Can we use anthropomorphic language in animal behaviour research?

A few months ago during the coffee break at an animal behaviour conference I was talking to a colleague about her research when she told me that to suggest that animals could feel fear or be afraid was anthropomorphism, the mistake of assigning of uniquely human characteristics to other animals. This view is not at all uncommon among practicing scientists and the term anthropomorphism is often extended to include a whole range of behavioural traits and emotions such as impatience, joy, expectation, boredom, anger, happiness or sadness, and yet there is good evidence that these emotions are not unique to humans. For example, dogs have been shown to exhibit jealousy, elephants have empathy, and Capuchin monkeys get visibly angry when treated unfairly as this video shows.

The possibility than animals can think for themselves is also often questioned and yet we know that some animals such as chimps and dolphins have a sense of self. There are also examples of animal behaviours that surely require some degree intelligence and forward planning such as innovative tool use by chimps and deception by ravens.

Deep in thought. Do chimps think like we do?
Deep in thought. Do chimps think like we do?

One of the main arguments against using anthropomorphic language to describe animal behaviours is that there is no way to know how an animal is really feeling, we can only describe what it looks like it’s feeling but not what’s actually happening inside it’s head. But the same is also true of humans, yet no one would question the use of anthropomorphic language to describe human behaviours.

If a person says they are excited we don’t actually know that what they feel as excitement is the same as what you or I feel as excitement, to them it may be a very different thing. All we can do is observe how that person acts and behaves and decide for ourselves if that matches up with our interpretation of what excitement is. The same is true of any emotion. If I say I am or happy or bored how could you tell that what I feel as happiness or boredom is the same as what you or anyone else feels as those things? At some point we have to use our subjective judgement to decide how a person is feeling. Do their actions match our expectations for a happy person? Then we can say they are happy. Do they behave as if they are sad? Then we can say they are sad. If this applies to humans then surely it can also apply to animals, at least in some cases.

I am not suggesting that we should abandon all caution and start using anthropomorphic terms carelessly. What I am suggesting is that so long as we clearly define our terms we should be able to use words like ‘afraid’ or ‘excited’ to describe animal behaviours when those terms well match what we see. If I want to describe anger in animals I should be able to use the word anger so long as I clearly state what I mean by the term and the behaviour that I am describing well matches what most of us would recognise as anger.

Of course, there are cases where using anthropomorphic terms really isn’t appropriate. If I read a paper that described ‘angry’ aphids or ‘jealous’ earthworms I would be dubious that those animals really could feel those emotions. In other cases I would have much less of a problem. Can chimps get angry? I think so. Are rats afraid of predators? It seems likely.

For many scientists, including people who I work with, the fear of using anthropomorphic language seems deeply ingrained and I think this affects how we view the behaviour of animals. Not all animals are mindless automatons that blindly follow their pre-programmed instincts. Many animals, especially among the vertebrates, have complex behaviours and emotions which are best described using the same terms we use for those things in human animals. I think it is time we started describing animals behaviours exactly as we see them. We must define our terms and we must be clear but so long as we are there should be little problem to this approach.

For those that still doubt that animals have can have thoughts and emotions like ours I recommend this TED talk.

For another view I also strongly recommend this post by Jilly at her blog fluffysciences

What do you think? If you have an opinion please leave a comment below.

 

 

Cooperative sperm, killer sperm and the competition for reproductive success

ResearchBlogging.org

In the closing paragraph of on the origin of species Darwin famously said that nature was a war in which individuals struggle against each other and the environment for survival. However, while survival may be important from an individuals point of view, from an evolutionary perspective mere survival is not enough. Reproduction is what matters and success or failure at producing offspring is what determines an individual’s evolutionary success. Of course, survival is important too, but only when it leads to reproduction.

In most species the reproductive success of females is limited by the rate at which they can produce offspring. When a female is pregnant or carrying eggs she has no choice but to wait until she has given birth or laid her eggs before she can reproduce again, and this can take a long time. Males have no such constraints to their reproductive success and can potentially mate with hundreds of females over their lifetime and raise an enormous number of offspring. The only thing stopping them is that there just aren’t enough females to go around. This shortage of females coupled with the need to reproduce leads to intense, and often aggressive, competition among males for limited mating opportunities.

Male red deer (Cervus elephus) compete for females by fighting
Male red deer (Cervus elephus) compete for mating opportunities by fighting

Male red deer (Cervus elephus) fight for their chance to mate by using their huge antlers to batter their rivals into submission, while male northern elephant seals (Mirounga angustirostris) grow to enormous sizes allowing them to dominate harems of many females and guard them against the advances of smaller, weaker males. Not all species are so aggressive in their tactics. Males of many bird species such as peacocks (Pavo cristatus) and birds of paradise produce fantastic and colourful displays with which they attempt to attract females, as do a large number of insects and fish. In these species, rather than fighting with each other, males try to out-perform and out-class each other in the hope that females will choose them while their rivals are left unwanted on the sidelines. This may seem a more peaceful strategy but make no mistake, although these males don’t actively fight each other the competition between them is every bit as intense as among more aggressive species.

Male peacock (Parvus cristatus) aim to attract females by out-perform their rivals displays.
Male peacock (Pavo cristatus) aim to attract females by out-performing the displays of rival males.

So fighting or displaying are two ways in which males can improve their reproductive chances, but what happens in species in which each female mates with lots of different males in quick succession? How is a male to improve his odds of being the true genetic father of the offspring? Well, as is often the case evolution has found a way and that way is called sperm competition (yes, really).

In species in which females mate promiscuously males compete not just for mating opportunities but also for direct access to eggs. In these cases competition between males happens after mating has occurred as the sperm of multiple males compete with each other within the females reproductive tract as they race towards the eggs. In species in which sperm competition is known to exist an incredible variety of different sperm adaptations have been found, all of which serve to improve the sperms chances of reaching the eggs first.

For individuals of many species adaptation to sperm competition simply means producing more sperm so as to swamp the sperm of their rivals and increase the odds that some of their sperm will make it to the eggs before anyone elses. For other species adaptation to sperm competition is more complex. For example, the wood mouse, Apodemus sylvaticus, has evolved sperm that have a hook-like structure on the head which allows them to intertwine with one another to form long sperm ‘trains’ which are much faster at swimming than individual sperm.

The sperm of the wood mouse (Apodemus sylvaticus). (a) Image of the sperm head with the hook clearly visible. (b) 50 sperm hooked together. (c) A clip from video footage of the sperm train. (d) Another view of the sperm train with an arrow and asterisk marking the position of hooks. (e) One sperm latching onto another. (f) Another view of a sperm hook.
The sperm of the wood mouse (Apodemus sylvaticus). (a) Image of the sperm head with the hook clearly visible. (b) 50 sperm hooked together. (c) A clip from video footage of the sperm train. (d) Another view of the sperm train with an arrow and asterisk marking the position of hooks. (e) One sperm latching onto another. (f) Another view of a sperm hook. Image from Moore et al. (2002).

In a similar and recently discovered case, a team led by Morgan Pearcy of the Université libre de Bruxelles looked for evidence of sperm competition in the desert ant, Cataglyphis savignyiThe queen ants of this species mate with up to 14 males in rapid succession and store their sperm jointly in a special storage organ called the spermatheca. Only those sperm which make it to this storage organ have any chance of fertilising an egg and so competition for access to the spermatheca is intense. In response to this pressure C. savignyi males have evolved highly cooperative sperm that team up into bundles of 50-100 cells which can swim much faster than they could alone and so are better able to outcompete their rivals.

Sperm from the desert ant Cataglyphis savignyi work together to increase their swimming speed. Image from Pearcy et al, (2014).
Sperm from the desert ant Cataglyphis savignyi work together to increase their swimming speed. Image from Pearcy et al, (2014).

It is not just the way sperm behave that can change due to sperm competition, the shape and function of sperm can change too. For example, Philip Byrne and his colleagues from the University of Western Australia found that in a group of Australian frogs those species under the most intense sperm competition produced sperm with the longest tails, possibly to improve their swimming speed. Other species known to have oddly shaped sperm include the water beetle Dytiscus marginalis which has sperm that fuse at the head into pairs with two tails, and the tiny fruit fly Drosophila bifurca which at 6cm long produces the longest sperm on earth.

Some species have taken a more sinister approach to sperm competition and have evolved infertile “parasperm” which contain enzymes capable of breaking down the sperm of rivals. A similar and fantastically named kamikaze sperm hypothesis has even been proposed for humans in which some sperm are adapted to kill the sperm of rivals rather than fertilise eggs. The evidence for this hypothesis is equivocal at best but given the adaptations that have been discovered in other species it is not entirely unbelievable. In fact, given the adaptations that have been discovered so far, almost nothing is completely unbelievable.


References

Sperm competition by producing large quantities of sperm
Moller, A. (1989). Ejaculate Quality, Testes Size and Sperm Production in Mammals Functional Ecology, 3 (1), 91-96 DOI: 10.2307/2389679

Sperm trains in the wood mouse
Moore H, Dvoráková K, Jenkins N, & Breed W (2002). Exceptional sperm cooperation in the wood mouse. Nature, 418 (6894), 174-7 PMID: 12110888

Cooperative sperm in the desert ant
Pearcy M, Delescaille N, Lybaert P, & Aron S (2014). Team swimming in ant spermatozoa. Biology letters, 10 (6) PMID: 24919705

Sperm competition in Australian frogs
Byrne PG, Simmons LW, & Roberts JD (2003). Sperm competition and the evolution of gamete morphology in frogs. Proceedings of the Royal Society B: Biological Sciences, 270 (1528), 2079-86 PMID: 14561298

The two tailed sperm of the water beetle
Mackie JB, & Walker MH (1974). A study of the conjugate sperm of the dytiscid water beetles Dytiscus marginalis and Colymbetes fuscus. Cell and tissue research, 148 (4), 505-19 PMID: 4836644

The world’s largest sperm in drosophila
Bjork A, Dallai R, & Pitnick S (2007). Adaptive modulation of sperm production rate in Drosophila bifurca, a species with giant sperm. Biology letters, 3 (5), 517-9 PMID: 17594959

Killer ‘parasperm’
Buckland-Nicks, J. (1998). Prosobranch parasperm: Sterile germ cells that promote paternity? Micron, 29 (4), 267-280 DOI: 10.1016/S0968-4328(97)00064-4

Kamikaze sperm
Baker, R., & Bellis, M. (1989). Elaboration of the Kamikaze Sperm Hypothesis: a reply to Harcourt Animal Behaviour, 37, 865-867 DOI: 10.1016/0003-3472(89)90074-2

Criticism of the kamikaze sperm hypothesis
Moore, H., Martin, M., & Birkhead, T. (1999). No evidence for killer sperm or other selective interactions between human spermatozoa in ejaculates of different males in vitro. Proceedings of the Royal Society B: Biological Sciences, 266 (1436), 2343-2350 DOI: 10.1098/rspb.1999.0929

A spider that masquerades as a bird dropping

ResearchBlogging.org
The power that natural selection has to sculpt both the appearance and the behaviours of creatures so that they intricately and precisely fit their respective environments is for me a source of endless fascination and wonder. Some of the most impressive examples of natural selection’s power lie among the mimics of the insect and spider world where a huge diversity of body forms are to be found, from insects which look uncannily like leaves or moss, to spiders that look just like ants. The benefits of these disguises vary from species to species. For many blending seamlessly into the background provides some protection against predators, while for others it allows them to creep up on their prey unnoticed or lure victims to their demise.

The south-east Asian orb-web spider known as Cyclosa ginnaga is a perfect example of how mimicry may be used to conceal an animal from its predators, in this case highly aggressive predatory wasps. Although by themselves individuals of this species are conspicuously silver in colour and not all that well disguised, they are able to spin white circular silk decorations which they stand on in the centre of their webs as a way of concealing themselves. That might not sound like a great way to hide but the size, shape and colour of the spider when viewed against the white background of its decoration look remarkably like a bird dropping which, of course, is of no interest to predators. This type of mimicry, in which animals mimic inanimate objects, is termed masquerading and the details of this particular case were recently published in a new paper by Min-Hui Liu and colleagues.

a) Cyclosa ginnaga standing on its web decoration. b) A bird dropping. Photos from Lui et al. (2014)
a) Cyclosa ginnaga standing on its web decoration.
b) A bird dropping.
Photos from Lui et al. (2014)

Liu and colleagues wanted to know if the decoration of C. ginnaga really did function as an anti-predator masquerade. To test this the researchers first used a technique called spectral reflectance imaging to examine how the spider and its decoration appears through the eyes of its predators. After all, what looks like a bird dropping to us may look completely different to a wasp. This method compared the way that light reflects from the body of the spider and its decoration to what is known about the sensitivity of insect eyes. The results were unequivocal, wasps cannot see the difference between bird droppings and the masquerade display of C. ginnaga.

bird dropping spider
A composite picture showing examples of Cyclosa ginnaga on its web on the second and fourth rows and bird droppings on the first and third rows. Image credit: Min-Hui Lui.

The crucial test however, was to show that mimicking a bird dropping really does reduce the predation risk for the spiders and lead to real fitness benefits for individuals. To do this the researchers divided 39 wild caught spiders into three groups. To one group they coloured the bodies of the spiders black while leaving their decorations untouched, to another they coloured the decorations black while leaving the spiders themselves untouched, and to the final group they coloured both the bodies of the spider and their decorations black. They then observed the frequency of predator attacks on each group over 13 days and compared this to the predation rate on untouched spiders. From these three groups a huge increase in predation was observed on those spiders that had only their decorations blackened. This suggests strongly that having a white decoration really does help C. ginnaga to hide itself from predators.

Figure from Lui et al. (2014) showing rates of predator attacks when the spider, the spiders decoration, or both were coloured black.
Figure from Lui et al. (2014) showing rates of predator attacks when the spider, the spiders decoration, or both were coloured black.

As shown in the figure above, when both the spider and its decoration were blackened no increase in the frequency of predator attacks was observed. This is not so surprising as in this case the black spider is likely to be well camouflaged against its black background. What is surprising  however, is that when the spiders body was blackened but the decoration was not there was also no increase in predator attacks. This seems strange since a black body on a white background might be expected to stand out very clearly to predators. It may be that the wasps recognise only silver spiders as their target species and so don’t see the black coloured spiders as potential prey. It could also be that when a black spider is on a white background it still looks like a bird dropping since bird droppings often have black bits in them. The authors don’t discuss this anomaly in their paper but it does cast doubt on the idea that the silver spider in combination with the white decoration together form a masquerade which reduces the risk of predation. Nonetheless it is clear from this study that the web decoration does substantially reduce predator attacks, why that is so remains an interesting question that is open for discussion.


Reference

Liu MH, Blamires SJ, Liao CP, & Tso IM (2014). Evidence of bird dropping masquerading by a spider to avoid predators. Scientific reports, 4 PMID: 24875182

Great tits hunt for Pipistrelle bats

ResearchBlogging.org
When under strong ecological pressure, or when a good opportunity arises, animals have often shown themselves to be surprisingly innovative in how they adapt to new pressures or take advantage of new resources. Many examples of this have been observed in the wild including the discovery of tool use by chimpanzees, problem solving in guppies and the development of a novel ‘body-slapping’ behaviour as a means of communication in grey seals. No behaviour has surprised me more however than the discovery that in Hungary a population of a small seed-eating song bird, the great tit (Parus major), has switched from its staple diet of seeds and insects and has learnt to search for, kill and eat hibernating bats (Pipistrellus pipistrellus).

At around five inches long great tits are small birds, but pipistrelle bats are even smaller at just an inch in size. During the winter these bats hibernate in cracks and crevices in dark caves or old buildings where they are safe and well hidden, but when they awaken they start making noises which draws the attention of nearby predators, including great tits.

A Great tit (Parus major). Not a typical carnivore.
A Great tit (Parus major). Not a typical carnivore.

The earliest suggestion that great tits might hunt for bats goes back to at least 1947 when a Swedish biologist named Olaf Ryberg observed dead bats in Sweden with “injury, caused e.g. by titmice (possibly also bigger birds)“. It was to be almost half a century before the subject was raised again when in 1996 a great tit was seen feeding on a dead bat in a cave in Poland. Three years later at the same site in Poland three more bats were found, one dead and two alive, with injuries which looked like they were caused by tit beaks. Despite these observations it was still not clear that in any of these cases great tits were actually hunting for bats actively and it remained a possibility that they were simply scavenging on bats which had already died. A chance observation of a great tit capturing a live pipistrelle in a cave in Hungary in 1996 provided the only evidence at this point that great tits ever actively preyed on live bats.

That first observation was made by Péter Estók from Germany’s Max Planck Institute for Ornithology and intrigued by what he had seen he and his research team returned to the cave in Hungary on three separate occasions from 2004 to 2009. Using experiments and old-fashioned observation  they aimed to discover whether feeding on bats by great tits was simply opportunistic, or whether great tits had learnt to deliberately and systematically hunt for and feed on pipistrelles.

A common pipistrelle bat (Pipistrellus pipistrellus). Image from http://www.naturephoto-cz.com/
A common pipistrelle bat (Pipistrellus pipistrellus). Image from http://www.naturephoto-cz.com/

The research team quickly found their answer. During the first winter of observations they witnessed great tits capture and consume live bats seventeen times in just ten days. Yet despite this it was still not known why this behaviour had developed in the first place.

One possibility was that great tits used bats as a last-ditch food source when their regular food was in short supply. To test this possibility the researchers left a mixture of sunflower seeds and bacon in feeders around the cave entrance to provide an easy and irresistible meal for any passing great tits. Sure enough, when plentiful food was provided they found that hunting for bats by great tits stopped almost completely with only one case observed over a ten-day period. This provided good evidence that feeding on bats was driven by an urgent need for food and did not represent a more general shift in diet.

Now just one question remained to be answered. How do great tits find the bats in the first place? It was thought that they might be able to home in on the bat’s calls so to test this possibility Estók recorded the bats and played their calls back to great tits from a speaker. Around 80% of the birds reacted strongly to the sounds often turning their heads towards the speaker and approaching to investigate. This was particularly interesting because in one study bat calls were shown to act as a deterrent to mammalian predators, possibly by signalling that the bats are awake and cannot be caught. For great tits however it seems that bat calls are far from a deterrent, possibly because they can easily outmanoeuvre a bat in flight.

Eight years passed between the first observation of a great tit preying on a live bat and the start of Estók’s study. Given that the typical lifespan of great tits is three years the birds observed in 2004 couldn’t possibly have been the same birds that were seen in 1996. This raises the fascinating possibility that the bat killing behaviour is passed from one generation to the next by some form of cultural transmission. Whether this is or is not the case is not yet known and so it seems there is still much to learn about the unassuming great tit.

                                                                            

References

For the study of great tits hunting bats

Estók P, Zsebok S, & Siemers BM (2010). Great tits search for, capture, kill and eat hibernating bats. Biology letters, 6 (1), 59-62 PMID: 19740892

Bat calls as a deterrent to mammalian predators

Martin, K., & Fenton, M. (1978). A possible defensive function for calls given by bats (Myotis lucifugus) arousing from torpor
Canadian Journal of Zoology, 56 (6), 1430-1432 DOI: 10.1139/z78-196

Innovative behaviour in other animals

Body slapping seals
Bishop, A., Lidstone-Scott, R., Pomeroy, P., & Twiss, S. (2013). Body slap: An innovative aggressive display by breeding male gray seals (Halichoerus grypusMarine Mammal Science DOI: 10.1111/mms.12059

Problem solving guppies
Laland KN, & Reader SM (1999). Foraging innovation in the guppy. Animal behaviour, 57 (2), 331-340 PMID: 10049472

Tool use in chimpanzees
Goodall, J. (1964). Tool-Using and Aimed Throwing in a Community of Free-Living Chimpanzees Nature, 201 (4926), 1264-1266 DOI: 10.1038/2011264a0

Nature on my doorstep

I know I’ve been away for a long time (has it really been four months?) but I have a good reason. I have just moved from Durham in the north of England all the way to Wales where I am working on a PhD project looking the effects of urban noise. It’s all very interesting and a lot of fun. Wales is also a beautiful place with lots of amazing countryside to explore and unique animals to see. I will talk more about my research soon but today I wanted to share a few pictures that I took while walking home from the beach this afternoon.

If you live in the UK you will know just how wet it has been recently, I don’t think I’ve seen the sun for two weeks and there is water everywhere. That’s why when I woke up this morning and saw the sun I planned to get out and make the most of it. There is a footpath that runs from just by my house and along the cliff tops by the beach. The views are fantastic and it is a great place to see seabirds wheeling and diving out in the bay, red kites flying overhead and I’m told that come summer it will also be possible to see dolphins swimming just offshore which I am inordinately excited about.

Thinking today would be a good opportunity for some wildlife photography I took my camera with me for a walk along the coast and managed to get what I think are some great shots of the town and a house sparrow (Passer domesticus*) perching in some bushes. I’ll be back with some proper posts soon but for now here are some pictures for you to enjoy. Ten points to whoever can guess the name of the town (without looking at my about page).

House sparrow (Passer domesticus) (7)

House sparrow (Passer domesticus) (3)

House sparrow (Passer domesticus) (4)

House sparrow (Passer domesticus) (5)

House sparrow (Passer domesticus) (6) _MG_0006

* Incidentally the house sparrow is the type species after which all song birds (Passerines) are named.

Awesome orcas

ResearchBlogging.org

It has been known for a long time that whales and dolphins are incredibly intelligent animals but it’s not often we see that intelligence so impressively displayed as when orcas (often called killer whales) hunt. Orcas can actually be divided into several different ‘types’ which are found in different areas of the world and often specialise in hunting different prey. Some, such as those around Norway and Greenland, are particularly adept at hunting herring and follow the fishes migration path. Others, such as those in the north-east Pacific are skilled salmon hunters, and some have even learnt to strip tuna fish from fisherman’s lines. There is one group however that outclasses them all, the orcas of the Antarctic peninsula have become specialised at taking seals from floating ice and the way they do it is simply breathtaking. Ingrid Visser and her colleagues were lucky enough to observe the attack in 2006 and described it like this

…one killer whale remained in position with its rostrum against the ice floe while four killer whales moved away from the ice floe with the seal on it. These four killer whales reappeared simultaneously, approximately 20 seconds later in line-abreast with all submerged just under the surface. All four were coordinated-swimming, with their left sides orientated towards the surface. A trail of bubbles emanated from each of the animals blowholes as they accelerated and passed directly under the ice floe, two on each side of the stationary killer whale. This generated a large wave, which tipped the ice floe initially towards the wave, then as the wave poured over and crested under the ice, it pivoted and tilted the ice in the other direction where the attacking whales were now waiting. The breaking wave washed the seal into the water…

Coordinated orcas about to launch a "wave washing" attack.
Coordinated orcas about to launch a “wave washing” attack.

This same hunting technique, sometimes termed “wave-washing”, was later filmed by the BBC for the series Frozen Planet (highly recommended if you haven’t yet seen it).

As someone who has worked with seals a lot over the last few years I have mixed feelings about this. On the one hand the seal is clearly distressed and is tormented for a very long time before it is finally killed, but on the other I can’t fail to be impressed by the skill and intelligence of the orcas that is required to pull off an attack like this. For this hunting strategy to be succesful there must be forward planning, and a high level of communication and coordination between individual orcas. These characteristics are not often associated with animals.

What is really interesting is that in the case described by Visser and her colleagues the seal was caught after around 15 minutes but then released and allowed back onto the ice. It then had to endure a second wave-washing attack before being finally killed almost 15 minutes later. Why did the orcas not kill and eat the seal immediately? The answer is not known, it could simply be play behaviour or, more interestingly, it may be that the adults are training their young to hunt. We clearly have a lot more to learn from these amazing animals and I expect there will be many more discoveries in the future.

                                                           

For a detailed description of this behaviour see:

Visser I.N., Smith T.G., Bullock I.D., Green G.D., Carlsson O.G.L. & Imberti S. (2008). Antarctic peninsula killer whales (Orcinus orca) hunt seals and a penguin on floating ice, Marine Mammal Science, 24 (1) 225-234. DOI:

Coelacanths are not living fossils

ResearchBlogging.org

The term ‘living fossil’ is often misleadingly used in the popular press to describe species which have, supposedly, stopped evolving. Commonly cited examples include horseshoe crabs, Ginkgo trees, hagfish and, perhaps the most famous of all, the coelacanths, a group of lobe finned fish with a very long evolutionary history of which two species still survive in the deep waters of the West Indian Ocean.

A modern day coelacanth (Latimeria chalumnae)
A modern-day coelacanth (Latimeria chalumnae)

Coelacanths have long been known from the fossil record with the oldest specimen dating back to the Devonian period, some 400 million years ago. They were however thought to have gone extinct, along with many other animals, in the end Cretaceous mass extinction event. That all changed one day in 1938 when a South African museum curator named Marjorie Courtenay-Latimer discovered a coelacanth amongst the catch of a local fisherman. The discovery was a sensation, a fish that had been thought to have been extinct had been rediscovered 65 million years later, it was not extinct! It was alive! It was amazing!

That’s how the story goes at least, and ever since it’s discovery journalists have talked about the fish that has been “left behind by evolution”. But is this really true? Can a species really exist for a span of time so great that it will have seen ice ages come and go, mountain ranges form and the great super-continent of Gondwana break apart, and through all this not change at all? Over recent years a mountain of evidence has been steadily growing showing that this is in fact not the case, coelacanths, like any other species, are constantly evolving to adapt to changing conditions.

A comparison of the living coelacanth (Latimeria) with some of it's extinct relative. The morphological differences are striking
A comparison of the living coelacanths (genus Latimeria) with some of its extinct relatives. The morphological differences are striking. Image from Casane and Laurenti.

It is sometimes claimed that there is a low rate of change in coelacanth DNA and that this leads slow evolution. However, this idea is now being challenged by systematic studies of the coelacanth genome which do not detect slow rates of genetic change. In one study forty-four genes were analysed and no dramatic decrease in the rate of change compared to other species was detected. Furthermore, there is no known reason why coelacanths should have slowly evolving genomes. Their environment in the deep ocean, while relatively stable, is not particularly unusual and is inhabited by other species which are not considered living fossils. Another factor that may lead to a slow rate of evolution is a slow generation time, however, the reproductive rates of coelacanths are not thought to be particularly long. Finally, coelacanth populations are small, and small population size is known to increase the rate of genetic change within a species. We might therefore expect these species to be evolving rapidly, not standing still.

Probably the most widely held belief about coelacanths is that, even if they are genetically different, they look exactly the same now as they did millions of years ago. This belief is mistaken. No fossils are known for either species of surviving coelacanth or even for members of its genus, Latimeria. This suggests that the scientists responsible for classifying the fossil and living species consider the morphological differences so great the they should be placed in widely separated groups. In fact, there are significant differences in the body shape and structure of modern and extinct coelacanth species. These include changes in the number of vertebral arches and substantial differences in skull morphology. The swim bladder of coelacanths has also changed from being filled with oil in the extinct genus Macropoma, to being ossified in modern species, suggesting that the two groups lived in very different environments. Lastly, there are substantial differences in size, with modern coelacanths being three and a half times larger than their closest extinct relative (one and a half vs half a metre).

Comparison of the skeleton of modern and extinct coelacanths. A) Latimeria chalumnae (a modern species), B) Macropoma lewesiensis (extinct), C) L. chalumnae skull D) M. lewesiensis skull, E) Pectoral fins of L. chalumnae (above) and Shoshonia actopteryx (another extinct relative) (below). Image from Casane and Laurenti.
Comparison of the skeleton of modern and extinct coelacanths. A) Latimeria chalumnae (a modern species), B) Macropoma lewesiensis (extinct), C) L. chalumnae skull D) M. lewesiensis skull, E) Pectoral fins of L. chalumnae (above) and Shoshonia actopteryx (another extinct relative) (below). Image from Casane and Laurenti.

The view that coelacanths are ancient prehistoric fish which have stopped evolving has been around for a very long time. However, the evidence is now in and it shows that it is time to put this mistaken idea to bed.

                                                                         

For a comprehensive review of the evidence showing that coelacanths are not living fossils see: –

Casane D, & Laurenti P (2013). Why coelacanths are not ‘living fossils’: a review of molecular and morphological data. BioEssays : news and reviews in molecular, cellular and developmental biology, 35 (4), 332-8 PMID: 23382020

For the study analysing forty-four coelacanth genes see: –

Takezaki N, Figueroa F, Zaleska-Rutczynska Z, Takahata N, & Klein J (2004). The phylogenetic relationship of tetrapod, coelacanth, and lungfish revealed by the sequences of forty-four nuclear genes. Molecular biology and evolution, 21 (8), 1512-24 PMID: 15128875

For a contrasting study claiming slow molecular evolution in these species see: –

Amemiya CT, Powers TP, Prohaska SJ, Grimwood J, Schmutz J, Dickson M, Miyake T, Schoenborn MA, Myers RM, Ruddle FH, & Stadler PF (2010). Complete HOX cluster characterization of the coelacanth provides further evidence for slow evolution of its genome. Proceedings of the National Academy of Sciences of the United States of America, 107 (8), 3622-7 PMID: 20139301