Teleost Diversity

slingjaw-wrasse-300x200
The protrusible jaw of the sling-jaw wrasse, Epibulus insidiator.
The term teleostei is derived from the Greek words teleios (meaning “complete”) and osteon (meaning “bone”). This infraclass of ray-finned fishes can roughly be identified by having true bony structures, a homocercal tail, a protrusible jaw and a spine that terminates at the caudal peduncle. In some estimates, 30,000 species of teleosts are known to exist. Other estimates place half the known vertebrate species to be members of teleostei. This easily raises the questions: why have teleosts become more successful than other vertebrates, and why are they so diverse? Theory suggests the answer lies in the genome.

An organism’s genome is made up of its genes or genetic material. It is what codes for the uniqueness of a species. Occasionally, mistakes are made when cellular machinery duplicates the DNA making up the genes. These mistakes are incredibly important as they sometimes provide an advantage to the organism which increases its overall fitness. Although these mutations can be advantageous, it is not necessarily an efficient vector or mechanism for evolutionary progress because the function of the mutated gene comes at the cost of the function of the old gene. In 1951, S. G. Stephens hypothesized that an increase of genetic loci would be the only way to overcome this genetic stalemate and promote evolutionary progress. He goes on to suggest a duplication of the entire genome would be one viable source of increasing loci. As technology has advanced, this hypothesis has been tested and confirmed. For example, in 1997 evidence was found that at some point in its evolutionary history the entire yeast (Saccharomyces cerevisiae) genome was duplicated. Furthermore, in 2002 it was determined that the entire genome of rice (Oryza sativa japonica) was duplicated between 40 and 50 million years ago. Perhaps even more interesting is the evidence suggesting the entire human genome appears to have been duplicated at least twice.

The human genome. Cytosine, guanine, adenine and thymine are the main bases in DNA that code for genes.
The human genome. Cytosine, guanine, adenine and thymine are the main bases in DNA that code for genes.
As genomes are duplicated, the event creates genetic redundancy. Each gene has a second copy that can be mutated and have no deleterious effect on the original function of the gene and to the host organism. Because of this genetic blank canvas, the mutation of the second gene copy can create a new function without hindering the function of the original copy. Both genes/functions can be kept ultimately promoting a much faster rate of speciation.

The scientific literature discovering genome duplication events within fishes is growing. A. Amores and others have suggested such an event took place after actinopterygians (ray-finned fish) and sarcopterygians (lobed-finned fish) diverged. This particular event might account for the greater species diversity within actinopterygians versus the diversity found within sarcopterygians. On a smaller scale, the teleost lineage is hypothesized to have risen between the mid Cretaceous and late Triassic periods of the Mesozoic era (ca 100 to 200 million years ago). A genome duplication event is thought to have occurred around the same time and facilitated the rapid radiation of the teleost group of fishes. With the duplicate genetic material available, the teleost group was able to keep and pass on the advantageous gene mutations without giving up the function of the original gene aiding in their rapid ascent to diversity. Without doubling the genome, there could not have been the genetic playground for teleosts to radiate into a brilliant display of diversity. As more of these genomic secrets are discovered in fishes, it becomes clearer that they are the culprit for the vast diversity we see today.

What's your favorite teleost?
What’s your favorite teleost?

 

– Chris

 

References and Photo Credits

Taylor, J. S., Y. Van de Peer, I. Braasch and A. Meyer. 2001. Comparative genomics provides evidence for an ancient genome duplication event in fish. Philosophical Transactions of the Royal Society of London 356:1661-1679.

Amores, A. et al. 1998. Zebrafish hox clusters and vertebrate genome evolution. Science 282:1711-1714.

Meyer, A. and M. Schartl. 1999. Gene and genome duplications in vertebrates: the one to four rule and the evolution of novel gene functions. Current Opinions of Cell Biology 11:699-704

Carroll, R. L. 1997. Patterns and processes of vertebrate evolution. Cambridge University Press.

Lydeard, C. and K. J. Roe. 1997. The phylogenetic utility of the mitochondrial cutochrome b gene for inferring relationships among actinopterygian fishes. Molecular Systematics of Fishes. pp. 285 – 303. San Diego, CA: Academic Press.

Taylor, J. S., I. Braasch, T. Frickey, A. Meyer and Y. Van de Peer. 2003. Genome duplication, a trait shared by 22,000 species of ray-finned fish. Genome Research 13:382-390.

Stephens, S., G. 1951. Possible significance of duplication in evolution. Advances in Genetics 4:247-265.

Wolfe, K., H. and D.C. Shields. 1997. Molecular evidence for an ancient duplication of the entire yeast genome. Nature 387:708-713.

Goff, S. A., et al. 2002. A draft sequence of the rice genome (Oryza sativa L. ssp. Japonica). Science 296:92-100.

http://journal.frontiersin.org/article/10.3389/fmars.2014.00053/full

Jason Isley, http://scubazooimages.com/

https://hms.harvard.edu/news/puzzling-out-variability-human-genome-7-10-12

Acceleration due to…fish?

Fish swim. Everyone knows this. What’s interesting is looking closer at how they swim and the mechanics of the forces they generate while swimming. Most people might take this for granted, but being a highly curious ichthyologist, I decided to look at the science. Instead of looking at mounds and mounds of data trying to compare apples to oranges, so to speak, I ran some calculations in order to compare apples to apples. Something I could understand. What I learned was both impressive and awesome, but first, some simple physics…

Acceleration and g-forces

Acceleration can be defined as the change in an object’s velocity over a given time frame. For example, if we are driving on the interstate at 31.3 meters per second (which is approximately 70 mph) and we accelerate to 35.8 meters per second (approximately 80 mph) in 10 seconds then our change in velocity is 4.5 m/s over a 10 second period, and our acceleration is 0.45 m/s2. Now, an object in free fall here on Earth will accelerate towards the ground at 9.8 m/s2 because of gravity. The odd thing is acceleration is an indirect cause of weight, which can be calculated by multiplying your mass by the acceleration due to gravity, 9.8 m/s2.

Acceleration also plays a role in a force we’re all familiar with – the g-force (noted as “g”). The g-force is the sensation of weight you feel when you accelerate in a fast car or on a thrilling rollercoaster ride. We’ve all felt it. So you might be wondering how it is calculated. It is calculated by dividing your acceleration by 9.8 m/s2. In simple terms, 1 g-force is the force of gravity (or your weight) while standing on Earth. 2 g’s is twice the force of gravity (or twice your weight) and so on. Ok, so what does all this have to do with fish? Well, I’m glad you asked.

Acceleration and fish

There have been several studies investigating the mechanics and intricacies of how fish swim. I sifted through the scientific literature and found several studies that measured the acceleration of a particular species for one reason or another. From these reported values I calculated the g’s each fish experiences when they accelerate. Before we look at those numbers let’s look at some common values to establish a baseline for comparison:

Usain Bolt accelerated 9.5 m/s2 out of the blocks during his world record 100 m dash. During this time he experienced 0.97 g’s.

Astronauts experience around 3 to 5 g’s during a shuttle launch.

An average person will lose consciousness somewhere around 5 g’s.

Jet fighter pilots are trained to withstand 9 g’s.

For an average person, serious injury and/or death will occur around 9 g’s.

 

Now for the calculations…

 

Species Common name Acceleration m/s2 g – force Study
Lepomis cyanellus Green sunfish 15.67 1.60 Webb 1975
Pomatomus saltatrix Bluefish 20.6 2.10 Dubois et al. 1976
Myoxocephalus scorpio Short-horned sculpin 22 2.24 Beddow et al. 1995
Cottus cognatus Slimy sculpin 22.7 2.31 Webb 1978
Perca flavescens Yellow perch 23.9 2.44 Webb 1978
Luxilus cornutus Common shiner 28.7 2.93 Webb 1978
Lepomis macrochirus Bluegill 28.8 2.94 Webb 1975
Etheostoma caeruleum Rainbow darter 32.3 3.29 Webb 1978
Oncorhynchus mykiss Rainbow trout 59.7 6.09 Harper and Blake 1990
Micropterus dolomieu Smallmouth bass 110 11.21 Webb 1983
Pterophyllum sp. Angelfish 114.7 11.69 Domenici and Blake 1993
Xenomystus nigri Knifefish 127.9 13.04 Kasapi et al. 1993
Esox lucius Northern pike 151.3 15.42 Frith and Blake 1991

 

It is incredible to note that Northern pike (Esox lucius; pictured above) can accelerate at 151.3 m/s2 and generate an astonishing 15.4 g’s! Let’s look at it in another way. Northern pike accelerate at 338.4 mph/s! Even the small common shiner (Luxilus cornutus; pictured below) accelerates at a rate that generates 3 times the g’s than that of Usain Bolt – the fastest human alive.

shiner

It puts things in quite the perspective, and undoubtedly demonstrates how incredible this group of vertebrates really are. Characteristics in their anatomy and physiology, such as body and muscle shape, allow them to perform at insane levels, but that is for another post.

 

–  Chris

 

References and photo credits

Webb, P.W. 1975. Acceleration performance of rainbow trout Salmo garidneri and green sunfish Lepomis cyanellus. Journal of Experimental Biology 63:451-465.

Dubois, A.B., Cavagna, G.A. and Fox, R.S. 1976. Locomotion of bluefish. Journal of Experimental Zoology 195:223-226.

Beddow, T.A., Van Leeuwen, J.L. and Johnston, I.A. 1995. Swimming kinematics of fast starts are altered by temperature acclimation in the marine fish Myoxocephalus scorpius. Journal of Experimental Biology 198:203-208.

Webb, P.W. 1978. Fast start performance and body form in seven species of teleost. Journal of Experimental Biology 74:211-226.

Harper, D.G. and Blake, R.W. 1990. Fast-start performance of rainbow trout Salmo gairdneri and northern pike Esox lucius. Journal of Experimental Biology 150:321-342.

Webb, P.E. 1983. Speed, acceleration and maneuverability of two teleost fishes. Journal of Experimental Biology 102:115-122.

Domenici, P. and Blake, R.W. 1993. The effect of size on the kinematics and performance of angelfish (Pterophyllum eimekei) escape responses. Canadian Journal of Zoology 71:2319-2326.

Kasapi, M. A., Domenici, P., Blake, R. W. and Harper, D. G. 1993. The kinematics and performance of the escape response in the knifefish Xenomystus nigri. Canadian Journal of Zoology 71:189-195.

Frith, H. R. and Blake, R. W. 1991. Mechanics of the startle response in the northern pike, Esox Lucius. Canadian Journal of Zoology 69:2831-2839.

Haslag, B. http://bioweb.uwlax.edu/bio203/s2008/haslag_bria/

Schmidt, K.P. http://www.fishbase.org/Photos/PicturesSummary.php?ID=2851&what=species