Category Archives: Fish

Love thy neighbor’s son: why do some animals care for the young of others?

by Piter Kehoma Boll

Leia em Português

Parental care, here defined as any behavior in which an animal takes care of its young, is a widespread practice in the animal kingdom, having evolved repeatedly in many taxa. It is not difficult to see, considering natural selection, why parental care is an adaptative trait. It enhances the chance of one’s offspring to survive and thus carry one’s genes to the next generation.

A bird feeding its babies. Photo by JJ Harrison.*

On the other hand, the related behavior known as alloparental care is not that easy to explain in every instance of its occurrence.

While parental care means caring for your own offspring, alloparental care means caring for the offspring of another individual. If you spend time and resources in taking care of an animal that is not your direct descendant, you must have a good reason to do it, a reason that somehow benefits you. Or you may just be too dumb.

Most animals reject or even kill the offspring of other individuals of the same species. A classic example is a male lion that kills the cubs that he knows are not his. He does that because he sees no advantage in allowing the offspring of another male to survive.

An extreme example of caring for juveniles that are not your direct offspring is found in social insects such as bees and ants. Worker ants usually do not reproduce but they raise their siblings as if they were their own children. In this case, it is more advantageous to make siblings than to make children because of the peculiar reproductive system of hymenopterans. I will not enter in details but, basically, ants share 100% of their father’s DNA and 50% of their mother’s DNA, so that two sibling ants have 75% of their genes in common, while the relationship between a female ant and her female offspring is of only 50%.

Bees help their mother to raise their siblings. Photo by Wikimedia user Waugsberg.*

However, alloparental care is found in many other animals, especially in mammals. Although not having 75% of similarity between siblings as in ants, many mammals and other animals help their mothers and/or fathers to raise their siblings. This has less direct advantages but they are still there. After all, your siblings (if they are of the same mother AND father) share 50% of your DNA, the same amount that you share with your children. But alloparental care may also happen with more distantly related relatives, such as grandchildren and half-siblings, which share only 25% of their DNA with you. This is not a problem, though, because if you are unable to have your own kids at that time, it is better to help raise those juveniles that share some DNA with you than to do nothing because 25% of your genes is still better than nothing.

A recently published paper reports the first observation of alloparental care in the field in the cichlid fish Neolamprologus savoryi. The team observed a male fish helping take care of the eggs of another male that was found to be his father, although the mother of the eggs was not his mother. The male helper was small and probably sexually immature, so that, as said above, helping his half-siblings, which have 25% of his genes, survive is better than doing nothing.

An immature male of Neolamprologus savoryi taking care of the eggs of his father with his stepmother. Credits to Josi et al. (2019).

A really hard thing to explain is why some animals accept to take care of the offspring of unrelated individuals, in which there is no clear adaptative advantage. Such a situation was recently discovered to occur with the common earwig Forficula auricularia. Females that had their egg clutches replaced with the eggs of an unrelated female took care of them as if they were their own. No advantage of any kind can be extracted from this behavior, so the most likely explanation is simply the lack of adaptative pressure to reject unrelated eggs. It is likely that, under natural conditions, a female earwig never encounters the eggs of another female. Thus, there was never a scenario in which the capacity to recognize one’s own eggs (and differentiate them from others) could evolve. Natural selection needs opportunities to act.

Forficula auricularia with a clutch of eggs. Photo by Tom Oates.*

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Endosperm: the pivot of the sexual conflict in flowering plants

Your mother loves you more when she loves your father… if you are a fish

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References:

Josi D, Taborsky M, Frommen JG (2019) First field evidence of alloparental egg care in cooperatively breeding fish. Ethology 125(3): 164–169. doi: 10.1111/eth.12838

Royle NJ, Moore AJ (2019) Nature and Nurture in Parental Care. In: Genes and Behaviour, pp. 131–156. John Wiley & Sons, Ltd. doi: 10.1002/9781119313663.ch7

Van Meyel S, Devers S, Meunier J (2019) Love them all: mothers provide care to foreign eggs in the European earwig Forficula auricularia. Behavioral Ecology. doi:10.1093/beheco/arz012

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

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Filed under Behavior, Entomology, Evolution, Fish

Your mother loves you more when she loves your father… if you are a fish

by Piter Kehoma Boll

Sexual selection is a frequent subject of my posts here but they are usually focused on how females and males behave regarding each other. However, there is a third element that results from their interactions: the children.

Females tend to select the best males to be the father of their children because they are interested in having a healthy and strong offspring with better chances of surviving. But what happens when a female has no choice but to mate with a low-quality male? Will she take care of their children the same way?

A recent study conducted with the Honduran red point cichlid, Amatitlania siquia, investigated this question. This fish species is native from Central America and, as usually between cichlids, a female and a male form a bond and take care of their eggs and young together.

A couple of Amatitlania siquia. Photo extracted from nvcweb.nl

The researchers placed a female in an aquarium with transparent walls in which she was able to visually analyze two males, one placed in a chamber to the left and another in a chamber to the right. One of the males was larger than the other, both being larger than the female. After 48 hours, the female was placed randomly with either the larger or the smaller male for them to mate.

The results indicate that females produce similar egg clutches and take care of the eggs in equal amounts when mated with either larger or smaller males. However, after the eggs hatch and the larvae develop to the fry stage, the female spends more time caring for them if their father is the larger one.

They don’t seem very excited to waste their time with low-quality children. Afterall, they may meet that handsome big fish again in the future.

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References:

Robart AR, Sinervo B (2019) Females increase parental care, but not fecundity, when mated to high-quality males in a biparental fish. Animal Behavior 148: 9–18. https://doi.org/10.1016/j.anbehav.2018.11.012

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Filed under Behavior, Evolution, Fish

Playful Womb: Baby sharks swim inside their moms

by Piter Kehoma Boll

Leia em português

Most female mammals are characterized by carrying their embryos in the uterus. As the embryos grow and develop, the space inside the uterus gets tight, which makes their ability to move very limited. In addition, mammal embryos are attached to the uterus by the placenta, so that moving too much may be harmful.

Things are different for sharks, which also tend to carry their embryos in the uterus. Lacking a placenta, shark embryos can move freely inside the uterus, and some recent observations revealed that they move a lot.

A specimen of Nebrius ferrugineus at the Great Barrier Reef. Photo by Anne Hoggett.*

Using an ultrasound device adapted to be used underwater, a group of Japanese scientists found out that the embryos of the tawny nurse shark Nebrius ferrugineus are very active inside the uterus. Female sharks in fact have two uteri, which are connected by a narrow passage just above the cervix (the “exit” from the uterus). The embryos were observed swimming constanly from one uterus to the other and in one occasion one of them even put its head through the cervix to “take a look” on things outside its mom.

Ultrasound images and schematic illustrations of a shark embryo swimming from one uterus into the other. Image from the original paper.

The reason for such an active life inside the uterus is not yet clear, but one hypothesis is that the embryos swim around looking for eggs and smaller embryos to eat. It may sound horrible, but baby sharks eating their siblings inside the uterus seems to be a common occurrence.

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Reference:

Tomita T, Murakumo K, Ueda K, Ashida H, Furuyama R (2018) Locomotion is not a privilege after birth: Ultrasound images of viviparous shark embryos swimming from one uterus to the other. Ethology. https://doi.org/10.1111/eth.12828

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

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Hundreds of lionfish were released in the Atlantic out of pity

by Piter Kehoma Boll

The red lionfish, Pterois volitans, is a beautiful and venomou coral fish native from the Indo-Pacific region. Due to its great beauty, it is a very popular in fish tanks all around the world.

799px-red_lionfish_near_gilli_banta_island

A red lionfish in its natural and native habitat in Indonesia. Photo by Alexander Vasenin.*

Since the 1980s, the lionfish started to be found in the waters of the Atlantic ocean around Florida. How did they get there? Certainly humans had something to do with it, but the exact way is yet unknow. Originally a small population, the species spread quickly by the beginning of the 21th century and in 2010 had colonized the Caribbean and the Gulf of Mexico.

Some original studies on the genetic diversity of the Atlantic population estimated that the minimum number of introduced specimens was around 10. If that was true, the established population may have been the result of an accident, like, for example, the fish of a single aquarium accidentally ending up in the sea.

800px-caribbean_lionfish3f_28519689049529

A red lionfish photographed in Curaçao, Caribbean. Photo by Laszlo Ilyes.**

A recently published study (see reference), however, reestimated this number using new models and additional data. The conclusions are that the number of fish that colonized the Atlantic was much bigger, around 272 individuals. Such a large introduction would unlikely occur by accident. Introductions by fish being transported from the Indo-Pacific region in the ballast water of ships is unlikely, as they would hardly survive the transport. The most likely answer is that these fish were introduced through several small releases that happened in Miami. How and why? Well, many people like to have fish in beautiful fish tanks at home, and when they get tired of managing the animals or cannot afford continuing to have them, they decide to simply release them in the ocean out of pity, because the alternative would be to kill them.

Now can you see what are the consequences of thinking this way? You care too much for a single specimen, has no ecological knowledge, and simply decide to release them in the wild. Years later, they have depleted whole ecosystems and caused a large-scale disaster. That’s what humans do. As they say, the road to hell is paved with good intentions.

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References:

Selwyn JD, Johnson JE, Downey-Wall AM, Bynum AM, Hamner RM, Hogan JD, Bird CE. (2017Simulations indicate that scores of lionfish (Pterois volitans) colonized the Atlantic OceanPeerJ 5:e3996 https://doi.org/10.7717/peerj.3996

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Friday Fellow: Ocean Sunfish

by Piter Kehoma Boll

Let’s swim to the world of fishes once more. And today we are meeting the heaviest of the bony ones, the ocean sunfish!

mola_mola

The ocean sunfish looks like a giant piece of mushroom, don’t you think? Photo by Per-Ola Norman.

Scientifically known as Mola mola, the ocean sunfish is found in tropical and temperate oceanic waters throughout the world and has a very strange look. And this is not the only strange thing about it. More than being the heaviest bony fish in the world, weighing up to 1,000 kg, it feeds almost exclusively on jellyfish, eating a huge amount of them to become that big. Also, the female ocean sunfish is known to produce up to 300 million eggs at a time, more than any other vertebrate!

The weird lump on their rear end is not a caudal fin. Actually, sunfish have no tail at all. This structure, called clavus, is formed by projections of the dorsal and anal fins.

Despite their huge size, sunfishes are not a direct threat to humans. People can swim among them without any problem. The most common forms of accidents with these fish are caused when boats collide with them or when a sunfish jumps out of the water and ends up inside a boat. Imagine a 500-kg fish landing on your head!

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References:

McGrouther, Mark (2011).”Ocean Sunfish, Mola mola“. Australian Museum Online. Available at <http://australianmuseum.net.au/ocean-sunfish-mola-mola&gt;. Access on December 8, 2016.

Wikipedia. Ocean sunfish. Available at <https://en.wikipedia.org/wiki/Ocean_sunfish&gt;. Access on December 8, 2016.

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Filed under Fish, Friday Fellow, Zoology

Friday Fellow: Flounder Glugea

by Piter Kehoma Boll

While looking for flatfish you may eventually find one with some grotesque growth on the body, like the one in the picture below:

glugea_stephani_xenoma

A xenoma caused by Glugea stephani on a flatfish Limanda limanda. Photo by Hans Hillewaert.*

This sort of tumor is called xenoma and, in flatfish, is caused by a microscopical and parasitic fungus named Glugea stephani, or the flounder glugea.

The flounder glugea is part of a group of fungi called Microsporidia that until recently were classified as protists. They are unicellular and parasite other organisms, especially crustaceans and fish.

Once inside a flatfish, the flounder glugea enters an intestinal cell and starts to develop. They induce the host cell to increase in size and may give rise to the xenomas, which are the most extreme stage in the development of the disease. The proliferating and active stage of the glugea are free in the cytoplasm of the host cell, but they may change into a spore-like form called sporoblast that remains inside a vacuole.

glugea_stephani

Image of electron microscopy of an intestinal cell of winter flounder (Pseudopleuronectes americanus) infected by flounder glugea (Glugea stephani). The S indicates sporoblasts inside the vacuole (SV) and the P the proliferating organisms inside the host cytoplasm (H). Image extracted from Takvorian & Cali (1983).

Fortunately most infections are mild and do not compromise the fish health, at least not very much…

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References:

Takvorian, P. M.; Cali, A. (1983). Appendages associated with Glugea stephani, a microscporidian found in flounder. Journal of Protozoology, 30(2): 251-256.

Wikipedia. Xenoma. Available at: < https://en.wikipedia.org/wiki/Xenoma >. Access on September 17, 2016.

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Friday Fellow: Winter Flounder

by Piter Kehoma Boll

Can you spot the two fish in the photo bellow?

pseudopleuronectes_americanus

Perfect camouflage. Two winter flounders, Pseudopleuronectes americanus. Photo by Brent Wilson.*

Belonging to the species Pseudopleuronectes americanus, commonly known as winter flounder or black back, it is a flatfish native to the North Atlantic coast of Canada and the United States. It may reach up to 70 cm in length and 3,6 kg in weight, although in most areas it is smaller.

As with other flatfish, the winter flounder is asymetrical. It lives on the substrate, lying on one of its sides (in this case, on the left side) and its left eye has migrated to the right side, so that both point upwards.

pseudopleuronectes_americanus_2

Condemned to lie on its left side.

Living in very cold waters, the winter flounder suffers the risk of freezing during winter. As a result, its blod has a set of proteins that have the ability to reduce the freezing point of water, allowing it to remain liquid below 0°C.

The winter flounder is an important commercial fish in the USA and regarded as having a delicious meat. It has been overfished in the past decades and some populations have been depleted. Despite a recent large reduction in fishing pressure, many populations are recovering very slowly due to other factors, such as habitat degradation and low genetic variability. Furthermore, there are still some areas where overfishing may still be happening.

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References:

Duman, J. G.; DeVries, A. L. (1976) Isolation, characterization, and physical properties of protein antifreezes from the winter flounder, Pseudopleuronectes americanusComparative Biochemistry and Physiology Part B: Comparative Biochemistry, 54(3): 375-380.

Wikipedia. Winter flounder. Available at: < https://en.wikipedia.org/wiki/Winter_flounder >. Access on September 17, 2016.

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