Tag Archives: sexual selection

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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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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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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Endosperm: the pivot of the sexual conflict in flowering plants

ResearchBlogging.org by Piter Kehoma Boll

The theory of sexual selection, based on the idea that there are conflict of interests between males and females, is quite recognized, but almost entirely focused on animals, especially dioecious animals, i.e., animals in which males and females correspond to separate individuals. Meanwhile, hermaphroditic animals and other organisms, such as plants, are usually ignored, but does hermaphroditism or “non-animalism” prevent the occurrence of sexual selection?

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.

In the last decades, hermaphroditic animals started to be investigated more deeply concerning sexual conflict as a considerable evolutionary force in these organisms. For example, some studies demonstrated that many hermaphrodites, during copulation, fight to play the role of male, or female, in something called “gender conflict” (which DOES NOT HAVE ANYTHING TO DO with any social aspect of the word “gender”. Here it refers to the sexual role that a hermaphroditic organisms plays during sex).

In plants, on the other hand, the subject is much less explored, especially due to the lack of direct interaction between the two mating organisms. Reproductive strategies in plants were seen, for a long time, as a mean to ensure the supposedly difficult task to unite male and female gametes when one is a sessile organism, i.e., an organism unable to move. After all, this disadvantage forces these organisms to develop special techniques that guarantee the transport of gametes through the environment. With such a relevant problem to assure that sex will happen, it seems absurd to think that plants could yet afford to choose with whom to get laid.

737px-Bee_merry_(8199716283)

Plants need external agents, such as wind, water or animals, to carry their gametes. Photo by psyberartist (flickr.com/people/10175246@N08).*

So far, the most approached point about sexual selection in plants is related to mechanisms developed by the female part to avoid the ovule to be fertilized by pollen of the same individual (the so-called self-fertilization) or of incompatible individuals (such as pollen of another species or of a close relative, because yes, incest can be a taboo even for plants). Another studied mechanism is related to the prevention of future attempts of fertilization once the zygot has been formed, as an already fertilized flower is not interested in receiving more and more pollen grains.

The passive travel of pollen from the male part to the female one gives us the impression that the male part cannot carry out any intersexual selection. After all, once the pollen arrives at a flower, it cannot leave, so its only chance is to try fertilization in any case, even if it is on an incompatible organism. This also highlights the fact that competition between pollen grains may occur on the female part, on a real race to see who gets first to the ovule. This competition may be controlled by the female part by changings in pollen receptivity.

Pollen_competition

When a pollen grain reaches the female part of a flower, it has no option but to germinate, creating a pollen tube that grows towards the ovule. In this picture, three pollen tubes are running towards the ovule and one of them has a clear advantage over the others. It may be because it arrived first or because the female part changed its receptivity to accept this specific grain more eagerly than the others.

An intriguing aspect in angiosperm reproduction is the phenomenon of double fertilization. When a pollen grain falls onto the female organ, it germinates, originating a long tube that grows towards the ovule, the so-called pollen tube. The pollen tube carries with it two male gametes: one of them will fertilize the egg cell, giving rise to the zygote that will form the embryo, and the other fertilizes the central cell, an auxiliary cell that accompanies the egg, giving rise to a second zygot that forms the endosperm, a tissue that feeds the embryo during its development.

double_fertilization

In the double fertilization of angiosperms, the pollen tube carries two male gametes to the ovule. One of them will fertilize the egg cell, leading to the embryo, and the other will fertilize the central cell, originating the endosperm.

Since the egg and the central cell, as well as both male gametes, are genetically identical, the endosperm is also identical to the embryo and may be seen as an altruist that sacrifices itself to assure the survival of its sibling. The evolutionary origin of the endosperm and its adaptive advantage remain subjects of much discussion and without much solution. The situation is yet more complicated because, in most angiosperms, the endosperm is triploid, having a duplicate maternal material because the central cell has two nuclei. In other words, the endosperm has two copies of the maternal genes and one copy of the paternal genes (configuration 2m/1p), while the embryo is an ordinary organism, having one copy of the maternal genes and one copy of the paternal genes (configuration 1m/1p).

Several hypothesis on the reason that led to the rising of this selfless triploid sibling have been raised and are usually based on different interpretations on the sequence of the events that happened during the evolution of the group. Functionally, the endosperm works are the female gametophyte of other plants, which is, in these, responsible for nourishing the developing embryo. The female gametophyte is the “mother” of the embryo, just like the pollen grain (male gametophyte) is the “father”. The plants with the flowers are, therefore, the embryo’s grandparents. Crazy, isn’t it? But that’s the rule for plants. One generation of large organisms (the sporophyte), gives rise to a generation of tiny organisms (the gametophyte), which in turn will “mate” to generate new large organisms.

Going back to the subject, the functional similarity between the endosperm and the female gametophyte seems to favor the hypothesis that the endosperm was initially a maternal tissue (having, therefore, an original configuration 1m/0p or 2m/0p) and the paternal intromission happened later. On the other hand, the phenomenon of double fertilization is also found in Gnetales (supposedly the closest group to angiosperms) and, in these, double fertilization originates two identical embryos. In addition, basal angiosperms also have diploid endosperms, with a single copy of chromosomes from each parent (1m/1p). This scenario points to a primitive situation of two embryos, in which one of them was deviated to the role of endosperm.

Here we need to include one more important concept in biology: genome imprinting. It is a phenomemon in which genes are differently expressed depending on the parent from which they came; and it is usually seen are a consequence of sexual conflict. What happens is that paternal cells may be silenced in some cells, so that the organism expresses, in those cells, only features inherited through the mothers. The opposite may also happen.

It is assumed that, in angiosperms, the paternal side benefits from the production of large endosperms that provide more nutrients to the embryo, so that there is interest both to express genes leading to a higher accumulation of resources coming from the mother and to silence genes that limit growth. In contrast, the maternal side would attempt to limit the nutrients destined to a single endosperm, as the excess of investment would compromise its future reproductive success. It is better for the mother to invest a little in each endosperm than to invest everything in a single one. Therefore, the maternal side would express genes that control the amount of resources invested in each embryo while inhibiting genes inducing an increased growth.

In such a scenario with genome imprinting, the increased expression of genes by duplication may be seen as a female strategy to counterattack a male attempt to express genes responsible for resource allocation. The paternal plant would express genes for resource collection, while the maternal plant, with two copies of its material in the endosperm, would express genes leading to a contrary response in higher intensity, trying to stop the paternal influence. Such a phenomenon has been attested in corn seeds, where 2m/0p endosperms are smaller than 2m/1p endosperms. As we can see, there is a fight between males and females even among plants!

In angiosperms, fertilization involves the direct interaction of five distinct organisms belonging to three generations: female sporophyte (maternal plant), masculine gametophyte (pollen grain), female gametophyte (ovule), embryo and endosperm. Each one of these organisms has an interest that may be contrary to one or more interests of the others, leading to a complex interaction still poorly defined and in which the endosperm certainly constitutes the most intriguing point and may be the consequence of certain strategies and, at the same time, lead to the emergence of new ones.

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References and further reading:

Alcock J (2001) Animal Behavior, 7th edn. Sinauer Associates, Sunderland

Arnqvist G, Rowe L (2005) Sexual Conflict: Princeton University Press, Princeton, N. J

Baskin, J., & Baskin, C. (2015). Pollen (microgametophyte) competition: an assessment of its significance in the evolution of flowering plant diversity, with particular reference to seed germination Seed Science Research, 25 (01), 1-11 DOI: 10.1017/S0960258515000033

Beale, K., & Johnson, M. (2013). Speed dating, rejection, and finding the perfect mate: advice from flowering plants Current Opinion in Plant Biology, 16 (5), 590-597 DOI: 10.1016/j.pbi.2013.08.005

Becraft, P. (2012). Endosperm Imprinting: A Child Custody Battle? Current Biology, 22 (3) DOI: 10.1016/j.cub.2011.12.043

Cailleau, A., Cheptou, P., & Lenormand, T. (2009). Ploidy and the Evolution of Endosperm of Flowering Plants Genetics, 184 (2), 439-453 DOI: 10.1534/genetics.109.110833

Charnov EL (1979) Simultaneous hermaphroditism and sexual selection. PNAS 76:2480–2484.

Davies NB, Krebs JR, West SA (2012) An introduction to behavioural ecology, 4th edn. Wiley-Blackwell, Oxford

Dresselhaus, T., & Franklin-Tong, N. (2013). Male–Female Crosstalk during Pollen Germination, Tube Growth and Guidance, and Double Fertilization Molecular Plant, 6 (4), 1018-1036 DOI: 10.1093/mp/sst061

Fetscher AE (2001) Resolution of male-female conflict in an hermaphroditic flower. Proc R Soc B 268:525–529. doi: 10.1098/rspb.2000.1395

Friedman WE (1995) Organismal duplication, inclusive fitness theory, and altruism: understanding the evolution of endosperm and the angiosperm reproductive syndrome. PNAS 92:3913–3917. doi: 10.1073/pnas.92.9.3913

Friedman WE (1998) The evolution of double fertilization and endosperm: an “historical” perspective. Sex Plant Reprod 11:6–16. doi: 10.1007/s004970050114

Friedman WE (2001) Developmental and evolutionary hypotheses for the origin of double fertilization and endosperm. Comptes Rendus de l’Académie des Sciences – Series III – Sciences de la Vie 324:559–567. doi: 10.1016/S0764-4469(01)01326-9

Grossniklaus U, Spillane C, Page DR, Köhler C (2001) Genomic imprinting and seed development: endosperm formation with and without sex. Curr Opin Plant Biol 4:21–27. doi: 10.1016/S1369-5266(00)00130-8

Haig D, Westoby M (1989) Parent-Specific Gene Expression and the Triploid Endosperm. Am Nat 134:147–155.

Haig D, Westoby M (1991) Genomic Imprinting in Endosperm: Its Effect on Seed Development in Crosses between Species, and between Different Ploidies of the Same Species, and Its Implications for the Evolution of Apomixis. Phil Trans R Soc B 333:1–13. doi: 10.1098/rstb.1991.0057

Härdling R, Nilsson P (1999) Parent-Offspring and Sexual Conflicts in the Evolution of Angiosperm Seeds. Oikos 84:27–34. doi: 10.2307/3546863

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Heroes and Whores, a sexual selection syndrome

By Piter Kehoma Boll

Hi, guys, today I’m going to talk about a polemic subject related to human society, but before I start, I’d better explain that I’m not a sexist, male chauvinist or anything else similar to that. This post is intended only to show how the different ways society sees promiscuity in males and females can be explained as a by-product of sexual selection in animals.

So, let’s start with a brief introduction of what defines an individual as being male or female. Typically, a female or feminine organism is one which produces the larger gamete, called ovum or egg, and a male or masculine organism is one which produces the smaller one, called sperm.

The difference in size between a sperm and an egg lets clear enough how the female has a higher investment.

So, as we can obviously see, the male gamete usually contributes only with its genetic material, while the female has to do all the hard work by itself since it invests a lot to ensure that the embryo will grow.

Well, these different approaches in reproduction by both sexes lead to different ways to behave during copulation.

As females invest a lot of energy in reproduction by producing larger gametes and usually raising the embryos, they tend to be very selective. If you spend a lot of resources in reproduction, you’d better choose the best mate to fecundate your eggs, right? Why would you risk losing all your investment by choosing a mate that would not produce healthy and strong offspring? So, if you are a female, you’ll try to find a good male to be the father of your children, so that you won’t copulate with the first one that appears in front of you. You are looking for quality.

Now if you are a male, you do not invest that much in your gametes, but you produce a lot of them and, since you are not the one responsible for raising the kids, the best option is to spread your seed as much as it’s possible, i.e., you’ll try to copulate with as many females as you can. That’s the best way to pass your genes to the next generation if you are a male. You are looking for quantity.

But since females are usually very selective about the males they let fertilize their eggs, it’s not that easy for a male to copulate. You gotta be the best male available to be chosen. So here we reach the central point of all this talk.

If you are a male and get to mate with a lot of females, it means that you are quite a male, the best one, the one all the females chose. You may be proud of it. You are a hero.

Image from polyamory.org via iamnotsohappy.com

Now if you are a female and get to mate with a lot of males, something is probably wrong. You are not choosing the best option, you are open to anyone, so your eggs are probably the worst among all females, since any male is good enough. You are a whore, you may be ashamed of yourself. You are not worth any effort.

This biological view of reproduction, arising from sexual selection by females, is usually reflected in human societies all around the world. A man that gets laid with many women is usually seen as an admirable man, while a woman that does the same with a lot of men is considered a whore, a bitch, something very low in society.

Image taken from phoenixpsbgbm.com

Now, again, I’m not defending this point of view. Actually I think we should not view things this way, specially because in our species the sexual intercourse is not used exclusively for reproductive purposes. Indeed, it’s more used as a kind of pleasant entertainment than anything else, and so we cannot go on judging it only through the reproductive side.

The purpose of this post is just to show that the idea of a promiscuous man being something desirable, while a promiscuous woman is depreciative, has a point when we look things in a biological and evolutionary way, but as a cultural species, we went a step further and we can deal with our lives through different approaches. Just as we don’t let deficient children die as a cat or bird would perhaps do, we don’t have to treat the number of sexual partners of anyone, male or female, as a feature to judge their character or their value as a person.

If you want to know more about how sexual selection and sexual investment shape sexual behaviour, I recommend the famous book The Selfish Gene, by Richard Dawkins.

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