Stickleback

Researchers with the University of British Columbia have witnessed one of the most rapid evolutionary cycles ever recorded amongst populations in the wild. It took just 3 short years, for the stickleback fish to develop a tolerance for frigid waters. The waters they have grown accustomed to are about 2.5 degrees Celsius lower than those that their ancestors had to endure.

The study was recently published in the current issue of the Proceedings of the Royal Society B, and gives is some of the first concrete evidence that evolution could help populations survive the effects of global warming.

The stickleback fish originated in the oceans, however they started to make their homes in freshwater lakes and streams just after the last ice age. For the past 10,000 some odd years, both marine and freshwater sticklebacks have evolved varying physical and behavioral pattersn, making them a perfect fit to the models for Darwin’s natural selection theory.

“By testing the temperature tolerance of wild and lab-raised sticklebacks, we were able to determine that freshwater sticklebacks can tolerate lower temperatures than their marine counterparts,” explained Rowan Barrett, the lead author who hails from the UBC Department of Zoology. “This made sense from an evolutionary perspective because their ancestors were able to adapt to freshwater lakes, which typically reach colder temperatures than the ocean.”

To figure out just how quickly this adaptation happened, Barrett, along with collegues from Switzerland and Sweden, “recreated history” by taking marine sticklebacks to freshwater ponds and they discovered that in as little as 3 years, they were remarkably able to tolerate the same minimum water temperature as the freshwater sticklebacks, 2.5 degrees Celsius less that their ancestors!

Critics har been raised that this is an example of mere adaptation not evolution.

If you’ve ever wondered how the eyes of flatfish like flounder and sole ended up on one side of the head, you should take a closer look at a newly published article by Dr Matt Friedman.

Dr Friedman, who recently took up a post at Oxford University, has been investigating this mysterious eye migration using 50-million-year-old fossilized Acanthomorph fishes from Italy and France, and has managed to show that the change was slow and gradual rather than abrupt. Over millions of years, the positions of the flatfish eyes have gradually changed, little by little.

Addressing the Society of Vertebrate Palaeontologists’ (SVP) annual meeting at the University of Bristol today, Dr Friedman said: ”Flatfishes and their profoundly asymmetrical skulls have been enlisted in many arguments against gradual evolutionary change, precisely because it is difficult to imagine how intermediate forms might have been adaptive. My work provides clear evidence of the kinds of intermediates deemed ‘impossible’ by earlier workers and answers this long-standing riddle in vertebrate evolution.”

The most ancient Acanthomorph fishes had asymmetrical skulls, but the eyes were still located on both sides of the head. From these foregoers, intermediate species evolved and one of the eyes gradually moved across the head until both eyes ended up on the same side – millions of years later.

The flatfish group puzzled 19^th century scientists trying to grasp the new Darwinian ideas, because during that epoch, the group’s fossil record was incomplete and it was unclear how the gradual migration of one eye could have come about. Today, a much broader range of fossil fish is available to science and Dr Friedman’s study included over 1,200 fossil specimens belonging to over 600 different species.

During recent years, massive jellyfish congregations have appeared along the Northeast U.S. coast, in the Gulf of Mexico, in the Mediterranean, in the Black and Caspian Seas, and in South-East Asian coastal waters.

“Dense jellyfish aggregations can be a natural feature of healthy ocean ecosystems, says Dr Anthony Richardson of the University of Queensland, but a clear picture is now emerging of more severe and frequent jellyfish outbreaks worldwide.”

A new study by Richardson and his colleagues at the University of Miami, Swansea University and the University of the Western Cape, presents convincing evidence that these massive jellyfish populations are supported by the release of excess nutrients from fertilisers and sewage, and that fish populations depleted by over-fishing no longer are capable of keeping them in check.

“Fish normally keep jellyfish in check through competition and predation but overfishing can destroy that balance,” Dr Richardson says. “For example, off Namibia intense fishing has decimated sardine stocks and jellyfish have replaced them as the dominant species. Mounting evidence suggests that open-ocean ecosystems can flip from being dominated by fish, to being dominated by jellyfish. This would have lasting ecological, economic and social consequences.”

In addition to this, the distribution of many jellyfish species may extend as a response to global warming and an increased water temperature could also favour certain species by augmenting the availability of flagellates in surface waters.

The study, which was lead by CSIRO Climate Adaptation Flagship, has been published in the journal Trends in Ecology and Evolution.

You can find more information about CSIRO Climate Adaptation Flagship here:

450 pound blobs filling up the Sea of Japan

The changing ecosystems affect a long row of different jellyfish species, but some of the most spectacular jellyfish congregations observed during recent years have involved the Nomura jellyfish (Nemopilema nomurai) living in the Sea of Japan (Also known as the East Sea). This colossal species, which can reach a size of 2 metres* across and weigh up to 220 kg**, is also present in the Yellow Sea as well as in the rest of the East China Sea.

After becoming a major problem in the region, the Nomura jellyfish population is now combated by a special committee formed by the Japanese government. Killing jellyfish or ensnaring them in nets will however only prompt these animals to release billions of sperm or eggs; aggrevating the problem rather than reducing it. Coastal communities in Japan have started to harvest jellyfish and sell them as a dried and salted snack, and students in Obama, Fukui have started making jellyfish cookies and jellyfish-based tofu.

* circa 6 feet 7 inches

** circa 450 pounds

We often think of evolution as something extremely slow that takes place over the course of thousands or even millions of years. The truth is however that certain adaptations can occur very quickly, sometimes over the course of just a few generations.

Male Guppy. Copyright www.jjphoto.dk

Eight years later, a time period equivalent of less than 30 guppy generations, the guppies living in the low-predation environment had adapted to this environment by producing larger and fewer offspring with each reproductive cycle.

“High-predation females invest more resources into current reproduction because a high rate of mortality,
driven by predators, means these females may not get another chance to reproduce,” explained Gordon, who works in the lab of David Reznick, a professor of biology.

The guppies living below the barrier waterfall where there were a lot of predators did not show any signs of producing fewer or larger offspring.

“Low-predation females, on the other hand, produce larger embryos because the larger babies are more competitive in the resource-limited environments typical of low-predation sites”, Gordon said. “Moreover, low-predation females produce fewer embryos not only because they have larger embryos but also because they invest fewer resources in current reproduction.”

The paper will be published in the July issue of The American Naturalist.

Swanne Gordon’s research team included David Reznick and Michael Bryant of UCR; Michael Kinnison and Dylan Weese of the University of Maine, Orono; Katja Räsänen of the Swiss Federal Institute of Technology, Zurich, and the Swiss Federal Institute of Aquatic Science and Technology, Dübendorf; and Nathan Miller and Andrew Hendry of McGill University, Canada.

Financial support for the study was provided by the National Science Foundation, the Natural
and Engineering Research Council of Canada, the Le Fonds Québécois de la Recherche sur la Nature
et les Technologies, the Swedish Research Council, the Maine Agricultural and Forestry Experiment
Station, and McGill University.

As reported earlier, fish populations may adapt and change in response to significant fishing pressure. Researchers are now suggesting that the genetic make-up of cod in the Atlantic Ocean might be changing, since cods genetically predisposition to seek out shallower waters are more likely to end up in nets or on fishing lines, while deep-dwellers are more likely to survive and reproduce.

If the current over-fishing of shallow living cod is not put to an end, evolutionary biologist Einar Árnason and his colleagues believes the genetic variant found in shallow-living cod will be lost all together. If the deep-water cods do not spread into the shallows, and Árnason doubts they will since they are adapted to deep water conditions, the shallows may be become devoid of cod within the next 10 years. This will decrease the size of the total cod population and will also force the fishing industry to either give up cod fishing altogether or switch to expensive deep-water trawling.

Árnason and his colleagues have studied cod populations off the coast of Iceland, where fish stocks are still in fairly decent condition compared to the severely depleted populations found in the western Atlantic. In their study, the researchers examined how the genotypes of Icelandic cod have changed between 1994 and 2003.

It was already known that cod living in the Icelandic shallows have a different variant of the pantophysin I gene than the cods found at much larger depts. In their study, Árnason and his colleagues found that the shallow-water variant of pantophysin I is becoming increasingly rare; a change which they attribute to the fact that most Icelandic cod fishers work in shallow waters near the coastline using lines and nets instead of carrying out deep-water trawling.

Árnason and his team also found that Icelandic cod are reaching sexual maturity at a younger age and at a smaller size than before. This is discovery is a chilling revelation for Icelandic fishermen and conservationalists alike, since that was exactly what happened in Newfoundland waters before that cod population crashed completely.

The study has been published in the journal PLoS ONE

The inclination to end up stuck on a hook seems to be a heritable trait in bass, according to a study published in a recent issue of the Transactions of the American Fisheries Society.

The study, which was carried out by researchers DP Philipp, SJ Cooke, JE Claussen, JB Koppelman, CD Suski, and DP Burkett, focused on Ridge Lake, an Illinois lake where catch-and-release fishing has been enforced and strictly regulated for decades. Each caught fish has been measured, tagged and then released back into the wild.

Picture by: Clinton & Charles Robertson from Del Rio, Texas & San Marcos, TX, USA

David Philipp and coauthors commenced their study in 1977, checking the prevalence of Largemouth bass (Micropterus salmoides) on the hooks of fishermen. After four years, the experimental lake was drained and 1,785 fish were collected. When checking the tags, Philipp and his team found that roughly 15 percent of the Largemouth bass population consisted of specimens that had never been caught. They also found out that certain other bass specimens had been caught over and over again.

To take the study one step further, the research team collected never caught bass specimens (so called Low Vulnerability, LV, specimens) and raised a line of LV offspring in separate brood ponds. Likewise, the team collected bass specimens caught at least four times (High Vulnerability, HV, specimens) and placed them in their own brooding ponds to create a HV line.

The first generation (F1) offspring from both lines where then marked and placed together in the same pond. During the summer season, anglers where allowed to visit the pond and practise catch-and-release, and records where kept of the number of times each fish was caught.

As the summer came to an end, HV fish caught three or more times where used to create a new line of HV offspring, while LV fish caught no more than once became the parents of a new LV line.

The second generation (F2) offspring went through the same procedure as their parents; they were market, released into the same pond, and subjected to anglers throughout the summer. In fall, scientists gathered the fish that had been caught at least three times or no more than once and placed them in separate ponds to create a third generation (F3) HV and LV fish.

A following series of controlled fishing experiments eventually showed that the vulnerability to angling of the HV line was greater than that of the LV line, and that the differences observed between the two lines increased across later generations.

If this is true not only for bass but for other fish species as well, heavy hook-and-line angling pressure in lakes and rivers may cause evolutionary changes in the fish populations found in such lakes. Hence, a lake visited by a lot of anglers each year may eventually develop fish populations highly suspicious of the fishermen’s lure.

More information can be found in the paper published in Transactions of the American Fisheries Society: Philipp, DP, SJ Cooke, JE Claussen, JB Koppelman, CD Suski and

DP Burkett (2009) Selection for vulnerability to angling in Largemouth Bass. Transactions of the American Fisheries Society 138, pp. 189–199.

Researchers at Tokyo Institute of Technology have undertaken what is believed to be the very first CT scan of eggs inside a coelacanth fish.

“I was surprised to see that all the eggs were the same size,” said Dr Norihiro Okada, a bioscience professor at the university and a member of the research team. “I hope to do research into why this is.”

Each coelacanth fish was roughly 170 cm (67 in) long and weighed about 70 kg (154 lbs). After being captured off the coast of Tanzania, both fishes were frozen and send to Japan where the CT scan showed how each fish contained roughly 40 eggs; each egg being about 7 cm (almost 2 ¾ in) in diameter.

The eggs of a coelacanth are never released into the water because the offspring hatch while still inside their mother. The young fish sometimes reach a length of 30 cm (12 in) before leaving their mother’s body.

Coelacanths were long believed to have gone extinct around the same time as the dinosaurs, until scientists realized that these fishes actually turn up in the nets of African and Asian fishermen now and then. The first confirmed finding is from 1938 when a specimen was captured in the Indian Ocean.

Coelacanths are of special interest to evolutionary biologists since they are thought to represent an early step in the evolution of fish to amphibians. You can read more about this in our coelacanth article.

An expansion of vertical seagrass occurring some 25 million years ago was probably what prompted seahorses to evolve from horizontal swimmers to upright creatures. If you live in vertical seagrass, an upright position is ideal since it allows you to stay hidden among the vertical blades.

This new idea is put forward in a report by Professor Beheregaray* and Dr Teske** published in the journal Biology Letters on May 6.

Sea horse picture from our Seahorse section.

Only two known fossils of seahorse have been found and this scarcity of fossil records has made it difficult for scientists to determine when seahorses evolved to swim upright. The older of the two fossils is “just” 13 million years old and no links between the two fossils and horizontally-swimming fish has been found.

“When you look back in time, you don’t see intermediate seahorse-like fish,” Beheregaray explains. There are however fish alive today that look like horizontally-swimming seahorses and Beheregaray and Teske have therefore studied them in hope of finding clues as to when seahorses made the transition from horizontal to vertical swimming.

By comparing DNA from seahorses with DNA from other species of the same family, Beheregaray and Teske were able to determine who the closest living relative to seahorses was.

“The pygmy pipehorses are by far the most seahorse-like fish on earth, says Beheregaray. “They do look like the seahorses, but they swim horizontally“.

When you have two closely related species, you can use molecular dating techniques to calculate when the two species diverged from each other. Beheregaray and Teske used a molecular dating technique that relies on the accumulation of differences in the DNA between the two species, and then used the two existing fossils to calibrate the rate of evolution of DNA in their molecular clock. By doing so, the two researchers could conclude that the last common ancestor of seahorses and pygmy pipehorses lived around 25 to 28 million years ago. At this point, something must have happened that led to the formation of two distinct species, and Beheregaray and Teske believe that this “thing” was the expansion of seagrass in the habitat where seahorses first evolved.

The time in history when seahorses arose, the Oligocene epoch, coincided with the formation of vast areas of shallow water in Austalasia. These shallow waters became overgrown with seagrass and turned into the perfect habitat for upright swimming seahorses that could remain hidden from predators among the vertical blades. The pygmy pipehorse on the other hand lived in large algae on reefs and had no use for an upright position, hence it continued to swim horizontally just like their common ancestor.

“The two groups split in a period when there were conditions favouring that split,” says Beheregaray. “It’s like us. We started walking upright when we moved to the savannahs. On the other hand, the seahorses invaded the new vast areas of seagrass.”

* Associate Professor Luciano Beheregaray of Flinders University

http://www.flinders.edu.au

** Dr Peter Teske of Macquarie University

http://www.macquarie.edu.au

The members of the genus Synodontis, commonly known as the squeaker catfishes of Lake Tanganyika, evolved from a single common ancestor according to a paper* published in a recent issue of the Journal of Evolutionary Biology.

synodontis catfish

Researchers Day, Bills and Friel** analysed 1697 base-pair sequences consisting of nuclear (ribosomal protein-codin gene S7), mitochondrial (cytochrome b) and transfer RNA gene fragments in 65 samples (representing about 40 species) of squeaker catfishes to study the evolutionary relationships of the group.

Through their research, the authors were able to track down a single origin for the Lake Tanganyika species flock. The members of the genus Synodontis all evolved within the last 5.5 million years which makes them a comparatively new addition to this Great Rift Valley Lake which is believed to be at least 9 million, perhaps even 12 million, years old.

Day, Bills and Friel also recovered a monophyletic group of southern African riverine species which seems to have diversified very rapidly (during the last 890,000 years). This group was believed to have been formed due to adaptive radiation within Lake Makgadikgadi; a lake which is now extinct.

* Day, JJ, R Bills & JP Friel (2009) Lacustrine radiations in African Synodontis catfish. Journal of Evolutionary Biology 22, pp. 805–817.

**Julia Day, Roger Bills and John Friel

The discovery of three new species of fossilized octopi in Lebanon has caused scientists to suspect that the first octopus appeared tens of millions of years earlier than previously thought.

In a paper published in a recent issue of the journal Palaeontology, researchers Fuchs, Bracchi and Weis describes three new species of fossil octopus placed in two new genera: Keuppia and Styletoctopus. The species have been given the names Keuppia levante, Keuppia hyperbolaris and Styletocopus annae.

The descriptions are the result of the fortunate discovery of three astonishingly well preserved octopus fossils from the Cenomanian, i.e. octopus that lived at some point between 93 and 100 million years ago.

Studying the history of octopi is difficult since the octopus, unlike dinosaurs for instance, is composed almost entirely of soft tissue; predominantly muscle, skin and viscera. When an octopus dies the body rapidly decomposes and vanishes, and extraordinary conditions are necessary for the animal to leave any fossil record behind.

Fortunately for science such extraordinary conditions must have been at hand in Lebanon some 100 million years ago, because the three newfound fossils are so well preserved that even traces of muscles, suckers, internal gills and ink can be distinguished.

This type of fossil is so rare that Mark Purnell, for the Palaeontological Association, remarked that finding an octopus as a fossil “is about as unlikely as finding a fossil sneeze”.

Before these three species were discovered, only one species of fossil octopus was known to science.

For more information, see the paper published in Palaeontology: Fuchs, D, G Bracchi and R Weis (2009) New Octopods (Cephalopoda: Coleoidea) from the Late Cretaceous (Upper Cenomanian) of Hakel and Hadjoula, Lebanon. Palaeontology 52, pp. 65–81.