Ormyrids: Attacking the Gall

Female of Ormyrus nitidulus, photographed by Penny Metal.

Everyone knows about God's supposed inordinate fondness for beetles, but it is my opinion that the true poster children for insect diversity should be the wasps. Wasps, admittedly, do not have as many described species as beetles (there are some who suspect that the actual number of species of wasp may eventually be higher, but that remains in the realm of the hypothetical). However, many species of beetle are very difficult to distinguish except by skilled specialists, being otherwise small, brown, and conservative. Wasps, on the other hand, come in a kaleidoscopic array of colours and shapes, such that even a novice may look at an array of wasps (see the top of this post, for instance) and be immediately struck by the disparity.

An unnamed species of Ormyrus, photographed by Simon van Noort.

The Chalcidoidea, commonly referred to as chalcids, are one of the largest subgroups of wasps, a clade of mostly small (often minute), mostly parasitoid wasps (some have larvae that feed on plants). Members of the Ormyridae, one of the commonly recognised families of chalcids, are generally about two to three millimetres long. Ormyrids are distinguished from other chalcids by their robust body form, with a strongly sclerotised gaster* (ormyrids and perilampids tend to look like steroid-abusing pteromalids). The segments of the gaster are usually ornamented by rows of coarse foveae (pits) that give it a distinctive rough appearance, though in some species these foveae are less obvious or are replaced by longitudinal ribs (Bouček 1988). Ormyrids are often recorded in association with plant galls, but are not gall-formers themselves: rather, they are parasites of the insect larvae that formed the galls (usually flies or other wasps). Some ormyrids are associated with figs and parasites of fig wasps.

*Wasp researchers generally refer to the sections of the body behind the head by terms such as 'mesosoma' and 'gaster' (or metasoma), rather than 'thorax' and 'abdomen'. This is because the section of the body that is the first segment of the abdomen in other insects has become the last segment of the mesosoma in Hymenoptera.

A female of Ormyrus on a knopper gall (a type of gall that develops when a developing acorn of the pedunculate oak Quercus robur is parasitised by the cynipid wasp Andricus quercuscalicis), photographed by Tristram Brelstaff.

There are about 125 known species of ormyrid (making this a quite small family by chalcid standards) according to the Universal Chalcidoidea Database (an absolutely wonderful resource). However, there isn't yet a really good classification system within the family. Ormyrids vary to a fair degree, particularly in the form of the antennae or the ornamentation of the gaster, but most authors have placed almost all species within the single genus Ormyrus. Attempts to subdivide this diverse group (for instance, that of Doğanlar, 1991, who recognised four genera of ormyrids with three subgenera within Cyrtosoma) have suffered from not considering the full range of ormyrid diversity. Some of the Australian forms referred to by Bouček (1988), for instance, may not be placeable in Doğanlar's system. Until an appropriately large-scale review is conducted, most authors will probably continue to recognise an all-purpose Ormyrus.

REFERENCES

Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).

Doğanlar, M. 1991. Systematic positions of some taxa in Ormyridae and descriptions of a new species of Ormyrus from Turkey and a new genus in the family (Hymenoptera, Chalcidoidea). Türkiye Entomoloji Dergisi 15 (1): 1-13.

An Introduction to Malaconothrus

Specimen of Malaconothrus monodactylus, from the Biodiversity Institute of Ontario (M. mollisetosus was listed as a synonym of M. monodactylus by Subías 2004).

Malaconothrus is a genus of about sixty species of oribatid mites found almost worldwide. The only continent from which Malaconothrus species have not yet been recorded is Antarctica, though M. translamellatus is known from Île Amsterdam in the subantarctic Indian Ocean (Subías 2004). Malaconothrus species specialise in damp habitats, often found among moss or in marshes. They are small yellowish mites, often covered with an ornamented cerotegument (a thick waxy cuticle) (Luxton 1987). They are also parthenogenetic, with females laying unfertilised eggs that hatch into more females.

Schematic drawing of Malaconothrus monodactylus (minus legs) from Luxton (1987).

Malaconothrus belongs to a group of oribatids called the Crotonioidea (often also referred to as nothroids). Because crotonioids are long-lived, slow-breeding and poor dispersers, they have received a certain amount of attention as potential indicators of environment health. In the context of the post linked to above, crotonioids are part of the Desmonomata, so outside the large oribatid clade of the Circumdehiscentiae or Brachypylina*. They have broad genital and anal plates that take up the greater part of the underside behind the legs (Balogh & Balogh 1992). Malaconothrus and its most closely related genus, Trimalaconothrus, differ from other crotonioids in having a band of soft cuticle across the underside between the levels of the second and third legs, i. e. they are dichoid rather than holoid (Norton 2001). They also lack bothridia, specialised enlarged sensory setae that are present at the rear of the prodorsum in the majority of oribatids. Malaconothrus and Trimalaconothrus are distinguished from each other by Malaconothrus having one claw at the end of each leg, while Trimalaconothrus has three. Subías (2004) divided Malaconothrus between two subgenera: in Cristonothrus, the dorsum is divided by a pair of longitudinal ridges, but in Malaconothrus sensu stricto there are no dorsal ridges.

*For some reason, oribatids seem to suffer something of an embarrassment of higher taxon names.

Dorsal and ventral view of Malaconothrus rohri from Balogh (1997). Note the pattern of ridges on the dorsum characteristic of Cristonothrus.

Malaconothrus has suffered a certain degree of confusion about its type status (Luxton 1987). When he first established Malaconothrus in 1904 (as a subgenus of Lohmannia), Berlese only listed one name in explicit combination, Lohmannia (Malaconothrus) egregia. However, in his discussion of this species, Berlese compared it to the pre-existing Nothrus monodactylus in a manner that implied the latter should also be included in his new subgenus. Subsequent authors have disagreed over whether L. egregia or N. monodactylus should be regarded as the type species of Malaconothrus, though more recent authors have settled on the latter.

REFERENCES

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

Balogh, P. 1997. New species of oribatids (Acari) from the neotropical region. Opusc. Zool. Budapest 29-30: 21-30.

Luxton, M. 1987. Mites of the genus Malaconothrus (Acari: Cryptostigmata) from the British Isles. Journal of Natural History 21 (1): 199-206.

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.

The State of Peridinium

As I've said on many an occasion before, dinoflagellates are complicated. Obscenely complicated. So when my search for a random post topic brought up the dinoflagellate genus Peridinium, I approached it with a certain amount of dread. If you're not familiar with dinoflagellates, the diagram at the top of this post will explain a lot of the terminology I'm about to use.

Specimen of Peridinium cf. cinctum, photographed by Kate Howell. Peridinium cinctum is the type species of Peridinium.

Peridinium is a genus that has been used in the past to cover a wide range of freshwater and marine dinoflagellates. For a long time, the standard diagnosis of Peridinium was that it contained species with four apical plates (the ring of plates at the front of the cell when it is moving), seven precingular plates (the ring of plates in front of the cingulum), five postcingular plates and two antapical plates (Carty 2008). However, the genus has been divided by differences in the shape and arrangements of the plates making up the theca into a number of species groups, and more recent studies have concurred that these species groups are not all closely related to each other. While support remains low in most phylogenetic studies of dinoflagellates, and many species remain to be analysed, indications are that all of the marine species and many of the freshwater species are not true Peridinium (Horiguchi & Takano 2006; Logares et al. 2007). As it currently stands, the probably monophyletic Peridinium sensu stricto includes two species groups, the P. cinctum and P. willei groups, and is exclusively freshwater. As well as the characters mentioned above, true Peridinium species have three apical intercalary plates between the apical and precingular plates, five cingular plates, and ridges on all the plates forming an areolate pattern. They are also united by a distinct combination of which plates in the front section of the organism break off when the theca is shed during cell division (Craveiro et al. 2009). The two species groups differ in the exact arrangement of the plates anterior to the cingulum: in the P. willei group they are symmetrical relative to the dorsal-ventral axis, vs asymmetrical in the P. cinctum group. Slightly surprisingly, though the presence or absence of an apical pore was one of the first characters used to subdivide the genus Peridinium, Peridinium sensu stricto includes both species with (such as P. bipes) and without (such as P. cinctum and P. willei).

SEM image of Peridinium gatunense, by Pawel Owsiany.

Peridinium species are photosynthetic, with a much-lobed chloroplast that ramifies through the cell. One species, identified by Hickel & Pollingher (1988) as P. gatunense, has been intensely studied as the creator of annual blooms in Lake Kinneret in Israel.

REFERENCES

Carty, S. 2008. Parvodinium gen. nov. for the Umbonatum Group of Peridinium (Dinophyceae). Ohio Journal of Science 108 (5): 103-107.

Craveiro, S. C., A. J. Calado, N. Daugbjerg & Ø. Moestrup. 2009. Ultrastructure and LSU rDNA-based revision of Peridinium group Palatinum (Dinophyceae) with the description of Palatinus gen. nov. Journal of Phycology 45: 1175-1194.

Hickel, B., & U. Pollingher. 1988 Identification of the bloom-forming Peridinium from Lake Kinneret (Israel) as P. gatunense (Dinophyceae). British Phycological Journal 23 (2): 115-119.

Horiguchi, T., & Y. Takano. 2006. Serial replacement of a diatom endosymbiont in the marine dinoflagellate Peridinium quinquecorne (Peridiniales, Dinophyceae). Phycological Research 54: 193-200.

Logares, R., K. Shalchian-Tabrizi, A. Boltovskoy & K. Rengefors. 2007. Extensive dinoflagellate phylogenies indicate infrequent marine–freshwater transitions. Molecular Phylogenetics and Evolution 45 (3): 887-903.

Mosses Have a Place for Reproduction

A Rhizogonium photographed in the Philippines by Leonardo L. Co.

The Rhizogoniaceae are a family of mosses found in tropical and subtropical parts of the world, with a concentration of diversity in the Southern Hemisphere. Many species in the family are epiphytic; in particular, many show a preference for growing on the trunks of tree ferns (O'Brien 2007). The family has been defined by features such as sharply toothed, usually bistratose (i.e. with two cell layers) leaves and sporophytes located in the basal half of the erect stems, but molecular studies have indicated that the Rhizogoniaceae in the broad sense are para- or polyphyletic, and for this post I'll be using Rhizogoniaceae in a more restricted sense, corresponding to the 'clade C' of O'Brien (2007), including genera such as Rhizogonium, Cryptopodium, Calomnium, Goniobryum and Pyrrhobryum. One member of the Rhizogoniaceae, Pyrrhobryum dozyanum, is often used in moss gardens (it appears that there may also be a moss doing the rounds under this name in the European aquarium trade, though I haven't found anything to confirm whether this species, also being referred to as "Mayaca fern" or "Indonesiae bogoriensis", is actually P. dozyanum. Many bryophytes and other such plants in the aquarium trade have been misidentified, sometimes dramatically so).

View under microscope of leaf of Pyrrhobryum dozyanum, showing the toothed margins characteristic of Rhizogoniaceae. Image from here.

Most attention on Rhizogoniaceae from an evolutionary point of view has focused on what they might say about the relationship between acrocarpy and pleurocarpy. To explain what these terms mean, we'll start with the following diagram (from here):

Like other plants, mosses go through an alternation of generations, with both haploid and diploid multicellular stages. The haploid stage of the life cycle, the gametophyte, is the leafy green part of the moss. The gametophyte produces perichaetia, whorls of modified leaves within which the gamete-producing organs are contained. When a female gamete is fertilised, the resulting diploid zygote grows into the sporophyte, the brown thread-like structure you will often see growing out of a moss. The sporophyte produces haploid spores that will be dispersed to grow into new leafy gametophytes.

The diagram above shows an acrocarpous moss, in which the perichaetium is produced at the end of a growing branch of the gametophyte. Other mosses, however, are pleurocarpous, with perichaetia produced on the side of a branch. Whether a moss is acrocarpous or pleurocarpous is one of the first things a botanist will look at when attempting to identify it. However, many Rhizogoniaceae do not easily fall on either side of the acrocarpous/pleurocarpous distinction. They are what is called cladocarpous: the perichaetia are produced at the ends of small side-branches. However, lest any moss enthusiasts accuse me of overly simplifying things, I must point out that a great deal has been written on the exact distinctions between acrocarpous vs cladocarpous vs pleurocarpous. Like so many distinctions in nature, there are examples that blur the distinction between these states. As the perichaetia-bearing side-branches in a cladocarpous moss get progressively shorter, they become less and less distinguishable from pleurocarpy. In light of this, recent authors have suggested that the distinction between cladocarpy vs pleurocarpy should be defined by whether or not the side-branch bearing a perichaetium also bears normal vegetative leaves. If it only bears perichaetial leaves, then it is pleurocarpous: by this definition, some Rhizogoniaceae (including the genus Rhizogonium) are truly pleurocarpous (Bell & Newton 2007).

Goniobryum subbasilare, photographed by David Tng.

The vast majority of pleurocarpous mosses belong to a clade called the Hypnanae, which is massively speciose (probably about half of living mosses are hypnanaens). Because the hypnanaen mosses are so successful, there is a lot of interest in their relationships with other mosses. And as it turns out, the Rhizogoniaceae (with their combination of cladocarpous and pleurocarpous members) are closely related to the Hypnanae. Indeed, the Hypnanae are nested within the older, paraphyletic grade referred to the Rhizogoniaceae (O'Brien 2007). The acrocarpous state is the plesiomorphic one for mosses, with cladocarpy evolving in numerous lineages. Pleurocarpous mosses, it seems likely, have then evolved from cladocarpous ancestors, though either a number of times or with a number of reversals.

REFERENCES

Bell, N. E., & A. E. Newton. 2007. Pleurocarpy in the rhizogoniaceous grade. In: Newton, A. E., & R. S. Tangney (eds) Pleurocarpous Mosses: systematics and evolution pp. 41-64. CRC Press.

O'Brien, T. J. 2007. The phylogenetic distribution of pleurocarpous mosses: evidence from cpDNA sequences. In: Newton, A. E., & R. S. Tangney (eds) Pleurocarpous Mosses: systematics and evolution pp. 19-40. CRC Press.

The Tuna-Lizards

The classic ichthyosaur Ichthyosaurus communis, from here.

Ichthyosaurs have long been one of the most famous examples of convergent evolution. These Mesozoic marine reptiles, as any textbook will tell you, evolved a body form similar to that of modern dolphins and sharks, and presumably held a similar niche as fast-swimming apex predators. But interesting as that might be, it's certainly not all there is to be said about ichthyosaurs.

The classic ichthyosaurs that said textbooks will usually depict are members of the clade Thunnosauria that first appeared in the upper Triassic (Thorne et al. 2011). Thunnosaurs differ from other ichthyosaurs in having a relatively short tail, shorter than the trunk, and hindfins that are much shorter than (usually less than half as long as) the forefins (Maisch & Matzke 2000). The name 'Thunnosauria' appropriately means 'tuna-lizards': as with modern tunas, the compact body of the thunnosaurs indicates greater specialisation for more powerful, tail-driven swimming.

Cast of the short-beaked Ichthyosaurus breviceps, from Charmouth Heritage Coast Centre.

In the Lower Jurassic, thunnosaurs are represented by the genera Ichthyosaurus and Stenopterygius, though the known fossil record for the former is earlier than that of the latter. Both genera are represented by hundreds (if not thousands in the case of Stenopterygius) of known specimens from Europe (Motani 2005): primarily England for Ichthyosaurus, Germany for Stenopterygius. Stenopterygius grew up to 4 m in length; Ichthyosaurus would have been somewhat smaller (Maisch & Matzke 2000). One species of Ichthyosaurus, I. breviceps, stands out for its particularly short and robust rostrum in comparison to other species. Another potential Lower Jurassic thunnosaur is Hauffiopteryx typicus, which also has a distinctively small rostrum, but in this case a particularly fine and slender one (Maisch 2008).

Mounted skeleton of Ophthalmosaurus icenicus, from the British Natural History Museum.

During the Lower Jurassic, the thunnosaurs were among a number of ichthyosaur lineages present. By the time of the Upper Jurassic, all surviving ichthyosaurs (with one possible exception*) belonged to a single thunnosaur lineage, the Ophthalmosauridae. Unfortunately, for most of the Middle Jurassic the ichthyosaur fossil record is missing, and a gap of more than ten million years separates Stenopterygius from Ophthalmosaurus. The only break in this gap is the Argentinan Chacaicosaurus cayi, which sits a few million years later than Stenopterygius. Intriguingly, Chacaicosaurus is not only intermediate in age, it is intermediate in morphology: while its skull is similar to that of Ophthalmosaurus, its forefin is more similar to that of Stenopterygius. As noted by Maisch & Matzke (2000), "It appears as if Chacaicosaurus cayi is one of the rare forms that are true structural intermediates".

*The possible exception is the Upper Jurassic Nannopterygius enthekiodon, some features of which suggest that it occupies a more basal Stenopterygius-grade position (Maisch & Matzke 2000). Unfortunately, it has not yet been adequately described and included in a formal phylogenetic analysis. This is rather frustrating: Nannopterygius promises to be a quite distinctive animal, with greatly reduced fins and long spinal processes on the anterior tail vertebrate.

Reconstruction of Platypterygius bannovkensis, by Olorotitan. Platypterygius was the latest surviving ichthyosaur genus.

The ophthalmosaurids survived from the late Middle Jurassic to the early Upper Cretaceous. Ophthalmosaurus had a slender rostrum with reduced dentition, while other genera such as Brachypterygius and Platypterygius had higher, more robust rostra with their full complement of teeth. Some ophthalmosaurids grew very large: Platypterygius reached up to 9 m. The name Ophthalmosaurus means 'eye lizard', and reference to the large eyes of this ichthyosaur seems to be de rigeur for any popular book in which it features, together with some speculation that it may have been a nocturnal hunter. However, a quick scan through the various ichthyosaur skulls illustrated by Maisch and Matzke (2000) indicates that ichthyosaur eyes were generally large. Those of Ophthalmosaurus were not the largest; the eyes of Eurhinosaurus longirostris are particularly ridiculous, with orbits filling almost the entire side of the cranium! So perhaps the question should not be why Ophthalmosaurus had large eyes, but why those ichthyosaurs without large eyes had reduced them.

REFERENCES

Maisch, M. W. 2008. Revision der Gattung Stenopterygius Jaekel, 1904 emend. von Huene, 1922 (Reptilia: Ichthyosauria) aus dem unteren Jura Westeuropas. Palaeodiversity 1: 227-271.

Maisch, M. W., & A. T. Matzke. 2000. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 298: 1-159.

Motani, R. 2005. True skull roof configuration of Ichthyosaurus and Stenopterygius and its implications. Journal of Vertebrate Paleontology 25 (2): 338-342.

Thorne, P. M., M. Ruta & M. J. Benton. 2011. Resetting the evolution of marine reptiles at the Triassic-Jurassic boundary. Proceedings of the National Academy of Sciences of the USA 108 (20): 8339-8344.

The Source

I was taking some photos today of the new house to send to my parents in New Zealand, when I thought I might take some extras to put up here and demonstrate the current state of my office. You never know, someone might be interested. I'm somewhat anachronistic in that I do still largely work from printed material rather than pdfs, and the ghosts of a thousand trees probably haunt my workspace.

The person who is able to identify the most of the books visible in these photos wins the grand prize of having identified the most books in these photos. Of course, most of my reference collection is not quite so photogenic:

Most of my papers lurk in large filing cabinets, while the boxes contain copies of particularly lengthy papers and out-of-print or otherwise unobtainable books that I haven't yet gotten ring-bound like the ones on the shelves.

Hat-tip to Darren Naish, of whom this post is something of a blatant rip-off.

Tetragraptines

Colonies of Tetragraptus quadribrachiatus, from the University of Oslo.

In preparation for this post, I have been attempting to develop an understanding of graptolite branching patterns. This is not something that should be attempted lightly, if at all. If anything in this post seems confused, it's because it is.

The Tetragraptinae were a group of graptolites that lived during the Lower Ordovician, and formed part of the early radiation of planktonic graptoloids. In one of the earlier phylogenetic (or at least quasi-phylogenetic) classifications of graptolites, that of Fortey & Cooper (1986), the tetragraptines (including the genera Tetragraptus and Pseudophyllograptus) were recognised on the basis of what was called the 'Tetragraptus serra proximal type'. In an earlier post, I explained how graptolite colonies grew as a series of branching zooids (individuals). The colony section for each individual zooid is called the theca, and graptolite workers usually refer to the thecae in discussions rather than the zooids (as the zooids are generally not preserved in fossils). A developing colony starts with the initial larval zooid, called the sicula. Out of the side of the sicula grows the first mature theca, which is referred to as th1¹ (the sicula is not included in the thecal count because it has a different growth pattern from the sequential thecae). The second theca, th1², then buds off from th1¹. The third theca to arise is th2¹, then th2², then th3¹, and so on and so forth. If all these bud in a simple sequence, the colony is not branching. However, if one or more of these basal thecae is what is known as a dicalycal theca (it produces two daughter thecae instead of just one), the colony branches. In most tetragraptines, th1² is a dicalycal theca, as are its two daughter thecae, so the mature colony has four branches. The basal canals of th1² and th2¹ crossing over the sicula, plus the proximal part of th2², make the lower part of the proximal region very robust: this massiveness is what characterises the Tetragraptus serra proximal type. Other characters listed by Fortey & Cooper (1986) as synapomorphies for the Tetragraptinae, reclined colony branches and a reduction in the number of branches, were also found in other lineages.

Proximal region of Tetragraptus bigsbyi, showing robust morphology, together with diagrammatic representation of thecal connections in early colony. From Bulman (1970).

The Tetragraptinae were one of a number of groups of Ordovician graptolites with four-branched colonies, though other taxa lacked the T. serra proximal region. In a phylogenetic analysis of graptoloids, Maletz et al. (2005) identified four-branched graptoloids as a single clade that they called the Tetragrapta. This is in contrast to Fortey & Cooper (1986), who placed these taxa at a number of places in the graptoloid tree. The analysis of Maletz et al. (2005) differed from that of Fortey & Cooper (1986) in being a computational analysis rather than being constructed 'by hand'. Some characters given high weight by Fortey & Cooper (1986), such as the presence of a structure called a virgella, were found to be less significant by Maletz et al. (2005). However, in some regards the coverage of the latter study was less complete than the earlier. Most notable for the present post is that Fortey & Cooper (1986) had also included 'Dichograptus' solidus in the Tetragraptinae. This species apparently also has the T. serra proximal region, but also has more than four branches in the colony. It is possible that its inclusion in a computational analysis would weaken the association of four-branched graptoloids as a clade.

By the end of the Ordovician, the graptoloid lineages with multi-branched colonies were extinct. There have been numerous suggestions for why this may have happened—buoyancy issues or competition between zooids are among the front runners—but for the rest of graptoloid history, simplicity would become the watchword.

REFERENCES

Bulman, O. M. B. 1970. Graptolithina with sections of Enteropneusta and Pterobranchia. In Treatise on Invertebrate Paleontology Part V 2nd ed. (C. Teichert, ed.) pp. V1-V149. The Geological Society of America, Inc.: Boulder (Colorado), and the University of Kansas: Lawrence (Kansas).

Fortey, R. A., & R. A. Cooper. 1986. A phylogenetic classification of the graptoloids. Palaeontology 29: 631-654.

Maletz, J., J. Carlucci & C. E. Mitchell. 2009. Graptoloid cladistics, taxonomy and phylogeny. Bulletin of Geosciences 84 (1): 7-19.