Agronomic conditions in ancient Near East 12,000 years ago

Researchers describe the characteristics of agriculture at its beginnings by comparing kernel and wood samples from ancient Near East sites —- the birthplace of Western agriculture -- with present day samples. It is the first time that direct evidences enable to know humidity and fertility conditions of crops, as well as the process of cereal domestication developed by humans from the Neolithic (12,000 years ago) to early Roman times (around 2,000 years ago).

A study co-headed by Josep Lluís Araus, professor from the University of Barcelona (UB), Juan Pedro Ferrio, Ramón y Cajal researcher at Agrotecnio of the University of Lleida (UdL), and Jordi Voltas, professor from Agrotecnio, describes the characteristics of agriculture at its beginnings by comparing kernel and wood samples from ancient Near East sites -- the birthplace of Western agriculture -- with present samples. It is the first time that direct evidences enable to know humidity and fertility conditions of crops, as well as the process of cereal domestication developed by humans from the Neolithic (12,000 years ago) to early Roman times (around 2,000 years ago).

The study has been published in the journal Nature Communications. Researchers Ramon Buxó, archaeologist and director of the Archaeological Museum of Catalonia-Girona, and Mònica Aguilera, UdL researcher who is now working at the Paris Natural History Museum, participated in the study too.
Researchers used crop physiology techniques to analyse archaeobotanical remains. In total, they analysed 367 kernels -- for instance, barley and wheat -- , and 362 wood samples obtained in eleven archaeological sites from Upper Mesopotamia, which includes present south-eastern Turkey and northern Siria, to the Near East. Studied kernels belong to present crops of wheat and barley species that are similar to the archaeological remains found in the region.

Progressive domestication
Researchers compared the size of kernel remains with present samples to determine the evolution of crop domestication. "The methodology used to date does not reproduce real size; it measures width and long of charred kernels," explains Josep Lluís Araus, professor from the Department of Plan Biology of UB. "We have reconstructed cereal kernel weight -- adds the expert -- and seen that it increased for a longer period of time than it was thought, probably during several millenniums." According to the researcher, the initial selection of kernel was "unconscious," in other words, first farmers selected the biggest kernels, so size increased progressively.

Wetter and more fertile soils

Sample analysis of carbon and nitrogen isotope compositions -- a technique used in crop physiology and improvement -- was a key factor to describe the conditions of the area. On one hand, "Carbon isotope composition enables to evaluate water availability for crops. It reached its maximum level 9,000 years ago, and then it decreased progressively until the beginning of our times," points out Araus. In any case, researchers have not found conclusive evidences about the use of irrigation as a common practice. "This information together with cereal kernel weight allows assessing the productivity of ancient crops," highlights Josep Lluís Araus.
On the other hand, nitrogen isotope composition provides information about soil's organic matter and fertility. Juan Pedro Ferrio (Agrotecnio-UdL) affirms that "although they were dryland crops, it can be affirmed that nitrogen was much more available than today: undoubtedly, soils were much more fertile than nowadays." Moreover, it can be observed a progressive decrease of soil fertility, probably due to over-exploitation or the use of less fertile soils, but also to more extreme climate conditions.
These data enable to describe more precisely agronomic conditions and the evolution of human populations linked to agricultural practices. "The study relates conditions like water availability or soil fertility to crops yield," states Josep Lluís Araus. Past yields, compared with average calorie needs of one person, enable, for example, to have a rough idea of the crop area needed to feed the population. "This information -- adds Araus -- can be used to know more precisely the borders of past settlements and the evolution of human communities. The aim is to include all this information in models in order to better understand the past," concludes the researcher.

Source:

http://www.sciencedaily.com/

José L. Araus, Juan P. Ferrio, Jordi Voltas, Mònica Aguilera, Ramón Buxó.Agronomic conditions and crop evolution in ancient Near East agriculture.Nature Communications, 2014; 5 DOI: 10.1038/ncomms4953

What can plants reveal about gene flow? That it's an important evolutionary force

How much gene flow is there between plant populations? How important is gene flow for maintaining a species' identity and diversity, and what are the implications of these processes for evolution, conservation of endangered species, invasiveness, or unintentional gene flow from domesticated crops to wild relatives?

A plant breeder discovers his experimental crops have been "contaminated" with genes from a neighboring field. New nasty weeds sometimes evolve directly from natural crosses between domesticated species and their wild relatives. A rare plant is threatened due to its small population size and restricted range. What do all these situations have in common? They illustrate the important role of gene flow among populations and its potential consequences. Although gene flow was recognized by a few scientists as a significant evolutionary force as early as the 1940s, its relative role in maintaining a species' genetic integrity and/or its diversity has been debated over the decades, vacillating from trivial to critical.
So how much gene flow is there between plant populations? How important is gene flow for maintaining a species' identity and diversity, and what are the implications of these processes for evolution, conservation of endangered species, invasiveness, or unintentional gene flow from domesticated crops to wild relatives?
Norman Ellstrand, a plant geneticist at the University of California, Riverside, is interested in many aspects regarding gene flow, especially in applied plant biology, and has spent more than 25 years considering the possibility and potential impacts of unintended gene flow from genetically engineered crops. As part of theAmerican Journal of Botany's Centennial Review series, Ellstrand reviews the history of gene flow, focusing on plants, and provides evidence for its importance as an evolutionary force.
Selection, mutation, gene flow, and genetic drift, are the four mechanisms that lead to biological evolution, or a change in allele frequencies in a population over time. Just how important are each of these forces relative to each other?
Interestingly, Ellstrand points out that evolutionary biologists' view on the importance of gene flow has waxed and waned over the last century. Although it was first seen in the 1940s to be the evolutionary glue that held species together, and thus a significant evolutionary force, a few decades later when quantitative data on gene flow in plant populations began being collected, this view changed as evidence seemed to indicate that gene flow was not all that significant.
Not only was intra-specific gene flow among populations seen to be minimal at that time, but, somewhat incongruously, inter-specific hybridization, or the movement of genes among species, was seen to be a much larger force in evolution than intra-specific allele movement. At the time the main concern for plant breeders was pollen movement between different strains of crops -- if a variety of sweet corn was contaminated by pollen from a popcorn variety, then the resulting hybrid offspring would produce seeds that were unusable for market purposes or for selecting new varieties. Increasing the distance between plots of different varieties was seen to be the best solution to this problem.
However, beginning in the 1980s the tide turned again due to mounting evidence from new approaches: parentage and spatial population genetic structure studies.
"When I first started doing plant paternity studies in the 1980s," Ellstrand comments, "our lab assumed that gene flow was limited. But we kept identifying 'impossible fathers' that could not be assigned to our study population. Surely, these couldn't be fathers from outside of our wild radish populations -- hundreds of meters away? But after excluding all other possibilities, the improbable turned out to be the answer. And the paradigm of limited gene flow in plants began to crumble."
Indeed, one of the amazing things that parentage studies revealed is just how far genes could flow -- from hundreds to thousands of meters in some cases. In one extraordinary case, a study found that the nearest possible paternal sire of an individual fig tree was 85 km away!
With the advent of more and more sophisticated ways to measure genetic variation and relatedness using molecular markers, such as allozyme polymorphisms and DNA-based markers, not only can individuals be tracked as to their parentage, but changes in allele patterns over time and thus the effects of evolution on populations can be "seen" in the genetic information.
As it turns out, despite the initial skepticism about the importance of gene flow, modern empirical and theoretical research using up-to-date molecular and DNA techniques have shown us not only how surprisingly far the flow of genes between distant plant populations can be, but also that the flow of alleles among populations is just as important, if not more so in some cases, as natural selection. Indeed, even just a low level of gene flow between populations can counter opposing forces of mutation, genetic drift, and selection.
"Just like selection, gene flow is one of the evolutionary forces -- and a potentially important one," notes Ellstrand. And plants are very well suited for studies on gene flow because individuals are stationary yet pollen and seeds are mobile.
However, an important caveat that Ellstrand reports in his review is that the relative importance of gene flow can vary tremendously among species and among populations, and can be as low as no gene flow at all to very high rates of gene flow.
"This review paper tells the story of gene flow's rise to respect among plant evolutionary biologists," he concludes, "a fact that hasn't yet penetrated biology in general that is still mired in selection/adaptation-only thinking."

Source:
http://www.sciencedaily.com/

N. C. Ellstrand. Is gene flow the most important evolutionary force in plants?American Journal of Botany, 2014; 101 (5): 737 DOI: 10.3732/ajb.1400024