The Legacy of a Leaky Dioecy

This is the second in a series of posts reviewing the 17 articles found in the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Science.

The Ecological Side of an Ethnobotanical Coin: Legacies in Historically Managed Trees by Nanci J. Ross, M. Henry H. Stevens, Andrew W. Rupiper, Ian Harkreader, and Laura A. Leben

As much as we like to think otherwise, pre-Colombian Native Americans altered the natural landscape in drastic and measurable ways. What we often consider an unaltered, pristine natural area before European colonization, actually has human fingerprints all throughout it. Determining just how deep these fingerprints go, however, is a challenge that requires careful and thorough anthropological and ecological studies.

Many such studies have been done, mostly at the community and ecosystem level. For example, Native Americans used fire extensively as a land management tool. This is how prairies were maintained as prairies. Today, forests in eastern North America that were once dominated by oaks have shifted over to maple dominated forests. This is largely (although not solely) because anthropogenic fires have ceased and wildfires are now suppressed. If fires had never been used as a management tool, would oaks (an important Native American food source) have ever maintained such dominance?

Native Americans participated in the domestication of numerous plant species. Much of this was done by way of – as Charles Darwin termed it – unconscious selection. Rather than selecting specific individuals and breeding them to achieve a desired type, they would simply discard undesirable plants and maintain desirable ones. Much of this selection, especially for woody, perennial species was done through land management techniques – such as fire – as opposed to typical cultivation. The authors of this article, interested in whether or not the “legacy” of this method of selection through land management could be observed today in an individual species, developed a preliminary study to begin to answer this question.

Diospyros – a genus in the ebony family (Ebenaceae) consisting of around 500 species – is mainly pantropical with a few species occurring in temperate regions. One temperate species is Diospyros virginiana – common persimmon – which “has a broad distribution throughout the United States from Connecticut south to Florida and west to the eastern edge of Nebraska.” Persimmons were used and managed extensively by Native Americans; however, they are “now viewed as a rare, weedy, wild fruit tree that is known primarily by hobbyists and wild harvesters.”

Fruits of common persimmon, Diospyros virginiana )photo credit: Wikimedia commons)

Fruits of common persimmon, Diospyros virginiana (photo credit: wikimedia commons)

D. virginiana is a dioecious species, meaning that it produces male flowers and female flower on separate individuals. Despite this, some individuals have been reported bearing both male and female flowers while others have been seen having perfect flowers along with either male or female flowers. Some trees have even been reported to be dioecious one year and then having perfect flowers and/or some combination of male, female, and perfect flowers the next year. This variation from the norm – what the authors call “leaky dioecy” – can either be a result of artificial selection or environmental pressures. The authors hypothesized that “leaky dioecy in D. virginiana is a result of historical selection by Native Americans for trees with copious fruit production.” This preliminary study was designed to see if climate and soil conditions might be the reason for the observed “sex expression.”

Skipping ahead, the authors found “no compelling evidence…to suggest segregation due to environmental factors,” signaling them to “move forward in [their] investigation of potential long-term impacts of historical management on the evolution of reproductive traits in American persimmon without the noise of a strong environmental driver.” The authors go on to discuss challenges in their study, including the length of time since “extensive management” making it hard to “uncover a signal of precontact management” and the limitations of having to rely on herbarium specimens. Either way, it is a worthy study to pursue. Even if it does not reveal the full story of how Native Americans managed persimmons in pre-colonial times, further insight into “adaptive flexibility in reproductive systems of long-lived perennial species” and other interesting things that persimmons might teach us will be well worth the effort.

Characteristic bark of common persimmon, Diospyros virginiana (photo credit: www.eol.org)

Characteristic bark of common persimmon, Diospyros virginiana (photo credit: www.eol.org)

 

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One thought on “The Legacy of a Leaky Dioecy

  1. Pingback: Speaking of Food: A Recap | awkward botany

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