Category Archives: Zoology

Friday Fellow: Sea Swallow

by Piter Kehoma Boll

As the second species of today, I’m bringing a terrible but beautiful predator of the Portuguese man o’ war, the sea swallow Glaucus atlanticus, which is, in my opinion, one of the most beautiful sea creatures.

Glaucus_atlanticus

Isn’t it a magnificent creature? Photo by Sylke Rohrlach.*

Also known as blue dragon, blue glaucus and many other names, the sea swallow is a small sea slug that measures up to 3 cm in length as an adult. This species is pelagic, meaning that it lives in the open ocean, neither close to the bottom nor close to the shore.  Although it is found in all three oceans, genetic evidences indicate that the populations from the Atlantic, the Pacific and the Indian oceans have diverged more than 1 million years ago.

The sea swallow has a gas-filled sac in the stomach that makes it float upside down in the water, meaning that its ventral side is directed upward. The wide blue-bordered band running along the body, as seen in the picture above, is the slug’s foot. It’s dorsal side, which is directed downward, is completely white or light gray.

Being a carnivorous species, the sea swallows feeds on several cnidarian species, especially the Portuguese man o’ war. It usually collects the cnidocytes (the sting cells) of its prey and put them on its own body, so that it becomes as stingy as or even stingier than its prey. If you find one lying on the beach, be careful.

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References:

Churchull, C. K. C.; Valdés, Á.; Foighil, D. Ó (2014) Afro-Eurasia and the Americas present barriers to gene flow for the cosmopolitan neustonic nudibranch Glaucus atlanticus. Marine Biology, 161(4): 899-910.

Wikipedia. Glaucus atlanticus. Available at < https://en.wikipedia.org/wiki/Glaucus_atlanticus >. Access on June 18, 2017.

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Friday Fellow: Hummingbird Bobtail Squid

by Piter Kehoma Boll

If you are digging through the sand at the bottom of the clear tropical waters around Indonesia and the Philippines, you may end up finding a colorful little creature, the hummingbird bobtail squid, Euprymna berryi, also known as Berry’s bobtail squid.

Euprymna_berryi

A beautiful specimen photographed in East Timor. Photo by Nick Hobgood.*

Measuring about 3 cm if male or 5 cm if female, the humminbird bobtail squid is actually more closely related to cuttlefish than to true squids. Its body has a translucent skin marked by many black chromatophores, and to the human eye the animal seems to have a color pattern formed by a blend of black, electric blue and green or purple dots.

During the day, the hummingbid bobtail squid remains most of the time buried in the sand, coming out at night to capture small crustaceans, which it hunts using a bioluminescent organ in its gill cavity.

In some areas around its distribution, the hummingbid bobtail squid is captured and sold in small fisheries, but as the data on the distribution and population dynamics of this species are very poorly known, there is no way to say whether it is vulnerable or endangered in any way. As a result, it is listed as Data Deficient in the IUCN Red List.

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ResearchBlogging.orgReferences:

Barratt, I., & Allcock, L. (2012). Euprymna berryi The IUCN Red List of Threatened Species DOI: 10.2305/IUCN.UK.2012-1.RLTS.T162599A925343.en

Wikipedia. Euprymna berryi. Available at <https://en.wikipedia.org/wiki/Euprymna_berryi&gt;. Access on March 8, 2017.

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Land snails on islands: fascinating diversity, worrying vulnerability

by Piter Kehoma Boll

The class Gastropoda, which includes snails and slugs, is only beaten by the insects in number of species worldwide, having currently about 80 thousand described species. Among those, about 24 thousand live on land, where they are a very successful group, especially on oceanic islands.

The Hawaiian Islands alone, for example, have more than 750 snail species and there are more than 100 endemic species in the small island of Rapa in the South Pacific. This diversity is much higher than that in any continental place, but the reason for that is not completely understood.

Mandarina

A land snail of the genus Mandarina, endemic to the Ogasawara Islands, Japan. Photo by flickr user kmkmks (Kumiko).*

One of the most likely explanations for this huge diversity on islands is related to the lack of predators. The most common predators of snails include birds, mammals, snakes, beetles, flatworms and other snails. Most of those are not present in small and isolated islands, which allows an increase in land snail populations in such places. Without too much dangers to worry about, the community of land snails n islands can explore a greater range of niches, eventually leading to speciation.

Unfortunately, as always, the lack of danger leads to recklessness. Without predators to worry about, insular land snails tend to lay fewer eggs than their mainland relatives. If there is no danger of having most of your children eaten, why would you have that many? It is better to lay larger eggs, putting more resources on fewer babies, and so assure that they will be strong enough to fight against other snail species. Afterall, the large number of species in such a small place as an island likely leads to an increased amount of competition between species.

But why is this recklessness? Well, because you never known when a predator will arrive. And they already arrived… due to our fault.

The diversity of insular land nails was certainly affected by habitat loss promoted by humans, but also by predators that we carried with us to the islands, whether intentionally or not. These predators include rats, the predatory snail Euglandina rosea and the land flatworm Platydemus manokwari, the latter being most likely the worst of all.

800px-platydemus_manokwari

The flatworm Platydemus manokwari in the Ogasawara Islands. Photo by Shinji Sugiura.

This flatworm arrived at the Chichijima Island, part of the Ogasawara Islands in the Pacific Ocean, in the early 1990s and in about two decades it led most land snail species on the island to extinction and many more are about to face the same fate on this island and on others. Not being prepared for predators, these poor snails cannot reproduce fast enough to replace all individuals eaten by the flatworm.

We have to act quickly if we want to save those that are still left.

See also: The New Guinea flatworm visits France – a menace.

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ResearchBlogging.orgReferences and further reading:

Chiba, S., & Cowie, R. (2016). Evolution and Extinction of Land Snails on Oceanic Islands. Annual Review of Ecology, Evolution, and Systematics, 47 (1), 123-141 DOI: 10.1146/annurev-ecolsys-112414-054331

Sugiura, S., Okochi, I., & Tamada, H. (2006). High Predation Pressure by an Introduced Flatworm on Land Snails on the Oceanic Ogasawara Islands. Biotropica, 38 (5), 700-703 DOI: 10.1111/j.1744-7429.2006.00196.x

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Friday Fellow: Crystalline crestfoot

by Piter Kehoma Boll

Even in the smallest pools or ponds of freshwater lost in a field, the diversity of lifeforms is amazing. Sadly, these environments are one of the most damaged of all ecosystems on earth and we probably have led many tiny species to extinction. Today’s fellow, however, is still alive, and its name is Lophopus crystallinus, or as I decided to call it, the crystalline crestfoot.

lophopus_crystallinus

A colony of Lophopus crystallinus. Photo by Natural History Museum, London.*

The crystalline crestfoot is member of the phylum Bryozoa, sometimes called moss animals. In fact, it was the first bryozoan to be described. As other bryozoans, the crystalline crestfoot lives as a colony of individuals attached to substracts in the lakes and ponds where they exist, which includes Europe and North America. The individuals are not fully independent and have specialized functions within the colony, thus acting as a single superorganism. As a general rule, bryozoans, including the crystalline crestfoot, are filter feeders, extracting particles and microalgae from water.

Despite being considerable tolerant to eutrophication (increase of  organic matter in water) and heavy metal pollution, the crystalline crestfoot is yet threatened by other forms of human impact, such as climate change and certainly by the destruction of its habitat. Once an abundant species, the crystalline crestfoot is now rare and declining. It is currently regarded as a threatened species in the United Kingdom and is the only bryozoan to have a Species Action Plan. Let’s hope we can find a way to avoid it to be wiped out from this world.

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ResearchBlogging.orgReferences:

Elia, A., Galarini, R., Martin Dörr, A., & Taticchi, M. (2007). Heavy metal contamination and antioxidant response of a freshwater bryozoan (Lophopus crystallinus Pall., Phylactolaemata). Ecotoxicology and Environmental Safety, 66 (2), 188-194 DOI: 10.1016/j.ecoenv.2005.12.004

Hill, S., Sayer, C., Hammond, P., Rimmer, V., Davidson, T., Hoare, D., Burgess, A., & Okamura, B. (2007). Are rare species rare or just overlooked? Assessing the distribution of the freshwater bryozoan, Lophopus crystallinusBiological Conservation, 135 (2), 223-234 DOI: 10.1016/j.biocon.2006.10.023

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Who came first? The comb or the sponge?

by Piter Kehoma Boll

The endless question is here again, but this time it appears to be settled. What animal group is the earliest of all? Who came first?

It is clear that there are five animal lineages that are usually regarded as monophyletic: sponges, placozoans, comb jellies, cnidarians and bilaterians. Let’s take a brief look at each of them:

Sponges (phylum Porifera) are always sessile, i.e., they do not move and are fixed to the substrate. They have a very simple anatomical structure. Their body is consisted of a kind of tube, having a large internal cavity and two layers of cells, an outer one and an inner one around the cavity. There are several small openings connecting the cavity to the outside, called pores, and one or more large cavities, called oscula (singular: osculum). Between the two cell layers there is a jelly-like mesohyl containing unspecialized cells, as well as the skeleton structures, including fibers of spongine and spicules of calcium carbonate or silica. Some species also secrete an outer calcium carbonate skeleton over which the organic part grows. Sponges lack muscles, nervous system, excretory system or any other kind of system. They simply live by beating the flagella of the choanocytes (the cells of the inner layer), creating a water flow entering through the pores and exiting through the osculum. The choanocytes capture organic particles in the water and ingest them by phagocytosis. All sponge cells can change from one type to another and migrate from one layer to another, so there are no true tissues.

porifera_body_structures_01

Body structures found in sponges. Picture by Philip Chalmers.*

Placozoans (phylum Placozoa) are even simpler than sponges, but they actually have true tissues. They are flat amoeboid organisms with two layers of epithelium, one dorsal and one ventral, and a thin layer of stellate cells. The ventral cell layer is slightly concave and appears to be homologous to the endoderm (the “gut” layer) of other animals, while the upper layer is homologous to the ectoderm (the “skin” layer).

701px-trichoplax_adhaerens_photograph

Trichoplax adhaerens, the only species currently in the phylum Placozoa. Photo by Bernd Schierwater.**

Comb jellies (phylum Ctenophora) resemble jellyfishes, but a closer look reveals many differences. Externally they have an epidermis composed by two layers, an outer one that contains sensory cells, mucus-secreting cells and some specialized cells, like colloblasts that help capturing prey and cells containing multiple cilia used in locomotion, and an inner layer with a nerve net and muscle-like cells. They have a true mouth that leads to a pharynx and a stomach. From the stomach, a system os channels distribute the nutrients along the body. Opposite to the mouth there is a small anal pore that may excrete small unwanted particles, although most of the rejected material is expelled through the mouth. There is a layer of jelly-like material (mesoglea) between the gut and the epidermis.

bathocyroe_fosteri

The comb jelly Bathocyroe fosteri.

Cnidarians (phylum Cnidaria) have a structure similar to comb jellies, but not as complex. They also have an outer epidermis, but this is composed by a single layer of cells, and a sac-like gut surrounded by epthelial cells (gastrodermis), as well as a mesoglea between the two. Around the mouth there is one or two sets of tentacles. The most distinguishing feature of cnidarians is the presence of harpoon-like nettle cells, the cnidocytes, which are used as a defense mechanism and to help subdue prey.

800px-cross_section_jellyfish_en-svg

Body structure of a cnidarian (jellyfish). Picture by Mariana Ruiz Villarreal.

Bilaterians (clade Bilateria) includes all other animals. They are far more complex and are characterized by a bilateral body, cephalization (they have heads) and three main cell layers, the ectoderm, which originates the epidermis and the nervous system, the mesoderm, which give rise to muscles and blood cells, and the endoderm, which develops into the digestive and endocrine systems.

500px-bilaterian-plan-svg

Basic bilaterian structure.

Traditionally, sponges were always seen as the most primitive animals due to their lack of true tissues, muscular cells, nervous cells and all that stuff. However, some recent molecular studies have put the comb jellies as the most primitive animals. This was highly unexpected, as comb jellies are far more complex than sponges and placozoans, which would suggest that muscles and a nervous system evolved twice in the animal kingdom, or that sponges are some weird simplification of a more complex ancestor, which would be very hard to explain. The nervous system of comb jellies is indeed quite unusual, but not so much that it needs an independent origin.

However, now things appear to be settled. A study published this month on Current Biology by Simion et al. reconstructed a phylogenetic tree using 1719 genes of 97 animal species, and applying new and more congruent methods. With this more refined dataset, they recovered the classical reconstruction that puts sponges at the base of the animal tree, a more plausible scenario after all.

But why other studies have found comb jellies as the most basal group? Well, it seeems that comb jellies have unusually high substitution rates, meaning that their genes evolve faster. This leads to a problem called “long branch attraction” in phylogenetic reconstructions. As DNA has only four different nucleobases, namely adenine, guanine, cytosine and thymine, each one can only mutate into one of the other three. When mutations occur very often, they may go back to what they were in long lost ancestor, leading to misinterpretations in the evolutionary relationships. That seems to be what happens with comb jellies.

So, it seems that after all the sponge indeed came first.

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References and further reading:

Borowiec ML, Lee EK, Chiu JC, & Plachetzki DC 2015. Extracting phylogenetic signal and accounting for bias in whole-genome data sets supports the Ctenophora as sister to remaining Metazoa. BMC Genomics 16: 987. DOI: 10.1186/s12864-015-2146-4

Littlewood DTJ 2017. Animal Evolution: Last Word on Sponges-First? Current Biology 27: R259–R261. DOI: 10.1016/j.cub.2017.02.042

Simion P, Philippe H, Baurain D, Jager M, Richter DJ, Di Franco A, Roure B, Satoh N, Quéinnec É, Ereskovsky A, Lapébie P, Corre E, Delsuc F, King N, Wörheide G, & Manuel M 2017. A Large and Consistent Phylogenomic Dataset Supports Sponges as the Sister Group to All Other Animals. Current Biology 27: 958–967. DOI: 10.1016/j.cub.2017.02.031

Wallberg A, Thollesson M, Farris JS, & Jondelius U 2004. The phylogenetic position of the comb jellies (Ctenophora) and the importance of taxonomic sampling. Cladistics 20: 558–578. DOI: 10.1111/j.1096-0031.2004.00041.x
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Friday Fellow: Pliable Brachionus

by Piter Kehoma Boll

Charles Darwin had already noticed that small animals, such as those found in zooplankton, are widely distributed around the world, even those that are found in small ponds of freshwater. This seemed to go against the speciation theories, but it was thought to be the result of passive transport by other animals, such as migratory birds. One of such species is the tiny rotifer Brachionus plicatilis, or the pliable brachionus, as I decided to call it, a 0.1 to 0.2 mm long species found worlwide in saline lakes.

brachionus_plicatilis

A specimen of the pliable brachionus. Photo by Wikimedia user Sofdrakou.*

The pliable brachionus is a euryhaline species, meaning it can tolerate a wide range of salinity. Recent molecular studies have shown that it is actually a complex of at least 22 different species, but as this was not yet taxonomically defined, I will continue to use the terms Brachionus plicatilis and plicate brachionus in the broad sense.

In the last half century, the pliable brachionus became a commercially important species, being raised as a food source for fish larvae. It may be fed with a variety of microorganisms, such as bacteria, algae and yeasts. In the natural environment, it is considered a generalist filter-feeding species.

As many rotifers, the pliable brachionus usually reproduces by parthenogenesis, where the so-called amictic females produce diploid eggs that originate other amictic females. Under certain conditions, however, they may produce eggs that originate mictic females, which only lay haploid eggs. Unfertilized haploid eggs originate males, while those that are fertilized originate new females. A bit complex, right?

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ResearchBlogging.orgReferences:

Gómez, A., Serra, M., Carvalho, G., & Lunt, D. (2002). Speciation in ancient cryptic species complexes: evidence from the molecular phylogeny of Brachionus plicatilis(Rotifera) Evolution, 56 (7) DOI: 10.1554/0014-3820(2002)056[1431:SIACSC]2.0.CO;2

Øie, G., Makridis, P., Reitan, K., & Olsen, Y. (1997). Protein and carbon utilization of rotifers (Brachionus plicatilis) in first feeding of turbot larvae (Scophthalmus maximus L.) Aquaculture, 153 (1-2), 103-122 DOI: 10.1016/S0044-8486(96)01514-1

Suatoni, E., Vicario, S., Rice, S., Snell, T., & Caccone, A. (2006). An analysis of species boundaries and biogeographic patterns in a cryptic species complex: The rotifer—Brachionus plicatilis Molecular Phylogenetics and Evolution, 41 (1), 86-98 DOI: 10.1016/j.ympev.2006.04.025

Walker, K. (1981). 13. A synopsis of ecological information on the saline lake rotifer Brachionus plicatilis Müller 1786 Hydrobiologia, 81-82 (1), 159-167 DOI: 10.1007/BF00048713

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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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