Field of Science

The Phaeogenini: Widdle Icky Newmans

Female Diadromus collaris on a pupa of a diamondback moth Plutella xylostella, from here.


The ichneumons are perhaps the best-known family of parasitic wasps. Most people will have come across a description of the classic ichneumon lifestyle at at least some point: a female lays an egg in the larva of another insect, which then hatches into a wasp larva that eats out its hosts insides before emerging at maturity, leaving an empty husk behind. It is easy to see why ichneumons have become the poster children for parasitoid wasps everywhere: not only are they one of the most diverse wasp families, they can often be dramatic in appearance, growing to remarkable sizes. However, not all ichneumons are giants.

Female Eparces quadriceps, copyright Tom Murray.


The tribe Phaeogenini includes some of the smallest ichneumons, with some species being only a few millimetres long (Rousse et al. 2013). They belong the the subfamily Ichneumoninae, within which they are distinguished from most other tribes by their possession of round rather than elongate spiracles on the petiole. They are otherwise quite diverse in appearance, and Gauld (1984) suggested that they may be a polyphyletic assemblage of species that had convergently evolved their common features as a result of their small size. However, molecular phylogenetic analyses have largely supported the monophyly of the Phaeogenini (e.g. Quicke et al. 2009). One genus, Lusius, tends to be placed elsewhere among the ichneumons, but this is probably due to its having an anomalous 28S rDNA sequence with a number of deletions; Quicke et al. (2009) implied that they thought it more likely to still be a true phaeogenin. Some authors have suggested a relationship between phaeogenins and another unsual small ichneumon genus Alomya (in which case, due to the vagaries of priority, the name of this tribe becomes the Alomyini), but molecular analysis does not support this association.

Dirophanes fulvitarsis encounters a smaller wasp (perhaps a figitid?). Copyright J. K. Lindsey.


Like other members of the Ichneumoninae, the Phaeogenini are parasitoids of Lepidoptera: specifically, in accord with their small size, micro-lepidoptera. However, identification of the hosts of phaeogenins can be difficult, as they tend not to attack them until after the host has formed a cocoon (Diller & Shaw 2014). Where hosts are known, they are often borers in plant stems or leaves. The phaeogenin Diadromus collaris attacks the diamondback moth Plutella xylostella, a significant pest on brassicas and related plants. As such, it has been widely introduced around the world to help in the control of this pest.

REFERENCES

Diller, E., & M. R. Shaw. 2014. Western Palaearctic Oedicephalini and Phaeogenini (Hymenoptera: Ichneumonidae, Ichneumoninae) in the National Museums of Scotland, with distributional data including 28 species new to Britain, rearing records, and descriptions of two new species of Aethecerus Wesmael and one of Diadromus Wesmael. Entomologist's Gazette 65: 109–129.

Gauld, I. D. 1984. An Introduction to the Ichneumonidae of Australia. British Museum (Natural History).

Quicke, D. L. J., N. M. Laurenne, M. G. Fitton & G. R. Broad. 2009. A thousand and one wasps: a 28S rDNA and morphological phylogeny of the Ichneumonidae (Insecta: Hymenoptera) with an investigation into alignment parameter space and elision. Journal of Natural History 43 (23–24): 1305–1421.

Rousse, P., S. van Noort & E. Diller. 2013. Revision of the Afrotropical Phaeogenini (Ichneumonidae, Ichneumoninae), with description of a new genus and twelve new species. ZooKeys 354: 1–85.

Metabiantes

Metabiantes leighi, from Schönhofer (2008).


The handsome fellow in the photo above represents a species of the genus Metabiantes, currently the largest recognised African genus of harvestmen in the family Biantidae. Metabiantes species are currently recognised from the greater part of sub-Saharan Africa, with species known from as far north as Kenya on the east coast and the Ivory Coast in the west (Staręga 1992). The bulk of study on this genus, however, has focused on the South African species. Kauri (1961) divided the southern African species between two groups based on genital morphology. Schönhofer (2008) recorded that the widespread Transvaal species M. leighi inhabits leaf litter in evergreen forests. It seems to inhabit slightly drier microhabitats than other harvestmen in the area.

Compared to many other harvestmen, Metabiantes species do not show a high degree of sexual dimorphism. The males' chelicerae tend to be a bit larger, and consequently the front of the carapace tends to be a bit broader (Schönhofer 2008). In some species, the metatarsus of the males' second leg bears a series of teeth (Lawrence 1937). While I haven't found any explicit investigation of the role that such modifications play, the fact that the second legs in harvestmen fill a sensory function (being used much like the antennae in insects) provides a likely suggestion.

REFERENCES

Kauri, H. 1961. Opiliones. In: Hanström, B., P. Brinck & G. Rudebeck. South African Animal Life: Results of the Lund University Expedition in 1950–1951 vol. 8 pp. 9–197. Almqvist & Wiksell: Uppsala.

Lawrence, R. F. 1937. The external sexual characters of South African harvest-spiders. Transactions of the Royal Society of South Africa 24 (4): 331–337.

Schönhofer, A. L. 2008. On harvestmen from the Soutpansberg, South Africa, with description of a new species of Monomontia (Arachnida: Opiliones). African Invertebrates 49 (2): 109–126.

Staręga, W. 1992. An annotated check-list of Afrotropical harvestmen, excluding the Phalangiidae (Opiliones). Annals of the Natal Museum 33 (2): 271–336.

I Said Primrose-Willows, Darling


The plant shown in the photo above (copyright Forest and Kim Starr) is Ludwigia octovalvis, commonly known (along with other species in the same genus) as primrose-willow. This is a very common plant in tropical and subtropical regions around the world; indeed, it is so widespread that we have little idea where in the world it originated*. The name 'primrose-willow' derives, of course, from its combination of primrose-like flowers with willow-like leaves, but it is no close relation to either. Primrose-willows belong to the Onagraceae, the same plant family as evening primrose or fuchsias. Ludwigia octovalvis is a shrubby plant, sometimes growing up to four metres in height. Lower parts of the stem may become woody with age, but the greater part of the plant is herbaceous. It prefers to grow in damp habitats, in swampy soil or alongside streams, even rooted in ponds. The seeds are minute and easily spread by water or mixed in with other materials. They are also durable: Raven (1977) refers to the possibility of propagating Ludwigia from seeds preserved in herbarium specimens.

*Which, if one were of a panbiogeographical bent, might be taken to indicate that it has survived unchanged since the Triassic at least.

Ludwigia octovalvis may even grow as floating mats upon the surface of water. The floating roots then produce spongy, upright branches called aerophores. These have been interpreted as floatation devices, but the plant is apparently perfectly buoyant without them. It is more likely that they allow oxygen to reach the waterlogged roots. The lower part of the stem may also become covered in aerenchyma, porous tissue that also aids in the diffusion of gases. If conditions dry up and the plant becomes rooted in the ground, the aerophores disappear and the roots resume their normal rootly business.

Close-up of flower of Ludwigia octovalvis, copyright Bob Peterson.


Primrose-willows are generally toxic to humans. In the usual way, I have come across references to Ludwigia octovalvis being used folk-medicinally, mostly to help with ailments of the digestive tract such as diarrhoea and worms. A quick look through Google Scholar indicates that this has lead to a certain degree of pharmaceutical research, but so far this doesn't seem to have lead to much major commercial application. At the present point in time, the main economic impact of Ludwigia octovalvis is as a weed. It can grow mixed in with fields of crops such as rice and taro, or particularly lush patches of primrose-willow may clog up waterways. On the flipside, I did find this summary of the species that notes that, "Its yellow flowers add a splash of color to areas often devoid of colorfully flowering plants".

REFERENCES

Raven, P. H. 1977. Onagraceae. Flora Malesiana, ser. I, 8 (2): 98–113.

The Diprotodontids: Marsupials Go Large

Reconstruction of Diprotodon optatum by Anne Musser, from Long et al. (2002). Offhand, running a search for Diprotodon through Google Image brings up some true horrors of digital imagery.


Prior to the arrival of humans, the Australian fauna included many strange, and often dramatic, animals that are sadly no longer with us. Enormous python-like snakes, monitors that would have made a Komodo dragon look underwhelming, drop bears, and of course the notorious demon duck of doom. But among the most iconic of Australia's extinct fauna were the Diprotodontidae, heavyset herbivores that included the largest of all marsupials. Diprotodontids are sometimes referred to in the popular press as giant wombats, but this is a bit misleading: though more closely related to wombats than any other living marsupials, they were a quite distinct group of animals (besides, they shared their world with actual giant wombats that reached the size of a cow). A potentially more appropriate descriptor that has been suggested is 'marsupial rhinos', though at least some diprotodontids were decidedly not like rhinos either.

Skull of Zygomaturus trilobus in Museum Victoria, photographed by Nigel Waring.


The most famous of the diprotodontids was also the first to be described, and indeed the first fossil mammal of any kind described from Australia. Diprotodon optatum, named by Richard Owen in 1838, was the largest of the diprotodontids, sometimes standing more than six feet tall at the shoulder, and reaching estimated weights of around two and a half tonnes. At the time of human arrival, Diprotodon would have been one of the dominant herbivores in the arid central region of Australia. A number of species of Diprotodon have been named over the years, but a review of the genus by Price (2008) recognised only a single species, with the two different size classes present probably representing the different sexes. In the less arid coastal regions, Diprotodon was replaced by various species of the slightly smaller (but still formidably sized) genus Zygomaturus (Long et al. 2002). The best known species in this genus, Z. trilobus, bore a distinctive large bony boss on the snout, giving its skull a profile reminiscent of a cartoon bear. Two other diprotodontid species that would have come into contact with humans are known from the Pleistocene of montane New Guinea, Hulitherium tomasettii and Maokopia ronaldi. Both these species were smaller than the mainland Australians, being about the 100 kg mark. Maokopia has been interpreted as a grazer, while Hulitherium has been seen as a browser, and suggested as a direct analogue of the Asian giant panda (Long et al. 2002).

Reconstruction of Hulitherium tomassettii as a panda analogue, by Peter Schouten.


The broader record of diprotodontids goes back to the Oligocene, with two main lineages being recognised, the Diprotodontinae and Zygomaturinae. Of the species referred to above, all but Diprotodon optatum are zygomaturines. The two groups are primarily distinguished by their dentition, with the premolars being generally more complex in zygomaturines than diprotodontines. In both lineages, the earlier members were smaller: Long et al. (2002) describe a number of genera as 'sheep-sized'. The smallest known diprotodontid, the late Oligocene Raemeotherium yatkolai, they describe as 'lamb-sized'. Black et al. (2012) estimated the weight of the middle Miocene Nimbadon lavarackorum as abut 70 kg. They also suggested that it was an adept climber, in a similar manner to the modern koala, making it the largest known arboreal mammal from Australia. It might seem odd to picture an animal of this size up in a tree, even allowing for the higher density of the canopy in Australia's Miocene rainforests. However, there are larger arboreal mammals alive even today: male orangutans, for instance, may weigh over 100 kg.

Reconstruction of a climbing pair of Nimbadon lavarackorum (adult and juvenile) by Peter Schouten, from Black et al. (2012).


Interestingly, Nimbadon is not placed as a particular basal diprotodontid in the phylogeny of zygomaturines presented by Mackness (2010). As other related marsupial families, such as koalas or thylacoleonids (marsupial lions), also include climbers, it would not be unreasonable to consider such habits plesiomorphic for diprotodontids as a whole. The 'rhino-like' appearance of the later giants would then be something of a novelty, an adaptation to the drier conditions and more open woodlands that arose at the end of the Miocene. If we are to regard the diprotodontids as marsupial rhinos, then we must consider the possibility of rhinos in trees.

REFERENCES

Black, K. H., A. B. Camens, M. Archer & S. J. Hand. 2012. Herds overhead: Nimbadon lavarackorum (Diprotodontidae), heavyweight marsupial herbivores in the Miocene forests of Australia. PLoS ONE 7 (11): e48213. doi:10.1371/journal.pone.0048213.

Long, J., M. Archer, T. Flannery & S. Hand. 2002. Prehistoric Mammals of Australia and New Guinea: One hundred million years of evolution. University of New South Wales Press: Sydney.

Mackness, B. S. 2010. On the identity of Euowenia robusta De Vis, 1891 with a description of a new zygomaturine genus. Alcheringa 34 (4): 455–469.

Price, G. J. 2008. Taxonomy and palaeobiology of the largest-ever marsupial, Diprotodon Owen, 1838 (Diprotodontidae, Marsupialia). Zoological Journal of the Linnean Society 153: 389–417.

The Cancellothyridids: A Modern Success Story

Northern lamp shels Terebratulina septentrionalis, from Oceana.


As has been noted on this site more than once before, brachiopods are a group of animals probably more familiar to the student of palaeontology than of zoology. From the brief gloss that tends to be their only coverage in textbooks, one might be forgiven for thinking them all but inconsequential in the modern fauna. But where conditions suit them (usually sheltered locations where low levels of light and water flow favour their slow metabolisms over the higher energy requirements of bivalves), brachiopods can still be abundant, and even dominant.

One of the most diverse families of brachiopods in the modern fauna is the Cancellothyrididae. Cancellothyridids first make their appearance in the Jurassic, becoming widespread in the Cretaceous (Cooper 1973). Members of this family have shells with a large foramen (the opening at the rear of the shell through which passes the pedicel or stalk by which the brachiopod is attached to its substrate), usually with the deltidial plates surrounding the foramen greatly reduced. The main defining feature of the Cancellothyrididae is the structure of the brachidium, the skeletal structure that provides the support for the base of the lophophore, the tentacle-like feeding structures. In cancellothyridids, the two sides of the brachidium coalesce in the middle to form a tube.

Dorsal valve of the Cretaceous cancellothyridid Cricosia filosa in (A) lateral, (B) ventral and (C) posterior views, from Cooper (1973), showing the tubular brachidium.


The brachidium does not extend into the arms of the lophophore, which are instead strengthened by unattached spicules. The tubular shape of the brachidium distinguishes the Cancellothyrididae from the closely related family Chlidonophoridae, whose members share the large posterior foramen but have the two sides of the brachidium open in back. Cooper (1973) recognised two subfamilies of cancellothyridids, the living Cancellothyridinae and the Cretaceous Cricosiinae; the cricosiines have the tubular section of the brachidium longer and narrower than the cancellothyridines.

Modern cancellothyridids are found in the Indo-Pacific and the North Atlantic, but seem to be absent from the South Atlantic. The majority of living species are included in the widespread genus Terebratulina, with the other living genera all having restricted distributions in the Indo-Pacific. However, a molecular phylogenetic analysis of species of Terebratulina and the Australian genus Cancellothyris by Lüter & Cohen (2002) indicated that both Atlantic Terebratulina and Cancellothyris were nested within Pacific Terebratulina. Paraphyly of the widespread genus would also correlate with its palaeontological distribution: while the other genera are known only from the Recent fauna, Terebratulina has a fossil record dating right back to the origins of the cancellothyridids in the Jurassic (Muir-Wood 1965). Lüter & Cohen (2002) tentatively suggested the possibility of a North Pacific origin for Terebratulina (and, by implication, for Cancellothyrididae as a whole), with dispersal to the North Atlantic occurring through the gap between North and South America before formation of Central America. Their preference for this option rather than the alternative of dispersal through the Tethys (the seaway that once separated Africa from Eurasia) was based on their estimate via molecular clock of a separation of about 100 million years between the Atlantic and Pacific species, supposedly too early for the Tethys option. However, it must be stressed that their sampling of even modern cancellothyridid diversity was not comprehensive. A trans-Tethys dispersal of cancellothyridids may also be indicated by the presence of the fossil genus Rhynchonellopsis in the lower Oligocene of northern Europe (Muir-Wood 1965). Of course, there is no inherent reason why cancellothyridids could not have travelled in both directions!

REFERENCES

Cooper, G. A. 1973. Fossil and recent Cancellothyridacea (Brachiopoda). Tohoku Univ., Sci. Rep., 2nd Ser. (Geol.), Special Volume 6: 371–390.

Lüter, C., & B. L. Cohen. 2002. DNA sequence evidence for speciation, paraphyly and a Mesozoic dispersal of cancellothyridid articulate brachiopods. Marine Biology 141: 65–74.

Muir-Wood, H. M. 1965. Mesozoic and Cenozoic Terebratulidina. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt H. Brachiopoda vol. 2 pp. H762–H816.

Sympiesis

Female Sympiesis, copyright Lyle J. Buss.


We often imagine that parasites select their hosts largely on the basis of type: one parasite prefers caterpillars, for instance, while another prefers flies. However, sometimes what is important is not so much what type of host a parasite attacks, as where they find it. The wasp in the photo above represents Sympiesis, a sizeable genus (the Universal Chalcidoidea Database lists over 130 species) of microscopic parasitoid wasps found worldwide. The majority of Sympiesis larvae attack the larvae of Lepidoptera, but others feed on the larvae of Diptera. A few have been recorded as hyperparasitoids, attacking the larvae of other parasitic wasps. The main thing that all hosts of Sympiesis have in common, though, is that they are all found in secluded, vegetative habitats: either mining in leaves, or in retreats formed by rolling or tying leaves (sometimes boring in stems). Depending on species, Sympiesis larvae may be either ectoparasites or endoparasites: those species feeding on leaf-rolling hosts tend to be ectoparasites, while those targeting leaf-miners are endoparasites (Miller 1970).

Sympiesis is a genus of the chalcid family Eulophidae. Eulophids used to be the subject of some disagreement between myself and a colleague of mine about their ease of recognition. Eulophids are a diverse group in appearance, coming in a bewildering array of shapes and colours. However, I have always maintained that they are nevertheless readily recognisable. Whatever their appearance, eulophids seem to always a distinctive stamp of 'eulophid-ness'. They tend to be slender, relatively soft-bodied wasps, often with a flat top to the gaster. Most identification guides will tell you to look out for their four-segmented tarsi (as opposed to the five-segmented tarsi of most other chalcid wasps); eulophid tarsi are rendered even more recognisable by the point that, though they have less segments than the tarsi of other chalcids, they are not any shorter so the individual tarsal segments are all relatively long. The features distinguishing Sympiesis from other eulophid genera are, of course, finer and require fairly close examination: notably, they have relatively few dorsal setae (only four on the scutellum) (Bouček 1988). As far as I know, they are mostly metallic green in coloration.

Male Sympiesis, showing branched antennae, from here.


As with many eulophids, males of Sympiesis usually differ from females in having long branches on the antennae. However, the first species of the genus to be described, the European Sympiesis sericeicornis, is distinctive in that these antennal branches are much reduced so that the males' antennae look little different from the females' (if you look very closely, they still have just a bit of a finger on each of the middle antennal segments). This led historically to a fair bit of confusion in the recognition of Sympiesis, with many species originally being placed in segregate genera (often with tongue-twistery compound names such as Asympiesiella or Sympiesonecremnus; thank you again, Alexandre Girault). Even now, the status of Sympiesis with regard to some related smaller genera could do with further investigation; we may yet see it grow again.

REFERENCES

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

Miller, C. D. 1970. The Nearctic species of Pnigalio and Sympiesis (Hymenoptera: Eulophidae). Memoirs of the Entomological Society of Canada 102 (Suppl. S68): 5–121.

The Velvet Spiders: High Society

Communal web of Stegodyphus, copyright V. B. Whitehead.


In John Wyndham's novel Web (published in 1979, some ten years after Wyndham's own death), a group of settlers attempting to establish a utopian society on a remote Pacific island find themselves besieged by spiders. Contrary to the usual solitary habits of their kind, the spiders of Web have evolved a social structure like that of wasps or ants, and form roving packs that can overwhelm and devour animals many times their size. Fortunately for us, no such rapacious beasts exist in real life. But there are social spiders, even if they do not present a threat to anything much larger than a big insect.

The social habit has evolved in spiders on a number of occasions, but is perhaps best developed in some species of the genus Stegodyphus. This is a genus of the family Eresidae, commonly known as the velvet spiders. Eresids are small spiders, distinguished from most others by their subrectangular carapace with the front edge produced into a hood above the chelicerae (Miller et al. 2012). They have the full spider complement of eight eyes, with the posterior median eyes generally enlarged and directed forwards. Together with their covering of plush fur (hence the name 'velvet' spiders), this gives them an appearance distinctly reminiscent of some sort of carnivorous muppet.

Male Eresus cinnaberinus, copyright Ferenc Samu.


There are nine currently recognised genera of eresids, though only Stegodyphus includes social species. The family is mostly restricted to the Old World, with a single species Stegodyphus manaus known from Amazonian Brazil. A second species, S. annulipes, was originally described as Brazilian, but has since been collected from Israel and appears to have been mislabelled (Miller et al. 2010). Members of the temperate Eurasian genus Eresus are commonly known as 'ladybird spiders' as males often have a striking abdominal colour pattern of black spots on a red background. Most eresids live in silken tubes under objects such as stones or underground, whereas Stegodyphus species construct their webs in vegetation (Miller et al. 2012).

Mature Stegodyphus lineatus feeding hatchlings, copyright jorgemotalmeida.


The communal webs of social Stegodyphus species may extend for several metres. When an animal becomes trapped in the web, as many spiders as are able to reach it swarm over, all biting and salivating as they can. As a result, the members of the colony are able to kill and digest much larger prey than they could otherwise handle alone. Sociality in Stegodyphus appears to have arisen as an extension of the parental care found in other eresids. Females of both Stegodyphus and Eresus will regurgitate food for newly hatched young (Kullmann 1972). In social Stegodyphus, young are cared for communally and females will feed the young of their nest-mates as well as their own. Eventually, the young begin feeding directly on the caring female herself, draining her haemolymph to the point of rapid death. Again, in social Stegodyphus, this fate awaits all mature adults in the colony, and there is no overlap between generations (Schneider 2002). After the death of their mother, juvenile Eresus and non-social Stegodyphus remain in a group until they are closer to maturity; social behaviour could have arisen through a simple delay in the time of dispersal.

REFERENCES

Kullmann, E. J. 1972. Evolution of social behavior in spiders (Araneae; Eresidae and Theridiidae). American Zoologist 12: 419–426.

Miller, J. A., A. Carmichael, M. J. Ramírez, J. C. Spagna, C. R. Haddad, M. Řezáč, J. Johannesen, J. Král, X.-P. Wang & C. E. Griswold. 2010. Phylogeny of entelegyne spiders: Affinities of the family Penestomidae (NEW RANK), generic phylogeny of Eresidae, and asymmetric rates of change in spinning organ evolution (Araneae, Araneoidea, Entelegynae). Molecular Phylogenetics and Evolution 55: 786–804.

Miller, J. A., C. E. Griswold, N. Scharff, M. Řezáč, T. Szűts & M. Marhabaie. 2012. The velvet spiders: an atlas of the Eresidae (Arachnida, Araneae). ZooKeys 195: 1–144.

Schneider, J. M. 2002. Reproductive state and care giving in Stegodyphus (Araneae: Eresidae) and the implications for the evolution of sociality. Animal Behaviour 63: 649–658.