Monthly Archives: June 2018

Friday Fellow: Common giardia

by Piter Kehoma Boll

Parasites are always a group eager to be featured here, and human parasites have a special place in our hearts… sometimes literally. Today’s species, however, has a special place in our small intestine.

Called Giardia lamblia, sometimes also identified under the outdated synonyms Giardia duodenalis or Giardia intestinalis, our species has not a common name, but as it is the most popular and widespread species of the genus Giardia, I decided to call it simply the common giardia.

The common giardia is a flagellated unicellular organism that affects not only humans but several other mammal species. In the wild, the common giardia exists in the form of an inert cyst that can survive for prolonged periods and under different environmental conditions.

giardia_cyst_wtmt3

A cyst of Giardia lamblia. Credits to Centers for Disease Control and Prevention.

When the cysts are ingested by humans or other mammals, they develop into the active stage, called trophozoite, once they reach the small intestine. The trophozoite is a flagellated cell with two well-developed nuclei that make it look like a smiling face. In this stage, the common giardia reproduced by simple binary fission. For a long time, it was thought that sexual reproduction did not occur at all in this species, but some recent evidence indicate that recombination may occur, although it is not very clear yet how it happens.

800px-giardia_intestinalis_28259_1729

Two trophozoites of the common giardia under the microscope. Credits to Josef Reischig.*

The ventral surface of the trophozoite is concave, forming an adhesive disk that attaches the cell to the wall of the intestine, preventing it to be transported downward the intestinal tract. Although not invading the intestinal cells, the infection of Giardia lamblia usually causes diarrhea and malabsorption. When exposed to biliar secretions, the common giardia may develop into a cyst and is thus eliminated with the feces, allowing the cycle to begin again.

Humans are very often contaminated by several means, such as by ingesting contaminated water, which may include both urban untreated water or clear water in the wild where other mammals may have defecated. It is, therefore, a common infection among hikers, people living under poor sanitary conditions and so on.

The common giardia has some peculiarities, such as the lack of mitochondria, which for some time led to the assumptions that they may belong to a very primitive group of Eukaryotes. Recently, however, a vestigial organelle that likely derived from mitochondria, named mitosome, has been found in this species, suggesting that this feature is a secondary loss caused by its parasitic life in an anoxic environment.

– – –

Like us on Facebook!

Follow us on Twitter!

– – –

References:

Adam, R. D. (2001) Biology of Giardia lambliaClinical Microbiology Reviews 14(3): 447–475.

Wikipedia. Giardia lamblia. Available at < https://en.wikipedia.org/wiki/Giardia_lamblia >. Access on 28 June 2018.

– – –

*Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Leave a comment

Filed under Parasites, protists

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 of which 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.

96158_580_360
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.

20172_580_360
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.

– – –

Like us on Facebook!

Follow us on Twitter!

– – –

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

– – –

Creative Commons License

*
This work is licensed under a Creative Commons Attribution-NonCommerical-NoDerivs 2.0 Generic License.

1 Comment

Filed under Friday Fellow, Zoology

Friday Fellow: Crescent-Cup Liverwort

by Piter Kehoma Boll

Today’s fellow is once more a small forest dweller, more precisely a liverwort. Scientifically called Lunularia cruciata, its common name is crescent-cup liverwort. The names Lunularia and crescent-cup come from the shape of its cups, structures that contain mass of cells called gemmae that are released in the environment and  can grow into a new plant, a form of asexual reproduction.

57980_orig

This close up of a crescent-cup liverwort reveals the crescent-shaped cups containing the gemmae. Credits to BioImages – the Virtual Fieldguide (UK).*

The crescent-cup liverwort appears to be native from Southern Europe, around the Mediterranean, but in the last decades, possibily due to human interference, it has expanded its distribution to the north of Europe and has reached other continents as well, especially the Americas.

In the United States, the crescent-cup liverwort has become a very common species living in green houses. Its quick spread is certainly related to its asexual reproduction. The gemmae found in its cups are usually released by water drops and germinate as soon as they fall on a humid surface, quickly originating a new plant.

Although most populations seem to reproduce only asexually, sexual reproduction occurs as well and follows the basic pattern seen in other liverworts. In sexual populations, the female gametophytes produce a long stem with four archegonia (the structure that bears the female gametes) arranged as a cross, hence the specific epithet cruciata (“crossed”).

12189_orig

The cross-shaped archegonia of the crescent-cup liverwort. Photo by Ken-ichi Ueda.**

Some extracts from the crescent-cup liverwort has shown the potential to be used for the development of new antibiotics.

– – –

Like us on Facebook!

Follow us on Twitter!

– – –

References:

Basile, A., Giordano, S., Sorbo, S., Vuotto, M. L., Ielpo, M T. L. & Cobianchi, R. C. (1998). Antibiotic Effects of Lunularia cruciata (Bryophyta) Extract Pharmaceutical Biology, 36 (1), 25-28 : 10.1076/phbi.36.1.25.4612

Wikipedia. Lunularia. Available at < https://en.wikipedia.org/wiki/Lunularia >. Access on May 26, 2018.

– – –

*Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 3.0 Unported License.

1 Comment

Filed under Botany, Friday Fellow

Why everybody laughs at Wickramasinghe and should continue to do so

by Piter Kehoma Boll

More than six years ago, when this blog was just starting, I wrote an article about a poor old scientist, Donald I. Williamson, and his absurd ideas of hybridogenesis, i.e., the idea that new organisms could arrive by hybridizing very distantly related species, such as crossing a beetle with an earthworm. Williamson passed away two years ago and continued to defend his baseless hypothesis to the end.

Later on, I presented two other scientists with similarly ridiculous ideas: Retallack and his land Ediacara hypothesis, and Duesberg and his AIDS conspiracy theory. Now, I’m here to talk about an even more severe case of dellusion, and one that is as serious as Duesberg’s, because it is also followed by a bunch of crazy people.

The dellusion has a name, the Hoyle-Wickramasinghe “””””theory”””””, or H-W theory for short. His main follower currently is Wickramasinghe himself, more precisely Chandra Wickramasinghe, since the other guy, Fred Hoyle, is already decomposing and emitting Galactic Center infrared waves (you’ll understand it soon).

chandra-wickramasinghe

Professor Chandra Wickramasinghe and cabillions of bacteria glowing behind him. Photo by Wikimedia user Davidnoy.*

Wickramasinghe is a Sri Lankan-born British mathematician, astronomer and astrobiologist who since the 1960 worked with the now galactic-center-like deceased astronomer Fred Hoyle. They seem to have found in each other someone to support their mental disorder, as they formulated the hypothesis that life came to Earth from space. No, wait… it’s not that simple. They stated that life COMES to Earth from space… all the time!

giphy

Excuse me?

We all have heard of panspermia, right? The idea that life perhaps did not originate on Earth, but arrived here from space. Well, that may be a plausible idea. Perhaps the first microorganisms that appeared on Earth indeed came from space, but we know for sure, based on molecular analyses, that all current life forms originated from a single ancestor that is thought, based on fossils AND molecular data, to have existed about 3.5 billion years ago. We are, therefore, all part of a big family.

The problem with Wickramasinghe and his puppies (which are more than I expected, I have to say) is that they claim that new organisms are arriving all the time in comets and asteroids. They consider that the “sudden” complexity of life on Earth as seen in the fossil record, such as, for example, the appearance of the first cyanobacteria or the Cambrian explosion, could not have happened by simple neo-Darwinian evolution. So the logical explanation for them is… ALIENS! Alien viruses arrive, infect cells, mix their genetic material with that of the host and, voilà, a new complex lifeform appears.

giphy1

During his career, Wickramasinghe made several statements that did not please the scientific community. He said, for example, that some pandemics, such as the 1918 flu pandemic and several other outbreaks of viral diseases are the result of cometary dust bringing the virus to Earth and scattering it throughout the planet. This view is, of course, dismissed by all serious researchers.

Recently, to my surprise, an apparently reputable journal, Progress in Biophysics and Molecular Biology, published a paper authored by Wickramasinghe and his puppies that defends again this nonsense idea of continuous extraterrestrial delivery of life. They suggest that the entire Galaxy comprises a gigantic biosphere and that life is being transported from here to there and back for billions and billions of years. But perhaps the most astonishing claim, and the one that made so many people become aware of this comedy disguised as science, is that octopuses came from space as eggs.

giphy2

Yes, that’s exactly what the team proposed! They propose that the genetic and structural complexity of octopuses, squids and and cuttlefish, which is, according to them, hard to explain by “tradional neo-Darwinian evolution or even by massive horizontal gene transfer from viruses” is the result of these creatures having evolved somewhere else in the Galaxy and later coming to Earth in frozen eggs.

Another hilarious evidence they present about the existence of life across the whole Galaxy is by comparing the mid-infrared spectrum emitted by a source in the Galactic Center to the mid-infrared spectrum emitted by partially degraded bacteria. The patterns are very similar and this is, according to them, an evidence that the Galactic Center is crowded with bacteria. But what are the references that sustain these data? Guess what? It’s Wickramasinghe’s own previous works! Throughout the whole paper the only thing that the team can find to sustain their claims is their own previous work. No one else publishes on this subject because it does not make sense!

I think we can all agree that Wickramasinghe would fit better in a sensationalist and anti-scientific place such as the nonsense shows of History Channel than in a science lab.

If you want to laugh more or torture yourself with more bullshit, you can read the whole paper:

Steele EJ, Al-Mufti S, Augustyn KA, Chandrajith R, Coghlan JP, Coulson SG, Ghosh S, Gillman M, Gorczynski RM, Klyce B, Louis G, Mahanama K, Oliver KR, Padron J, Qu J, Schuster JA, Smith WE, Snyder DP, Steele JA, Stewart BJ, Temple R, Tokoro G, Tout CA, Unzicker A, Wainwright M, Wallis J, Wallis DH, Wallis MK, Wetherall J, Wickramasinghe DT, Wickramasinghe JT, Wickramasinghe NC, & Liu Y (2018). Cause of Cambrian Explosion – Terrestrial or Cosmic? Progress in Biophysics and Molecular Biology 136: 3–23.

And you can also read more about the adventure that is Wickramasinghe’s dellusional life on Wikipedia:

Wikipedia. Chandra Wickramasinghe. Available at < https://en.wikipedia.org/wiki/Chandra_Wickramasinghe >. Access on June 11, 2018.

– – –

Like us on Facebook!

Follow us on Twitter!

– – –

*Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

7 Comments

Filed under Evolution

Friday Fellow: Common Pelomyxa

by Piter Kehoma Boll

It’s time to dig deep into the mud again and bring up a peculiar protist, the third species of the clade Amoebozoa to be featured here. Its binomial name is Pelomyxa palustris, and I decided to call it the common pelomyxa.

Measuring up to 5 mm in length, although usually having less than 1 mm, the common pelomyxa is considered a “giant amoeba”. In fact, the Giant Amoeba Chaos carolinense, previously featured here, was once classified in the genus Pelomyxa, but currently we know that they are not closely related at all. While the true giant amoebas of the genus Chaos are closely related to the common amoebas of the genus Amoeba, the species in Pelomyxa belong to a completely different group of amoebas.

02807_orig

A specimen of the common pelomyxa. The large pseudopod is to the right and the small uroid can be seen projecting from the cell at the upper left. Credits to Proyecto Agua.*

The cell of the common pelomyxa has a somewhat cylindrical shape with a single, large, semicircular pseudopod at the front, thus moving basically always in the same direction, forward, differently from the more classical amoebas with several pseudopods and the ability to move in any direction. At the opposite side of the cell, the common pelomyxa has a small, also semicircular appendix called the uroid that is covered by several small non-motile flagella. The flagella are surrounded by small cytoplasmic projections (villi) that are easily seen under the microscope.

The common pelomyxa lives buried in the sediments of freshwater lakes throughout the northern hemisphere, especially those rich in decaying organic matter. It slides through the mud while feeding on smaller microorganisms and organic debris. Such an environment is characterized by the complete absence or extremely low concentrations of oxygen. As a result, the common pelomyxa is anaerobic and even lacks mitochondria. For this reason, it was once considered part of a very primitive group of eukaryotes that diverged before the incorporation of the endosymbiotic bacteria that would evolve into mitochondria. Currently, however, it is known that their lack of mitochondria is actually due to a secondary loss and they seem to be related to true amoebas and slime molds.

More than only lacking mitochondria, the cell of the common pelomyxa has a lot of peculiar features. Depending on the size of the cell, it may contain a few to several hundred nuclei. The cytoplasm also appears to lack several typical eukaryotic organelles, such as the Golgi apparatus and the endoplasmic reticulum. There are, however, many, many small vacuoles, so many that the cell usually has a foamy appearance.

Endosymbiotic bacteria are also found in great numbers in the cytoplasm of the common pelomyxa. After several years of research, it seems that these bacteria are obligate symbionts. Perhaps they help this strange amoeba to perform some of the tasks that should be done by the several organelles that it lacks.

– – –

Like us on Facebook!

Follow us on Twitter!

– – –

References:

Goodkov, A. V.; Chistyakova, L. V.; Seravin, L. N.; Frolov, A. O. (2004) The concept of pelobionts (Class Peloflagellatea): Brief history and current stateEntomological Review 84(Suppl. 2): S10–S20.

Wikipedia. Pelomyxa. Available at < https://en.wikipedia.org/wiki/Pelomyxa >. Access on May 26, 2018.

– – –

*Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Generic License.

Leave a comment

Filed under Friday Fellow, protists

Whose Wednesday: Allan Octavian Hume

by Piter Kehoma Boll

Today we celebrate the birthday of the British ornithologist Allan Octavian Hume.

Hume was born on 6 June 1829 at St Mary Cray, England, the son Maria Burnley and Joseph Hume, a radical member of the Parliament. He was educated at home until he was 11 and then attended the junior school of University College London (UCL) from 1840 to 1844. Later he attended the UCL itself from 1844 to 1846, studying medicine and surgery, and then spent two years at the East India Company College, Haileybury, from 1847 to 1848.

In 1848, Hume sailed to India and joined the Bengal Civil Service at Etawah in the North-western Provinces (currently Uttar Pradesh), serving as a district officer. In 1853, he married his wife Mary Anne Grindall.

Having shown interest in natural history from early life, Hume started a personal collection of bird specimens in India. Nine years after arriving in the country, he has started 181 free schools in Etawah with more than 5 thousand students. The same year, he faced the Indian Rebellion of 1857, becoming involved in several military actions. During this time, his bird collection was destroyed, but he started it afresh after the incident and planned to survey and document the birds of the Indian subcontinent. From 1856 to 1867, he was Collector and Magistrate of Etawah and during this time he made several expeditions to collect birds, leading him to accumulate the largest collection of birds in the world, which was housed at his home in Rothney Castle on Jakko Hill, Simla. In 1863 he stated that imprisoning juvenile deliquents only turned them into hardened criminals and led to the creation of juvenile reformatories for those individuals.

From 1867 to 1870, Hume was Commissioner of Customs for the North West Province and in 1870 became the Director-General of Agriculture. He was supported by Lord Mayo, the viceroy of India at the time, and made many suggestions to improve agriculture in the country. With the help of Lord Mayo, Hume negotiated with the Secretary of State of India for setting up a Department of Revenue, Agriculture and Commerce and Hume was made secretary of this department in 1871, moving to Shimla. Lord Mayo was murdered in 1872 and Hume lost support for his work, but he continued reforming the department.

In 1873, Hume started to publish the journal Stray Feathers, a journal of ornithology for India and its dependencies. In his works published in the journal he described many new bird species.

Hume was very outspoken and did not fear to criticize the government when he thought it was wrong. This reduced his freedom when Lord Northbrook succeeded Lord Mayo as the viceroy and the situation worsened even more when Lord Lytton succeeded Lord Northbrook. In 1879, while going again against the authorities, Hume was dismissed from his position as secretary by Lord Lytton’s Government.

Moving back to the North-West Provinces, Hume did not resign immediately from service, apparently because he needed the salary to be able to publish The Game Birds of India on which he was working at the time. In 1883, one year after retiring, he wrote an open letter to the graduates of the Calcutta University and called them to form their own national politival movement and this led to the first session of the Indian National Congress in Bombay in 1885. Later, in 1887, he stated that he considered himself a Native of India.

435px-a_o_hume

Hume in 1889.

Still in 1883, while returning from a trip, Hume discovered that many pages of the manuscripts that he maintained over the years had been stolen by a servent and sold off as waste paper. This let him completely devastated and made him began to lose interest in ornithology. Things got even worse when a landslip caused by the heavy rains damaged his museum and many specimens. He then wrote to the British Museum, wishing to donate his collection, but imposed certain conditions, one of which was that the collection should be inspected and packed by the zoologist Robert Bowdler Sharpe (1847–1909) and that Sharpe’s rank and salary should be raised due to the work he would have. The British Museum couldn’t afford all the demands. In 1885, however, after finding out that Hume himself destroyed almost 20 thousand specimens (because they were damaged by beetles), Sharpe got alarmed and the Museum’s authorities let him visit India to supervise the transfer of the specimens to the British Museum. The material consisted of 82 thousands specimens, of which 75,577 were placed in the museum.

Hume left india in 1894 and settled in London. He died on 31 July 1912, aged 83, and his ashes were buried in the Brookwood Cemetery.

– – –

Like us on Facebook!

Follow us on Twitter!

– – –

References:

Collar NJ, Prys-Jones RP (2012) Pioneer of Asian Ornithology, Allan Octavian HumeBirdingAsia 17: 17–43.

Wikipedia. Allan Octavian Hume. Available at < https://en.wikipedia.org/wiki/Allan_Octavian_Hume >. Access on June 6, 2018.

 

Leave a comment

Filed under Biographies

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

by Piter Kehoma Boll

During the evolution of life, sex was certainly a great innovation. It allows organisms to reproduce while mixing their genes with that of another individual. Although it usually makes your offspring to have only half of your genes, which does not seem to be as great as an offspring that carries you as a whole into the next generation, there are certainly advantages in mixing. The most evident advantage is that your genes can combine with other versions and, as a result, produce a better team of genes than the one that you had. Even though each of your children carries only half of you, that half is more likely to survive than a child that carries you as a whole. In other words, sex gives the possibility for a population of genes (those that make up an individual) to get rid of some of the less efficient ones and replace them with better copies.

As you know, most sexual organisms make such a recombination by fusing two sexual cells, the gametes, and those are usually of two different kinds: a small one (the male) and a large one (the female).

In some species, each individual can only produce either male or female gametes, therefore being either a male organism or a female organism. In such species, sexual reproduction requires a male to mate with a female. This is the pattern found, for example, in most vertebrates and arthropods.

lossy-page1-799px-19_ixodes_ricinus_pareni-tif

A female (large) and a male (small) of the tick Ixodes ricinus mating. Image by Jana Bulantová.*

In other species, each individual can produce both male and female gametes, therefore being called a hermaphrodite. The advantage of such a system is that hermaphrodites can mate with any individual of their species, sometimes even with themselves! One of the main problems with hermaphroditism is when you decide to play only one role, which may lead to conflict during sex.

800px-weinbergschnecke_paarung

Two snails Helix pomatia (hermaphrodites) making love. Photo by Wikimedia user Jangle1969.**

Now what evolved first? Dioecious species (those having male and female individuals) or hermaphrodites (allso called monoecious species)? It’s hard to tell, but we can be sure that during evolution many lineages switched from one system to the other and back. And the coolest part is that such switches still happen today.

You may know that most flowering plants are hermaphrodites. Flowers usually have both male and female organs, although they are rarely able to fertilize themselves (self-fertilization). Among plants, the cases of dioecious species seem to be mainly due to some mutation that ended up partially sterilizing an individual. For example, a mutation could appear that makes the plant unable to produce male organs, thus becoming only female. Other individuals in the population that lack this mutation continue to be hermaphrodites, so we have an “unbalanced” species with two sexes, females and hermaphrodites, but no males. Although unusual at first, such a system can remain stable if reproduction occurs through cross-fertilization and not self-fertilization. As both females and hermaphrodites need pollen (which produces the male gametes) from other plants, they can coexist as long as the pollinator carries pollen to both sexes. The same happens if the sexes are male and hermaphrodite. As long as the pollinator carries the male’s pollen to hermaphrodite flowers, both sexes can do just fine.

584px-geranium_sylvaticum_enbla02

The plant Geranium sylvaticum includes hermaphrodites and females, but no males. Photo by Enrico Blasutto.**

Species composed of males and hermaphrodites are called androdioecious (from Greek andro-, man, male + di-, two + oikos, home, house; therefore “male in two “houses”, i.e., in two different kinds of organisms), while those composed of females and hermaphrodites are called gynodioecious (from Greek gyno-, woman, female; therefore “female in two different kinds of organisms).

Androdioecious and gynodioecious species occur among animals as well, but in this case their existance indicates something happening in the other direction, i.e., it is a transition from a dioecious species (with males and females) to a hermaphrodite species. And this is much more complicated that the other way round. Actually, it can get really, really bad for the “single-sex sex”.

This unbalanced sexual system in animals usually happens like this. There is a happily dioecious species with male and female individuals, but one day a new mutation appears and allows one of the sexes to produce both male and female gametes, thus becoming an hermaphrodite. However, such hermaphrodites are usually unable to play the role of the new sex while mating, i.e., they have the gametes, but not the tool to mate using them. Thus, the only way to use both gametes is to fertilize themselves.

One problem that comes from doing that is inbreeding. When you fertilize yourself, you are not increasing genetic diversity. On the contrary, you have very high chances of producing offspring with two copies to the same gene, thus decreasing genetic diversity. In order to continue to have recombination, you must mate with the single-sex individuals, which means you can only play the role of your original sex and your hermaphroditism is irrelevant. You are producing useless gametes. Or are you?

maleintrofig3b

A male and a hermaphrodite of the nematode Caenorhabditis elegans an androdioecious species. Credit to Worm Atlas.

The problem with inbreeding happens when an organism ends up with two copies of a deleterious gene, which is fairly common in species where cross-fertilization is the rule and such deleterious genes are maintained in the population through individuals with a single copy that is not enough to cause any trouble. That is why having kids with your parents, children of siblings is usually a bad idea. When a species evolves from a system of cross-fertilization to one of self-fertilization, inbreeding can be a serious problem at first, producing many descendants that will die soon. However, eventually this will “purge” the set of genes. If individuals only mate with themselves, the number of deleterious genes will sharply decrease after some generations and inbreeding will not be such a big problem anymore.

When this happens in a species with unbalanced sex, the single-sex individuals will be in trouble. Two androdioecious animals have been studied regarding this conflict, the nematode and model organism Caenorhabditis elegans and clam shrimps of the genus Eulimnadia, such as Eulimnadia texana. In both groups, the hermaphrodites do not seem to be very interested in mating with males. They have even lost most phenotypic clues that help males identify them as potential mates. The only thing left for the males is to insist, to look for hermaphrodites and force them to mate with them, but it is a hard battle. Even when mating does occur, the hermaphrodite usually discards the male’s sperm.

drylakeclam

A hermaphrodite (left) and a male (right) of the clam shrimp Eulimnadia texana. Credits to arizonafairyshrimp.com

The persistence of males in the population depends basically on their ability to fertilize hermaphrodites against their will and the sex-determination system of the species. When hermaphrodites produce males by self-fertilization, they are destined to remain for at least some time even if they cannot fertilize that much. Now if self-fertilization only produce hermaphrodites, the poor males have to be really persistent or otherwise they will soon perish.

– – –

You may also like:

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

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

– – –

Like us on Facebook!

Follow us on Twitter!

– – –

References and further reading:

Chasnov JR 2010. The evolution from females to hermaphrodites results in a sexual conflict over mating in androdioecious nematode worms and clam shrimp. Journal of Evolutionary Biology 23: 539–556.

Ellis RE & Schärer L 2014. Rogue Sperm Indicate Sexually Antagonistic Coevolution in Nematodes. PLoS Biol 12: e1001916.

Ford RE & Weeks SC 2018. Intersexual conflict in androdioecious clam shrimp: Do androdioecious hermaphrodites evolve to avoid mating with males? Ethology 124: 357–364.

– – –

*Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

**Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

1 Comment

Filed under Behavior, Evolution, worms