Category Archives: Zoology

Having few females turns male tortoises into rapists

by Piter Kehoma Boll

The war between the sexes and the endless conflicts that result from that are a common theme in behavioral and evolutionary research and have been addressed several times here too.

As we know very well, even from examples in our own species, males are usually not very good parents, being more interested in producing as many descendants as possible with little effort. Females, on the other hand, due to their great investment on eggs (and usually other resources for the offspring) are much more selective and will not accept any male to mate with them.

One of the most common solutions for males to resolve this sexual conflict is by forced copulation, or rape as it is called when it happens in our own species. Sometimes this forced copulation is extreme, with males heavily injuring females in order to make them surrender. One of those violent species is the Hermann’s tortoise, Testudo hermanni, a tortoise found around the Mediterranean areas of Europe.

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“I’m gonna bang you, bitch!” This photo of a juvenile male trying to mount on an adult female may look funny, but sex is no fun for female tortoises. Photo by Wikimedia user Palauenc05.*

Forced copulation is much more common in species in which males are bigger and stronger than females. This is not the case with tortoises, but male Hermann’s tortoises have found a way to deal with that. They pursue the females, sometimes for hours, pushing them, biting them, sometimes to the point of making them bleed, and eventually the poor females surrender. It is also common for the males to “stimulate” the cloaca of the females with their pointed tail, resulting in a swollen cloaca and sometimes severe injuries that let the females with horrible scars and deformities. Yes, it is not a nice face of nature.

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The tail of a male. Photo by Wikimedia user Bizarria.**

A recent study with two populations of the Hermann’s tortoise in Macedonia revealed that male aggressiveness is linked to female availability. The team of researchers studied one population in which the female:male ratio was close to 1:1 and other in which it was extremely male-biased to the point of 1 female to 17.5 males.

The results indicate that in the more balanced population forced copulation was less common and usually only adult females presented injuries caused by males, while in the male-biased population the lack of females made males go mad to the point that they forced copulation even with immature females. The situation as a whole is clearly maladaptive, as females end up injured and males end up exhausted and no offspring is generated.

I can only see two possible outcomes for such a population: either more resistant females will be selected or the population will go extinct after all females die by male violence.

As we see, sexual conflict is one of those deleterious side effects that natural selection created. Afterall, nobody is perfect, not even the fundamental laws of life.

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You may also like:

Male dragonflies are not as violent as thought

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

Badass females are unpopular among praying mantids

Having more females makes you gayer… if you are a beetle

Male resistance: when females disappear and hermaphrodites don’t like you

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Reference:

Golubović, A.; Arsovski, D.; Tomović, L.; Bonnet, X. (2018) Is sexual brutality maladaptive under high population density? Biological Journal of the Linnean Society 124(3): 394–402. https://doi.org/10.1093/biolinnean/bly057

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Friday Fellow: Truncate Trapdoor Spider

by Piter Kehoma Boll

Today I’m bringing you a species that fascinates me and that I was willing to introduce for a while. Unfortunately, there isn’t much information available about it, that being the reason for my delay in showing it here. However, as new information seems unlikely to appear soon, I can only show it with whatever is avaible.

Named Cyclocosmia truncata, today’s fellow is a trapdoor spider found in the East of the United States and sometimes referred to as truncate trapdoor spider. As all trapdoor spiders, it is a mygalomorph spider, such as tarantulas, and lives in a tunnel that it burrows in the ground and that is covered by a trapdoor. Trapdoor spiders in general rarely leave their burrows and hunt prey at night by standing behind the closed trapdoor and waiting for a prey to pass nearby, then jumping out and capturing it.

A truncate trapdoor spider in southeastern United States. Photo by iNaturalist user jimstarrett.*

Because trapdoor spiders are highly sedentary, they are very vulnerable to predators and parasites that can easily find them by locating their burrows. Species in the genus Cyclocosma have developed a fascinating morphological adaptation to cope with that. Their abdomen is abruptly truncated, giving the impression that someone just cut half of the abdomen off. This region of the abdomen is covered by a heavily sclerotized disc. When the spider is not active, it enters its burrow head first and the sclerotized disc fits perfectly to the walls of the tunnel, forming a false bottom that is impenetrable.

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A nice view of the peculiar disc of Cyclocosmia truncata. Author unknown. Photo taken from imgur.com

Not much more is known about the truncate trapdoor spider or its close relatives. They seem to be considerably rare, living in very restrict habitats, and their burrows are so well hidden that it is hard to find them in the wild.

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References:

Gertsch, W. J.; Platnick, N. I. (1975) A revision of the trapdoor spider genus Cyclocosmia (Aranae, Ctenizidae). American Museum Novitates 2580: 1–20.

Hunt, R. H. 1976. Notes on the ecology of Cyclocosmia truncata (Aranae, Ctenizidae) in Georgia. Journal of Arachnology 3: 83–86.

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Friday Fellow: Sharp-Toothed Venus Seed-Shrimp

by Piter Kehoma Boll

We reached again one of those problematic weeks in which I have to talk about something I know very little. This time the problem is called Euphilomedes carcharodonta, a small crustacean of the class Ostracoda, known as ostracods or seed shrimps. I decided to adapt the name of this species as sharp-toothed Venus seed-shrimp.

Although seed shrimps form a very diverse and species-rich group of organisms, I cannot find much details on particular species, so it is a challenge to present one here, but I decided to talk a little about the sharp-toothed Venus seed-shrimp, so let’s go.

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A male of the sharp-toothed Venus seed-shrimp. The dark spot is a lateral eye. Photo by Ajna Rivera.*

Measuring only a few milimeters, the sharp-toothed Venus seed-shrimp is found in the sea along the west coast of the United States. It has a typical ostracod appearance, looking like a small shrimp within a bivalvian shell.

Males and females of the sharp-toothed Venus seed-shrimp show sexual dimorphism, part of which is not only related directly to sex, but actually to the different niches that each sex occupies in the environment. Females pass most of their time buried in the sediments where light and predators are limited and, as a result, they have poorly developed eyes. The males, on the other hand, spend a lot of their time swimming in the water and are very vulnerable to predators, such as fish. Therefore, males have very well developed eyes that allow them to see fish from the distance. Experiments have shown that the eyes do not help them to identify the tiny females, but are essential to survive predation.

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A female sharp-toothed Venus seed-shrimp. Notice how she does not have the lateral eye seen on the male. Photo by Ajna Rivera.*

And that’s what I got about this fellow. As I asked before while talking about other groups of organisms, such as foraminiferans, if you have good resources on more detailed knowledge about species in this group, please share them in the comments. We need to give more visibility to those tiny and neglected souls that share this planet with us.

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References:

Sajuthi, A., Carrillo-Zazuetta, B., Hu, B., Wang, A., Brodnansky, L., Mayberry, J., & Rivera, A. S. (2015). Sexually dimorphic gene expression in the lateral eyes of Euphilomedes carcharodonta (Ostracoda, Pancrustacea) EvoDevo, 6 : 10.1186/s13227-015-0026-2

Speiser, D. I., Lampe, R. I., Lovdahl, V. R., Carrillo-Zazueta, B., Rivera, A. S., & Oakley, T. H. (2013). Evasion of Predators Contributes to the Maintenance of Male Eyes in Sexually Dimorphic Euphilomedes Ostracods (Crustacea) ntegrative and Comparative Biology, 53 (1), 78-88

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Having more females makes you gayer… if you are a beetle

by Piter Kehoma Boll

Homosexual behavior, as you may know, is a widespread phenomenon across the animal kingdom, especially male-male sexual behavior. Like many other aspects of life, this behavior likely evolved independently many, many times and plays different roles in different species.

A study recently published in the journal Animal Behaviour investigated the male homosexual behavior of the red flour beetle, Tribolium castaneum. The team wanted to verify whether a large supply of females or a large number of rival males would influence the occurrence of males having sex with other males.

The red flour beetle, Tribolium castaneum. Credits do CSIRO.*

In order to test that, the researchers directed the evolution of some populations of the red flour beetle in the lab. Some populations were maintained in a male:female ratio of 1:9 and others of 9:1, i.e., in the first group the population consisted of 10% males and 90% females, so males had a greater chance of finding a female than a male and competition between males was very week. In the second group, 90% of the population was made up of males, so females were harder to find and males had to fight for them.

After about 100 generations in which the sex ratios were maintained, the researchers compared the occurrence of male-male sex in both treatments. The results show that males that evolved in an environment where females were abundant and competition between males was low were more likely to engage in homosexual behavior than males that evolved in an environment were competition between males was high and the chances of finding a female were much lower.

The most likely explanation for this difference is that males in highly competitive enviroments need to be better in identifying female individuals to mate with, while in environment where there are plenty of females available, most of the encounters are with females, so the strategy to “have sex with whomever you find” is good enough. The few instances in which such males find other males and mate with them is not enough to reduce their reproductive fitness. In other words, when you live among few females, it is crucial for you to recognize someone as a female and mate with her, otherwise you may end up not passing your genes to the next generation. Now if there are plenty of females you may have sex whenever you want and you certainly will have some children, even if you sometims have fun with your male pals.

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You may also like:

Endosperm: the pivot of the sexual conflict in flowering plants

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

Male dragonflies are not as violent as thought

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Reference:

Sales K, Trent T, Gardner J, Lumley AJ, Vasudeva R, Michalczyk Ł, Martin OY, & Gage MJG 2018. Experimental evolution with an insect model reveals that male homosexual behaviour occurs due to inaccurate mate choice. Animal Behaviour 139: 51–59. https://doi.org/10.1016/j.anbehav.2018.03.004

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Friday Fellow: Blue Coral

by Piter Kehoma Boll

Sorry, guys! It has been about three weeks since my last post, but I was too busy with a lot of personal and academic stuff and wasn’t able to dedicate any time to the blog, but I’m back!

Let’s return with a marine animal as today’s Friday Fellow, the called blue coral, Heliopora coerulea.

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A colony of the blue coral in Thailand. Credits to Chaloklum Diving.*

Found in tropical waters of the Pacific and Indian oceans, the blue coral is a peculiar species, being the only one in the genus Heliopora and in the family Helioporidae. It is the only species in the subclass Octocorallia that has a massive skeleton, a feature more common in the stony corals of the subclass Hexacorallia. As a result, the ecological role of the blue coral is usually closer to that of stony corals that to that of its closer relatives.

The skeleton of the blue coral is composed of aragonite and has a distinctive bluish-gray color caused by the presence of iron salts. There are fossils of bluish corals with the same morphology that date back to the Cretaceous, indicating that this is a very old species.

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A skeleton of the blue coral in the Natural History Museum, London. Photo by Wikimedia user Kinkreet.**

Although widespread, the blue coral is currently considered a vulnerable species, with some population showing very low genetic diversity. This species is threatened mainly by the jewelry and aquarium trades and by the acidification of the oceans.

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References:

Babcock, R. (1990) Reproduction and development of the blue coral Heliopora coerulea (Alcyonaria: Coenothecalia)Marine Biology 104: 475–481.

EOL: Encyclopedia of Life. Heliopora coerulea. Available at < http://eol.org/pages/1006937/overview >. Access on May 14, 2018.

Wikipedia. Heliopora coerulea. Available at < https://en.wikipedia.org/wiki/Blue_coral >. Access on May 14, 2018.

Yasuda, N.; Taquet, C.; Nagai, S.; Fortes, M.; Fan, T.-Y.; Phongsuwan, N.; Nadaoka, K. (2014) Genetic structure and cryptic speciation in the threatened reef-building coral Heliopora coerulea along Kuroshio Current. Bulletin of Marine Science 90(1): 233–255. https://doi.org/10.5343/bms.2012.1105

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Friday Fellow: C. elegans

by Piter Kehoma Boll

Despite its small size, today’s fellow is one of the most important organisms in current scientific research. Named Caenorhabditis elegans and usually called simply C. elegans, this worms is a nematode and reaches about 1 mm in length and lives in the soil of temperate areas.

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An adult hermaphrodite of C. elegans. Photo by Bob Goldstein.*

There are only four bands of muscles that run along the body of C. elegans and they only alow the worm to bend the body dorsally or ventrally, but not to the sides. Thus, while moving on a horizontal surface, the worms are forced to lie on their left or ride side.

The main food source of C. elegans are bacteria that live on decaying organic matter, although they can also feed on some yeast species. Therefore, they thrive in soils rich in organic matter, where bacteria occur in abundance.

The sex of C. elegans is unusual. An adult organism can be either a male or a hermaphrodite, without a pure female form. Hermaphrodites are the most common form and usually self-fertilize, although they can, and apparently prefer, to mate with males. The larvae pass through four larval stages before reaching the adult stage, but this happens very quickly, since in ideal conditions the lifespan of C. elegans is of about 2 to 3 weeks. However, in conditions of insufficient food, an alternative third larval stage called dauer can be formed. The dauer stage has the body sealed, including the mouth, which doesn’t allow it to take in food, and can remain as such for a few months until the conditions are good again.

As most nematodes, C. elegans presents eutely, i.e., the adult worm has a genetically determined number of cells in the body. This number is fixed and does not change, because cell division ceases in adults. Male C. elegans have 1031 cells and hermaphrodites have 959 cells.

Due to its small size, small and fixed number of cells, transparent body and because it is easy to raise it in the lab, C. elegans became a perfect model organism. It was the first organism to have its genome fully sequenced and up to now it is the only organism with a complete connectome (the map of his neuron connections). It has been used in studies related to ageing, development, apoptosis and all sort of gene expressions.

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References and further reading:

Brenner, S. (1974) The genetics of Caenorhabditis elegans. Genetics 77(1): 71-94.

Klass, M. R. (1977) Aging in the nematode Caenorhabditis elegans: Major biological and environmental factors influencing life span. Mechanisms of Ageing and Development 6: 413–429. https://doi.org/10.1016/0047-6374(77)90043-4

Peden, E.; Killian, D. J.; Xue, D. (2008) Cell death specification in C. elegans. Cell Cycle 7(16): 2479–2484. https://doi.org/10.4161/cc.7.16.6479

Wikipedia. Carnorhabditis elegans. Available at < https://en.wikipedia.org/wiki/Caenorhabditis_elegans >. Access on April 16, 2018.

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Friday Fellow: Réaumur’s Desert Woodlouse

by Piter Kehoma Boll

We all know that crustaceans are mainly aquatic animals, but that some species have conquered the land, especially the woodlice. But did you know that some woodlice went as far as to find a way to live in the desert? Today’s Friday Fellow is one of those species. Actually, it is the woodlouse that lives in the driest habitat where a crustacean can be found. Its name is Hemilepistus reaumuri, which I decided to call the Réaumur’s Desert Woodlouse.

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A specimen of Hemilepistus reaumuri in Tunisia. Photo by Ferenc Vilisics.*

Found in the deserts of North Africa and the Middle East, the Réaumur’s Desert Woodlouse is considerably large, reaching up to 22 mm in length. It feeds on leaves and is mainly active at dusk. Being found in great densities, this little fellow is also an important food source for some predators, especially the large-clawed scorpion Scorpio maurus.

In order to tolerate the high temperatures and the low relative humidity of the air in the desert, the Réaumur’s Desert Woodlouse constructs burrows that are at least 40 cm deep, so that it can find an environment in which the relative humidity is of at least 6%, since it cannot survive when it drops below that value. When it gets lost, it usually finds its burrow again in a few minutes by using a systematic search behavior in the environment, exploring regularly the area around the point in which it became lost until its home is located.

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About to enter its burrow. Photo by Ferenc Vilisics.*

One peculiar aspect of the Réaumur’s Desert Woodlouse is that it take care of its offspring. A male and a female form a monogamous couple and construct together a burrow where they live and take care of their young. The female usually bears 50 to 100 live young and those remain in the burrow for 10 to 20 days, being fed by their parents. Members of the same social group are able to recognize each other using pheromones, and when the young leave the burrow they may be captured by adults of other groups, killed and offered as food to that adult’s offspring.

Having a lifespan of only 15 months, the Réaumur’s Desert Woodlouse produces only one brood during their life. Having a long life does not seem to be a privilege for desert crustaceans.

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References:

Hoffmann, G. (1983) The random elements in the systematic search behavior of the desert isopod Hemilepistus reaumuriBehavioral Ecology and Sociobiology 13(2): 81-92.

Linsenmair, K. E. (1985) Individual and family recognition in subsocial arthropods, in particular in the desert isopod Hemilepistus reaumuriFortschritte der Zoologie 31: 411-436.

Wikipedia. Hemilepistus reaumuri. Available at < https://en.wikipedia.org/wiki/Hemilepistus_reaumuri >. Access on March 25, 2018.

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