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.

New publication: Big bucks for small critters

One of the most important chapters of my research has recently been published in the journal Marine Policy. The paper explains that scuba dive tourism focused on small critters (“muck diving”) has a very high value and how muck diving can be a sustainable alternative to more destructive uses of the environment. This is the link to the paper, but since it is behind a paywall, is rather detailed and perhaps a bit to dry for those of you who are not economists, below is a summary that is easier to digest.

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A typical muck diving scene: a sandy bottom with few defining features. In the foreground an Estuary seahorse (Hippocampus kuda) holding on to algae (Photo by Dragos Dumitrescu).

If you don’t know what muck diving is, I invite you to have a look through this site to get a feel for it. But in short: muck diving is scuba diving in sandy areas, usually without coral or other landscape features. The goal is to find weird critters (like flamboyant cuttlefish or hairy frogfish)  that you’d rarely see on normal dive sites. It is very popular in places like Lembeh Strait and Dauin in Southeast Asia, but it is done by divers and photographers all over the world.

Typical for muck diving is that the people doing it are very experienced, with an average of 580 logged dives. Most of them (73.5%) use underwater cameras, often the expensive dSLR cameras, to photograph all the weirdness down there. Many of the divers are well-educated and have a high yearly incomes. Importantly, most divers would be willing to pay for marine conservation if it benefits the species they come to see.

So what does it matter if some fanatic divers like to spend their holidays rooting through the sand instead of cruising by pretty coral reefs? Well, for starters, those fanatic divers spend a combined whopping $152 million per year in Indonesia and Philippines alone. The real value is probably much higher, as this estimate is only for dive centres that specialise in muck diving, and does not include liveaboards or more general dive centres that visit muck dive sites. The real value could be over $200 million per year! Also bear in mind that this number is for Indonesia and Philippines only, it does not include muck dive tourism in Malaysia, Papua New Guinea, or the rest of the world. With more than 100,000 divers visiting Indonesia and the Philippines to go muck diving, you would expect to get the attention of people managing tourism or ocean resources. Especially since many of the divers said they would not have visited the region, or even the country, if they could not muck dive.

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Diver and Ornate ghostpipefish (Solenostomus paradoxus) in Dauin, Philippines

While these numbers might not change anything in your life, they make a huge difference for the thousands of local people that work in this branch of the dive industry. Muck diving is often done in remote locations with limited other forms of income besides fishing. Working as a dive guide and looking at fish is not only more sustainable than catching fish, it also pays a lot better. Roughly $51 million is paid in wages to the local staff working in muck dive tourism annually, and dive guides can earn nearly 3 times more than the minimum wages in the area….

Just stop and think about that for a minute. Imagine the minimum wage in your own country, now triple it. Got the number? OK, now imagine this choice: you can either make that amount by showing cool animals to divers, or you can work your ass off in a factory or risk your life fishing for a third of that amount. Small wonder that many people prefer the first choice, which is great news for marine life in the area, because it means less people fishing and more people trying to protect this valuable source of income.

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The future generation of muck dive guides? Not without a healthy ocean (Photo: Luke Gordon)

That is what it comes down to in the end, protecting these extremely interesting and valuable ecosystems. Make no mistake, muck sites can be threatened as well. Coral reefs might bleach because of climate change, mangroves might be cut to make space for shrimp ponds and seagrass might be dredged to mine for sand, but sandy habitats could face other risks with equally bad consequences. All the habitats above receive far more research and conservation attention than the “barren” sandy sites in the tropics. If this paper proves anything, it is that soft sediment habitats have a very high value, and that it should get more attention to avoid loosing amazing biodiversity and the subsequent loss of income for the thousands of people that depend on it.

And that does not even consider loosing that feeling of pure joy when you finally find a critter you’ve dreamed of seeing for years 😉

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Muck diving scene: a diver (the science hobbit) taking a picture of a frogfish (black Hairy frogfish – Antennarius striatus)

Fluo time

If this isn’t the first time you’ve read this blog, you probably know I am interested in the phenomenon of biofluorescence. I’ve previously talked written about what it is and what it might be used for. In the near future I’ll be tell you all about the details what I was actually doing. But I realized I haven’t shared any pictures recently that show just how beautiful and otherworldly it can be. So here is a random selection of fluo shots I took over the last two years. Enjoy!

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A bubble snail (Hydatina physis) photographed in Lembeh Strait, Indonesia

 

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Thorny seahorse (Hippocampus histrix) in Bima Bay, Indonesia

 

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West Australian Seahorse (Hippocampus subelongatus) in Perth, Australia

 

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Amazing coral in Raja Ampat, Indonesia

 

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Reptilian Snake Eel (Brachysomophis henshawi) in Amed, Indonesia

 

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Lizardfish (Synodus sp.) in Lembeh Strait, Indonesia

 

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Cockatoo Waspfish (Ablabys sp.) in Lembeh Strait, Indonesia

 

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Sea spider (Pycnogonid sp.) in Tulamben, Indonesia

 

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Painted frogfish (Antennarius pictus) in Lembeh Strait, Indonesia

 

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Juvenile Painted frogfish (Antennarius pictus) in Dauin, Philippines)

 

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Barred moray (Echidna polyzona) in Nusa Kode, Indonesia

 

New publication: Fluo frogfish lures

After a weekend looking for vagrant fish in the cold waters of Shark Bay (more about that later this week), I came home to find a pleasant email in my inbox. A new publication has been published online last week. This one is in the journal “Coral Reefs” and is about biofluorescence in the Striated Frogfish (Antennarius striatus), more commonly known as the Hairy Frogfish. The article can be found here, but is restricted access. For those of you who cannot access it, here is what it is about.

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Hairy Frogfish by day. Photo: Luke Gordon

 

As I have written previously, I have been doing a fair bit of work looking at biofluorescence in fishes. During these surveys i had noticed something strange going on with the Hairy Frogfish: their bodies are not fluorescent, but their lure is (very strongly). As you might know, frogfish use their lure as a fishing rod, attracting small fish closer, which are then eaten whole. The fact that the Hairy Frogfish’s lure alone is fluorescent but their bodies are not, hints at the possibility that this fluorescence could be used in what is called “aggressive mimicry”. Aggressive mimicry is the term used for animals who pretend to be something harmless (the “model”) and use that to get close enough to eat their prey.

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Hairy Frogfish (Antennarius striatus) with fluorescent orange lure

But the question was, what would it be trying to mimic? Are there animals out there that resemble this fluorescent lure? Cue my last Philippines trip. During a nightdive with the unparalleled science hobbit, we found three more Hairy Frogfish (with fluo orange lures). More importantly, we also found a lot of freeswimming worms near them. Most of them a similar size as the lure of the frogfish, AND the same colour fluorescence as those lures. The resemblance between the lures and the worms went further than just size, shape and movement, but also the fluorescence is imitated. We found our model species!

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Fluorescent worm (top orange squiggle) and fluorescent lure (bottom orange squiggle)

This is very exciting, as it is the first time anyone found strong indications that biofluorescence might be used to help fish catch prey. To prove whether it is really used to hunt, lab experiments or extensive observations would need to be done to check if this fluorescence really makes a difference. So while this is a very exciting glimpse into an unexplored part of hunting strategies in the ocean, much more work needs to be done to understand all the details.

If you can’t access the article but want to read it, or you just want to know more, send me an email or ask in comments and I can send the publication to you.