Freshwater | Erin Zimmerman

February 21, 2013

Axolotls in Never Never Land

Common Name: Axolotls

A.K.A.: Ambystoma mexicanum

Vital Stats:

Grow to a length of 15-45cm (6-18”)
Can live up to 15 years
Have no eyelids
Usually black or brown in colour, but mutation occasionally produces pink skin
Eat insects, worms, and small aquatic animals
Commonly kept as pets and, in parts of Mexico, food

Found: In the Xochimilco lake system, near Mexico City

It Does What?!

Axolotls are the Lost Boys of the amphibian world… they never grow up. These bizarre little salamanders are found only in a single lake system near Mexico City and, if the city’s pollution gets much worse, may soon not be found there, either.

First, a little background on salamanders in general. These amphibious, lizard-like creatures begin life in a larval stage. While adult salamanders have lungs and spend much of their time out of the water, larvae have only gills and are completely aquatic. They commonly undergo a metamorphosis in which the gills are lost and the body changes shape, thinning out and losing its ‘tadpole with legs’ appearance. Many salamanders have displayed the ability to occasionally forego metamorphosis, remaining in their larval stage for life. This phenomenon of looking like a juvenile even during adulthood is called “neoteny.”

caption(via:) — The “fully cooked” version.
(Via: Wikimedia Commons)

What makes axolotls special is that they’re what’s called “obligate neotenes,” meaning they simply never go through metamorphosis… every adult axolotl looks like the larval stage of other salamander species. At some point in their evolution, it became either more beneficial or downright necessary for them to remain aquatic. Biologists have speculated that this is because their smaller larval form requires less food, and because the lakes where they live are low in iodine, an element required for their transformation.

Interestingly, while axolotls almost never go through metamorphosis in the wild, in a certain percentage of them, the genetic instructions for doing so seem to still be intact. If you have a larval axolotl and you want an adult form, you can either give it an injection of iodine, or, for the more deranged among you, gradually deprive it of its pool of water. Either method of forced metamorphosis has a high mortality rate and, at best, causes a hugely decreased lifespan, but it does show they haven’t entirely lost that capacity.

caption(From:) — The future of multi-tasking.
(From: McCusker & Gardiner (2011) Gerontology 57: 565)

An eternally youthful appearance isn’t even the axolotls’ only superpower. The creatures also possess a Wolverine-like ability to heal themselves. Not only can they – and other salamanders – regrow lost limbs, they can actually regenerate parts of vital organs, including sections of the brain, spinal cord, and, in one study, up to 50% of the heart ventricle. Axolotls can also receive organ transplants from other individuals without rejection or problems with lack of function in the new tissue. Obviously, these traits have made them of intense interest to a certain species which doesn’t regrow limbs, hearts, or spinal cords. Researchers hope that by studying the genetic and biochemical basis of these heightened healing abilities, they can create their own army of X-Men help amputees and victims of spinal cord injuries. But this research is still in its early stages. In the meantime, it would probably be in our best interests not to drive them to extinction.

Fun Facts:

Axolotls have tiny vestigial teeth, which in other salamanders only grow during metamorphosis.
Sometimes, an axolotl with a heavily damaged limb will both repair the old limb and regrow a new one, ending up with an extra leg (see above).
Forced metamorphosis can be only half-successful, producing adult forms with juvenile characteristics, such as a thickened neck.
Obligate neotenes like axolotls end up with a lot of extra “junk” DNA [biologists: via duplications of the pseudogenes created when their life history changed], which has actually resulted in their having larger cells than other salamanders.
It’s hard not to look crazy when you have no eyelids.
(Via: Aquadisiac News)

Says Who?

Chernoff (1996) International Journal of Developmental Biology 40: 823-831
Martin & Gordon (1995) Journal of Evolutionary Biology 8: 339-354
Neff et al. (1996) International Journal of Developmental Biology 40: 719-725
Rosenkilde & Ussing (1996) International Journal of Developmental Biology 40: 665-673

October 10, 2012

Theft: Better Than Sex (Bdelloid Rotifers)

Common Name: Bdelloid Rotifers

A.K.A.: Families of Order Bdelloida

Vital Stats:

Around 360 asexual species
All species likely descended from the same ancestor
Common ancestor lived 50-100 million years ago

Found: Fresh water bodies of any size, on every continent, including Antarctica

It Does What?!

Here’s a creature that truly exhibits questionable evolution- as in, the kind that tends to make you go extinct in a hurry. Bdelloid rotifers (the ‘B’ is silent) are microscopic animals found in all kinds of moist, freshwater habitats- puddles, ponds, mossy areas; you name it, they’re probably there. What’s so unusual about these guys is that they’re entirely asexual, and have been for a very, very long time. In fact, bdelloid rotifers are all female, a consequence of how they reproduce.

Don’t drink pond water.
(Via: TopNews.in)

Now, asexual reproduction isn’t so uncommon. If you look at a field of dandelions, chances are, they’re all clones derived from asexual reproduction in a single common ancestor- no second parent needed. Even such advanced creatures as komodo dragons do this periodically- a baby dragon is formed from an unfertilized egg inside the mother. What differentiates bdelloid rotifers from other asexual reproducers is that it’s all they’ve done for the last 50 million years or more. Outside of our friends the rotifers, a species must either have sex from time to time, or face extinction.

Why? Because sex solves two major problems in life (your individual results may vary..). First, it weeds out errors which tend to accumulate in DNA over time. Unlike asexuals, which pass on a copy of a copy of a copy (etc.) of their genes, sperm and egg cells contain DNA which has been mixed and matched via a process called meiosis. The gist of this is that an organism can procreate without necessarily passing on any genetic errors it may have to the next generation. Second, this same process of mixing and matching creates new combinations of DNA sequences, which in turn create the natural variation between individuals that evolution can select for or against.

NHM — Not the most visually interesting creatures, these rotifers…
(Via: Natural History Museum)

For example, a genetic combination which caused a polar bear to be born with a white nose would be selected for, since it would make a more effective camouflage for hunting. On the other hand, a combination which gave polar bears big black patches on their fur would be selected against, because they’d have a harder time hunting and would therefore starve more often. Asexuals, however, can neither quickly generate useful new combinations, nor purge their populations of harmful mutations.

So on the surface, it comes as a surprise to biologists that bdelloid rotifers have been able to survive for such an epic amount of time with no sex (in addition to the absence of males, genetic tests are able to show that meiosis hasn’t occurred). However, the rotifers have two impressive ways of dealing with this. First, when times get tough, they already have a pretty good defence mechanism worked out- they just dry up. The rotifer dehydrates itself and forms a dormant cyst in which it can remain in this state until conditions improve. This is called anhydrobiosis.

Space Travel — …but what do you expect from sexless pond scum?
(Via: SpaceTravel.com)

Second, and more importantly, they steal genes. This is the true secret to the successful asexual lifestyle. When a rotifer emerges from dormancy and needs to patch itself up, it’s actually able to incorporate random genetic material from its environment into its own genome. A nearby bacterium, some fungus, a passing bit of rotting leaf? All fair game, apparently. Researchers have found genes from each of these three groups in the rotifer genome. Incorporating these new bits of sequence seems to give rotifers the variation they need to develop new traits and stay off the evolutionary chopping block. In fact, given the success of the bdelloid rotifers – they’ve evolved into over 300 species since giving up sex – and the ease of asexual procreation – no need to find a partner – an argument could be made that when it comes to new genes, theft really is better than sex.

Says Who?

Gladyshev et al. (2008) Science 320(5880): 1210-1213
Harvard Magazine, Nov.-Dec. 2000 “An Evolutionary Scandal”
Welch & Meselson (2000) Science 288(5469): 1211-1215
Wilson & Sherman (2010) Science 327(5965): 574-576

September 5, 2012

Randomly Assembled and Surprisingly Dangerous: The Platypus

Common Name: The Duck-Billed Platypus

A.K.A.: Ornithorhynchus anatinus

Vital Stats:

Only species of Family Ornithorhynchidae
Males average 50cm (20”) long, females 43cm (17”)
Weigh between 0.7 and 2.4kg (1.5 – 5.3lbs.)
Body temperature of 32 degrees Celcius; five degrees lower than placental mammals
Live up to 17 years in captivity
Eat freshwater crustaceans, worms, and insect larvae

Found: Eastern Australia and Tasmania

It Does What?!

Besides looking like it was assembled from spare parts? We’ve all seen pictures of platypuses (yes, “platypuses”, not “platypi”) before, and everyone knows what total oddities they are: the duck-like bill, the beaver-esque tail, the fact that they lay eggs, despite being mammals; but behind these weird traits lie… even more weird traits! So let’s take a moment to appreciate the lesser-known eccentricities of the platypus, shall we?

First off, these cuddly looking freaks are actually dangerous. Male platypuses have a spur on each hind foot which is filled with a venom powerful enough to kill a large dog. While it isn’t enough to take out a human, it does cause severe, incapacitating pain whose after-effects can last for months. One of only a very few venomous mammals, the male’s venom production increases during the breeding season, suggesting its purpose may lie in competition with other males.

And speaking of breeding, reproduction in platypuses isn’t exactly ‘mammal standard’, either. Unlike all other mammals, which have two sex chromosomes (X and Y; XX for females, XY for males, with rare exceptions), the platypus has ten. Talk about evolutionary overkill. A male platypus has the pattern XYXYXYXYXY, while a female has ten Xs. Researchers have found that the actual genetic structure of these sex chromosomes is actually more similar to birds than mammals, although 80% of platypus genes are common to other mammals.

After this alphabet soup of chromosomes arranges itself, up to three fertilised eggs mature in utero for about four weeks; much longer than in most other egg-laying species (in birds, this may be only a day or two). Once laid, the eggs are only about the size of a thumbnail, and hatch in around ten days. While platypuses produce milk, they don’t actually have proper teats to suckle their babies- the fluid is released from pores in the skin. A small channel on the mother’s abdomen collects the milk, which is then lapped up by the young. Strangely, the babies are actually born with teeth, but lose them before adulthood. Such is the impracticality of platypus design…

babies — Adorably impractical.
(Via: noahbrier.com)

Finally, let’s explore platypus hunting methods. Platypuses are the only mammals with the sixth sense of electroreception. Those leathery duck bills of theirs are actually precision receptors that can detect the electric fields created in the water by the contractions of muscles in their prey. Considering the prey in question is largely worms and insect larvae, we’re talking big-time sensitivity here. The bill is also very receptive to changes in pressure, so a movement in still water can be picked up in this way as well. Researchers have suggested that by interpreting the difference in arrival time of the pressure and electrical signals, the hunter may even be able to determine the distance of the prey. This would be especially useful, given that platypuses close both their eyes and ears when hunting. In fact, they won’t even eat underwater; captured food is stored in cheek pouches and brought to land to be consumed.

So there you have it. The platypus: even weirder than you thought.

[Fun Fact:The female platypus has two ovaries, but only the left one works.]

adult — Intelligent Design’s Worst Nightmare
(Via: Animal Planet)

Says Who?

Brown (2008) Nature 453: 138-139
Grant & Fanning (2007) Platypus. CSIRO Publishing.
Graves (2008) Annual Review of Genetics 42: 565-586
Moyal (2002) Platypus: The Extraordinary Story of How a Curious Creature Baffled the World. Smithsonian Press.

June 27, 2012

How to Stay Cool the Lungfish Way

lungfish_square — Via: Science News for Kids

Common Name: The Lungfish

A.K.A.: Subclass Dipnoi

Vital Stats:

6 species; 4 in Africa, 1 in South America, 1 in Australia
Some species can reach up to 2m (6.6’) long and weigh 43kg (95lbs.)
Omnivorous, eating plants, insects, crustaceans, worms, fish, and frogs
Largest genome of all terrestrial vertebrates at ~133 billion base pairs

Found: Slow-moving freshwater bodies in South America, Africa, and Australia

It Does What?!

Well, they’re not much to look at, but in the “quietly carrying on while everything drops dead around you” department, the lungfishes are tops. These large, eel-looking creatures are what biologists refer to as “living fossils”, species which have existed in more or less their present form for a very, very long time. In the case of the lungfishes, around 400 million years. For the sake of comparison, this was around the same period that plants developed roots and leaves. That long ago. In fact, researchers believe that the lungfishes are the closest living relatives of the terrestrial vertebrates (that is, anything with a spinal column that lives on land).

OMG-Trivia-04-25-11 — These will probably outlast humanity.
Via: One More Generation

So what makes these things so interesting, besides being old? First off, they breathe air, as you might have guessed from their name. Australian lungfishes have a single lung, and, while they normally breathe through their gills, are able to supplement their oxygen intake with air during times of high exertion or when their water gets stale (Fun side note: During mating, Australian lungfishes make loud burping noises at the surface of the water which are thought to be part of the courtship ritual. I’ll refrain from making any Aussie jokes here… ). African and South American lungfishes, on the other hand, have two lungs and breathe nothing but air. Their gills are completely atrophied, such that they could actually drown if kept under for much longer than their usual 5-8 minutes between breaths.

Praet_u2 — “Hey! I’m trying to aestivate in here!”
Photo by: Tobias Musschoot

This ability to breathe without water results in the other fantastic ability of subclass Dipnoi. South American and African lungfish live in habitats which often dry up completely during the hottest part of the year. The fishes’ gross but brilliant answer to this is to burrow up to half a metre down into the soft mud and excrete a huge amount of mucous. As the surrounding mud dries up, the mucous forms a hard shell which keeps the curled up lungfish moist and cool. A small hole at the top of this snot-cocoon allows the fish to breathe. It’s metabolism slowed to only a small fraction of the normal rate, the creature will aestivate (like ‘hibernate’, but without the cold) like this for several months until the rains return. Laboratory experiments have shown that an African lungfish can remain alive under these conditions for as long as six years.

Shedd-AquariumAustralian_Lungfish — “Granddad”: probably older than ***your*** Granddad
Via: Shedd Aquarium

Aside from their amazing survival abilities, these fish have unusual lives, as fish go. They are extraordinarily long-lived. The Shedd Aquarium in Chicago holds an Australian lungfish known as “Granddad” which arrived there as an adult in 1933, making him at least 80 years old. Females of this species don’t even mate until they’re at least 22 years old (or so they tell their parents). What’s more, some species actually care for their young. The mother and father build an underwater nest for their offspring, which can only breathe via their semi-atrophied gills for the first seven weeks, and the father uses his body to release additional oxygen into the surrounding water, helping them to breathe. So, dual childcare: not such a new idea after all.

[Extra Credit – Here’s a short video of a lungfish being stalked by a pelican. Spoiler: It ends badly for the lungfish.]

Says Who?

Brinkmann et al. (2004) Journal of Molecular Evolution 59: 834-848
Fishman et al. (1992) Proceedings of the American Philosophical Society 136(1): 61-72
Glass (2008) Respiratory Physiology & Neurobiology 160: 18-20
Joss (2006) General and Comparative Endocrinology 148: 285-289
Lee et al. (2006) General and Comparative Endocrinology 148: 306-314
www.fishbase.org

April 25, 2012

The Plight of the Spheroid Seaweed (Aegagropila linnaei)

Marimo_lake_akann — Everyone’s Favourite Freshwater Pet
(via: http://commons.wikimedia.org/wiki)

Common Name: Lake Balls, Marimo

A.K.A.: Aegagropila linnaei

Found: Japan, Iceland, Scotland, Estonia, Germany

It Does What?!

Sure, you’ve had dogs and cats as pets, maybe even fish or lizards… but what about a big ball of algae? Probably not, but if you live in Japan, this idea won’t seem so odd.

Lake balls, or marimo, as the Japanese refer to them, are a rare and unique growth form of the filamentous green algae species Aegagropila linnaei. They occur in only a few isolated habitats worldwide because, unlike most algae, the species lacks a desiccation (dryness) resistant life stage which would allow it to be carried to distant bodies of water. The balls are formed from a densely-packed clump of algal strands which grow outward in all directions, and can reach up to 25cm (10 inches) in diameter. New balls can form from the free-floating form of the same species, or from the breakup and re-growth of an old ball. Found in shallow lakes with sandy bottoms, gentle wave action rolls the clump around, forming a near-perfect sphere and allowing all sides of the ball to receive light for photosynthesis. Seen rolling lazily around the lake bottom, and even rising and falling on columns of warm water, the marimo can almost seem sentient.

It is this bizarre movement and their strangely beautiful appearance which have made marimo so popular in Japan, where they are protected as a “natural monument” and even appear on postage stamps. Unfortunately, it has also been their downfall. Because the algae reside in fresh water and are adapted to low light conditions, they are easily cared for, leading many people to collect them and keep them in their homes. The Japanese believed that a healthy, well looked-after marimo would make the owner’s wishes come true. Lake balls eventually became so rare, due to both human collecting and pollution, that in the early 1950s, a campaign was launched asking Japanese citizens to return their beloved marimo to the lakes from which they had been taken. Impressively, people did so, and in large numbers. In honour of their selflessness, the first annual marimo festival was held, and has continued ever since. Today, the lake ball has become an important environmental symbol in Japan, and children even have their own stuffed marimo toy character, Marimokkori, to play with.

marimokkori1 — Japanese kids have the best toys, no?

Says Who?

Boedeker et al. (2010) BioScience 60(3): 187-198
Soejima et al. (2009) Aquatic Ecology 43: 359-370
www.marimoballs.com