Outbreeding depression in the fernAsplenium ruta-murariaL.: Evidence from enzyme electrophoresis, meiotic irregularities and reduced spore viability

Abstract

Asplenium ruta-muraria is a mainly inbreeding, highly specialized, rock or wall inhabiting, autotetraploid fern. Enzyme electrophoresis combined with cytological investigations and spore measurements revealed that outbreeding depression occurs in natural populations when two different genotypes cross. Crossing results in irregularities in meiosis and reduced spore fertility. Two hypotheses are formulated to explain this phenomenon. The First hypothesis suggests a multiple origin of autopolyploids and assumes that long distance dispersal by spores mixes very distant and locally adapted genotypes. Thus, the consequence is the observed outbreeding depression. The second hypothesis assumes that inbregding has a very high adaptive value in this ecologically specialized, autopolyploid species. This fact and strong selection for regular meiosis have led to fully fertile inbred lines, which are capable of founding populations by single spores. Crossing of two genetically different lines may disturb the control of pairing in meiosis and thus cause outbreeding depression.