Ceratium...er...Neoceratium...er...Tripos humilis

The dinoflagellate formerly known as Ceratium humile, from here.

Ceratium has long been a popular choice as a representative dinoflagellate genus for textbooks, because as micro-organisms go, they're fairly specky. The theca of Ceratium is characterised by protruding horns, with an elongate anterior horn and one to three posterior horns. The posterior horns may be directed back from the theca, or they may curve around towards the front to produce an anchor-like shape. These horns increase the cell's buoyancy, though they do make them fairly slow swimmers. The concept of Ceratium has been fairly stable since the early 1800s, but Gómez et al. (2010) found when conducting a molecular analysis of a number of 'Ceratium' species that there was a deep divide between freshwater and marine Ceratium species. As well as the molecular divide, there is also a morphological difference: freshwater species have six plates around the cingulum (the groove around the theca body in which sits one of the flagella), while marine species have five cingular plates. As a result, Gómez et al. proposed dividing the two clades between two genera, with the name Ceratium being restricted to the freshwater species. The marine species were all transferred into a new genus Neoceratium. However, Gómez (2013) later recognised that there were a number of older generic names floating about that had been given to marine taxa, and the marine species were moved again into a resurrected genus Tripos. Among the taxa affected by this double transfer was the species shown in the photo above, now known as Tripos humilis.

There are a large number of anchor-shaped Tripos species, and distinguishing them is apparently a difficult process. Tripos humilis has the anterior part of the theca in front of the cingulum (excluding the anterior horn) fairly low, the upper surface of the theca (i.e. the side away from the origin of the flagella) strongly convex, and the right-hand posterior horn much longer than the left, with the right horn tending to converge towards the anterior horn while the left horn diverges (Subrahmanyan 1968). The cingulum is also distinctly angled relative to the posterior margin of the theca. While other Tripos species are found in a range of habitats, T. humilis appears to be a more specifically tropical species. It is found pantropically, though seemingly nowhere abundantly.

Chain of Tripos, from here.

Dinoflagellates can sometimes form long chains when dividing individuals don't fully separate but continue to multiply. In Ceratium and Tripos species, the members of a chain remain connected through the apical horns. Chaining individuals may be somewhat morphologically distinct from isolated individuals; in T. humilis, the horns of chained individuals are relatively much shorter. Chains are apparently commoner when dinoflagellates form 'red tides' or algal blooms, and one suggested function is that a chain is able to swim faster overall than an individual, improving the dinoflagellates' ability to compete when moving to occupy suitable places in the water column for light or food.

REFERENCES

Gómez, F. 2013. Reinstatement of the dinoflagellate genus Tripos to replace Neoceratium, marine species of Ceratium (Dinophyceae, Alveolata). CICIMAR Oceánides 28(1): 1-22.

Gómez, F., D. Moreira & P. López-García. 2010. Neoceratium gen. nov., a new genus for all marine species currently assigned to Ceratium (Dinophyceae). Protist 161: 35-54.

Subrahmanyan, R. 1968. The Dinophyceae of the Indian Seas. Part I. Genus Ceratium Schrank. Marine Biological Association of India, Memoir 2: 1-129.

Pitchfork Mosses

Dicranum flagellare, photographed by Sue. The upright green stalks are the brood branches.

The subject of today's post is the cosmopolitan moss genus Dicranum, sometimes known as fork mosses or, apparently, wind-blown mosses. Dicranum species are characterised by elongate narrow leaves and an erect, often forked growth habit. In some habitats, Dicranum species may form reasonably extensive turfs. The genus name comes from the Greek word for a pitchfork and apparently refers to the teeth of the peristome (the ring of teeth around the opening of the spore capsule) though, if this is true, naming these mosses after a feature of the spore capsule may not necessarily have been the best idea. Many Dicranum populations produce sporophytes relatively rarely (a diagram of the moss life cycle was included in this post). Instead, these populations more commonly reproduce asexually through the production of vegetative propagules by the gametophyte. Once such species, the Holarctic Dicranum flagellare, produces terminal clusters of reduced branches, called 'brood branches'. If detached from the parent plant, these brood branches can grow into a new moss. A notable dispersal agent for brood branches, as it turns out, is slugs (Kimmerer & Young 1995). Brood branches break off the parent plant as the slug crawls past them, adhering to the slug by means of its slime. The trail of slime left by the slug also greatly improves the chance of a brood branch adhering to a suitable substrate once it becomes separated from its transport.


Dicranum scoparium, photographed by Li Zhang.

Because of the rarity of sporophytes, species of Dicranum are mostly distinguished by features of the leaves. Dicranum leaves may be straight or curved, the edge of the leaf may be smooth or toothed, and the blade of the leaf may be composed of one or two cell layers. Many species are characterised by the shape of the leaf in transverse section (Hedenäs & Bisang 2004). When sporophytes are produced, Dicranum species are dioicous: that is, they have separate male and female plants. However, in a number of species, the male plants are reduced in size and grow epiphytically on the leaves or rhizoids of the larger female plants. At least one species, Dicranum scoparium, has both dwarf and full-sized males (Hedenäs & Bisang 2004). Some Dicranum species have wide distributions, with a number found almost throughout Eurasia and North America, but others have more restricted distributions (D. transsylvanicum, for instance, is known from a single location in western Romania). Dicranum species are often very selective habitat-wise, with species differing in their choice of habitat, and they have been used as indicators of environmental conditions. This habitat selectivity can result in fragmented species distributions: for instance, Dicranum muehlenbeckii (which grows in dry, calcareous or mineral-rich environments) is found in central Europe, but is also known from a single locality in central Sweden. Dicranum scoparium, a more generalist species found in both humid and dry conditions, is widespread in Eurasia and North America, but is also known from New Zealand and a single region of Australia, near Mt Kosciuszko in New South Wales. As noted in a previous post, much ink has been spilled as regards the biogeographic processes underlying disjunct distributions in moss taxa. In that light, it should be pointed out that, while Australian and New Zealand specimens of Dicranum scoparium do tend to be less robust than the average Holarctic specimen, no molecular differences have yet been identified between the populations (Klazenga 2012).

REFERENCES

Hedenäs, L., & I. Bisang. 2004. Key to European Dicranum species. Herzogia 17: 179-197.

Kimmerer, R. W., & C. C. Young. 1995. The role of slugs in dispersal of the asexual propagules of Dicranum flagellare. The Bryologist 98 (1): 149-153.

Barn Owls and Such

European barn owl Tyto alba, photographed by Nuno Barreto.

I have no idea where the 'wise old owl' stereotype originally came from. Perhaps it simply originated from their appearance: their broad faces, sedate manner, and slightly supercilious half-lidded gaze (those last two, of course, only applying under the circumstances most people would actually see an owl: as a half-asleep night-dweller rudely awakened during the day). Whatever the cause for their associations, owls are one group of birds that have commonly featured in popular culture. The Eurasian barn owl Tyto alba is one owl species that has long held a particular association with humans. Owls mostly do not build their own nests, but make use of suitable hollows and crannies that they find ready-made. The preferred food of barn owls is small mammals such as rats and mice (though they will not turn up their beaks at alternative fare such as reptiles or large insects when their favourite is not available). Put these two facts together, and human constructions (i.e. barns) can be paradise for a barn owl: ready-made secluded nesting spots in the roof-space, and a steady supply of rodents attracted to stored foodstuffs and/or refuse.

Greater sooty owl Tyto tenebricosa arfaki, photographed by Nik Borrow.

The European barn owl is just one species in the genus Tyto, within which König & Weick (2010) recognised 25 species from around the world. While some Tyto species, like T. alba, are found over a wide range, others are found in restricted localities (many on particular oceanic islands). Some are very poorly known: the Taliabu masked owl Tyto nigrobrunnea from Indonesia was described from a single specimen in 1939, with only a handful of sight records since to attest to its continued existence. The Itombwe owl Tyto prigoginei of central Africa was similarly unknown between its initial description in 1952 and the mistnet capture of a live female in 1996. Prior to its transfer to Tyto by König & Weick (2010), this last species was included in the genus Phodilus, the bay owls, which is the living sister group to Tyto. Together, these two genera form the family Tytonidae, separate from all other owls in the family Strigidae. Tytonid owls differ from strigid owls in a features such as having the inner and central toes of the foot similar in length (versus the inner toe being distinctly shorter than the central one in strigids), with the central toe being serrated on the underside. The species of Tyto have a distinctly heart-shaped facial disc (that of Phodilus species is almost reminiscent of Hello Kitty). Many Tyto species, such as T. alba, prefer open habitats, but some, such as the sooty owls Tyto multipunctata and T. tenebricosa of eastern Australia and New Guinea, inhabit rainforests. The smallest Tyto species are T. prigoginei at about 24 cm total length and the Galapagos barn owl T. punctatissima at about 26 cm, and the largest is the Tasmanian grass owl T. castanops, reaching up to 55 cm in length and about 1.25 kg in weight.

Tasmanian grass owl Tyto castanops, photographed by Murray Lord.

Other extinct species would have also probably broken the 1 kg mark. Tyto species have a long fossil record, going back to the Middle Miocene European species T. sanctialbani (Kurochkin & Dyke 2011). Tytonids of now-extinct genera had been abundant in Europe before that time, but Mlíkovský (1998) suggested that they had become temporarily extinct there in the Early Miocene, owing to a gap in the fossil record. Tyto sanctialbani was similar in size to the modern T. alba (Mlíkovský 1998), but a number of giant fossil barn owls are known from islands around the world. The largest include Tyto pollens and T. riveroi in the West Indies (the Bahamas and Cuba, respectively), and T. robusta and T. gigantea from Gargano. Gargano is a peninsula of southern Italy that was a separate island during the Late Miocene to Early Pliocene, at which time it was home to a distinctive endemic fauna including such animals as the absolutely insane small ruminant Hoplitomeryx, which possessed both a crown of five spike-shaped horns and long dagger-like canines. It has been suggested that this over-exuberant armature had evolved as a defence against Gargano's main predators, an assemblage of raptors including the aforementioned Tyto species. The larger of the two, T. gigantea, was about twice the size of a living European barn owl, and perhaps larger than any living owl (Ballmann 1976), though it was more gracile in build than the largest living Bubo species. Ballmann provides measurements for leg bones of T. gigantea and not wing bones, but if we assume similar proportions to a modern barn owl then we'd be looking at a wingspan for T. gigantea of about two metres. That, I submit, is enough to scare seven colours of crap out of any number of small mammals.

REFERENCES

Ballmann, P. 1976. Fossile Vögel aus dem Neogen der Halbinsel Gargano (Italien), zweiter Teil. Scripta Geol. 38: 1-59, 7 pls.

König, C., & F. Weick. 2010. Owls of the World, 2nd ed. Christopher Helm: London.

Kurochkin, E. N., & G. J. Dyke. 2011. The first fossil owls (Aves: Strigiformes) from the Paleogene of Asia and a review of the fossil record of Strigiformes. Paleontological Journal 45 (4): 445-458.

Mlíkovský, J. 1998. A new barn owl (Aves: Strigidae) from the early Miocene of Germany, with comments on the fossil history of the Tytoninae. J. Ornithol. 139: 247-261.

Surviving the Reader Apocalypse

And it came to pass that Google did speak from on high, and say unto them: "You know that whole Reader service that you've been using multiple times every day for the past several years? We've decided to ditch it. Bye!" And there was a great wailing and gnashing of teeth, but at the end of the day, thou canst only complain so much about losing something thou didst not pay for. And so the people didst follow Google's instructions, and download their subscription data, and seek upon high for a suitable replacement.

And yea, replacements came forward to offer themselves, and the people did choose among them, and offer their subscriptions. But lo! when muggins here did look upon his subscriptions, he discovered that only some of them had transferred, and many were lost. And now he speaks unto the people, "Dost thou knowest of RSS subscriptions good and true, that you think I should partake of?"

Answers, please, not to the office of the Uniting Church, but in the comments below. Cheers.

Loaches

European spined loach Cobitis taenia, from here.

The spined loaches of the Cobitidae are a family of small freshwater fishes found across Eurasia, with a single species (Cobitis maroccana) making it to the northern tip of Africa. A recent catalogue of the family by Kottelat (2012) recognised twenty-one genera in the families, though phylogenetic studies suggest that some reshuffling may be necessary: the Chinese Paramisgurnus dabryanus, for instance, may be nested within the genus Misgurnus, while the Sino-Japanese genus Niwaella may be a polyphyletic grouping of elongate species adapted to fast-flowing mountain streams (Šlechtová et al. 2008).

Eel loach Pangio anguillaris, photographed by Thomas Frank.
As a whole, loaches are more or less worm-like fishes that feed by benthic scavenging. Most species are small, less than ten centimetres long, though the Thai Acantopsis spectabilis gets up to around 15 centimetres (Kottelat 2012), and the weather fish Misgurnus anguillicaudatus reaches about 25 cm. Phylogenetically, the family was divided by Šlechtová et al. (2007) into two groups, a 'northern clade' containing the northern Eurasian species in the genera Cobitis, Misgurnus and related taxa, and a paraphyletic 'southern group' containing the remaining southern and south-east Asian species. The ranges of the northern and southern subdivisions overlap in northern Vietnem, but otherwise the two groups are geographically disjunct. A potential morphological synapomorphy of the northern clade is a horizontal ossified structure, called the 'scale of Canestrini', on the second ray of the male's pectoral fin, but if so this character has been lost in some subtaxa such as the western Eurasian genus Sabanejewia.

Weather fish Misgurnus anguillicaudatus, photographed by Emma Turner.
One interesting detail about the northern spined loaches is the existence in various localities of natural polyploid populations: such polyploids have been identified among European Cobitis species, and in the Japanese Misgurnus anguillicaudatus. These mostly triploid (sometimes tetraploid) populations of loaches reproduce clonally, but are always found in association with a sexually-reproducing diploid population. This is because the parthenogenetic females are what is referred to as 'sperm parasites'. The parthenogenetic females still mate with sexual males, not to be fertilised but in order that the act of mating will stimulate egg production. In external appearance, these polyploids are generally indistinguishable from their co-existing diploid associates. European polyploid Cobitis are believed to have arisen through hybridisation between closely related sexual species, possibly through male sperm fertilising an unreduced diploid egg.

Protocobitis typhlops, from Kottelat (2012).

Oh yes, and there are cave-dwelling loaches out there: two Chinese species, placed in the genus Protocobitis, are blind species collected from groundwater. How they relate to the above-ground species remains unknown.

REFERENCES

Šlechtová, V., J. Bohlen & A. Perdices. 2008. Molecular phylogeny of the freshwater fish family Cobitidae (Cypriniformes: Teleostei): delimitation of genera, mitochondrial introgression and evolution of sexual dimorphism. Molecular Phylogenetics and Evolution 47: 812-831.

Kottelat, M. 2012. Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei). Raffles Bulletin of Zoology, Supplement 26: 1-199.