mosses

Mating System and Population Structure of the Annual Moss Physcomitrium pyriforme in a Newly Restored Wet Prairie

Bryophytes at Batelle-Darby Prairie Restoration

To improve the ecological integrity of the nationally recognized Darby Creek watershed, resource managers at Battelle Darby Creek Metro Park have recently undertaken substantial wetland/prairie restoration projects on two sites at the western edge of Franklin County that were, until now, farmland. One of these areas, called “Darby Dan Farms” is a 700-acre plot on the east side of Darby Creek Drive, just south of Kuhlwein Road. In autumn 2010, after blocking drainage tiles to recreate natural wetland hydrology on the 500-acre southern portion of the tract, park managers sowed seeds of more than 30 species of prairie forbs and about a dozen graminoids. Similar restorations were planted in 2012 on the remaining 200-acre northern portion of the Darby Dan site (immediately adjacent to Kuhlwein Road) and also at a site approximately 5 km north-northwest, at the “Morgan Headwaters” portion of Prairie Oaks Metro Park.

Darby Dan Wetland Restoration, December, 2012.

Darby Dan Wetland Restoration, December, 2012.

During the first two years at the Darby Dan restoration, mosses were especially abundant and widespread. Nearly all of these were species having the acrocarpous (cushion moss) growth form, wherein the gametophyte stems are erect, and produce gametangia (and later, sporophytes) at their tips.  The most abundant and widespread of these is bird’s-claw beard-moss, Barbula unguiculata (Pottiaceae).

Barbula unguiculata is a cushion moss in the family Pottiaceae.

Barbula unguiculata is a cushion moss in the family Pottiaceae.

Several members of the Funariaceae were prominent, as is typical on arable land. “Goblet moss,” Physcomitrium pyriforme was especially widespread on the site. This is a fast-growing moss that produces gametangia in autumn, with sporophytes developing over the winter, to release spores in early spring.

Physcomitrium pyriforme in early winter.

Physcomitrium pyriforme in early winter.

Bryophyte Reproduction

Like most other members of the Funacriaceae, Physcomitrium pyriforme is autoicous, bearing archegonia and antheridia in separate inflorescences on the same plant. Below, see an individual stem; note how it is forked at the base into separate male and female branches.

Physcomitrium pyriforme is autoicous. Left branch is male; right branch is female.

Physcomitrium pyriforme is autoicous. Left branch is male; right branch is female.

Because moss gametophytes are haploid, producing gametes asexually by mitosis, and because Physcomitrium is autoicous, there are three scenarios whereby this species can mate, with respect to the potential to produce sporophytes that are either necessarily homozygous at all loci, or, potentially at least, heterozygous at some loci. In scenario 1, sperm travels between genetically different gametophytes in close proximity to one another, resulting in sporophytes that are a blend of the two genotypes.

Mating between genetically different gametophytes would produce heterozygous offspring.

Mating between genetically different gametophytes would produce heterozygous offspring.

In scenario 2, mating takes place within a gametophyte, resulting in sporophytes that are homozygous at all loci. This can occur either from sperm transfer between branches of the same gametophytic stem, or between stems of a cluster of stems that all developed from the same same spore.

Mating within a gametophyte would produce homozygous offspring.

Mating within a gametophyte would produce homozygous offspring.

Scenario 3 yields a result identical with scenario–wholly homozygous sporophytes –a result of inter-gametophytic matings wherein the two gametophytes developed from genetically identical spores (the result of intra-gametophytic selfing as described in scenario 2).

Mating between genetically identical gametophytes would produce homozygous offspring.

Mating between genetically identical gametophytes would produce homozygous offspring.

By whatever means insofar as their genetic makeup is concerned, in spring P. pyriforme sporophytes are abundant. In a typical April, they are nearly mature.

Nearly mature Physcomitrium pyriforme sporophytes in late winter.

Nearly mature Physcomitrium pyriforme sporophytes in early spring.

About a month later, in May, the sporphytes are mature and releasing spores.

Mature, spore-releasing  Physcomitrium pyriforme sporophytes in mid-spring.

Mature, spore-releasing Physcomitrium pyriforme sporophytes in mid-spring.