Seahorse tales and pregnant males
Video | Updated 6 months ago
Dr Glenn Moore, Fish Section, WA Museum
Presented as part of the In the Wild West Lecture Series in 2012.
Discover the fascinating secret world of the seahorse, where fish hold on by their tail, mates dance for their partners and males get pregnant!
I have, as Felena said, worked on seahorses for 17 years, off and on. Sometimes it was almost daily and at the moment it’s a lot less frequent. My love for seahorses came when I was a graduate student trying to decide on a project that I wanted to spend a lot of time working on, and at that time, one of the main seahorse scientists in the world published a popular article on seahorses in the National Geographic magazine, and when I saw that, instantly I thought “That’s something I could do.”
The trouble was that we really knew nothing about the Western Australian seahorse. So in order for me to answer the questions that I was interesting in answering, I needed to actually do a lot of the background work first, so that we could find out something about them.
So tonight, what I’m going to do is take you on a journey through the secret life of seahorses in general, but I’m also going to throw in some little snippets of some of the information about our local species, the Western Australian Seahorse, and I will touch on some of the work that I’ve been doing. As Felina said, I’m particularly interested in evolutionary type questions and some of those get a little heavy and a little theoretical. So I won't get too bogged down in those, but I’ll try and give you some idea of what I do.
The first thing that I would like to point out about seahorses is that they belong to a family of fish called the Syngnathidae and as you can see there, Syngnathidae means they have fused jaws. So they have this very long snout and you can see up here, and the mouth is only right at the very end there. There are many, many species within the family Syngnathidae. There are somewhere between 47 and 80 species of seahorses. I leave both numbers there, the range of numbers, because with most species there is some discussion about how many species, what constitutes the species, so we don’t really know the exact number just yet.
There are only two species of sea dragon and you’re probably familiar with both of them because they are found only in southern Australia. They’re very special. Then pipefishes, there are at least 200 species, I’m guessing probably more like 300 species found throughout the world. However, tonight I am really just going to be talking about seahorses.
The first thing I think that I want to make sure everybody is well aware of is that seahorses are fish, are true fish, just like a herring, just like a salmon. There’s nothing different in that regard. They are very special fish of course.
If I flip our little fish over, our seahorse over and align him there with our ubiquitous herring - probably everybody’s caught one at some stage in their life – you will see that we have a typical fish head – well perhaps an atypical fish head - they have a general body plan and they have a tail of sorts, and I will return to the tail in a moment. But it means that it’s not an insect, it’s not some other sort of invertebrate. That is something that is often said to me. They think that it is something like a crab or a prawn or something like that.
Importantly, the seahorses have gills. So they respire, they breathe. They get their oxygen by passing water across their gills, just like every other fish. They have these set of fins and you can see the pectoral fin here is exactly the same position here, the dorsal fin and then they have these ones here. Even those these little fins, anal fins at the end here are really reduced in seahorses, they are still there. Of course, the swimbladder. All fish require some ability to control their buoyancy in the water and most fish, not all though, most fish use a swimbladder and it’s just basically a pocket of gas that they can control the amount of gas that’s in that and they can change the way that they sit in the water.
However, they are also of course not entirely like regular fish. The first thing that probably is most familiar about a seahorse is that they have a bent neck. Most other fish, in fact no other fish has a bent neck. There’s a couple in the Syngnathidae that you might say do. So that’s really quite unique when it comes to seahorses and of course, the herring has a head very much like every other fish. Seahorses are able to move their neck which is also very special. There’s very, very few fish in the world that are capable of moving their neck.
Most fish have scales. Everybody’s seen the scales and scaled a fish probably, but seahorses have their scales that have been modified into these bony plates. They’re still scales, and if you look at this photo here, you can see this shape here is essentially the same as one of these. So the scales have just been modified to form this bony plate and the fish now is encased in this hard body, but they’re still scales.
The thing that perhaps is most unique about seahorses is that they don’t have a tailfin, the thing that propels most of the fish through the water. Instead they’ve evolved with this curly tail, just like a monkey or a possum, and that is a prehensile tail and they can use that to hold on and they do use it to hold on.
There are a couple of other things that are quite special for seahorses. They’re not unique to seahorses. There are other species of fish that are also the same, but seahorses have no teeth and they also have no stomach. They’re not the only ones as I said, that are like that, but it’s something that makes them different from probably most fish.
The thing that stands out perhaps when you see them in the water is that seahorses swim vertically and their propulsion relies on this dorsal fin, the one that’s on their back here – I knew I was going to do that once – on their back here, where this is the fin that would normally sit on the herring across here. Of course most fish either propel themselves by the tailfin here, or this pectoral fin here which is quite common for things like Wrasses and Parrotfish. So when you see them swimming through the water in this position here, really they don’t look right, they don’t look like a fish, but trust me, they are.
Okay, so a little bit about seahorses then in general. They are found throughout the entire world and hopefully you can see the blue on the map here. That gives you some vague idea of their distribution around the world. They are generally in warmer water, so tropical, subtropical type waters, but there are a few species that you do find further in cooler waters and we have a couple of species along the south coast of Australia, and Tasmania and New Zealand have some species in reasonably cold water. But generally they prefer the warmer waters.
I forgot to say they are exclusively marine or perhaps inter-estuarine conditions and right out here is perhaps one of the best places in the world to see seahorses in fact, one of the easiest places to see them.
They range in all sorts of habitats. They are commonly found in tropical areas in seagrasses. As you move away from the tropics, seagrasses are probably not quite as important for them, although they still occur in there, but they love silty habitats, high sediment load, not the greatest places to dive generally. They love places like jetty pylons, boat moorings, things like that. They’re all the real – especially our local one. That’s its favourite spot.
Generally seahorses are found in shallower water, but there are a couple of species that you will get down in slightly deeper water, perhaps even down about 90 metres. Who knows beyond that, because it’s a bit far out of most diving depths.
As I said, they rely on this small dorsal fin on their back to propel themselves through the water and as a consequence, it’s so tiny that they are actually very, very poor swimmers. They can’t escape predators very well and they also can’t chase their prey very well. So instead, they rely on a mastery of camouflage, and hopefully in here if you look carefully, this little guy here is gorgeous. He’s pretending to be the soft coral that he’s attached to there. Likewise, this purple one here, if you can see, there’s his eye and his snout, and there’s his body and his tail is tucked down in here, and you can see just how remarkable that camouflage is. This one here is our local one, the yellow one and it’s capable of changing colour and in this case, it’s obviously hiding itself and next to an Ascidian soft sponge. Light’s not the best for me from here.
Almost exclusively they feed on crustaceans but they do eat other things. They’ll eat worms, they’ll eat small fish and unfortunately they also eat baby seahorses. I’ve seen them eat baby seahorses. So they are happy to cannibalise, particularly the females. They eat the babies more than the males do, I’ve noticed. But generally, it is small crustaceans.
They are eaten by many things of course, given that they can’t swim away very well. I think probably their biggest predator is fish. Octopus – definitely I’ve seen a lot of octopuses hanging onto them or pieces of seahorse lying on the ground that have clearly been ripped apart by an octopus. Crabs you will see, birds. This gull here looks like he’s got a fantastic meal for the day, and this here, yes, that’s a bowl of soup with two seahorses floating in it. So humans have been for a long time predators of seahorses and continue to be.
So what threats do seahorses in general face? You’ve probably heard media about seahorses. Not so much now, but in the past it was really quite active. One of the biggest threats that people know about is their use in traditional medicines and traditional Chinese medicine is what is most commonly known, but it’s also used in many other cultures around the world, in Asia as well as elsewhere. Particularly in the Chinese medicines, seahorses are considered to improve your general health, your general wellbeing, your Chi if you like. One part of Chi is that it acts as an aphrodisiac, but that’s not the only reason that they eat them, despite what many people think.
Here you can see there’s a whole range of collections that people have for sale and when I’ve travelled with my wife we’ve seen some of these markets where they have huge numbers of seahorses lined up. It’s quite sad to see, but it has been going on for a long time. However, there are some estimates that suggest around about 20 million seahorses a year are taken for this market. That’s a lot of animals. There is an awful lot of conservation efforts going on around the world to try and remedy this, both locally within the small communities, but also outside of that trying to aquaculture and so forth.
One that perhaps most people don’t think about and that we often place some responsibility in, is that they are popular as curios and I understand that. They’re absolutely charismatic animals. They’re beautiful and people like to have a seahorse in their bathroom, on a key ring, somewhere hanging off their ears. I can see that and I understand that, and even in our local markets you will see this sort of thing, seahorses strung up here, dried seahorses. You will see them in our local markets. Of course, what most people don’t think about is that these were probably taken live. They were probably hung up by their neck to die and left to dry in the sun. So if you have an urge to have a seahorse, find your own that’s been washed up on the beach, that’s already dead and keep that, but please try and think about not buying them from a market. To me the same also applies to all of our other marine life. You will see dried starfish, you will see all sorts of dried – you will see dried fish, dried shells. Most of those have been taken live. So just think about it before you buy them.
A big or perhaps a growing market is for aquaria and in the past, most of those animals were taken from the wild, including our local one. I had a big population here that I was studying. I had about 40 animals that I’d been watching for several months at a time and I had some aquarium collectors come in and take the whole lot one night, and I lost my whole study site. So it’s changed a little bit now and I’ll come back to that in a moment.
They’re very difficult to keep alive in aquaria and they require a lot of experience, a lot of expertise and live food, generally. That makes them very, very hard. So a lot of the animals that end up in aquaria, particularly with inexperienced aquarists, end up dying. It’s changing a lot now. There’s a lot more knowledge about seahorses and they are now doing a lot of captive breeding. So there’s a lot of animals that are used to being in captivity and have been raised in captivity. So they’re a lot easier to look after. So this threat is probably improving for them.
Ones that are perhaps more insidious and unseen is fishing methods. Trawling – we all eat seafood – well perhaps not, but most of us eat seafood, and one of the most common methods of catching seafood around the world is by trawling, but of course it’s dragging a net across the bottom and often they avoid reef areas because the nets get tangled up. So it’s often the muddy, silty areas which is where seahorse like to live. So I’m not saying we need to stop trawling, because that’s obviously a critical part of our diet, but it certainly is something we need to think about in terms of seahorses. Dredging – clearly that’s going to destroy habitats, but again, it’s going to be things that we need. We need to build harbours and so forth. So it just needs to be managed in various ways.
One that I think perhaps we don’t think about that much and something that I get quite emotional about and angry about is the word ‘reclamation’ because to me, we’re not reclaiming the sea, because it was never land before that. We’re actually filling in the sea. So it’s ‘infill’. It’s not ‘reclamation’. I hate that word. So I didn’t use it. It’s reclamation to me – well…
So [Ko Sarella 33:55] – this is actually Hong Kong. They’ve run out of space. So they’re filling in the coastal areas so that they can build further out. Okay, we have an expanding population. We have these problems all around the world. I don’t know how you solve it. It’s not my field, but this is something – all of these sort of areas are the typical areas where seahorses live, the seagrasses, the shallow coastal areas. So we really do need to be thinking about those.
Fortunately there are some things that have been put in place to help our seahorses. CITES at the top there has all of the seahorses around the world. Every single species was dumped into this CITES Appendix II 10 years ago or more in fact, and this protects the trade in seahorses. So if you want to trade them around the world, you need to have licences, you need to have permits. You need to report so that it can be managed, it can be tracked and followed. So, that’s a huge improvement.
They are listed in IUCN Red List which is our international list of species that are threatened, but they’re listed as data deficient which means that they don’t actually receive any specific protection, but they are recognised that we don’t know enough about them. So the cautionary principle applies. Before we do something, we need to make sure we know, well at least we’ve thought about what impacts it might have, and of course they are also protected locally in Australia. They are protected under various other acts and our Fisheries Legislation even more locally than that. So, it’s not all doom and gloom, but it’s something we definitely need to think about.
Alright, let’s move onto the diversity of these animals. They are highly diverse I think. I think they are really special. As I said, there’s somewhere between 40 and 80 species of them and we’ll look at some of them in just a moment. They all belong however, to a single genus. So hopefully most of you are aware that a scientific name has a genus and a species, and the genus for want of a better word, is like a surname. It’s the name that groups the similar ones together, and the name Hippocampus comes from a horse-like sea monster and this wonderful roman tile over here at the top, I think it’s fabulous. So they've been known for a long time. They’ve been recognised for a very long time.
But all of the seahorse have more or less the same body plan. They all look like this little guy up here which is our local one. Sorry, little girl I should say. That’s a lady. There is a difference in shape and size of these animals. There’s also differences in colours, and how much ornamentation they have, and if you’ll allow me a couple of minutes, I’d just like to expose you to some of the beauty of them.
Before I do, I would like to say that they do come in a range of sizes. A milk carton here just to give you some idea. The largest, this Potbelly Seahorse over here, which is actually an Australian species. It occurs on the south east of Australia and Tasmania and New Zealand, and it gets as an adult to about 30cms. That’s a big fish. That’s a very big fish.
The smallest ones, there’s a whole series of them and I guarantee there’s a whole lot more we haven’t found yet, are these Pygmy-Seahorses and they are as adults, around about 1cm. Tiny, tiny, tiny little things, and you’ll see in some of these photos when they’re this big and are that well camouflaged, they are really hard work to find. We’ve been lucky enough to dive in south east Asia through the Philippines and in New Guinea and Indonesia looking for these things. I’ve spent a lot of time looking for seahorses and I’m glad that there was a local person there to find them for me because I couldn’t see them.
So, if you’re not convinced about how tiny that is, hopefully the observant among you have suddenly realised, yes, that is a fingertip in the background. I was waiting for that sigh. Isn’t that amazing? That’s the tip of a finger, and that’s an adult.
Okay, so this is one of the Pygmy-Seahorses and again, these things are tiny. This one’s just over a centimetre long and it lives in amongst this perfect camouflage he has, and you can see there, if you really didn’t know what you were looking for, you would never see that, you really wouldn’t. This has all of the polyps, all of these things here have all closed, but they also open and you probably remember the photo I showed you at the beginning. So they can sit in there and just basically not be seen by anything. It’s quite remarkable. Painted Seahorse with these incredible colours, just magnificent colours and then of course just plain beautiful colours. He’s almost iridescent, but with no ornamentation. You see he’s pretty much just smooth, completely covered over. Short snout on that one.
This one is not alive. He’s one come out of a collection because no one’s actually ever seen this one live. I don’t think so, or may be someone has now, but bizarre. Every change in body shape you could imagine. It still has the same body plan though.
This one from the Black Sea and you can see he’s got a little trailing filament sticking out of the top of his head there, or her head. I should get that right.
This is a Bullneck one. This one has only just recently been described off very deep water of south western Australia in fact, and this is a male and I will come back to it in a moment. No, in fact I won't get back to it, but this one’s a male.
This one is from the north west of Australia and I think that this just looks like a starry night, a red sky with all these glittering stars in it. I just think it’s stunning, absolutely stunning.
This is the Bigbelly Seahorse. This is the larger species and he’s just – those patterns. I could look at them all day, they’re beautiful.
This is that tiny one, the Denise’s Pygmy-Seahorse and the one that I had next to the milk carton, that’s the same fish. Doesn’t really look much like a fish, but trust me, it is. This beautiful orange with these saddles on it and all of the ornamentation. You can imagine how much that helps this animal hide in the wild.
That’s pretty sexy isn’t it? So that one occurs off the north coast of Australia as well. I’m hoping to see one. We’ve got a project starting up there very soon and I’m hoping that I’ll be lucky enough to see one.
This is one from Europe and you can see how much ornamentation he has all over his head, all over his body and I’ll show you some footage of this guy swimming around in a moment.
Now this is our local one. So after seeing all that beauty, then this is what we get. But, we get this one because this is where it likes to live. If anybody has ever swum in the Swan River or even just walked in it and pull your foot up and look what it’s like, that’s perfect for living in the Swan River, and Cockburn Sound. That’s probably the two strongholds of this species. So there’s two there. Hopefully, you can see both fish there. But, this fish is also not just brown. This young female you can see is a fantastic yellow colour. I’ve got to say, all those photos that I’ve shown you, I’m astounded by the skill of some of our underwater photographers as well. I’ll acknowledge them at the end, but they’ve allowed me to use their slides.
So the Western Australian Seahorse as I said is the animal that I was working on and continue to work on. This is the sort of places that I dive. That’s usually what it looks like when I’m diving, and if you’ve dived in the river, you probably know exactly what I’m talking about, or in places in Cockburn Sound. It’s not a lot of fun when you first get in but it makes it all worthwhile when you see a seahorse.
So this is our local species and just very quickly, it occurs only in Western Australia and only on the West Coast of Western Australia, and I think this is something that we really should think about. There are a lot of - it’s called endemism - a lot of endemic species that occur just in that south west corner, and particularly even on our west coast it’s even more special because of things that happened during glacial cycles in the past, but this fish we should hold very, very, very tight.
It loves muddy, silty habitats. It’s generally only found in quite shallow water. I’ve seen it in water less than one metre deep as well. It loves algae, it loves sponge and it’s holding onto an Ascidian in that photo there, that young female. Jetty pylons and moorings – if you dive around moorings or jetty pylons during the summer you are almost guaranteed to have them there. Whether you see them or not is another thing, but they’re there.
That’s quite a large species on a world scale. So they get to about 20 odd centimetres and weigh more than 10 grams, perhaps even a little more than that when they’re pregnant. Here I’ve said they’re brown, white, yellow and red are their common colours. I’ve seen bright red ones. I have even seen purple and I’ve seen one that I would say, I’d almost call black, not quite black, but very close to black, and they change colour. So one day it might be brown and then the next day I see it, it actually turns to this bright orange colour. It’s fabulous.
They breed in summer. That’s it. That’s the only time they breed and we don’t know too much about what they do in winter, but certainly in the river during the winter you will rarely see them, and we think they probably head out to sea. We don’t know where or how far, but they definitely head out to sea somewhere.
So my work as I said at the start, I really needed to learn a lot about the biology of these fish before I could start to answer the sort of evolutionary type questions that I was interested in. So in order to do that, I got to spend hours and hours and hours underwater with these animals, and I mean hours. I would probably be diving three to four hours a day, four or five days a week. So, a lot of time.
So what we did, we caught these animals, we tagged them and if you look very carefully you will see this male here has this little string around his neck and that has a little number attached to him so that I can tell who he is. You get used to them when you’ve seen them and they’re little patterns, their behaviours. You can tell them apart, but sometimes you can’t and you need the number just to make sure. So we tagged them. We took their measurements so that we knew how big they were because that was going to answer some other questions later on, but of course it’s still basic biology. We need to know that about our fish.
As I said, I returned to the site time and time and time again. We monitored them, we tracked them, we followed them, looked how far they moved, saw where they would like to be, saw who they liked to hang out with, those sort of things, when they moved, and of course a lot of the time that these seahorses are active, is very early in the morning. So if I wanted to watch how they were interacting, I was getting into the water at about 4.30 or 5 o’clock in the morning. So, yeah, it’s a lot of work.
What we did also, we clipped a little tiny piece of the fins of each one of these, less than a millimetre. It’s like cutting a little piece of hair or a little piece of fingernail, and we can use that to get their genotype. So we can tell each individual in our population exactly - we can tell them apart just based entirely on their genetics, and I will return to that in a moment about why that was really important for us.
I’ve covered the seahorse tales. The second part of my talk is about pregnant males, and this is probably what interests me the most because I was interested in the evolution of the mating system, of the breeding of these animals, and as I go through it, it will probably make some more sense.
So we have the female up here on your left, yes, and you can see the male compared to her. They’re almost identical. The snout in this instance is a little different, but the snout’s quite variable in some cases. But the main difference is you will see here this is about where the female stops, here, her body, and in the male it continues down onto his tail, and this part here, all of this, is his pouch and that pouch is where he gets pregnant. That’s where the eggs sit, in the pouch there.
Actually now I’ll do it. I was just going to put it in later, but I’m actually going to say it. Many people then say “If the male gets pregnant, why is it a male?” It’s a very simple answer. What makes a male a male is that he has sperm and what makes a female a female is that she has the eggs. That hasn’t changed, okay. The fact that the male gets pregnant, I’ll come to why I don’t think it’s as important as everybody thinks.
As I said, I did lots of observations in order to understand these animals and in order to understand the way they interacted with each other. I spent many hours in the water, but I also brought many of them back into the laboratory and into aquaria and we spent a lot of time watching them, and again, to make it a bit easier so I could sleep in, I changed the light settings. So in the middle of the day, it was first thing in the morning for the seahorses. So I didn’t have to get up at 4 o’clock in the morning. I cheated.
Perhaps the most amazing thing about seahorses - when you’ve seen it you will never ever forget it, it’s something that will stay with you forever - is the courtship and it absolutely is beautiful. These animals have a very stereotyped display. They do the same thing over and over and over again, and they do it day after day after day. It’s part of pair bonding. It’s how they bond their partner, keep them together.
The first thing that they do when they arrive to see each other first thing in the morning, they come out of the gloom and they find each other, and they start to change colour and they start to – I call it a dance – and they start to swim, swim very slowly past each other. They will rub against each other. It’s all very sensual. They’ll lean against each other. The male will then start to swim around. This fabulous series of photos by David and Leanne Atkinson of this white seahorse from New South Wales, and they allowed me to use this series of photos, and they were very lucky to be there and catch this.
So here you can see they’re just approaching each other and they’re just starting to sort of – this is the female here in the yellow coat and the male here in the brown coat. So in this case you will see that – this is what I described when I was describing all the behaviours of these fish – this is called synchronised swimming and they really just – they completely mirror each other. Everything that they do, every movement they do is copied and copied almost to the millimetre. It is perfect. It is really quite incredible. If there’s any chance that you get to see this, I highly recommend you do.
In this instance here you can see the male now has hold of the female by her tail and she is, perhaps – she’s tempting him. She’s saying “Okay, I’m interested, but you’re going to have to give me a bit more here.” So he is now holding on and he will be swinging around her, spinning around. He pulls her by the tail and tries to get her to move and here now you can see they’re lined up again and they’re synchronised swimming. This is a great example here. He’s got his fin completely fanned out there and he’d be fluttering his fin, showing off to her. At this point he’s also probably lifting his head. He does this all the time, and in this instance you can see just how pale she is. She’s really pale down here, and our local one, when the females during this, they’ll almost go pure white, really ghostly white, as will the male in many instances also. But this male here, you can see just how bright his spots are now. He’s really, really showing off. He’s putting all the effort in.
The other thing that he’s done in this case, this neck – he’s got his chest and his neck, it’s all gone jet black and this – he’ll be lifting up his head and he’s showing her and he’s really trying hard, but she’s responding and that’s why he keeps going. If she doesn’t respond, he lets go and swims off. He’s got to come back another day. She’s not ready.
In this case here, you can see his pouch is all crumpled up, and what he does, he inflates it with water and he shows her, “Size really does matter.” He says “Look how big my pouch is,” and he will stretch it right out. You might see if you Google “seahorses”, there’s a few species, but there’s some that just look absolutely perverse, these bulbous bellies, it’s ridiculous, but he is showing off and again, this is part of the evolutionary questions that I’m interested in, because of course, a big pouch, means you can take more eggs. It’s important for a female to know.
In this case you here you will see the male has opened up the entrance, the opening to the pouch. Now what the female does, she has an ovipositor. It’s basically an egg tube and she inserts the egg tube into the male’s pouch, and she will then squirt all of the eggs into that pouch, and you will see here, there we go. So they juxtapose front to front and they raise up in the water column and they will come up a metre, a metre and a half or so, rising up and you can imagine just how vulnerable they are to predators at that point, but this is the only way it works.
At that point, she is depositing all of the eggs into his pouch, and I might add, many hundreds of eggs into his pouch, and then once that’s done – where am I, on the next one, okay – so once this is over, then the male, they separate. The female, she’s gone. That’s it. Her job’s done. She’s out of there. The male will then roll around, he’ll settle the eggs and he will fertilise them. He will spray his sperm across all of the eggs and swish it around to make sure that all of the eggs get fertilised.
Now, this is a fantastic piece of footage from Portugal and I will just play it and I’ll talk a little bit, but I’ll kind of let it roll mostly. Now, before it starts actually, just let me point out. You’re going to be looking about here. It’s a bit blurry at the moment, but once it starts rolling you’ll see. There’s two seahorses here and I also just want you to have a look just in case – sorry, a light – one of these ones here, I can’t tell which one it is at the moment, there’s another seahorse that just sits there and watches. He doesn’t do anything. But watch the middle ones here.
So here you can see this is the male with his back to us and the female – there’s the head. See the head bobbing? Stretching the head up, the female is doing it and the male’s just doing it now to show her the same. They’re responding to each other. He’s about to grab her by the tail and there’s all this swimming. There’s a lot of rubbing going on here. This is slightly different to our local one, but it’s more or less the same. Now, very soon you will see he gets his pouch and stretches it out. Okay, see his pouch is now quite swollen? He’s got it all filled up showing her, and now there you go, so she’s now depositing the eggs into his pouch as they swim up.
So you can see there’s a fish swimming in the background. So the predators could easily just come straight in the middle of this right now. She’s now given him all the eggs and they’ll come back down to the safety of the sea floor. You can see his tail, he’s wrapping it around. He’s trying to find something to hold onto, but he doesn’t. The female, that’s it. Her job’s done. She’s out of there. Now the male, you see him rolling around there. He’s trying to settle the eggs down into his pouch and fertilising them at this time. It’s fantastic, isn’t it? Very lucky to get that too. It’s fantastic. Once you’ve seen this, trust me, it stays with you forever. It’s fantastic. Even if it’s in the aquarium, it’s fabulous to watch.
So one of the things about seahorses that perhaps we found out really early on is that they’re monogamous. So they have one partner. What we really didn’t know was how strong that monogamous bond is, whether they can have just one partner for their whole life or for just one time. It’s a very hard thing to figure out because it means you need to keep tracking these animals and keep following them in a natural situation. We can tell you a few things about them.
So on the Western Australian Seahorse, as I said, we took little pieces of tissue from them, a little tiny piece of fin. So then we knew every female that was in our study site. We then could get the males that were pregnant and we could collect the babies from those males, and we could subsample some of the babies from within that male’s brood, and then we could take the genetics from those babies and using that, we could tell who their mother was. We already knew who their father was, because we watched him give birth. We usually brought him back to the lab and put him in a little tank so we could collect all the babies. So we could actually then use the genetics to find out who their mother was, who the baby’s mother was.
Now what we found was that every single brood that we got, all of the babies in the pouch had the same mother. So what you just saw, only ever happens once. The male’s pouch is filled by that one female and that’s it. He doesn’t go and find another female. But what we also found in the Western Australian Seahorse at least, is that 57% there were monogamous. It was the same female the next time which is in the same summer. So they were monogamous over successive broods.
We also found quite a few – again it's really hard to track them for this long – but we did find some that were over three broods. We didn’t get to follow any males any longer than that unfortunately. So we don’t know how long it goes. We also take that little collar off at the end of the summer because we don’t want to leave it on there over the winter because we might never see the animal again and we don’t want it to disappear with a piece of string tied around its neck because it’s not the best thing for it. It could get tangled up. It could get stuck. At least when we’re watching them all day every day, we can keep an eye on it. So we don’t know between years what’s going on either. So, this is what the babies look like by the way and we’ll see some more of those in a while.
So why monogamy? What’s the advantage of being monogamous? This starts to get into the sort of questions of evolution that I was really interested in. There’s got to be a reason for it. So it turns out that there are some advantages in being monogamous, and sorry, there’s a little bit of science here, but this one here, if we look here, all this is, is the distance that they move between the broods. So from brood number one - they have another brood a few weeks later - the distance that they swim, and you see straight away if they’re monogamous, if they have the same partner in between those broods, they don’t have to go very far. They can basically just sit on the spot because they know their partner’s going to come back and they’re guaranteed a mate. So they save an awful lot of energy and a lot of risk of being eaten by something. It’s really, really important. Where if they’re polygamous, you can see they have to move a huge distance and that increases their risk of predation greatly.
The other thing that’s really important for them is what we called interbrood interval. So this is how long it takes for them to start one brood, to when they start the next brood, and if they’re monogamous, it’s about three weeks long. If they change partners, add another week to that. So if you think about it, these things are breeding across a whole summer. If it takes an extra week each time to change partners, that’s one less brood a year probably that you’re going to get. That’s 3/5/700 babies less that you could produce. So it’s actually quite important for them.
Alright, now, we’ll get into sexual selection and I’ll try and do this as painlessly as we can. Again, it is quite heavy in theory, but it’s actually something that most of us are aware of. Even non-scientists have probably thought about it to some extent. Sexual selection is based around the idea that every individual wants to maximise their reproductive success. So that means they want to have the best babies, the biggest babies, the most babies, basically the best success for the next generation. Every individual is trying to do that. So, what they need to do is – how it’s managed I guess is about their investment.
So we look at it in a really simple way. There’s lots and lots of facets to it, but in terms of the most simple way, sperm that the males produce is very, very cheap to produce in terms of the amount of energy that it costs. It’s almost nothing and in fact, if you do the mathematical calculations, we basically don’t even count sperm on the maths. We just ignore it. In contrast, eggs are very, very expensive to produce. It takes an awful lot of energy for a female to produce eggs. This is true for all animals, not just seahorses. This is animals in general.
Pregnancy of course, I probably don’t need to say too much to the women in the room, but it is a very costly exercise. It uses an awful lot of energy. It increases all sorts of risks. So, there’s a big investment with producing eggs and being pregnant. So, if you look at this column here, the investment for females is really high and the investment for males is really low. So what does this mean? It means that the females have this big investment, so they then get to choose who the best mate is to maximise their chance of their offspring surviving and of being as good as they can.
So the females are the choosy ones, and the males then, as we all know, have to compete for access to those females. Right men? Yeah. So what we know of course, the really common things, these crazy antlers, and they get ridiculously big in some species. So this is the competition between the males. So they have to compete with each other for access to a female. But then they also have this one, the peacock. So he’s not got this fancy tail to show off to another male, although they do use that a little bit, it’s mostly to show off to the female. So they have to fight with each other, and they have to show off to the female. So this is sexual selection, selection that’s driving evolution to create these sort of bizarre attributes, and I’m sorry men, but it's all driven by the women. In most animals it’s the women’s fault. That’s why of course men are always so ruggedly handsome and well built because they’re attracting the females.
In seahorses though of course, we have this slightly different situation. We have the males which still have cheap sperm, but now they’re pregnant. So the males now carry this extra cost, but don’t forget, the females still have the high cost of the eggs. So, what we don’t know is what’s happening to the investment. We haven’t figured out yet, and a lot of my research has been trying to figure this out and there’s a lot of other people around the world that are trying to figure it out as well, but exactly what balances up the investment between these things? So does it mean that the roles have been reversed? Does it mean that the males can then choose the females and the females have to show off to each other, or show off to the male and fight with each other?
It doesn’t quite. What we’re finding is that the males are still the most active ones in the fighting, but there’s a lot of evidence that sexual selection is actually working on the females. We haven’t figured it out yet. Who’s choosing who? That’s what we really want to know. We haven’t got there yet.
So as I said, males get pregnant, and you can see here I was talking about some bizarre pouches. How cumbersome is that. You’ve got to feel sorry for the poor things. When they're really full term, they are quite bloated and when they’re full term they pretty much don’t move. They just sit there. It’s just too much effort for them.
So seahorses have this pouch and you can see the pouch there. That’s one of the photos I had before. In our Western Australian Seahorse, as the graphs indicated before, it takes two to three weeks for the clutch to come through, and a little bit longer if they need to change mates, but in pipefish it’s a whole range of adaptations. Some of them have a fully enclosed pouch just like a seahorse. Some of them, like this one here – you probably can only just see them – but it has these little flaps that cover the eggs, so it’s an open pouch, and some of them have no pouch at all, and just have the eggs stuck straight on the tail. In the sea dragons at the bottom here, they really do just glue the eggs straight onto the tail and if you are lucky enough to ever see these things in the water, you will see these incredible eggs stuck on their tail. If you see them at the right time, you can actually look through the eggs and see the embryonic sea dragons in there.
But male parental care, to me, I think is fantastic. But seahorses are really not that special. What makes them special is they’ve got a pouch, but they’re not that special because in most fish, if there is parental care, if the parents do actually care for the babies – most fish just squirt it into the water – but if there is parental care, in most cases it is the male that looks after it, more often than not. You’ll see these are Cardinalfish, this fabulous guy here. He has to carry them in his mouth. He doesn’t get to eat while he’s carrying them around, and later on as the babies hatch, he has the babies in his mouth and if he wants to eat, he has to spit the babies out, eat, and then suck the babies back into his mouth again. Big risks. Big risk for dad and for babies.
Then you get things – you get the Damselfish, they build a nest and it’s the male that builds the nest, it’s the male that has to attract the female, it’s the male that guards nests, stops predators, he cleans the nest, he does all of that, and then of course the betta, or the Siamese Fighting Fish, probably familiar to many of us. The male blows this bubble nest on the surface and he has to look after it and make sure all the bubbles are still there and all the eggs get tangled up in the bubbles. So it’s the male that does it usually. The seahorse is no different.
What makes the seahorse different is that it has a pseudo-placenta. So inside the lining of the pouch there’s membranes, there’s tissues that have a connection. So the eggs sit in there and you can see these eggs with these little embryos – you can just see the embryos – and that actually forms a connection through the lining of the pouch. So it’s not a true placenta the same way that a mammalian, human placenta works, but it has the same function. It transfers nutrients across there for the developing embryos. It exchanges gases. So it is a placenta in every way except that it’s not evolved the same way as a mammalian one.
I think perhaps the first time I ever really felt sad for a male seahorse, other than this ridiculous belly, was when I watched one go through labour and I hope that humans never evolve for men to go through labour because these poor things, they actually release hormones that are related to the labour hormones in mammals. They go through contractions. They absolutely look in agony, at times. Sometimes it all looks like it happens easily, but other times it looks really, really painful. They convulse, they try and squirt these babies out of there. It can take hours, even days. I’ve seen one seahorse that it took three mornings before he’d emptied his whole pouch out. So it’s quite an onerous task for them and I’m very sympathetic. Poor things. But afterwards, when they’re finished, they will often just hang onto a holdfast and they’re just trying to recover. They really, really are exhausted. I’m not getting a lot of sympathy from the women in the room I don’t think.
Okay, so this fantastic photo. I just think this is just – you would think it’s Photoshop, but I know it’s not. It’s just incredible. This is our local one, and you can see the male. There’s two females there and that’s quite interesting actually, but the male, he’s still got quite a lot of babies in the pouch I suspect. So that’s probably only one of the first ejections that he’s had, and they are forcibly ejected. They are really… he really squirts them out. He really gets them out of there. So the larger ones can have five, seven, even up to 1,000 – 500 or 700, or even up to 1,000 babies. The little ones here, perhaps only a few, up to 5 may be, so the little Pygmy-Seahorses. This is also beautiful to watch.
So the babies, as you can see, look just like their mum and dad, the proportions perhaps are slightly different, but more or less they look the same and they are completely independent. Mum and dad don’t care about them after that. As I said earlier on, I’ve even seen the females eating them. I’ve never seen a male eating one, although I’m sure they might, but the females, they seem to – it doesn’t really matter. Eat your baby. But it might not be theirs. They don’t know.
Alright, just when you think that the male’s been through this whole thing and you feel sorry for him – well some of us might – and he’s sitting there exhausted, I’m going to wind the clock back just a couple of days, and what happens? She turns up again. There’s this male sitting there with his big belly and she turns up and she starts this dance, and she wants him to show off to her. She wants him to start this whole process all over again. Why? Because she’s got the clock. She knows, “Your time’s just about up. You’re going to get rid of this brood. I’m back.” So she turns up a few days beforehand. She makes sure that he knows she’s ready.
Once she’s got that commitment from him, she hydrates her eggs. So all her eggs, they’re sitting there, just sort of dormant waiting, and then because she’s been building them up over the last few weeks, she then gets them finally ready to give to him. But once she’s made that decision, that’s it. She has to either give them to a male or she’ll just squirt them out into the water column and waste them, and that is a huge investment. It’s a huge loss.
So she makes sure she gets there early and says “Alright mate. Get ready. I’m ready. It’s time,” and “I know you’re getting close.” So she turns up and she starts this dance again. This guy with the big belly and he’s having to do this whole thing again. He’s had to do the synchronised swimming, the dancing, the change colour, the fancy clothes, get the haircut, shave, all that, and she’s getting him really – it’s such an important thing, but it’s sad to watch, I must say.
He goes through labour, he watches the babies swim off and in the worst case scenario, she’s sitting on the same piece of stick and she will swim over to him and say “Are you ready?” He usually will wait a little while. He’s probably still in quite a bit of pain, but it can be just a few hours. Often it’s probably the next day, but certainly we’ve had examples where it’s even just a few hours later. She gives him the eggs, she’s gone. That’s it. She’s happy. She’s done what she needed to do. Leave it up to him again, and then he goes through this whole process again and then guess what? A few days later, a few days before he’s about to give birth again, she turns up again and he’s “Come on. Give me a break.”
So this happens probably - well it’s across the whole summer, so it depends how early in the season they start to breed, but he could have 10, 12 of these broods across the summer, if it’s a really long summer. So it’s a lot of work.
Alright, so I think that’s it. There’s one more seahorse that I think is worth seeing. So as I said, there was a whole bunch of photographs that allowed me to use their photos and I’d like to thank those. Project Seahorse is a very large conservation group that works around the world and works on trying to conserve populations of seahorses and they’ve allowed me to use some of their footage as well. I’ve been lucky enough to work a little bit with Project Seahorse and we got to go to the Philippines and work on some of the groups that were there.
So thank you very much and I’m more than happy to take any questions.
This video recording was made possible with the support of Chevron Australia.