Algal Threads (Taxon of the Week: Myrionemataceae)

Discs of Myrionema strangulans on a blade of Ulva lactuca. Photo from here.

The brown algae of the Phaeophyceae* are one of the predominant groups of multicellular algae in the modern ocean. Though not the most speciose of the three (that title belongs to the red Macrorhodophytina), they are in many places the most ecologically significant, as this is the group that includes the gigantic kelps that predominate and shape many parts of the marine environment. As significant as kelps are, though, they are not my focus for today. Instead, I'm going to look at a much smaller group of brown algae, the Myrionemataceae.

*The names "Phaeophyceae" or "Phaeophyta" have usually been used to refer to the monophyletic clade of multicellular brown algae. Cavalier-Smith & Chao (2006) recently proposed an expanded "class Phaeophyceae" to include the unicellular Phaeothamniophyceae and the very-basically-multicellular Schizocladia, with the traditional Phaeophyceae referred to as "subclass Melanophycidae". As Cavalier-Smith & Chao did not dispute the monophyly of the traditional Phaeophyceae, this is a simple ranking issue and I suspect it will probably be largely ignored by everyone else.

Myrionemataceae are minute filamentous algae, usually only a couple of millimetres in size (Abbott & Hollenberg, 1993). They generally grow in a disc only one or two cells deep, with numerous filaments growing upwards from the strands of the disc. These filaments may be uniserial or branching; they may or may not carry lateral processes or sporangia. Myrionemataceae most commonly seem to be epiphytic on much larger marine plants and algae.


Close-up of Microspongium globosum, an Atlantic myrionematoid alga. Image from Taşkin et al. (2006).

Myrionemataceae (and small filamentous brown algae in genera) have been a royal pain in the neck for algal taxonomists, and as a result they have been widely shunned. For instance, the main distinguishing characteristic between the Myrionemataceae and the similarly filamentous Ectocarpaceae has been that the former is discoidal and the latter is not (Clayton, 1974). However, the genus Hecatonema (included by some authors in Myrionemataceae and excluded by others) includes some species that always grow in a disc, and others that do not. Some "Myrionemataceae" have been suggested to represent divergent growth forms or dimorphic generations of other brown algae placed in different families (many marine algae have very distinct alternating generations). This seems very probable for some species, but proving such relationships is not easy and Clayton (1972) claimed that at least some cases of myrionematoid algae being grown from cultures of other algae represented contamination instead of relationship. Other Myrionemataceae that have been cultured show no signs of alternating generations, while yet others have only ever been recorded reproducing asexually.


Individual filament of Myrionema strangulans, showing close-up structure. From DeCew's Guide.

It seems almost certain that the "Myrionemataceae" are a polyphyletic grouping, with their overall lack of distinguishing features obscuring a diversity of origins. Peters (2003) found the type genus, Myrionema, to be itself polyphyletic. The type species of Myrionema, M. strangulans, has a fairly isolated position within the Ectocarpales sensu lato in Draisma et al. (2001), but it is pretty much anyone's guess as to how many of the so far unanalysed myrionematoid species belong with it*. Some species may be established as growth-forms of other taxa and shipped off accordingly, but others may prove more intractable and remain in the "family" - not so much a wastebasket as an inedible core.

*Das et al. (2005), in a paper that had me completely baffled but which I rather suspect was complete twaddle to begin with, cite a later phylogeny which they attribute to Draisma et al. (2002) that positions Myrionema strangulans in the Chordariaceae - unfortunately, Draisma et al. (2002) has absolutely no mention anywhere of Myrionema, chordariaceous or otherwise, so I wouldn't know what reference Das et al. really had in mind.

REFERENCES

Abbott, I. A., & G. J. Hollenberg. 1993. Marine Algae of California. Stanford University Press.

Cavalier-Smith, T., & E. E.-Y. Chao. 2006. Phylogeny and megasystematics of phagotrophic heterokonts (kingdom Chromista). Journal of Molecular Evolution 62: 388-420.

Clayton, M. N. 1972. The occurrence of variant forms in cultures of species of Ectocarpus and Giffordia. Br. phycol. J. 7: 101-108.

Clayton, M. N. 1974. Studies on the development, life history and taxonomy of the Ectocarpales (Phaeophyta) in southern Australia. Australian Journal of Botany 22: 743-813.

Das, S., J. Chakrabarti, Z. Ghosh, S. Sahoo & B. Mallick. 2005. A new measure to study phylogenetic relations in the brown algal order Ectocarpales: The “codon impact parameter”. J. Biosci. 30: 699–709.

Draisma, S. G. A., J. L. Olsen, W. T. Stam & W. F. Prud'homme van Reine. 2002. Phylogenetic relationships within the Sphacelariales (Phaeophyceae): rbcL, RUBISCO spacer and morphology. European Journal of Phycology 37: 385-401.

Draisma, S. G. A., W. F. Prud'homme van Reine, W. T. Stanm & J. L. Olsen. 2001. A reassessment of phylogenetic relationships within the Phaeophyceae based on RUBISCO large subunit and ribosomal DNA sequences. Journal of Phycology 37: 586-603.

Peters, A. F. 2003. Molecular identification, distribution and taxonomy of brown algal endophytes, with emphasis on species from Antarctica. In Seventeenth International Seaweed Symposium (A. R. O. Chapman, R. J. Anderson, V. J. Vreeland & I. R. Davison, eds) pp. 293-302. Oxford University Press.

Taşkin, E., M. Öztürk & M. J. Wynne. 2006. First report of Microspongium globosum Reinke (Phaeophyceae, Myrionemataceae) in the Mediterranean Sea. Nova Hedwigia 82 (1-2): 135-142.

Before the Word for World was Forest

...though to be perfectly honest, I've never read The Word for World is Forest, I just thought that it'd supply a catchy name for this post.


The environment of the Devonian Rhynie Chert, as illustrated by Zdenek Burian (via Palaeos.com.

If you want to find out about the evolution of terrestrial life for vertebrates, there are countless sources out there for you to turn to. But if you want to find out about the evolution of terrestrial life for plants, then your options are probably much thinner. Which is just one more example of how screwed up our priorities as humans are, because there's no doubt which is the greater achievement. When the first terrestrial vertebrates emerged, they found a world already made lush by a covering of vegetation. But the first terrestrial plants would have found nothing waiting for them but bare, hostile rock*. It's amazing that they ever managed at all.

*To be honest, I lie slightly. In places where there was available moisture, I'm sure that a film of bacteria would have grown. Ditto for unicellular algae and other such organisms. If lichen-type associations were around at the time (and a cyanobacteria-zygomycete association is preserved in the Rhynie Chert - Selosse & Le Tacon, 1998), the world would have been their mollusc. Sadly, with little potential for their fossilisation and discovery, we may never really know about the contributions of these first unicellular pioneers.


Reconstruction of the trimerophyte Psilophyton, from here.

But manage they did, and by the early Devonian the world was home to a small but respectable diversity of land plants. Most of the vascular plants of the time have been divided between the rhyniophytes, lycophytes, trimerophytes and cladoxylopsids (doubtless there were also moss- and liverwort-like plants around too, if not actual mosses and liverworts, but the spotty fossil record of bryophyte-grade plants doesn't quite reach that far back). Almost all of them, admittedly, would have been fairly similar to the non-expert eye - small, shrubby affairs with simple branching systems and no true leaves or roots. Examination of their fine structure (particularly of their vascular systems) is necessary to recognise their true affinities - rhyniophytes in the stem lineage for all vascular plants; lycophytes including the ancestors of modern Lycopodium, Selaginella and Isoetes; trimerophytes on the stem leading to modern ferns and seed plants; and cladoxylopsids on the stem of modern ferns*. Each of these groups quite possibly represents a grade rather than a clade, but in most cases it is not possible to actually demonstrate this one way or another.

*It is worth noting (especially in relation to a question asked in the comments to a previous post) that the vascular cells of rhyniophytes, lycophytes and trimerophytes each have distinct morphologies from each other** (Friedman & Cook, 2000), and this has led some authors to suggest that the vascular system may have developed independently in each of the three lineages. For now, though, it seems more parsimonious to assume a common origin followed by evolutionary divergence.

**It is also worth noting that when Friedman & Cook (2000) wrote their review, we actually knew more about the structure of the vascular cells in Devonian lycophytes and trimerophytes than in living lycophytes and ferns. Previous studies of vascular cell structure in living plants had almost exclusively looked at seed plants alone.

Trimerophytes differed from the more basal rhyniophytes in their mode of branching - whereas the basalmost land plants had branched dichotomously (dividing into two branches with each branch growing equivalently), trimerophytes branched anisotomously (one branch growing more than the other), effectively giving the trimerophytes some degree of a central stem (this process is called overtopping). Secondary branches from the central stem still branched dichotomously. Sporangia were borne on the tips of the branches, and at least some trimerophytes grew elongate sporangia in pairs that twisted around each other (Gerrienne, 1997).

One particular trimerophyte, Psilophyton princeps, holds a particular significance for palaeobotany as the first Devonian plant to be reconstructed, by William Dawson in 1859 (Taylor & Krings, 2008), with a large creeping rhizome extending successive upright shoots. But perhaps even more significant was the size reached by some trimerophytes. While most Devonian vascular plants would have been struggling to reach half a metre in height, the trimerophyte Pertica dalhousii has been estimated to have reached up to three metres (Mauseth, 2008) - about the height of the ceiling of an average house (the related but smaller species Pertica quadrifaria is shown to the left, in a reconstruction from the Maine Geological Survey). Together with the similarly-sized cladoxylopsid Pseudosporochnus, these were effectively the first trees - not much compared to their modern successors, perhaps, but very impressive compared to anything that came before them (with the exception, of course, of the primordial oddity Prototaxites). It is interesting to imagine what the environment of these early "forests" would have been like. How did they handle the weather, for a start? In the absence of a strong root system to anchor them down, were they prone to collapsing in the wind? If this was so, did they grow rapidly to compensate for their short lives, or did the rhizome readily send up new shoots to replace lost ones? (Remember, with no leaves either, the entire stem would have probably been photosynthetic.) How did this affect life for the early terrestrial animals taking advantage of their presence? There may have been the beginnings of a forest, but a world recognisably our own was still a long way off.

REFERENCES

Friedman, W. E., & M. E. Cook. 2000. The origin and early evolution of tracheids in vascular plants: integration of palaeobotanical and neobotanical data. Philosophical Transactions of the Royal Society of London Series B 355: 857-868.

Gerrienne, P. 1997. The fossil plants from the Lower Devonian of Marchin (northern margin of Dinant Synclinorium, Belgium): V. Psilophyton genseliae sp. nov., with hypotheses on the origin of Trimerophytina. Review of Palaeobotany and Palynology 98: 303-324.

Mauseth, J. D. 2008. Botany, 4th ed. Jones & Bartlett Publishers.

Selosse, M.-A., & F. Le Tacon. 1998. The land flora: a phototroph-fungus partnership? Trends in Ecology and Evolution 13 (1): 15-20.

Taylor, E. L., & M. Krings. 2008. Paleobotany, 2nd ed. Academic Press.

Like, Wow. Just... Wow.

This is something I saw this morning at Small Things Considered, that I thought was just so spectacularly brilliant that I just had to copy it:



One hundred and sixty-seven species of ciliate, artfully arranged and all drawn to scale, from the gigantic Stentor to the sinuous Homalozoon to the infinitesimal Cinetochilum. The image comes from here, where not only can you see it in its full glory, but you'll find the key to the numbering that tells you what each one of these marvels is. The species are partially arranged in line with their chosen habitats - those towards the top left are found in the open water column in lakes, those around the centre of the bottom are anaerobes, while the others make their homes among sediment. And there's even little extra bits of detail hidden within - see if you can find the Chilodonella crawling along the Epistylis stalk, for instance. Enjoy!

Then if you're in the mood for more details on ciliates, including comments on their mind-blowingly complicated genetic system, take a look at my earlier posts here and here. And if anyone is feeling really generous and wants to get this printed out as a wall poster for me...

More Things in Heaven and Ocean

Following on from the post just put up on xenophyophores, I couldn't pass on without mentioning these fellows:



This is Haeckel's (1889) plate of members of the Ammoclathrinidae, taken from here. Haeckel described members of this family* among his "Deep-Sea Keratosa", the other examples of which have since been identified as xenophyophores (and not, as Haeckel thought they were, sponges). Like xenophyophores, ammoclathrinids had coverings constructed from foreign objects, and when I wrote the page on xenophyophores for Palaeos.com, I interpreted ammoclathrinids as being xenophyophores. True, Haeckel had originally identified separate cells inside his ammoclathrinids, but I suggested that this could have been an artefact caused by his use of acid to prepare the specimens, and they might have originally been coenocytic. However, when I wrote that I was working from Tendal's (1972) recounting of Haeckel's work, and hadn't seen the original description. Looking at it now, I have to admit that the illustrations in Haeckel's plate look very different from xenophyophores.

*Which he called Ammoconidae, but this name was changed by Tendal (1972) for reasons of preoccupation.

Unfortunately, Haeckel's original material no longer exists (it seems likely that he pulled it apart in the process of describing it), and no-one has ever laid eyes on a recognisable ammoclathrinid since. The nature of these organisms, therefore, is a complete mystery. Such a situation is more common than you may think, particularly in microbiology. The protistological literature is littered with examples of organisms seen and described by someone looking down a microscope in the 1800s, and never recorded since. It might be tempting to wonder whether the original describer ever really saw what they thought they saw at all, but that may be ignoring one of the major issues in microbiology itself - the world is very, very large, and the things being looked for a very, very small. If comparatively large mammal species can elude attention for numbers of years, how much more so can tiny micro-organisms? Or something like Ammoclathrinidae, lurking somewhere in the little-explored deep sea?

REFERENCES

Haeckel E. 1889. Report on the Deep-Sea Keratosa. Report on the Scientific Results of the Voyage of H. M. S. Challenger during the years 1873–76. Zoology 32 (part 82): 1–92.

Tendal, O. S. 1972. A monograph of the Xenophyophoria (Rhizopodea, Protozoa). Galathea Report 12: 7-99.

Living with Poo - A New Xenophyophore

Scattered individuals of the xenophyophore Reticulammina labyrinthica. Image from Ocean Planet.

And if you don't know what a xenophyophore is, then shame on you! Xenophyophores are sessile deep-sea protists that often reach comparatively gigantic sizes. One species, Stannophyllum venosum (which looks something like half a plate sitting on its edge), can be nearly a foot across (Tendal, 1972). Images from deep-sea submersibles have shown that xenos can be spectacularly abundant, carpeting the ocean floor in some places.

Xenophyophores are sometimes referred to as the largest unicellular organisms, but as I've mentioned before, that's arguably not entirely appropriate. Rather, xenophyophores have a coenocytic or hyphal organisation, with numerous nuclei scattered throughout long branching cytoplasmic tubes. The name "xenophyophore" means "bearer of foreign objects", and refers to the external test of the organism, which it constructs by cementing together objects it collects from the sediment around it - sand grains , for instance, or shells of other organisms - using a polysaccharide cement. The xenos also sequester their faecal pellets, which they may also integrate into their skeleton. Different species of xeno can be distinguished by the nature and arrangement of the foreign particles in the test (they are often quite picky about what they use), and the proportion of foreign particles to cement or faecal pellets. The species Cerelasma massa, for instance, differs from other xenos in using no foreign particles whatsoever, but only cement and its own faecal pellets - hence also being a contender for the title of most disgusting organism in existence. Species that use a high proportion of foreign particles in their construction are generally quite rigid, while those using more cement are softer.


The new xenophyophore species Shinkaiya lindsayi. In the long section, the central white strands are the xenophyophore's cytoplasm, while the black strands are strings of faecal pellets. Figure from Lecroq et al. (2009).

Yesterday saw the publication of a new xenophyophore species, Shinkaiya lindsayi (the genus is named, offhand, after the submersible that was used to collect the type specimen) by Lecroq et al. (2009). One of the most significant features of the new paper is that it includes a molecular phylogenetic analysis of the new species. Xenophyophores have been sequenced on one occasion before, by Pawlowski et al. (2003), who placed the species Syringammina corbicula among basal Foraminifera. It is good to see that Lecroq et al. place Shinkaiya as the sister to Syringammina, and the two together fit in the same position among forams originally found by Pawlowski et al.. The closest relative to xenophyophores identified is a foram called Rhizammina, which is also sessile, constructs a test of foreign matter, and even sequesters faecal pellets in a similar manner to xenophyophores.

This is a noteworthy achievement - these are not easy organisms to sequence. Not only is there a shortage of accessible material, but xenos and forams both tend to have large numbers of bacteria and other micro-organisms living around them, just aching to contaminate DNA samples (the very first molecular phylogenetic analysis of a foram, for instance, suggested a close relationship between forams and dinoflagelates, only to have it later shown that the sequence analysed belonged not to the foram but to parasitic micro-organisms living in the foram*). So the fact that Lecroq et al.'s results are not only well-supported, but make a lot of intuitive sense morphologically, makes this a very nice study indeed.

*Still, if the recently suggested SAR clade is correct, there is a certain irony to this - forams may be somewhat related to dinoflagellates after all.


Haeckel's (1889) illustrations of species of Stannophyllum, including the gigantic S. venosum at the bottom. Stannophyllum belongs to a family of xenophyophores called stannomids that differ from other xenos such as Shinkaiya (called psammetids) in having reinforcing threads (probably made of mucopolysaccharides) running through their tests. Stannomids are more plate-like, upright and flexible than the lumpy psammetids. Image via here (Haeckel referred to xenophyophores as "Deep-Sea Keratosa", as he was under the impression that they were sponges).

REFERENCES

Haeckel E. 1889. Report on the Deep-Sea Keratosa. Report on the Scientific Results of the Voyage of H. M. S. Challenger during the years 1873–76. Zoology 32 (part 82): 1–92.

Lecroq, B., A. J. Gooday, M. Tsuchiya & J. Pawlowski. 2009. A new genus of xenophyophores (Foraminifera) from Japan Trench: morphological description, molecular phylogeny and elemental analysis. Zoological Journal of the Linnean Society 156: 455-464.

Pawlowski, J., M. Holzmann, J. Fahrni & S. L. Richardson. 2003. Small subunit ribosomal DNA suggests that the xenophyophorean Syringammina corbicula is a foraminiferan. Journal of Eukaryotic Microbiology 50: 483-487.

Tendal, O. S. 1972. A monograph of the Xenophyophoria (Rhizopodea, Protozoa). Galathea Report 12: 7-99.

Southern Moss (Taxon of the Week: Ptychomitrium muelleri)

There don't seem to be any images of Ptychomitrium muelleri available online, so here's another Ptychomitrium species, P. gardneri from China. Photo by Li Zhang.

Mosses are often treated as the poor relation in plant diversity. Popular presentations of plant evolution often tend to have even more of a Scala Natura-esque slant to them than presentations of animal evolution, and so mosses and other non-vascular plants get glossed over as mere stepping stones to their more upright "descendants", if they even warrant a mention at all. This is, of course, complete rubbish - mosses have a very respectable diversity of species (about 10,000, according to Tree of Life). I've met a few moss researchers over the years, and a more devoted following a taxon could not hope for.

Ptychomitrium muelleri is a haplolepidous moss of the family Ptychomitriaceae (I'll explain what that means in a minute). It grows to a maximum height of one and a half centimetres, and if the type specimens are any indication, prefers to grow on rocks. Ptychomitrium mosses seem to be found more or less worldwide, but Ptychomitrium muelleri itself is found in south-eastern Australia, New Caledonia, southern South America and southernmost Africa. What is interesting about this species' distriution is that it was thought to be endemic to Australia until very recently when Cao et al. (2001) established that species described from each of the other localities were conspecific with P. muelleri. As a result, P. muelleri has what might be described as a classic "Gondwanan" distribution, but I rather doubt that Gondwana had anything to do with it. After all, moss spores are very light and extremely easily dispersed, and surely it is no coincidence that all the localities where P. muelleri can be found lie roughly along the same wind belt.



The diagram of a moss life cycle above has been stole from Palaeos.com. For the nonce, the important details are these - mosses, like other plants, are multicellular at both the haploid and diploid stages of the life cycle, but unlike vascular plants, the larger, dominant stage of the life cycle is the haploid gametophyte. When a female gametophyte is fertilised, the diploid sporophyte remains attached to the gametophyte and grows a spore-filled capsule that eventually breaks open (after the loss of the protective calyptra) to release the spores. Around the mouth of the capsule is a ring of "teeth", the peristome. In basal mosses, the peristome is made up of entire cells, but in the class Bryopsida, the arthrodontous mosses (which includes the larger part of the mosses), the teeth are reduced to cell wall remnants. Most of the bryopsid lineages have two rows of teeth in the peristome, an outer and an inner, but Ptychomitrium belongs to a group called the Haplolepideae or Dicranidae which have only the inner row of teeth. The haplolepidous mosses form a monophyletic clade within the Bryopsida.


Ptychomitrium polyphyllum from Scotland, showing the calyptra on the left capsule and the exposed peristome on the right. Photo from here.

Most of the features separating moss taxa are microscopic and relate to such things as cell arrangement (which is my weaselly method of saying that I don't understand a word of them), but Ptychomitrium is distinguished by having a mitrate calyptra (and those unsure what "mitrate" means might want to look at the Taxon of the Week post of two weeks ago) with characteristic lobes around the lower edge (Hernández-Maqueda et al., 2008, compare it to a Hawaiian skirt). Ptychomitrium muelleri has (amongst other features) lingulate (tongue-shaped, I'm guessing) leaves with smooth margins, and ovoid capsules.

REFERENCES

Cao, T., S. Guo & Y. Zhang. 2001. Distribution of Ptychomitrium muelleri (Bryopsida), with its synonyms. The Bryologist 104 (4): 522-526.

Hernández-Maqueda, R., D. Quandt, O. Werner & J. Muñoz. 2008. Phylogeny and classification of the Grimmiaceae/Ptychomitriaceae complex (Bryophyta) inferred from cpDNA. Molecular Phylogenetics and Evolution 46 (3): 863-877.

Knocked Off the Perch (Taxon of the Week: Percidae)

The rainbow darter, Etheostoma caeruleum, a representative of the North American radiation of small and often colourful freshwater fish known as darters. This species breeds on fast gravel riffles, where pairs mate with the female half buried in the gravel so the eggs are automatically covered over (Reeves, 1907). Photo by Jim McCormac.

Okay, this post has been delayed again. It's been an unusual week, is all I can say. I'd tell you all about, but I have very good reasons to believe that that would be extremely dull.

In earlier posts, I have ranted in a rather esoteric manner about my distaste with the commonly recognised fish order "Perciformes", really a random multi-paraphyletic assemblage of the more generalised members of the clade Percomorpha. In the recent partial reclassification of the Percomorpha by Li et al. (2009), the name "Perciformes" was ditched entirely, and the clade containing the family Percidae was instead called Serraniformes (suggesting, offhand, that some sort of taxonomic karma is dooming this taxon to be associated with confusing names - the family Serranidae as commonly recognised itself seems likely to be polyphyletic, and a number of "serranids" are not guaranteed Serraniformes). But even before the Perciformes of common use were recognised as a wastebasket assemblage (if, indeed, there ever really was such a time), Percidae was always a slightly odd choice for the type family. The Percidae, the perches and darters, are not particularly average Perciformes.

Among the percomorphs, percids are unusual for one main reason - they're almost entirely freshwater (a few European species stray into brackish waters, but only one species - Sander marinus, the estuarine perch of the Black and Caspian Seas - is a permanent resident in them). While the percomorphs have achieved true world dominance in the upper parts of the ocean, including the vast majority of coastal and surface-pelagic fish species, they have never made such significant inroads into fresh water. A few percomorph lineages have been very successful in fresh water, such as the Cichlidae, the Anabantiformes and various members of the Smegmamorpha*. But in contrast to their surface-marine monopoly, percomorphs have to share dominance of the fresh-water environment with members of the clade Otophysi - Cypriniformes, Characiformes and Siluriformes.

*No, honestly, it's a real name.


The zander, Sander lucioperca, a much larger Eurasian percid. Photo from EoL.

The Serraniformes also include the Trachinidae (weevers), the circum-Antarctic notothenioids and the majority of what were the Scorpaeniformes. Relationships within the Serraniformes are yet to be hammered out, but the Percidae probably divide from the others reasonably basally. Ten genera of living Percidae are currently recognised, with more than two hundred species. Phylogenetic analysis of the family by Sloss et al. (2004) recognised three main clades of unresolved relationships - the Holarctic genus Perca, the mostly Eurasian clade of Gymnocephalus plus Luciopercinae (genera Romanichthys, Sander and Zingel, with three species of Sander in North America), and the North American clade of Etheostomatinae (Ammocrypta, Crystallaria, Etheostoma and Percina). [The tenth genus includes the single uncommon species Percarina demidoffi of rivers running into the Black Sea, and was not analysed by Sloss et al. due to lack of material. Percarina was previously classified in the possibly non-monophyletic Percinae* with Perca and Gymnocephalus and differs from most other Percinae in spawning in brackish waters, so establishing its relationships would be very interesting.] While the greater phylogenetic disparity of Percidae is concentrated in the western Palaearctic and the family is believed to have originated in that area, the greater diversity of species is definitely found in North America. Well over two-thirds of percid species belong to the Etheostomatinae, with the greater part of those in the genus Etheostoma (which, however, may not be monophyletic).

*Though the non-monophyly of Percinae found by Sloss et al. is in contrast to their breeding behaviour - Percinae differ from other percids in laying their eggs encased in long gelatinous strands, while Luciopercinae and (ancestrally) Etheostomatinae are broadcast spawners.


The European perch, Perca fluviatilis. A very similar species, Perca flavescens, is found in North America. Photo from here.

Human interest in the Percidae (as with most matters, really) has usually been related to one of two things - eating or sex. The larger percids of the "Percinae" and Luciopercinae are widely caught for food, and the European perch Perca fluviatilis has been introduced to many localities outside its native range such as New Zealand for the amusement of anglers. Some percids, such as the walleye Sander vitreus, have been recorded reaching lengths of over a metre (though such sizes are, of course, exceptional - a more average walleye would be about twenty centimetres). Species of the Etheostomatinae, known as darters, are not targets of fishing - members of this subfamily (as well as some species of Luciopercinae) are smaller than other percids, less than ten centimetres in length*, and wouldn't offer much in the way of eating. Still, darters more than make up their interest in the other regard of sex. They show a wide diversity of breeding behaviour, from broadcast spawners to some that bury their eggs in sediment or gravel to species that lay their eggs safely hidden on the underside of rocks. Other species may glue their eggs to vegetation (Winn, 1958a, b). During the breeding season, most (but not all) darters move from deeper to shallower waters (many species favour riffle areas) where the males usually establish a breeding territory (as reported by Winn, 1958b, the presence of other males seems to be required to incite the successful establishment of a territory - solitary males tended to lose interest in a potential territory and wander off). Some darter species are fairly relaxed about their territories and only fend off males of their own species, but other darters may be decidedly pugnacious and attack just about anything that moves. Challenging males approach each other with fins held high, and their colours will often become brighter. They may circle each other and butt or bite at each other's tail regions. After a male has mated with a female and she has laid her eggs, he may or may not remain in the area to guard them. Experiments have shown that if the eggs are removed or replaced, the male continues to guard the same spot, so it is the territory that induces guarding behaviour rather than the presence of eggs. Hybrids have been recorded between a number of darter species and seem to be not uncommon, especially where species have been spread outside their native range (Stauffer et al., 1995).

*As a corollary of their smaller size, it is worth noting that darters (and the smaller Luciopercinae) also lack swim bladders.


Percarina demidoffi as illustrated by N. Kondakov in a 1957 Russian textbook. For some reason, I find a certain whimsy in this illustration of what is perhaps one of the more mysterious percids. Image via NOAA Photo Library.

REFERENCES

Reeves, C. D. 1907. The breeding habits of the rainbow darter (Etheostoma cœruleum Storer), a study in sexual selection. Biological Bulletin 14 (1): 35-59.

Sloss, B. L., N. Billington & B. M. Burr. 2004. A molecular phylogeny of the Percidae (Teleostei, Perciformes) based on mitochondrial DNA sequence. Molecular Phylogenetics and Evolution 32 (2): 545-562.

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