The Eyes Have It

Biology concepts – asymmetry, lateral polymorphism, flatfish, evolution, copepod, ecology, niche

Ray Harryhausen was the most famous of the stop

motion artists in the movies. This version of the

Cyclops was his creation for the 1958 movie, The 7^th

Voyage of Sinbad. I can’t see how the Cyclops could

catch anything with just the one eye – he had no

depth perception.

We have been talking about bilateral symmetry in the past few weeks, and this would include having two eyes, one on each half of your face. Two eyes must be a pretty important evolutionary adaptation; can you think of an animal that has just one eye – other than a cyclops, that is? (the answer is somewhere in post) Some protists have a single eyespot for sensing light – but they aren’t animals.

Predators need to catch their food, so they need depth perception. For this you need two overlapping images. You don’t do the math consciously, but your brain uses the differences in each image to tell you how far away the target prey is. To get two images simultaneously, you need both eyes to be on the front of your face.

Prey animals, usually herbivores, have to worry about being chased down by a predator. Prey animals are usually quick, but they need clues to get a good start before the predator gets too close. Their eyes are designed to pick up motion; it doesn’t matter how far away it is. If something moves in their line of sight, they assume it’s a predator and they bolt. By having their eyes on the sides of their head, they have a maximal range of vision which gives them the best chance to see that lioness coming.

Just to show you how important evolution thinks it is to have at least two eyes, let’s discuss a group of animals that have found a way to make two drastic changes work for them. Flatfish have evolved to lie on their side, but they’re predators so they can’t afford to have one eye constantly seeing nothing but the sandy ocean bottom. Consequently, they have moved one eye to the other side of their head!

This is a winter flounder (Pseudopleuronectes

americanus). Notice how it blends in to the floor. It

does more by flapping and tossing sand on its back.

The mouth points up when the fish is vertical, so the

left most eye is the one that migrated. Makes sense,

you wouldn’t want to move an eye under your chin –

that would be silly.

Flatfish are all from the order Pleuronectiformes (pleuro = toward the side), sometimes called the Heterosomata (hetero = differently, and soma = bodied). There are some 715 species of flatfish in 11 families, and they include the turbots, sole, flounder, plaice, and halibut. They are all predators that lie in wait on the ocean-, lake-, sea-, or riverbed. But they don’t start out that way.

All the Pleuronectifromes start out as fry that swim upright. Their top is at the top, and the bottom is toward the bottom. They live nearer the top of the water than the bottom, have pigment coloration on both sides of their body, and feed on phyto- and zooplankton. But the surface isn’t the safest place to live; bigger fish are always around to eat the small fry.

So, as they start to develop into adults, many changes take place. They swim down to the floor of whatever body of water they call home. One eye starts to move! It travels over the top of their head and onto the other side, like the Mr. Potato Head of some deranged child.

As you can imagine, moving an eye isn’t an easy thing to do. Their brain has to move, as do the cranial and facial bones. Their mouth has to make room for the eye coming its way. All in all, it’s a tough piece of work.

The top image is the visible side of a rock sole, the

bottom image is the lower side of the same fish. As the

fish matures and lies on its side, the coloring changes.

Pigments are energetically expensive to make, so why

waste them. The middle image shows the line where it

goes from pigmented to unpigmented. What control!

Moving an eye from one side of the head to the other seems illogical, why not just develop with both eyes on one side, or make do with one eye? Creationists have used the flatfishes as an argument against evolution. We have fish with eyes on each side of their head, and fish with both eyes on one side of their head. They argued that if natural selection was responsible for the change in flatfish, there should be fossils or fish that are intermediates.

Well, there are evolutionary intermediates – even some living examples. A paper in 2008 introduced us to two extinct species of flatfish. In each (Amphisitium and Heteronectes), one eye had migrated, making the fish asymmetric, but it had not crossed the crown of the skull and made it to the other side. These are definitely intermediate species, but we can go one better.

The Psettodes genus of flatfish (the turbots - yummy by the way) have one eye that is located right at the crown of their skull. Perhaps technically you could say that is has migrated to the other side, but just barely. And this brings us to another question, which eye moves?

Some flatfish are right-eyed (dextral) that swim left side down. Others are left-eyed (sinistral) and swim with their right side down. Some species are strict and some are more likely to have reversants (individuals that lay on their other side). A 2005 paper stated that only about 7 of the 700 species of flatfish show lateral polymorphism (lateral = side, poly = more than one, and morph = shape), ie. some right-eyed and some left-eyed individuals.

The bottom image has on the left side depicts the two

extinct species of flatfish where the migrating eye hadn’t

quite made it to its destination. The middle cartoon is

the extant Psettodidae, like the Indian Halibut on the top.

The eye has just made it to the crest of the cranium. The

right cartoon on bottom shows a species where the eye

has completely migrated. Looks like great support

for evolution.

For example, a 2009 paper describes reversants for two right-eyed flounder species which are the first left-eyed individuals ever seen in these two species (Microstomus achne and Cleisthenes pinetorum). It goes the other way too – a 2013 study describes the first right-eyed individual ever seen in a megrim (sometimes called a whiff, Lepidorhombus whiffiagonis). But in the left-eyed California halibut (Paralicythys californicus), up to 40% of the individuals are right-eyed. Perhaps right-eyed species are stricter than left-eyed species.

The exception to that rule is the starry flounder (Platichthys stellatus). It’s a member of a right-eyed family of flounders, but in some cases half of the individuals are left-eyed. In this case, there seems to be more to the story - the lateral polymorphism occurs only in populations of specific geographic areas.

A paper from 2007 looked into the mystery that 7 species that show lateral polymorphism, but only two (starry flounder and P. fleusus) show a geographical distribution in their polymorphs. Off the coasts of Japan and Russian, 100% of the starry flounders are left-eyed, but near Alaska they are only 75% sinistral and from Washington state to central California the populations are about 50/50.

The researchers looked into several questions. Was there more to being left-eyed or right eyed than just which side the eye went to? Does the side make a difference that could account for the geographic distribution? They found out – yes, and yes.

They saw that the right and left-eyed individuals have more asymmetries between them than just the side of the body that the eye migrates to. They have differences in mouth size and angle, as well as tail size of all things. Right-eyed individuals had significantly longer and wider tails than did left-eyed individuals!

The research also shows that in areas where the two groups compete the most, the differences between the dextral and sinistral individuals are the greatest. This suggested to them that the differences allow them to compete for different prey – to fill different ecological niches. The hypothesis is that the polymorphic asymmetries give them different advantages which they then exploit and this is why there is a stable geographic distribution in populations.

A very complicated but informative chart from the paper

on pitx2 reactivation during metamorphosis. Note which

side is right and left and then follow what happens for

the two species, one right-eyed and one left-eyed. The

right side shows what can happen if you block pitx2. In

the reversed individual, the left habenula (dd. l) enlarges

instead of the right.

Well, that’s cool, but how is it controlled – what makes a fish right- or left-eyed? A 2009 paper started to investigate this. During development of the embryo, certain internal asymmetries develop (will talk more about this in a few weeks). In fish and other vertebrates, this is controlled by expression of certain genes in the habenula of the brain. One of the gene products (proteins) in the habenula is called pitx2.

There are actually two habenulae, one in each hemisphere of the brain, as part of the thalamus. The researchers looked at the brains of right-eyed and left-eyed flounder species and detected some things that were the same and some things that were different.

After the pitx2 did its job in the embryo, it was turned off. But right before metamorphosis – when the eye migrates and the fish lies down on one side, pitx2 was turned back on – only in the left habenula, regardless of which way the fish’s eye was going to migrate and which way it was going to lie down.

Not only that, but the right habenula started to grow bigger than the left habenula in both dextral and sinistral species. The only thing that was different was the rotation of the brain, with the left habenula moving forward in the right-eyed species and the opposite occurring in the left-eyed species. The same changes occurred in fish no matter which eye migrated!

This copepod is about to swim into the top border of

this image. The reason for this is that he only has one eye

(the light spot between the antennae), so he has no depth

perception! By the way, he’s only 2 mm long, so he

probably will just bounce off the edge.

However, in those fish that they experimentally blocked the second round of pitx2 activity, you could get a normally turned fish or a reversant. The only difference - when you got a reversant, it was the left habenula that enlarged, not the right. I think we still have some more to learn.

By the way – at the beginning of today’s post I asked if there were any real animals with one eye. I made it sound like there aren’t but in fact there are exceptions. In some small crustaceans (arthropods) called copepods, the majority of species have a single eye right in the middle of their head! What’s more, a 1994 study showed that the holdfast of a particular copepod parasite is asymmetric (like we saw last week) and this particular copepod is a parasite of only flatfishes! How symmetric this tale of asymmetry turned out to be!

Next week - can a single tooth render an animal asymmetric? Well, that depends on the tooth, doesn't it.

MacDonald P (2013). A rare occurrence of reversal in the common megrim Lepidorhombus whiffiagonis (Pleuronectiformes: Scophthalmidae) in the northern North Sea. Journal of fish biology, 83 (3), 691-4 PMID: 23991885

Suzuki, T., Washio, Y., Aritaki, M., Fujinami, Y., Shimizu, D., Uji, S., & Hashimoto, H. (2009). Metamorphic pitx2 expression in the left habenula correlated with lateralization of eye-sidedness in flounder Development, Growth & Differentiation, 51 (9), 797-808 DOI: 10.1111/j.1440-169X.2009.01139.x

Goto T (2009). Reversals in two dextral flounder species, Microstomus achne and Cleisthenes pinetorum (Pleuronectida; Teleostei), from Japan. Journal of fish biology, 74 (3), 669-73 PMID: 20735586

BERGSTROM, C. (2007). Morphological evidence of correlational selection and ecological segregation between dextral and sinistral forms in a polymorphic flatfish, Platichthys stellatus Journal of Evolutionary Biology, 20 (3), 1104-1114 DOI: 10.1111/j.1420-9101.2006.01290.x

Friedman, M. (2008). The evolutionary origin of flatfish asymmetry Nature, 454 (7201), 209-212 DOI: 10.1038/nature07108

For more information or classroom activities, see:

Flatfish –

https://www.youtube.com/watch?v=L66qpRL6mfw

http://www.amnh.org/explore/news-blogs/news-posts/dawn-roje-tracing-the-metamorphosis-of-flatfishes

http://bogleech.com/flatfish.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCUQFjAB&url=http%3A%2F%2Fnefsc.noaa.gov%2Fpublications%2Fcrd%2Fcrd1415%2Fcrd1415.pdf&ei=oF32VPv4OYqaNr2agqgJ&usg=AFQjCNGvlBB3CL1rCNq29nhB3HXPSjpMGA&sig2=4gJD9UkkojsswQjJTiSBng&bvm=bv.87269000,d.eXY

http://scienceblogs.com/grrlscientist/2008/07/09/the-mysterious-origin-of-the-w-1/

http://www.pbs.org/wgbh/nova/next/evolution/flatfish-evolution/

https://www.youtube.com/watch?v=6LZftSciYNY

http://www.dtmag.com/Stories/Marine%20Life/11-03-whats_that.htm

http://mostlyopenocean.blogspot.com/2012/07/flatfish-eyes-twice-solved-mystery.html

http://biochemicalsoul.com/2009/03/flatfish-eye-development-video-update/

Copepods –

http://invertebrates.si.edu/copepod/

http://www.fcps.edu/islandcreekes/ecology/copepod.htm

http://fmel.ifas.ufl.edu/kits/

http://2010.polarhusky.com/logistics/greenland/fauna/crustacea/copepod/

http://marinediscovery.arizona.edu/lessonsF00/bryozoans/2.html

http://www.sacsplash.org/critter/copepods

http://www.montereybayaquarium.org/animal-guide/invertebrates/copepod

http://www.discovery-zone.com/sapphirina-copepod-beautiful-animal-youve-never-seen-video/

https://vimeo.com/114822659

http://news.discovery.com/animals/endangered-species/best-animal-jumper-crustaceans.htm

Habenula -

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3447364/

http://www.pnas.org/content/111/32/11858.abstract

http://www.jneurosci.org/content/34/34/11366.short

http://www.nature.com/neuro/journal/v17/n9/full/nn.3779.html

http://www.iflscience.com/brain/scientists-find-area-brain-motivates-us-exercise

http://www.neuroscientificallychallenged.com/blog/what-is-the-habenula

http://www.sciencedaily.com/releases/2014/07/140728153937.htm

http://journal.frontiersin.org/researchtopic/1559

http://www.ncbi.nlm.nih.gov/pubmed/24478666

http://www.jneurosci.org/content/28/46/11825.full

http://www.cnsspectrums.com/aspx/articledetail.aspx?articleid=1588

Looking Sideways In The Mirror

Biology Concepts – platyhelminthes, asymmetry, bilateral symmetry, evolution, cephalization, natural selection, fish, lepidophagy

What is the largest living structure on Earth? No, it’s not the 2200 acre Armillaria ostoyae fungus in Oregon that we talked about previously. That is the largest single organism, but there is something bigger.

The Great Barrier Reef houses more species of

coral than any other place on earth, more than 600

species call the reef home. You see how many shapes

they can take. Does this mean they are

asymmetric animals?

The Great Barrier Reef off the northeast coast of Australia is alive. Reefs are made of the exoskeletons of coral polyps, with the new corals growing next to and on top of the older ones. With all the nooks and crannies available, coral reefs are some of the most diverse ecosystems on Earth, with thousands of species per square mile.

This can add up quickly, because the Great Barrier Reef is more than 132,973 sq. miles (344,400 sq. km) in area. And if you still don’t believe it is a living structure, get this; it’s moving south! Climate change is warming the waters off the coast, and corals and tropical fish are moving south with the warmer temperature. Meanwhile, the northern edge recedes as the waters get too hot for corals.

Corals take all sorts of shapes (see picture above), and despite what we talked about last week, they don’t seem to be either bilaterally or radial symmetric. Sure, brain corals look radial, but most corals don’t have a repetitive shape. Are these asymmetric animals?

Nope - remember that the coral you see is the exoskeleton of the polyp, not the animal itself. Just because the apartment building isn’t symmetric, it doesn’t mean the animal is as well. Coral polyps are definitely radially symmetric, so our discussion of last week still holds.

Corals and other radial animals are exceptions, since 99% of animals are actually bilaterally symmetric. But there are exceptions with the bilateral animals as well. Some species that have been bilateral for millions of years then evolved a tweak to the system. Some part them became asymmetric in order to give them an advantage. Their stories are exceptional and we should explore some of them.

Coral polyps are cnidarian animals. They live inside

the calcium shells they produce, and it is the shells

that seem asymmetric in many cases. But the polyps

show radial symmetry. Each stalk and white “flower”

is an individual polyp.

But we begin with a challenge –as we discuss the different animals that break symmetry in the next few posts, see if you can find something else that is common to many of them.

Let’s start with the first animals that became bilaterally symmetric– the platyhelminthes, or flatworms. Most flatworms are small, just barely visible with the human eye, and most swim in the water. There are free-living versions and parasitic species and it is in the parasites that we find our first animal that has decided that completely bilateral isn’t necessary.

Polyopsithocotylea monogenea is a group of flatworms that live on and feed on fish gills. About 0.05-1 mm long, these platyhelminthes attach themselves to one of the gill ridges and take up residence there for life. The attachment they use is called a haptor, and they come in different shapes and sizes.

The oncomiracidium stage of the worm is directly after the egg stage and before it becomes an adult. This stage is completely bilaterally symmetric. But when the adult stage is reached and it’s time to settle down and starting feeding on some fish’s gills, they become asymmetric via their haptor attachment.

Opisthaptors, or just haptors, are the attachment

organs for many parasites, including parasitic

flatworms. They can use suckers or clamps and hooks

in order to anchor the worm in its preferred habitat.

You can see that these haptors maintain animal

symmetry, but not all do.

Different host species fish have different gill anatomy, so the attachment point and position will be different. The haptor(s) have to be located where attachment is possible. This means that they may be on one side of the body or the other, or two on one side and one on the other, etc.

The initial haptor is usually located on the posterior end, on one side only. So much for bilateral symmetry. In some species this haptor has suckers, in others it has hard clamps, and yet other species have both.

As the adult grows, more haptors may develop, just where the animal touches the gill. Some may have 50 or more haptors arranged around their posterior, becoming more and more asymmetric. But there is a plan, they only grow where attachment is possible; some signal is generated by contact and this stimulates growth of more attachments.

Here we have a family of parasitic worms that aren’t symmetric living within a phylum of worms that were the first to be bilaterally symmetric - exceptional. But, take one step up the chain and you see the fish they live on. It just so happens that at least one group of fish parasitized by P. monogean worms are asymmetric themselves.

These are the profiles of some monogean flatworms. The

haptors of these parasites grown in odd places and

destroy the bilateral symmetry of the animal. But it is

necessary for the worm to attach to the gills of their

prey fish.

Cichlid fish are one of the most diverse family of animals known, with more than 1700 known species. They are found in the Old World and the New. They exhibit some amazing adaptations, especially when many are found in one place, Lake Tanganyika on the border of Tanzania and the Democratic Republic of the Congo.

The cichlids are successful because different species have developed different feeding niches, and this is where we meet our asymmetric cichlids – they eat the scales off other fish! One genus, Perissodus, has at least six species that eat scales, all endemic to Lake Tangayiki (although there are also other scale eaters in other locations).

Scale ripping and eating is called lepidophagy (lepido = scale, and phagy = eat). Scales are an unexpectedly good source of nutrition. They chock full of protein and calcium phosphate, and their attachments are both cartilaginous, fatty, and come with some carbohydrate. Remember that the next time you order fish in a fancy restaurant. Tell the chef not to scale it – you’ll be quite the topic of conversation in the kitchen.

Fish scales have many uses. Some, especially from

herrings, are used to make the pearlescent cosmetics

that are sold today. Gals, your putting fish scales on your

eyes and lips. Fish scales can also be turned into artificial

bone, or they can be food for lepidophageous fish.

Mind you, this isn’t eating the scales of dead fish, or eating the scales that drop off live fish. Lepidophagy means eating the scales that are still attached to live fish. It’s a fish smorgasbord. This is both good and bad. Scales on live fish grow back fast, so there is always a ready supply of food.

But, you can imagine that the fish being unfrocked don’t appreciate it very much and fight back or swim away quickly. That doesn’t even take into account how hard it is to bite the scales off a swimming fish. Therefore, lepidophages must evolve anatomies and behaviors that give them a chance to succeed. Or perhaps it would be better to say, they acquired characteristics that made being a lepidophage an advantage.

Here are two P. microlepis scale eating fish. One is right

mouthed and the other is left mouthed. You can see how

the way their mouth develops breaks their bilateral

symmetry. The right-mouthed version (on the left) will

only eat scales from the left side of fish. How is it that both

versions can be maintained in a population?

The species P. microlepis has developed one particularly amazing way to help it eat the scales off of neighbor fish. It’s mouth and jaws have evolved so that they bend sideways. There are right-mouthed P. microlepis and left-mouthed individuals. The difference is obvious, right-mouthed individuals will feed only from the left side of their prey and vice versa. They have an asymmetry, or lateralization, of both anatomy and behavior

A 2012 video study showed that right-mouthed individuals almost always attack prey from the left, and their strikes are more powerful and successful when coming from the preferred side. One could ask, why are their both types? How did right- and left-mouthed individuals come to evolve and why are there still both types?

A different 2012 study shows that juveniles prefer one side or the other, even before their mouth bend has become pronounced, so it is a deeply penetrating characteristic, both heritable and perhaps partially acquired. There’s evolution and genetics at work here.

The prevailing model is that at any one time, right or left-mouthed individuals will predominate in a population. Let’s say that right now, right-mouthed feeders are the majority. The prey fish will learn to pay more attention to their left side, as this side is more vulnerable.

This makes it harder for right-mouthed individuals to feed, but easier for left-mouthed fish, because the prey fish ignore their right side relative to the left. In time, the right-mouthed individuals breed less well and the numbers in the population will shift. The left-mouthed feeders will become the majority. This is an example of negative frequency-dependent selection, where as a trait becomes more common it becomes less advantageous, and there is a balancing selection.

The flu virus comes with one of many hemagglutin proteins

and one of many neuraminidase proteins. If one genetic

version is too successful, most people will develop

immunity to it and it becomes less fit in the population of

hosts. Its success is its downfall and a more rare version

will rise up. This is negative frequency-dependent selection.

The cycle will begin again after left-mouthed individuals come to dominant in the population. Back and forth the population will go. If the population stayed 50/50, nobody would gain an advantage, and overall, they would all suffer. The system only works if a small number develop opposite to the majority. The gene regulatory complex that controls if an individual will be right- or left-mouthed must be very complex if it can take into account that a few need to be lateralized the other way.

However, a 2012 study throws this into question. They found equal distributions of right-and left mouthed individuals in five populations they studied. Also, left-mouthed and right-mouthed individuals mated with each other just as often as they mate with same-sided individuals (called disassortative mating). Perhaps the mouth bend is not a true dimorphism (di = two, and morph = shape).

Or, as a 2008 study suggests, negative frequency-dependent selection works best when there is disassortative mating. This may be necessary since a 2007 study showed that lefty:lefty matings give 2:1 lefty offspring, right:lefty mates give equal righty and lefty offspring, but righty:righty pairs ONLY give righty kids. Figure out the genetics of that. The authors proposed two possibilities – mendelian genetics with lefty being dominant and dominant homozygous being lethal, or cross-incompatibility that is predominant in lefty:lefty homozygotes, (meaning lefty homozygotes can’t mate successfully mate with the other types).

Today we have seen a swimming flatworm that feeds on some fish, and some fish that feed on the scales of other fish. And both of them achieve this only because they have adapted their bilateral symmetry to become just a bit asymmetric.

Next week, there are other animals that break symmetry to survive. Flatfish lay on their sides at the bottom of lakes and oceans, yet they still use binocular vision. How can that be?

Takeuchi, Y., Hori, M., & Oda, Y. (2012). Lateralized Kinematics of Predation Behavior in a Lake Tanganyika Scale-Eating Cichlid Fish PLoS ONE, 7 (1) DOI: 10.1371/journal.pone.0029272

Lee, H., Kusche, H., & Meyer, A. (2012). Handed Foraging Behavior in Scale-Eating Cichlid Fish: Its Potential Role in Shaping Morphological Asymmetry PLoS ONE, 7 (9) DOI: 10.1371/journal.pone.0044670

Kusche, H., Lee, H., & Meyer, A. (2012). Mouth asymmetry in the textbook example of scale-eating cichlid fish is not a discrete dimorphism after all Proceedings of the Royal Society B: Biological Sciences, 279 (1748), 4715-4723 DOI: 10.1098/rspb.2012.2082

Takahashi, T., & Hori, M. (2008). Evidence of disassortative mating in a Tanganyikan cichlid fish and its role in the maintenance of intrapopulation dimorphism Biology Letters, 4 (5), 497-499 DOI: 10.1098/rsbl.2008.0244

Hori, M., Ochi, H., & Kohda, M. (2007). Inheritance Pattern of Lateral Dimorphism in Two Cichlids (a Scale Eater, Perissodus microlepis, and an Herbivore, Neolamprologus moorii) in Lake Tanganyika Zoological Science, 24 (5), 486-492 DOI: 10.2108/zsj.24.486

For more information or classroom activities, see:

Great Barrier Reef –

http://www.greatbarrierreef.org/

http://whc.unesco.org/en/list/154

http://video.nationalgeographic.com/video/oceans-narrated-by-sylvia-earle/oceans-barrier-reef

http://www.gbrmpa.gov.au/about-the-reef/facts-about-the-great-barrier-reef

http://www.pbs.org/wgbh/nova/education/activities/2215_reef.html

http://geography.mrdonn.org/greatbarrierreef.html

http://www.reefteach.com.au/about-the-reef/links/eduresources/

http://education.nationalgeographic.com/archive/xpeditions/lessons/14/g912/geoactreef.html?ar_a=1

http://www.reefcheckaustralia.org/for-teachers.html

http://www.mesa.edu.au/resources/ourgbr06.asp

http://science.uniserve.edu.au/school/curric/stage4_5/coralreefs.htm

http://video.nationalgeographic.com/video/oceans-narrated-by-sylvia-earle/oceans-barrier-reef

http://www.discovery.com/tv-shows/other-shows/videos/discovery-atlas-australia-revealed-great-barrier-reef/

http://www.sciencekids.co.nz/videos/nature/greatbarrierreef.html

http://www.smithsonianchannel.com/shows/secrets-of-the-great-barrier-reef/0/134605

https://www.youtube.com/watch?v=2T2i29M92RQ

http://www.animalplanet.com/video-topics/wild-animals/great-barrier-reef-playlist/

Coral polyps –

http://www.calacademy.org/educators/lesson-plans/build-a-coral-polyp

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CDkQFjAG&url=http%3A%2F%2Fcoast.noaa.gov%2Fpsc%2Fseamedia%2FLessons%2FG3U3L2%2520Coral%2520Structure%2520and%2520Function.pdf%3Fredirect%3D301ocm&ei=WeXsVI3NFI2PyASq44LgCw&usg=AFQjCNEhqIwraaKbhPdUaAw_EHjlwmOQZA&sig2=uWH06Am2pFOOWUv_hRZLQA&bvm=bv.86475890,d.aWw

http://www.teachoceanscience.net/teaching_resources/education_modules/coral_reefs_and_climate_change/access_classroom_resources/

http://www.educationworld.com/a_lesson/00-2/lp2134.shtml

http://www.cpalms.org/Public/PreviewResource/Preview/25461

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=0CCMQFjABOAo&url=http%3A%2F%2Fwww.si.edu%2FContent%2FSE%2FEducator%2520Guides%2FCRA-Educators-Guide.pdf&ei=weXsVI36CsL2yQTgtoDoBg&usg=AFQjCNHY3JSYr7ODQc4DJoihRH9e2j9E7w&sig2=kpBDF8NsWAYbDdVyLheTvQ&bvm=bv.86475890,d.aWw

https://www.youtube.com/watch?v=_zpiEY77Ujk

https://www.youtube.com/watch?v=11KV00yDnbY

http://www.discovery.com/tv-shows/other-shows/videos/short-attention-what-is-a-coral/

http://www.wri.org/resources/videos/coral-reefs-polyps-peril

http://oceanexplorer.noaa.gov/explorations/03mountains/logs/jul17/media/coralpolyp.html

http://animal-world.com/Aquarium-Coral-Reefs/Stony-Corals-LPS

http://www.coralscience.org/main/articles/biochemistry-2/how-reefs-grow

http://animals.howstuffworks.com/marine-life/coral-reef1.htm

Cichlids –

http://www.cichlid-forum.com/articles/lake_tanganyika_diverse.php http://www.news.leiden.edu/news/super-fast-evolution.html

http://www.amazon.com/The-Cichlid-Fishes-Experiment-Evolution/dp/0738205281

http://video.nationalgeographic.com/video/cichlid_mouthfighting

http://news.stanford.edu/news/2014/september/fish-genome-fernald-092214.html

http://malawicichlids.com/mw01100.htm

http://www.futurity.org/cichlids-vertebrate-evolution-759392/

http://animalguide.georgiaaquarium.org/home/galleries/river-scout/gallery-animals/cichlid

http://www.aquaticcommunity.com/cichlid/tang.php

http://www.biodiversityscience.com/tag/adaptation-2/

Carp Diem - Polyploid Fish Seize The Day

Biology concepts – polyploidy, invasive species

There are 60,000 different species of weevils, a type of

beetle. And almost all of them are polyploid! Polyploidy

benefits speciation, so maybe them being polyploid is

why there are 60,000 species. On the left is

Trachelophorus giraffa, named for obvious reasons, and

on the right is Rhigus nigrosparsus. You’ll have to go to

Brazil to see one in person.

We think that polyploid animals are the rare exceptions, and they certainly are in the case of mammals, but there are other groups of animals don’t think twice about being polyploid. Arthropods are notorious for developing polyploid lines, while amphibians and reptiles are probably the most well studied polyploids. But there are more - that cedar planked salmon you enjoyed the other night – it was probably triploid as well.

We pointed out last week that polyploidy in plants has done a lot to promote speciation events, and this seems to be the case in fish as well. While some families have a few polyploid members, like the loaches, or the carps and minnows, other families are completely polyploid, like the Salmonidae (salmon). Wat is more, the families with the greatest number of polyploid members also have the highest number of species overall. Of the 28,000 known species and >60 orders of fish, 63% fall into the 9 orders that include polyploidy – coincidence? I don’t think so.

Remember that polyploidy in plants is well behaved, not much genome restructuring goes on even though there can be subfunctionalization and neofunctionalization leading to speciation at the molecular level. In contrast, fish polyploidy seems to induce a tolerance of change, and gene ordering and genome restructuring seem to run rampant. This seems to be at least one reason for high rates of new species development in fish that are polyploid.

The effects of polyploidy on fish are similar to those we have talked about previously. Polyploid fish tend to be larger, ie. the gigas effect, and they tend to live longer and grow faster, ie. heterosis. Inductions of triploidy or formation of auto- or allopolyploid species tend to have fewer diseases. For some reason, sexual maturation in fish is linked to higher infection rates – most likely due to stress. Finding a mate and having kids is stressful, ask any adult. Stress is directly related to infection rates, as one of the effects of the stress hormone cortisol is to turn down the immune system.

The sunshine bass on top is a diploid female which

is filled with eggs (gravid). In contrast, the female

on the bottom is triploid. She is bigger, even

compared to a gravid fish. The gigas effect in

polyploids is real, and effects sport fishing. Everyone

wants to catch a bigger fish.

Whether or not ploidy level itself has an effect on immune fitness is up for argument. A 2012 opinion paper from three prominent researchers states that increased gene numbers could lead to expression of more immune proteins, and antibodies to more different parasites, so it could increase resistance. They also offer that the mere increase in genes could end up producing more immune cells in total, therefore conferring more resistance.

In plants, a recent study indicates that a disease resistance cluster of genes in soybeans indicates that production of new disease resistance genes could develop by polyploid development. In an autopolyploid soybean, the number of disease resistance genes doubled, but they didn’t produce twice as much protein. It seems that they have begun to evolve independently. This may in turn produce newly functional resistance genes, or on the other hand, may eliminate one of the clusters. It appears that specific immune function and polyploidy may be interpreted only on a case by case basis.

But there negative effects that are similar to plants as well.  Triploid species are often less reproductively active, due either to difficulties in gamete production or to aberrant sex steroid levels as a result of dosage imbalance.

In some cases though, sterility has been used to the advantage of humans - triploid salmon are less likely to return to spawning grounds, which means they stay in the ocean longer, growing fat and happy. For wild salmon fisheries, this means a greater number of bigger fish. For salmon hatcheries and commercial growers, it means less stress on the animals and a greater harvest. Triploidy can be induced in the salmon (and other species) by cold shocking the eggs near the time of fertilization or using chemicals to prevent chromatid separation during meiosis.

Triploid oysters on the west coast are raised so that they can be 

harvested year round. They are bigger and taste better 

than spawning diploids. They are also more disease 

resistant, and this might affect pearl formation, since most 

natural pearls are induced by parasites that bore through the shell.

For a reason completely different than organism size or stress, oyster farmers have also induced triploidy in their product organisms. It seems that spawning reduces the sweetness and size of the oysters. They taste “spawny.” Since triploid oysters do not spawn, they retain their size and sweetness throughout the summer, when diploid oysters would be less tasty and are not harvested.

Pacific oyster species use up to 80% of their body weight for production of sperm and eggs – not good for food harvesting. This can last for most of the late spring and summer, so the triploids allow for harvesting when people are accustomed to avoiding oysters – typically, the rule is don’t eat oysters in any month without an “r.”

But if we harvest fewer diploids, and introduce more triploids – could we end up with a glut of oysters? The diploids that would have been caught are free to reproduce and we end up eating the triploids that wouldn’t have been reproducing anyway. What ecological niches might be disturbed by too many oysters? You can discuss amongst yourselves whether this is a good idea in the long run – I render no opinion one way or the other.

You can argue both sides of the polyploid introduction argument; human efforts to enhance (alter) the zoological face of the planet have met with some disastrous failures, but remember that majority of foreign introductions have been ecologically moot. This point is often overlooked, but we have talked about it before.

Polyploidy in wild salmon is extremely common, so would there really be that great a change? The use of triploid induction is more common in commercial fisheries and in the shellfish industry because they believe it provides a hedge against escapement and breeding with wild populations. Triploid fish and shellfish are sterile, so even if they did escape into the wild, they would be unlikely to breed with the wild type populations.

But Mother Nature always finds a way, doesn’t she? There have several cases of reversion to diploidy in triploid oysters. These shellfish are then free to breed with wild species. And what is more, induction of triploidy is not 100% efficient in fish, so some organisms will remain diploid. The incomplete induction of triploidy has been illustrated brilliantly by the invasion of the asian carp.

What we call the asian carp is actually four different

species. But they all get big. O.K. usually not this big!

They are moving up the Mississippi River and

threaten to enter the Great Lakes. If they do, they could

destroy a multibillion dollar a year fishing industry.

What we refer to as asian carp is actually a mix of four species, the bighead carp, the black carp, the grass carp, and the silver carp. The grass carp was introduced into Geogria from China and the USSR in the 1960’s as a way to control overgrowth of grass and weeds in local ponds – that's what they eat. The interested parties did consider escapement and breeding, so they instituted a program of triploid induction. However, since some eggs escaped triploid development and some fish escaped the ponds, they became invasive. In the late 1980’s a program was introduced to assure that all released fish were triploid, but by that time the damage was done.

The bighead carp and silver carp were introduced into the US in sewage treatment plants and aquaculture ponds as a way to produce clearer water. These two species eat zooplankton and the waste of other animals, so naturally they were a good choice to improve water quality. But as with the grass carp, they ended up in the Mississippi and now have become a great problem. As far as I can tell, bighead carp and silver carp were not required to be tested as triploid before release until 2005 or later.

Nobody wants to bite into their striped bass fillet and find a 

yellow grub. Black carp were introduced to destroy the 

snails that serve as one life cycle stages of the grub. My Gosh! 

Did this guy actually circle the grub with his wedding ring?!

The black carp was also introduced to help aquaculture farms. In raising striped bass, the yellow grub had become a major problem. The grub arrives in the waste of wading birds and can then wreak havoc by multiplying in snails and then attacking the striped bass fry. They burrow into the fish and cause large cysts to form. You can’t sell a food fish that releases a worm when you cut into it.

Black carp love snails, so they were introduced into fish farm ponds in the 1990’s to interrupt the yellow grub life cycle. The plan worked, and worked well; too bad the work to induce sterility did not work as well - the black carp has ended up in the Mississippi as have the other species of asian carp.

The result of these escapes is that rivers in 23 states are choked with asian carp, to the point that many native fish die off. True - the fish are big, very big, so they could provide a source of food. But they haven’t caught on as a food fish, and some places (like Canada) won’t even allow them to be sold for food. Fishing them for sport isn’t going to work as well, as their diets don’t help. How would you bait a hook with a piece of grass or a zooplankton?

The numbers have grown so large in recent years that other problems have developed. The silver carp has a strange habit of leaping out of the water when a boat motor approaches; there have been hundreds of instances where people have been struck by the fish. Noses have been broken, boats have been damaged, and this is all on top of losing the native species in the rivers. Check out this video of the silver carp problem and the birth of a new sport, aerial bowfishing.

Jeff Goldblum said it in Jurassic Park – life finds a

way. There is no way of predicting which turn life

will take, or the lengths evolution will go to help

life persist in the face of huge obstacles. Too often,

we are that obstacle.

There are no exceptions to two rules of nature: one - life will find a way to exist in every form you can imagine and using strategies that you can’t even imagine; and two – altering nature through anything other than natural selection is going to have unintended consequences. Thus, polyploidy is a strategy that fish have employed to diversify and fill niches, and polyploidy used by humans has been both a benefit and a bane.

But we haven’t even talked about one of the most interesting exceptions in nature that is related to polyploid development; the link between extra sets of chromosomes and the abandonment of sexual reproduction. To illuminate this exception, we will focus on the insect, lizard and amphibian polyploids next time.

Ashfield, T., Egan, A., Pfeil, B., Chen, N., Podicheti, R., Ratnaparkhe, M., Ameline-Torregrosa, C., Denny, R., Cannon, S., Doyle, J., Geffroy, V., Roe, B., Saghai Maroof, M., Young, N., & Innes, R. (2012). Evolution of a Complex Disease Resistance Gene Cluster in Diploid Phaseolus and Tetraploid Glycine PLANT PHYSIOLOGY, 159 (1), 336-354 DOI: 10.1104/pp.112.195040

King, K., Seppala, O., & Neiman, M. (2012). Is more better? Polyploidy and parasite resistance Biology Letters, 8 (4), 598-600 DOI: 10.1098/rsbl.2011.1152

For more information and classroom activities, see:

Polyploidy in aquaculture –

http://www.sciencedirect.com/science/article/pii/S0044848609004104

http://www.nature.com/scitable/content/the-advantages-and-disadvantages-of-being-polyploid-1554633

http://books.google.com/books?id=UaT8gZaOA04C&pg=PA216&lpg=PA216&dq=polyploidy+aquaculture&source=bl&ots=Y4vQHYI5I1&sig=2l9WIstm3A1E_KNGtBQdS1kKRI0&hl=en&sa=X&ei=91f0UM_gEcfg0gGnvYDwCA&ved=0CD0Q6AEwAg#v=onepage&q=polyploidy%20aquaculture&f=false

http://theoystersmyworld.com/tag/polyploidy/

http://www.thefishsite.com/articles/869/sterile-salmon-a-sustainable-future

http://www.organicconsumers.org/Patent/frankenfish0302.cfm

http://www.kokaneepower.org/projects/projects_salmon_triploid.php

http://www.foodsafetynews.com/2010/09/frankenfish-created-with-creepy-science/#.UPRY2YVf13I

http://www.imr.no/nyhetsarkiv/2011/mai/gode_resultat_med_steril_oppdrettslaks/en

Asian carp –

http://www.ideastream.org/lsi/enemy

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CEEQFjAD&url=http%3A%2F%2Fhcpssenhancingalgebra2.wikispaces.com%2Ffile%2Fview%2FAsian%2BCarp%2BInvasion%2BLesson%2BPlan.doc&ei=9Vv0UNbJFtGF0QHo_YDYCg&usg=AFQjCNHhLw_I1Yy5YIJkOozHm1uhqXdxHA&bvm=bv.1357700187,d.dmg

http://www.scholastic.com/teachers/article/invasion-asian-carp

http://www.nwf.org/Wildlife/Threats-to-Wildlife/Invasive-Species/Asian-Carp.aspx

http://www.glfc.org/fishmgmt/carp.php

http://www.watershedcouncil.org/learn/aquatic%20invasive%20species/asian-carp/

http://asiancarp.us/

http://oklahomainvasivespecies.okstate.edu/silver_carp.html

http://mdc.mo.gov/discover-nature/field-guide/silver-carp

http://www.carpbusters.com/profile_black.shtml

http://deltafarmpress.com/black-carp-threat-aquaculture

http://www.ecy.wa.gov/programs/wq/plants/management/aqua024.html