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gonna have to dig up the recent article that I can't seem to remember at the moment that discussed a similar question: evolution and speciation in tropical rain forests. Apparently, very subtle changes in underlying geology created nearly imperceptible barriers and created isolated groups where no barriers were obvious to anyone. The sea floor, from shelf to plain is known to be very active. The activity noted is often short lived. However, with a life expectancy of a month or two, forams, I suspect can demonstrate a great deal of evolutionary change that, when the isolating event is ended, can be dispersed into other temporarily isolated groups. Throw major climatic changes a pinch of salt maybe some cayenne pepper and your speciating right past a rue and into the gumbo phase. (Whoa, I gotta get some sleep!) Fact is that evolution is not so mysterious, the environmental factors that exist are. ---------- From: R. Gietl[SMTP:gietl@uni-bremen.de] Sent: Tuesday, April 22, 1997 11:24 PM To: Multiple recipients of list Subject: Evolution in larger foraminifera Dear all, being involved with biostratigraphy/taxonomy of Alveolinids, it is probably not the most intelligent question to ask: "What allows larger foramifera to evolve?" - but maybe out there are some people sometimes also almost being driven into insomnia in wondering about this, since regarding to MAYR (1942) a species is defined as "...groups of actually or potentially interbreading natural population which are reproductively isolated from such other groups." Based on this definition speciation is the result "..of reproductive isolation between two formerly interbreeding populations" (CHARLESWORTH, 1990) or in other words the breakdown of genetic exchange between the two groups. If we consider speciation as an evolutionary process we can conclude that genes are the basic unit of evolution and recombination of genes is the main process. This leads to the conclusion that only the sexually reproduced generation has the abillity to evolve. On the other hand it is wellknown, that many larger foraminifera reduced sexual reproduction (ROETTGER & SCMALJOHANN, 1976). In Alveolinids microspheric forms are very rare or unknown (e.g. A. sicula (De Stefani), WHITE, 1994). For example: In 200 thin slides (7,5x9,5cm, content of alveolinids approx. 15-20%, most specimens between 2-4 mm in axial diameter) I found one microspheric form of A. ellipsoidalis Schwager. The question is now: How works evolution in larger foraminifera?? Thanks to all ----------------------------------------------------------- Ralf Gietl University of Bremen Tel. (0049)0421/218-7152 Faculty of Geosciences FAX. (0049)0421/218-4515 P.O.B 330 440 D-28334 Bremen /Germany
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