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Abstract Detail



Pteridological Section/AFS

Johnson, Anne Kathleen [1], Grusz, Amanda [2], Beck, James [3], Pryer, Kathleen [4], Windham, Michael [4].

So, if they are evolutionary dead-ends, why are apomictic cheilanthoid ferns more widely distributed than their sexual diploid progenitors?

Apomixis (the production of embryos without sex) is common in ferns, where about 10% of named species are obligate apomicts or include apomictic populations. This reproductive pathway is especially prevalent among cheilanthoid ferns (Pteridaceae), a clade of ca. 500 species that exhibits a variety of adaptations to terrestrial xeric habitats generally avoided by other ferns. Apomixis actually may be one of these adaptations, allowing ferns occurring in xeric habitats to complete their life cycles in the absence of the mesic conditions required for sexual reproduction by means of free-swimming sperm. Although apomicts often are considered evolutionary dead-ends and recent work in the cheilanthoid species Astrolepis integerrima reveals a rapid turnover rate of apomictic lineages, there is at least one realm in which apomicts have an apparent advantage over their sexual relatives. Among cheilanthoid species with both sexual diploid and apomictic populations, the apomicts are nearly always more abundant and broadly distributed than their sexual diploid counterparts. What explains this apparent discrepancy between basic evolutionary theory and observed geographic distributions? Ferns in general are thought to have a high potential for long-distance dispersal (with very small spores easily transported by wind) and establishment (with bisexual gametophytes that could, through selfing, give rise to new sporophytes following dispersal of a single spore). However, our research shows that this potential is rarely realized in the sexual diploid cheilanthoids we sampled. In these species, individual gametophytes remained exclusively unisexual for the duration of the experiment, thus requiring interactions with gametophytes derived from other spores to produce viable sporophytes. Such a highly outcrossed breeding system places severe constraints on establishment following a long distance dispersal event. All apomictic individuals, on the other hand, produced new sporophytes from a single spore in a remarkably short period of time. This ability to establish a new sporophytic population from a single spore confers a clear advantage on apomictic individuals and might explain why they tend to occupy much broader geographic ranges.

Broader Impacts:


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1 - Duke University, Department of Biology, Durham, NC, 27708, USA
2 - Duke University, Box 90338, Durham, NC, 27708, USA
3 - Wichita State University, Biology, 1845 Fairmount, Box 26, Wichita, KS, 67260-0026, USA
4 - Duke University, Department of Biology, Box 90338, Durham, NC, 27708, USA

Keywords:
apomixis
breeding system
gametophytes
cheilanthoid ferns
long-distance establishment
xeric
Pteridaceae.

Presentation Type: Oral Paper:Papers for Sections
Session: 34
Location: Melrose/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 2:45 PM
Number: 34006
Abstract ID:803
Candidate for Awards:Edgar T. Wherry award


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