BACKGROUND AND AIMS Active growth in post-embryonic sporophytes of desert mosses is restricted to the cooler, wetter months. However, most desert mosses have perennial gametophytes. It is hypothesized that these life history patterns are due, in part, to a reduced desiccation tolerance for sporophytes relative to gametophytes. METHODS Gametophytes with attached post-embryonic sporophytes of T...

Early in their evolution, plants acquired a life cycle that alternates between a multicellular haploid organism, the gametophyte, and a multicellular diploid organism, the sporophyte. Angiosperms have both female and male gametophytes. The female gametophyte is critical to many steps of the angiosperm reproductive process, including pollen tube guidance, fertilization, the induction of seed dev...

6 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7 Beyond Principles: What Has the Inclusion of Data from the Fossil Record Contributed to 8 Evo-Devo Plant Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

The strength of purifying selection varies among loci and leads to differing frequencies of deleterious alleles within genomes. Selection is generally stronger for highly and broadly expressed genes but can be less efficient for diploid expressed, deleterious alleles if heterozygous. In plants expression level, tissue specificity and ploidy level differ between pollen specific and sporophyte sp...