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Like probably everyone reading this, I have always thought that spiders are carnivorous, sucking the precious bodily fluidsA from their prey. I mean, those fangs!

And I was wrong, for it seems that some spiders eat some plant material alongside their liquid meals - and some are almost fully vegetarian. A just-published paper (Painting, Nicholson, Bulbert, Norma-Rashid & LI, 2017) notes that while most of these spiders take nectar from flowers, there's even one - with the delightful name of Bagheera kiplingiB - where much of its diet comprises the nutrient-rich leaf tips of acacia trees (more on that later).

The nectar-eating spiders don't rely exclusively on sweet treats; the sugar they obtain supplements their main diet. Apparently the sugar-sipping habit incurs a certain amount of risk. This is because 'extrafloral' nectaries (eg at the bases of leaves, or on the leaves themselves) are used and guarded by ants. This behaviour itself is an interesting one, as it's an example of a mutualistic relationship between the ants and the plants. The ants obtain nutrients, and their aggressive behaviour towards other animals can reduce damage by herbivores. Painting and her colleagues comment that other invertebrates - such as spiders - typically feed from these nectaries only when the ants are absent, but found evidence that 

the jumping spider Orsima ichneumon guards extrafloral nectaries through active confrontation with ants and by depositing silk barriers to inhibit their competitors.

The researchers were intending to investigate the hypothesis that the flamboyant little spiders are ant mimics, an hypothesis which - given the bright colours of this species and the generally uniform dark colours of ants - sounds a little unusual. Their plan was derailed by a landslide that meant they couldn't get to their field station, but that didn't stop them making roadside observations instead.

Figure 1

Figure 1: a male Orsima ichneumon showing off his medley of colours. From Painting et al., 2017

The team spotted a female O.ichneumon feeding from a nectary on a leaf, a behaviour that didn't take them totally by surprise as other scientists had already reported such behaviour in spiders. What was unexpected was the fact that she then laid down patches of silk around each nectary, after feeding there. Nor was this behaviour isolated to a single individual. And what's more, the researchers also observed the spiders chasing smaller ants away from their feeding spots, and avoiding larger ones. As a result they formed the hypothesis that the silk deposits - made at some energy cost to the spider - act as a deterrent to the ants, although they note that this suggestion has yet to be tested, along with the idea that the silk might be a form of spider GPS, identifying the location of food sources. But why hang around on plants where there are aggressive ants to contend with, rather than go somewhere else with more insect prey & fewer ants? Painting el al. suggest that moving around between plants may increase the risk of predation, whereas staying put might afford some passive protection due to the ants guarding 'their' plants. Plus, the energy pay-off from nectar feeding may outweigh the costs of making the silk & chasing away the smaller ants.

Now, on to Bagheera! I was sent a delightful link about this little jumping spider as a result of tweeting my surprise that vegetarian spiders are even a thing :) B.kiplingi lives on a Central American species of Acacia that's also defended by ants, and which produces structures called Beltian bodies for ant consumption. The spider gives adult ants a miss (although it eats their larvae - and plant nectar), but it eats a lot of the Beltian bodies: in the original paper Meehan, Olson, Reudink, Kyser & Curry (2009) note that these plant structures make up 60-91% of the spiders' diets. This is strange, to say the least, as they turn out to be very high in fibre and low in fat.

Fig. 2 Evidence of herbivory in the jumping spider Bagheera kiplingi. (A) Adult female consumes a Beltian body harvested from the tip of an ant-acacia leaflet. (Photo: M.Milton.) (B) B. kiplingi diet estimated from field observations. Beltian bodies contributed more to the spider's diet than did other food sources, especially in Mexico (sample sizes refer to numbers of food items observed). From Meehan, Olson, Reudink, Kyser & Curry (2009)

Meehan & his colleagues noted that the spiders live almost exclusively on acacias guarded by ants, living mostly on older leaves where ant patrols are less frequent, and avoiding ants when they're encountered. That they can survive on a high-fibre diet suggests that their gut physiology is quite different from that of their carnivorous relatives; either that, or they've acquired some gut commensals that do the job for them. The fact that they've cut out the 'middle man' (the ant larvae) to consume plant material directly may allow more spiders to live on a single plant than would be the case if they were still carnivorous.

Meehan et al. conclude by noting how the spider's unusual change in diet was dependent on the ant-Acacia relationship:

The host-specific natural history of B.kiplingi demonstrates that commodities modified for trade in a pairwise mutualism can, in turn, shape the ecology and evolutionary trajectory of other organisms that intercept these resources. Here, one species within an ancient lineage of carnivorous arthropods - the spiders - has achieved herbivory by exploiting plant goods exchanged for animal services. While the advanced sensory-cognitive functions of salticids may have preadapted B.kiplingi for harvesting Beltian bodies, this spider's unprecedented trophic shift was contingent upon the seemingly unrelated coevolution between an ant and a plant.

 

A Sorry, couldn't resist a Dr Strangelove reference :)

B how could you not love a cute little creature with a name like this?

 

CJ Meehan, EJ Olson, MW Reudink, TK Kyser & RL Curry (2009) Herbivory in a spider through exploitation of an ant-plant mutualism. Current Biology 19(19) R892-893. doi: http://doi.org/10.1016/j.cub.2009.08.049

CJ Painting, CC Nicholson, MW Bulbert, Y Norma-Rashid, & D Li (2017) Nectary feeding and guarding behaviour by a tropical jumping spider, Frontiers in Ecology and the Environment 15(8). DOI: 10.1002/fee.1538

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Back in 2012 the Herald ran a series on alternative 'therapies' that included a somewhat uncritical piece on the use of leeches - the practitioner concerned claimed, for example, that they could be used to 'treat' diabetes. I blogged on this back then, as did fellow Sciblogger Siouxsie Wiles, &  the criticisms we made then still stand.

However - colour me gobsmacked - it seems that this practice continues, with the same practitioner now adding the claim that this is a valid therapy for Parkinson's disease and for cancer. According to the Stuff article I've linked to above, he appears to be also advising those seeking his help that they eschew "medical interventions such as chemotherapy or medication", because otherwise his 'treatments' won't work.

On that basis alone I really really hope that Medsafe takes things further. Alarmingly, at least one commenter on the article suggested that there should be a clinical trial to compare leech 'therapy' to the outcomes of chemo and other medications. As another person said, in response (my emphasis):

I wouldn't want to tell a patient that they're not getting their effective treatment because some crackpot said that leeches work and we need to test the theory. Ethically it would be a disaster.

What's more - leeches used in mainstream medical procedures are bred under carefully controlled, clean conditions. The company producing them refused to sell them to our alt.med practitioner. But the Stuff article makes it clear (including a photo) that, to continue offering leech 'therapy', 

he collected his own leech supply that is kept in a pond to use on his clients...

A pond. Outside. No control of water quality or diet. What could possibly go wrong?

 

 

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I mean, really - have you ever seen something like this before?
 

Melibe engeli is a type of sea slug, and a most unusual one. Its body is partly translucent, and has projections called cerata, themselves covered with smaller projections called papillae, down both sides. The animal is an active hunter - but what a hunter. It lacks the toothy radula seen in most gastropods, & instead has that amazing, extendible, 'hood' around its mouth. Tiny, highly-sensitive hairs detect prey & trigger the animal to close the hood; the prey animal is engulfed whole, to die during the digestive process.

I don't think sci-fi could come up with anything stranger than this!

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So, I own a pocket wolf.

...

...

Oh, OK, I own a little black mini-poodle. But, like all dogs, he has the same number of chromosomes as a wolf!

There've been several articles posted recently about the evolution of domestic dogs. While we've tended to think that domestication didn't begin until humans began to settle down & develop agriculture, DNA analysis suggests that wolves and humans may have begun a relationship up to 100,000 years ago. And a paper published in Science back in June presents evidence that there were two domestication events, one in Asia and once in either the Near East or Europe. There's a nice visualisation and explanation of the doggy family tree here.

A few weeks ago, I was discussing domestication with RadioLive's Graeme Hill, and one of the questions he asked was, why do we have so many different body forms in domestic dogs, and so little variation in form in cats? Was it because the dog genome is more 'plastic' & susceptible to change? My answer was that I suspected it had more to do with the length of the species' association with humans. Cats are sometimes described as 'semi-domesticated', and our shared history may go back just 10,000 years (with the possibility, again, of at least two separate domestication events). Whereas 100,000 years gives a lot of time for selective breeding by humans to produce all those different dog breeds.

Which takes us to bulldogs - the subject of a Scholarship Biology question in 2014. Bulldogs were originally bred to drive cattle, and had the strength and the ferocity (and presumably also a high pain threshold!) to subdue an animal by grabbing its muzzle and hanging on. They were subsequently used in bull-baiting, a cruel 'sport' that the UK banned in 1835.

Instead, the dogs were then bred for show. While their physical characteristics remained pretty much the same (short & squat, very muscular, the familiar very short face/muzzle with deeply folded skin) - by 1860 they had already begun to develop, as a result of selective breeding, their now-familiar gentle, non-aggressive temperament.

Unfortunately, selection for that very distinctive body form has brought with it a whole host of inherited disorders. You've probably met a bulldog with that snorfling, stertorous breathing - this respiratory problem is called brachycephalic syndrome, due to the very short face & nasal passage. Other heritable disorders include:

  • hip dysplasia (seen too in other breeds, such as labradors), where the hip joint can partially dislocate - this one is due to polygenic inheritance ie there are a number of different genes involved. 
  • a hole between the two ventricles of the heart. This is called ventricular septal defect (VSD), and an animal must inherit 2 copies of a recessive allele to express this disorder. It's autosomal, which means that male and female bulldogs are equaliy likely to express it.
  • cryptorchidism - one or both testes remains up in the body cavity instead of descending to the scrotum. This one is an autosomal dominant trait - only one copy of the allele is required. 
  • and - with all those wrinkles - dermatitis, also considered to be an autosomal dominant trait. The dermatitis often leads to bacterial infections. 

Poor bulldogs :( 

The actual exam question gave this background information & asked students to discuss two things: how humans may have manipulated the evolution of bulldogs from wolves; and how further selective breeding could be used to try to eliminate EACH of the named disorders AND evaluate how effective this might be. For students intending to sit these exams: remember that when you're answering these questions you need to provide both 'evidential' statements and justifications for them. And to do that, you'll need to integrate the resource materials provided in the exam paper with your own biological knowledge. 

The first part's pretty straightforward: you might consider, for example, why humans would want to select for non-aggressive wolves (eg for help in protecting a human or group of humans from other predators). Or what about the founder effect, which would come into play because of that small population of proto-dogs? The small sample of the wolf gene pool found in those first 'dogs' could mean that particular alleles were simply lost in the dog population, while others could become much more common.

You'd then want to address the sort of things a breeder would focus on to get from generalised doggy form to the highly specialised bulldog: insensitivity to pain; the short, powerful, upwards-facing jaw; the squat, heavily-muscled body. Don't forget the explanation: that the physical features would allow the dog to drive or subdue much larger animals, and that selection for those traits, if they had a genetic component, would see those particular alleles to increase in frequency in the bulldog gene pool.

And of course, once bull-baiting was banned, selection for gentleness/docility came into play. Because that called for further inbreeding in the existing bulldog population, it would likely result in a higher frequency of any existing harmful alleles as well.

The second part of the question tests understanding of students' knowledge of concepts around inheritance. In some cases it's probably possible to remove the deleterious alleles from the bulldog gene pool - but as a result the dogs would diverge from what's currently viewed as the breed standard. For example, selective breeding for a longer, less-wrinkled face could reduce the frequency of brachycephalic syndrome and dermatitis - but the resulting animals would be much less bulldog-like!

The same approach is less likely to be effective for hip dysplasia, however, due to the polygenic nature of this disorder, because it involves multiple genes rather than a single gene locus.

But selective breeding could help with VSD & cryptorchidism. For example, a dog that doesn't express VSD is either homozgyous dominant (with 2 copies of the normal allele) or heterozygous. So at the population level, breeding heterozygous individuals will on average produce 25% of pups with VSD, with the rest not expressing the disorder. Using a test-cross would allow you to breed only from parents homozygous for the normal allele, but it would take more time.  

And with cryptorchidism, you'd avoid breeding from males who had the disorder (which would have very poor fertility anyway, I'm guessing), and from females whose sons had undescended testes (because these females would be 'carriers' for the allele - while cryptorchidism is a dominant trait, you're only going to see it in males). 

Of course, you could also try out-breeding with other dog breeds - but then, the resultant pups may well not conform to the bulldog 'standard'. 

I must say, it does bother me that adhering to a breed standard - a human construct - can perpetuate known health problems in a breed such as this.

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There's a lovely, life-size bronze sculpture of a Powelliphanta land snail sitting on my china cabinet. I love it because a friend made it for us - and because snails in this genus are rather special, for they are all carnivorous.

Now, I 'knew' this fact, but I'd never actually seen one feeding. Snails being normally rather slow, sedate creatures, it was hard to imagine how they'd ever catch anything other than even slower prey. That was until I saw this video

Every earthworm's nightmare!

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The semester's begun, teaching has started, admin isn't letting up any time soon, & there are days when I feel like a zombie by home-time. So it seems entirely appropriate to revivify a post I wrote 3 years ago, on that very subject.

Honestly, sometimes I think the zombie apocalypse is already here. Certainly zombies seem to be flavour of the month (& whatever friends say, I still can't bring myself to watch Walking Dead). And I've written about them myself: well, the insect variety, anyway.

But our developing understanding of how parasites 'zombify' their hosts has been developing since well before the latest iteration of human zombies grabbed the popular imagination. I was reminded of this when I saw the video below (in all its over-the-top hyperbolic glory), for I was first introduced to the concept of zombie snails years & years ago by one of David Attenborough's TV programs**. (According to my aging memory, it would have been an episode of Life on Earth.) 

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Tunicates are more commonly known as 'sea squirts' - little blobby marine creatures that squirt water when you touch them (hence the name). We don't hear about them often, except perhaps when they make the news for all the wrong reasons. But from an evolutionary perspective they are fascinating little creatures - and it's largely due to their larvae.

As an aside: why do we call them tunicates? Because the body of the adult organism is enclosed in an outer sheath, aka a tunic. The majority of tunicate species belong to a group known as ascidians, which as adults live in shallow waters, attached to rocks or maritime structures (including boats). The remainder are planktonic & found out in the open ocean.

The larvae of many ascidians are free-swimming and, because of their body form, are often described as 'tadpole larvae'. (Some of the non-ascidian tunicates have adults with the same morphology.) These little animals have a number of features (shared with creatures such as the cephalochordate formerly known as Amphioxus) that link them with the chordates: a hollow dorsal nerve cord, a post-anal tail, a pharynx with slits in it (which feeds into the gut), and a living cartilaginous rod known as the notochord, against which the animal's muscles work. (The larvae, and the adults of some non-ascidian tunicates, are basically little swimming filtration units.)

In fact, because of their rather simple structure, tunicates have long been viewed as representing the likely common ancestor of both chordates (a group that includes us) and the slightly-more-complex cephalochordates like Amphioxus. However, a newly-published & fascinating article by Linda Holland (2016) looks at 

the highly derived body plans and life styles of the tunicate classes, their importance in the marine food web and their genomics [with an] emphasis ... on the impact of their especially rapid evolutionary rates on understanding how vertebrates evolved from their invertebrate ancestors.

It turns out that a genomic comparison, using nuclear genes from chordates, cephalochordates and tunicates, indicates that it's actually Amphioxus that sits at the base of this particular group. This in turn means that tunicates

have lost a lot of what the long extinct ancestral tunicate once possessed. 

This genomic work is fascinating on a number of levels. For example, the 'textbook wisdom' is only bacteria (ie Prokaryotes) have their genome organised into operons, where a single mRNA transcript contains several genes. But it turns out that tunicates, which have a rather small genome.

[have] a high percentage of genes in operons

something that Holland states they share with roundworms (nematodes) and some flatworms, which apparently also have "reduced genomes". In tunicates, it seems that among the genes that have been lost are some of the 'Hox' genes - genes that control the development and patterning of body form. 

I learned heaps of new things from this paper: tunicates are able to regenerate most of their bodies, for example (makes sense, I guess, as the sessile adult sea squirt can't exactly avoid being snacked on by predators). Apparently this is achieved by pluripotent stem cells in the animals' blood, though how it's done is still something of a mystery. And I had no idea at all that the animal's 'tunic'

contains cellulose, synthesized by a cellulose synthase that was evidently acquired in an ancestral tunicate by horizontal gene transfer from a bacterium. 

An animal that produces cellulose! Nature never ceases to surprise :)

L.Z.Holland (2016) Tunicates. Current Biology 26: 4 pR146–R152 DOI: http://dx.doi.org/10.1016/j.cub.2015.12.024

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So, last night I was asked how hedgehogs mate. 

The obvious answer was, carefully! My interlocutor suggested that perhaps face-to-face was most likely, but as far as I know, very few species (& that short list includes our own) do that. It turns out that care is indeed needed, for the male approaches the female from behind, & she must adopt what's coyly called a 'special posture' and flatten her spines so that the sensitive portion of his anatomy doesn't take on the appearance of a kebab.

The question was actually part of a wider discussion around the architecture of sexual reproduction: the mechanics of how the bits fit. If you'd like to hear the entire thing, it's here on the RadioLive site.) Entomologists, in particular, seem to spend quite a bit of time studying this architecture, not least because these details may help them distinguish between species that are otherwise pretty much identical in their appearance. (There's a lovely story about Michael May's work on dragonflies here, complete with etchings illustrations.)

In many cases the structures - which can be quite bizarre - are driven by competition. Competition between the males, but also between males and females. So in those dragonflies, for example, the males' penes have all sorts of features that are related to sperm competition - they allow a male to scoop out, scrape out, or otherwise displace semen deposited by another male, and replace it with their own. And in mallard ducks, which are highly promiscuous, a sort of male/female arms race has driven the evolution of extremely complex genital anatomy in both males & females, discussed here by Ed Yong. Incidentally, that link also includes a video - perhaps not for the faint-hearted! - of the rather explosive uncoiling of & ejaculation from the drake's corkscrew penis.

Some of these structures can be rather large: we're talking a metre long for male African elephants, for example (according to wikipedia), around 2.7m in right whales, and up to 3m in Blue whales (the largest animals alive). And as one might expect, this has been attracting human attention for a long, long time. Sadly, some of that attention has been seriously harmful to the survival of some species - witness the aphrodisiac claims made for the sex organs of tigers by Traditional Chinese Medicine, for example. But there's also the point-&-wink sort of interest, shown in a painting of a dead sperm whale dating from 1606 and described by Menno Schilthuizen in the excellent book, Nature's Nether Regions:

On an otherwise nondescript Dutch beach likes the Leviathan, its beak agape, its limp tongue touching the sand. A smattering of well-dressed seventeeth-century Dutchmen stand around the beast. Prominently located, and closest to the dead whale, stand a gentleman and his lady. With a lewd smile, face turned towards his companion, he points at the two-metre-long penis of the whale that sticks out obscenely from the corpse. Centuries of smoke-tanned varnish cannot conceal the look of bewilderment in her eyes.

These few square feet of canvas ... [exemplify]... the unassailable fact (supported by millenia of bathroom graffiti, centuries of suggestive postcards, and decades of internet images) that humans find genitals endlessly fascinating.

However, it's only relatively recently that this fascination has really been reflected by scientific interest: interest in the structures, their function, and their evolutionary history. But, as Brian Switek points out in his book My Beloved Brontosaurus (which is also an excellent read), we still have no idea how dinosaurs - especially the big ones - actually mananged to mate. Particularly the big spiny ones. This may well remain one of life's not-so-little mysteries. 

 

It has occurred to me that the search history on my computer will look really, really odd as a result of doing a spot of research for this post!

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Demodex mites are tiny little creatures that live in mammals' hair follicles. I first heard about them years ago, when I watched a documentary with my science class back at PN Girls' High. It was about animals that are parasitic on humans, and after the segment on eyelash mites, I don't know about the girls but I felt itchy for days!

For eyelash mites live where the name suggests, in the follicles of our eyelashes. (There are 2 species: Demodex folliculorum and D. brevis.) The common name gives an idea of just how small they are: adult length is 0.3 to 0.4 mm. They spend a lot of time inside the eyelash follicles, snacking on the sebum and dead cells (or maybe the bacteria) that accumulate there. But at night... at night, they come out and wander across our faces as we sleep, achieving a speed of 10cm/hr or more. Which doesn't sound much, but when you remember how small they are, that's quite an achievement. Presumably that's also when they mate, which they do where an eyelash follicle opens to the skin's surface. 

I was surprised to discover that these mites lack an anus. This sounds somewhat problematic, but the eyelash mites have survived, with their human hosts, for at least tens of thousands of years, so they obviously cope somehow. And when they die, their little bodies degrade and release their contents. On your face. Or in the follicles where they spent most of their lives.

Though demodex mites are tiny, there are an awful lot of them. There may be only one or two per hair follicle (they don't restrict themselves to the eyelashes), but an individual human has around 5,000,000 hairs on their body (Thoemmes et al., 2014), so that's an awful lot of available places for a mite to set up home in.

Thoemmes & her co-workers were interested in the genetic diversity of these mites. They predicted there'd be geographically-distinct lineages, because the tiny animals are very closely associated with their hosts and don't seem to be particularly mobile between hosts. However,

if Demodex lack strong geographic structure, it suggests the movement of mites among humans must occur very frequently (perhaps even with social greeting rituals) and across large geographic distances.

To test this hypothesis, the team examined adults (from a single North American population) visually, but also tested skin scrapings for the presence of mite DNA. The results showed that despite being able to see mites on only 23% of their sample population, 16S rDNA sequencing indicated that 100% of those sampled actually had mites present. The latter matched other research showing that 100% of dead bodies tested positive for the presence of Demodex.

Figure 2 from Thoemmes et al. (2014): Maximum likelihood (ML) phylogeny of mites based on 18S rDNA sequences.

While the results of their phylogenetic analysis of the mite DNA are based on samples from only 29 people, they're interesting nonetheless. It appears from that analysis that the 2 species, D.folliculorum & D.brevis, probably colonised humans at different times. Because D.brevis' DNA indicates that their nearest living relatives are mites living on dogs, then the researchers suggest that we acquired this species from our doggy friends, perhaps as recently as 11,000 years ago but possibly as many as 40,000 years ago. There does appear to be some regional variation (based on a comparison of the US data with earlier sequencing results from Chinese populations), but there's also quite a bit of variation within populations, due perhaps to individual humans picking up different mites on different occasions as individual humans came into close physical contact.

And after reading all this & watching a few videos, I feel itchy again!

Thoemmes MS, Fergus DJ, Urban J, Trautwein M, Dunn RR (2014) Ubiquity and Diversity of Human-Associated Demodex Mites. PLoS ONE 9(8): e106265. doi:10.1371/journal.pone.0106265

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Occasionally it's nice to just post a pretty picture. This is one that I took back in July 2015, while we were in France. We'd gone to visit the ruins of of an old Cathar castle called Peyrepertuse and there, on one of the scraggly plants growing on a patch of gravel by the side of the track, was this butterfly. It's a European Swallowtail, and oh how I love the camera in my phone!


Thumbnail image for butterfly  closeup.jpg

 

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