Friday, 22 January 2016

Eccentricity and Natural History

On 16th January, The Independent carried an article by Jeremy Parrott about the various people who contributed to All The Year Round, a weekly magazine owned, and edited, by Charles Dickens [1]. Much was made in the article of Frank Buckland, whom Parrott describes as "an epitome of British eccentricity" for keeping a wide variety of animals in his home and for the habit, infused by his eminent father (William Buckland, Dean of Westminster from 1845 to 1856), of eating many kinds of animals, both for pleasure and as a means of investigating whether they should be farmed [2].

Buckland is often mentioned alongside Charles Waterton, another eccentric Natural Historian; Waterton as much for his ascetic way of life, climbing habits, and attitudes to medicine, as for his love of animals. There was an exception to his affection – the brown rat. As a Roman Catholic Squire, he was strongly anti-Hanoverian and believed that brown rats were brought to Britain on ships conveying the future George I, making them proxy hate obects. It didn't help that his home, Walton Hall, was infested with the rodents. Waterton also gained notoriety for riding on the back of a cayman during one of his visits to South America, despite this being the best way to subdue the animal for the neat kill required for the preservation of an undamaged skin. Waterton was an accomplished taxidermist and also composed groups of animal skins in cabinets to convey satirical messages [3].

Waterton is given a whole chapter to himself in Edith Sitwell's The English Eccentrics [4] and he is included, together with Frank Buckland, in William Donaldson's more eclectic Brewer's Rogues, Villains and Eccentrics [5], subtitled An A-Z of Roguish Britons Through the Ages. It is difficult to avoid the conclusion that eccentricity is a characteristic of English, or British, society, but I'm sure that is not the case and eccentrics are found everywhere. However, it seems that English cultural norms are especially suited to eccentricity and Edith Sitwell celebrated this in The English Eccentrics [4]. In it she writes:

The man of genius and the aristocrat are frequently regarded as eccentric by the ordinary because both genius and aristocrat are entirely uninfluenced by the opinions and vagaries of the crowd.

I doubt whether either Frank Buckland or Charles Waterton would have regarded themselves as being eccentric and they were protected from constraints that most face because of their privileged upbringing and way of life. However, the ordinary (to use Sitwell's term) often think of eccentrics in a negative light and that is reflected in Donaldson's book, where they are quite undeservedely grouped with rogues and villains. That seems harsh.

It is tempting to ask whether eccentrics provide a valuable function in addition to being figures of fun (as they are commonly regarded in private). I think they do and I'll draw an analogy. In science, we commonly investigate the relationship of two variables; for example, weight against length in a group of insects. Mostly, points fall close to a line but occasional ones do not and we call these outliers; one individual may be noticeably heavier than others of the same length, for example. The initial reaction of students to outliers is that they represent an error in measurement and this may indeed be the explanation. However, some outliers are real and, after careful checking, remain outside the trend. Students find this annoying as it can affect the significance of the relationship they are trying to establish. In our example this would be that weight increases in a linear fashion with increase in length and an outlier individual may be unusually heavy because it has a thicker body covering for some reason.

Just as outliers in science are interesting, so eccentrics are similarly interesting as they show ways and attitudes that are different from the accepted norm of the time. There may be one eccentricity or, in individuals like Frank Buckland and Charles Waterton, a suite of them.

Most of us prefer to conform to conventions because they allow us to feel comfortable and have a sense of belonging. Indeed, the need to conform can bring pressures to "keep up with the Joneses" as it has been termed, even though we may feel that doing so is rather silly. There is always the pressure to conform, but the eccentric has no worries on that score as they need only their own personal view and the freedom to pursue whatever they wish. We sometimes look on eccentrics with suspicion, as they challenge our view of what is "normal", but this is a narrow way of thinking. Just as I was always interested in outliers when working in science, so I am fascinated by eccentrics and what they have to say. I always enjoy reading about Buckland and Waterton and wonder who their contemporary equivalents may be.

Having general agreement about ways to proceed do not necessarily mean that those ways are the best, so we should embrace eccentrics and challenge conventions. The conventions that are valuable will persist, but others will be seen only as trends. That applies to the study of animals that so consumed Buckland and Waterton, but it applies generally too.

[4] Edith Sitwell (1933) English Eccentrics. London, Faber and Faber.

[5] William Donaldson (2002) Brewer's Rogues, Villains and Eccentrics: An A-Z of Roguish Britons Through the Ages. London, Cassell.

Thursday, 14 January 2016

The amazing three-toed sloth

There are two common types of sloth – the three-toed (below) and the two-toed – living in Central and South American forests. Three-toed sloths do not move around as widely as their distant relatives [1] and they usually have a greenish colouration. This was described by Charles Waterton in his pioneering observations of sloths in their natural environment made at the beginning of the Nineteenth Century [2]:

I observed, when he was climbing, he never used his arms both together, but first one and then the other, and so on alternately.. ..His fur has so much the hue of the moss which grows on the branches of the trees, that it is very difficult to make him out when he is at rest.

If Waterton had a microscope, he would have observed that the green colouration resulted from algae growing over the surface of the hairs making up the coat; hairs of the three-toed sloth having [3]:

..irregular transverse cracks that increase in number and size with age. A wide variety of organisms have been reported to occur in the grooves and cracks of sloth hair.. ..the greenish color of the hair.. due to green algae, which in most cases have been identified as Trichophilus welckeri.. ..The hair of the three-toed sloth absorbs water like a sponge, perhaps making it an even more ideal habitat for algae, and prompting speculations that the sloth perhaps receives nutrients from the alga via diffusion along the spongy outer portion of the hairs, followed by absorption into the skin. The algae growing on sloth hair may also produce exopolymeric substances that may give the hair a desired texture or allow beneficial bacteria to grow.

This is speculation, but we know that exopolymers are ubiquitous and have many important roles to play, both for the organisms that exude them and in the wider environment [4]. It is likely that they are a significant part of the sloth fur ecosystem.

Algae are not found abundantly in the fur of very young sloths and they are probably acquired during close contact with the mother [3]. It has been suggested that the relationship of Trichophilus welckeri with the sloth is mutualisitic [3]; the alga gaining nutrients that are released by the microbial community on the hairs and also befitting from being carried up into the canopy where light is more available for photosynthesis. The sloth grazes this good quality food resource (it is rich in lipids [1]) during grooming and it also benefits from the green colouration that the algae convey to the fur, acting, as Waterton pointed out, as a form of camouflage.

Renowned as slow movers, sloths have a very low metabolic rate that enables them to survive on a poor-quality diet, but considerable energy is expended in climbing down to the ground to defecate and in climbing back up to the canopy, with the sloth made heavier by the water retained in the fur. Three-toed sloths defecate on the ground in scrapes that they prepare with their hind claws, while clinging to vines or other trailing vegetation with their fore limbs. The mass of faecal pellets is then covered with leaves and the sloths begin their steady climb back to the canopy [5]. The sloths are vulnerable when on, or close to, the ground and the greatest mortality of sloths occurs during this activity. As the diet is poor and the rate of metabolism low, visits to defecate are approximately weekly, but why has the three-toed sloth evolved this habit, when two-toed sloths defecate from the canopy? The advantage to the sloth may be that egesta provide a fertiliser for their preferred trees (each three-toed sloth not moving far from a few favoured trees); the possibility of using the latrine as a form of marking or communication; and the opposite effect of hiding odours from predators that may hunt from the ground and be more mobile than the sloths [1].

So far we have seen an association between algae, micro-organisms and sloths, but the fur also harbours several types of invertebrates, one of which is found only on sloths and has a remarkable life cycle adapted to the behaviour of its host. This is the moth Cryptoses cholopei (above). Gravid females collected from sloths laid their eggs on any solid surface but the larvae that hatched did not feed on sloth hair, or on leaves, but only on sloth dung [5]. During sloth defecation, female moths descend to the faecal mass to lay their eggs and larvae emerge to feed exclusively on the faecal pellets. They do so within silk tubes [5] that bind pellets and which also form a cocoon for pupation. Adult moths then emerge to fly up into the canopy and locate a three-toed sloth and complete the life-cycle. Cryptoses gains from the relationship through:

(i) the enhancement of oviposition-site location (that is, being carried by the sloth to the next fresh dung pile), (ii) the use of the sloth as a refuge from avian predators, and, perhaps, (iii) the enhancement of its diet with secretions of the host or associated algae [5].

The second explanation may not be completely true, as jays have been seen feeding on the fur of sloths [6], but there are a wide variety of other invertebrate colonists that may provide food for the birds. Indeed, the ecosystem within the fur of the three-toed sloth is a complex one, consisting of algae, micro-organisms and protozoans, a wide range of invertebrates and the exudates of the sloth and of all the other members of the community. Among the micro-organisms are fungi that digest detritus, including dead moths, and which, in turn, release nitrogen-rich nutrients that can be utilised in growth by bacteria and algae. The fungal community is diverse [7] and some of the fungi living in sloth fur produce antibiotics that may affect the rest of the community living there. As Higginbotham and colleagues write [7]:

The high abundance and diversity of fungi associated with sloth hair, coupled with their bioactivity, may speak to a biological importance to sloths that is yet unexplored.

As if watching sloths is not wonderful enough, their exobiology presents an extraordinary story. How fascinated Charles Waterton would have been if the sloth fur ecosystem had been known to him. Isn't Natural History amazing? Just think of how much more we have yet to learn about the world around us.

[1] Jonathan N. Pauli, Jorge E. Mendoza, Shawn A. Steffan, Cayelan C. Carey, Paul J. Weimer and M. Zachariah Peery (2014) A syndrome of mutualism reinforces the lifestyle of a sloth. Proceedings of the Royal Society B 281: 20133006.

[2] Charles Waterton (1825) Wanderings in South America, the North-west of the United States, and the Antilles, in the years 1812, 1816, 1820, and 1824. London, J. Mawman.

[3] Milla Suutari, Markus Majaneva, David P. Fewer, Bryson Voirin, Annette Aiello, Thomas Friedl, Adriano G. Chiarello and Jaanika Blomster (2010) Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with Trichophilus welckeri (Chlorophyta, Ulvophyceae). Evolutionary Biology 10:86

[4] Roger S. Wotton (2005) The essential role of exopolymers (EPS) in aquatic systems. Oceanography and Marine Biology: An Annual Review 42:57-94.

[5] Jeffrey J. Waage and G. Gene Montgomery (1976) Cryptoses cholopei: a coprophagous moth that lives on a sloth. Science 193:157-158.

[6] Kelsey D. Neam (2015) The odd couple: interactions between a sloth and a brown jay. Frontiers in Ecology and the Environment 13:170-171.

[7] Sarah Higginbotham, Weng Ruh Wong, Roger G. Linington, Carmenza Spadafora, Liliana Iturrado and A. Elizabeth Arnold (2014) Sloth hair as a novel source of fungi with potent anti-parasitic, anti-cancer and anti-bacterial bioactivity. PLOS ONE 9:e84549.

Thursday, 7 January 2016

Two paintings – two aspects of Nature

The Hay Wain is John Constable's best-known painting and most of us are familiar with Snow Storm: Steam-Boat off a Harbour's Mouth [short title Snow Storm] by J.M.W.Turner. The pictures create quite different emotional responses in the viewer and we can easily imagine how the scenes might change with time. Looking at each of the paintings in more detail:

The Hay Wain (above)

A cart (wain) has been driven into a shallow river, perhaps for the horses to drink. A spaniel tries to attract the attention of the farm workers and, while there are dark clouds, there is only a chance of rain. The atmosphere is benign and many would take it to be their idea of a natural rural idyll, yet much of what we see is anthropogenic. Apart from the cart, there is a building, a separate artificial channel for the river, a boat, domesticated animals, and a field used for growing hay.

The field is part of the floodplain of the river and it is easy to see that flooding could still occur (it might even be encouraged to enhance the growth of grasses). The river would not be wadeable at that time and, indeed, it would be dangerous to enter the water. Imagine the same scene in February, on a day when strong easterly winds are blowing and the temperature is near freezing. The atmosphere would be very different to the comfortable one that Constable projects in his painting.

Snow Storm: Steam-Boat off a Harbour's Mouth (above)

There is no comfort here and the roughness of the sea, together with the white-out conditions of the blizzard, are a potential danger to life. There is only one anthropogenic subject – the paddle steamer angled in the rough sea – and the swirling smoke from the stack, together with the bend in the mast, highlight the power of Nature as a destructive force. Added to that, we know from the long title of the painting that the steamer was trying to enter harbour and safety.

Now imagine the same scene on a different day, perhaps a similar one to that of The Hay Wain. There would then be little threat and the deck would be a pleasant place to sit and look out over the calm sea and the passing coast.

The two paintings certainly represent two aspects of Nature: the one warm, comforting and familiar; the other frightening and isolating. Most would agree that these paintings are easily recognisable as being by Constable and Turner, respectively, although Turner, produced a huge, and varied, collection of landscape art. The Hay Wain dates from 1821, when Constable was 45 years old, and Snow Storm from 1842, when Turner was 67 years old. The two artists have been discussed widely and, recently, I read an essay by Ronald Rees that appeared in The Geographical Review of 1982 [1]. Rees makes the following comments:

Constable decided to paint only landscapes that he knew and to rely as much as possible on direct observation.. ..Place was not important to Turner.. ..As a painter he needed not familiar places but locations where he could observe the interplay of his favorite phenomena: water, mist, and sunlight.. .. Occupied with essences rather than appearances and universals, not particulars, Turner presented nature as a system of mysterious and often threatening cosmic energies. Constable's view of nature was more optimistic and more comprehensible that Turner's.. .. Its manifestations were a genuine love of nature and a consciousness that human beings are diminished if they weaken the binding connection to the world of real and natural things.

The warmth of a summer day in a water meadow provides a quite different feeling to being out on a rough sea in a howling winter gale, yet both make us realise that being in Nature is a positive experience, albeit with occasional discomfort. Respect for the power of natural forces on the one hand (as seen in Snow Storm) counteracts the sense of our being able to control Nature (as in the many anthropogenic references in The Hay Wain). Turner and Constable were thus interested in the extremes that we find in the "world of real and natural things", although we can add that the threatening powers of Nature that we see today are nothing compared to those that have occurred in earlier geological time periods. Although we have a good understanding of natural forces, our ability to control Nature is not a given and that applies to both non-living, and living, threats. They are always going to challenge us and days like those shown in The Hay Wain are never going to be part of a constant idyll, just as rough seas will be followed by calm.

[1] Ronald Rees (1982) Constable, Turner, and views of Nature in the Nineteenth Century. The Geographical Review 72: 253-269.