Category Archives: worms

Friday Fellow: Brown’s Dagger Nematode

by Piter Kehoma Boll

Nematodes are famous because of their parasitic members, which do not only parasitize animals but also plants. People that deal with gardening or agriculture may know that sometimes a plant becomes sick because of “nematodes”.

A genus of nematodes that is commonly associated with grapevines is Xiphinema, whose species are known as dagger nematodes. The two most widely studied species are Xiphinema americanum, the American dagger nematode, and Xiphinema index, the California dagger nematode, but during the last decades it became clear that those species are actually a complex of very similar species and new ones are constantly been described. One of them, described in 2016, is Xiphinema browni, which I decided to call Brown’s dagger nematode. It was named after the nematologist Derek J. F. Brown.

Brown’s dagger nematode was found associated with the roots of grapevines and apple trees in Slovakia and the Czech Republic. Among 86 identified females there was only one male, indicating a huge disparity in sex ratios and the probability that females are parthenogenetic, i.e., they can lay fertile eggs without being fertilized by a male. Females measure up to 2.5 mm in length and the only known male measured 1.8 mm.

Female (left) and male (right) of Xiphinema browni. Modified from Lazarova et al. (2020).*

Since Brown’s dagger nematode was found associated with grapevines, its life cycle is likely similar to that of most other dagger nematodes. Adults are external parasites of grapevine roots and eventually of other woody plants. They live on the root surface and use their long odontostyles (a needle-like proboscis) to perforate the roots and suck the content of their vascular tissue. As a reaction, the plant produces swollen club-like galls on the root tips. The root then branches behind the swollen tip, only to be attacked again, developing another gall and having to branch again. This starts to weaken the plant, which can compromise grape production.

Anterior end of a female with the odontostyle slightly exposed. Modified from Lazarova et al. (2020).*

Females lay their eggs scattered through the soil, not forming clusters, and juveniles pass through about 4 stages in the soil before turning to the parasitic mode.

As another grapevine-feeding dagger nematode, Brown’s dagger nematode is probably also a vector of the grapevine fanleaf virus, which is transmitted to grapevines by the California dagger nematode. This happens when the nematode feeds on an infected plant and then moves to a healthy plant, carrying the virus with it. Grapevine fanleaf causes chlorosis (loss of chlorophyll) and distorts the leaves, making them look like fans, hence the name. As you can imagine, the poor plant becomes even weaker than it already was due to the nematodes sucking it. This can be a nightmare to vineyard owners.

The grapevine fanleaf virus can be a devastating disease for grapevines but in the nematode’s body it seems to have benefitial effects, increasing the survival of these small roundworms. Perhaps this stimulates the dagger nematodes to spread it further, in a sort of “evil coalition”.

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You may also like:

Tospovirus and thrips: an alliance that terrifies plants

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References:

Lazarova S, Peneva V, Kumari S (2016) Morphological and molecular characterisation, and phylogenetic position of X. browni sp. n., X. penevi sp. n. and two known species of Xiphinema americanum-group (Nematoda, Longidoridae). ZooKeys 574:1–42. https://doi.org/10.3897/zookeys.574.8037

van Zyl S, Vivier MA, Walker MA (2012) Xiphinema index and its Relationship to Grapevines: A review. South African Journal of Enology and Viticulture 33(1):21–32.

Wikipedia. Xiphinema. Available at <https://en.wikipedia.org/wiki/Xiphinema>. Access on 29 June 2020.

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

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Friday Fellow: Common Horse Tapeworm

by Piter Kehoma Boll

Flatworms are the fourth largest animal phylum after arthropods, mollusks and chordates and most species known to date belong to the clade Neodermata, which includes parasitic species such as flukes and tapeworms, some of which infect humans. Among tapeworms, the species that infect humans and belong to the genus Taenia are certainly the most popular, but it is expected that all vertebrates can have at least one tapeworm parasite, so that it is only a matter of time and opportunity for us to discover them all.

Among the species known to parasitize horses, the most widespread is Anoplocephala perfoliata, which I decided to call the common horse tapeworm. As tapeworms in general, the adult common horse tapeworm lives in the intestine of its definitive host, in this case a horse.

Different from species of Taenia, which can grow up to several meters in length, species of Anoplocephala are much smaller. The whole body of adult specimens measures about 5 to 8 cm in length and 1 to 2 cm in width and is divided into the same parts seen in other tapeworms. The anteriormost part of the body includes the scolex, which has 4 large suckers. Although the scolex of most tapeworms measures less than 1 mm, in the common horse tapeworm it reaches up to 3 mm.

A preserved specimen. Photo extracted from alchetron.com

After the scolex there is a small neck of undifferentiated tissue that grows constantly to build new proglottids, which form the rest of the body. Proglottids are connected to each other in a chain fashion and the posteriormost ones are continuouly lost and released into the environment. Each proglotid contains male and female sexual organs and is released when it contains mature eggs.

Mature proglottids are released in the environment through the horse’s feces and release their eggs on the ground and the vegetation. The eggs can survive outside a host for as long as 9 months. During this time, they hope to be accidentally ingested by oribatid mites that live in pastures. If this happens, the egg hatches inside the mite due to the mechanical action of the mite’s mouth parts and releases the first-stage larva called the oncosphere.

An egg of Anoplocephala perfoliata. The small 20-µm-diamter sphere is the oncosphere waiting to be released. Photo by Martin K. Nielsen, extracted from msdvetmanual.com

When the oncosphere reaches the mite’s gut, it is activated, probably via ions present in this environment, and uses a group of hooks to penetrate the mite’s tissues. After about 8 to 20 weeks, the oncosphere develops into a cysticercoid. This stage looks like an inverted miniaturized tapeworm inside a bladder-like vesicle, having already a protoscolex inside it.

While horses are grazing, they always ingest some invertebrates together with the grass. It they happen to ingest an infected mite, the cysticercoids are released during digestion, evert the protoscolex and attach to the intestinal walls of the horse. There, the tapeworm develops into an adult, restarting the cycle.

Attached to the intestine of their hosts, tapeworms do not feed on blood or other tissues as many parasites do. Instead of that, they collect nutrients directly from the host’s gut by absorbing them via the worm’s body surface.

For a long time its has been thought that the common horse tapeworm was a harmless parasite since most horses did not seem to have any symptom and the tapeworms were often only discovered during dissection after the horse’s death by other causes. The preferred area for the common horse tapeworm to attach is the caecum and the ileocaecal junction but in heavily infected animals some individuals can be found in suboptimal sites throughout the small and large intestines. In such heavily infected horses, the tapeworms can cause colics and even intestinal obstruction.

Large number of adult tapeworms in a heavily infected horse. Credits to Tomczuk et al. (2014).*

The common horse tapeworm can infect other equids as well, such as donkeys and zebras. Ironically, domesticated horses seem to be the most infected individuals exactly because horse owners treat them with anthelmintics. Most modern anthelmintics do not affect tapeworms and only remove other parasites, such as roundworms, which reduces competition and allows tapeworms to thrive.

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More parasitic flatworms:

Friday Fellow: Green-banded broodsac (on 09 March, 2018)

Friday Fellow: Salmon Fluke (on 11 January, 2019)

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References:

Gasser RB, Williamson RMC, Beveridge I (2005) Anoplocephala perfoliata of horses – significant scope for further research, improved diagnosis and control. Parasitology 131(1): 1–13. https://doi.org/10.1017/S0031182004007127

Tomczuk K, Kostro K, Szczepaniak KO, Grzybek M, Studzińska M, Demkowska-Kutrzepa M, Roczeń-Karczmarz M (2014) Comparison of the sensitivity of coprological methods in detecting Anoplocephala perfoliata invasions. Parasitology Research 113(6): 2401–2406. doi: 10.1007/s00436-014-3919-4

Wikipedia. Anoplocephala perfoliata. Available at < https://en.wikipedia.org/wiki/Anoplocephala_perfoliata >. Access on 11 June 2020.

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From headache to migraine: is Xenacoelomorpha a basal bilaterian clade or a group of weird deuterostomes?

by Piter Kehoma Boll

Seven years ago I discussed the phylogenetic position of Acoelomorpha and their close relative, Xenoturbella, which together form the clade Xenacoelomorpha. Being very simple bilaterian animals, lacking almost every major structure common to most other bilaterians, their exact position is usually considered to be basal inside Bilateria but the idea that they are deuterostomes was raised after some molecular studies grouped them with the clade Ambulacraria, which includes echinoderms and hemichordates.

Being deuterostomes would mean that Xenacoelomorpha suffered a huge simplification of their anatomy. Back in 2013, when I wrote the other article, this was causing a lot of controversy but, a time after that, new molecular studies confirmed the basal position of Xenacoelomorpha and it became kind of well accepted that they are, indeed, the basalmost clade in Bilateria.

A simplified version of the animal tree of life showing the uncertain position of Xenacoelomorpha. The position of Placozoa and Ctenophora is not very clear too.

But once a trouble, always a trouble.

By 2019, a new study that tried to anticipate effects of systematic errors during molecular phylogeny studies, such as long-branch attraction, concluded that the basal position of Xenacoelomorpha is an artifact and that, when one tries to minimize the errors, their position as sister-group of Ambulacraria becomes clear. However, their tree also suggests that Deuterostomia is not monophyletic, as Chordates appear as sister-group to Protostomia and Xenacoelomorpha+Ambulacraria is the basalmost group, i.e., the sister group of the rest of the Bilateria. However, the idea of Deuterostomia not being monophyletic is very unexpected.

As I mentioned in my old post, the main problem in Xenacoelomorpha appearing inside Deuterostomia is related to their oversimplification. They lack almost everything that any typical bilaterian has. What would have forced them to become that simple?

Xenoturbella japonica, a xenacoelomorph. Credits to Nakano et al. (2017).*

Another recent study suggested that, in the case of Xenoturbella at least, this may be the result of their soft-substrate burrowing habits. They compare Xenoturbella to nudibranchs, among which some species have similar lifestyles. One of these nudibranchs, Xenocratena, was actually discovered at about the same time as Xenoturbella living in the same environment. They have a paedomorphic (more simplified, “baby-like”) anatomy compared to other nudibranchs. However, it is not at all as simple as Xenoturbella.

The burrowing nudibranch Xenocratena suecica. Credits to Martynov et al. (2020).*

On the other hand, there is another genus of nudibranchs that is indeed oversimplified, Pseudovermis, and it lives burrowed in soft substrate as well. Molecular analyses revealed that Pseudovermis is not closely related to Xenocratena but to Cumanotus, another burrowing nudibranch, which suggests that this simplification occurred twice among nudibranchs.

Phylogenetic relationships among nudibranchs. See Pseudovermis and Cumanotus at about 2 o’clock and Xenocratena at about 7 o’clock. Credits to Martynov et al. (2020).*

This is not an evidence that Xenoturbella is a simplified deuterostome, but it is a good argument. But what about the simplifications of Acoelomorpha? I think that if Xenoturbella was not closely related to Acoelomorpha I would be more willing to accept this hypothesis. My heart leans toward the hypothesis of basal Xenacoelomorpha, though. However, as any cientist should do, I will accept Xenacoelomorpha as deuterostomes if enough evidence is presented.

Xenoturbella is always the main problem in this equation, The nervous system of Acoelomorpha, for example, although simplified, has kind of the basic pattern found in all bilaterians and could have evolved from the oral ring in a cnidarian-like ancestor according to some hypotheses. In Xenoturbella, though, the nervous system is much weirder, being formed by a simple network of difuse neurons below their skin. I guess addressing the organization of the nervous system in all these groups is a good topic for another post.

If there is one thing, in my opinion, that makes the position of Xenacoelomorpha within Deuterostomia somewhat convincing is the fact that many features of Deuterostomia seem to be more primitive inside Bilateria when compared to those in Protostomia, so the position of Xenacoelomorpha among Deuterostomia is more plausible than their position among Protostomia(although this is not even considered possible anymore) for sure. We tend to think that deuterostomes are more “derived” simply because humans are deuterostomes. But this discussion is also a subject for another post.

What do you think? Are you team basal or team deuterostome?

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You may also like:

Hagfish: another phylogenetic headache

Xenoturbella: a growing group of weirdoes

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References:

Cannon JT, Vellutini BC, Smith J, Ronquist F, Jonfelius U, Hejnol A (2016) Xenacoelomorpha is the sister group to Nephrozoa. Nature 530: 89–93. doi: 10.1038/nature16520

Jondelius U, Raikova OI, Martinez P (2019) Xenacoelomorpha, a Key Group to Understand Bilaterian Evolution: Morphological and Molecular Perspectives. In: Pontarotti P (ed) Evolution, Origin of Life, Concepts and Methods. Cham: Springer International Publishing, . pp. 287–315. doi: 10.1007/978-3-030-30363-1_14

Martynov A, Lundin K, Picton B, Fletcher K, Malmberg K, Korshunova T (2020) Multiple paedomorphic lineages of soft-substrate burrowing invertebrates: parallels in the origin of Xenocratena and Xenoturbella. PLoS ONE 15(1): e0227173. doi: 10.1371/journal.pone.0227173

Philippe H, Poustka AJ, Chiodin M, et al. (2019) Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xenacoelomorpha and Ambulacraria. Current Biology 29(11):1818–1826. doi: 10.1016/j.cub.2019.04.009

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

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Filed under Evolution, mollusks, Systematics, worms, Zoology

Friday Fellow: Grasshopper Nematode

by Piter Kehoma Boll

About one and a half year ago, I presented the long and thread-like wood cricket’s worm, a parasite that can control the behavior of the wood cricket and leaves its body once becoming an adult. The wood cricket’s worm belongs to the phylum Nematomorpha, commonly known as horsehair worms. They are closely related to phylum Nematoda, the roundworms. And just like horsehair worms, roundworms also love to infect crickets and grasshoppers.

One of those species is Mermis nigrescens, known as the grasshopper nematode. This worm can be found all over the world where grasshoppers exist, although they seem to be more common in Eurasia and the Americas.

An adult, gravid female. Photo by wikimedia user Beentree.**

Adults of the grasshopper nematode live in the soil and are very large for a nematode. Males measure about 5 cm in length and females can reach 20 cm, which is much larger than most nematodes that infect insects. They are, therefore, very similar to horsehair worms in appearance and behavior. The body has a smooth surface and a pale brown color, with females having a red spot on their head, the chromatopore, which functions like an eye.

After adults mate in spring or summer, males usually die but females remain in the soil through fall and winter and emerge in the following spring after a rainfall. They show a black stripe running along the body that is caused by thousands of eggs inside. They climb the nearby vegetation, up to 3 m above the ground, and lay their eggs, which measure about 0.5 mm in length, on it.

A female climbing the vegetation. Photo by Wikimedia user Notafly.**

In order to be able to climb the vegetation, female grasshopper nematodes show positive phototaxis, i.e., they are attracted by light sources, which is the opposite of what happens with most nematodes that have eyes. In fact the female’s eye, the chromatopore, is a single structure, like a single eye, and seems to have evolved independently from other nematode eyes. Its red color is caused by a hemoglobin, like the one that makes our blood red, but in this case it seems to function as a light receptor.

A closeup of the female eye and a transverse section through it. Extracted from Burr et al. (2000).*

When the eggs are ingested by an orthopteran insect (usually a grasshopper but sometimes a katydid), they hatch almost immediately. The young worm pierces the grasshopper’s gut and enters its hemocoel, the “blood cavity” of the body.

An adult around its dead host, a katydid. Photo by Wikimedia user Beentree.**

There, the worm develops by absorbing nutrients from the insect’s blood directly through its cuticle. This leads to serious depletion in the insect’s levels of blood sugar, especially trehalose (the insect storage sugar) and body proteins. After reaching 5 cm or more in size, they leave the insect, killing it in the process, and continue their development in the soil until reaching the adult stage and starting the cycle all over again.

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References:

Burr AHJ, Babinzski CPF, Ward AJ (1990) Components of phototaxis of the nematode Mermis nigrescens. Journal of Comparative Physiology A 167: 245–255. doi: 10.1007/BF00188117

Burr AHJ, Hunt P, Wagar DR, Dewilde S, Blaxter ML, Vanfleteren JR, Moens L (2000) A Hemoglobin with an Optical Function. Journal of Biological Chemistry 275: 4810–4815. doi: 10.1074/jbc.275.7.4810

Burr AHJ, Schiefke R, Bollerup G (1975) Properties of a hemoglobin from the chromatrope of the nematode Mermis nigrescens. Biochimica et Biophysica Acta (BBA) – Protein Structure 405(2): 401–411. doi: 10.1016/0005-2795(75)90105-1

Gordon R, Webster JM (1971) Mermis nigrescens: Physiological relationship with its host, the adult desert locust Schistocerca gregaria. Experimental Parasitology 29(1): 66–79. doi: 10.1016/0014-4894(71)90012-9

Rutherford TA, Webster JM (1974) Transcuticular Uptake of Glucose by the Entomophilic Nematode, Mermis nigrescens. Journal of Parasitology 60(5): 804–808. doi: 10.2307/3278905

Rutherford TA, Webster JM (1978) Some effects of Mermis nigrescens on the hemolymph of Schistocerca gregaria. Canadian Journal of Zoology 56(2): 339–347. doi: 10.1139/z78-046

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A balanced diet may kill you sooner… if you are a land planarian

by Piter Kehoma Boll

There’s one thing that I should do more often here, and that is presenting my own research for the readers of the blog, so today I am going to do exactly that.

As you may know, the group of organisms with which I work is the family Geoplanidae, commonly known as land planarians. Here in Brazil, the most speciose genus is Obama, of which I have talked in previous posts. This genus became considerably famous after one of its species, Obama nungara, became invasive in Europe, which called attention of the public especially because of the curious name of this genus, even though it has nothing to do with the former president of the United States.

Anyway, during my Master’s study, it became clear that species in the genus Obama feed on soft-bodied invertebrates, mainly slugs and snails, although some species also feed on earthworms or even other land planarians. Obama nungara, for example, feeds on all three groups, although it seems to have some preference for earthworms.

A specimen of Obama anthropophila with its testicle freckles. Photo by myself, Piter K. Boll.*

One common species of Obama in urbans areas of southern Brazil is Obama anthropophila, whose name, meaning “lover of humans” is a reference to this habit precisely. This species has a uniformly dark brown dorsal color, sometimes mottled by the mature testicles appearing as darker spots on the first half of the body. The diet of this species includes snails, slugs, nemerteans and other land planarians, especially of the genus Luteostriata, and more especially of the species Luteostriata abundans, which occurs very often in urbans areas too.

Watch Obama anthropophila capture different prey species.

So I wondered… if O. anthropophila feeds on different types of invertebrates, does it mean that each type provides different nutritients, so that a mixed diet is necessary or more beneficial than one composed of a single prey type? To assess that, I divided adult specimens of O. anthropophila into three groups, each receving a different diet:

Group Dela: fed only with the common marsh slug, Deroceras laeve
Group Luab: fed only with the abundant yellow striped planarian, Luteostriata abundans
Group Mixed: fed with both prey species in an alternating way

The results were not what I expected. The Mixed group showed a lower survival rate than the groups receiving a single diet. Another interesting feature was that the Mixed group showed a tendency to skip the slug meal and eat only the planarian after some days receiving the alternating prey types.

Based on the hypothesis that a mixed diet is more nutritious, I was expecting the Mixed group to have the best performance, or at least being similar to the single-diet groups if there was no increase in nutritional value with an additional prey type. However, the results indicate that a mixed diet may be bad for the planarian, at least if the animal has to eat a different food on every meal.

We don’t know what causes this, but my idea is that maybe different prey types demand different metabolic processes, such as the production of different enzymes and stuff, and having to constantly reset your metabolism is too costly. As a result, the fitness of specimens receiving such a diet decreases and the animals start to avoid one of the food types, because eating less is less dangerous than mixing food.

A “pregnant” Obama anthropophila about to ley an egg capsule. Photo by myself, Piter K. Boll.*

Another interesting aspect is that planarians receiving a mixed diet, even though they died earlier, laid heavier egg capsules than the single-diet groups. Heavier egg capsules generally mean that they have more embryos or are more nutrient for the embryos, increasing the reproductive success. But how can a dying animal be better at reproducing than a healthy one?

Well, this may be related to the terminal investment hypothesis. It is thought, and proven in some groups, that an organism may increase its investment on reproduction when future reproductive events are not expected, i.e., when the organism “realizes” it is about to die, it puts all its effort to reproduce in order to garantee that its genes will pass successfully to future generations.

We cannot be sure about anything yet. More studies are necessary to better understand the relationship of land planarians and their food. What we can assure is that, just like Obama nungara, O. anthropophila may end up in Europe or anywhere else soon because its relatively broad diet and its proximity to humans make it a potential new species to be spread accidentally around the world.

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Reference:

Boll PK, Marques D, & Leal-Zanchet AM (2020) Mind the food: Survival, growth and fecundity of a Neotropical land planarian (Platyhelminthes, Geoplanidae) under different diets. Zoology 138: 125722.

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

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Filed under Ecology, Evolution, flatworms, worms

The land planarian community of FLONA-SFP and how it gets along

by Piter Kehoma Boll

(First of all, I wish it were Bolsonaro, that piece of diarrhea-shaped cancer, who were dying by fire instead of the Amazon forest.)

(Now let’s go to the post itself:)

The São Francisco de Paula National Forest (FLONA-SFP) is a protected area for sustainable use in southern Brazil. Its was originally covered by Araucaria forest but currently is composed of a mosaic of the native forest and plantations of Araucaria, Pinus and Eucalyptus trees. This protection area is one of the main study areas of Unisinos’ Planarian Research Institute, where I conducted my undergradate, Master’s and PhD studies.

After studying the land planarian community of FLONA-SFP for many years, we conclude that it includes a fairly large number of species. Take a look at some of them and how cool they are:

Obama ladislavii, the Ladislau’s leaf-like flatworm. Photo by Piter Kehoma Boll.*
Obama anthropophila, the brown urban leaf-like flatworm. Photo by Piter Keehoma Boll.*
Obama josefi, the Josef’s leaf-like flatworm. Photo by Piter Kehoma Boll.*
Obama ficki, the Fick’s leaf-like flatworm. Photo by Piter Kehoma Boll.*
Obama maculipunctata, the spotted-and-dotted leaf-like flatworm. Photo by Piter Kehoma Boll.*
Cratera ochra. The ochre crater flatworm. Photo by Piter Kehoma Boll.*
Luteostriata arturi, the Artur’s yellow striped flatworm. Credits to Instituto de Pesquisas de Planárias, Unisinos.**
Luteostriata ceciliae, the Cecilia’s yellow striped flatworm. Photo by Piter Kehoma Boll.*
Luteostriata pseudoceciliae. The false Cecilia’s yellow striped flatworm. Credits to Instituto de Pesquisas de Planárias, Unisinos.**
Luteostriata ernesti, the Ernst’s yellow striped flatworm. Photo by Piter Kehoma Boll.*
Luteostriata graffi, the Graff’s yellow striped flatworm. Photo by Piter Kehoma Boll.*
Supramontana irritata, the irritated yellowish flatworm. Photo by Piter Kehoma Boll.*
Pasipha backesi, the Backes’ shiny flatworm. Photo by Piter Kehoma Boll.*
Pasipha brevilineata, the short-lined shiny flatworm. Photo by Piter Kehoma Boll.*
Matuxia tymbyra, the buried Tupi flatworm. Photo by Piter Kehoma Boll.*
Choeradoplana iheringi, the Ihering’s swollen-throated flatworm. Photo by Piter Kehoma Boll.*
Choeradoplana benyiai, the Benya’s swollen-throated flatworm. Photo by Piter Kehoma Boll.*
Choeradoplana minima, the lesser swollen-throated flatworm. Photo by Piter Kehoma Boll.*
Cephaloflexa araucariana, the Araucaria’s bent-headed flatworm. Photo by Piter Kehoma Boll.*
Paraba franciscana, the Franscican colored flatworm. Photo by Piter Kehoma Boll.*
Paraba rubidolineata, the red-lined colored flatworm. Credits to Instituto de Pesquisas de Planárias, Unisinos.**
Imbira guaiana, the Kaingang bark-strip flatworm. Photo by Piter Kehoma Boll.*

Land planarians live in the leaf litter of forest soils and prey on other invertebrates. The 22 species shown above are the ones found in FLONA-SFP that are formally described but there are still some awaiting description. We could say that there are at least 30 different species coexisting in this protected area.

How can they all persist together? Isn’t there any sort of competition for food? Thinking of that, I conducted my master’s research investigating the diet of those and other land planarians. My results suggest that, although some species share many food items, most of them have a preferred food or an exclusive food item that could be considered what Reynoldson and Pierce (1979) called a “food refuge”.

Here is what we know about the FLONA-SFP’s species until now:

  • Obama ficki feeds on slugs and snails and seems to prefer large slugs;
  • Obama ladislavii feeds on slugs and snails and seems to prefer snails;
  • Obama maculipunctata feeds on slugs and snails with unknown preference;
  • Obama anthropophila feeds on slugs, snails and other land planarians, especially of the genus Luteostriata, and prefers the latter;
  • Obama josefi apparently feeds on other land planarians only;
  • All species of Luteostriata feed exclusively on woodlice;
  • Species of Choeradoplana apparently feed on woodlice and harvestmen;
  • Cephaloflexa araucariana apparently feeds on harvestmen;
Obama ladislavii capturing a slug. Photo by Piter Kehoma Boll.*

The diet of the remaining species is still completely unknown but, based on other species of the same genera, it is likely that species of Pasipha feed on millipedes, species of Paraba feed on slugs and planarians, and Imbira guaiana feeds on earthworms.

Luteostriata ernesti near some juicy woodlice. Photo by Piter Kehoma Boll.*

There are plenty of different invertebrate groups that share the leaf litter with land planarians. Despite the apparently simple anatomy of these flatworms, they were able to adapt to feed on different types of prey and have muscular and pharyngeal adaptations for that. And attempt to relate anatomical adaptations to the diet of land planarians was part of my PhD research. As soon as it is published, I’ll make a post about it. There are some nice results!

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More on land planarians:

Friday Fellow: Abundant Yellow Striped Flatworm

Friday Fellow: Ladislau’s Flatworm

Darwin’s Planaria elegans: Hidden, extinct or misidentified?

How are little flatworms colored? A Geoplana vaginuloides analysis

Obama invades Europe: “Yes, we can!

The fabulous taxonomic adventure of the genus Geoplana

The hammerhead Flatworms: Once a mess, now even messier

The New Guinea flatworm visits France: a menace

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References:

Boll PK & Leal-Zanchet AM 2015. Predation on invasive land gastropods by a Neotropical land planarian. J. Nat. Hist. 49: 983–994.

Boll PK & Leal-Zanchet AM 2016. Preference for different prey allows the coexistence of several land planarians in areas of the Atlantic Forest. Zoology 119: 162–168.

Leal-Zanchet AM & Carbayo F 2000. Fauna de Planárias Terrestres (Platyhelminthes, Tricladida, Terricola) da Floresta Nacional de São Francisco de Paula, RS, Brasil: uma análise preliminar. Acta Biologica Leopoldensia 22: 19–25.

Oliveira SM, Boll PK, Baptista V dos A, & Leal-Zanchet AM 2014. Effects of pine invasion on land planarian communities in an area covered by Araucaria moist forest. Zool. Stud. 53: 19.

Reynoldson TB & Piearce B 1979. Predation on snails by three species of triclad and its bearing on the distribution of Planaria torva in Britain. Journal of Zoology 189: 459–484.

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Loneliness made me female: more on the hermaphrodite’s dilemma

by Piter Kehoma Boll

Some time ago I wrote about the conflicts of hermaphrodite organisms while they have sex, i.e., how both could be the male and the female at the same time, but that is usually not of their interest, especially if playing the female role would force you to end up with low-quality sperm for your eggs.

Two banana slugs ready to copulate. Photo by Andy Goryachev.

But sex is usually much more complex and how it occurs is usually shaped by environmental conditions, especially by the presence of competitors. In dioecious species, males usually compete for the females but is there a similar behavior applied to hermaphrodites?

According to the sex allocation theory, hermaphrodite organisms have to choose how much they invest in the male versus the female function. If you produce more eggs, thus preferring the female side, you end up producing less sperm and vice versa. So what should hermaphrodites do?

Sometimes there is competition. Photo by Wikimedia user Miekemuis.*

One way to try to take the best of this situation is allocating resources to the female or the male role according to what will give you more advantages in the current scenario. This would be determined mainly by the number, or the density, of individuals in the population.

When there are a lot of individuals, there is a lot of sperm, and being able to fertilize the eggs becomes more difficult. Thus, hermaphrodites would increase their investment in the male function to have a better chance against the sperm of the others. In other words, it is better to be a male when there are too many guys around you.

On the other hand, when finding a mate is rare, there is little sperm competition, so focusing on being a female is more advantageous. After all, the little sperm you produce is enough to fertilize the eggs of the few other individuals around there.

Most studies looking for evidence of the sex allocation theory found conflicting results. In many organisms, only one of the sexual functions changes according to population density, with either the number of eggs or the amount of sperm remaining the same and sometimes both functions are enhanced at the same time, going against the idea of a trade-off that the sex allocation theory predicts.

The problem may be simply a matter of how to look at things. Most studies focused on gamete production only, but sex is much more than that. One important part that has been neglected is sexual behavior. In order to test whether behavioral investment may show sex allocation differences, a recent study compared the investment of the hermaphrodite polychaete worm Ophryotrocha diadema in a female-related and a male-related behavior. According to their hypothesis, a low density of organisms would increase parental care, a female-related behavior, while a high density of organisms would increase motility in order to find a mate, a male-related behavior.

Two individuals of Ophryotrocha diadema. The yellow marks on the upper one are eggs. Photo by Viriginie Boutias. Extracted from http://leec.univ-paris13.fr/new/animals_en.html

And their hypothesis proved to be correct! Worms kept in pairs, i.e., with few mating opportunities due to the low density of individuals, moved less but took more care of the eggs. On the other hand, worms kept in groups, i.e., with more mating opportunities, moved more and did not take so much care of their eggs.

More than being nice evidence for the sex allocation theory, this study highlights the need to look beyond gamete production to assess sex allocation not only in hermaphrodites but in all organisms.

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Reference:

Picchi L & Lorenzi MC 2019. Gender-related behaviors: evidence for a trade-off between sexual functions in a hermaphrodite. Behav Ecol. doi: 10.1093/beheco/arz014

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Friday Fellow: Common Peanut Worm

by Piter Kehoma Boll

Leia em português

Today our fellow is a peculiar marine animal that is also a common food in China and Vietnam. Named Sipunculus nudus, or the common peanut worm, it is a member of the clade Sipuncula, usually called peanut worms.

A dead specimen of Sipunculus nudus found on the Mediterranean coast of France. Photo by Benoit Nabholz.*

As other peanut worms, the common peanut worm has considerably simple anatomy. Its body is consistent of basically two parts, a sac-like trunk and a proboscis, also called the introvert. The introvert is a retractile structure and, when the animal is not feeding, is pulled inside the trunk by a group of muscles. At the end of the introvert, when everted, there is a series of tentacles that takes the food, composed of detritus, into the gut.

The common peanut worm is commonly found burrowed into the substrate in intertidal waters all around the world, with its mouth directed upward. They may reach about 20 cm in length when the introvert is everted, with about 1/4 of this length being composed by the trunk.

As mentioned above, the common peanut worm is used as a food in China, especially in southern regions, and Vietnam. Although the species seems easy to be raised in captivity, currently most, if not all, harvest happens in the wild, which may lead to overexploitation and eventually a serious decrease in the populations.

A bucket full of peanut worms for sale in China. Photo by Wikimedia user Vmenkov.**

Molecular analyses have revealed that, contrary to what is currently considered, Sipunculus nudus is not actually a cosmopolitan species. There are at least four clearly distinct lineages that certainly correspond to four distinct species. Of those, only one is found in waters around Europe, from which the species was originally described. The other three lineages correspond to those found in China and Vietnam (and the one used as food), the Atlantic Coast of the Americas (from Brazil to the USA) and the Pacific Coast of the Americas (around Panama). Let’s hope that soon this taxonomic problem will be solved.

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References:

Du, X., Chen, Z., Deng, Y., Wang, Q. (2009) Comparative analysis of genetic diversity and population structure of Sipunculus nudus as revealed by mitochondrial COI sequences. Biochemical Genetics 47: 884. doi: 10.1007/s10528-009-9291-x

Kawauchi, G. Y., Giribet, G. (2013) Sipunculus nudus Linnaeus, 1766 (Sipuncula): cosmopolitan or a group of pseudo-cryptic species? An integrated molecular and morphological approach. Marine Ecology 35(4): 478–491. doi: 10.1111/maec.12104

Trueman, E. R., & Foster-Smith, R. L. (2009). The mechanism of burrowing of Sipunculus nudus. Journal of Zoology, 179(3), 373–386. doi:10.1111/j.1469-7998.1976.tb02301.x

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Think of the worms, not only of the whales, or: how a planarian saved an ecosystem

by Piter Kehoma Boll

Leia em português

Due to the massive interference of human practices on natural habitats during the past decades, ecosystem restoration has become a trend in order to try to save what is still savable. Unfortunately, the effort of ecologists and other experts alone is not enough to achieve that, and a larger section of the society needs to be engaged in helping reach the goals. In order to do so, it is common to appeal to the beauty and cuteness of endangered species, which usually include mammals and birds, since they are more likely to caught the public’s attention. However, most of the endangered species are invertebrates or other less charismatic beings, and they are often ignored even by biologists.

Hopefully, things are able to change on this matter. Recently the first ecosystem restoration directed to save an invertebrate was successful, and I am here to tell you about it.

The invertebrate in question is a freshwater planarian named Dendrocoelum italicum. It was discovered in 1936 in a cave in northern Italy named Bus del Budrio. Inside the cave, there was a small freshwater pool, about 5 × 5 m or little more, caused by a waterfall from a small stream coming through a narrow elevated corridor. The species is apparently found only in this pool and nowhere else.

There are no available photos of Dendrocoelum italicum, but it should look similar to the widespread Dendrocoelum lacteum seen here, but D. italicum lacks the eyes. Photo by Eduard Solà.*

During the 1980’s, a pipe was installed to divert the water from the stream to a nearby farm. The waterfall ceased to exist and the pool dried up permanently. The planarian survived in a very narrow rivulet that formed inside the cave and some small isolated ponds resulting from water drips. This critical condition of the population was discovered in 2016 by a research group from the University of Milan. They informed the administrators of the cave about the situation and, together, the team started to raise awareness about the situation of the cave among the citizens that benefitted from the reservoir formed by the diverted water, which made the farmer responsible for diverting the water agree to remove the artificial structure.

Image of the inside of the cave. Photo by Livio Mola. Extracted from https://www.naturamediterraneo.com/forum/topic.asp?TOPIC_ID=57050

The removal happened on December 3, 2016 after all the planarians occurring in the rivulet were collected and stored in plastic tanks inside the cave. When the waterfall was restored, it quickly started to fill the old pool again and, one day later, the planarians were released into the pool.

The ecosystem was monitored during the following two years until January 2018. The number of planarians varied greatly during the survey, but was not significantly larger after the restoration from what it was before. However, there was a significant increase in the population of a bivalve species, Pisidium personatum, and a small increase in the population of a crustaceon of the genus Niphargus. Additionally, annelids of the family Haplotaxidae, that were absent in the cave, appeared after restoration. Thus, it is clear that the ecosystem benefited from the reappearance of the pool.

Thanks to the efforts of those researchers, Dendrocoelum italicum now has a better chance to avoid extinction. However, this is not an isolated case. There are many cave-dwelling planarian species all around the world living under similar conditions, usually restricted to a single small pool inside a single cave. Many of those occur, or occurred, as D. italicum, in Italy, but the help came to late for some of them. For example, a closely related species, Dendrocoelum beauchampi, was discovered in 1950 in a cave in northwestern Italy named Grotta di Cavassola, but a recent survey found no planarians inside the cave, which seems to have suffered great alteration due to human activities. Similarly, the species Dendrocoelum benazzi was discovered in 1971 in central Italy in a cave named Grotta di Stiffe, but nowadays, with the cave open to turists and its water polluted, the planarians disappeared. It is very likely that both D. beauchampi and D. benazzi are now extinct. The situation is the same for other Italian species.

Out of Italy, a recently described species living a similar small environment is the Brazilian cave planarian Girardia multidiverticulata, which is known to occur in a small pool about 10 m² inside a cave named Buraco do Bicho in the Cerrado Biome.

Girardia multidiverticulata is a planarian species restricted a small 10 m² pool inside a cave in Brazilian cerrado. Credits to Souza et al. (2015)**

The case of Dendrocoelum italicum shows us it is possible to save small endemic populations of threatened habitats, but we need the help of the public. Let’s hope other ecosystems have a similar happy ending.

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References:

Manenti R, Barzaghi B, Lana E, Stocchino GA, Manconi R, & Lunghi E 2018. The stenoendemic cave-dwelling planarians (Platyhelminthes, Tricladida) of the Italian Alps and Apennines: conservation issues. Journal for Nature Conservation.

Manenti R, Barzaghi B, Tonni G, Ficetola GF, & Melotto A 2018. Even worms matter: cave habitat restoration for a planarian species increased environmental suitability but not abundance. Oryx: 1–6.

Souza ST, Morais ALN, Cordeiro LM, & Leal-Zanchet AM 2015. The first troglobitic species of freshwater flatworm of the suborder Continenticola (Platyhelminthes) from South America. Zookeys 470: 1–16.

Vialli PM 1937. Una nuova specie di Dendrocoelum delle Grotte Bresciane. Bollettino di zoologia 8: 179–187.

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Friday Fellow: Rowell’s Velvet Worm

by Piter Kehoma Boll

Velvet worms form an intriguing group of animals that are the sister group of arthropods and also the only animal phylum with only terrestrial species, although aquatic species are known from fossil records.

Today I decided to bring one velvet worm species to be our fellow. Scientifically known as Euperipatoides rowelli, I decided to give it the common name Rowell’s velvet worm.

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A specimen of the Rowell’s velvet worm in the lab. Photo by Alan Couch.*

The Rowell’s velvet worm is found in south-east Australia inhabiting humid, temperate forests. They are small animals, with about 5 cm in lenght, and live in decaying wood, dwelling in crevices and feeding on small invertebrates, such as termites and crickets.

Logs are usually inhabited by groups of several individuals that live in a sort of social relationship and are composed of females, males and juveniles, with females being larger and occurring in larger numbers than males. A sort of hierarchical organization also seems to occur, with one female being dominant and followed in dominance by other females, with males and juveniles occupying the bottom of the pyramid. Prey capture often happens in group, and after a prey is subdued, the dominant female will eat first and only after being satiated she will allow other females to eat. Males and juveniles eat the remains left by the females.

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Welcome to our log! Photo by Andras Keszei.**

New logs are colonized by wandering males. Those release feromones that attract more males and later females. Thus, newly colonized logs have a male-biased aggregation, but the number of females later surpasses that of males. It has been suggested that the initial aggregation of males helps them to attract females due to the increased concentration of feromones.

During reproduction, the male places spermatophores on the skin of the female, With the aid of the female blood cells, the body wall below the spermatophore is breeched and the sperm is released in the female’s body cavity, where it swims to the female reproductive tract.

Due to its abundance in south-east Australia, the Rowell’s velvet worm is an easily obtained species and is slowly becoming one more interesting model organism.

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References:

Barclay S, Ash JE, Rowell DM (2000) Environmental factors influencing the presence and abundance of a log-dwelling invertebrate, Euperipatoides rowelli (Onychophora: Peripatopsidae)Journal of Zoology 250: 425–436.

Barclay S, Rowell DM, Ash Je (2000) Pheromonally mediated colonization patterns in the velvet worm Euperipatoides rowelli (Onychophora)Journal of Zoology 250: 437–446.

Reinhardt J, Rowell DM (2006) Social behavior in an Australian velvet worm, Euperipatoides rowelli (Onychophora: Peripatopsidae)Journal of Zoology 250: 1–7.

Sunnucks P, Curach NC, Young A, French J, Cameron R, Briscoe DA, Tait NN (2000) Reproductive biology of the onychophoran Euperipatoides rowelliJournal of Zoology 250: 447–460.

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