on spiders is Bagauda cavernicola, from India. Its spider-eating habits are known since the first decades of the 20th century.

The second species, Phasmatocoris labyrinthicus, was found almost a century later, in 2013, in Arizona, USA. More than only preying on spiders, such as the species Eidmanella pallida that lives in the same cave, P. labyrinthicus seem to have developed the ability to manipulate abandoned spiderwebs and use them to detect and capture prey for their own consumption. Only a single instance of such a behavior has been recorded and the species’s behavior needs further studies.

phasmatocoris_labyrinthicus_eating

Phasmatocoris labyrinthicus feeding on the spider Eidmanella pallida in the Kartchner Caverns, Arizona, USA. Photo extracted from Bape, 2013.

Now, only 3 years later, there are new evidences of more thread-legged assassin bugs molesting spiders in caves. And this time the observations were made in Minas Gerais, Brazil. One individual of the bug species Emesa mourei was seen standing on the web of a recluse spider (Loxosceles similis) while the spider was at the web’s edge. Another specimen of E. mourei was seen feeding on a fly near the web of a pholcid (cellar spider). The fly and the legs of the bug had vestiges of silk, indicating that the bug stole the fly from the spider. Another bug species, Phasmatocoris sp., was observed on a web of the cellar spider Mesabolivar aff. tandilicus. If this species of Phasmatocoris manipulates spider webs the same way that P. labyrinthicus seems to do is something yet to be investigated.

emesa_mourei_eating

Nymph of Emesa mourei feeding on a fly that it apparently stole from a pholcid spider in the cave Lapa Arco da Lapa, Minas Gerais, Brazil. Photo by Leonardo P. A. Resende, extracted from Resende et al., 2016.

With three different and very distant records of thread-legged assassin bugs associated with spiders in caves, it is clear that the poor arachnids cannot get rid of those bugs even if they run down into the bowels of the Earth.

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ResearchBlogging.orgReferences:

PAPE, R. (2013). Description and Ecology of A New Cavernicolous, Arachnophilous Thread-legged Bug (Hemiptera: Reduviidae: Emesini) from Kartchner Caverns, Cochise County, Arizona Zootaxa, 3670 (2) DOI: 10.11646/zootaxa.3670.2.2

Resende, L., Zepon, T., Bichuette, M., Pape, R., & Gil-Santana, H. (2016). Associations between Emesinae heteropterans and spiders in limestone caves of Minas Gerais, southeastern Brazil Neotropical Biology and Conservation, 11 (3) DOI: 10.4013/nbc.2016.113.01

Wignall, A., & Taylor, P. (2010). Predatory behaviour of an araneophagic assassin bug Journal of Ethology, 28 (3), 437-445 DOI: 10.1007/s10164-009-0202-8

Wygodzinsky, P. W. 1966. A monograph of the Emesinae (Reduviidae, Hemiptera). Bulletin of the American Museum of Natural History, 133:1-614.

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Friday Fellow: Persian Carpet Flatworm

ResearchBlogging.orgby Piter Kehoma Boll

A flatworm again, at last! Not a land planarian, but a flatworm nonetheless.

If there is a group of flatworms that may put land planarians in second plan regarding beauty, those are the polyclads. Living in the sea, especially in coral reefs, polyclads are colorful and curly and may be mistaken by sea slugs.

The species I’m introducing here today is Pseudobiceros bedfordi, commonly known as the Persian carpet flatworm or Bedford’s flatworm. It is about 8 cm long and lives in coral reefs along Australia, Indonesia, Philippines and adjacent areas. See how beautiful it is:

A flatworm (Pseudobiceros bedfordi). Raging Horn, Osprey Reef, Coral Sea

The Persian carpet flatworm with its beautiful colors. Photo by Richard Ling.*

The colorful pattern of this and many other polyclad species is likely a warning about their toxicity, although there are few studies regarding toxicity in these animals. Being active predators, polyclads may use their toxins as a way to subdue prey as well.

But the most interesting thing regarding the Persian carpet flatworm is its sexual behavior. As with most flatworms, they are hermaphrodites, so when two individuals meet and decide to have sex, they have to choose whether they want to play the male or the female role (or both). Unfortunately, most individuals prefer to be males, so those encounters usually end up in a violent fight in which both animals attack the partner with a double penis, a behavior known as penis fencing.

mating_pseudobiceros_bedfordi

Two Persian carpet flatworms about to engage in penis fencing. Photo from Whitfield (2004), courtesy of Nico Michiels.**

At the end, the winner spurts its sperm onto the partner and leaves. The horrible part is yet to come, though. The sperm appears to be able to burn like acid through the receiver’s skin tissue in order to reach the inner tissues and thus swim towards the eggs. In some extreme cases the sperm load may be high enough to tore the receiver into pieces! If that’s not a good definition of wild sex, I don’t know what is.

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

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References:

Whitfield, J. (2004). Everything You Always Wanted to Know about Sexes PLoS Biology, 2 (6) DOI: 10.1371/journal.pbio.0020183

Wikipedia. Pseudoceros bedfordi. Available at: <https://en.wikipedia.org/wiki/Pseudobiceros_bedfordi&gt;. Access on November 24, 2016.

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What is behavior? Baby don’t ask me, don’t ask me, no more

ResearchBlogging.orgby Piter Kehoma Boll

One of the most difficult concepts to explain in biology is certainly life itself. But I am not here today to talk about the definition of life, but rather of another puzzling concept: behavior.

Behavior is the central subject of ethology and psychology, but it is also something more commonly understood by personal intuition, just like life, but no formal and widely accepted definition exists.

The simplest definition would be that behavior is something that is done. But in that case we fall into another difficult concept, the concept of “doing”, because what exactly is doing something?

araneus_diadematus

Nobody doubts that a spider building a web is a behavior. Photo by Hedwig Storch.*

Some definitions of behavior that have been published are the following:

  • Tinbergen (1955): “The total movements made by the intact animal”. According to this definition, only animals can behave, so an unicellular alga swimming towards light, or a plant closing its leaves after being touched cannot be considered behaviors. On the other hand, the fact that an animal is orbiting the Sun because it is on Earth could be a behavior.
  • Beck et al. (1991): “External visible activity of an animal, in which a coordinated pattern of sensory, motor and associated neural activity responds to changing external or internal conditions”. Here again only animals would behave and only animals with some sort of nervous system. A behavior needs to include a response to a changing condition, i.e., a stimulus.
  • Starr & Taggart (1992): “A response to external and internal stimuli, following integration of sensory, neural, endocrine and effector components. Behavior has a genetic basis, hence is subject to natural selection, and it commonly can be modified through experience.” This definition does not use the word “animal”, but includes the need for neural components, which is almost the same thing.
  • Wallace et al. (1991): “Observable activity of an organism; anything an organism does that involves action and/or response to stimulation”. A more simple and broad explanation that encompasses many things that the previous definitions would exclude, but still includes at least the criterion that it is a response to stimuli.
  • Raven & Johnson (1898): “Behavior can be defined as the way an organism respond to stimulation”. A definition similar to the previous one.
  • Davis (1966): “What an animal does”. Very ambiguous and contradictory, as the same book includes a section on behavior of plants.
  • Grier & Burk (1992): “All observable or otherwise measurable muscular and secretory responses (or lack thereof in some cases) and related phenomena such as changes in blood flow and surface pigments in response to changes in an animal’s internal and external environment.” Another confuse, long, complex and ambiguous definition.
dionaea_muscipula

When a venus flycatcher closes its leaf to capture a fly, is it behaving? Photo by Stefano Zucchinali.*

Trying to find a way to create a unified definition of what is behavior, a group of researchers from the University of California, Berkeley, made a survey, published in 2009, in which they presented two lists to several biologists. The first contained a series of statements regarding behavior and the respondents should agree or disagree with the statement based on their assumption of what is behavior. The 13 statements were:

(A) ‘A developmental change is usually not a behavior.’
   (B) ‘Behavior is always a response to the external environment.’
(C)’A behavior is always an action, rather than a lack of action.’
(D) ‘All behaviors are directly observable, recordable and measurable.’
   (E) ‘People can all tell what is and isn’t behavior, just by looking at it.’
   (F) ‘Behavior is always influenced by the internal processes of the individual.’
   (G) ‘Behavior always involves movement.’
   (H) ‘Behaviors are always the actions of individuals, not groups.’
   (I) ‘Behavior is something whole individuals do, not organs or parts that make up an individual.’
   (J) ‘A behavior is always in response to a stimulus or set of stimuli, but the stimulus can be either internal or external.’
   (K) ‘Behavior is something only animals (including people) do, but not other organisms.’
   (L) ‘In humans, anything that is not under conscious control is not behavior.’
   (M) ‘Behavior is always executed through muscular activity.’

alopex_lagopus

An arctic fox changing its fur color between seasons is a behavior or not? Photo by Wikimedia user Longdistancer.*

The second list included a set of 20 phenomena and the respondents should say whether they considered each phenomenon as representing a behavior or not. (In parentheses are the above statements under which the phenomenon would not be considered a behavior).

  1. Ants that are physiologically capable of laying eggs do not do so because they are not queens. (C, G).
  2. A sponge pumps water to gather food (B, M).
  3. A spider builds a web.
  4. A rabbit grows  thicker fur in the winter (A, G, I, M).
  5. A plant’s stomata (respiration pores) close to conserve water (I, K, M) .
  6. A plant bends its leaves towards a light source (K, M).
  7. A person’s heart beats harder after a nightmare (B, I, L).
  8. A person sweats in response to hot air (G, I, L, M).
  9. A beetle is swept away by a strong current (F, M).
  10. A rat has a dislike for salty food (B, C, G, J, M).
  11. A person decides not to do anything tomorrow if it rains (B, C, G, J, M).
  12. A horse becomes arthritic with age (A, B, E, G, M).
  13. A mouse floats in zero gravity in outer space (E, F, G, M).
  14. A group of unicellular algae swim towards water with a higher concentration of nutrients (F, H, K, M).
  15. A frog orbits the Sun along with the rest of the Earth (F, M).
  16. Flocks of geese fly in V formations (H).
  17. A dog salivates in anticipation of feeding time (B, G, I, M).
  18. Herds of zebras break up during the breeding season and reform afterwards (H).
  19. A chameleon changes color in response to sunlight (G, M).
  20. A cat produces insulin because of excess sugar in her blood (B, G, I, M).

Only four statements (A, F, I, J) were generally agreed, while seven (B, C, E, G, H, L, M) had general disapproval and two (D, K) were neither strongly approved nor strongly disapproved.

Considering the phenomena, seven (2, 3, 11, 14, 16, 17, 18) met the criterion for approval as behaviors based on the results of the statements and seven (4, 8, 9, 12, 13, 15, 20) met the criterion for rejection. The remaining six phenomena (1, 5, 6, 7, 10, 19) had major divergences as to whether they were behaviors.

Several respondents contradicted themselves. For example, many of them agreed that only animals can behave (statement K) but also considered that algae swimming towards water with higher concentration of nutrients is a behavior (phenomenon 14).

blowing_dandelion

Most people would not consider that dandelion fruits carried by the wind are behaving.

Despite the high rate of disagreement, the group decided to propose a definition of behavior. And it is:

“Behavior is the  internally coordinated responses (actions or inactions) of whole living organisms (individuals or groups) to internal and/or external stimuli, excluding responses more easily understood as developmental changes.” (Levitis et al., 2009)

The question is not settled, though, and probably never will. Later, Dr. Raymond M. Berger, discussing the same subject, tells us that under the view of Descriptive Psychology, a behavior always includes eight parameters in the following formulation:

<B> = <I, W, K, K-H, P, A, PC, S>, in which:

B = behavior (e.g., Mary playing her queen of hearts in the contexts of a game of bridge).
I = identity of the person whose behavior it is (e.g., Mary)
W = want, the thing the person is attempting to achieve (e.g, to win a trick in the bridge game).
K = know, the cognitive parameter, the knowledge of how things work (e.g., queen vs. king, hearts vs. diamonds).
K-H = know-how, the ability to do what is being done (e.g., the ability to understand the rules of bridge, or the ability to move physical objects).
P = performance, the bodily processes involved in the behavior (e.g., Mary grasping and laying down her queen).
A = achievement, the outcome of the behavior (e.g., Mary takes the trick).
PC = personal characteristics, the indivudual’s difference parameter (e.g., Mary’s deep knowledge of strategy).
S = significance, what the behavior mean (e.g., Mary is playing bridge).

cardgame_bridge

Playing a cardgame is certainly a behavior. A very complex one.

Such a “definition” is, in my opinion, too complex for most circumstances of animal behavior. However, I’m not completely happy with the definition by Levitis et al. either. I think it is hard to tell the difference between a response given by the whole organism vs. one of its parts. For example, when I cough because water entered my trachea, is my whole organism responding or only part of it? Would that be a behavior?

Also, I’m not sure whether we should really consider developmental changes as something different from other responses. If I had to define behavior, I most likely would say it is:

“An activity performed by an organism that is a response to a stimulus and is dependent on the organism’s internal processes”.

eye_dilate-thumb_300px

Why should a pupil changing size according to the environmental light not be considered a behavior?

And you? What do you think is behavior?

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References:

Bergner, R. (2011). What is behavior? And so what? New Ideas in Psychology, 29 (2), 147-155 DOI: 10.1016/j.newideapsych.2010.08.001

Bergner, R. (2016). What is behavior? And why is it not reducible to biological states of affairs? Journal of Theoretical and Philosophical Psychology, 36 (1), 41-55 DOI: 10.1037/teo0000026

Levitis, D., Lidicker, W., & Freund, G. (2009). Behavioural biologists do not agree on what constitutes behaviour Animal Behaviour, 78 (1), 103-110 DOI: 10.1016/j.anbehav.2009.03.018

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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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Filed under Behavior, Evolution, Paleontology, Zoology