Stanton D. answered • 12/10/19
Tutor to Pique Your Sciences Interest
Hi Sam A.,
A mechanism, huh? Well, consider the mechanics of sporophyte propagation in mosses: the sporophyte body is enclosed by, and obligately nourished by, the stalks of the gametophyte plants. To achieve independence, the sporophytes had to develop both the physical structures and biochemical capabilities to survive on their own. And they had to do it better than the gametophytes were doing it. For example, simple mosses are generally uniform over large mats and quite sessile on limited soil covering rock; whereas club mosses are discrete, erect and branched and happily live on richer soil media. Now, that alone doesn't confer and advantage, unless light is limited, and that additional height and breadth enables better photosynthesis, perhaps. But, first you'd have to have some structure development of the sporophyte generation, and only then could you start miniaturizing the gametophyte generation. But what powers the overall turnover? It must be evolution of adaptability in that diploid structure, via assortment of traits. I'd suggest that you look for structural complexity, both macro and micro, in the club mosses vs. the simple mosses, for clues, then build a case for evolving that complexity, through gene duplication, mutation, and recombination processes. Then specify how the 2 generations might start to share roles, and finally turn the structural primacy over to the sporophytes.
If you were inclined to pun about it, you might say that "a role-ing moss gathers not on stone". Whatever!
Good luck, Cheers, -- Mr. d.
