http://www.youtube.com/watch?v=HBxn56l9WcUI’ve always liked frogs. I remember, when I was probably around 4 years old, being fascinated by the tadpoles that Dad brought home in a big jar from a farm pond. Mum explained about how they’d gradually metamorphose (thought I doubt she used that word!) & we watched their legs slowly grow & their tails disappear as they swam around in an old tub, until the point where they became frogs. Frogs are amphibians, along with newts & mud-puppies & axolotls and the legless caecilians (which look like a cross between an eel and an earthworm). As a group, frogs are much younger – in geological terms – than the others: most fossil frogs date back only about 50 million years, although the earliest-known frog-like creature, Triadobatrachus, lived about 250 mya in the early Triassic. Like almost all terrestrial amphibians, adult frogs use not only lungs for gas exchange, but also their skin and the membranous lining of their mouths. (Lungless salamanders are an exception – as the name suggests, they must rely on their skin alone, which is very convenient for those researching amphibian gas exchange.) This reliance on transcutaneous respiration has meant that amphibians are very susceptible to harm due to to chytrid fungus infection, which severely damages the skin and markedly reduces the animals’ ability to exchange O2 & CO2 with the atmosphere. In addition, using your skin as a gas exchange surface means that you have to keep it moist. This means that we’d expect to find frogs only in environments that are humid and damp year-round, & in general that’s the case. But there are always exceptions. and the desert rain frog is one of them. Breviceps macrops lives in one of the most inhospitable environments there is, a dry coastal strip of land in Namibia & South Africa. Hardly a place for a frog! It spends most of its time in burrows dug deep enough to reach into moist sand, but comes out at night when the air is cooler & more humid. While there’s very little actual rain, moisture-bearing sea fogs roll in from the ocean on at least 100 nights each year, bringing some water to the habitat as the fogs condense onto dunes & vegetation – enough to allow these little amphibians to survive. (There’s no actual tadpole stage in their life cycle; little froglets develop directly from eggs in the burrows.) And like other amphibians, they vocalise to advertise their presence. I hesitate to say the sound is a croak. In fact, it drove my dog to distraction when I played the following clip. I give you – ‘the sonorous war cry of a very angry frog‘.
Posts Tagged animal behaviour
a mantis? or a fly? Feb 28No Comments
So, which is it? A mantis? Or a fly?
(Image by kind permission of Daniel Llavaneras)
In fact, the creature shown in this gorgeous image by Daniel Llavaneras is neither mantis nor true (Dipteran) fly, although its common name is ’mantisfly’. Instead, it belongs to the insect family Mantispidae (a group that includes lacewings and antlions). Like real praying mantids, matisflies walk on 4 legs, with the front pair folded as shown, and the head is somewhat mantis-like. The adults hunt as mantids do, shooting out those raptorial front legs to catch small insects, while the larval diets vary: some are also active predators, while others consume wasp & beetle larve, or spider eggs (later pupating in the spider’s egg sac). In adult form & behaviour, the mantisflies are an excellent example of convergent evolution.
only the bones remained Feb 19No Comments
And at the end, there weren’t many of those.
One of the things we talk about in biology class is the importance of decomposers. Most students think in terms of bacteria when this topic’s raised, & maybe things like fungi. But there is more to the breakdown of a body than those microorganisms.
Think worms, for example. In his final bookA, Charles Darwin highlighted the significant role played by earthworms in breaking down ‘vegetable matter’ (eg leaves) to produce what he called ‘vegetable mould’.
And of course there are ants. While we may think of them as those irritating little critters that overrun the kitchen if they find a food source, & produce anthillsB of sand in the cracks in paving, they also act as what could be called macro-decomposers. As this video demonstrates:
B Those with small children (&/or a fondness for kinetic sand!) might enjoy this blog post about ants, kinetic sand, & learning opportunities :)
a tale of two tails Feb 182 Comments
Lizards, like us, are chordates. One of the defining characteristics that all chordates share at some point in their development is the presence of a notochord: a stiff rod of tissue that runs along the dorsal side of the animal, just beneath the hollow dorsal nerve cord. (Yes, hollow. This is the result of its origins in the neural tube that forms early in chordates’ embryonic development.) In most vertebrates the notochord’s replaced by the spinal column. Another chordate feature is the presence of pharyngeal pouches (homologous to gills in fish, and to structures in the jaw and inner ear in mammals), and there’s also the tail. A tail that extends beyond the anus. And it’s that last fact that sets lizards & scorpions apart, when it comes to losing their tails.
This ability to shed the tail is known as autotomy, and it seems to have evolved in response to predator pressure: the tail may even continue to wriggle for a while, which would help to distract a carnivore long enough for the lizard to escape and to live another day.
And that longer-term survival post-autotomy has much to do with the fact that a chordate’s tail is ‘post-anal’. For when a lizard (eg a gecko, or a skink) loses its tail, the animal’s gut remains intact; it can continue to take food in at one end & pass faeces out the other.
Scorpions are arachnids, related to spiders and mites. As a paper published earlier this year in PLoS ONE notes (Mattoni et al, 2015), scientists have known about autotomy in arachnids, but up until now they’d only observed the voluntary loss of legs. However, Mattoni & his co-workers augmented data from the field, and from museum specimens, with some (very careful!) experiments on live animals to demonstrate that at least some species of scorpions are able to detatch their tails.
As for lizards, a tail (more correctly, a ‘metasoma’) continues to wriggle for a while after it’s detatched, and may also act as a distractor to allow the animal to escape a predator. There is, however, a drawback – with its tail the scorpion also loses its anus and the penultimate portion of its digestive tract. And neither metasoma nor gut regenerates.
On the face of it, you have to wonder why caudal autotomy (the ability to voluntarily shed the tail) would ever have been selected for in scorpions. They’re unable to sting ever again, which would leave them with a much-reduced ability to defend themselves or to kill large prey items. And once the open end of the intestine is closed by scar tissue – which takes about 5 days – they can no longer pass faeces from the gut, which must put a dampener on their ability to take food in at the other end – a case of enforced constipation? (The authors note that in at least some cases, the pressure of accumulating poo may trigger another autotomic event, when the animal loses the segment at the ‘new’ end of the tail.)
However, for the scorpions, all was not lost. The researchers’ lab experiments showed that the tail-less arachnids still managed to survive for up to 8 months post-amputation, occasionally eating small prey items. Which would be irrelevant if they were unable to pass their genes on – but the animals were also able to reproduce. In mating experiments, tail-less males were nonetheless able to court and mate with females on multiple occasions. This means that tail-shedding may still provide a selective advantage, in that it allows animals to escape predation and go on to reproduce.
You should also read Ed Yong’s take on how the scorpion lost its tail :)
C.I.Mattoni, S.Garcia-Hernandez, R.Botero-Trujillo, J.A.Ochoa, A.A.Ojanguren-Affilastro, R.Pinto-da-Rocha,& L.Prendini (2015) Scorpion sheds ‘tail’ to escape: consequences and implications of autotomy in scorpions (Buthidae: Ananteris) PLoS ONE. doi: 10.1371/journal.pone.0116639
true facts about owls Feb 182 Comments
A lot of my friends seem to like owls, if their tendency to post photos of adorable fluffy feathered faces on Facebook is anything to go by. I rather like them too; we live close to a gully & it’s lovely hearing the moreporks calling at night. Once or twice one has sat in a tree just outside our window – very special!
Of course, behind the beauty lies a fierce, predatory nature, and that is well captured (in a most humorous way) in this video from the wonderful ‘True Facts’ series:
I do not remember reading any fairy tales involving the ripping off of small persons’ faces by an owl. I’m sure he just made that bit up!
… 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)
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 Oct 312 Comments
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
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 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:
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