PT  - JOURNAL ARTICLE
AU  - Paul Bilinski
AU  - Patrice S. Albert
AU  - Jeremy J. Berg
AU  - James A Birchler
AU  - Mark Grote
AU  - Anne Lorant
AU  - Juvenal Quezada
AU  - Kelly Swarts
AU  - Jinliang Yang
AU  - Jeffrey Ross-Ibarra
TI  - Parallel altitudinal clines reveal adaptive evolution of genome size in <em>Zea mays</em>
AID  - 10.1101/134528
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 134528
4099  - http://biorxiv.org/content/early/2017/05/05/134528.short
4100  - http://biorxiv.org/content/early/2017/05/05/134528.full
AB  - While the vast majority of genome size variation in plants is due to differences in repetitive sequence, we know little about how selection acts on repeat content in natural populations. Here we investigate parallel changes in intraspecific genome size and repeat content of domesticated maize (Zea mays) landraces and their wild relative teosinte across altitudinal gradients in Mesoamerica and South America. We combine genotyping, low coverage whole-genome sequence data, and flow cytometry to test for evidence of selection on genome size and individual repeat abundance. We find that genetic drift alone cannot explain the observed variation, implying that clinal patterns of genome size are likely maintained by natural selection. Our modeling provides little evidence of selection on individual repeat classes, suggesting that repetitive sequences are under selection primarily due to their contribution to genome size. To better understand the phenotypes driving selection on genome size, we conducted a growth chamber experiment using a highland teosinte from a single population varying more than 1Gb in 2C genome size. We find no evidence of a correlation between genome size and cell size, but do find statistical support for a negative correlation between genome size and cell production. Re-analysis of published shoot apical meristem data further identifies a negative correlation between cell production rate and flowering time. Together, our data suggest a model in which variation in genome size is driven by natural selection on flowering time across altitudinal clines, connecting repetitive sequence variation to important differences in adaptive phenotypes.