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Posts Tagged animal behaviour

it’s the season for ‘best-of’ science compilations… Alison Campbell Dec 17

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… and so here are a couple of compilations.

The first is Sciencealert's top 10 animal videos for this year. They include a lone porcupine seeing off a pride of 17 (!) lions; an octopus 'walking' on land (which is really really strange: it must take an awful lot of effort to do this, unsupported by water, & to what end?); and – reminiscent of someone slurping down spaghetti – a giant red leech engulfing an even larger earthworm

Or, if 'cute' is your thing, then try the year's 'top 10 cutest animals in science' from the Washington Post. In a win for video instruction, it seems that marmosets can learn new tricks by watching the instructor on video. I must take a compass with me when walking the dog, so that next time nature calls I can see if he's lining himself up with the earth's magnetic field! But I think the little koala wins on the squee! factor :) (Image credit Reuters/Daniel Munoz)

the amazingness of lyrebird vocalisations Alison Campbell Nov 12

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This is one impressive lyrebird – laser guns and kookaburras! (Not quite at the same time.) I found him on a ScienceAlert page, which has more info and also links to other videos of these vocally talented birds.

sticky little lizard feet Alison Campbell Oct 31

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Evolutionary change can be fast – Peter and Rosemary Grant’s long-term & ongoing research project on the Galapagos finches documented rapid responses to environmental changes, for example, as does the  recent work on cane toads in Australia. And biologists have known since Darwin’s time that competition can be a strong driver of evolutionary change. (Take Gause’s principle of competitive exclusion & its implications, for example.) A just-published paper about Anolis lizards demonstrates this very well (Stuart et al., 2014).

The way in which different species of this little lizard divvy up their habitat is used as an illustration of niche partitioning by many textbooks (you’ll find an example here). Stuart & his co-authors describe some elegant experimental work over a period of 15 years, on artificial islands in a Florida lagoon. Initially they used six of these islands, all of which were already colonised by the green native anole, Anolis carolinensis: three of the islands acted as controls, while brown anoles from Cuba (Anolis sagrei) were introduced to the other three. The two species are described as being “very similar in habitat use and ecology”, including diet, so they’d be expected to compete fairly strongly when brought together.

In other areas where the two species are found together, A.sagrei perches lower in trees than carolinensis, which left to itself would occupy most of the tree. So the prediction was that on islands where sagrei was introduced the same thing would happen: carolinensis would come to occupy a reduced niche, perching higher than the ‘invader’. And this is indeed what happened, in the space of three months:

by August 1995,on treatment islands already showed a significant perch height increase relative to controls, which was maintained through the study.

The researchers also predicted that this change in niche would be accompanied by a change in morphology; specifically, that there would be selection for larger, sticker feet in A.carolinensis, on the basis that

[toepad] area and lamella number (body-size corrected) correlate positively with perch height among anole species, and larger and better-developed toepads improve clinging ability, permitting anoles to better grasp unstable, narrow, and smooth arboreal perches.

This prediction was tested through observations on 11 islands, five with only the native species and six with both the native and the Cuban invader. Again, carolinensis perched significantly higher in trees on islands where sagrei was also present – and on those islands carolinensis anoles also had “larger toepads and more lamellae” than were found on the same species living without the competitor (an example of character displacement) – and this happened within about 20 lizard generations.

Careful analyses allowed the researchers to rule out other explanations:

In sum, alternative hypotheses of phenotypic plasticity, environmental heterogeneity, ecological sorting, nonrandom migration, and chance are not supported; our data suggest strongly that interactions with A. sagrei have led to evolution of adaptive toepad divergence in A. carolinensis.

So, just as with the cane toads, we are seeing rapid evolutionary change in real time.

Y.E.Stuart, T.S.Campbell, P.A.Hohenlohe, R.G.Reynolds, L.J.Revell & J.B.Losos (2014) Rapid evolution of a native species following invasion by a congener. Science 346 (6208): 463-466. doi: 10.1126/science.1257008 

rapid evolution in cane toads Alison Campbell Oct 27

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In her book Paleofantasy, Marlene Zuk discusses cane toads (Bufo marinus) as an example of just how rapidly evolutionary processes can work. These amphibian pests were introduced into Australia in 1935 to control borer beetles in sugar cane. Unfortunately the toads never got the memo about this expectation, and have spread rapidly across the continent, damaging a range of native ecosystems as they go. (They’re aided by the fact that they’re toxic, killing many of the predatory animals that might otherwise eat them.)

And it’s not just that the toads are and always have been fast hoppers. As this article says

When the toads were first introduced, they spread at a rate of about six miles (ten kilometers) per year. Today cane toads advance more than 31 miles (50 kilometers) annually.

In other words, they’re getting faster, with animals at the ‘invasion front’ moving up to 1.8km in a night. (The researchers were able to measure the toads’ speed by fitting them with miniature radiotransmitters, strapped to their waists.) Phillips & his colleagues (2006) point out that speed of movement in toads is correlated with leg length, and asked the question: is there a difference in average leg length between toads at the front of the amphibian wave spreading across Australia, and those at the back of the bunch? The answer:

As the toad invasion front passed our study site, we measured relative leg lengths of all toads encountered over a 10-month period. Longer-legged toads were the first to pass through, followed by shorter-legged conspecifics (order of arrival versus relative leg length: r = -0.34, n =552, P = 0.0001). Longer-legged toads therefore moved faster through the landscape.

And the evolutionary changes don’t stop there. In a paper just out, Brown, Phillips & Shine (2014) describe how the animals’ tendency to travel in a straight line has changed too:

Radio-tracking of field-collected toads at a single site showed that path straightness steadily decreased over the first 10 years post-invasion.

The research team found that this behavioural change had a genetic underpinning. The progeny of toads from the invasion front moved in straighter paths than the offspring of toads from older, well-established populations to the east. In addition, “offspring exhibited similar path straightness to their parents.” Brown & his colleagues concluded that

The dramatic acceleration of the cane toad invasion through tropical Australia has been driven, in part, by the evolution of a behavioural tendency towards dispersing in a straight line.

G.P.Brown, B.L.Phillips & R.Shine (2014) The straight and narrow path: the evolution of straight-line dispersal at a cane toad invasion front. Proc.R.Soc. B 281(1795) doi: 10.1098/rsph.2014.1385

B.L.Phillips, G.P.Brown, J.K.Webb & R.Shine (2006) Invasion and the evolution of speed in toads. Nature 439: 803. doi: 10.1038/439803a

Teachers: there’s an open-access summary of the 2006 paper here.

if fish had nightmares, these spiders would feature in them Alison Campbell Jun 19

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If asked, “what do spiders eat?”, my answer would probably include insects, spiders, other arthropods, and maybe birds. I’d never have thought of fish!

And yet it seems that fish-eating by spiders is, if not common, then not exactly rare, although other food items still account for most of the spiders’ diets. In a paper just published in PLoS ONE, Nyffeler & Pusey (2014) present evidence – from an extensive literature review – for eight-legged piscivores on every continent other than Antarctica, although they’re more often found in tropical & sub-tropical regions. And it seems they’re not alone: the authors list a number of other arthropods with similar tastes, including water scorpions, backswimmers, caddis flies and water boatmen.

The spiders involved were mostly from the genera Dolomedes & Nilus ie they are large (as spiders go: a big female Dolomedes can have a leg-span of 6–9 cm and weigh ~0.5–2 g) and semi-aquatic, spending a lot of time at the water’s edge. Here’s an image of a female Dolomedes from the UK, settling in to consume a stickleback:

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Image: Nyffeler & Pusey (2014) doi:10.1371/journal.pone.0099459.g007

Incidentally, while we have spiders of this genus in New Zealand, it seems our small freshwater fish have little to worry about. Nyffeler & Pusey report that

only the largest of New Zealand’s three species of Dolomedes (Dolomedes dondalei) was capable of catching fish in laboratory experiments whereas the two smaller species (Dolomedes aquaticus and Dolomedes minor) were not.

When hunting fish – & for most spiders the researchers note that fish are a relatively rare component of the diet – the arachnids seem to use touch (mechanoreception) rather than vision. They sit at the water’s edge with their front pairs of legs spread out & resting on the water surface, and the others anchoring them to a rock or a plant. In some cases, especially when the water is calm, it seems that the spiders may detect their prey from ripples in the water, but in others their attack is triggered by the fish’s dorsal fin actually contacting one of their legs. And while spiders usually eat other animals smaller than themselves, in the case of fishing spiders their prey may be more than twice as large as the predator, which means that there’s quite a lot of effort involved in subduing dinner (usually done by biting the fish behind the head). and then dragging it out of the water to feed.

Nyffeler & Pusey cite experimental evidence showing that spider venom is quite capable of killing small fish, although it may take 20 minutes or more to do so. In the wild, that would be a long time to hang onto a wriggling fish. And why then drag it out of the water? Perhaps because the digestive enzymes injected into the prey would otherwise be diluted – remember that spiders are ‘liquid feeders’ who must wait until the prey’s innards have been liquified by those enzymes before slurping up the resultant soup.

While the fish these spiders eat are a large prey item, & capturing them must incur some risk, the researchers argue that such hunting may well be advantageous at times when other prey items are rare. However, they conclude that

Complete piscivory is probably rare and restricted to those occasions when semi-aquatic spiders gain easy access to small fish kept at high density in artificial rearing ponds or aquaria or in small shallow waterbodies.

Owners of home aquaria and fish ponds may never view Dolomedes in quite the same way again…

Nyffeler M, Pusey BJ (2014) Fish Predation by Semi-Aquatic Spiders: A Global Pattern. PLoS ONE 9(6): e99459. doi:10.1371/journal.pone.009945

something reassuringly disgusting… Alison Campbell May 04

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This post's title comes from Something Fishy where, talking about sea cucumbers, Illya wrote "But there's something else they can do. Something reassuringly disgusting. Something totally Sea Cucumber." I was mildly let down to find he was talking about bioluminescence, & not self-evisceration.

Yes, that's right. When threatened (or repeatedly prodded by some uncouth human in a wetsuit), some types of sea cucumber can forcibly expel part of their gut (& other organs) through the body wall – not the cloaca, but various points on the body wall. I knew that the self-evisceration happened, but not how it happened. For that, I went to the most excellent echinoblog, and you should too, for not only is there an excellent explanation but there are pictures

And so I have learned that holothurians have got this really weird connective tissue that they can soften very quickly indeed, so that the gut's normal connections to other internal bits & pieces is weakened, fast. At the same time regions of the body wall also weaken, and then strong muscle contractions expel parts of the body that would normally never see the light. 

The adaptive significance of all this? (You might regard the practice as a fast track to evolutionary oblivion, but these extraordinary animals are able to regenerate the missing bits.) The 'standard' explanation has been that it's a defence against predators, but echinoblog offers another option: that it's a means of getting rid of excretory byproducts that would otherwise build up to harmful levels in the body. This is borne out by the observation that some sea cucumbers expel their innards – & regenerate them – on an annual basis.

There's the potential to learn a lot from these unusual creatures.

 

another see-through animal (& a rather lovely image) Alison Campbell May 02

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I saw this little critter a while back, over on Pharyngula, & put it on the list of Things To Blog About. Somehow, it took me a while to actually get onto it, but we've got there in the end :)

Image credit: Laurence Madin, Woods Hole Oceanographic Institution/CMarZ, Census of Marine Life

I was a bit puzzled when first I saw this picture – the animal has a vague flavour of jellyfish to it, but I knew it couldn't be one due to its tubular gut. (Jellyfish and their relatives have a sac-like gastrovascular cavity, where a single opening serves as both mouth and anus). So I read on, and found out that it's actually a sea cucumber, in the same phylum as starfish, sea urchins, brittle stars, and the less-familiar feather stars and sea lilies.  It belongs to the genus Enypniastes, but has been dubbed the 'headless chicken fish' in this most entertaining blog over at Something Fishy.

I was surprised to find that Enypniastes is able to swim (although apparently this behaviour isn't all that unusual), something it does v-e-r-y s-l-o-w-l-y using the cape of tentacles at its anterior end. It feeds on detritus in the deep ocean, and like all sea cucumbers, the contents of its digestive tract exit the body through a cloaca, a 'multipurpose' structure. In the case of the holothuroids, this multipurposing includes gas exchange, using complex 'respiratory trees branching off from the cloaca. A while back I wrote more about these structures, which may also serve as both anti-predator devices and homes for small fish…

I think perhaps I should add the see-through Enypniastes to the list of creatures for my next talk on the weird and the wonderful :)

 

 

 

 

a strange but beautiful bird Alison Campbell Apr 30

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In terms of plumage and behaviour, some of the birds of paradise have to be strong contenders in any 'most unusual' list. I mean, take a look at this:

http://upload.wikimedia.org/wikipedia/commons/c/c4/Wilson%27s_Bird_of_Paradise_Best.jpg

(Image source: Wikpedia (Creative Commons))

This is a male Wilson's Bird of Paradise (Cicinnurus respublica), a species that's found only on a couple of small islands off the coast of West Papua. That bizarre blue cap is actually bare skin! It's certainly eye-catching, but I find those gorgeous curled tail feathers just as fascinating. They certainly stand out in this video of a male bird, which is clearing its display floor in preparation for the song-&-dance routine used to attract a female.

 

Like many birds of paradise, C.respublica is a sexually dimorphic species, and the female is quite drab in comparison to the male. She comes into view about halfway through this video from Sir David Attenborough, which gives a good idea of the birds' size (they're surprisingly small). The video also shows the male's display – as Sir David says, the dance moves are poor but the costume is amazing :)

 

‘slow life’ – corals and anemones strut their stuff Alison Campbell Mar 29

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When I was a kid we used to go to the beaches of the Mahia peninsula most weekends. (Well, memory says 'most weekends' – it might not have been that often!). Sometimes we'd stop at the sweeping sandy shores of Blue Bay, but on other days we'd go round to the exposed rocky coast & spend happy hours messing around in the rock pools. I used to love floating my fingers past the sea anemones & feeling the tiny tugs as we touched (at the time, of course, I had no idea that those tiny tugs were the anemones discharging nematocysts into my fingers!) And to me it seemed that these intriguing little animals, which retracted into blobs of jelly when touched less gently, didn't really seem to do much.

Similarly corals – when we've snorkelled around corals I've been amazed by the forms they take and – in living corals – by their colours. But it's hard to see much actually happening.

But tonight a friend of mine posted this video – "Slow Life" – on their Facebook page. It's gorgeous, visually stunning – and it shows the hidden life of cnidarians in glorious technicolour. Best on the big screen, I think; I'm looking forward to showing it to my first-year class next week.

Enjoy!

it’s not all fun & games being a crocodile, you know Alison Campbell Mar 09

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Crocodiles (& their relatives, alligators) are generally viewed as top predators. They're 'ambush' hunters1, lunging up out of the water to snatch at their prey at the last moment.

But sometimes, they come off second-best. Check out this video on the National Geographic site, of a jaguar stalking, catching, & killing a caiman.

And how about these images of a rather large boa chowing down on a metre-long crocodile? Or an otter, eating a juvenile alligator?  Yep, it's not all fun & games being a crocodile.

 

1 Having said that, when I was writing this post I came across the intriguing suggestion that some crocodilians use sticks to lure birds within lunging distance ie that they use tools. They've been observed doing this only during the birds' breeding season, when their feathery cousins2 are looking around for sticks to use in nest-building.

2 Taxonomically speaking, crocs and birds are both archosaurs. Early crocodilians – the pseudosuchians – were a predatory force to be reckoned with & it's possible that the pseudosuchians' demise, in the mass extinction that marked the end of the Triassic, was a factor that opened things up for the expansion of the dinosaur lineages.

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