Independent origins of Sphagnum cribrosum waveform

The appearance of drastic morphological variants has been connected to the “punctuated equilibrium” theory of evolution. Here we consider a morphological variant within Sphagnum cribrosum, found at only two lakes, 15 km apart, in the NC Coastal Plain. At the margin of these Carolina Bays,S. cribrosum is so variant that samples in the Duke Herbarium have been mis-identified as the “true moss” Fontinalis. Duke bryologist Lewis Anderson coined the nickname “waveform,” reflecting the hypothesis that the form is an ecological response to wave action at the lake margins. We tested this with a preliminary reciprocal transplant, which suggested that the waveform morphology is genetically, rather than environmentally based.A reasonable hypothesis would be that the waveform diverged from normal form at Singletary Lake, where it co-occurs with the normal form, and then spread to Jones Lake, where there is no normal form. We tested this, using genetic data (3 nuclear DNA sequence loci and 15 microsatellite loci) for samples collected across the entire range from NJ to FL. The results were very surprising: the two wave forms are not at all related! Waveform at Singletary Lake comes from a genetic background that is very different from normal form at Singletary Lake and different from waveform at Jones Lake. Sexual reproduction (evidenced by sporophyte formation) is rare, occurring only in one site in Georgia (which also happens to have the majority of gentic diversity in the species).My role: This study spans nearly the entirety of my scientific career through the first part of grad school– I helped collect the samples as an undergraduate in the Shaw Lab, then learned how to use genetics programs such as Structure and GenAlEx to complete the analysis, and finally published my first first-author paper!

Johnson, M. G., B. Shaw, P. Zhou, and A. J. Shaw. 2012. Genetic analysis of the peatmoss Sphagnum cribrosum (Sphagnaceae) indicates independent origins of an extreme infra‐specific morphology shift. Biological Journal of the Linnean Society 106:137–153. Wiley Online Library. Link. PDF.

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  1. Pingback: Genetic erosion of Platanus racemosa by hybridization - mossmatters

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