What is a species?

As promised in a previous blogpost, it is time to get into another hotly debated topic in biology that most non-biologists wouldn’t even think was an issue at all. This is a big one, as it underpins pretty much all biology: “What is a species?”. I would argue that this question needs two important additional questions: “Why does it matter?” and “To whom does it matter?”. Since I am only human and like postponing difficult tasks at hand, let’s start with the follow-up questions.

speciesTo whom does it matter that we are capable of telling one species from another? Besides looking like a smart cookie when telling your fellow divers/birdwatchers/plant enthusiasts which species you’ve just seen, it doesn’t matter very much to be honest. We are no longer hunter-gatherers, so being able to tell which species you can eat, and which ones will will eat/kill you, doesn’t matter that much anymore. In other words, the discussion in the rest of this blog is mostly an issue for taxonomists, but it gives an interesting insight in how simple concepts can be quite complicated when you look closer.

Why does it matter then? For two reasons:

  1. People in general and scientists in particular like putting labels on objects around them, it helps us structure and understand the world we see.
  2. Being able to tell two species apart that look very similar can have big consequences for conservation action: Two birds/fish/plant might look similar, but they could be different species, one of which reasonably common, but the other one rare and on the brink of going extinct. If we don’t realise they are different, we might lose that species.

A logical follow-up question (in my mind) would be: “what does it matter if one species that looks a lot like the next goes extinct?”. This is a valid question, but would require a long (and interesting) scientific and philosophical discussion.

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Struggling to define what a species is? Don’t worry, so did Charles Darwin (photo source: www.brainpickings.org)

Back to the species concept, which seems obvious, but really is not. The question has been asked for centuries by many renowned scientists. Two of which were none other than Charles Darwin and Alfred Russel Wallace. It could even be claimed that this question is what eventually led to the theory of evolution, which essentially tries to explain how different species come into existence. It is obvious that you need to know what a species is before you can answer that question. Sometimes it is easy: the majority of people can tell the difference between a cat and a dog, but it becomes a lot more difficult when species look very similar. Try asking a marine biologist what the difference is between a Slingjaw wrasse (Epibulus insidiator) and a Latent slingjaw wrasse (Epibulus brevis), or between a Thin Ghostpipefish (Solenostomus leptosoma) and a Robust Ghostpipefish (Solenostomus cyanopterus). Go on, give it a go, it’ll be fun to see them struggle! (Smart-ass tip: a spot on the dorsal fin & smaller adult size / No difference, they are most likely the same species).

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They might look different, but are the same species. Photo source: www.dogguide.net

The problem is how do you define a species? At what point is an individual that looks different than “the norm” a different species, rather than just natural variation? Dogs can look as different as Danish dogs and (rats) Chihuahuas but are all the same species. Compared to those two, lions and tigers look much more alike, yet they are very different species. The classic definition of a species (if they cannot have fertile offspring they are different species) works in most cases. Lion + Tiger = Liger, but ligers are infertile. I don’t know what Danish dog + Chihuahua would look like and I wouldn’t get ethics approval from my university to test it, but presumably the result would be a fertile dog.

So far the normal situation, but what happens when different species mate and have fertile offspring (hybrids)? This is surprisingly common in the ocean. Hybridising fish are not that rare if you know what to look for. I have personally seen it in Clownfish and Surgeonfish and almost certainly in Frogfish and Ghostpipefish. But is has also been recorded in groupers, manta rays, butterflyfish, angelfish and wrasses.

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Hybridising surgeonfish: r: Acanthurus lineatus s: Acanthurus sohal t: A. lineatus x A. Sohal hybrid (Source)

In this case, can we say the parents are different species because they look different, behave differently, and typically live in different regions? Or are they a single, highly variable species, the way dogs are? Traditional taxonomy focused on what species looked like, would say they are different species, but not everyone agrees with this. A recent example from the pygmy seahorse world: Hippocampus severnsi and Hippocampus pontohi were described as two different species. However, new (yet unpublished) research shows that they are genetically identical, so the name H. severnsi was removed and they are now all called H. pontohi. I’d imagine much to the annoyance of Mike Severns, who no longer has a cool animal with his name on it.

Is genetics the solution to the problem? Depends on who you ask. Geneticists tend to say yes, old-school taxonomists tend to be a bit less convinced. Each side has very valid arguments, one of which is how genetically different do individuals have to be before they are considered different species (sound familiar?). Different cut-offs have been proposed, but as far as I know, there is no real consensus (please correct me if I am wrong geneticist-readers). Another serious issue is how to classify small life forms like microbes, this article has a great summary on that if you are interested.

If you think this is getting too complicated, it might be best not to become an evolutionary biologist or taxonomist, because things actually get a lot more complicated than what I described. Suffice to say, for biologists the term “species” is still not a clearly defined concept. But luckily for non-specialists, the essence of the debate is about such fine details that it really shouldn’t be keep you up at night.

Growing up

Growing up isn’t always easy, going from the playful life of a child to become a (seemingly) functional adult takes blood, sweat and tears. Anyone reading this blog who longingly remembers the awkward changes your body goes through puberty, please feel free to share in comments below whether it was the pimples, the voice changes, gangly limbs or any other similar affliction you’d like to get back in your life. I am fairly confident the comment section won’t be overly populated. If you think growing up was hard for you or any other human, take some time to consider how much more extreme becoming an adult is for fish.

As you or may not know, most fish start their life as transparent larvae, floating through the blue. Once they are large enough to become proper fish, they “settle” on the reef. This settling is the first big growing up fish have to do.  Forget about years to grow from a baby into a teenager. Typically within less than 2 days, the freshly arrived larvae change colour and massively grow in size. If you think changing colour and doubling in size within a month isn’t hard enough as a childhood, consider the following. Over 50% of baby fish arriving on the reef get eaten within the first two days of arriving on the reef! Talk about a bad first day at school…

Childhood might be the most dangerous time for fish, but that doesn’t mean puberty is any easier. While we humans complain about acne and high pitched voices, fish have got other things to cope with. Many fish change colour again as they become adults, which is a minor nuisance compared to the fact that some radically change shape. Good examples are batfishes, which start by looking like leaves or flatworms to then turn into a relatively boring plate-looking fish.

Shapeshifting is peanuts compared to a process many fish have go through during puberty: sex change. Many fishes are born as one sex, but will turn into the opposite sex as they grow up. The best known example are clownfishes, which are all born as a male, but turn into females later in life. Including this process would have made “Finding Nemo” a much more interesting film in my humble opinion. Other species, such as parrotfishes and wrasses are born as females, but then turn into males as they grow up. While surprising to most people, the whole sex change thing is actually very common in the ocean.

Part of growing up in humans is learning to appreciate different kinds of food: whether it’s vegetables, olives or alcohol, children like different things than adults. The same goes for many fish species. Frogfishes for example start by mostly eating small shrimp, and then evolve a more delicate palate including fish like seahorses, lionfish, or pretty much any other fish that fits in their mouth. Interestingly, for frogfish growing up can mean that you start of as prey for a fish, but turn into a predator for that same fish once you’re big enough. Conclusion: growing up can be difficult for any animal, but some have it worse than others.

Valentine special: Sex on the sand

In the aftermath of valentine’s day, I figured a post about nautical naughtiness was suitable. Popular media such as romantic comedies, reality tv-shows or more dubious videos available on the internet might have you believe that a moonlit fondle on a tropical beach is the highlight of romance. They are, however, very much mistaken! Late night walks on the beach turning into passionate, steamy scenes of desire and lust are in fact the best way to discover that sex and sand really don’t mix well. No matter how hard you try, sand will get where you absolutely don’t want it to get. But for creatures that spend their entire lives on soft sediments there is no way around it. They have no choice but to deal with the gritty truth that is sex on sand. As you can imagine, this blog is not going to be a pretty story, but if you think you can handle it, here is how things go down in the muck…

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A small male frogfish (Antennarius pictus) risking his life to get closer to a larger female

Getting started with one my favourites, frogfishes, immediately proves my point on how difficult romancing is on the sand. As in humans, competition for females is fierce, but competition is made worse because frogfish are usually quite rare, so there aren’t many females around. The result is that males will often stalk a female for multiple days or even weeks, waiting until she might be ready to mate. This is a very risky strategy though. At best, the larger female will reject a male by pushing him away or swimming off. At its worst, the grumpy female might decide to eat the male! It sure would make Tinder a lot more exciting if this trend would catch on in humans. Have a look at a cannibalistic frogfish below (Video by Albert Kang).

When the female frogfish is in the mood however, the male will gently put its pectoral fin on her belly when they’re almost ready to mate. He’ll prod her until she’s ready, at which point the female swims up, partially pushed by the male, and releases her eggs. The male then releases his semen over the eggs, after which the now fertilised eggs drift off, forming a sort of raft until the young frogfish hatch. The attentive blog-reader will have noticed that frogfish also avoid the sand when mating, clever! Here is a rather explicit video of two hairy frogfish in action (video by BlueWaterLife1)

Unlike frogfish, the blue ringed octopus wastes no time on small talk or courtship. Male blue ringed octopuses just pounce upon any opportunity, inserting their hectocotylus (scientific slang for “penis-arm”) in any other blue ringed octopus they encounter. The problem is that males unfortunately can’t tell the difference between males or females. So they will try any octopus and only know if they hit the jackpot or got themselves into a rather embarrassing situation until after attempting to copulate (not unlike some drunk male tourists in dodgy bars in Thailand or the Philippines). The unfortunate males on the receiving end don’t seem to take it too badly and do not react aggressively, preferring to wait passively until the mistake becomes obvious. The females however are more feisty and tend to finish the act by “forcefully pulling the males from their body“, occasionally attacking or even killing and eating the males (is it me or am I seeing a trend here?). The actual deed takes on average 90 minutes, but I think we can all agree it hugely lacks in romanticism.

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A blue ringed octopus on the prowl. For what I don’t know, and turns out neither does he…

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Male Thorny seahorse (Hippocampus histrix) showing off its pregnant belly

Seahorses are more romantic, forming stable couples that sometimes stay together for life. The couples greet each other every morning by doing a little dance. When mating their dance gets more elaborate and ends up with both fish swimming up in the water-column and doing the act at the highest point of their dance. But then it gets a bit kinky, as it is the female who penetrates the male! She deposits her eggs in the male’s pouch, who then fertilises the eggs, gets pregnant and gives birth to baby seahorses. Shortly after giving birth the couple mates again (within as little as 30 minutes for pygmy seahorses!), and the males gets pregnant all over again. No rest for these little guys!

At least for nudibranchs life is a bit simpler, there is no such thing as a male or female nudibranch, since they are both at the same time. It is believed that being hermaphrodites (simultaneously male and female) is an adaptation to being rare and not being able to move very far during their lifetime. After all, you wouldn’t want to spend half of your life on your own, getting increasingly horny, to then finally meet a single other individual of your species and find out you can’t reproduce with them. So when nudibranchs mate, they usually get pregnant and make the other one pregnant in one go, talk about efficiency. Being efficient at mating does not mean mating is a boring occasion. Nudibranchs are some of the most deviant critters in the ocean. They occasionally indulge in mating aggregations (aka orgies),  S&M (most of their penises have backward pointing spines), mating with different species than our own (a slug’s a slug), and some species even practice protandry (adults mating with juveniles). But it gets even worse….

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Nubibranch sex: These Gymnodoris nudibranchs clearly show how both animals penetrate each other at the same time

Some species amputate their own penis after mating, mostly because pulling out is just too much effort with those backwards pointing spines. They do have spares and the amputated penis regrows, so no harm done. In what is probably one of the most bizarre cases of sex on the sand, a species of Siphopteron-slugs uses a part of its forked penis to stab its partner through the head during mating! You read that correctly, they use an adapted penis to stab each other in.the.head while having sex. Not the mouth, not any other orifice, the head, right above the eyes. As if that’s not enough, they even inject prostate fluid into the head as well. A process beautifully coined as “cephalo-traumatic secretion transfer”. Call it what you want, this stuff is a bit too kinky for my liking. Oh, and the reason why? You guessed it…we don’t know, although researchers have suggested it might change the behaviour of the receiving slug, go figure…

As you see, sex on the sand is a lot more complicated (some might argue interesting) than in more conventional places. Try to remember that during your next romantic walk on the beach.

 

 

 

 

 

 

Explosions of colour in the centre of marine biodiversity

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Sea Safari 6

I recently returned from another liveaboard trip, this time in Raja Ampat. I’m writing this blog in Sorong, after just having disembarked from the Sea Safari 6. We spent 10 days diving both the south and north of Raja and it was pretty spectacular. I was lucky enough that Safari Bali saved me a free spot on the boat again, allowing me to do research. The only thing I had to do in return, was talk about fish, since I do that all the time anyway, I consider this to be a pretty sweet deal.

The Raja Ampat region is found in the east of Indonesia, in the province of West Papua. The name “Raja Ampat” means “Four Kings” and comes from a local legend. The legend tells of 6 eggs that were found and from which 4 kings, a woman and a ghost hatched. In marine biology circles, the area is known as the global centre of marine biodiversity. It lies in the very centre of the Coral Triangle and is home to nearly 600 coral species and 1600 fish species. For comparison, the entire Caribbean has less than 70 species of coral.

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Raja Ampat: Painemu Lagoon

 

Unknown to most people, the Birds of paradise found here and in the Halmahera region further west also played an important role in publishing the theory of evolution. Between 1854 and 1862 Alfred Russel Wallace traveled and conducted research in Borneo, Sulawesi, Halmahera. He was collecting specimens of all kinds of animals, amongst others the birds of paradise found in the region. His observations of these birds helped him develop his own theory of evolution, parallel to Darwin. Darwin had been working on his manuscript for many years, but was hesitant to publish any of it. A letter from Wallace to Darwin, in which Wallace explained his ideas, sparked Darwin to finally publish his magnum opus. Darwin presented the article “On the Tendency of Species to Form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection” in 1858 at the Linnean Society as a joint work from himself and Wallace. Once Darwin’s “On the Origin of Species” was published, Darwin ended up getting all the credit for the theory, but if not for Wallace and his birds of paradise, things could have turned out very different indeed.

While the birds of paradise are pretty amazing (we did go on land for a few hours to try and spot a few), the reason for this trip was to observe the diversity under water. This was the second time I dived Raja Ampat, and I can tell you it is fantastic. I’ve never dived anywhere else where the colours are so…everywhere, just everywhere. The quantity of soft coral, gorgonian seafans, corals, sponges, ascidians, etc is just staggering. You’ll find shades of every colour everywhere, some sites are so overwhelming that you’d almost forget to look for small critters and instead just float around to try and take it all in. Especially when there is a lot of sunlight and strong currents ensure all soft corals look like pink, orange, yellow, purple or white balls of fluff spread out over the reef. One such dive prompted the comment “This must be the campest divesite ever!”, and I couldn’t agree more. Many of the divesites around Raja Ampat look like the marine equivalent of letting a 6 year old kid decorate the Christmas tree…

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Explosions of colour (source)

Of course the diversity extends beyond corals, the fish life is just as great. It might be harder to find critters than Komdo or Lembeh, but there is a lot to make up for that. One of my favourites are the wobbegongs you find everywhere, especially at the northern divesites. But it’s also great to see all the schooling fish, and a very healthy amount of predators. We’ve seen a fair few sharks, tunas, Spanish mackerels, and other pelagic predators you don’t see very often in Indonesia. It’s also great to see lots of large groupers, since they are a very popular food-species, having a lot around means that protection is working and fishing pressure is not too high.

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Fish soup in Pulau Daram

This protection can be credited to the efforts of many local and international NGOs working in the region. Their work helped motivate local and national governments to establish Indonesia’s first MPA (Marine Protected Area) network. Raja’s 15 MPAs protect nearly 6 million hectares of marine habitats. The area is also a shark sanctuary where capture and killing of sharks, rays, dugongs and turtles is prohibited. To me, knowing that this beautiful area is being protected in the best possible way makes diving it an even more rewarding experience.