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Intergeneric hybridization and speciation between two leptosporangiate ferns
Abstract:
The oosphere of Pteridium aquilinum is surrounded by a 'special membrane' which does not appear to resist the fertile spermatozoon of Gymnogramme calomelanos var. chrysophylla and monospermy results. Our hybridization findings also indicate that the membrane maintains speciation. The spermatozoon of Gymnogramme is strongly attracted but some injury is sustained during its passage through the mucilage of the archegonium neck. Nevertheless, rupture of the membrane, herein designated the cortical complex of speciation (CCS), is followed by expulsion of the oosphere-cytoplasm for which an osmotic mechanism is proposed.
Insights
A special membrane surrounding the Pteridium aquilinum oosphere allows fertilization by Gymnogramme sperm, maintaining speciation. This membrane, the cortical complex of speciation (CCS), ruptures, expelling oosphere-cytoplasm via an osmotic mechanism.
Area of Science:
- * Plant reproductive biology
- * Pteridophyte genetics and evolution
Background:
- * The oosphere of the fern Pteridium aquilinum is enclosed by a unique membrane.
- * Fertilization mechanisms in ferns involve complex interactions between gametes.
Purpose of the Study:
- * To investigate the role of the oosphere's surrounding membrane in interspecific hybridization.
- * To identify the membrane's function in maintaining plant speciation.
- * To elucidate the mechanism of oosphere-cytoplasm expulsion post-fertilization.
Main Methods:
- * Observational studies of sperm-oosphere interactions during hybridization.
- * Analysis of fertilization success between Pteridium aquilinum and Gymnogramme calomelanos var. chrysophylla.
- * Microscopic examination of membrane integrity and sperm passage.
Main Results:
- * The oosphere membrane does not prevent fertilization by Gymnogramme sperm, leading to monospermy.
- * Hybridization findings suggest the membrane plays a role in maintaining speciation.
- * Sperm sustains minor injury passing through archegonium neck mucilage before membrane rupture.
Conclusions:
- * The membrane, termed the cortical complex of speciation (CCS), facilitates fertilization while potentially preserving species integrity.
- * Post-rupture, an osmotic mechanism drives the expulsion of oosphere-cytoplasm.
- * The CCS is crucial for understanding fern reproductive isolation and evolutionary divergence.