Evolution in larger foraminifera

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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