Introducing Cambridgea foliata

Now that I’ve divided my facebook friend into arachnophobes, arachnophiles and arachno-mehs, I should probably get to posting things about spiders. Or at least things about the species that I’m working with at the moment. So consider this a crash course on the primary Auckland Cambridgea species: Cambridgea foliata

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C. foliata male

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C. foliata female

 

 

 

lads and ladies

A couple specimens (sorry that they’re covered in ethanol and therefore very shiny). Male on the left with large jaws and genital bulb on his pedipalp. Female on the right without.

For wee NZ these are relatively large spiders (body length can be almost a couple centimetres). Males tend to have longer chelicerae (jaws) than females and have bulb-like structures on their pedipalps. If you have a microscope, you can see that these bulbs actually look more like this:

palp

NB: This is a Cambridgea palp but I can’t remember if it’s C. foliata specifically because I’m in a cafe avoiding eye contact with punters rather than at my desk doing the same thing. Anyway, these structures are highly complex secondary genitalia because, as I’ve been gleefully telling people who didn’t want to know, spiders don’t have penises.

Males still produce ejaculate out of their down there’s but rather than transferring directly to the female epigyne (external genital opening), they place it in their pedipalps and, from there, “deposit” it in the female.

Imma leave this here for y'all

Imma leave this here for y’all

Despite how widespread these spiders are, particularly in the Waitakere ranges, they’re relatively unknown because they’re nocturnal and hide in retreats during the day. Retreats can be tunnels drilled in live or dead wood by other invertebrates, tunnels in banks or even folded over nikau palms.

The thing people are probably more familiar with are their webs. New Zealand sheet-web spiders will spend weeks generating a giant mass of silk consisting of a main sheet guyed from below and a nightmare of knock-down threads above the web. Most (but not all) Cambridgea build these webs and C. foliata make the largest (up to a square metre in area).

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Just one of the many webs you will see if you ever go into Waitakere. Mainsheet and knock-down threads should be apparent.

 

 

At nightfall, the resident emerges from his or her retreat and will sit either at the entrance of the retreat or in its hub (centre). Flying insects from moths to huhu beetles blindly crash into the knock down threads and fall into the web. The disturbance of the insect attracts the spider who grabs it through the silk and gets down to the business of feeding.

If you go out at night between November and February you may be fortunate enough to see multiple spiders on a web. In the summer, males depart their lovingly constructed webs in search of females. When they find one, they take up residence with her and will even live in her retreat during the day (this sort of cohabitation is rare in spiders). I’ve already written/depicted what happens when a male enters a female’s when another male has already taken up residence.

So hopefully that’s enough of an introduction to the weird little world of spider life in Auckland. Happy now, Meg?

 

 

 

 

A week on Burgess Island; Fun titles are hard

About a week ago I shirked mainland life and mainland PhD work for just under a week of remote island living. Burgess Island of the Mokohinau Islands is situated off the North East coast of the North Island. The island is a scenic reserve and key field site for another PhD student, Megan, who is studying colouration of sea birds such as the diving petrel (Pelecanoides urinatrix). While Megan and another PhD candidate are still on the island, I went along for the first half of their trip to take an opportunistic fossick around the undergrowth for Cambridgea. I didn’t have much luck (at most I found a couple outgroup species for phylogenetic analysis) which made it all just a fantastic holiday before I start knuckling down to begin my own field work.

This post is just a large photo brag.

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The last photograph is there to prove that there was work going on. (Even if it wasn’t mine). Big thanks to Megan for letting me come along on the trip that she organised (field trip without having to do all the admin = literally the best thing).

Not depicted: The 45 knot winds and the 110m, 45 degree incline hill that the hut was on.

Update on mite situation

So I mentioned my bouncing bundle of a billion-or-so surprises that I found in Cambridgea eggs to my supervisor about a fortnight ago. He was unsure of what they would be but recommended that I send some down to a colleague of his at Canterbury museum who is their resident “mite guy”. So had another dig around in the egg cases, pulled some mites out and dropped them into a vial of ethanol to send down.

When working with animals <1mm long, surface tension is the bane of my existence. i.e. very small animals stick to damp surfaces like Gollum to the one ring and any you really just want to squash the damn thing and then you do by accident and feel bad.

Anyway.

So last week I got an email back from mite expert. He had mounted them (the notion of mounting these suckers blows my mind) but doesn’t have the appropriate microscope to properly identify them with certainty to anything below family level(1).

So the mites were identified as to the order Sarcoptiformes (the only thing I can find in my Greek dictionary for this name is that they have fleshy bodies?). Matt (mite expert) also believes that they are of the family Acaridae and says that there are several genera of this family which will colonise mouldy grain or rotting carcasses of invertebrates. “If humidity is high enough they can colonise virtually anywhere” he says.

When I mentioned that the mites were found inside the egg cases, he also raised the point that they breed explosively and, if they are parthenogenic(2). then only a very small number of females would have to make it into the egg sac.
So it’s basically it’s not clear whether the mites were feeding on the eggs themselves or on mould or something similar. When I asked about the dusty contents of one of the egg cases (Fig. 1) he said that it could be bits of the eggs themselves although they could also just be mite faeces. Which makes the granola analogy even “better”.

Egg e4

Fig. 1: Photographs of C. foliata egg case and mites going nom nom nom

 

 Notes that are longer than original post:

Tangent 1: Pretty much everyone is familiar with the idea of binomial nomenclature even if you didn’t know that that’s what it’s called: i.e. all species have a unique pair of latin names such as Homo sapiens. These two words designate different levels of classification.

e.g. In this case Homo refers to a specimen’s “genus” (plural “genera”) which is a broader level of classification which will contain several species while sapiens is the “species” proper. So Homo neanderthalensis is in the same genus as modern humans but is a different species. There are several higher level groupings are used in taxonomy (The practice of classifying species. “taxis” (ταξις) referring to arrangement and “nomos” (νομος) referring to a practice or convention). Genera are nested with families and families within orders etc. From the most broad to the most specific, these taxonomic levels are Kingdom, Phylum, Class, Order, Family, Genus, Species.

Also known as King Phillip Came Over For Grilled Sausages.

(NB: There are several other classifications between these main ones such as “tribe” and the names of the classifications can differ between botanists and zoologists.)

So humans are, in full:

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Primates

Family: Hominidae

Genus: Homo

Species: H. sapiens

Tangent 2: Parthenogenesis is a form of asexual reproduction in which females produce only daughters without having to mate with males (παρθένος = parthenos = maids or young women. I can’t figure out whether it’s implying that parthenogenesis only generates females or whether it is reproduction by unmated females/maids). It occurs in several invertebrates but at significant physiological cost for the female. In the springbok mantis (Miomantis caffra), females readily laid egg cases without mating with males and these did produce viable young. However, in a species from the same genus, the nymphs (young) produced from these egg cases often didn’t make it to adulthood or were in poorer condition. Even with this cost parthenogenesis can be a powerful way for females to rapidly generate identically (or virtually identical) young who will succeed provided that the environment is relatively stable

First forays into μ-CT scanning

Now I’m just using this blog to validate the work I do each day…

And on this particular day I’ve been messing around with a CT scan of a spider jaw (chelicera). As I might’ve mentioned previously, during the summer, the male sheet-web spiders (who have massive jaws – far bigger than those of the females) go wandering in search of females/their webs.

Lads and ladies (Cambridgea foliata)

Lads and ladies (Cambridgea foliata)

When they find one, the male sits in the hub of the web and will stay there all night. If the male wanders into a web with another male already resident, they will fight. What determines the outcome is the differential in “resource holding potential”. RHP is combination of an individual’s body size, weapon size, physiological condition and previous experience. The individual with the higher RHP is more likely to win.

I’m looking at the evolution of exaggerated male weaponry and it has been suggested that extreme male weapons evolve to help males win these competitions i.e. contribute significantly to RHP. The idea is that a bigger weapon makes for a better fighter or that a large weapon makes a male look like a better fighter so other males are less likely to approach. Both processes would result in a male who is able to monopolise the female.

The problem is that weapon size is highly correlated with body size so it’s been very difficult to determine statistically whether larger weapons actually make any meaningful contribution over and above that of a larger body size. Try to imagine a giant bare-fisted boxer who had massive hands which were big relative to the boxer himself. Like, hands bigger than own face. One could argue that bigger hands/fist could help him to win a fight but how do you actually prove that? You would have to separate the effect of his hands from the effect of just being a big person. You can’t consider the two traits in isolation because that would require removing his hands which only shows that you need hands to box effectively and that a disembodied pair of hands is…just that.

maim_anakin

thing00

Jedis and Thing are the only exceptions

There are a couple ways that people have tried to circumvent this when studying animals. One is that people have used force transducers to get direct measurements of bite force or nipping force, depending on the type of weapon. Another avenue is doing finite element analysis on the structures. Some biologists already use finite element analysis to look at loading on things like leg bones in different species of moa and have used various traits to estimate bite strength from crocodile skulls. Recently someone has done this sort of analysis on spider fangs.

One of the first steps to doing such an analysis is doing a micro-CT scan (computed tomography) of the weapons and the musculature. I went along for my first CT training session a couple weeks ago. I was told to bring a sample to scan so I decided to take along part of a male Cambridgea foliata. Unfortunately I was an eejit who decided to dissect off the jaw to scan rather than taking the whole head. The result is that you can’t see the full length of the muscles controlling fang movement but the scan I got has given me the chance to play around with different bits of software and generally get a first look into the structure.

The end result is an 8 second video which I’m more proud of then I really should be. *tadaa* *spirit fingers*

 

 

Spontaneous generation feat. bisecting things is fun

So something happened today which would neither surprise nor impress someone who actually had any experience studying spiders. But this is my first year of it so I’m going to bring it up anyway.

So I had spiders in my house over the summer for observations and some of the females laid egg cases.

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Female C. foliata and spawn

These were roughly spherical orbs slightly less than 1cm in diameter which would be hung from the roof of their mesh cages. Sheet-webs in the wild will incorporate forest floor debris into the egg casing. In the case of my spiders their cages were a little Spartan so they had to make do with the left over legs of the insects I had fed them.

When the females died I removed the egg cases and kept them in little pottles (plastic jars), trying to keep them suspended if I could. Demonstrating an innate aptitude for husbandry, these various eggs were starved of oxygen i.e. lids on until I realised this was dumb; they were exposed to extreme desiccation i.e. left on the window sill during the summer; and then they endured several months of Auckland winter in a cold student flat.

Then I read somewhere that, in some cases, the female spider actually has to open the egg case for the young to escape.

Needless to say, when I brought a couple of the egg cases into the lab a full 6 months after they were laid, I was expecting, at best or at worst, to open up the sacs to find puckered, charcoal eggs. Either that or the bodies of hundreds of spiderlings squashed together until they were indistinguishable or utterly dismembered, mutilated in the Battle Royale which I had imposed on them with one engorged baby spider lying prone, ultimately unable to escape the silk prison.

battle royale

Amazingly, only two males were cannibalised

The outer casing of the sac is white with the feel of a tough napkin which I had to cut through with my dissection scissors. On the inside there was a cluster of eggs (each egg <1mm diameter) held together with an off-white cement. This cluster hung in the centre of the sac, suspended in fine, kinked threads which came in every direction from the inside surface of the outer sac.

A nice word for it would be that the eggs sat in a harness, a more amusing one would be that the egg sac is basically a spider zorb.

(The block of eggs broke)

I pulled some of the eggs away a cut them open but the magnification on the dissecting microscope wasn’t really up to the task of distinguishing the contents. The eggs themselves ranged between dark brown and pale orange and some did indeed look pretty much dried up and there wasn’t a whole lot of evidence of anything breaking out of the egg.

egg 1 bissected

 

But it was at this point while I was looking at a block of the cluster that had broken off that I saw little pale blobs moving around. I think that they might be mites.

You can see some little orange legs just above the top egg.

egg 1 friend

The suckers are <0.5mm and move around so I couldn’t really get a good focus on them. You can see the pale oval (it’s abdomen) with an orange head on the dark egg.

 

 

egg 1 single 2 marked

egg 1 friend marked As a hint

 

A similar surprise met me when I opened up the other one, albeit a more…plentiful one. This egg was almost completely full of what looked like fine grain sawdust but *surprise* the sawdust is little animals!

Who fancies some granola?

Egg e4

Yep. ALL of the little pale ovals are…arachnids of some description

If these things are mites then it looks like they have chewed up the eggs hence the mess.

What does this have to do with anything? Not a whole lot. I have the animals in a mesh cage in the lab at the moment and will try to rear them in the time honoured tradition of “let’s see what happens”.

I like an animal which can survive in spite of me.

(Here’s a quick sketch of them (the abdomen isn’t big enough). Makes me think mite).