Abstract Detail

Reproductive biology

Bonacorsi, Nikole [1], Leslie, Andrew [2].

Strobilus evolution in lycophytes: architectural constraints and reproductive convergence.

Reproductive strobili, or aggregations of fertile tissues, have independently evolved many times across plants, and are present in members of lycophytes, horsetails, Ophioglossales, nonflowering seed plants (e.g. conifers, Ginkgo), and flowering seed plants (e.g. the catkins of Betulaceae). These strobili often appear strikingly similar; they tend to have high concentrations of sporangia, minimal amounts of other tissues, and are often long and thin. Such similarities may reflect convergent evolution towards a high proportion of fertile tissue for the production of large amounts of spores or pollen, although this idea has rarely been tested explicitly. In this study, we focus on lycophytes, the sister group to other vascular plants, which show both compact strobili and more diffuse “fertile zones” of sporangia. We use the extensive fossil record and living diversity of lycophytes to ask if they converge on the strobilus morphology found in seed plants, particularly the pollen producing cones of conifers, which have a similar overall function. Using published literature combined with fresh and herbarium specimens, we compiled a data set of morphological characters describing cone size, sporangium size, and plant architecture that includes over 100 extinct and extant lycophyte taxa. We find that lycophytes show a more diverse range of strobilus shapes and sizes than conifer pollen cones, but this variation reflects branch diameter and branching architecture of the parent plant rather than fundamental differences in reproductive biology. For example, herbaceous, arborescent, and smaller, single-trunked “pseudoherbaceous” lycophytes all show different scaling relationships in cone size, sporangium size, and axis diameter. Branching architecture is also more important in determining strobilus morphology than specific differences in reproductive biology within lycophytes, as megasporangiate and microsporangiate strobili of heterosporous lycophytes have essentially the same cone construction. The degree to which lycophyte strobili converge on morphologies seen in euphyllophyte cones therefore appears to reflect plant architecture and branching patterns more than similarities in reproductive biology. Nevertheless, lycophytes show a restricted range of branching patterns and therefore compact strobili that resemble those of conifers and other euphyllophytes are a recurring feature of their evolutionary history.

1 - Brown University, Ecology and Evolutionary Biology, Providence, RI, 02912, USA
2 - Brown University, Ecology and Evolutionary Biology, 80 Waterman Street, Box G-W, Providence, RI, 02912, USA

Keywords:
lycopsids
pollen cone
convergent evolution
conifers
strobilus.

Presentation Type: Oral Paper
Session: 42, Reproductive Biology
Location: 205/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 10:45 AM
Number: 42003
Abstract ID:289
Candidate for Awards:None