Monthly Archives: April 2018

Friday Fellow: Pear Rust

by Piter Kehoma Boll

Beautiful and deadly, today’s fellow appears during spring as gelatinous orange projections coming out of juniper trees in Europe and North America. Its name is Gymnosporangium sabinae, commonly known as the pear rust.


The jelly-like horns of the pear rust on a juniper tree. Photo by Mark Sadowski.*

The pear rust is a basidiomycete, i.e., a fungus of the phylum Basidiomycota, therefore related to the common mushrooms, but belonging to a different class, the Puccioniomycetes.

During winter, the pear rust remains in a resting state inside branches and twigs of juniper trees. After wet days in spring, the fungus sprouts and appears as horn-like growths covered by an orange gelatinous mass, which are called telia. The telia produce wind borne spores called teliospores that can infect pear trees.


The pear rust on pear leaves. Photo by Jan Homann.

Once reaching the pear tree, the teliospores germinate and infect the leaves of the new host. The infection appears in summer as rust-colored spots on the leaves, hence the name pear rust. In heavily infected plants, the effects of the pear rust can be severe, sometimes causing the plant to lose all its leaves.

In pear trees, the fungus produce reproductive structures known as aecia. They come out from the underside of pear leaves and produce spores called aeciospores, which are able to infect new juniper trees.


The aecia coming out of the rust on a pear tree. Photo by H. Krisp.**

Due to the economic importance of pear trees to humans, the pear rust is a species of great concern. Some countries have policies intended to reduce the spread of the disease, such as preventing transportation of juniper trees from areas known to have the fungus to areas in which it is unknow. In areas where the fungus exist, the solutions to reduce the damage include the use of chemical fungicides, the removal of infected branches in juniper trees and sometimes the removal of any juniper tree around the areas where pear trees are cultivated.

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Fraiture, A.; Vanderweyen, A. (2011) Gymnosporangium sabinae: such a beautifiul disease. Scripta Botanica Belgica 11: 193–194.

Ormrod, D. J.; O’Reilly, H. J.; van der Kamp, B. J,; Borno, C. (1984) Epidemiology, cultivar susceptibility, and chemical control of Gymnosporangium fuscum in British Columbia. Canadian Journal of Plant Pahology6: 63–70.

Wikipedia. Gymnosporangium sabinae. Available at < >. Access on April 27, 2018.

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Whose Wednesday: Joseph Maiden

by Piter Kehoma Boll

Today we celebrate 159 years since the botanist Joseph Maiden was born.

Joseph Henry Maiden was born on April 25, 1859 in London, being the son of Henry Maiden, a china dealer and later accountant, and Mary Elizabeth Maiden (née Wells). In school, he excelled in sciences, later starting to study them in the University of London. However, due to its ill health, he was unable to complete the course.

As part of the treatment of his condition, he was advised to take a long sea voyage, so in 1880 he sailed to New South Wales, Australia, establishing in Sydney, where he at first was invited to deliver a course of lectures by the Working Men’s College. In 1881, Archibald Liversidge (1846–1927), a friend of his chemistry professor, offered him a post of curator at the new Technological Museum in Sydney.

Although intending to return to London within a year, Maiden accepted the job and ended up enjoying it more than he thought he would. This led him to stay longer, and longer, and he started to dedicate himself to the study of the local flora. Unfortunately, in 1882, the Garden Palace, which housed his botanical collection, was destroyed by fire. He, however, started it again with his small staff.

In November 30, 1883, Maiden married Eliza Jane Hammond in Melbourne, which reduced even more his chances of ever going back to England. In 1885, he began to study at the University of Sydney but started to have health issues once more…

Maiden’s interest in Australian flora quickly made him an expert in economic botany. He encouraged the study of the properties of Australian timbers and essential oils. In 1889, he published The Useful Native Plants of Australia. In 1890, he was appointed consulting botanist to the Department of Agriculture and in 1894 became Superintendent of Technical Education.

In 1896, Maiden became Government Botanist and Director of the Botanic Gardens. In this new position, he quickly led to the establishment of Australia’s first herbarium, as well as a museum, a library and a playground.


Joseph Henry Maiden, circa 1900

Maiden became an expert in the genera Acacia and Eucalyptus and his work A Critical Revision of the Genus Eucalyptus, in 8 volumes, remained a major reference for more than half a century. He was also worried about the environment, promoting the preservation of large areas of native forests, and published important works on the use of plants to establish soils and mitigate floods.

In 1924, Maiden retired and moved to Turramurra. He died on November 16, 1925, aged 66, of a heart disease, leaving his wife and four daughters. His only son was lost at sea many years earlier.

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Mark Lyons and C. J. Pettigrew, ‘Maiden, Joseph Henry (1859–1925)’, Australian Dictionary of Biography, National Centre of Biography, Australian National University,, published first in hardcopy 1986, accessed online 25 April 2018.

Wikipedia. Joseph Maiden. Available at < >. Access on 25 April 2018.

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Friday Fellow: C. elegans

by Piter Kehoma Boll

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

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

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

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

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

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

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

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References and further reading:

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

Klass, M. R. (1977) Aging in the nematode Caenorhabditis elegans: Major biological and environmental factors influencing life span. Mechanisms of Ageing and Development 6: 413–429.

Peden, E.; Killian, D. J.; Xue, D. (2008) Cell death specification in C. elegans. Cell Cycle 7(16): 2479–2484.

Wikipedia. Carnorhabditis elegans. Available at < >. Access on April 16, 2018.

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Whose Wednesay: Eduard von Martens

by Piter Kehoma Boll

Today is the 187th birthday of the German zoologist Carl Eduard von Martens.

Born in Stuttgard on April 18, 1831, von Martens had three older sisters. His father was a councillor in the Würtemburg Civil Service, but is better known as an explorer of the Fauna and Flora of southern Germany. As both his father and his sisters showed great interest in the natural world, von Martens followed their paths and since an early age he became interested in collecting and studying shells. In school, he was always an astonishing student and showed little interest in playing with the other boys, preferring to dedicate his time to his passion for shells.

Later, he went to Tübingen and studied medicine at the local university. Under the tuition of Hugo von Mohl (1805–1872) and Friedrich August von Quenstedt (1809–1889), von Martens expanded his studies on natural history and became particularly interested in the structure and distribution of animals in space and time. After graduating in 1855, he moved to Berlin, attracted by the fame of Johannes Peter Müller (1801–1858). After returning from a vacation tour to Norway with Müller, von Martens obtained an appointment at the Berlin Zoological Museum (currently the Natural History Museum, Berlin), which at the time was under the direction of Hinrich Lichtenstein (1780–1857). From 1859 on, von Martens was attached to this institution, being assigned to the division of invertebrates (excluding insects). Under his care, the collection of mollusks grew hugely, becoming one of the largest in the world up to the present.

In 1860, von Martens embarked on the Thetis expedition of the Prussian government to Eastern Asia, remaining with the expedition until 1862. When the ship returned to Europe, he remained for two additional years in Asia and studied intesively the local Fauna, especially the mollusks of the Sunda and Moluccas Islands.

Carl Eduard von Martens, around 1901.

During his career, von Martens described almost 1800 animal species, of which 1680 were mollusks, becoming one of the most influential names in malacology.

He died on August 14, 1904, aged 73, leaving a wife and a daughter, as well as an immeasurable contribution to biology.

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Wikipedia. Eduard von Martens. Availablat at < >. Access on 17 April 2018.

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Friday Fellow: Pellucid Four-Tooth Moss

by Piter Kehoma Boll

It’s time to go back to the tiny ones, the mosses. The third species of this group to be featured here is called Tetraphis pellucida or the pellucid four-tooth moss. Found in the northern hemisphere, this species is common in deciduous forests and grows almost exclusively on decaying wood of coniferous trees.


The general appearance of the pellucid four-tooth moss on a decaying log. Photo by Hermann Schachner.*

The pellucid four-tooth moss can have two different modes of reproduction: sexual and asexual. The sexual reproduction occurs in a way similar to that found in most mosses. The asexual one, however, is somewhat peculiar and happens through the production of propagules called gammae. Gemmae can occur along a stalk, being called stalk gemmae, or inside a cup formed by three to five large leaves, a structure called gemmae cup. Gemmae from both stalks and cups are propelled by the power of raindrops. What is interesting is that the type of gemmae structure seems to be related to the inclination of the surface in which the moss grows. From a horizontal surface to one with an inclination of about 18°, cups are more common, possibly because a water drops falling inside a cup propels the gemmae with great speed upward. On surfaces with inclinations above 18°, stalks are more common, as a cup lying on its side wouldn’t be very useful, and water can wash down gemmae from stalks more easily.


A closer look showing several gemmae cups. Photo by Hermann Schachner.

Regarding dispersal, spores from sexual reproduction seem to be able to move farther away from the mother, but they are not as successful in germinating and occupying a new substract as gemmae. Thus, the different reproduction modes seem to help this amazing little moss to spread by adapting to the most adequate means.

However, when other moss species arrive at the substrate, the pellucid four-tooth moss is rapidly replaced. It has, therefore, a very low success when competing with other species. How can it be one of the most common species in its habitat then? Well, it is so because the specialized propagules of the pellucid four-tooth moth allow it to quickly colonize newly-formed substrates, which arise from the common disturbances on the forest floor. No other species can colonize that quickly, but as they can easily dislodge our fellow, there is an endless struggle to survive. The pellucid four-tooth moss relies on disturbance to go on.

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Kimmerer, R. W. (1991) Reproductive ecology of Tetraphis pellucida. I. Population density and reproductive mode. The Bryologist 94(3): 255-260.

Kimmerer, R. W. (1991) Reproductive ecology of Tetraphis pellucida. II. Differential Success of Sexual and Asexual Propagules. The Bryologist 94(3): 284–288.

Kimmerer, R. W. (1993) Disturbance and dominance in Tetraphis pellucida: a model of disturbance frequency and reproductive mode. The Bryologist 96(1): 73-79.

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Whose Wednesday: Graziela Maciel Barroso

by Piter Kehoma Boll

The scientist whose birthday we celebrate today is a bit out of the standard from the previous weeks. Moving away from Europe and from the male gender, today I bring you the Brazilian botanist Graziela Maciel Barroso, who will be turning 106 if she was still alive. She is usually called the First Lady of Brazil’s Botany.

Born in Corumbá, Brazil, in 1912, Graziela Maciel was raised to be a housewife, as it was expected at that time. When she was only 16, she married the agronomist Liberato Joaquim Barroso and, due to her husband’s work, she lived in several places throughout the country.

In 1940, when she was 28, the couple became established in Rio de Janeiro. Two years later, when she was 30 and her children had already grown up, her husband asked her if she wanted to continue studying and, as she accepted, he started to teach her botany at home. In the same year she started to work in the Botanical Garden of Rio de Janeiro as an intern. In 1946, she passed an examination to start working as a botanist in the institution along her husband. When he died three years later, she continued his work, receiving new students and interns from many places in the country and teaching them botany.

Only much later, in 1959, aged 47, Graziela entered the University of the State of Guanabara (currently University of the State of Rio de Janeiro) to study biology. About 14 years later, in 1973, aged 60, she received her doctorate degree from the State University of Campinas.


Graziela Barroso in her late years. Credits to Rio de Janeiro Botanical Garden.

During her career, Graziela teached hundreds of students, becoming an important influence for many of the current Brazilian botanists. She published several works on plant systematics, having dedicated most of her time to the study of the family Asteraceae (Compositae) and later giving some attention to the family Myrtaceae, because she considered it to be an important but neglected group.

She died on May 5, 2003, aged 91. Several plant species were named after her, including the genus Grazielodendron, which includes the single species Grazielodendron riodocensis.

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Friday Fellow: Réaumur’s Desert Woodlouse

by Piter Kehoma Boll

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


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

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

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


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

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

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

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

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

Wikipedia. Hemilepistus reaumuri. Available at < >. Access on March 25, 2018.

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