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 19th 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.
Zoology Prof. Yossi Loya at the Tel Aviv University in Israel has discovered that corals changes sex to survive periods of stress, such as high water temperatures. By observing the behaviour of Japanese sea corals he discovered that stressed female mushroom coral (fungiid coral) change gender to become males, and that male corals are much better at handling stress and fare better at surviving on limited resources. Not all females go through his change but many do and most of the population is therefore male during periods of intense stress.
Yossi Loya says: “We believe, as with orchids and some trees, sex change in corals increases their overall fitness, reinforcing the important role of reproductive plasticity in determining their evolutionary success. One of the evolutionary strategies that some corals use to survive seems to be their ability to change from female to male, As males, they can pass through the bad years, then, when circumstances become more favourable, change back to overt females. Being a female takes more energy, males are less expensive to maintain. They are cheaper in terms of their gonads and the energy needed to maintain their bodies. Having the ability to change gender periodically enables a species to maximize its reproductive effort.”
Loya’s discoveries have been published in the Proceedings of the Royal Society B. The professor hopes that this new knowledge will help coral farmers by allowing them to reproduce the hardy Fungiid corals more effectively.
Loya has been studying coral reefs for more than 35 years and won the prestigious Darwin Medal for a lifetime contribution to the study of coral reefs. He is also involved in coral rehabilitation projects in the Red Sea and is a professor at the Tel Aviv University in Israel.
According to a new study from Uppsala University, the origin of fingers and toes can be traced back to a type of fish that inhabited the ocean 380 million years ago. This new finding has overturned the prevailing theory on how and when digits appeared, since it has long been assumed that the very first creatures to develop primitive fingers were the early tetrapods, air-breathing amphibians that evolved from lobed-finned fish during the Devonian period and crawled up onto land about 365 million years ago.
Lead author Catherine Boisvert[1] and co-author Per Ahlberg[2], both of Uppsala University in Sweden, used a hospital CT scanner to investigate a fish fossil still embedded in clay. “We could see the internal skeleton very clearly, and were able to model it without ever physically touching the specimen,” says Ahlberg. The scan revealed four finger-like stubby bones at the end of the fin skeleton. The bones were quite short and without joints, but it was still very clear that they were primitive fingers. “This was the key piece of the puzzle that confirms that rudimentary fingers were already present in the ancestors of tetrapods,” Catherine Boisvert explains.
The scanned fossil was that of a meter-long Panderichthys, a shallow-water fish from the Devonian period. Panderichthys is an “intermediary” species famous for exhibiting transitional features between lobe-finned fishes and early tetrapods, while still clearly being a fish and not a tetrapod. The specimen used was not a new finding; it had just never been examined with a CT scan before.
So, why have researchers for so long assumed that digits were something that evolved in tetrapods without being present in their fishy ancestors? The main reason is the Zebra fish (Danio rerio), a commonly used model organism when vertebrate development and gene function is studied. If you examine a Zebra fish, you will find that genes necessary for finger development aren’t present in this animal. Researchers therefore assumed that fingers first appeared in tetrapods and not in fish.
It should be noted that similar rudimentary fingers were found two years ago in a Tiktaalik, an extinct lobe-finned fish that lived during the same period as Panderichthys. Tiktaalik is however more similar to tetrapods than Panderichthys.
The Panderichthys study was published in Nature on September 21.