Taxonomic disjunction in time and space: Atlatlia a genus of tiny flies from Australia, New Caledonia, and Baltic amber
Presented by Dr Daniel Bickel
Senior Fellow, Entomology, Australian Museum
Recorded Wednesday 28 September 2022
This all started by my walking around and staring at Eucalyptus trunks. Now, this is a strange thing to do, and people have remarked on this, but nevertheless, I was looking for tiny flies of the subfamily Medeterinae. It's the subfamily of flies that I study, the Dolichopodidae, they are resting on tree trunks. Now I had revised in the Arctic fauna the genus Madetera, which is a type genus of the subfamily and I was looking for Australian taxa. Well, there were lots of taxa, it was almost like a totally unexplored environment to look at.
This is the subfamily I was studying, Medeterinae, there are some 20 genera, there's other undescribed genera, it has very distinctive taxonomic characters. It has a flattened thorax, you can see here, they also don't have the legs are rather bare. They often have a large male genitalia capsule, which you can see here and here a little bit, but you'll see more of that later on. The genitalia of flies are very interesting in terms of getting good species level characters, and you'll see some. So they're very useful and also, they are important in sexual selection as well. But that's another whole topic. Now this characteristic of the sub families, they often rest on tree trunks and vertical surfaces. And they feed on small soft bodied invertebrates. And the larvae are subcortical, that's means they're under the bark, and they often predators and scavengers, and they have a long fossil history, at least since the Eocene since the amber.
Here's the genus that I was studying. This is the type genus the subfamily there's some 350 described species, but there's still more out there, especially from the tropical areas. What's of great interest in this group is that the larvae of many of the Holarctic or the circumboreal species are predacious on bark beetle larvae. Now bark beetles, you can see this cute little fella down here in the left hand corner, can cause tremendous damage to forests, and they often increase in numbers and they have aggregation, they aggregate and they can cause widespread damage, they burrow underneath the bark and they destroy the bark, with galleries there, and then they lay their eggs there. And this is often when the trees become stressed, they actually are vulnerable to bark beetle attacks. And this is a scene from British Columbia where you can see the number of dead trees they often break out and over large areas. Here are the galleries that they form under the bark. And here's the larva itself and here's another photograph of the gallery. So the females of these are actually attracted to bark beetle aggregation pheromones, and they use this to oviposit at the gallery entrance, then the Medetera larvae go into the gallery, they work their way through the galley, feed on the bark beetle larvae and then come out. So there's a lot of interest in this group, at least in terms of as a biological control agent for these bark beetles. And one of the defences trees has is resin. And we're going to be talking about resin later on, resin can turn into amber when it's fossilised. So we're going to look at this in more detail.
Well, I was looking around, and one thing I want you to notice is here and one of the characteristics of many fly species, they have this crossfade here. So one of the things I found when I was looking at tree trunk is this new genus, which I called Atlatlia, it's very small, it's less than two millimetres, you can see them if you go to a small bark eucalypt, let's say just go out, say into the local national parks and a smooth bark eucalypt on a hot, humid day, in November, December, and you see tremendous amount of activity in the tree trunks. And there's a lot of little flies that are that are on the tree trunks as well, including this genus here. And when I first saw this, I knew it was unusual, and probably a new genus because this cross vein was missing, and I'd only had the females but when I got the males, I found the great long stock and then the male genitalia is at the end of a stock. So that's really quite bizarre. And also there are other characteristics as well. So, I found two species, there is one species wide spread along the eastern Australian coast and another species in southwestern Australia. And here are some better drawings of the genitalia. And you can see when you look at these fly genitalia, there's all sorts of structures, little hairs, branched arms, and so forth. And it makes it very useful for identification, oftentimes, these genitalia structures are quite constant. So very useful in terms of identifying them.
The problem is they're very hard to catch because they're so tiny. They just bombed up the trunk and you know, you I was trying to put a vial over them and so I spent a lot of time looking at these trunks. So another way, which was suggested to me is use sticky traps. Now a sticky trap, you can see a sticky trap here, this is just a piece of plastic, and you tack it to the trunk and you put this Tanglefoot on it. Now Tanglefoot is a commercially available sticky substance that you can buy, and you just paint it on. And then you see there's a lot of activity on the tree trunks. There's insects crawling on up the trunk. They're insects that just drift onto the trunk from like sort of aerial plankton, there's flying insects that land on it, and so forth. So it's a way of sampling, what's going on in the trunk and it's a very messy job and you have to get them in the material, you have to dissolve where this Tanglefoot, with mineral chirps. So it's not a pleasant thing. But you get the goods, you get lots of specimens, you get things that you would never otherwise collect. So that's just a method of trapping and it's quite useful.
Also, there were three species that were found in New Caledonia, and these were collected in Malaise traps. One of the things about the New Caledonian fauna I know these are kind of dried specimens and look very exciting, is they have a lot of silvery pruinosity, which is like these orientated scales and sometimes when they look at, when you look at a certain angle, you see like a silvery colour coming out. So there were three species in New Caledonia. And here's some drawings of the genitalia from the New Caledonian species. Again, you can see all these structures, I mean, stray hairs, branched arms, and so forth. So it's very, very useful for taxonomy, so you get very good characters out of it.
Well, let's look at New Caledonia. That's an interesting place. And if you've ever been there, it's very rich biologically. And it's got a lot of strange relic groups. It's as a very rich endemic flora. There's like 43 species of conifers there, the most for any southern hemisphere landmass. Here is up on Mount Panié, the highest point in New Caledonia is, I guess, this Montana forest here. And here's Araucaria humboldtensis on Mont Humboldt, so it's a very strange place, it’s got five species of Nothofagus, five endemic families of angiosperms, including primitive angiosperms. So it's a strange place for many people and in fact, because of this setting, with all the angiosperms, the conifers, they actually use New Caledonia to shoot a lot of those dinosaur re-enactment movies, you know, because it gives you that background with a conifers.
Now biogeographically, it's very strange, but let's look and see what the what the context is. New Caledonia is the northern most part of what is recently recognised as a continent of Zelandia. So this is, people have been talking about it but now finally, geologists have said, well, we can consider this to be an actual continent, but most of it is actually submerged. So
New Zealand doesn't necessarily have to beat Australia and rugby anymore. They've got the, they can say we're a continent as well! And you can see here, this is the outline of the continental crust. And so that's what they call Zelandia. And that also includes Norfolk Island, Lord Howe Island, and at the top here is New Caledonia. So Zelandia is a geological continent with a continental crust. And it has unusual histories, many strange groups, relic groups, and so forth.
Right now there's a very large, but geographic debate regarding New Caledonia. It's traditionally seen as supporting and exemplified vicariance. In other words, harbouring all sorts of ancestral Gondwanan relics, primitive angiosperms, a wide range of, of conifers and so forth. However, it's becoming increasingly clear that geological record says that the main island, the Grande Terre, was submerged between 75 and 60 million years ago, in other words, totally underwater. So a lot of these relic groups must have arrived there much later. And so they may not be the actual, ancient flora and fauna that people have normally associated with New Caledonia. And so there's been a lot of debate, a number of researchers support that New Caledonia was submerged and then you have long distance dispersal to New Caledonia. This especially the group at the Paris Museum, which of course, New Caledonia is part of France, and they do a lot of research there. However, there's debate about this because for some taxa they're very unlikely dispersals such as many clades of soil dwelling invertebrates. And here are some of them. I think the mollusc people may know what this is. I'm not going to talk about any names. But these are some very unusual sort of relic type groups that are present in New Caledonia. And if New Caledonia, the Grande Terre had actually been totally submerged so recently, how did they get there? These are not very good dispersals so there is still there's quite a bit of debate about New Caledonia. And there's quite a large literature on this.
So if we look at it, at this genus Atlatlia, and by the way, I named it that largely because the genitalia were on the end of a long arm. And so it's almost like an atlatl, which was a throwing stick for spears and so that's, that's where the name comes from. Anyway, here was a distribution you found you find the southwestern Australia, the east coast of Australia, from about the Tropic of Capricorn, down to Victoria, it's probably in Tasmania, but it hasn’t been collected there, and a little outlier here at Carnarvon gorge. And also, there's three species here on New Caledonia, where this is the island of New Caledonia right here. And this is what sclerophyll forest up but where it can be National Park, where you can get these, you can find them among other places.
So it's just a Gondwanan distribution? Well, that's what I thought. But then I was contacted by a German colleague about finding Atlatlia in Baltic amber so this became a much more interesting story. Let's now talk about Amber. Because we have to put this in context. And Amber is a fossilised resin. It has offered us a very low specific gravity of 1.5. It's almost the same as seawater, therefore, it gets easily carried by seawater. And especially the Baltic amber is often washed up on the shore along the beaches, and people go and collect it. It's very soft, and it burns. In fact, when you burn, it gives off a sort of a coniferous scent to it as if you're burning pine with resin in it. And it's from the Bernstein, which is a German word for burns, burning stone or burn stone in middle German. So that's the name in German, it's a natural sticky trap. Now you remember before I talked about these sticky traps on tree trunks? Well, many of these, if you have a sticky tree resin on a tree trunk, let's say here, the fly accidentally lands on it and then there's more flow of this resin coming over and eventually becomes in entombed. And not all the amber that's formed is actually external and actually has these inclusions. A lot of it can be internal in the trunk, for example, under the bark, but here it would be for example, if you had a flow of this resin coming out, it could be very sticky and things get caught there and that's how you get this entrapment. This of course is a part of the defence system. For example, many of the conifers have this resin and the resin is actually sticky and it means that defence against such invasive species like those bark beetles we saw before. So there is a lot of ambers around the world, and people are becoming much more interested in and it's like a window to the past as we'll see.
Here are some of the major amber deposits around the world. The most famous of these is the Baltic Hamburg, which is found along the Baltic coast here. There's also a Bitterfeld in Germany, which is similar but it's the same age. But there's other ambers of great interests that Dominican Republic Ember is also incredibly rich. And that doesn't come from a conifer, it comes from a leguminous tree. Also, there’s Chiapas amber in Mexico. And there's also other ambers as well. The tertiary amber's are more common but there are Cretaceous ambers and they are of great interest because you're actually another world there. If you look at the insect fauna of Baltic amber, it's very modern looking whereas if you go to the Cretaceous, and you have all these weird families and even orders that are now extinct, and one of the most famous one of these is the Lebanese amber, there is now a Burmese amber, which is becoming incredibly well known, it's been mined. And there's quite a problem, there are human rights issues, and also it's been sold on the market. And so a lot of the goods specimens, don't get into museums, but this is a problem. Anyway, and also Australia has amber, Cape York amber which washes up in the beach, the far north of Cape York Peninsula and Amber down here in Victoria and also there's bits of amber in Tasmania. So a lot of it isn't meant finding it, looking for it and sorting it out.
We’ll just go back to the Baltic amber, Baltic amber has a very long history in Europe. It's known from prehistoric times and you even find like prehistoric objects that were carved with it. And when you have a big storm people go on to the beach, you can find it washed up, because it has such a low specific gravity, gets washed up in here you find it among the seaweed and stuff. This whole area from Kaliningrad, down to Gdansk on the Baltic Sea is particularly rich for collecting. And it appears that there must have been a big river system in the Eocene and you had this whole river drainage system and it drains out right here. And this is like the outline of Europe here, and right around here this is where the Baltic Sea comes in, and it's carried along all the Baltic Sea, is carried along the coast quite far to Denmark and even occasion to England with by these currents and so a lot of this resin, the resonance trees would have been rafted down.
This is a reconstruction of a scene from Det Bernsteinwald or the Amber forest. And you could see here in the background was like one of these big predacious birds like Diatryma and maybe over here is a sort of early horse or rhinoceros sort of thing. But it was thought that the Eocene was a pine tree, Pinus succinifera. In other words, from giving out all this amber and here you see all this flow of amber. The problem is the volume of amber, like you see in trees now, you don't see so much but there are enormous deposits of this Baltic amber, it's even mined and made it to varnish and so forth. So some people thought it's a genus Pinus, other, think it's not Pinus at all based on the signature but it could be Pinaceae, which is now only representative by one relic species, the Japanese umbrella pine. So anyway, that's a little bit more.
One of the things interesting about these Baltic amber's you get these assemblages. Now, here's a piece of Baltic amber right here. And you can see, there's quite a number of specimens here, I think there's some 40 specimens, and you can see just the diversity. So in other words, you had this, this resin flow, then all these things got caught in there. Maybe they were attracted to insects that were trapped here, probably not unlike this famous mural of the La Brea Tar Pits, which is actually within the city of Los Angeles, but they had the sort of seepages of oil and tar, and a lot of animals were there, that's where all the Sabre-toothed tiger skeletons come from. There were these giant ground sloths, they got trapped, and the birds of prey and vultures would come and then you'd have Sabre-toothed tigers, they all got trapped in it.
So that is a very interesting source. It's sort of like a mass assemblage and you find this with Baltic amber's generally, you get associations, you even get behaviour, you get predation, preserved. In other words, there was an insect feeding on another one, it gets covered by the resin, then it gets preserved. Also, the most interesting thing about amber generally, is that you can tell about the age and the origin of many groups, it gives you a fossil record. Now for most insects in particular, or arthropods generally, they just don't preserve well in sediments. So unless you have very, very fine lake sediments, things just get totally just destroyed. But amber it just gets preserved in incredible detail. Here, for example, is one of the oldest ants, and it was used as the front piece, or that cover for the book, but on insect societies by EO Wilson. So it tells you a lot about the evolution of groups.
Well, my group is actually very well represented in amber and I didn't realise this. But it was through this association of being contacted by a German saying that they found this and I got involved with Baltic Amber and flew to Europe a few times and looked at some of the collections, enormous amounts of material. Now people collect this and then they have to polish it because there's sort of irregular lumps and you have to look and you see things and you have to polish and sometimes you get beautiful specimens like this, too. This is not the group we're looking at right now, but it's another specimen. It's like a dancing couple, perfectly preserved. This is the male here with the big genitalia capsule here, this is the female so it’s like they're dancing, both were preserved. And you get exquisite detail right down to the hairs and everything. So it's probably the finest type of fossil preservation and it's a way that you can get very delicate things, preserved flowers, all sorts of things. So there's a lot of material around, but the best material is in private collections. Now, there's amber fairs that are held in various cities and in Europe, and people go and they buy pieces. And there are people who are very interested, there's a lot of citizen scientists who are interested and they also have some money. I think, when the man who first got involved with the amber was Hans Ulrich, he was from Bonn, he used to buy pieces and at the time for first 10 Euros, you could get a really good specimen. Now, of course, the price has gone way up and there's a lot more international interest and people want this for, there's a tremendous trade in amber for jewellery as well. But the best collections are definitely in private hands. So what this means for the study of science, especially the inclusions are in private hands, because they've been purchased from dealers, and they're in good condition and they're selected. In other words, you say I want this piece, I'm not going to look at this other stuff. Whereas many museum collections are old, they're unselected and often they've been obscured or damaged. The amber itself often gets a crazy, tiny little cracks on it, so you can't really see very well through it.
Up here on the top is the thing, that guy said, this is the same genus you have. And I have to admit, look at look at the wing here, this loss of the crossvein, and the long genitalia on a stock, not as long as some but definitely I would say this is very, very close. And here's a female, again, with the with the venation just going show you it. It turns out and Baltic amber there's some 12 species or 13 species from this genus, I can't believe it. Here are two males of the same species and here's an enlargement. And here's an enlargement of the male genitalia, again, showing the exquisite detail of what’s preserved with these tiny, the hair, every hair that you can see. Here's another species, that are just folded up like that. Here's another group that's also lacking that vein, but it's a whole group that was only in Baltic amber, these big rounds, spheroidal type of genitalia. And you can get all sorts of detail. If you see enough specimens, you get them in the right position, you can actually see quite a bit of detail on them. So yeah, that's very useful. Here's more. You can see some of these are quite obvious differences between the genitalia. And it's the genitalia that many, well, at least people who study flies and many other groups like Lepidoptera. And often, genitalia are very important in determining species. So you get, you get the species well preserved and you can actually see and determine the species and amber plus new genera as well.
So it turns out this is genus Atlatlia is not Gondwanic, but it's pseudo-Gondwanic. It's a genus found in Australia, New Caledonia, and Baltic amber. So what do we do with a distribution like this? The genus must have been much more widespread because this Paleogene Baltic amber from the Eocene period is quite different from Australia in both time and space. So was it once widespread across the whole say Eurasian landmass and just become relic to Australia, New Zealand? And why isn't it found anywhere else? I mean, it could be somewhere else, it could be for example, somewhere in Indonesia that hasn't been collected. It could pop up but we still have the question that it's a very old group, it's become extinct over much of its range or must have ranged much more widely and now we find it only relic to Australia, New Zealand. It's not that it's doing badly either. I mean, if you took one out to any of the local national parks, Ku-ring-gai Chase or the Royal National Park on a warm summer's day, you'll find it if you look, they're tiny. They're only less than two millimetres long, but you'll find it, if you if you know how to look for it. So they're doing alright, it's not that there's anything wrong with them. So this is one of the big problems in distribution and biogeography, it’s extinction. It's a major process in the distribution of organisms, along with dispersal and vicariance. And I'm going to give you a couple more examples of extinction from the insect world. And to show you how we can actually give you a different impression of what actually happened. And unless you have a fossil record, you can't do much about it.
Tsetse the flies, now this is the family Glossinidae. It has a very distinctive venation. Also, it has this big hard biting proboscis. It's a blood feeder, mainly on large mammals. The females give birth to live mature larvae. That's a very interesting thing about some of the more advanced Diptera groups, they actually give live birth. In other words, they don't lay eggs, the females develop inside the female, the eggs develop with inside the female and then they give birth to live or mature larvae and they just pupate, and then they're ready to go. And the females actually have glands which they feed. So it's very, it's very strange, almost like mammals. But the Tsetse flies of course are known for transmitting trypanosomes, which cause seeking sickness. Currently is restricted to Africa with 22 species, but it was also known from the early Tertiary of North America. And here's a fossil from the Florissant shales, which is Miocene in age and you can see the proboscis. And also it has the distinctive venation. Here's a modern species and this is what a reconstruction of mid tertiary grassland mammal fauna of the interior North America so you can see all these different types of ungulates, and so forth, running around and the Tsetse flies would have been quite happy with him. So what happened? Why did they go extinct? We don't know. But it could be climatic changes. Who knows?
Here's another one closer to home. This is a termite family Mastotermitidae. It has one current species, it’s found in the Northern Territory and New Guinea, it’s Mastotermes darwiniensis. It's the most primitive living termite, it's related to cockroaches. Termites are essentially just social cockroaches, let's put it that way. They're not going to run away with you, from you, when they turn on the lights, they want to talk and say hello. But this is a very primitive family. It once had a very wide distribution until just a few million years ago. And it's now it’s found in Northern Australia, and in adjacent New Guinea. And it's not even that rare. I mean, it's not uncommon, and sometimes it's even an occasional pest. But here's a list, 15 species of fossil Mastotermes from the Early Cretaceous in Europe, Tertiary of Europe, Africa, Mexico, and Dominican Republic. So this is a list of all the species of Mastotermes that have a fossil record. And so if you came, if you didn't have this fossil record, you’d say, oh, this is a weird, strange group only relative to Northern Australia? No, it's relic because it's become extinct everywhere else. This is what the fossil record will tell you and this is not necessarily apparent just by studying the recent fauna. Here's a Mastotermes from Dominican Republic amber right here, so here's this, this fellow up here. So that's from Northern Australia.
So biogeographic interpretation must rely on recent distributions. For most organisms, we have no fossil evidence. In other words, you just have to say this is what it is, but we don't know and sometimes you get fossils that can tell you more. However, the current distributions may or may not be what it seems. Extinction is as important a process as vicarious and dispersal to explain current biogeographic distributions. Now I'm just going to leave you with a quote, some people would say he's a war criminal. He was the fifth, sixth Secretary of Defence for the US, he did make the statement, which I think is rather interesting, rather funny depending on how you interpret it. He says, “There are no knowns, these are the things that we know, we know. And there are known unknowns as to say there are things we know we don't know. But there are also unknown unknowns. These are things we don't know we don't know”. So a lot of these things when you're studying biology, you're studying life there are a lot of things we know or we partially know we're trying to find out what actually is.
So I'd like to just say in summing up I'd like to thank various people, Hans Ulrich for his hospitality and loan of selection. John Martin and Scott Ginn for photography. Hannah Matthew’s for figures, Natalie for plate preparation and excerpts from various books and so forth. So, that's it.
Many years ago, while collecting small long-legged flies off smooth-barked eucalypt trunks, Dan Bickel captured a striking new genus. This genus has two strong apomorphies(novel characteristics), lacking a major wing cross vein and male genitalia on a stalked projection (like a spear-throwing stick or “atlatl”). Dan found more on tree trunks and some in collections, all from southern Australia, forming a classical Bassian distribution. Three more species were collected in New Caledonia, suggesting it was a Gondwanic genus (an Australia-New Caledonia connection occurs in a number of plants and terrestrial invertebrates, possibly an ancient connection with the “lost continent” of Zelandia).
Later a German worker found Atlatlia in Baltic amber, and the genus was transformed from “Gondwanic” to “Pseudogondwanic”. This opened the world of Baltic amber studies: the enormous number of inclusions, and the enthusiasm and expertise of amateurs, where the best collections are private. The genus now includes an additional ten amber species, a major radiation in Paleogene time.