Spring is, at last – and in the branches of the trees boil battle. Robin returns to his nest with earthworms. Her nests all beg, but only one will get that food. And while Mama has an interest in making sure all her babies are thriving, every little bird is more selfish. So the baby reopens its beak again and again: Give me more!
Now imagine a similar clash playing in the same tree. A new study at St. Louis University, Washington, reveals the surprising way in which family quarrels in seeds cause rapid evolution. Researchers in the arts and sciences find that the conflict around the amount of resources the offspring receives from its parent seems to play a special role in the development of certain tissue seeds. The study will be published on the week of April 22 in London Notifications of the National Academy of Sciences,
The plant seeds contain tissues that represent three different genetic relatives: the mother, the embryo, and the strange triple tissue called the endosperm involved in the transfer of nutrients from the mother to the embryo.
Katherine Geist, PhD candidate in the lab led by David S. Cooler, Professor of Biology in Arts and Sciences Spencer T. Olin, and Joan Strasman, Professor of Biology Charles Rebstock, used genomic data from the model installation, Arabidopsis thaliana, to highlight the dispute between these three countries about how much resources should be given to the embryo.
"When we think of how conflicts between parents and offspring may occur, we tend to think there should be two different interacting parties, mother and baby," said Geist. Every baby wants more for herself than for her brothers and sisters, while the mother wants a fair division between her offspring.
Robin breeds begging for the earthworm, for example. Human babies cry.
"It might not be so obvious in the seeds," said Geist. "But all this happens at the hormonal and cellular level.
"These are different parties with different genetic interests," she said.
Everything in the family
This year, Queller and Strassmann work as scholars at the Wissenschaftskolleg, an advanced institute in Berlin. They are best known for their work on social evolution in amoeba and in societies. The new study deals with plant issues and is a test of the theoretical selection model Quell has studied decades ago, initially as a student.
Evolutionary conflict often leads to a faster evolution – sometimes referred to as the "arms race" – as competing interests strive to build one after another generation after generation. This interaction is best recognized where conflicts are very strong, such as the host-pathogen conflict.
"But connectivity is expected to reduce the conflict," Queller said. "We wanted to see if conflicts between relatives nevertheless lead to rapid evolution in line with the evolutionary arms race."
Earlier published genomic data on Arabidopsis identified the genes specializing in different parts of the body of the parental plant, as well as those for its seminal tissues and sub-tissues. Graduate student Geist thoroughly scanned through numerous reps of this data about his focus type Arabidopsis and several of his cousins.
It compares adaptive evolution rates in genes that control growth in different parts of plants.
Geist finds higher levels of adaptive evolution for genes regulated in seeds than in other plant organs such as floral buds, stems, leaf rosettes and roots. In addition, she finds more evidence of adaptive evolution in genes expressed in endosperm and maternal tissues than in embryos and more in sub-tissue of seeds that are specifically involved in nutrient transfer.
"We see the predicted pattern of molecular evolution of rapid adaptation in the regions of genes involved in resource allocation, but not in those likely to be just storage," Geist said.
The results support the predictions that weapons competitions come not only from irreconcilable enemies – such as hosts and pathogens – but also from smaller battles in families. They also suggest that the families of the plants have the same kinds of quarrels as the animals.
The social interactions studied in this study may have an impact on the size of the seeds that can be investigated in future work, researchers say. The final size and nutritional value of seeds is important for people who rely on grains such as rice, wheat, barley and cinema as the world's main food sources.
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