Fish eat fruit?!?! Who knew?

I guess I shouldn't be so surprised by this but Anderson JT et al. have recently published a paper in the Proceedings of the Royal Society of London Society B about an Amazonian frugivore called Colossoma macropomum.  Animals will become adapted to eat pretty much anything they can find in their environment so I'm not sure why a fruit eating fish is so amusing and surprising to me.  Apparently a large amount of fruit falls into floodplains in the Amazon during flood season and the authors showed that these fish eat the fruit and retain the seeds in their gut for several days.  The fish travel fairly long distances during this time period allowing seeds to be dispersed 100's of meters and in some cases over 1,000 meters away from where the fruit was originally dropped.  In addition most of the seeds dispersed by a fish were likely to wind up in a suitable habitat.  Of course like most ecological stories this one comes with a warning.  Colussoma macropomum are currently being overfished, potentially threatening the dispersal mechanisms of some Amazonian plants.

The Ability to Change One's Mind

One of the qualities I most admire in a scientist is the ability to look a pattern of scientific results and say "well I guess my pet theory was wrong, I need to change the way I think about this."  The difference between science and religion or philosophy is that science is not based on beliefs; scientific theories must be based on concrete observations. No matter how elegant and seductively intuitive an idea might be we must be vigilant about molding our ideas to the data and not the other way around.  In order to stay relevant and cutting edge throughout our careers we should be nimble in our thinking, constantly taking in and assimilating new information.  This is what is so exciting about being a scientist; there is always more to learn and new discoveries to make.

A recent article in Nature News titled "Beautiful Theory Collides with Smashing Particle Data" highlights the fact that a much beloved theory of particle physics called supersymmetry has thus far not been supported by the Large Hadron Collider experiments being performed in Europe.  Now I am no physicist but from what I understand theoretical physicists like this theory because the math behind it is beautiful and provides an elegant solution to some sticky problems.  A major problem in physics right now is that theories that work on the very small scale (quantum physics) are difficult to reconcile with those that work on the very large scale (general relativity).  This has lead physicists to search for a "unified theory of everything" (a grand title indeed.)  Super symmetry is one component of theories used to solve this problem and suggests that every particle has a "supersymmetrical partner."  However, these super particles have not yet been found leading many to suggest that as elegant of a solution supersymmetry may be for solving some of physics' darkest mysteries it might simply not be true.  Some physicists say that the jury is still out on this and more experiments are being completed but others suspect it might be time to go back to the drawing board.

I would love to hear from you.  Have you ever had the experience of disproving your own (or worse yet your advisor's) favorite hypothesis?  Are there contentious debates in your field with prominent scientists lined up on both sides of the debate and completely sure that they are right?

Symbiosis, sex change and olfactory imprinting: Clownfishes are more than just cute

After coming up to the boat from a dive on the Great Barrier Reef my dive companion (a somewhat macho Australian) said to me "Did you see that big coral trout?"  I said "no I totally missed it" to which he replied "you,re too busy staring at the dopey little damselfishes."  And it's true I love the little fishes.  I find it endlessly fascinating to watch them going about their business.  Damselfishes, for example, tend to be site attached and very aggressive.  They will attack much larger intruders (including divers) that stray into their territory by chasing and nipping them.  Because they have a tendency to make a home of a particular coral head, sea anemone, or other substrate you can easily observe their behavior and I have the distinct impression of a coral reef as a large and bustling metropolis.

Amphiprion melanopus on the Great Barrier Reef, Australia

One subfamily of damselfish are the clownfish or anemonefish (Amphiprion); the cute orange and white striped fish that gained fame as the star of Finding Nemo.  These fish have many of the types life history traits and behaviors that I think make damselfish so interesting.  As their name suggests anemonefishes have a special coating on their scales that allows them live and hide in the tentacles of sea anemones.  Sea anemones, like other species of cnidarians (a phylum including jellyfish) have stinging nematocysts which can be fatal to most small fish, but sea anemones and clownfish have a symbiotic relationship.  The clownfish are protected from predators and provided with food by the sea anemone and the anemone receives housecleaning, oxidation and nutrients from the anemonefish.  Different species of fish are adapted to live in different species of anemones; some clownfish can choose from several species of anemones while others can only live in one specific anemone species. 

In a clownfish colony the breeding female is the big boss.  All clownfish start out as male. The biggest, most dominant fish within a group will turn into a female and the second biggest fish becomes the mature breeding male while the rest of the fish remain in an immature juvenile male state and are chased and harassed by the breeding pair.  If the female fish dies the breeding male will grow larger and become a female and the most dominant juvenile will become a mature male.  The female lays the eggs on a hard substrate near the sea anemone and the male fish fertilizes the eggs and is responsible for fanning the eggs to oxidize them and removing dead or unfertilized eggs.  The female fish makes sure the male does his job by chasing him toward the eggs, she is quite the task master and bully.  About two weeks later the eggs hatch and the little larvae are carried out to sea where they spend about two weeks in the plankton developing further.  

After this time the little larvae start to develop orange coloration and deeper body, the tiny juvenile fish return to a reef.  Once they are on the reef finding the correct species of sea anemone to settle in as quickly as possible is essential for survival.  Anemonefishes recognize their host sea anemone by smell and they learn the odor of their host sea anemone when they hatch next to it, before they leave the reef. Anemonefish larvae that hatch in the absence of a sea anemone cannot recognize the smell of their host anemone when they return and settle on the reef.  This process of learning an odor during a specific period during development and then using that odor later in life is called olfactory imprinting.

Symbiosis, sex change and olfactory imprinting are three fascinating aspects of biology each of which could inspire a lifetime's worth of study and they're all found in one ridiculously cute, orange and white stripey fish.

Pigeons Go for the Big Money

Blue Rock Pigeon. Picture by J.M. Garg from Wikipedia.org

We all have a tendency to do things we know are not good for us like overeating, putting off to tomorrow what we could do today, failing to save for retirement, etc..  One reason for some of these behaviors is that we value immediate rewards over more distant ones.  Studies in species from fish and birds to primates including humans have shown that animals prefer a smaller reward (such as food or money) immediately to a larger reward in the future.  For example if given a choice pigeons will choose to receive a smaller number of food pellets immediately over a larger number of pellets later.  Similarly human subjects will choose to receive a smaller amount of money today rather than receive a larger amount of money weeks or months down the road.  In both these cases if the future rewards become large enough  then the larger reward will be chosen.  Thus we tend to "discount" future rewards and perceive immediate rewards as being more valuable.  This may help explain why I am driven to continue to spend time watching my favorite TV show even though I know that I will be happier in the long term if I spend that time working out or writing manuscripts.  Researchers have used the study of delay discounting to understand human behaviors such as procrastination and addiction. 

A recent paper by Zentall and Stagner in the Proceedings of the Royal Society B (278:1203-1208) uses a similar paradigm to provide a model for human gambling behavior.  Pigeons were given the choice between a symbol that alway predicted a reward of 3 food pellets or another symbol that 80% of the time provided zero food pellets and 20% of the time provided 10 food pellets.  So over the course of 10 trials a pigeon that always went for the sure thing would receive a total of 30 food pellets while a pigeon that went for the possibility of a big payoff would receive 20 food pellets.  Despite the fact that the three pellet payoff was a better bet and resulted in acquiring more food over time the pigeons consistently chose to go for the more uncertain, larger reward.  Thus the pigeons, like human gamblers, were lured by the prospect of a big payout even though it was a bad strategy over time.  It appears that animals and humans are primed to value larger and/or immediate rewards over smaller but consistent rewards or rewards that occur later in time.  

Good Morning Sunshine!

My search for monogamous fishes turned up this interesting behavior in seahorses which I thought was just too cute not to share. Now I'm not exactly what you would call a "morning person" and would prefer not to engage in any complex social interactions before a certain hour, but this is not the case for a family (Syngathidae) of fish which includes seahorses and piepfishes.  In these species the male fish has a brood pouch where he fertilizes and incubates the embryos for two weeks to a month.  Seahorses maintain stable pair bonds over the course of the breeding season and appear to be monogamous.  One way pair bonds are maintained and reproduction is synchronized is through morning greetings.  Males and females each have their own partially overlapping territories and every morning just after dawn the pair will meet at the spot where they last spawned and "change color, promenade and pirouette together" according the project seahorse website then they will part for the day, each to do their own thing.  They keep this up every morning that the male is pregnant and then after the male gives birth they spend up to 9 hours together dancing and courting after which they mate and the whole process begins again.

Vincent, A. C. J. (1995) A role for daily greetings in maintaining seahorse pair bonds. Animal Behaviour. 49:258-260.

"Defending" monogamy

I just want to clarify that as I stated in my previous blogpost I don't believe in using biology to either decry or condone individual human behavior and of course human sexuality is way more complicated than that of a damselfish. I do think it's interesting to explore the factors that lead to different types of mating systems and bi-parental care is one factor that can lead to monogamy. Of course though parental care in humans is time-consuming and costly, as many amazing single parents have demonstrated, humans are not obligately bi-parental. In the case of the Acanthochromis if one mate is removed the remaining mate will abandon the brood to their fate and find a new partner.  The idea that the high cost of parental care may push humans towards a monogamous mating system can give us a glimmer of an idea of why our social systems have evolved the way they have but is not a value judgment on how people choose to live their lives.