The Barrington Tops Stag Beetle

The stag beetles of the Lucanidae are among the most dramatic of all beetles. They are large, glossy, and the adult males often have greatly enlarged mandibles that are used in conflict with other males. As larvae, lucanids are found feeding on rotting wood; adults may feed on nectar and are largely nocturnal. Australia is home to its share of lucanid diversity though the need for suitable food for larvae means that they are mostly restricted to damper regions of the country. As a result, many Australian stag beetles have limited ranges, rendering them vulnerable if not (in this time of rising temperatures and reduced rainfalls) actively endangered. One such species is the Barrington stag beetle Lissapterus tetrops.

Female (left) and major male Lissapterus tetrops, from Coleptera7777.

The Barrington Tops is a mountain range forming part of the Great Dividing Range in New South Wales, direct north from Newcastle. The Barrington stag beetle was described from this range in 1916 by Arthur Lea, one of Australia's most prolific coleopterologists, and is restricted to rain forests at the upper heights of the range. Lissapterus is an endemic Australian genus of flightless stag beetles distinguished from other members of the family by the shape of the antennae. The terminal club that is usually characteristic of the antennae of stag beetles is less defined in Lissapterus with the last few segments of the short antennae being little larger than the rest. Like most other species in the genus, L. tetrops is almost entirely black, only becoming slightly reddish on the legs and antennae. It grows about an inch in length, males and females being not that dissimilar in size. Lissapterus tetrops differs from other species in the genus in lacking foveae on the pronotum and (mostly) on the head, being relatively sparsely punctate dorsally, and having the eye completely divided by a canthus. Major males have long curved mandibles with a pair of teeth internally near the midpoint, placed one above the other. Minor males and females have much smaller, more ordinary looking mandibles.

The natural history of this species is little known but it presumably resembles that of other species in the genus. Adults are found under rotting logs partially buried in the forest floor that provide food for the larvae. Adults may live for a long time, potentially up to about a year, though it is unclear what exactly they feed on. Other species of Lissapterus are mostly found in disjunct locations up and down the Great Dividing Range, their populations presumably becoming separated as the warming and drying of Australia's climate as it moved northwards forced them out of the lowlands. As the climate continues to become warmer and drier, these beetles may find themselves having to retreat higher and higher, and eventually they may find themselves with no further to go.

REFERENCE

Lea, A. M. 1916. Notes on some miscellaneous Coleoptera, with descriptions of new species. Part II. Transactions of the Royal Society of South Australia 40: 272–436, pls 32–39.

Oribatid Time Again

The oribatid mite genus Neogymnobates was first recognised from Illinois in 1917. Since then, the genus has been found to be more widespread in North America and has also been described from Korea and Tibet. Species of Neogymnobates are known from arboreal habitats or in association with fallen wood, and live as grazers of micro-vegetation such as lichens.

Neogymnobates luteus, copyright Monica Young.

Neogymnobates belongs to the Ceratozetidae, a diverse family of oribatids whose characteristic features include a tutorium (a projecting tooth-like structure) on the side of the prodorsum and immovable pteromorphs on either side of the front of the notogaster. Neogymnobates has the lamellae on either side of the prodorsum widely separated from each other and connected by a transverse translamella at the front. There are thirteen pairs of setae on the notogaster and four pairs of porose areas (Balogh & Balogh 1992). One species, N. marilynae of British Columbia and Washington State, is known to have an extra unpaired porose area on the midline near the rear of the notogaster (Behan-Pelletier 2000), an unusual feature among oribatids but one whose significance is uncertain). Their legs end in three claws, a feature that (as I've commented before) correlates with their arboreal habits.

Half a dozen species of Neogymnobates have been recognised to date (Subías 2004). The species are distinguished by features such as the size and appearance of the setae, and the development of the prodorsal lamellae and translamella. One Korean species, N. parvisetiger, has been awarded its own subgenus Koreozetes due to its particularly small, almost indiscernable notogastral setae and its anteriorly notched rather than rounded rostrum (Aoki 1974). Most species are only known from limited ranges except one, N. luteus, for which separate subspecies have been recognised in northern North America and in Korea. Rather unexpectedly, this last species has also recently been recorded from Zanzibar (Ermilov & Khaustov 2018). This is a remarkable range increase, both geographically and ecologically (enough so that I can't help feeling it would benefit from double-checking) that raises the possibility that we may yet have a lot to learn about this oribatid genus.

REFERENCES

Aoki, J. 1974. Oribatid mites from Korea. I. Acta Zoologica Academiae Scientiarum Hungaricae 20 (3–4): 233–241.

Balogh, J., & P. Balogh. 1992. The Oribatid Mites Genera of the World vol. 1. Hungarian Natural History Museum: Budapest.

Behan-Pelletier, V. M. 2000. Ceratozetidae (Acari: Oribatida) of arboreal habitats. Canadian Entomologist 132: 153–182.

Ermilov, S. G., & A. A. Khaustov. 2018. A contribution to the knowledge of oribatid mites (Acari, Oribatida) of Zanzibar. Acarina 26 (2): 151–159.

Subías, L. S. 2004. Listado sistemático, sinonímico y biogeográfico de los ácaros oribátidos (Acariformes, Oribatida) del mundo (1758–2002). Graellsia 60 (número extraordinario): 3–305.

Predators of the European Eocene

Among mammals in today's modern fauna, the role of terrestrial carnivore is dominated by members of one particular lineage, known (appropriately enough) as the Carnivora. But travel back in time to the Eocene period, roughly 56 to 34 million years ago, and you'll find a range of now extinct groups sharing that role. This post is looking at one of those groups, the proviverrines.

The Proviverrinae are a subgroup of the Hyaenodontidae, one of the two families of carnivores commonly associated as the creodonts. I've discussed creodonts before, and the overhanging question of whether they form a coherent evolutionary group. Currently, my impression is that most mammal palaeontologists seem inclined to think that hyaenodontids and oxyaenids probably do not share an immediate common ancestry. However, nor is there any clear idea of what else either group may relate to.

Skull of Cynohyaenodon cayluxi, photographed by Ghedoghedo.

Historically, proviverrines have been treated as the basal grade from which other groups of hyaenodontids were derived with representatives known from Europe and North America. However, a phylogenetic analysis of early hyaenodontids by Solé (2013) lead to a division of the 'proviverrines' between three monophyletic subfamilies: the Proviverrinae proper, the Sinopinae and the Arfiinae. Under this system, the Proviverrinae are a uniquely European group. As is standard in mammalian palaeontology, proviverrines (in the strict sense) are distinguished from other hyaenodontids by features of the teeth. Notable among these is the presence of a double root on the first lower premolar of most proviverrines; other hyaenodontids have a single root on this tooth.

The earliest proviverrines are known from the very beginning of the Eocene (Solé et al. 2014). Current thinking is that their ancestors probably immigrated into Europe around this time from Africa. The Late Paleocene Tinerhodon disputatum from northern Africa resembles a proviverrine in overall appearance but was probably more basally placed in respect to hyaenodontids as a whole. The name 'Proviverra' can be read as 'early civet' and while proviverrines were not related to modern civets (which are, of course, true carnivorans) this is probably not a bad indication of the overall appearance of their original appearance. These were very small animals, probably less than 100 g in body weight, and probably had a fairly generalised diet of small vertebrates and invertebrates. At first, proviverrines seem to have been restricted to southern Europe, what is now Spain and the very southernmost part of France. Northern Europe was inhabited by the Arfiinae and Sinopinae, as well as species of Oxyaenidae (the other 'creodont' family). Sinopinae were also found in southern Europe and may have excluded the proviverrines from evolving larger size. However, the other hyaenodontids and oxyaenids went extinct in Europe not to long after the beginning of the Eocene. A turnover in the mammalian fauna of North America around this time appears to be due to a cooling of the climate; though the evidence for climate cooling is less clear in Europe, it seems reasonable that it was going through similar changes. With their competitors out of the picture, the proviverrines rapidly diversified into the regions and niches that had been left unoccupied.

Lesmesodon edingeri, photographed by Ghedoghedo.

The largest proviverrines, members of the genera Prodissopsalis, Paenoxyaenoides and Matthodon, would eventually reach weights of close to twenty kilograms, about as large as a medium-sized dog. They would also diversify in their habits. Members of the genera Oxyaenoides and Paenoxyaenoides were cursorial hypercarnivores, their dentition specialised for a diet almost exclusively of meat*, like that of a modern cat. Matthodon and Quercytherium, in contrast, were genera whose dentition showed more adaptations for cracking hard materials such as bone. They may have had lifestyles more like those of hyaenas, with Matthodon (which combined adaptations for hypercarnivory and bone-cracking) perhaps being more of an active hunter than Quercytherium.

*These two genera also provide an excellent example of the role of convergent evolution in the evolution of mammalian carnivores. Their appearance to other hypercarnivorous hyaenodontids was such that it was only recently that they were recognised as proviverrines rather than members of other subfamilies no longer thought to have been found in Europe. And not only are they remarkably convergent on other subfamilies, the phylogenetic analysis of proviverrines by Solé et al. (2014) suggests that they're not even directly related to each other within that clade.

Proviverrines remained the dominant mammalian carnivores in Europe for about the next twenty million years but then went into a sharp decline. This reversal of fortunes may have been due to the increasingly cool, dry conditions developing at this time, and/or it may have been related to competition from the first true carnivorans arriving in Europe. The larger, more specialised proviverrines disappeared rapidly when their time came. The last surviving genus, Allopterodon, was a small form, little more than one kilogram in weight, and had a generalised dentition indicating a relatively unspecialised diet. This may have been a return to something like the lineage's original form but it would not save it: by the end of the Eocene, the proviverrines would be completely extinct.

REFERENCES

Solé, F. 2013. New proviverrine genus from the Early Eocene of Europe and the first phylogeny of Late Palaeocene–Middle Eocene hyaenodontidans (Mammalia). Journal of Systematic Palaeontology 11 (4): 375–398.

Solé, F., J. Falconnet & L. Yves. 2014. New proviverrines (Hyaenodontida) from the early Eocene of Europe; phylogeny and ecological evolution of the Proviverrinae. Zoological Journal of the Linnean Society 171: 878–917.

Anabaena

Way back in the day, back when blogging was actually a thing that people paid a modicum of attention to (as opposed to its current status as a way for old fogies to scream into the void), I used to have a link to this blog at some indexing/promotional site that advertised its coverage as including, among other things, "multicellular bacteria". Now, when one is considering micro-organisms, the line between 'multicellular' and 'colonial' is a vague one. Nevertheless, there are certain lineages of colonial bacteria in which individual cells within the colony may become differentiated in a way that renders them incapable of surviving on their own. A definite argument could therefore be made that such colonies have crossed the boundary into true multicellularity.

Light microscopy image of Anabaena circinalis at 400–600×, copyright Imre Oldal. The lighter coloured cells are heterocysts.

A particularly diverse such bacterial lineage is the heterocyst-forming members of the Cyanobacteria, the blue-green algae, of which the genus Anabaena is a widespread representative. Anabaena species grow as long strings of cells referred to as trichomes. These trichomes are often embedded within a layer of dense mucilage though Anabaena species lack the hard external sheath produced by some other cyanobacterial genera. The cells within a trichome are more or less spherical, cylindrical or barrel-shaped and are not differentiated from each other in such a way that a trichome could be said to have a 'base' or 'apex'. Trichomes may be planktonic or benthic, depending on the species. Benthic species are capable of slow movement and the cells at each end of a trichome are conical in shape. Planktonic species are immobile; the cells contain gas vesicles to provide buoyancy and those at the ends of the trichomes are not differentiated from the remainder (Boone et al. 2001).

The aforementioned heterocysts are specialised cells within the trichome of Anabaena species and related Cyanobacteria that are capable of fixing molecular nitrogen from the surrounding environment (trichomes growing in a medium providing a surfeit of previously fixed nitrogen will not produce heterocysts). The enzymes responsible for nitrogen fixation require the absence of oxygen to function and so heterocysts devlop a thick, multi-layered envelope outside the original cell wall. They also lose the capacity to conduct their own photosynthesis. As a result, the heterocyst becomes completely dependent on the surrounding cells in the trichome for the production of carbohydrates, supplying them in turn with nitrogen incorporated into amino acids (Golden & Yoon 2003). Anabaena species will generally have individual heterocysts separated by about ten to twenty photosynthetic cells; the heterocysts are most commonly at internal positions within the trichome though they may occasionally occupy a terminal position. One species usually included in Anabaena, A. azollae, lives in close association with the small, floating aquatic ferns of the genus Azolla. Anabaena azollae trichomes are contained within cavities on the underside of the leaves. Heterocyst formation is much more extensive than in free-living Anabaena with fully 20–30% of the cells being heterocysts. Developing sporocarps on the Azolla also become infested with A. azollae akinetes (thick-walled cells that act as resting spores) that are picked up by emerging embryos so the symbiont is transmitted down through the generations (Peters 1989). Because of this association, Azolla growth is often encouraged as a source of nitrogen for crops grown in water such as rice. Other Anabaena species, conversely, are less welcomed by humans due to their production of harmful toxins.

The advent of molecular studies of bacterial phylogeny has confirmed the integrity of the heterocyst-formers as a monophyletic lineage within the Cyanobacteria. However, the internal classification of this clade is far more uncertain. Though well recognised from a morphological standpoint, molecular studies have questioned whether the genus should continue to be recognised in its current form. A study by Gugger et al. (2002) comparing planktonic strains of Anabaena with another genus Aphanizomenon, distinguished by differences in cell and trichome shape, found that the two were well and truly intermingled genetically. Some of the features hitherto used in cyanobacterial classification may be affected by the environment. For instance, Anabaena azollae will, under certain conditions, produce hormogonia, small, motile chunks of trichome that function as disseminules. Hormogonia production is supposed to be a feature of another cyanobacterial genus, Nostoc, rather than Anabaena (and it is worth noting that other Cyanobacteria involved in symbioses with plants have been assigned to Nostoc) (Peters 1989). There is a need out there for an extensive investigation into the relationships of these genera, and maybe a thorough re-analysis of their definitions.

REFERENCES

Boone, D. R., R. W. Castenholz & G. M. Garrity (eds) 2001. Bergey’s Manual of Systematic Bacteriology 2^nd ed. vol. 1. The Archaea and the Deeply Branching and Phototrophic Bacteria. Springer.

Golden, J. W., & H.-S. Yoon. 2003. Heterocyst development in Anabaena. Current Opinion in Microbiology 6: 557–563.

Gugger, M., C. Lyra, P. Henriksen, A. Couté, J.-F. Humbert & K. Sivonen. 2002. Phylogenetic comparison of the cyanobacterial genera Anabaena and Aphanizomenon. International Journal of Systematic and Evolutionary Microbiology 52: 1867–1880.

Peters, G. A., & J. C. Meeks. 1989. The Azolla-Anabaena symbiosis: basic biology. Annual Review of Plant Physiology and Plant Molecular Biology 40: 193–210.