Polish scientists on the trail of evolutionary arms race
PAP © 2012 / Tomasz K.Baumiller
Predation influences the evolution of some organisms, it can drive it or lead to the extinction of the unfit forms. Polish scientists described this mechanism in the prestigious American journal "PNAS" using the example of sea urchins and crinoids. Crinoids are marine animals belonging to the echinoderms, distant relatives of starfish, brittle stars and sea cucumbers. At first glance, they resemble plants, because their bodies are composed of arms and calyx, and often a stem. Crinoids appeared i
They can be found also today. Only a small part of them are sedentary forms, permanently attached to the sea bottom. They can only be found in the depths, where they are a group of relics. Many more crinoids are able to move, which allows them to quite successfully avoid attacks by predators.
Przemyslaw Gorzelak of the Institute of Paleobiology PAS, Dr. Mariusz Salamon of the University of Silesia, and Polish scientist living in the U.S. Prof. Tomasz Baumiller of the University of Michigan examine the evolutionary history of crinoids.
Already in 2010, Prof. Baumiller and colleagues presented in "PNAS" ("Proceedings of the National Academy of Sciences") the results of analyses of more than 2.5 thousand fragments of crinoid fossils found in Central Europe, including the Polish territory. They determined that 225 years ago crinoids had been falling prey to predatory sea urchins (spherical, marine animals, with bodies densely covered with lime, movable spikes). This was evidenced by the characteristic bite marks preserved in fossils.
The paper published in the latest "PNAS" refers to the time period covering 185 million years (from 250 million years ago until the end of the Mesozoic, 65 million years ago). Fossils from this period allowed to follow the interaction between crinoids and sea urchins and its evolutionary implications.
The researchers found that in the geological past, the proportions between the different forms of crinoids had been changing. "Moreover, these changes correlate closely with changes in predatory sea urchin diversity" - Przemysław Gorzelak told PAP. Periods, in which the diversity of sea urchins became larger, saw a greater development of crinoids capable of movement, and the disappearance of sedentary forms. The opposite happened when diversity of sea urchins decreased. Then, more forms of crinoids permanently attached to the bottom developed - explained the scientist.
Thus, the development of predatory sea urchins, preying on crinoids for nearly 250 million years, contributed to the evolutionary success of "mobile" crinoids observed today and the disappearance of sedentary forms, which formerly dominated the oceans - the researchers conclude.
"Our research shows that ecological processes observed today in marine ecosystems may have long-term evolutionary consequences. In the case of crinoids, pressure from predators stimulated the evolution of mobile forms, which developed innovative defensive adaptations, at the same time yet causing the extinction of +unfit+ sedentary forms. This is consistent with the so-called escalation hypothesis, created by the eminent paleobiologist Geerat J. Vermeij. According to the hypothesis, development of predators drives the evolution of their prey" - said Gorzelak.
Publication authors believe that the findings on the evolution of crinoids can also be applied to progressive destruction of reefs, related to the destructive activities of sea urchins. "Today\'s reefs suffer not only because of global warming, they are also being destroyed by predators. Uncontrolled fishing, decreases the population of fish, natural predators for sea urchins, making it easier for sea urchins, which devastate shallow reefs" - noted Gorzelak.
The work was financed the Ministry of Science and Higher Education, and in the U.S. by the National Geographic Society and the National Science Foundation.
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