Chondria: Turf of the Surf

Of the major groups of multicellular algae (or 'seaweeds' in the common parlance) found in the world today, the red algae are unquestionably the most speciose. In this post, I'm looking at a widespread genus of red algae going by the name of Chondria.

Chondria coerulescens, copyright Alan Thurbon.

Chondria is a genus of fifty or more known species of marine algae belong to the Rhodomelaceae, one of the most diverse families of red algae, found in tropical and temperate regions of the world. Species vary in size and are found in a range of habitats from intertidal to subtidal. They may live attached to rock or growing over other seaweeds. Turfs of Chondria may form a significant part of local habitats, but like many smaller red algae they tend not to receive a great deal of attention from humans (I did come across webpages referring to it as a weed in marine aquaria). In the majority of Chondria species, the thallus is erect; more rarely, it grows prostrately against its substrate or free-floating. The thallus is attached to the substrate by a discoid holdfast or by haptera growing from stolons. The greater part of the thallus is filamentous and more or less irregularly branched. The branches may be cylindrical and compressed; the younger branches are often constricted at their bases. The tips of the branches may end in a depression or in a tapering filament. Structure-wise, filaments are solid in cross-section without internal hollows. A central axial cell is surrounded by a ring of five pericentral cells, with the outside of the filament composed of smaller cortical cells.

Like other red algae, Chondria species have a complicated triphasic life cycle. The haploid gametophytes are dioecious: that is, there are separate male and female individuals. Males produce flat, disc-shaped or slightly lobed spermatangia that release male gametes. Female gamete-producing structures grow from the base of lateral filaments on the thallus; fertilised female gametes grow into a diploid, more or less ovoid cystocarp that remains attached to the parent gametophyte. Diploid spores released by the cystocarp grow into independent tetrasporophytes. These produce haploid spores by meiosis that will be released and grow into new gametophytes, and the cycle begins again.

REFERENCE

Womersley, H. B. S. 2003. The Marine Benthic Flora of Southern Australia. Rhodophyta—Part IIID. Ceramiales—Delesseriaceae, Sarcomeniaceae, Rhodomelaceae. Australian Biological Resources Study: Canberra, and State Herbarium of South Australia: Adelaide.

Crystal Butterflies of the Sea

All chains of life in the open ocean are ultimately dependent on plankton. Photosynthetic micro-plankton convert the energy of sunlight into their own stores that are in turn commandered by animal plankton through consumption and digestion. Both animal and photosynthetic plankton provide food sources for larger animals, both plankton and nekton, and even deeper dwelling organisms may take their sustenance from the rain of planktonic corpses settling from above. A wide range of animal lineages may be identified among oceanic plankton, one of the most prominent being the gastropod group known as the Thecosomata.

An orthoconch thecosomatan, Clio pyramidata, copyright Russ Hopcroft.

The Thecosomata are small gastropods, rarely exceeding a couple of centimetres in size at their largest. Many marine molluscs will spend at least part of their lives as planktonic larvae but relatively few mollusc groups have taken the route that the Thecosomata have, remaining part of the plankton through their entire life cycle. They maintain their position in the plankton by means of broad expansions of the foot on either side of the mouth, known as parapodia. The appearance and movement of these parapodia have given the Thecosomata the vernacular name of 'sea butterflies'. They also inspired the name Pteropoda ('wing-foot'), used for a clade that unites the Thecosomata with another group of planktonic gastropods, the Gymnosomata. Historically, many authors have questioned the association of the pteropods, in part because of the differing dispositions of the parapodia in the two component groups (Gymnosomata, commonly known as 'sea angels', have the wings of the parapodia located further back on the body rather than around the mouth). Nevertheless, more recent studies have corroborated pteropod monophyly (Klussmann-Kolb & Dinapoli 2006). The Thecosomata themselves fall between two major sublineages, known as the Euthecosomata and Cymbulioidea (or Pseudothecosomata). Members of the Euthecosomata have well-divided parapodia and the viscera are contained within a delicate, translucent, calcareous shell. In some euthecosomes such as the genus Limacina, this shell is coiled like that of other gastropods, but in others the shell has become straight and bilaterally symmetrical, being conical or globular with lateral projections. Recent phylogenetic analysis suggests that the straight-shelled sea butterflies may form a single monophyletic lineage known as the Orthoconcha* (Corse et al. 2013). In the Cymbulioidea, the parapodia are fused around the front of the animal to form a single swimming plate. Of the three families of cymbulioids, the Peraclidae have a calcareous shell as in the euthecosomes. The Cymbuliidae shed the larval calcareous shell over the course of their development and replace it with a pseudoconch, a hardened gelatinous, slipper-shaped structure that is still secreted by the mantle. In the third family, the Desmopteridae, the shell has been lost entirely.

*In the early days of invertebrate palaeontology, pteropod affinities were suggested for a number of groups of early Palaeozoic conical shells of uncertain affinities, such as the hyoliths and tentaculitoids. It is worth noting that, at the time, the pteropods themselves were often thought to represent a distinct molluscan class independent of the gastropods. Such proposals have long since fallen by the wayside. Not only is there nothing to connect such Palaeozoic forms with modern pteropods but the most superficial of resemblances in overall shape to certain Orthoconcha, but all indications now are that the Orthoconcha themselves did not evolve until some time in the Cenozoic (Corse et al. 2013), leaving a gap of some hundreds of millions of years between them and their erstwhile forebears.

Cymbulia peronii, copyright Vincent Maran.

Live sea butterflies feed on a wide range of organisms, including both micro-algae and other planktonic animals. The ancestral radula is reduced or lost and prey is captured by means of a mucous web, globular in euthecosomes and a funnel-shaped sheet in cymbulioids (Gilmer & Harbison 1986). This web may be absolutely gigantic relative to the animal itself, reaching up to two meters in diameter. While the web is extended, the sea butterfly does not swim actively but hangs suspended in the water column below, drawing food into the mouth by means of tracts of cilia on lobes of the foot. A further mucous array may trail away from the animal containing faecal particles and/or particles rejected as food; this may keep such particles from re-entering the feeding web. Should the animal be disturbed, the mucous web is rapidly ingested or abandoned before swimming away. Sea butterflies have commonly been referred to as suspension feeders but Gilmer & Harbison (1986) noted that a case could potentially be made for considering them as predators. Though micro-algae make up a large proportion of thecosome gut contents, the mucous web allows them to also capture active prey such as copepods that might have otherwise eluded them. It is possible that such prey is in fact more important overall for satisfying the sea butterfly's nutritional requirements. A number of sea butterflies possess brightly coloured mantle appendages that may lure active prey; the faecal trails may also assist in this way.

Limacina helicina, copyright Russ Hopcroft.

Sadly, any discussion of Thecosomata is forced to end on a tragic note. Recent increases in atmospheric carbon dioxide have lead to oceanic waters becoming more acidic than previously, which in turn reduces the concentration of dissolved carbonate. Because carbonate is a vital component of molluscan shells, ocean acidification compromises shell production. Studies of recent thecosome samples show that their shells have become thinner and more porous as acidification increases (Roger et al. 2012). If this trend continues, we may reach a point where shell secretion becomes impossible for these animals, leading to tragic consequences both for the thecosomes themselves and for the countless other organisms ecologically dependent on them. In recent years, concern has been expressed that ecological degredation may mean that we can no longer see butterflies flying in our gardens; their marine analogues are no less vulnerable.

REFERENCES

Corse, E., J. Rampal, C. Cuoc, N. Pech, Y. Perez & A. Gilles. 2013. Phylogenetic analysis of Thecosomata Blainville, 1824 (holoplanktonic Opisthobranchia) using morphological and molecular data. PLoS One 8 (4): e59439.

Gilmer, R. W., & G. R. Harbison. 1986. Morphology and field behavior of pteropod molluscs: feeding methods in the families Cavoliniidae, Limacinidae and Peraclididae (Gastropoda: Thecosomata). Marine Biology 91: 47–57.

Klussmann-Kolb, A., & A. Dinapoli. 2006. Systematic position of the pelagic Thecosomata and Gymnosomata within Opisthobranchia (Mollusca, Gastropoda)—revival of the Pteropoda. Journal of Zoological Systematics and Evolutionary Research 44 (2): 118–129.

Roger, L. M., A. J. Richardson, A. D. McKinnon, B. Knott, R. Matear & C. Scadding. 2012. Comparison of the shell structure of two tropical Thecosomata (Creseis acicula and Diacavolinia longirostris) from 1963 to 2009: potential implications of declining aragonite saturation. ICES Journal of Marine Science 69 (3): 465–474.

The Halictidae: Short Tongues and Waxy Chambers

In an earlier post, I introduced you to the diverse group of bees known as the Halictinae. In this post, I'm going to take a step back and consider the family of bees to which the halictines belong, the Halictidae.

Nomia sp. feeding at a flower, copyright Graham Wise.

The Halictidae are one of the families of what are known as 'short-tongued bees' (the other short-tongued families recognised by Michener, 2007, are the Andrenidae, Colletidae and Stenotritidae). Bees have their mouthparts modified compared to those of other wasps to form a mobile proboscis. The tongue works in three main sections from base to tip. The first two sections work like the upper and lower parts of your arm, or of the arm of a crane, to extend and fold back the proboscis against the underside of the head. The third section beyond these two includes a flexible structure, the glossa, that may be thought of as working like the tongue proper to collect nectar and pollen from the inside of flowers. Somewhat self-explanatorily, this glossa is extremely long and slender in the families of 'long-tongued bees' (the Apidae and Megachilidae) but relatively shorter and broader in short-tongued bees. Naturally, these differences in tongue structure may be reflected in differences in which types of flowers the different types of bees chose to visit. Just to confuse matters, some species of Halictidae may have relatively long proboscides overall, but in this case the extra length is achieved by extending the length of the middle 'arm' section rather than of the glossa itself. The primary features separating Halictidae from the other families of short-tongued bees relate to the structure of particular sclerites incorporated into the proboscis that I'm not going to go into here, but notable points include that the glossa of Halictidae is pointed at the tip and hairs on it are usually branched or bifid at the tips.

Male Halictus tetrazonianellus with proboscis extended (the glossa is the orange structure at the end of the proboscis), copyright Gideon Pisanty.

For the most part, halictids are moderately built bees: neither remarkably slender nor particularly robust. Halictids vary extensively in size: many are small, even minute, but some may be relatively large by bee standards. Coloration is similarly variable, with both metallic and non-metallic species belonging to the family. Members of the genus Nomia (which tend to be relatively large for halictids) often bear contrasting bright bands across the back of the metasoma. Michener (2007) recognised four subfamilies within the halictids: the Rophitinae, Nomiinae, Nomioidinae and Halictinae, with the Halictinae being considerably more diverse species-wise than the other three. Nomioidines have sometimes been included by other authors within the Halictinae but, as there is a general agreement that nomioidines form the sister lineage of the halictines in the strict sense, the question of whether to combine them or not is purely a matter of semantics. Rophitines differ from other halictids in having a relatively large labrum whose tip remains visible between the mandibles when they are closed (other subfamilies have the labrum hidden by the closed mandibles). Rophitines, as well as kleptoparasitic halictines, also have the tip of the labrum simply truncate or rounded; in other subfamilies, the tip of the labrum in females is produced into a distinct process. Rophitines also have the scopa (the array of long pollen-carrying hairs on the hind leg) less developed on the trochanter and femur than on the tibia whereas other subfamilies (excluding, again, kleptoparasitic forms in which the scopa is reduced) generally have the longest scopal hairs on the femur. Nomiines commonly have the third submarginal cell on the wing (if present) as long as the first submarginal cell or at least more than twice the length of the second. In nomioidines and halictines, the third submarginal cell is much shorter. Another notable feature of the last two subfamilies is that the basal vein (the upper of the three veins radiating from the basal midline of the wing) is much more strongly curved near the base than in other bee families; this feature may or may not be discernable in rophitines and nomiines.

Just to show that bees can sometimes get insane: a male of the Colombian species Chlerogella anchicaya, from Engel et al. (2014).

For the most part, halictids construct their nests in burrows in the ground (some halictines nest in rotting wood). Cells of the burrows are generally lined with a wax-like membrane secreted by the parent bee. The membrane is duller and less watertight in Rophitinae than in other subfamilies; one rophitine genus, the southwest North American Protodufourea, appears to not produce such a membrane. Most non-halictine halictids are solitary nesters though some nomiines are known to work communally, and may even show low levels of division of labour. Kleptoparasitism is not known outside the Halictinae.

REFERENCE

Michener, C. D. 2007. The Bees of the World 2^nd ed. John Hopkins University Press: Baltimore.

The Melolonthinae: Chafers and June Bugs

Within the bewildering array that is beetle diversity, one of the more readily recognisable groups is the Scarabaeoidea, the assemblage that includes dung beetles (which, as it happens, are what I currently spend most of my days looking at) and related forms. Members of this group are easily distinguished from other beetles by their distinctive antennae, ending in an asymmetrical club with segments extending to one side like a set of fingers. Several families, many of them further subdivided into subfamilies, are currently recognised within the scarabaeoids. One of the most commonly encountered scarabaeoid subgroups is the subfamily Melolonthinae, commonly known as the chafers.

Green scarab beetles Diphucephala sp., a common genus of day-flying melolonthines here in Australia, copyright Boobook48.

Somewhere in the region of eleven thousand species around the world have been assigned to this grouping; as always, doubtless many more could be recognised by those who take the time. Melolonthinae is generally recognised as a subfamily of the family Scarabaeidae, sharing with other scarabaeids features such an antennal club in which the segments are relatively narrow and can be smoothly pressed against each other, and an exposed pygidium (the last dorsal plate on the abdomen, forming what you might think of as the 'butt plate'). Some authors have recognised melolonthines as a distinct family but this is the less commonly utilised option. Melolonthines belong to a group of mostly plant-feeding subfamilies in which the row of abdominal spiracles bends downwards towards the rear so at least the last pair remains visible when the elytra are closed. Within this cluster, melolonthines tend to be characterised more by lacking the features of the other subfamilies than by distinctive features of their own (more on that in a moment) but general features include mandibles that are not visible when looking down on the top of the head, fore coxae that do not protrude much ventrally, equal claws on each leg (at least on the mid and hind legs) and only one visible spiracle when the elytra are closed. The labrum (the piece at the front of the mouthparts that might be thought of as the insect's top lip) is usually hardened and may be more or less fused with the clypeus (the lower- or foremost section [depending how you look at it] of the front of the head capsule). Many melolonthines are noticeably hairy and/or dull in comparison with other scarabaeoids but others may be shiny and/or metallic in coloration.

Sugarcane white grub beetle Lepidiota stigma, copyright Bernard Dupont.

For the most part, melolonthines are plant-feeders at both larval and adult stages of the life cycle (Lawrence & Britton 1991). The greater part of the active life cycle is taken up by the larval stage which may last for many months (Britton 1957). Larvae mostly live underground, feeding on plant roots and humus. A number of species have made themselves known as significant pests in this manner because of the damage they may inflict on pastures or agricultural crops (the grass grub Costelytra zealandica comes immediately to mind as a good example of this in my native New Zealand). Pupation also occurs underground in subterranean cells and mature adults may remain dormant in these cells for some months waiting for conditions to be just right for emergence. Once they do emerge from the ground, however, the adult life span is quite brief, only lasting a few weeks or even days. Because of this brief emergence, and because their habit of waiting for specific environmental cues means that large numbers may appear seemingly all at once, many species have been awarded vernacular names that reflect their seasonality such as June bug (in the Northern Hemisphere) or Christmas beetle (in the Southern). Some species will feed on foliage as adults, some may visit flowers for pollen and nectar, other particularly short-lived species will not feed as adults at all. The majority of adult melolonthines are active at dusk or night, spending the days sheltered in secluded locations, but a number of flower-feeding species are active by day (Britton 1957).

The infamous grass grub Costelytra zealandica, illustrated by Desmond Helmore.

The classification of melolonthines can charitably be described as an absolute mess. As noted above, we can confidently say that they belong to a clade with other subfamilies of plant-feeding scarabaeids (the Cetoniinae, Rutelinae and Dynastinae) but the features setting them apart from these other subfamilies are likely to be primitive for the group. As such, it comes as little surprise that phylogenetic studies have failed to establish the Melolonthinae as monophyletic (e.g. Eberle et al. 2018; Woolley 2016). However, it seems that no-one thinks that an adequately expansive study that would allow them to be appropriately divvied up has yet been done. Matters are not helped by the absence of a well-established internal classification for melolonthines. Various distinct subgroups can be recognised and between twenty or thirty tribes have been recognised around the world. But the relationships between these tribes remain uncertain, as does the tribal position of many genera. Much of the revisionary work that has been done has been conducted at a regional level only. Thus, for instance, the tribal classification of Australian melolonthines established by Britton (1957) applies only to Australian species and the tribal distinctions Britton recognised may end up falling apart if one attempted to apply them to species from elsewhere. Not that the authors should be criticised for this situation: after all, when one is dealing with over 11,000 species, things rapidly tend to become unmanageable.

REFERENCES

Britton, E. B. 1957. A Revision of the Australian Chafers (Coleoptera: Scarabaeidae: Melolonthinae) vol. 1. British Museum (Natural History): London.

Eberle, J., G. Sabatinelli, D. Cillo, E. Bazzatto, P. Šípek, R. Sehnal, A. Bezděk, D. Král & D. Ahrens. 2018. A molecular phylogeny of chafers revisits the polyphyly of Tanyproctini (Scarabaeidae, Melolonthinae). Zoologica Scripta 48: 349–358.

Lawrence, J. F., & E. B. Britton. 1991. Coleoptera. In: CSIRO. The Insects of Australia: a textbook for students and research workers 2^nd ed. vol. 2 pp. 543–683. Melbourne University Press.

Woolley, C. 2016. The first scarabaeid beetle (Coleoptera, Scarabaeidae, Melolonthinae) described from the Mesozoic (Late-Cretaceous) of Africa. African Invertebrates 57 (1): 53–66.

The Ornithocheyletiini: Making a Living off Birds

In an earlier post, I commented on the carnivorous mites of the family Cheyletidae. These rapacious micropredators are commonly associated with the nests and burrows of terrestrial vertebrates, attacking debris-feeders drawn in by the host's leavings. With such a close association already in place, it should come as little surprise that some lineages within the Cheyletidae have learnt to bypass scavenger predation and go directly to the source, becoming parasites of the vertebrate hosts themselves.

Slide-mounted female of Bakericheyla chanayi (left; scale bar = 50 µm) and nest webs on the skin of a heavily parasitised chaffinch Fringilla coelebs (right), from Filimonova (2013).

One such lineage is the Ornithocheyletiini, members of which are parasites of birds. Like other parasitic cheyletids, ornithocheyletiins have a relatively small, simple gnathosoma (the 'head' of the mite), no eyes, and lack the large, pectinate, claw-like setae found on the palps of free-living predatory cheyletids (instead, the setae at this position are small and smooth though they do still have hooked ends). Ornithocheyletiins are further distinguished from other cheyletids by having particularly large claws at the end of each leg that are overhung by a well developed knob on the end of the tarsus (Bochkov & Fain 2001).

Ornithocheyletiins live on the skin of their bird hosts. In the genera Ornithocheyletia and Bakericheyla, the mites spin a protective web beneath which they live and feed. Members of the tribe have been recorded from a number of bird orders, mostly smaller land birds (Passeriformes, Columbiformes, Piciformes, Coraciiformes, Psittaciformes and Apodiformes). At least one species of Ornithocheyletia was described from the Natal spurfowl Pternistis natalensis, a galliform. Members of the genus Apodicheles are restricted to species of Apodiformes (swifts) but other genera are found on a wider range of hosts. One cosmopolitan species, Bakericheyla chanayi, has been found on hosts of both the orders Passeriformes and Coraciiformes. The exact method of exploiting their host may vary: species of Bakericheyla feed on blood whereas Ornithocheyletia species feed on lymph fluid.

Historically, parasitic cheyletids were treated as a separate family Cheyletiellidae but are now classified with their free-living relatives. The exact relationships between free-living and parasitic cheyletids remain open to question. A morphological phylogenetic analysis of cheyletids by Bochkov & Fain (2001) did recover the parasitic forms as a clade but this result was questioned by the authors themselves. Instead, they suggested that the various parasitic tribes of Cheyletidae represented independent lineages whose shared features represented convergent adaptations to the parasitic lifestyle. The Ornithocheyletiini might, for instance, be compared to tribes such as the Cheletosomatini that inhabit the quills of bird feathers but feed on other quill-inhabiting mites rather than the birds themselves. Did ornithocheyletiins evolve from using birds as hunting grounds to using birds as food, or did they carry their parasitic habits with them from some other host?

REFERENCE

Bochkov, A. V., & A. Fain. 2001. Phylogeny and system of the Cheyletidae (Acari: Prostigmata) with special reference to their host-parasite associations. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, Entomologie 71: 5–36.

Variations on a Tayra

Subspecies can be a funny thing in the world of animal taxonomy. Millions of litres of ink have been spilt over the years arguing over how one defines a species but a lot less has been invested in discussing the nature of subspecies. For some popular species concepts (such as the most popular iteration of the 'phylogenetic species concept'), one might question whether any concept of subspecies could be applied at all (I could suggest some hypothetical situations but just how applicable or practical they are is a further matter). Essentially, most subspecies concepts distill down to 'a population that is distinct enough to warrant recognition but somehow doesn't quite qualify as a species'. Historically, the rank has tended not to receive a lot of usage among animals outside groups subject to particularly high levels of taxonomic attention—most particularly, vertebrates and butterflies—and many currently recognised animal subspecies were first named in days when taxon descriptions tended to be much briefer and taxonomists were under less pressure to explain their reasoning. Because subspecies tend to be, by their nature, vague and difficult to define, and because evaluating them often requires detailed population analysis within a species, these historical subspecies have a tendency to linger, unchallenged, in taxonomic listings. And with that as background, tayras.

Tayra Eira barbara photographed in Peru, copyright eMammal. Photography location would indicate this individual to be either E. b. madeirensis or E. b. peruana.

The tayra Eira barbara is a large mustelid (a member of the family including weasels, otters and badgers) found in warmer regions of Central and South America, its distribution extending down to about the level of the southern edge of Brazil. They are long-bodied but robust animals, kind of looking like a 'roided-up stoat. They grow to a head-body length of two feet or more (up to about 71 centimetres) with a tail about two-thirds as long again. Adult males tend to be a third as large again as females and more muscular around the fore quarters. Comparisons have often been made between tayras and the martens Martes of the Northern Hemisphere and molecular studies confirm a relationship between these two genera, as well as the wolverines Gulo. Closer fossil relatives are known from North America and it seems likely that the tayra originated on that continent then spread southwards. Ruiz-García et al. (2013) suggested that the degree of genetic divergence between tayras found in South America might indicate the species may have arrived there about eight million years ago, before the formation of the Panamanian land bridge. Tayras are not the only species for which this possibility has been suggested; these early arrivals may have reached South America by island-hopping between earlier-emerging segments of the eventual connection.

Tayras are diurnal omnivores, their known diet ranging from fruits to small animals to honey. In captivity, it seems they will accept pretty much anything offered to them. Tayras are the only animals other than humans that have been recorded caching unripe fruit in order to eat it after it finishes ripening. It is still not certain to what degree tayras are solitary or social; though commonly regarded as solitary, they have been recorded hunting howler monkeys in groups (Shostell & Ruiz-Garcia 2013). Tayras are mostly found in forests; in some areas they may adjust to more open habitats but seemingly only under sufferance (Presley 2000). Though not regarded as 'arboreal' per se, tayras are adept climbers. Their well developed carpal vibrissae ('whiskers' on the wrists) presumably contribute to this ability. Their wide distribution and adaptability mean that tayras are not currently regarded as of conservation concern though habitat degradation has reduced their numbers in some areas.

Tayra from Belize, presumably the light-headed Eira barbara senex, from Wikimedia Commons.

The body and tail of tayras are generally dark brown or black with the head being distinctly lighter in coloration (light brown or grey to yellow). Leucistic and albino individuals are not that uncommon (yellow tayras are apparently particularly common in Guyana). A patch of pale coloration, varying from a spot to a broad triangle, is often (but not always) present on the chest and throat. Recent taxonomic listings (e.g. Presley 2000) have recognised seven subspecies of tayra distinguished by coloration. The Mexican Eira barbara senex has a greyish white head with the light coloration extending to dark yellow shoulders and a dark brown body. Eira barbara inserta, found in southern Honduras and Nicaragua, is a dark subspecies with a dark brown head, black body and no throat patch. The Colombian E. b. sinuensis is darker than E. b. senex with the nape a darker brown than the head; it may or may not possess a throat patch. Eira barbara barbara, found in southern Brazil, eastern Bolivia and Paraguay, is lighter than E. b. sinuensis but darker than E. b. senex and has a yellowish throat patch. The northern Brazilian E. b. madeirensis is a chocolate brown with the head slightly lighter than the body; again, a throat patch may or may not be present. The Peruvian and western Bolivian E. b. peruana is similar to the last subspecies but has darker legs and a black tail. Finally, E. b. poliocephala, which has a distribution centred on the Guianas, is similar to E. b. barbara but with a darker yellow throat patch and yellow shoulder patches that sometimes merge with the throat patch to form a complete collar.

Tayra photographed in a zoo in Panama, copyright Dirk van der Made. Being a zoo individual, its origins are a bit more open than the other individuals shown on this page, but Panama is home to Eira barbara inserta and E. b. sinuensis.

Such is the received wisdom as recorded by Presley (2000) but does it accurately reflect population distributions? Ruiz-García et al. (2013) conducted an analysis of mitochondrial genes from tayras representing the five South American subspecies (i.e. excluding E. b. senex and E. b. inserta). They found that of these five subspecies, only E. b. poliocephala (as represented by specimens from French Guiana) could potentially be differentiated genetically. Samples from the ranges of the other four 'subspecies' were intermingled in analyses, leading Ruiz-García et al. to suggest that they should be merged into a single subspecies E. b. barbara (it may also be worth me mentioning that, when I was looking for images to illustrate this post, I had difficulty finding ones in which the supposed differences between subspecies were recognisable). Of course, that leaves the status of the two Central American subspecies undetermined. It may be of note that they seem to be more distinct in appearance than some of the hitherto-recognised South American subspecies but it remains to be seen just how significant this is.

REFERENCES

Presley, S. J. 2000. Eira barbara. Mammalian Species 636: 1–6.

Ruiz-García, M., N. Lichilín-Ortiz & M. F. Jaramillo. 2013. Molecular phylogenetics of two Neotropical carnivores, Potos flavus (Procyonidae) and Eira barbata (Mustelidae): no clear existence of putative morphological subspecies. In: Ruiz-Garcia, M., & J. M. Shostell (eds) Molecular Population Genetics, Evolutionary Biology and Biological Conservation of Neotropical Carnivores pp. 37–84. Nova Publishers: New York.

Shostell, J. M., & M. Ruiz-Garcia. 2013. An introduction to Neotropical carnivores. In: Ruiz-Garcia, M., & J. M. Shostell (eds) Molecular Population Genetics, Evolutionary Biology and Biological Conservation of Neotropical Carnivores pp. 1–34. Nova Publishers: New York.

Actinobacteria: From Monads to Moulds

Perhaps no field of biology was revolutionised more by the advent of molecular phylogenetics in the 1990s than bacteriology. Previously, the higher classification of bacteria and their analysis from an evolutionary perspective had mostly an unattainable dream. Though some major groups such as cyanobacteria and spirochetes possessed biochemical and ultrastructural features that had already set them apart, most bacterial lineages could not be robustly associated with each other much above about the genus level. Molecular phylogenetics changed that, allowing the recognition of a number of genetically supported diverse lineages that, between them, divvied up the greater number of described bacterial species. One of the first of these lineages to be formally recognised was the Actinobacteria.

Colour-enhanced SEM of Streptomyces griseus hyphae, from the Actinomycetes Society of Japan.

Actinobacteria are one of the major lineages of what had already been recognised as the Gram-positive bacteria, so called because they can be stained with crystal violet using the technique developed by Hans Christian Gram. The absorption of this stain is not a mere sartorial manner: it relates to the structure of the cell wall which in typical Gram-positive bacteria has a thick layer of peptidoglycan outside the cell membrane (standard Gram-negative bacteria have a thinner peptidoglycan layer and a second cell membrane overlaying it). In some texts from the 1990s, you may encounter the Actinobacteria being referred to as the 'high G+C Gram-positive bacteria', in reference to a tendency for the genomes of these bacteria to have a relatively high proportion of cytosine and guanine. As it turns out, this feature is not universal within the actinobacterial lineage, but this group remains recognisable by phylogenetic analysis, gene arrangements, and the presence of distinctive indels and inserts in certain genes (Goodfellow et al. 2012).

Many Actinobacteria have a filamentous growth habit and an assemblage of these forms had been recognised even before the molecular revolution as the 'actinomycetes'. However, the diversity of cell forms among the Actinobacteria ranges from spherical cocci to complex branching hyphae forming a fungus-like mycelium. Mycelial forms may form complex sporulating structures, sometimes distinctive enough to make them among the relatively few bacteria that may be identified by their external morphology alone. Their selections of habitat run the gamut but the highest diversity of species may be found in soils under aerobic conditions. Thermophilic and anaerobic Actinobacteria are much less numerous. Most are chemo-organotrophs, obtaining energy from the break-down of organic compounds.

Goodfellow et al. (2012) recognised a division of the phylum Actinobacteria between six classes. The largest of these classes includes by far the majority of actinobacterian species and goes by the name of...wait for it...Actinobacteria. Yes, apparently bacterial nomenclature sees no problem with having 'phylum Actinobacteria' and 'class Actinobacteria' co-existing in the same classification but not referring to the same assemblage of organisms. This. Is. Insane. Even a scan of Goodfellow et al.'s own text provides examples of the name being referred to without the rank explicitly specified. Seriously, how could anyone even begin to consider this acceptable? The remaining classes–Acidimicrobiia, Coriobacteriia, Nitriliruptoria, Rubrobacteria, Thermoleophilia–each contain only a handful of descried species but, as always with bacterial taxonomy, doubtless countless more remain to be described. Members of one of these classes, the Nitriliruptoria, were not described at all before 2009.

It is hardly surprising that a group as diverse as Actinobacteria should include many representatives of significance to humans. For a start, their status as one of the most diverse groups of soil-living bacteria means that they play a major role in decay processes. A number of species are pathogens of plants and animals; perhaps the most notorious of these are Mycobacterium species such as the tuberculosis-causing M. tuberculosis and the leprosy-causing M. leprae. Members of the genus Frankia are found living in nodules on the roots of certain plants where they provide the host with nitrates by fixing nitrogen from the air. Actinobacteria are also massively significant from a biochemical point of view. Actinobacteria species produce close to half of the known microbial bioactive secondary metabolites (Goodfellow e tal. 2012) and about two-thirds of all known antibiotics (Barka et al. 2016). Particularly significant (providing over 80% of all known actinobacterial antibiotics) in this regard are the various species of Streptomyces, which are also among the most morphologically complex Actinobacteria. When conditions under which Streptomyces mycelia are growing begin to decline, cells within the terrestrial vegetative hyphae will begin to die off in order to provide nutrients to support the growth of spore-producing aerial hyphae. As noted by Barka et al. (2016), production of antibiotics at this time would help to prevent other micro-organisms from swooping in to take advantage of this flood of suddenly released nutrients. I hardly need point out how much the discovery of antibiotics changed the pace of medical progress; it might be argued that our modern society simply could not exist without them. Without Actinobacteria, you might not be alive to read this today.

REFERENCES

Barka, E. A., P. Vatsa, L. Sanchez, N. Gaveau-Vaillant, C. Jacquard, J. P. Meier-Kolthoff, H.-P. Klenk, C. Clément, Y. Ouhdouch & G. P. van Wezel. 2016. Taxonomy, physiology, and natural products of Actinobacteria. Microbiology and Molecular Biology Reviews 80 (1): 1–43.

Goodfellow, M., P. Kämpfer, H.-J. Busse, M. E. Trujillo, K. Suzuki, W. Ludwig & W. B. Whitman (eds) 2012. Bergey's Manual of Systematic Bacteriology 2^nd ed. vol. 5. The Actinobacteria, Part A and B. Springer.