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Yvonne d'Entremont (aka SciBabe) recently posted an article on 'alternative' foods and health products for pets, in her usual no-holds-barred style. It's always good to see pseudoscience called out for what it is, and in the case of pet-focused quackery it's a message that needs multiple repeats. Why? Because pets are dependent on us, & we have a responsibility to get things right. Homeopathy is not going to clear a dog of tapeworms, and garlic (often advocated as a flea treatment) is actually rather toxic to cats.

As she says

My Buddy is 11 lbs. He’s afraid of the rain. He needs prescription dog food or else crystals build up in his urinary tract and he pisses blood. He and nature don’t coexist very well. Nature really doesn’t give a shit whether Buddy lives or dies. And since I do care, I’m not so sure that we should use nature as a credentialed source of vitality for a small animal who fears common weather phenomena. Most pets aren’t “natural,” they’re domesticated. They live and thrive on our care.

So much like with human health, don’t leave it up to the internet. Bring your questions about your animal’s health to your veterinarian. Keep observing their behavior and any changes to skin, coat, reactions to food, energy levels, and weight. Get them vaccinations and preventative treatment for appropriate things like fleas and heartworm.

At one point, d'Entremont discusses various diet fads for pets, including veganism (for cats, which are obligate carnivores!!!) & raw food diets. One of her links is to a Nature paper on the impact domestication has had on dogs' digestive systems (Axelsson, Ratnakumar, Arendt, Maqbool et al., 2013), which reports on the genomic evidence for adaptation for a diet that contains a lot more starch than dogs' progenitors, wolves, would ever eat.

That adaptation has occurred over at least 10,000 years. Axelsson & his colleagues note that bones found in burials with humans, from an Israeli site that dates back to 12,000 years before present (ybp) could well be the earliest confirmed dog remains. They cite genomic data suggest that canid domestication began in SE Asia, or the Middle East, around 10,000 ybp, but also comment that the evolution of domestic dogs may well have begun in several regions at much the same time.

While we don't know why dogs were domesticated, it's likely that traits enabling cohabitation with humans would have undergone relatively strong selection: Axelsson et al. suggest that these could include behavioural traits such as reduced aggression and changes in abilities related to social interactions, along with morphological features. 

This paper is based on whole-genome sequencing of both wolves and dogs, in order to identify regions of the genome that might have been subject to natural selection as dogs became domesticated. The research team identified 19 regions that contain genes involved in brain functioning, including several that might be involved in behavioural changes.

But they also found 10 genes key to starch digestion & fat metabolism that also appeared to have undergone evolutionary change during domestication. These genes are involved in breaking starch down into maltose (& other smaller molecules), digesting these molecules into glucose, and moving the glucose into the cells that line the intestine. In humans, salivary amylase begins this process in the mouth, but dogs produce only pancreatic amylase - and the team found a marked increase in the number of copies of the gene coding for this form of amylase in dogs, compared to wolves. They also identified mutations in dogs that could enhance the actual uptake of glucose.

They concluded that 

Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves, constituted a crucial step in the early domestication of dogs. 

In other words, dogs are no longer adapted to a wholly-carnivorous diet. But nor are they suited to veganism. Fad diets for pets are not a good idea. 

 

E.Axelsson, A.Ratnakumar, M-L.Arendt, K.Maqbool, M.T.Webster, M.Perloski, O.Liberg, J.M.Arnemo, A.Hedbammar & K.Lindblad-Toh (2013)  The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature 495: 360-364. doi:10.1038/nature11837

 

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Tomtits and robins were the focus of the first question in the 2016 Schol Bio paper. Specifically, Chatham Island tomtits and robins, which are found only on the Chathams. While at one point they were common and widespread on the islands, the tomtit is classified as nationally endangered, while the black robin is nationally critical & at very high risk of extinction.

The question paper provides two pages of resource materials (maps, photos, and text), and asks students to

Analyse the information provided in the resource materialA and integrate it with your biological knowledge to discuss

  • the reasons why the black robin has a higher risk of extinction than the Chatham Island tomtitB
  • the impact of human intervention on the survival AND evolution of the black robin population.

Compared to the more generalist tomtits, black robins are quite specialised in their habitat and diet. The robins prefer mature forest, with a closed canopy and open understory, while tomits live in mature forest but also venture into shrublands and tussock. This means that the tomtits' options in terms of food and nest sites are less limited. The fact that the robins' poweres of dispersal are limited, so they can't move to suitable habitat on other islands, doesn't help.

One of the fun things about encountering robins in bush on the mainland is that they are ground feeders - you can scuff up some of the leaf litter, step back, and watch them come down to peck through it in search of the invertebrates that they prey on. Tomtits feed at multiple levels in the forest, taking fruit & leaves as well as invertebrate animals. Their more specialised diet means the robins are more at risk following loss of habitat - or a dry year that makes their prey harder to come by. Their ground-feeding habit also means that they're more exposed to predation, something that is also the case for their nesting habits: robins prefer cavities in trees, while tomtit nests are generally quite well concealed (not that this would stop a hungry rat, possum, or mustelid from seeking them out). 

It also takes longer for black robins to replace any losses to predation, let alone grow their population. This is because, compared to tomtits, they have a lower reproductive rate: normally the robins produce one (sometimes two) clutches of 1-4 eggs a year, while tomtits may rear up to three lots of offspring a year, with 3-4 eggs per clutch. (The fact that robins can produce that extra clutch, if the first doesn't survive, was crucial to the efforts to save them when their effective population size was down to a single breeding pair.) The result is that the robins are at greater risk of extinction. 

The fact that the robin population got so low (down to 5 birds in total, with that single breeding pair) means that they went through a severe bottleneck event. As a result of this, and of the subsequent unavoidable inbreeding, there is very little genetic diversity in their population, even though there are now around 250 birds on two islands. This means that the population may not have sufficient variation to allow at least some individuals to survive any significant environmental change. The discovery of birds with deformed beaks, poor bone development, or a distinct lack of feathers has been attributed to that high level of inbreeding.

As the resource information (& a couple of the links above) makes clear, human intervention was the only thing that brought the robins back from the brink and ensured their survival to date. Thus, inducing double clutching, by taking the first clutch and placing the eggs with surrogate parents (first warblers & then, when that wasn't successful because the warblers couldn't provide the right food, tomtits) saw a marked increase in population size. (However, this did come with the risk that the robin chicks would imprint on the wrong parents, something that did actually happen.) Translocating the robins to other islands not only provided suitable habitat and food for the growing population, it also meant that their eggs weren't 'all in one basket': if a predator or disease knocked out the birds on one island, the other could still survive. 

However, conservation workers were pretty much developing their techniques with the robins as they went along, and their interventions did have an impact on the birds' gene pool. I've already mentioned the impact of inbreeding, which can result in increased odds of harmful alleles being expressed. Back in 1984, when someone noticed that a robin had laid her egg on the rim of the nest rather than in the bowl, nudging the egg back into the nest seemed the right thing to do. Unfortunately, by 1989 over 50% of the females were laying rim eggs - the DoC team had inadvertently selected for a dominant, harmful, allele (you can read the original paper here). That is, human action had countered natural selection: normally the egg would have fallen from the nest, or at the least would not have been incubated. Once researchers identified the problem, egg nudging stopped, with the result that natural selection kicked in and the frequency of the allele dropped markedly: now only 9% of females lay eggs on the nest's rim. 

Translocation and fostering could also affect the population's gene pool, and thus its evolution. If there are different selection pressures on the different islands, this could change allele frequencies in the gene pool. And, as previously mentioned, using another species as surrogate parents - while essential at the time - can lead to robins imprinting on the wrong parents and hybridising with them, something that's been confirmed by analysis of microsatellite DNA.

But if it weren't for the dedication and hard work of scientists and conservation workers, the black robin (and many other NZ species) would already have gone the way of the dodo.

 

A I wrote about this in my previous post

B Remember, this question asked students to compare the two species. So a good answer would make that comparison explicit; you shouldn't focus on the robin alone.

 

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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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I'm currently supervising a graduate student who's writing a review of the literature on tool use in wild chimpanzees. This has become a most enjoyable interaction: it's a topic I've been interested in for quite a while now, so the supervision role is an excuse to extend my own knowledge, and it's great helping the student to enhance their own skills in relation to academic research and writing. 

Anyway, a couple of days ago I came across a new paper (Boesch et al., 2016) on an intriguing aspect of chimpanzee behaviour, and my student and I had a stimulating discussion about it at our regular weekly meeting this morning. (There's a general summary of the findings and the project which generated them here.) I'd previously heard of (& shared with her) what appeared to be an isolated incident of 'fishing' by an orangoutan, but this new paper documents wild common chimpanzees, Pan troglodytes, using a new technique to obtain freshwater algae. (Of interest in the orangoutan example were the claims that the image of the animal in action were faked, claims discussed here and dismissed as false.)

It seems that it's unusual for primates to eat aquatic plants, although they may eat fish and invertebrates when available. Both bonobos (Pan paniscus) and gorillas eat plants growing in swampy areas. Common chimpanzees do the same, but have also been reported eating algae - something that's really unusual in animals apart from marine species. And it's highly unusual in chimps too: 

despite decades of chimpanzee research, there are only a few observations of algae harvesting, suggesting that this behavior is indeed rare

and in most of these observations the chimps used their hands, rather than tools, to scoop algae from the water. It's possible, of course, that the local ecology of other well-studied chimpanzee groups just don't favour consumption of aquatic algae. But this behaviour could also be due to cultural evolution in a few small social groups.

So, Boesch and his team set up a research station at Bakoun, in Guinea (not far south of the equator), as part of a continent-wide attempt to 

contribute to a fuller understanding of the extent of chimpanzee behavioral variation and flexibility

in order to help get a handle on the actual level of behavioural diversity in wild chimps, and to answer questions around the relative effects of ecological diversity and cultural evolution on differences in behaviour shown by different groups of animals.

The chimps in the study area at Bakoun hadn't been studied before, and to minimise the potential impacts of interaction with humans, all observations were made using 'remote video camera traps', triggered to begin recording on detecting movement. These cameras were set up at sites where there was other evidence of chimp activity, such as remains of tools. Obviously they captured much more than chimpanzee activity, but of the 1,473 video clips that showed chimps, 486 (from 11 different sites), showed the animals 'fishing' for algae (Spirogyra sp.). Most of these events happened during the dry season, when water levels were lower, peaking in the 'hot dry' season when chimps returned repeatedly to the same sites over several days. 


The chimpanzees were observed to fish for algae at sites where the algae occurred in large accumulations at the bottom of the river bed.We rarely observed free floating, surface algae being targeted... [and we] observed all age and sex classes perform and succeed in fishing for algae from deep ponds or river shores.

Interestingly, the researchers found that every single animal used a tool to collect algae, even those only 2 or 3 years old - and they tended to use the same hand each time they fished. They fished by holding one end of a long stick, reaching it down to the bottom of the water, and then twirling the stick so that strings of algae were wound onto it. They then withdrew the stick and pulled the algae off with their lips. And, when algae fishing, the chimps usually avoided getting wet as much as possible. 

To see how successful this was as a food-gathering strategy, two of the research team used a discarded chimp tool - they managed to collect 400g of Spirogyra in just 10 minutes. Since individual chimps were seen fishing for an hour at a time, algae fishing could make quite a contribution to their seasonal diet:

chimpanzees may be fulfilling substantial dietary requirements [for protein, carbohydrates, and lipids, plus antioxidants and minerals] by ingesting large amounts of Spirogyra algae during the dry season

And just what were these tools? Mostly woody branches, modified by stripping off smaller branches and fraying one of both ends; some of these branches were up to 4m long, allowing access to algae that was otherwise unreachable in deeper parts of the river. In around 20% of events chimps arrived at their fishing sites already prepared ie bringing tools with them.

As I commented to my student, research like that described by Boesch and his colleagues goes well beyond simply documenting the activities of our close cousins. This is because, while it's likely our own hominin ancestors used a variety of plant-based tools, these aren't the sort of thing that's likely to be found by palaeontologists, and so 

research on primates can illuminate the potential repertoire of tool use behaviors that may reasonably be assumed to have been present in our last common ancestor (Boesch et al. 2016).

For example:

we suggest that in Bakoun, tool use permits a more efficient access to a rarely available but highly preferred resource, such as algae, that permits chimpanzees to flourish in an environment otherwise more limited in food and water. It is therefore probable that our last common ancestor would have similarly made and used tools to also engage in rudimentary fishing, to collect and consume rich aquatic fauna, and perhaps flora too (ibid.).

And

This [research] demonstrates the flexibility in [chimpanzee] technical skills and how this helps them to obtain access to valuable resources in a drier habitat and new context. Such technological skills have been suggested to be present in our human ancestors when they invaded drier, savanna habitat during the course of human evolution (ibid.).

C.Boesch, A.K.Kalan, A.Agbor, M.Arandjelovic, P.Dieguez, V.Lapeyre, and H.S.Kuhl (2016) Chimpanzees routinely fish for algae with tools during the dry season in Bakoun, Guinea. American Journal of Primatology 78(12), published on-line 3 November 2016. DOI: 10.1002/ajp.22613

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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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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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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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Once upon a time, I wrote about traumatic insemination in bedbugs. (Those of my friends who are still traumatised by learning about the reproductive habits of various slug species may not wish to follow that link.) Now, two papers just published in Nature Communications describe the results of sequencing & examining the genome of the common bedbug, Cimex lectularius

Bedbugs have probably been with us since humans first lived in caves, where the bugs jumped (possibly literally) from bats to Homo. They're now a widespread human ectoparasite (found on every continent apart from Antarctica) and have developed resistance to the pesticides once used to control their populations. In introducing their paper on their analysis of the C.lectularius genome, Rosenfeld & his colleagues (2016) comment that

There is a limited molecular understanding of the biology of the bed bug before, during and after feeding on human blood, which is essential to their life cycle since bed bugs are temporary ectoparasites, whereby they access their hosts for blood feeding and then seek the refuge of the indoor environment for digestion, waste production and mating.

To increase our understanding of the bugs' life cycle, Rosenfeld's team looked not only at the genome sequence but at changes in gene expression, finding the most pronounced changes occurred after the insect had sucked its fill of human blood. They also found that these changes in expression 

included genes from the Wolbachia endosymbiont, which shows a simultaneous and coordinated host/commensal response to haematophagous activity. 

In other words, gene expression in both host and parasite changes in a synchronous way after the bug has fed. (Just as an aside, Wolbachia is a bacterium that has a significant impact on the reproductive lives of its host.) In the bugs the change could be described as huge: "20% of all stage-regulated genes" showed differential changes in expression after a blood meal.

As you'd expect, the bugs have a number of genes with anticoagulant activity - after all, having blood coagulate in their needle-like mouthparts while feeding would really gum things up - plus other genes associated with blood-feeding. The research team also identified a number of mutations that confer resistance to pesticides such as pyrethroids & cyclodienes, plus others that may underlie metabolic changes that speed up detoxification. Genes that have an impact on the thickness of the bugs' cuticle also have an impact on resistance (also noted by Benoit et al. 2016). 

In the second paper, Benoit and his colleagues (2016) also analysed the common bedbug genome to produce

a comprehensive representation of genes that are linked to traumatic insemination, a reduced chemosensory repertoire of genes related to obligate hematophagy, host–symbiont interactions, and several mechanisms of insecticide resistance.

Traumatic insemination involves male bugs stabbing their sexual partners pretty much anywhere on their bodies with a sharp, pointy, penis. It's a habit that can lead to the females picking up a range of pathogens, and unsurprisingly natural selection has driven the evolution of a range of adaptations minimising the physical harm and risk of infection. 

Because the bugs are obligate blood-feeders (haematophagous), their chemosensory system has evolved to allow them to find their particular hosts (ie us). The team observed that the genes involved in this system differed between C.lectularius & the related species that feeds on bat blood, as the 2 species have specialised on different hosts. They identified a total of 102 genes involved in chemosensory pathways, well down on the number found in related bugs (hemipterans) that feed on a range of plant species. (On the other hand, they have a much-expanded repertoire of salivary enzymes, compared to the plant-sucking bugs.)

The bedbugs' specialisation on human blood as their sole food source did have some potential pitfalls, as apparently vertebrate blood lacks some of the micronutrients that arthropods require. And that's where Wolbachia comes back into the story: 

such specialization also drives obligate associations with symbionts, including Wolbachia, that generate critical micronutrients that are deficient in vertebrate blood (Benoit et al., 2016).

Wolbachia does this by providing its host with 

a cocktail of specific B vitamins that are critical for reproduction and development

The research team also found genes encoding proteins (aquaporins) that allow the bugs to rapidly shed the excess water imbibed in a blood meal, and concluded that differential expression of aquaporin genes (and others) allow the bugs to survive periods of starvation and dehydration in between hosts.

In their conclusion, Benoit et al. comment that the wealth of information uncovered by these genomic studies may allow us to move towards an answer to a pressing question: 

What triggered the current bed bug resurgence?

To which harassed travellers would probably add, and how can we bring them back under control?

J.B.Benoit, Z.N.Adelman, K.Reinhardt, A.Dolan, M.Poelchau, E.C.Jennings, E.M.Szuter, R.W.Hagan, H,Gujar, J.N.Shukla, F,Zhu, M.Mohan, D.R.Nelson, A.J.Rosendale, C.Derst, V.Resnik, S.Wernig, P.Menegazzi, C.Wegener, N.Peschel et al. (2016) Unique features of a global human ectoparasite identified through sequencing of the bed bug genome. Nature Communications 7 Article number 10165 doi:10.1038/ncomms10165

J.A.Rosenfeld,D.Reeves, M.R.Brugler, A.Narechania, S.Simon, R.Durrett ,J.Foox, K.Shianna, M.C.Schatz, J.Gandara, E.Afshinnekoo, E.T.Lam, A.R.Hastie, S.Chan, H.Cao, M. Saghbini, A.Kentsis, P.J.Planet, V.Kholodovych, M.Tessler et al. (2016) Genome assembly and geospatial phylogenomics of the bed bug Cimex lectularius.  Nature Communications 7 Article number: 10164 doi:10.1038/ncomms10164

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February 2018

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Recent Comments

  • Richard: High dose resveratrol (5g was used in the study) actually read more
  • Alison Campbell: Or you could, you know, summarise your own reasons for read more
  • marc verhaegen: For recent info, google "aquatic ape theory made easy 2017". read more
  • Alison Campbell: I feel that may have connotations of 'night soil', which read more
  • herr doktor bimler: Would it sound better as "liquid soil"? read more
  • Alison Campbell: The results in the study you linked to look promising read more
  • Alison Campbell: Thanks, Ed. Totally agree - it's just a matter of read more
  • Ed Darrell: Plague? Antibiotics, plus we know the vector and how to read more
  • Matthew: At least you came at this with an open mind. read more
  • Alison Campbell: No, I think you're wrong. You do get people there read more