ESCAPE FROM EVOLUTIONARY STASIS BY TRANSPOSON-MEDIATED DELETERIOUS MUTATIONS

Evolution within a rugged fitness landscape is limited by the tendency for organisms to become trapped on local optima resulting in evolutio nary stasis. It is presently unclear how founder populations escape fr om an adaptive peak to found a new species. Insertion sequences, trans posons and other mobile DNA elements are found in all species of eukar yotes, bacteria and archaebacteria, where they have been sought and ar e usually considered to be genomic parasites or selfish genes. However , many transposons and other mobile repetitive DNA are remarkably spec ies or phyla-specific, indicating that infection with transposable ele ments coincides with speciation events and is involved in promoting ev olutionary change. We propose here a model in which transposable eleme nts are involved in speciation events by their ability to produce irre versible deleterious mutations that promote escape from evolutionary s tasis. We have constructed a genetic algorithm designed to model both spontaneous and transposon-mediated mutations in populations of asexua l digital organisms. We use this model to investigate the effect of tr ansposon-mediated mutations on the rate of evolution of digital organi sms as they compete for resources within an artificial adaptive landsc ape. In the absence of transposon mutations the seed organisms quickly evolve to occupy the nearest adaptive peak but thereafter evolutionar y stasis ensues and adjacent empty peaks are left unoccupied. In the p resence of transposon mutations, evolution is again dominated by stasi s but is punctuated by bursts of rapid evolution in which consecutive unoccupied adaptive peaks are filled with organisms derived from singl e transposition events. Rapid evolutionary events Leading to founding of new biological species, may be similarly initiated by irreversible deleterious mutations induced by transposition. (C) 1997 Academic Pres s Limited.