Being a fish out of water

It might be tricky to keep mangrove rivulus in your typical aquarium. Mangrove rivulus are rather found of jumping out of water – and staying there.

Being out of water is a rather different place from being in the water, and so this fish obviously have some evolutionary adaptations that allow it to pull off this stunt. But a new paper asks a different, possibly more subtle: do mangrove rivulus adapt to being in or out of water in the short term?

Mangrove rivulus have an advantage for studying these sorts of short-term physiological changes, as many of them are genetically identical, because they are hermaphrodites - not all that unusual among animals, but that they are self-fertilizing hermaphrodites is a rare and exceptional feature among vertebrates.

Turko and colleagues first did a simple correlative study, allowing the fish to jump out of their tanks as often as they want. Most stayed in the water most  of the time, but a few appeared to have what would have been a death wish in most other fish: they were out of the water almost two thirds of the time (64%). The authors saw differences in the gill shape that were correlated with the amount of time fish spent in or out of water.

But because correlation does not mean causation, the authors sensibly went back and did an experiment. They monitored animals for a week, then prevented them all from leaving the water, sacrificed half to check on their gills, and then left the remaining half go back to being free to leave the water if they chose.

The first that were prevented from leaving the water had different gill shapes than those that were allowed to return to the air. This strong suggests that the fishes’ behaviour drove the changes in the gill morphology.

But there is a problem in interpretation here. At the start of the second experiment, the fish were leaving water rather less than in the first correlation study. And there were no correlations between gill shape and the fish’s behaviour after the first week, as there was in the first study. The differences in gill shape emerged only after the week were the fish were forced to stay within water. The researchers suggest that there may be a minimum time the fish have to spend out of water for the gill remodeling effect to occur.

This makes me wonder if there were be a way to do the experiment were fish were forced to stay out of water for set periods of time. Here, the experimenters were at the mercy of the fish voluntarily leaving the water. It may be a little bit trickier, but the results would be much easier to interpret.





Related posts

Conquest of the land, a la Chubby Checker (on NeuroDojo)
Celebrate diversity: The fish that fertilizes itself

Reference

Turko A, Earley R, Wright P. 2011. Behaviour drives morphology: voluntary emersion patterns shape gill structure in genetically identical mangrove rivulus. Animal Behaviour 82(1): 39-47. DOI: 10.1016/j.anbehav.2011.03.001

Molting in a nightclub

AT least, molting in a nightclub is the best explanation I have at hand for the soundtrack on this video.

Crayfish kryptonite

When I talked on Dr. Kiki’s Science Hour last week about Marmorkrebs, Kirsten asked me at one point, “What’s their kryptonite?”

On the show, thinking on my feet, I said that Marmorkrebs might have some competitive disadvantages because they are a small species, and size is a very important factor in crayfish competition when animals are in one-on-one interactions. (When you match individuals for size, Marmorkrebs hold their own, however).

This is a similar question to the one I fielded at the Ecological Society of America meeting a few weeks ago. One crayfish get loose in a watershed, there is not much that you can do.

In a bit of l’esprit d’escalier, I might have added in my reply to Kiki that the kryptonite of marbled crayfish might be their reliance on humans. In general, crayfish are not all that mobile. Yes, some species are comfortable with leaving the water and making a portage to a new home, but in general, they will spread from one watershed to another only fairly slowly. They are horrible once they get established, but they have a hard time getting that first toehold without humans moving them around.

Left to their own devices, Marmorkrebs never would have made it to Madagascar, or Japan, or anywhere else. In North America, Marmorkrebs are human captives. Let’s keep it that way.

Dr. Kiki’s Science Hour

This week, I had a lovely live chat with Dr. Kirsten Sanford, a.k.a. Dr. Kiki on Dr. Kiki’s Science Hour! She titled Episode 110, “Invasion of the Marmorkrebs!”

You can listen to the audio, as well as subscribe to the show’s audio and video feeds, here.

Additional: And the video is now up on iTunes, YouTube, and elsewhere!

Celebrate diversity: Stingrays

This news story is a good example of the surprises animal keeping throws up:

Sea Life London Aquarium staff were shocked to discover two female stingrays were pregnant, despite that they have had no male contact for two years. ...

It is not unknown for rays to store sperm and wait until “they decide the timing is right” before they give birth, head curator at the central London attraction Paul Hale said.

Could it be parthenogenesis? A quick peek in Google Scholar reveals no records of parthenogenesis in the group. Stingrays’ cousins, sharks, can reproduce without sex, however (previously covered here). That means it is at least plausible to be parthenogenesis rather than sperm storage.

Somebody better be collecting DNA from all those baby stingrays to test this!

At any rate, this story does give me an excuse to watch this:




Hat tip to David Shiffman. Photo by by TGIGreeny on Flickr, used under a Creative Commons license.

An Achilles’ heel?

Last week, at my Ecological Society of America talk, one of the questions asked afterwards was, “Could the fact that Marmorkrebs are genetically identical be exploited to control introduced, unwanted populations?”

I said, “No.”

One of the things I admire about crayfish is that they are tough little survivors. Unfortunately, this means that they are hard to get a handle on once they’re loose.

I think it’s fair to say that the weapons used to control crayfish populations are blunt instruments. There have been culls to lower the numbers. Dams to try to stop the spread (Dana et al., 2011). And an approach that might be best summarized by this famous quote by Sigourney Weaver:



Peay and colleagues (2006) have conducted a number of trials with broad applications of biocides. These are the freshwater equivalent of nuking everything from orbit. Their results have been variable at best in eliminating crayfish from water bodies.

We are so far from any kind of control that targets crayfish in general that something that targets Marmorkrebs in particular is a pipe dream.

References

Dana ED, García-de-Lomas J, González R, Ortega F. 2011. Effectiveness of dam construction to contain the invasive crayfish Procambarus clarkii in a Mediterranean mountain stream. Ecological Engineering 37:1607-1613. http://dx.doi.org/10.1016/j.ecoleng.2011.06.014


Peay S, Hiley PD, Collen P, Martin I. 2006. Biocide treatment of ponds in Scotland to eradicate signal crayfish. Knowledge and Management of Aquatic Ecosystems 380-381: 1363-1379. http://dx.doi.org/10.1051/kmae:2006041

Got recipes?

Marmorkrebs probably don't make very good eating compared to other crayfish species, as they are a rather small crayfish. But many that shouldn't stop you from checking out Invasivore.org, a site devoted to the notion that one of the best features about invasive species is the sense of retribution we can get for the harm they do to ecosystems when we eat them.