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Dr. Dolores Piperno, Research
List of Piperno Current Research Projects
Developmental Plasticity and Crop Plant Evolution
Fundamental new insights about the origin of phenotypic variation and novel traits are arising from the related fields of evolutionary developmental biology (a recent merging of evolutionary and developmental biology) and phenotypic (developmental) plasticity. This and other research is leading to a broadening of the Modern Synthesis and a revolution in our understanding of how evolution works. However, these concepts, which encompass plastic responses by organisms to perturbations in their external and internal environments through developmentally-mediated changes in gene expression have not been applied to the domestication of plants. Piperno and colleagues at STRI and Jeff Ross-Ibarra at University of California, Davis recently started an investigation of the effects of environmental change on phenotypic characteristics in maize’s wild ancestor teosinte (Zea mays ssp. parviglumis). Environmental growing chambers at the STRI are being used to re-create the atmospheric CO2 and temperature conditions that characterized those of the late-glacial and terminal Pleistocene periods, shortly before maize and other crops were taken under cultivation and domesticated (see image). Among the questions we are asking is if environmental inductions caused either by natural or human factors could have been directly responsible for some of the important phenotypic traits that separate wild and domesticated maize. These domestication traits have traditionally been considered a result of human selection during cultivation that acted on genetic mutations. Under the scenario investigated here, human influence would have begun after nature and gene expression engineered some of the phenotypic steps by re-organizing pre-existing variation early in plant development.
This research will continue for at least the next six years and will incorporate necessary molecular and other work. Gene expression studies focusing on whole transcriptome work will be carried out in Ross-Ibarra’s laboratory with new methods such as RNA-Seq to investigate whether phenotypic changes are a result of plastic responses to environmental perturbation and not to mutational changes, and to examine broader characteristics of the transcriptome-related features associated with domestication in the plants. In addition, we will carry out artificial selection studies on interesting phenotypes, in part to test a concept called genetic assimilation, which could plausibly account for the heritability of the phenotypes and ultimately their expression in all environments. This concept was advanced by some prominent scholars during the early period of the Modern Synthesis, but was shoved out of the mainstream of evolutionary thinking when population genetics began to ascend. It is envisioned that other wild progenitors of important crops may be similarly studied in this research in the future.
This research will also provide some of the first information on phenotypic and other characteristics of plants (e.g., growth rates and developmental strategies; seed size/morphology, fertility, and yield; pollen, starch, and phytolith characteristics; pollen production and fertility) in ice age environments, which world-wide contained 33% less ambient CO2 concentrations and were much cooler and drier than today’s over much of the planet. Many plants in addition to wild progenitors of domesticated species existed in these conditions for 80% of the time during the past two million years. Because future phenotypic and physiological responses by plants to environmental change will be largely effected through gene expression, a successful result would also shed light on the possible effects of future climate change.
Pre-Columbian Human Alteration of Amazonian Forests
Some prominent anthropologists and archaeologists now believe that most of prehistoric Amazonia was a "A Cultural Parkland" or a human-created "Built landscape", inferring from a limited number of archaeological sites that lowland forests throughout the Amazon Basin were densely inhabited and significantly altered by pre-Columbian human populations. Despite the limited evidence for such a major human presence, this view (dubbed by Piperno and colleagues the "1491" hypothesis after its sympathetic treatment in a 2005 book of that name by popular science writer Charles Mann) has been prominently featured in the mass media and may come to influence views and policy on Amazon forest resilience and sustainability. Three years ago, Piperno and Mark Bush and Crystal McMichael of Florida Institute of Technology, supported by a three-year NSF grant, began a large-scale test of the 1491 hypothesis. Soil profiles have been sampled from underneath forest along long transects through the Peruvian and Brazilian Amazon, and their phytolith and charcoal records are being analyzed. Results are providing vegetational and fire histories spanning a broad area of yet unstudied terra firme (non-riverine forest) landscape. The information is also being expressed at finer spatial scales than possible with sedimentary records from lakes and swamps, which offer a single, homogenized picture derived from a large source area that may have seen variable environmental histories exhibited at smaller distance scales.
In addition to its anthropological importance, our research has significance for modern ecological research and conservation efforts. Ecologists would like to know if past vegetation, fire, and soil dynamics are affecting the current state of the vegetation and carbon balances. Furthermore, the sustainable development of the Amazon's remaining biodiversity and natural resources, in part dependent on their history and regenerative capacity, is a crucial issue facing conservation biologists and planners. They would benefit from an empirically-robust picture of how resilient these forests are after major disturbances.
Agricultural Origins and Dispersals in Lowland Mesoamerica, Central and South America
The major projects related to this topic involve analyzing microfossil remains of plants (phytoliths, starch grains, and pollen) and continuing to build modern reference collections of them. A few years ago Piperno and colleagues from STRI and Temple University finished the first phase of a project that explored early human settlement and agriculture in the Balsas River Valley of Mexico, where molecular research indicates maize was domesticated. Human settlements dating to the early Holocene were found, and phytolith and starch grain analysis of grinding stones dating to 8700 BP indicated the presence of domesticated maize and squash at that time (see Piperno et al. 2009 in PNAS). This information adds to the corpus of interdisciplinary data indicating that maize was domesticated by about 9000 years ago and then spread not long afterwards into other regions of the lowland seasonal tropical forest. Other archaeological and molecular work has provided a considerable amount of information recently on the geography and chronological history of the numerous crop plants domesticated in the lowland Neotropical forest (see images).
Other research involves on-going archaeobotanical work at Huaca Prieta, a famous archaeological site located on the coast of Peru that was first excavated many years ago by Junius Bird. The Peruvian government recently asked archaeologist Tom Dillehay to re-excavate and re-analyze the various kinds of cultural remains present at the site. Piperno is carrying out starch grain work on human teeth, stone tools, and sediments from the new excavations. The new excavations are revealing much about early settlement and agriculture in the region and appear to be leading to new interpretations of crop plant presence and antiquity, as well as on the overall nature and chronology of human occupation.
Piperno Current Research Projects
- Developmental Plasticity and Crop Plant Evolution
- Prehistoric Human Alteration of Amazonian Forests
- Agricultural Origins and Dispersals in Lowland Mesoamerica, Central and South America
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