Why living in the tropics is Awesome?

Living in the tropics, surrounded by jungle-covered hills, corals, picture-perfect beaches and cocktails sounds like a dream. Imagine listening the gentle music of the waves, bird songs, or the characteristic ‘zzzzzzzzzz’ of mosquitoes while enjoying a cup of coffee at the sun set. Walk along the beach, go for a swim to cool off from the sun’s warmth and do some snorkeling. This is paradise.

This is a dream that comes true for testate amoebae.

Travelling through tropical countries is such an experience that most people dream of returning; the same holds true for testate amoebae. Visiting tropics is one thing but by actually accumulating down some shells, testate amoebae gained a much better perspective on just how awesome the warmer part of the world is compared to the cold and dark side of the world. With the sun, sand and sea at your pseudostome-door and a relaxed way of life, the tropics has it all.

Tropics are so diverse that testate amoebae can enjoy various and nice places to live in. Sphagnum mosses in the Galapagos is an obvious spot to enjoy the tropics (Fournier et al. 2015), but why always live in a moss while you can experience other habitats? Living in the tropics also means sometimes living differently from what you already know. In such purpose, the jungle seems appropriate! The jungle is a great place to go hiking and trekking, and incidentally see how diverse and valuable these ecosystems are. Plus, it’s usually the best place to spot new habitats, particularly if you are an amoebae. Pseudopoding through the dense and muddy vegetation gives a sense of true exploration, you never know what you’ll find. That’s what happened to testate amoebae when they ended up in tank-bromeliads as they wanted to cool off after a hike through the humid jungle.

Bromeliads include mainly epiphytic rosette plants occurring mostly in Central and South America. They collect rain water and particulate materials in tanks (cisterns) formed by the coalescing leaf axils. These tanks form micro-ecosystems above the ground where groups of freshwater organisms ranging from algae, fungi, bacteria and protozoa through insects to frogs are represented and constitute considerable populations (Frank 1983, Laessle 1961, Maguire 1971, Picado 1913, Richardson 1999). Of special interest to us, these tanks are inhabited by many characteristic protists and small metazoans (Picado 1913; Maguire 1971; Martinelli 2000; Schönborn 2003). The only way for Nebela tincta, a widely distributed species, to meet Polyplaca globosa (Figure 1), P. monocornica and P. invaginata is to visit a Brazilian tank-bromeliad (Torres-Stolzenberg 2000).

 

Figure 1: Polyplaca globosa; an endemic testate amoebae from tank-bromeliads (Picture from Torres and Schwarzbold, 2000)

 

The vibe is unbelievable in the tropics! The common view is that no one seems to be in a hurry for anything. Such a cliché is obviously false; this includes testate amoebae in tank-bromeliads. Life in tank-bromeliads is not so quiet but rather dangerous. The aquatic food web inhabiting tank-bromeliads consists of micro- and macroinvertebrates (Kitching 2000) and microorganisms such as bacteria, algae, flagellates, fungi and protozoa (Carrias et al. 2001). While testate amoebae can be fearsome predators (Gilbert et al. 2000, Geisen et al. 2015) in mosses and soils, they are neither the largest nor the most dangerous in tank-bromeliads (Carrias et al. 2001). Micro- and macroinvertebrates can be very interested to feed on testate amoebae, and when you’re trapped in a tank, your chance to escape a predator are very low. This may explain why testate amoebae abundance is so low in tank-bromeliads compared to other protists such as ciliates (Carrias et al. 2012).

Tank-bromeliads are fascinating to me. Recent studies showed that microbial communities in bromeliads are highly distinct from the surrounding environments, for example soil, with sometimes a strong shift towards crucial ecosystem functions such as methanogens (Goffredi et al. 2011a, b; Mattinson et al. 2010, Louca et al. 2016). In temperate and subarctic ecosystems, testate amoebae are abundant and suggested to be key in ecosystem processes such as decomposition (Lamentowicz et al. 2013; Geisen et al. 2015; Jassey et al. 2016) or carbon uptake (Jassey et al. 2015). The low abundance of testate amoebae in tank-bromeliads suggest either they are not key species in microbial interactions and connected ecosystem processes, or they are a key trophic-link between microorganisms and micro- and macro-invertebrates as preferential food resource.

Clearly, more studies focusing on the role of testate amoebae in tank-bromeliads are needed. There are so many reasons to go and live in the tropics. If you need a good excuse to go in the tropics and see how living there is awesome, I hope this post will give you a good one. For the others who hate warm temperatures, corals, picture-perfect beaches, and rather love winters, but who would like to study testate amoebae in tank-bromeliads, I heard that some testate amoebae found an alternative to the tropics by living in bromeliads…from florist wholesalers (Kolicka et al. 2016).

References

Carrias et al. A preliminary study of freshwater protozoa in tank bromeliads. Journal of Tropical Ecology, 17, 611–617 (2001).

Carrias et al. An ant–plant mutualism induces shifts in the protist community structure of a tank-bromeliad. Basic and Applied Ecology. 13, 698–705 (2012).

Fournier et al. A legacy of human‐induced ecosystem changes: spatial processes drive the taxonomic and functional diversities of testate amoebae in Sphagnum peatlands of the Galápagos. Journal of Biogeography 43, 533-543 (2015).

Frank. Bromeliad phytotelmata and their biota, especially mosquitoes. Pp. 101–128 in  Frank, J. H. & Lounibos, L. P. (eds). Phytotelmata: terrestrial plants as hosts for aquatic insect communities. Plexus Publishing Inc., Medford (1983).

Goffredi, Kantor & Woodside. Aquatic microbial habitats within a neotropical rainforest: bromeliads and pH­associated trends in bacterial diversity and composition. Microbial Ecology 61, 529–542 (2011a).

Goffredi et al. Bromeliad catchments as habitats for methanogenesis in tropical rainforest canopies. Frontiers in Microbiology 2, 256 (2011b).

Jassey et al.. An unexpected role for mixotrophs in the response of peatland carbon cycling to climate warming. Scientific Reports, 1–10 (2015).

Jassey et al.. Loss of testate amoeba functional diversity with increasing frost intensity across a continental gradient reduces microbial activity in peatlands. European Journal of Protistology, 55, 190–202 (2016).

Kitching. Food Webs and Container Habitats: The Natural History and Ecology of Phytotelmata. Cambridge University Press, Cambridge (2000).

Kolicka et al. Hidden invertebrate diversity – Phytotelmata in Bromeliaceae from palm houses and florist wholesalers (Poland). Biologia 71, 194-203 (2016).

Laessle.  A micro-limnological study of Jamaican bromeliads. Ecology 42:499–517 (1961)

Louca et al. High taxonomic variability despite stable functional structure across microbial communities. Nature Ecology & Evolution, 1, 1–12. (2016).

Maguire. Phytotelmata: biota and community structure determination in plant-held waters. Annual Review of Ecology and Systematics 2:439–464 (1971).

Martinelli. Gefährdete Raritäten. Bromelien im at- lantischen Regenwald. Spektrum der Wissenschaft 6/2000, 66–73 (2000).

Martinson et al. Methane emissions from tank bromeliads in neotropical forests. Nature Geoscience 3, 766–769 (2010).

Picado. Les Broméliacées epiphytes considérées comme milieu biologique. Bulletin Scientifique de la France et de la Belgique 47:215–360 (1913).

Richardson. The bromeliad microcosm and the assessment of faunal diversity in a neotropical forest. Biotropica 31:321–336 (1999).

Schönborn. Lehrbuch der Limnologie. Schweitzerbart, Stuttgart (2003).

Torres and Schwarzbold. Procta em associacao com Vriesea sp. (Bromeliaceae): tres novos taxa de amebas tes- taceas (Protoctista: Rhizopoda, Testacealobosea). Not. Faun. Gembloux 41, 105–113 (2000).

Fashionable testate amoebae!

Fashion phenomena strongly influence our societies. These phenomena mostly affect young people and can be very worrysome. Many sociological studies seek to understand these phenomena, based on community background, culture and society tendencies but none seem to have considered a simple possibility: are our young people not just copying nature?

Recently, a very interesting study highlighted an intriguing fashion phenomenon within the testate amoeba community. Gomaa et al. (1) indeed revealed that all mixotrophic testate amoebae dressed up with the same algal-underwear!

Mixotrophic testate amoebae are species able to combine two nutrition modes; phototrophy and phagotrophy (predation). Using light energy thanks to their algal symbionts, mixotrophic testate amoebae are able to fix inorganic carbon through photosynthesis, whilst in parallel they are also able to assimilate organic carbon by feeding on prey items such as bacteria, fungi and other protists (2-5). This mixotrophic energetic mode thus gives them an important trophic advantage when food resources are low.

Figure 1| Some mixotrophic testate amoebae we can find in mosses : Placocista spinosa (A), Archerella flavum (B), Amphitrema wrigthianum (C), Hyalosphenia papilio (D) and Heleopera sphagni (E). Scale bar on E = 50 μm

Most mixotrophic testate amoebae show different characteristics, with for instance, different body sizes, shape and test composition. However, visually under the microscope, it seems that all of these species choose their algal symbionts in the same shop, copying each other! Probably intrigued by such fashion phenomena, Gomaa et al. (1) investigated the genetic diversity of the algal symbionts harboured by several mixotrophic testate amoeba species such as Archerella flavum, Hyalosphenia papilio, Heleopera sphagni and Placocista spinosa. These analyses showed that most algae found in testate shells shared the same kind of gene sequence (ribulose- 1,5-bisphosphate carboxylase/oxidase), thus revealing a close genetic proximity (1). The phylogenetic analysis further placed all surveyed testate amoebae symbionts close to Chlorella variabilis, a species known for forming symbiotic relationships with the ciliate Paramecium bursar (6). However, the authors also underlined that it is probable that some other endosymbiotic species occur in mixotrophic testate amoebae. Some symbionts morphologically clearly differ from C. variabilis in shape and colour, in particular within genus Placocista (Figure 1).

The modalities of symbiont acquisition by mixotrophic testate amoebae are still poorly kown and would require more investigations. Who is copying whom? Did Archerella flavum make Hyalosphenia papilio jealous with such nice colours in its shell leading the latter to feed on it to steal these nice coloured symbionts (Figure 2)? Is Placocista spinosa a weak copy of Archerella flavum and Hyalosphenia papilio, selecting its symbionts from a cheaper shop? Many questions remain unanswered. Could some of these require a sociological approach?

 

Figure 2 | Hyalosphenia papilio taking its revenge on Archerella flavum.

 

References

1. Gomaa, F. et al. One alga to rule them all: unrelated mixotrophic testate amoebae (amoebozoa, rhizaria and stramenopiles) share the same symbiont (trebouxiophyceae). Protist 165, 161–176 (2014).
2. Gilbert, D., Amblard, C., Bourdier, G., Francez, A.-J. & Mitchell E. A. D. Le régime alimentaire des thécamoebiens (Protista, Sarcodina). L’année Biologique 39, 57–68 (2000).
3. Gilbert, D., Mitchell, E. A. D., Amblard, C., Bourdier, G. & Francez, A.-J. Population dynamics and food preferences of the testate amoeba Nebela tincta major-bohemica-collaris complex (Protozoa) in a Sphagnum peatland. Acta protozoologica 42, 99–104 (2003).
4. Jassey, V. E. J., Shimano, S., Dupuy, C., Toussaint, M.-L. & Gilbert, D. Characterizing the feeding habits of the testate amoebae Hyalosphenia papilio and Nebela tincta along a narrow ‘fen-bog’ gradient using digestive vacuole content and 13C and 15N isotopic analyses. Protist 163, 451–464 (2012).
5. Wilkinson, D. M. & Mitchell, E. A. D. Testate Amoebae and Nutrient Cycling with Particular Reference to Soils. Geomicrobiology Journal 27, 520–533 (2010).
6. Hoshina, R., Iwataki, M. and Imamura, N. (2010) Chlorella variabilis and Micractinium reisseri sp nov (Chlorellaceae, Trebouxiophyceae): Redescription of the endosymbiotic green algae of Paramecium bursaria (Peniculia, Oligohymenophorea) in the 120th year. Phycological Research, 58, 188-201.

Hotel Testate Amoebae

Imagine, after a long journey, you arrive alone in a hotel. The radio is playing a nice song…

“On a dark desert highway, cool wind in my hair

Warm smell of colitas, rising up through the air

Up ahead in the distance, I saw a shimmering light

My head grew heavy and my sight grew dim

I had to stop for the night”

You’re lucky, all of the rooms are free, and you can choose the one you like. You try all of the rooms and choose the largest, most comfortable room, with the best view and a well-stocked fridge.

“Welcome to the Hotel Testate Amoebae

Such a lovely place (Such a lovely place)

Such a lovely face

Plenty of room at the Hotel Testate Amoebae

Any time of year (Any time of year)

You can find it here”

After some time, you realize you start getting bored alone in this hotel and call some friends to share your room and your fridge. Your friends delight greatly in your hotel and thus call their own friends to continue parties, reducing the space and resources available.

“They livin’ it up at the Hotel Testate Amoebae

What a nice surprise (what a nice surprise)”

You decide to move with your friends in another hotel, nicely situated in the mountains. Here again, the local food is great and parties abundant… decreasing food and drinks quickly after few weeks… Why not moving again? Seems a good choice and you move not so far in new hotel.

Just get in the hotel,     “You called up the Captain, ’Please bring me French red wine’

He said, ‘We haven’t had such wine here since nineteen sixty nine’

Some voices are calling from far away,

‘They only have Coca Cola there…’

Just to hear them say…”

What do you do? You have some good old whiskey in stock and therefore decide to mix it with Coca Cola… Unfortunately, this mixture is not good enough for your friends forcing them leaving one by one…

“Last thing I remember, they were

Running for the door…”

 What do testate amoebae do when different nutrient resources are available? This is the question posed by Krashevska et al. (2014). These authors found that testate amoebae from tropical mountain rainforests significantly responded to moderate nutrient additions. They investigated rainforests along an altitudinal transect to get insight into variations in the effects of nutrient inputs with altitude. They found that both diversity and density of testate amoebae benefited from the addition of N (e.g. French red wine), whereas the addition of P detrimentally affected their diversity and density (e.g. Whiskey-Coca Cola mixture). They also found that Nutrient-mediated changes in microbial PLFA community structure contributed only little to these changes, suggesting that testate amoebae communities are structured predominantly by abiotic factors rather than by the availability of food, but a more detailed analysis of microbial communities are needed to test these suggestions.

In conclusion, the results of Krashevska et al. suggest that testate amoebae communities of tropical mountain rainforests are structured by both positive and negative interactions via both biotic and abiotic factors, and that the response of testate amoebae to nutrient addition is dependent from altitude.

 

Krashevska, V., Sandmann, D., Maraun, M., & Scheu, S. (2014). Moderate changes in nutrient input alter tropical microbial and protist communities and belowground linkages, The ISME Journal 8(5), 1126–1134. [http://www.nature.com/ismej/journal/v8/n5/abs/ismej2013209a.html]

How shall I build my test?

How do testate amoebae build their tests? How they chose the components to build it? How do they assemble organic or inorganic particles that shape their shell? These are questions I’m often asked. Unfortunately, these questions are very difficult to answer using common tools like the light microscope.

During the last couple decades, testate amoebae have been increasingly used as proxies for reconstructing Holocene environmental change in peatlands. Community composition primarily reflects surface wetness and pH, and can be used to study mire development, climate change and human impacts. However, little is known regarding the factors that may alter quantitatively or qualitatively the test composition of these organisms. Recently studies observed variations in shell composition of some testate amoebae in acidic environments, and suggested that a better understanding of how testate amoebae build their test may improve paleo-reconstruction models (Mitchell et al. 2008).

Historically, many researchers have worked on characterizing the shell of testate amoebae (e.g., Moraczewski 1971, Netzel 1972, Saucin Meulenberg et al. 1973, Eckert et al. 1974, Stout & Walker 1976, Hedley et al. 1976, Golemansky & Couteaux 1982, Ogden 1980a, b, 1983, 1984). Unfortunately, this line of research on testate amoebae has diminished over time.

Structural variability of the shell of testate amoebae (Source; Maxence Delaine)

So, when I heard that a PhD student – Maxence Delaine – had recently worked on this topic in France I was very curious. To satisfy my curiosity, I met Maxence Delaine and he explained me what they found in their recent paper (Armynot du Chatelet et al. 2013).

Across 14 sites situated in north-eastern France, Maxence collected samples from different microhabitats, such as mosses and soil, to study variations in testate amoeba shell composition.

Sites sampled for determination of shell construction of testate amoebae

3D representation of one species of testate amoebae, Difflugia oblonga.
This picture was obtained by numerical recombination and correction of numerous 2D slides which are given by X-Ray microtomography.  The picture highlights the variability of the grains constituting the shell: small vs big or smooth vs angular particules. (Source Maxence Delaine)

The authors explored the potential application of 3D X-ray micro-tomography in addition to 2D techniques (Environmental Scanning Electron Microscope, Electron Probe Micro-Analysis, and cathodoluminescence) to characterize specimens such as Difflugia oblonga. The goal of this work was to test whether 3D morphology of testate amoebae in aqueous environments was governed by sediment size distribution and mineralogical composition.

From the 3D images, the authors calculated different parameters characterising the geometry of the specimens (size and mass) and of the individual grains forming the specimen (grain size distribution and volume). Combining chemical, mineralogical and morphological analyses allowed them to compare the grains forming the test with those of the sediment. Surprisingly, they found that Difflugia oblonga selectively picked up the small size fraction of the sediment with a preference for low-density silicates close to quartz density (~2.65). They also found that the maximum-sized grains are used for the pseudostome (i.e. shell aperture).

The following diagram shows that Difflugia oblonga is able to select the grains based on size, because the grain-size of the sediment is completely different from the grain-size of the particles constituting these amoeba shells. Moreover, no particles exceed the limit ‘‘αβ’’, which corresponds to the maximal measured size of the pseudostome of these 2 individuals. It seems likely that all the particles must pass through the pseudostome before being distributed by the amoeba for the shell’s construction.

Histograms of the particles size which constitute the shell of 2 individuals (Difflugia oblonga), compared to the grain-size curve of the sediment (in which these amoebae lived).

Amazing isn’t it? A single-celled organism selecting the “bricks” for its house! Research on this topic is very promising, and these results highlight that there is still much to learn shell composition of these amazing organisms.

References

ARMYNOT DU CHATELET E., NOIRIEL C., DELAINE M. (2013). 3D morphological and mineralogical characterisation of testate amoebae.  – Microscopy and Microanalysis, 19, 1511-1522.

ECKERT B.S., MCGEE-RUSSELL S.M., 1974, Shell structure in Difflugia lobostoma observed by scanning and transmission electron microscopy. – Tissue & Cell, 6, 215-221.

HEDLEY R.H., OGDEN C.G. & MORDAN N.J., 1976, Manganese in the shell of Centropyxis (Rhizopodea: Protozoa). – Cell Tiss. Res., 171, 543-549.

GOLEMANSKY V. & COUTEAUX M.M., 1982, Etude en microscopie électronique à balayage de huit espèces de thécamœbiens interstitiels du supralittoral marin. – Protistologica, 18, 473-480.

MITCHELL E.A.D., PAYNE R.J & LAMENTOWICZ M., 2008, Potential implications of differential preservation of testate amœba shells for paleoenvironmental reconstruction in peatlands, – J. Paleolimnol., 40, 603-618.

MORACZEWSKI J., 1971a, La composition chimique de la coque de Arcella discoides Ehrbg. – Acta Protozool., 8, 407-422.

NETZEL H., 1972, Die schalenbildung bei Difflugia oviformis (Rhizopoda, Testacea). – Z. Zellforsch, 135, 55-61.

STOUT J. D. & WALKER G. D., 1976, Discrimination of mineral particles in test formation by thecamœbae. – Trans. Amer. Micros. Soc., 95, 486-489.

OGDEN C.G. & HEDLEY R.H., 1980a, An atlas of freshwater testate amœbæ, Oxford University Press, 113 p.

OGDEN C.G., 1980b, Shell structure in some pyriform species of Difflugia (Rhizopodea). – Arch. Protistenk., 123, 455-470.

OGDEN C.G., 1983, Observations on the systematics of the genus Difflugia in Britain. – Bull. Br. Mus. Nat. Hist. (Zool.), 44, 1-73.

OGDEN C.G., 1984, Shell structure of some testate amœbæ from Britain (Protozoa, Rhizopoda). – Journal of Natural History, 18, 341-361.