Australasian Mistletoes

Australia is home to a fair diversity of parasitic mistletoes, nearly ninety species in all. In a previous post, I described one of our most remarkable species, the terrestrial Nuytsia floribunda. But, of course, the remaining species occupy the more typical aerial mistletoe habitat, growing directly attached to the branches and trunk of their host. And within Australia, the most diverse mistletoe genus is Amyema.

Amyema pendula growing on Acacia, copyright Groogle.

Species of Amyema are found in southeast Asia, Australia, and islands of the Pacific as far east as Samoa. A revision of the genus by Barlow (1992) recognised 92 species with the greatest diversity in the Philippines, Australia and New Guinea. They are found in a range of habitats, from wet rainforests to arid woodlands. Some species (particularly in arid habitats) grow from a single central haustorium (the structure by which a parasitic plant attaches to and draws nutrients from its host); others (particularly rainforest species) produce numerous haustoria from runners stretching along the outside of the host. Most rainforest species tend to have low host specificity but those growin in arid habitats may be more likely to restrict themselves to a small number of host species. Those species which restrict themselves to a single host may have leaves closely resembling that host, making them difficult to spot within the host canopy.

Amyema species are mostly characterised by their flowers which are typical borne in triads with the triads often then being clustered in loose umbels. In some species, the triads are reduced to pairs or single flowers. The flowers themselves are bird-pollinated and have four to six long petals that are generally separated right to the base, at most forming only a very short tube at the base of the flower. The flowers are hermaphroditic though a study of some Australian species by Bernhardt et al. (1980) found a tendency for anthers to mature before the stigma, presumably to prevent self-pollination.

Flowers of Amyema miquelii, copyright Kevin Thiele.

Not surprisingly, attention on mistletoes in Australia has commonly been focused on their effect on host trees. Mistletoe infestations may be heavy and have commonly been blamed for tree mortalities. However, one might legitimately question whether mistletoes themselves cause fatalities: does mistletoe infestation cause a host tree to become unhealthy, or are unhealthy trees more vulnerable to infestation by mistletoes? A study by Reid et al. (1992) on Amyema preissii infesting Acacia victoriae found that, though there was a relationship between mistletoe volume and host mortality, they were unable to demonstrate that mistletoe removal improved host survival. Conversely, such a positive effect was found by Reid et al. (1994) for removal of Amyema miquelii growing on two Eucalyptus species (the methods of this latter study also include the great line, "the highest mistletoes had to be shot down with a .22 rifle"). However, the authors remained conservative when it came to advocating mistletoe removal. Not only do a number of native birds and other animals depend on mistletoes for food and nesting sites, mistletoe removal can be an expensive process and may not itself be devoid of adverse effects on the host tree. Where rates of infestation are not extreme, it may still be better to just live and let live.

REFERENCES

Barlow, B. A. 1992. Conspectus of the genus Amyema Tieghem (Loranthaceae). Blumea 36: 293–381.

Bernhardt, P., R. B. Knox & D. M. Calder. 1980. Floral biology and self-incompatibility in some Australian mistletoes of the genus Amyema (Loranthaceae). Australian Journal of Botany 28: 437–451.

Reid, N., D. M. Stafford Smith & W. N. Venables. 1992. Effect of mistletoes (Amyema preissii) on host (Acacia victoriae) survival. Australian Journal of Ecology 17: 219–222.

Reid, N., Z. Yan & J. Fittler. 1994. Impact of mistletoes (Amyema miquelii) on host (Eucalyptus blakelyi and Eucalyptus melliodora) survival and growth in temperate Australia. Forest Ecology and Management 70: 55–65.

Moles, Tortoises, Calves and Cowries

The cowries of the family Cypraeidae are one of the most readily recognisable groups of tropical and subtropical shells. Their distinctive shape (with no spire and a long narrow aperture running the length of the shell) and highly polished appearance are guaranteed to catch the eye (to the extent that one species, the money cowry Monetaria moneta, famously has a history of being used as a form of currency in many regions around the Indian Ocean). Though there are a large number of cowry species found around the world, they tend to be similar enough to each other that, until relatively recently, many authors would place all within a single genus Cypraea. This approach has fallen out of fashion in more recent years and, indeed, the current favoured approach divides the family between several subfamilies. One such subgroup is the subfamily Luriinae.

Live mole cowry Talparia talpa, copyright Juuyoh Tanaka.

In a phylogenetic analysis of the cowries, Meyer (2003) recognised the Luriinae as including two tribes, the Luriini and Austrocypraeini. This concept of Luriinae was essentially based on molecular phylogenetic analysis though it was also corroborated by radular morphology (with a reduced shaft on all teeth). The underside of the shell in luriines is mostly smooth with the 'teeth' being restricted to alongside the aperture. As in other cowries, the mantle is widely extended and mostly covers the shell in life (this is how cowry shells stay so shiny). In most luriines, the mantle is covered by warty papillae. In species of the genus Luria these warts are obsolete (Schilder 1939) but they are particularly prominent in the Indo-west Pacific mole cowry Talparia talpa. Members of the Luriinae vary greatly in size: the Pacific Annepona mariae is only a centimetre or two in length but the tortoise cowry Chelycypraea testudinaria of the Indian and western Pacific Oceans grows to ten centimetres or more. Species of Luriini have shells that are banded in coloration, with three or four broad dark bands divided by narrower light bands. The Austrocypraeini are most commonly marked with brown speckles or blotches on a pale background; these blotches may be irregular as in Chelycypraea testudinaria or more regularly rounded as in Annepona mariae. The calf cowry Lyncina vitellus of the Indo-Pacific is marked with white spots on a brown background, and some species or forms of Austrocypraeini may have coloration patterns more like the banded arrangement of Luriini.

Lynx cowry Lyncina lynx, copyright Patrick Randall.

My impression is that species of Luriinae tend to be mostly nocturnal, sheltering in crevices in coral reefs during the day before emerging to feed at dusk (the name of the aforementioned mole cowry is, I suspect, more likely to refer to its appearance in some way than to any actual burrowing habit). Though I haven't (though a cursory search, at least) found any reference to species of Luriinae in particular being endangered, a number of cowries in general have been threatened by overcollecting for their shells. Certainly, luriines would be subject to the broad range of threats that currently hang over coral reefs and their inhabitants anywhere in the world.

REFERENCES

Meyer, C. P. 2003. Molecular systematics of cowries (Gastropoda: Cypraeidae) and diversification patterns in the tropics. Biological Journal of the Linnean Society 79: 401-459.

Schilder, F. A. 1939. Die Genera der Cypraeacea. Archiv für Molluskenkunde 71 (5–6): 165–201.

Aidanosagitta

If you've ever spent time, as I certainly did back in my undergraduate days, thumbing through textbooks of animal diversity, then you may be familiar with the so-called 'minor phyla'. These are those isolated subgroups of the animal kingdom that are phylogenetically remote from other such taxa but which, owing to low diversity and/or low exposure, are commonly not regarded as warranting more than a cursory summary in the end-papers of some other more prominent group. One such group is the arrow worms (Chaetognatha), and for this post I'm focusing on the arrow worm genus Aidanosagitta.

Arrow worms are marine micropredators, slender-bodied animals mostly growing to a bit less than a centimetre in length but generally not seen without the aid of a microscope due to being mostly transparent. The greater number of arrow worm species are planktonic and could be described as superficially fish-like with paired fins running down the side of the body. The front of the head forms a flexible hood within with the mouth is flanked by elongate spines, used for grasping prey.

Two Aidanosagitta species: A. bella (above) and A. venusta (below), from Kasatkina & Selivanova (2003).

A review of the arrow worms by Tokioka (1965) recognised fifteen genera within the phylum. Aidanosagitta is one of the planktonic genera; currently, about thirty species are recognised within this genus. Distinguishing features of the genus include a firm, muscular body, diverticula arising from the gut, and the posterior pair of fins being located on the 'tail' section of the body (behind the anus) (Kasatkina & Selivanova 2003).

The majority of Aidanosagitta species are found in tropical and subtropical waters, most commonly in inlets and lakes. An exception is provided by a number of species found in colders waters adjoining the north-west Pacific, in the Sea of Okhotsk and the Sea of Japan (Kasatkina & Selivanova 2003). Species are distinguished by features such as the sizes of the fins, the size and position of the large subenteric ganglion, and the presence and extent of a layer of spongy tissue that may partially cover the outside of the body. Particular species of arrow worms may be associated with particular bodies of water (such as particular currents) and changes in their distribution may indicate changes in the greater environment.

REFERENCES

Kasatkina, A. P., & E. N. Selivanova. 2003. Composition of the genus Aidanosagitta (Chaetognatha), with descriptions of new species from shallow bays of the northwestern Sea of Japan. Russian Journal of Marine Biology 29 (5): 296–304.

Tokioka, T. 1965. The taxonomical outline of Chaetognatha. Publications of the Seto Marine Biological Laboratory 12 (5): 335–357.

Apiocera: Flower-Loving Flies that Don't Particularly Care for Flowers

The insect world is full of animals that may be striking in appearance but about which we know relatively little. Such, for instance, are the flies of the genus Apiocera.

Male Apiocera, copyright Chris Lambkin.

Apiocera is a genus of a bit over 130 known species of relatively large flies, about half an inch to an inch in length, that are found in hot, arid habitats in disparate parts of the world: western North America, southern South America, southernmost Africa and Australia. Records of Apiocera from Borneo and Sri Lanka were regarded by Yeates and Irwin (1996) as probably errors. They are similar in their overall appearance to the robber flies of the family Asilidae, differing lacking the piercing mouthparts of robber flies or the moustache of bristles below the antennae. The venation of their wings is more similar to that of the mydas flies of the Mydidae, but they differ from most mydids in having shorter antennae and the regular triangle of three round ocelli on top of the head (Woodley 2009).

Observations of Apiocera species have been fairly few. A study of North American species by Toft & Kimsey (1982) found them to be restricted to sandy habitats with a fair amount of subsurface moisture, such as the shores of lakes and rivers or among sand dunes. The larvae, so far as we know, are similar to those of robber flies and are probably burrowing predators in the sand. Adults emerge from holes in the ground late in the growing season. In some places (such as Wikipedia), you may find Apiocera referred to as 'flower-loving flies' but visits to flowers are few. Toft & Kimsey (1982) found that the species they observed emerged after most plants had finished flowering and, indeed, questions have been raised historically as to whether adult Apiocera feed at all. Nevertheless, they may take honeydew from plant-sucking insects, and I will direct you to the photo below by Jean & Fred Hort that seems to show at least one Apiocera individual feeding at a flower. Males may congregate at certain locations, seemingly to form leks, though it is unclear whether they maintain territories. Toft & Kimsey (1982) noted that tussels between males of A. hispida were common, observing that "two males would make rapid contact in mid-flight, and stay together in a buzzing, tumbling ball for several seconds".

There seems to be little question that Apiocera and mydas flies are closely related. In fact, an analysis of Apiocera's phylogenetic relationships by Yeates & Irwin (1996) lead to a number of other genera that had previously been classified with Apiocera in the family Apioceridae being reassigned to the Mydidae (I suspect that it is the behaviour of these other 'apiocerids' that is behind the erroneous association of Apiocera with the 'flower-loving' moniker). Apioceridae is still maintained as a distinct family for Apiocera alone but, as noted by Woodley (2009), one could be forgiven for questioning whether Apiocera would be better treated as a very basal mydid. But that, of course, is simply a question of categories.

REFERENCES

Toft, C. A., & L. S. Kimsey. 1982. Habitat and behavior of selected Apiocera and Rhaphiomidas (Diptera, Apioceridae), and descriptions of immature stages of A. hispida. Journal of the Kansas Entomological Society 55 (1): 177–186.

Woodley, N. E. 2009. Apioceridae (apiocerid flies). In: Brown, B. V., A. Borkent, J. M. Cumming, D. M. Wood, N. E. Woodley & M. A. Zumbado (eds) Manual of Central American Diptera vol. 1 pp. 577–578. NRC Research Press: Ottawa.

Yeates, D. K., & M. E. Irwin. 1996. Apioceridae (Insecta: Diptera): cladistic reappraisal and biogeography. Zoological Journal of the Linnean Society 116: 247–301.