Posts Tagged sunday spinelessness

Sunday Spinelessness – Hairy snails David Winter Jul 29

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Here’s another of these tiny native snails I talked about last week. Aeschrodomus stipulatus:

Not the best photo I’ll admit, but it records enough detail to see the two things that set Aeschrodomus apart from most of its relatives in New Zealand. It’s tall and hairy. I’m not sure if there is an accepted definition of “hair” when it comes to snail shells, but plenty of different land snails groups have developed processes that extend form the shell. In New Zealand we have the fine bristles of Suteria ide, the filaments of Aeschrodomus and the spoon-shaped processes of Kokopapa (literally ”spoon-shell”):

K. unispathulata Photo is from David Roscoe / DoC and is under Crown Copyright

I try very hard to avoid the sloppy thinking that presumes there is an adaptive explanation for every biological observaton, but it’s hard to see how these hair-like processes would evolve if they didn’t serve a purpose. The larger hairs are presumably made from the same calcium carbonate minerals as the rest of shell, and calcium is a precious resource for snails (so much so that empty shells collected from the field often show signs of having been partially eaten by living snails). In those species with finer projections, the hairs are an extension of the “periostracum”, a protein layer that covers snail shells.  If we presume that snail hairs come at a cost, in either protein or calcium, what reward are they hairy snails reaping from their investment?

Markus Pfenninger and his colleagues asked just that question by looking at snails from the Northern Hemisphere genus Trochulus (doi: 10.1186/1471-2148-5-59). This genus contains many species that sport very fine and soft hairs. Pfenninger et al.collected ecological data for each species, and used DNA sequences to estimate a the evolutionary relationships between those species. From these data, they were able to infer the common ancestor of modern Trochulus species was probably hairy, and three separate losses of hairyness can explain all the among-species variation in this trait. Moreover, it appears the loss of hairs in Trochulus is associated with a switch for wet to dry habitats. Given this finding, Pfenninger’s team hypothesised that, in Trochulus at least, hirsute snails might stick to host plants more effectively than their bald brethren. Indeed, in experiments it took more force to dislodge a hairy shell from a wet leaf than non-hairy one.

Pfenninger’s study makes a neat case for the maintenance of hairy shells in Trochulus, but I don’t think adherence to leaves can explain all the hairy snails we know about. In New Zealand, most snails with shell processes are limited to leaf litter, a habitat that would seem to make adhering to leaves a positive hindrance to getting around. I don’t know if we’ll ever have a simple answer as to why some of our snails sport these attachments, but Menno Schilthuizen‘s work might give us a couple of clues as to why these sorts of shell sculpture arise and stick around. In 2003, Schilthuizen proposed many shell features may arise because those individuals that have them are more likely to procure a mate (or perhaps a desirable mate) (doi: 10.1186/1471-2148-3-13). Although there is quite a lot of evidence for sexual selection in land snails, I don’t know of a study testing Schilthuizen’s hypothesis on shell sculpture. On the other hand, Schilthuizen’s group has found evidence that elebaroate shell sculpture can arise as a response to predation (doi: 10.1111/j.0014-3820.2006.tb00528.x). Opisthostoma land snails from Borneo have extradonary shells, with unwound shapes, ribs and spines:

Opisthostoma mirabile
In Borneo, Opisthostoma species live alongside a predatory slug that attacks these snails by boring a hole into their shells. The unique shape and ornamentation of Opisthostoma shells appears to have evolved to hinder slug attacks. Even more interestingly, geographically distinct populations of slug appear to attack snails in different ways. This local variation in predator behavior could well be a response to local variation in the shell ornamentation – a so called Red Queen process in which each population evolves rapidly while maintaining more or less the same relative fitness

There are certainly plenty of snail-eating animals in New Zealand. Several species of Wainuia land snail appear to specialise in eating micro snails, which they scoop up and carry off using a “prehensile tail” (Efford, 1998 [pdf]). It’s entirely possible that the relatively small projections that some our snails sport are preforming the same job that those weirdly distorted Opisthostoma shells serve.

Sunday Spinelessness – New Zealand microsnails David Winter Jul 22


When I tell people I study snails for a living I get one of two replies. There’s either some version of the “joke” that goes “that must be slow-going” or “sounds action packed”, or there’s “oh, you mean those giant killer ones we saw when we went tramping?”. I guess the joke is funny enough, but I want to make it clear that those giant killer snails from the family Rhytidae, cool as they might be, are not the most interesting land snails in New Zealand.

The local land snail fauna displays a pattern that is quite common for New Zealand animals – we have a very large number of species but those species are drawn from relatively few taxonomic families. Since taxonomic groups reflect the evolutionary history of the species they contain, that pattern most likely arises because New Zealand is (a) quite hard to get to, so few would-be colonists make it here and (b) full of ecological niches and geographic pockets that can drive the formation of new species. In total, there are are probably about 1200 native land snail species in New Zealand – about ten times the number found in Great Britain, which is approximately the same size. That diversity extends to the finest scales – individual sites in native forest might have as many as 60 species sharing the habitat. New Zealand forests probably have the most diverse land snails assemblages in the world (although tropical ecologists, who generally hold that diversity in terrestrial habitats almost invariably increases as you approach the equator, have argued against this conclusion).

You may now be asking why, if this land snail fauna is so diverse, have you never seen a native snail. Well, you’ve probably walked past thousands of them without noticing. Most of our native land snail species are from the families Punctidae and Charopidae, groups that are sometimes given the common name “dot snails”. Meembers of these families are usually smaller than 5 mm across the shell, and are restricted to native forest and in particular to leaf litter. But in native forests, where there’s leaf litter there’s snails. Grab a handful of leaves, or pull up a log and you’re likely to find a few tiny flat-spired snails going about their business. Hell, down here in Dunedin you can even find charopids living under tree-fuschia in a suburban garden.

Like so many native invertebrates, we know very little about our land snails. Lots of people have dedicated substantial parts of their lives to documenting and describing the diversity of these creatures, but even so we don’t have a clear understanding of how the native species relate to each other or to their relatives in the rest of the world, or even where one species starts and another ends. Without such a basic understanding, its very hard to ask evolutionary and ecological questions about these species, so for now we remain largely ignorant of the forces that have created the New Zealand land snail fauna.

For the time being I can tell you that a lot of them are really quite beautiful. Since most people don’t have handy access to a microscope to see these critters, I thought I would share a few photos from this largely neglected group over the next few weeks. The 2D photographs, with the relatively fine depth of field, don’t quite record the beauty of these 3D shells, but I hope it’s at least a window into the diversity of these snails.

 Let’s start with a snail that is very common in Dunedin parks and forests. This is a species from the genus Cavellia (the strong, sine-shaped ribs being the giveaway) but I won’t be able to place it to species until a new review of that genus is published. 

This particular shell is from an immature specimen, and is about 2mm across. When flipped, you can see an open umbilicus that lets you see straight through to the apex of the shell.

Sunday Spinelessness – Cuttlefish in drag deceive their rivals David Winter Jul 08


One awesome mollusc deserves another, so let’s follow up last weeks octopus post with one on that group’s close relatives the cuttlefish.

Cuttlefish are relatively small (the largest grow to 50cm) squid-like cephalopods that present a nice soft and digestible meal to predatory fish and marine mammals. Having lost the shell that most molluscs use to protect themselves cuttlefish have had to develop other defences. Most strikingly, cuttlefish are masters of camouflage


The deceptive patterns that cuttlefish put on come from their remarkable skin, and are controlled by a pretty impressive nervous system. The skin is covered in cells called chromatophores which contain granules of pigment. When a cuttlefish decides it’s time to disappear it looks around its surroundings and, with the aid of nerves that lead from the brain to the the skin, stretch and twist the chromoatophores  on the skin’s surface in such as way as to change the colour of their cells, and ultimately their whole bodies. 
That impressive trick is principally used for camouflage, but cuttlefish and also use their skin as a sort of billboard to signal to other members of their own species, and even put on a strobing light show (possibly used to startle their own prey):

Just this week, researchers have reported evidence for a other trick that cuttlefish can pull off. When males of the Austrian Mourning Cuttlefish (Sepia plangon) see a female they put on a show, producing striped patterns that evidently impress the female. But these animals form male-dominated groups, and rival males often interrupt would-be woo-ers  in mid-display. So, when they spy a receptive female, males want to put on their flamboyant show for her to judge, but also want to make sure they don’t attract the attention of rival males that might want to spoil the party. The male Mourning Cuttlefish’s answer to this problem? Using only half of his body to put on the female-impressing show, and throwing would-be spoilers off the scent by mimicking a female with the other half.

This gender-splitting  tactic seems to be pretty common. In aquarium experiments about 40% of males would  attempt the deceptive signal when they were displaying in the presence of a rival. Just as the cuttlefish camouflage response requires information from the physical environment, the gender-splitting trick is influenced by what the male can learn of the social environment. If more than one female is available the male will display to both  without bothering to hide his intentions for observers (probably because working out an angle from which he could excite two females while staying under the radar is just not possible). Likewise, if more than one rival male is about that don’t bother with the deception – since it wouldn’t be possible to maintain the illusion for two rivals viewing from different positions.

Brown, Garwood & Williamson (In press) It pays to cheat: tactical deception in a cephalopod social signalling system. Biology Letters.

Sunday Spinelessness – The other mollusc shell David Winter Jul 01

Here’s a really cool animal, a female argonaut (sometimes called a paper nautilus):

It may not be immediately obvious from the photo, but argonauts are octopuses. Strange octopuses, because the seven species that make up the family Argonautidea are among a handful of octopuses that are capable of swimming through the water column (rather than hanging out on the ocean floor) and they are the only octopuses that fashion themselves a shell. 
The argonaut shell has been a topic of consideration, confusion and conjecture for biologists for a long time. Only females produce the shell. Male argonauts are tiny (about a tenth of the size of the female) and only really serve as sperm donors (in fact, they donate an entire sperm-transferring organ, called the hectocotylus). Once mated, a female argonaut starts producing her shell and lays her eggs in its base. This behaviour has lead some biologists to conclude the shell’s primary function is to act as an egg case.  We now know that shell is also used to help the argonaut maintain its position in the water column. By propelling herself to the surface and rocking back and forth an argonaut can introduce an air bubble into her shell. While she’s near the surface that air bubble will make her buoyant, but by diving downwards she can reach a point where the increasing water pressure (which compresses the air bubble, decreasing its buoyancy) cancels out the buoyant effect, letter her float in the water colum. At that point she’s free to swim about in two dimensions without having to maintain her vertical position.

You can watch this remarkable behaviour  here:

I don’t want to talk too much more about the purpose of the argonaut shell, partly because it has already been well covered. Ed Yong wrote a predicably clear and interesting post on the research which uncovered it (which also produced an interesting comments thread) and the lead researcher, Julian Finn from Museum Victoria in Australia, also discussed his work in a really great video.

Instead, I want to talk about the origin of the argonaut shell. Octopuses are molluscs, part of a group of soft-bodied animals that includes clams and mussels and snails. Most molluscs have shells. In fact, despite being arugably the most morphologically diverse of the 35 animal phyla, only a few small groups of molluscs don’t contain at least some species that produce shells. The easiest way to explain the presence of shells in so many different molluscan groups is to hypothesize that the last common ancestor of all molluscs had a shell, and most of that ur-mollsuc’s descendants have retained this organ. 

In evolutionary biology we call traits that are shared between organisms as a result of their shared evolutionary history “homologies”. Homologous traits are often compared with “analgous” ones, parts of organisms that are similar as the result of independent innovations in different evolutionary lineages. We can illustrate the concept using a bat’s wing as an example. The forelimbs of bats and whale are made up of the same bones, despite the fact that whales swim and bats fly. That’s because bats and whales are both mammals, and they inherited their forelimb bones from a common ancestor before each group radically repurposed their limbs. On the other hand, despite the fact that both bats and stoneflies fly, the insect wing and the bat wing are separate evolutionary inventions and not something the two groups share as a result of shared evolutionary history:


The protective shells of snails and clams are homologous to each other, and to the internatilized shells that some squids use to stay afloat. But the argonaut shell is something entirely different. The argonaut shell is made of calcite, where most molluscan shells are argonite. Moreover, the minerals that make up the argonaut shell are extruded from the octopuses tentacles, where other molluscs have an organ called the mantle that they use to produce their shell. 
The fact the argonaut shell is made of different stuff than other molluscan shells, and with the aid of  a different organ, suggests it is a unique evolutionary innovation. So how did shells evolve twice within the molluscs? I can’t provide you with a definitive answer, but I do like one (only slightly crazy) speculation. Earth’s oceans used to be dominated by another group of shelled molluscs called ammonites. Adolf Naef pointed out that argonaut shells are very similar to some ammonite shells, and suggested the ancestors of ammonites might have laid their eggs in discarded ammonite shells (some modern octopuses certainly spend time hanging out in mollusc shells). Naef suggested ancestral argonauts might then have acquired the ability to repair broken shells (developing the mineral secreting organs on their tenticles) and finally to create their own. 
It’s a pretty out-there sort of an idea, and I don’t know how you could actually test it. But wouldn’t it be cool if the ammonite shell was still being dutifully copied every day, 65 million years after the last ammonite died?

Sunday Spineless – How some snails became red-blooded David Winter Jun 17

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Here’s something cool that I’ve meaning to write about for a long time. A native Powelliphanta land snail with an apparently pigment-less foot and head:

That snail (a close relative of speedy carnivore featured here) popped up in Kahurangi National Park at the end of last year. Apart from just being kind of cool, the un-pigmented individual is interesting for a geneticist that studies land snails. For the most part, dark pigmentation in snails results form melanin  (which is perhaps the most common pigment in the animal world). That’s true for pigmentation of the shell as well as the animal that caries it around. As you can see, this snail has normal pigmentation on its shell, so clearly its still able to make melanin. The genetic mutation (or developmental defect) that has left this snail white hasn’t broken the genes for pigmentation, just the mechanism that moves that pigment around the body wall of the snail.

The ghost Powelliphanta is a pretty cool snail, but there’s actually an albino snail that’s even more interesting. Every now and again a truly albino individual of the freshwater snail Biomphalaria glabrata pops up. Looking at these mutants we can learn something about the evolutionary history of the these snails:

Photo is CC 2.5 and comes from Lewis FA, Liang Y-s, Raghavan N, Knight M et al in PLoS Tropical Diseases

Free from the pigments that would usually make shell opaque we can see the feature that sets Biomphalaria and other species form the family Planorbidae (ramshorn snails) apart from every other snail. The planorbids are the only red-blooded snails on earth. So why are these snails so different?

As we all know, in order to live animals need to get oxygen from their environment into their bodies. For small animals this doesn’t represent a huge problem. Oxygen will flow form areas of high partial pressure (a concept analgous to concentration, but accounting for some of the weird ways gasses behave) to areas in which Oxygen is being used up. So, for instance, most insects pull air directly into their bodies with a set of open tubes (called tracheae). Once the air makes it into those tubes oxygen will passively diffuse into the insect’s tissues.

Big animals have a much bigger problem*. Not only do larger animals need much more oxygen to fuel their bodies, they also have to actively transport that Oxygen because the distances it is required to travel can’t be achieved by passive diffusion. Lungs and gills are both organs dedicated to pumping more oxygen into animal bodies, and many  animals use blood, and special proteins dissolved in blood, to move oxygen about.

In vertebrates the oxygen-carrying protein is called hemoglobin. Very simply, a hemoglobin molecule is   a cage used to hold iron atoms in such a way that they will bind to an oxygen atom. The iron containing group in the hemoglobin protein (called heme) gives our blood its red colour and its hemoglobin circulating through that snail’s body that makes it red.

Heart of Steel is Julian Voss Andreae’s sculpture based on the structure of hemoglobin proteins. Pleasingly, the weathering process depicted across  these photos is the result of iron molecules in the steel sculpture binding with oxygen – the very process that underlies the function of hemoglobin. Photo is CC 3.0 care of the artist.

As with every problem life faces, invertebrates have come up with many more interesting ways to move oxygen around than their spined relatives. Annelids (earthworms and their kin), brachiapods and spoon worms have a whole set of iron-containing proteins to do the job. Even more interestingly, molluscs and some arthropods have a protein that uses Copper rather than Iron atoms to co-ordinate an oxygen molecule. This molecule, called hemocyanin, takes on a green-ish blue hue when oxygen binds to it and changes its conformation.

Most snails get through life fine with hemocyanin as the only oxygen-carrying molecule in their blood, so why have Biomphalaria and their cousins become red-blooded? Part of the reasons lies in their lifestyle. Planorbid snails breath with lungs (which only work in air) but live underwater. If you make your living by holding your breath while diving then you really want to have some way of holding on to as much of the oxygen you get form each breath for as long as possible. It seems that Biomphalaria hemoglobin is more efficient at using the oxygen stored  in lungs while diving than any hemocyanin could be.

It’s all well talking about why an animal might have evolved a particular trait. But in evolutionary biology it’s generally much more intresting to try and work out how. How does an air-breathing snail make its own hemoglobin from scratch? A team lead by Bernhard Lieb asked just that question a few years ago, and found the answer: Biomphalaria hemoglobin was made by cobbling together parts of existing proteins. When Lieb et al (2006, doi: 10.1073/pnas.0601861103) isolated hemoglobin from red-blooded snails they found it was made up of two different components (called peptides), each of which has 13 different sub-components (called domains). When the team compared the sequence of those peptides and their domains to other molluscan proteins they found similarties between the hemoglobin sequences and another iron-containing protein called myoglobin.

Myoglobin is a small molecule that is usually restricted to muscles where is acts as a store of Oxygen (in snails, myoglobin is most commonly found in the muscles that drive the radula, the rasp like organ used to break down food). The Biomphalaria hemoglobin sequences are more closely related to each other than they are to myoglobins from any other species. This pattern suggests the sequences that make up the snail hemoglobin descend from a single common ancestor. Subsequent changes to each of these descendants have allowed the descendants proteins to group together and become ”super myoglobins” capable of transporting oxygen through the body.

*The huge number of ways size matters in biology were wonderfully explained by JBS Haldane. I’d reproduce the most famous passage here, but it’s probably even better if you discover it by yourself.

Sunday Spinelessness – Nothing to see here David Winter Jun 03

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I’m off to the Transit of Venus Forum next week. I’m looking forward to meeting all sorts of clever and interesting people (and escaping the coming snow), but travelling and conferring won’t leave much time for a few projects I really need to work on. So, today’s blog post is going to have to be squeezed down to its smallest possible form (a queen ant that dropped in to read an early draft of my thesis last spring):

Sunday Spinelessness – Lazy Link Blogging Edition David Winter May 20

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I though I’d do something a little bit different today. Instead of coming up with anything new to say or show you I’m going to steal from give a shout-out to a few New Zealand organisations that highlight  some of the amazing ways that spineless creatures get on with business of living.

Let’s start with Landcare Research (Manaaki Whenua), the Crown Research Institute that focuses on bioiversity and environmental issues. As you’d expect, Landcare do lots of work on invertebrates an that’s refelected in their public face. Their “What is this bug?” site is a great starting point for anyone trying to put a name to some weird critter that’s crawled out from the garden, and topic pages on some of our most interesting creatures (Onychophora, stick insects and our amazingly diverse moth fauna) make for a nice introduction to these groups.

The Landcare site I really want to pull out for special focus is their recently developed guide to freshwater invertebrates. Freshwater invertebrates are often use as “indicator species”. Because certain groups of stream invertebrates are very susceptible to pollution or changes to a stream’s natural flow, the presence or absence of these groups in particular stretch of water can give us an idea of the health of that water. In order to help community groups or landowner monitor their streams, Landcare has produced some beautiful photographs of stream invertebrates (along with information on how to sample them, and how well each species acts as an indicator). You really should check out the whole site, because some of them are quite beautiful, I’ll just give you a taster here:

Left: Kempynus lacewing sporting some impressive ‘tusks’. Right: Head shot of the larvae of an Onychohydrus diving beetle. Both images © Landcare Research

The other Crown Research Institute with a special interest in biodiversity is NIWA (the National Institute of Water and Atmosphere, if really wanted to know), who have a particular focus in the strange and wonderful creatures that live in the deep seas. NIWA scientists were part of the team that pulled up those mega-amphipods and I’m really pleased to say they have a great Facebook page dedicated entirely to their invertebrate collection. The NIWA Invertebrate Collection page has recently featured Phronima (one of favourites), Nematodes (perhaps the most under-studied group of animals on earth) an cold-water corals. Again, I encourage you to check out (an follow!) the page, but here are a couple of recent photos to entice you:

Phronima having recently evacuate its salp (© Owen Anderson). Tiny octopus! (photo from Ocean Survey 20/20)

Finally, let’s leave the Crown Research Institutes behind and go to Massey University and “Soil Bugs: A guide to New Zealand’s soil invertebrates“. Soil bugs is run by Dr Maria Minor and contains information and photographs of some of the thousands of species that live in the soil, leaf litter and rotting logs that cover the floors of our forests. Soil invertebrates a hugely important animals, being as they help to release the nutrients locked up in dead wood, but I’ve gone on about that plenty of times. So let’s look a couple of my favourites GIANT Springtails and native land snails:

Left: Holacanthella spinosa Right: Flamulinna zebra. Note, these images are © Massey University, and premission sought be sought to use them elsewhere.

Sunday Spinelessness – Each thing by its right name David Winter May 06

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In Dr Zhivago Boris Pasternak describes an epiphany that sneaks up on one of his characters thus:

For a moment she rediscovered the purpose of her life. She was here on earth to grasp the meaning of its wild enchantment and to call each thing by its right name…

It’s probably not spoiling the story to tell that Lara doesn’t dedicate her life to taxonomy at this point of the novel.I can’t say I really know what Pasternak was getting at with these sentences, but I’ve always liked them because they really do describe the driving force that makes taxonomists and lovers of natural history seek to understand and even name the wild diversity of life on earth.

I’ve recently learned the name of two species that turned up on these pages unnamed. So, let me introdue you to Thalassohelix igniflua (last seen in “they’re alive!”):

And Phenacohelix pilula (seen in Incertae sedis)

The drive that naturalists feel to call each thing by its right name can seem oddly obsessive to people that aren’t pulled by the same forces. But species are the fundamental units of biodiversity, and thus a natural point of comparison for studies in ecology, evolution and many other fields. If we want to understand biology we need to know about species, and if we want to know something about a species the we need to have a name that uniquely identifies that species in any scientific work. The species above got its name from Lovell Reeve and, being a New Zealand endemic invertebrate, only a little information has been tacked on that name since. Even so, knowing the name of this species is enough for me to learn that it is widespread across New Zealand, and down here in the southern end of the South Island it can co-exist with a close relative called P. mahlfelda. (From this last fact we can infer that it’s likey that P. mahlfeldae and P. pilula occupy slightly different ecological niches, as it is generally though two species can’t co-habitate while trying to take up the same sopt in nature’s economy).
I can also look at an unpublished study by the late Jim Goulstone, who collected snails from all around Dunedin and the surrounding patches of bush, and learn that its a bit of a surprise that our urban garden (we are 400 m away from the Octagon, Dunedin’s answer to a town square) has such a thriving population of this snail. Goulstone only found P. pilula at two sites in Dundedin, both in old-growth forests on the slopes of Mt Cargill. In both of those sites he only records one shell for P. pilula. Land snail distributions are notoriously patchy, but it’s still interesting to wonder how what seems like a fairly rare and habitat-restricted species ended up as the only native land snail in our garden. 

Sunday spinelessness – live-bearing land snails David Winter Apr 29

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People seemed to like the idea of a marsupial land snail, so today I thought I’d go one step further, and introduce you to land snails that give birth to live young. 
I was lucky enough to spend a little time in Vanuatu a while ago, and, although I was really there to relax and see in a new year, I couldn’t travel that far and not spend a little of my time looking for snails. As it turns out the island on which we stayed  is heavily modified, and there is not much natural habitat left for native land snail species. In fact, the only really interesting snails I found were living on the side of our host’s house. I collected a few of those snails, transported them to the fridge in our lab and forgot about them for the best part of year.
More recently it dawned on me that these snails would be useful for a project I am working on, so I grabbed them from the fridge, set them up under the microscope ready to dissect away a tissue sample for genetic work and saw this:

Embryos developing inside the shell of their mother. 
We sometimes think of live-bearing as being a trait that sets the mammalian branch of the tree of life apart from other animals, but that’s wrong. Most of the major groups of animals have some species that give birth to live young – there are live-bearing frogs, snakes, lizards, insects, fish, crustaceans and star fish. In fact, the only large group without live-bearing species that I can think of is birds (and, it seems, dinosaurs, a group that contains birds). Most land snails lay a clutch of many eggs, each containing a single-celled zygote which is left to develop on its own. A few species, like theses ones, have evolved a different reproductive strategy: producing fewer eggs than their relatives, but retaining those eggs within their shell before giving birth to much more developed young.

This behaviour seems to be particular common in snails that live in rocky outcrops, and those that live in the tropics, especially the Pacific. I’m not sure about what species the snail depicted above fall into – but they are from the sub-family Microcystinae, which is one of the dominant groups of land snails in the Pacific and is made up entirely of live-bearing species. The large evolutionary radiations that used to live in Hawai’i and the Society Islands were also all live-bearers.

So why give birth to live young? It is easy to see why live-bearing is an advantage to snails living in rocky habitats with few places to deposit eggs. It’s less clear why the Pacific is full of live-bearers. It has been suggested that tropical weather can lead to unpredictable patterns of boom and bust – with snails that can hold on to and grow their offspring in the bad times and release them “ready to go” when conditions are better having an advantage over egg-layers. As far as I know no one has ever come up with a way of testing that idea, so the reasons for the prevalence of live-bearers in the Pacific remains an open question.

Sunday Spinelessness – What’s brown and sticky? David Winter Apr 22

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Yup, I’m continuing with last week’s theme of terrible jokes. Of course you know the punchline for this one, what’s brown and sticky? A stick:

Both the objects in that photograph are brown and fairly sticky, but the one in the background is a bit more interesting.

That’s not a stick – it’s an insect doing a very convincing impersonation of a stick. Stick insects ( ‘walking sticks’ in North American, Phasmatodea everywhere in the world) are among the most impressive mimics in the biological world. As you can see, their bodies mirror the tiniest details of the plants they live on – right down to having stems and buds. The stickyness of stick insects goes deeper than their remarkable appearence – they also act like sticks. The rigid pose you see above is the result of my disturbing this one while trying to take a photo. The insect was so dedicated to its role I could easily pick it up and place it on its leaf while it maintained its spread-eagle pose.

A few minutes later it was on the move:

I don’t know what species we are looking at here. There are about 20 named species in New Zealand, though that is probably an underestimate of the true diversity. There seems to be lots of interesting biology going on among those species – species with sexual and asexual populations, a genus that arose by hybridisaton and one genus known only from two specimens. It’s possible this one is Niveaphasma annulata - a species that has patchy distribution across much of the southern half of the South Island and is pretty common in and around Dunedin. What ever the species name, here’s the beast making a bid for freedom from the faked-up leaf litter I put together for this little photo-shoot:

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