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Sunday Spinelessness – A Clearwing moth David Winter Dec 09

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At last, Dunedin has managed to arrange a proper summer day for a weekend.

The extra heat and sun saw plenty of bugs out and about, and I spotted plenty of familiar critters (native bees,  cicadas, drone flies and magpie moths) for this first time this year.  The real find of the weekend though, was something entirely new to me:
 

You might be a little surprised to learn that you are looking at a moth.

I’m helping design an undergraduate lab on systematics and taxonomy at the moment.  Since the new lab is about insects I’ve suddenly become very aware of the traits that distinguish various insect groups.  Moths, along with butterflies, make up the order Lepidoptera. You can see a few lepitoperan characters in the above photo: a mouth designed for siphoning nectar from flowers and a body covered in fine scales.

“Lepitoptera” actually mans “scaley wing”, and, indeed most butterflies and moths have scales on their wings. This species, though, has got rid of most of it’s wing scales (there are plenty of scales on the trialing edge though):

Synanthedon tipuliformis * is member of the “clear wing” moth family Sesiidae. Although I think this one is pretty neat, the family contains some striking species, the most interesting of which are wasp-mimics
Bembecia ichneumoniformis photographed by Lamois and licensed CC3.0



Yes, that’s a moth! Sesis apiformis from Flickr user Oldbilluk. Licensed CC2.0




*The species name means, I guess, “looks like a crane fly“… don’t see it myself

Sunday Spinelessness – Bark Lice David Winter Dec 02

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I should have known that the little challenge I put up last week wouldn’t so much as wrinkle the brow of the bug-blogo-sphere’s best. The Atavism‘s two homes means there were two winners. Ted MacRae of Beetles in the Bush chimed in at he blogspot version, correctly identifying the insect as a “bark louse” or psocopteran, and recognizing those stubby white protrusion as yet-to-be expanded wings . Morgan Jackson of Biodiversity in Focus did the same at SciBlogs.

Thanks too to Deborah from Bee of a Certain Age, who hazarded a guess that those white protrusions might be eggs. Certainly a more reasonable guess that my own first thoughts at seeing these bugs crawling over the the Big Tree* in our garden. The plump abdomens and long antennae made me think of the large (but certainly not GIANTspringtails. Ripping up a couple of pieces of bark revealed a whole colony of these odd-looking bugs, and evidence for just how wrong I was. 

The adults have wings, which they hold tent-like over their bodies. Insects are the only invertebrates with wings, so, since spring tails aren’t insects, my first guess was horribly inaccurate (glossing over about 400 million years of evolutionary divergence).

As Ted and Morgan worked out, these are “bark lice”, members of the order Psocoptera. Although they are related to the “true lice” (Order Phthiraptera), psocopterans are not parasites. Rather, they wander around their trees eating algae, fungi and whatever detritus might be clinging to the bark. The only species that could be considered pests are the “book lice” – small flightless psocopterans that sometimes turn up in old books where they eat the paste that binds pages together. (I have it on good authority that book lice can also destroy botanical collections, so certainly a pest)

A couple of weeks ago I gave Veronika Meduna a tour of our garden and its bugs, and I gather you can hear the result on Radio New Zealand’s Our Changing World next week. While I was catching my breath between talking about the mating habits of spiders, and how our native slugs are much more sluggish then their introduced counterparts she asked the obvious question – “why?”. Why do I care so much about odd little creatures like bark lice and slugs and spiders? I’m not sure I managed a coherent answer at the time, but I can tell you now, spineless creatures need evangelists because most people have a very skewed view about the way biology works. If your vision of biodiversity is limited to pandas and dolphins and lions and tigers then you are missing out on millions of other ways to be alive.

Take bark lice as an example. I’ll admit that I’d never given these creatures a moments thought  before running into them last week. But, in researching this post I found out there are more than four thousand psocopteran species. That is to say, there are almost as many bark lice species as there are mammals – all the lions, tigers, bears, dolphins, whales, marsupials, rodents and bats in the world add up to about 5 400. That matters because species are the fundamental units of biological diversity. Each species represents a distinct evolutionary lineage – free to take up different ecological niches, develop new morphological features or occupy a different geographic range.

To try an illustrate how diverse these unassuming little critters really are, I’ve put together a “treemap“. In the plot below, each of the stained-glass window panels represents the number of species in one psocopteran genus, nested within a family (the heavier lines, with labels ending in -DAE) which in turn is nested within a suborder (the very heaviest lines, labeled -MORPHA). These higher taxonomic ranks are not fundamental units in the way species are. Even so, species placed within a taxonomic group share evolutionary history, and are united by particular morphological characters which they share.  It turns out there are quite a few ways to be a bark louse:

And that’s just bark lice!

For me, this chart is the best answer to “why?”. How can you know you share the world with all this extraordinary diversity and not want to want to spend your time working out how it got here?



*This is not a botany blog… I really have no idea what the tree is

Sunday Spinelessness – An ID challenge David Winter Nov 25

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OK, here’s a chance for the bug nerds to show off. A photo of a strange-looking beast I recently ran into:

 

The challenge to readers is to answer the two questions that went through my head when I first uncovered the creature (1) What the hell is that? (2) What’s going with those opaque white projections?
Unlike others, I can’t often you anything cool as a prize for being right, but surely an electronic record to your entomological know-how will be enough?

Sunday Spinelessness – Shocked from sloth by a beautiful spider David Winter Nov 18

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Regular readers will know that I’ve been pretty slack in posting here in recent weeks. Just the same old boring reason – lots of “real” work to get done and, as much as I enjoy it, blogging necessarily floats to the bottom of TODO lists.

But I was shocked from my sloth this afternoon when I passed that accursed agapanthus and saw a spider I really had to share with the world:

It’s an orb-weaving (araneid) spider, a relative of the familiar garden spiders like the very common Eriophora pustulosa that spin orb-shaped webs and catch unlucky flying insects. I can’t be sure on the identification of this one, but I reckon (with some support from twitter’s resided spider experts, [1], [2]) its a species a species of Novaranea. According to Ray and Lyn Foster’s  Big Spider Book New Zealand Novaranea species are most commonly encountered in in grasslands and tussocks, so perhaps this one blew in from the tall grass that covers some the abandoned gardens in our block.

However it made it our garden, I’m very happy to have encountered a such a neat looking spider, and even done a half-decent job capturing some of its beauty:

All the media! David Winter Sep 25

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Oh, hi there. Yeah, it’s been a while h’uh? Just been crazy busy lately you know – one thing after another with manuscripts and datasets to analyse, then I got a whole bunch of lab reports to mark. We should totally like, get back to writing/reading about science though. I’ll put something up in a bit and…*

So, things have been a little quite here lately. That wasn’t a plan to have me an that ridiculous hat up on the front page for a few weeks – just the result of having little spare time. As it turns out, a few things that might be of interest to readers here have been published over that fallow period, here’s the links:

  • I’m in a book! As I related last year, my post on the partulids land snails of Society Isalnds was selected for The Best Science Writing Online which is now available from all good book sellers. I’m ridiculously excited by this. There is also a short review in The Listener 
  • My latest little piece for stuff.co.nz deals with Colin Craig and his idea that research tells us sexual orientation is a choice, and that this is relevant to marriage equality. 
  • I was on the radio – an hour of talking about science, peer review and skepticsm on Radio One, the student radio station.

I guess to complete the set I’d need to make a TV appearance, though I can’t see that happening!



*For people with whom I’ve had exactly this conversation lately – it’s true, I have been busy, I am a terribly friend and we will catch up soon!

Graduation, nerd blogging and a talk David Winter Aug 28

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The most dedicated readers of The Atavism may have noticed a few Sundays have passed without celebration of a spineless creature. Well, you know how blogging is sometimes. A few of the things that have kept me from blogging might be of interest to readers here. This weekend was dedicated to the wearing of silly hats, posing somewhat awkwardly and the conferring of my PhD. It was almost a big enough event to make me wear a tie:

So far I’ve rested the urge to change the name that appears under these posts to Dr David Winter, we’ll see how long that lasts.

I’ve also been working a little on some more software for evolutionary biology. Since I very much aim this blog at a lay-level, and there is no reason on earth why a lay-person ought to care about the computer programs scientists use to collect and analyse their data, I’ve decided to set up a dedicated nerd blog. The first post their introduces an R library that can help researchers quickly download data from molecular biology and medical databases.

Finally, I should say their probably won’t be a new post here this weekend either, as I’ll be at the New Zealand Skeptics Conference, right here in Dunedin. I’ll be giving a talk about how the the creation-evolution “debate” as it usually plays out has very little to do with evolutionary biology, and how getting past popular misconceptions about the way evolution works makes most creationist objections to evolution into non-starters. I’ll also say why I think good old fashioned creationism is a more respectable position than “intelligent design”, so that ought to be fun. If you’re in Dunedin you can still register for the whole meeting, my talk is on at 9:50am on Saturday in Archway 3 (the best, and perhaps only, way to find this lecture theatre is to walk into the Archway building and wander around opening doors at random).

Measuring population differentiation in R David Winter Aug 09

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ResearchBlogging.org

This is a little bit different than most posts here. I have a paper out today in Molecular Ecology Resources:  “mmod: an R library for the calculation of population differentiation statistics” (doi: 10.1111/j.1755-0998.2012.03174.x). Looking around the web, there aren’t many simple expositions of just what a “differentiation statistic” might be, and why the “modern measures of differentiation” my little R package can calculate might improve on the more traditional ones. So,  I thought I’d have a go here. 

Biologists often want to be able to measure the degree to which a population is divided into smaller sub-populations. This can be an important thing to quantify, because sub-populations within highly structured populations are, to some extent, genetically distinct from other sub-populations and therefore have their own evolutionary histories (and perhaps futures).

To illustrate this point I’ve run some simulations. Imagine if we had 5 subpopulations, each with a thousand individuals. In each population we will follow the fate of a locus with two alleles, R and r that have no effect on survival or reproduction and start with frequencies 0.8 and 0.2 respectively (these numbers motivated by this post). In the absence of gene flow between these populations (Panel 1) the frequency of the r allele bounces around due to genetetic drift (evolutionary change, after all, is inevitable). Crucially though, changes in one population can’t effect other populations so we end up with substantial among-population differences in allele frequency. In the next two panels, in each generation a proportion of each population’s individuals (0.001 and 0.01 respectively) are drawn from the other populations in the simulation. Now that the populations are sharing genes the lines that represent their allele frequencies pull together  (that is, the among-population variation is reduced). 




 

One way to quantify the among-population variation displayed in these simulations is to look at the number of heterozygotes you expect to observe across the entire population. The final values for P(r) in the first simulation were {0.33, 0.47. 0.88. 0.10. 0.33} with a mean frequency of 0.42 (so the frequency of the R allele would be 0.58). Knowing our Hardy Weinberg, if we had one big population with two alleles, one being at a frequency of 0.42 we’d expect to get 2pq = 2 * 0.42 * 0.58 = 0.40 heterozygotes. We can call that number Hfor expected total heterozygosity. But thats not what we’d actually see in this case. The sub-populations that make up this larger population have their own allele frequencies, when we calculate the expected proportion of heterozygotes for each of these populations by themselves we end up with {0.44, 0.49, 0.21, 0.18, 0.44} for a within-population expected heterozygosity (HS) of 0.35*. This lack of heterozygotes within sub-populations compared with the total population expectation will always arise when genetic drift makes sub-populations distinct from each other. 
Masatoshi Nei  used this pattern to propose a statistic to quantify population divergence called G
ST, which he defined like this:

 GST = (HT HS HT

Nei’s motivaton with GST was to generalise Sewall Wright‘s FST **, which was defined for diploid organisms and two-allele systems, so that it could be used for any genetic data. But there’s a problem with this formulation. Because HT  is always larger than H and can’t be greater than one, the maximum possible value of 
GST  is 1-HS. This dependency on the within-population genetic diversity means comparisons between studies, and even between loci in one study, are difficult (since Hwill likely be different in each case). This is particularly worryingly for highly polymorphic makers like microsatellites, which can give values of HS as high as 0.9, severely constraining the possible values of GST.


Although the problem of 
GST‘s dependence on HS has been known for a while, it’s taken some time for new statistics that get around this problem to be developed. Philip Hedrick (doi: 10.1554/05-076.1) along with Patrick Meirmans (doi: 10.1111/j.1755-0998.2010.02927.x) introduced G”ST  - a version of GST that is corrected for the observed value of HS as well as the number of sub-populations being considered. Meirmans used a similar trick to define φ’ST  (doi: 10.1111/j.0014-3820.2006.tb01874.x), another FST analogue that partitions genetic distances into within- and between-population components. Most recently, Lou Joust introduced an entirely separate statistic, D, that  directly measures allelic divergence (doi 10.1111/j.1365-294X.2008.03887.x). 


The statistical programming language R is becoming increasingly popular among biologists. Although there is a strong suite of tools for performing population genetic analyses in R, code to calculate these “new” measures of population divergence have not been available. My package, mmod, fills this gap.  I won’t give too many details of the package here, as that’s detailed in the paper and the package is will documented. Briefly, mmod has functions to calculate the three statistics described above (and Nei’s 
GST ), as well as pairwise versions of each statistic for every population in a datastet. It also allows users to perform bootstrap and jacknife re-sampling of datasets, the results of which are returned as user-accessable objects which can be examined with any R function (there is also a helper function to easily apply differentiation statistics to bootstrap sample and summarise the results) . The library is on CRAN, so installation is as easy as typing “install.pacakge(“mmod”)”, the source code is up on github. If want to use the package I’d suggest reading the vignette (“mmod-demo”) before you dive in.



I’m keen to hear about bugs or feature requests from users, just email them to




Reference:


Winter, D.J. (in press). MMOD: an R library for the calculation of population differentiation statisticsMolecular Ecology Resources : dx.doi.org/10.1111/j.1755-0998.2012.03174.x

* mmod actually uses nearly unbiased estimators for these parameters, to deal with the way small population samples can mis-represent the actual allele frequencies in populations.

** I don’t want to write an entire history of F-statisitcs here, because it’s a big and murky topic, but I did want to make the point that the formulation I gave for GST  is often presented as “Wright’s FST ” in genetics courses. Wright was certainly aware that his statistic was related to the proportion of heterozygotes you expect to get in a populaiton, but, when he introduced F-statistics in general, and FST  in particular, he was really dealing with correlation among gametes at various levels of population structure. Unfortunately, there are now many many definitions of FST  floating around, and it’s probably pointless to argue about a “right one”. If you use my package I encourage you to be explicit about, and cite, the particular statistic that you are using. For each of the the FST  analogues that the package calculates the in-line help contains the correct reference. 

Sunday Spinelessness – How snails conquered the land (again and again) David Winter Aug 05

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Christie Willcox wrote a nice article this week on how one small group of organisms called “vertebrates” first evolved to live on land. Since you are a vertebrate who lives on land, you should probably go and read Christie’s piece. I wouldn’t want you, however, to go around thinking those first fish to leave the ocean behind were pioneers making a uniquely difficult transition. By my figuring, onycophorans (velvet worms like peripatus), tardigrades, annelids, nematodes, nemerteans (ribbon worms) and quite a few arthropod lineages have also taken up a terrestrial lifestyle. Many of those lineages were already breathing air before Tiktaalik, Ichthyostega and your other long-lost relatives came along to join them on land. But if you want to talk about transitions from marine to terrestrial lifestyles then you really want to talk about snails. You can find snails living in  almost every habitat between the deep ocean and the desert, and snails have adapted to life on land many different times. In fact, a litre of leaf litter taken from a New Zealand forest can contain snails representing three separate transitions from water to land.

Almost all the land snails I’ve talked about here at The Atavism are descendants from just one invasion of the land. We call these species the stylommatophorans and you can tell them from other landlubber-snails because they have eyes on stalks (as modeled here by  Thalassohelix igniflua):

These snails are part of a larger group of air-breathing slugs and snails (including species living in fresh water,  estuaries and even the ocean) called pulmonates or “lung snails”. As both the common and the scientific names suggest, pulmonates breathe with lungs. Specifically, the mantle cavity, which contains gills in sea snails, is perfused with fine veins that allow oxygen to permeate the snails’s blood. In relatively thin-shelled species you can often see this “vasculated” tissue in living animals:

Blacklight photo of Cepaea nemoralis showing ‘vascularised’ lung. Photo is CC BY-SA via Wikipedian Every1Blowz
The pulmonates can also regulate the amount of air entering their lungs with the help of an organ called the pneumatostome or breathing pore –  an opening to the mantle cavity that the snail can open or close at will:

A leaf-veined slug from my garden – the small opening near the “centre line” of the slug is the pneumatostome. Interestingly, leaf-veined slugs don’t have lungs, the pneumatostome opens to a series of blind tubes not unlike an insect’s respiratory system

So that, along with a whole load of adaptations that prevent a fundamentally wet animal from drying out, is your basic land snail. But those little leaf-litter snails I’ve been talking about for the last couple of weeks provide a good reminder that other snail lineages have left the life aquatic. Here’s a species you find almost everywhere there is native forest in Otago, Cytora tuarua:

Holotype of Cytora tuarua B. Marshall and Barker, 2007. Photo is from Te Papa Collectons onlne, and provided under a CC BY-NC-ND license
Cytora is from the superfamily Cyclophoroidea, a group of snaisl that have indepedantly adapted to life on (relatively) dry land. (The weirdly un-twisted Opisthostoma is in this post is another cyclophoroid).  Cyclophoroids share some stylommatophoran adaptations to life on land, they’ve lost their gills and replaced them with a heavily vesculalised mantle cavity. Slightly oddly, cyclophoroids also breathe with their kidneys. Or, at least, the nephridium, an organ which does the same job as a vertebrate kidney, includes “vascular spaces” that the snail can use to collect oxygen from the air. Cyclophoroids don’t have an organ equivalent to the breathing pore to control the flow of air into the mantle cavity. Instead the mantle cavity is open and air enters by diffusion, or in larger species, as the result of movements of the animals head. 
For the most part, the respiratory and excretory systems in cyclophoroids are not as well adapted to life on land as those in their stylommatophoran cousins. For this reason, most cyclophoroids are only active in very humid conditions. In my limited experience, Cytora species are usually found deep in moist leaf litter and soil samples, and I’ve never seen one crawling about. Nevertheless, some species can survive in drier situations, and these are certainly terrestrial snails.
Local leaf litter samples reveal a third move from the water to land. I don’t have nice photo of Georissa purchasi, and I can’t find anything else on the web either, so you’re stuck with a crumby drawing from my notebook:




I did warn you that it was a crumby drawing. In life G. purchasi have an orange-red sort of a hue, and you can often see patches of pigment from the animal through the shell.  Georissa species are from the family Hydrocenidae and are quite closely related to a group of predominantly freshwater snails called nerites. Just like the other lineages discussed, the Hydrocenidae have given up their gills and breathe through a vasculated mantle cavity. Very little is known about the biology of these snails. G. purchasi is sometimes said to be limited to very wet conditions, but I’ve collected (inactive) specimens form the back of fern fronds well above ground so it can’t be completely allergic to dry . 
So, in a handful of leaf litter collected from a Dunedin park you might have cyclophoroids, hydrocenids and  stylommatophorans – descendants from three different moves from sea to land. If we look a little more broadly,  there are are many more examples of this transition.  I’ve written about the the helicinids before, then there are terrestrial littorines (perwinkle relatives) some of which have both gills and lungs. Plenty of other pulmonate lineages that have also taken up an entirely terrestrial lifestyle. Because some of these groups have adapted to life on land multiple times, there have probably been more than 10 invasions of the land by snails.

Most of the description of Cyclophoroids here is taken from:

Barker, GM (2001) Gastropods on land: phylogeny, diversity and adaptive morphology In Barker (Ed.),  The biology of terrestrial molluscs (pp 1146) CABI Publishing.

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

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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.

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