Allelic variation in these loci have been associated with flowering time variations between plants. For example, "Arabidopsis thaliana" ecotypes that grow in the cold temperate regions require prolonged vernalization before they flower, while the tropical varieties and common lab strains, do not. Much of this variation is due to mutations in the "FLC" and "FRIGIDA" genes, rendering them non-functional. Many genes in the flowering time pathway are conserved across all plants studied to date. However, this does not mean that the mechanism of action is similarly conserved. For example, the monocot rice accelerates its flowering in short-day conditions, while "Arabidopsis thaliana", a eudicot, responds to long-day conditions. In both plants, the proteins "CO" and "FT" are present but in "Arabidopsis thaliana" "CO" enhances "FT" production, while in rice the "CO" homolog represses "FT" production, resulting in completely opposite downstream effects. There are many theories that propose how flowers evolved. Some of them are described below. The "Anthophyte Theory" was based on the observation that a gymnospermic family Gnetaceae has a flower-like ovule. It has partially developed vessels as found in the angiosperms, and the megasporangium is covered by three envelopes, like the ovary structure of angiosperm flowers. However, many other lines of evidence show that gnetophytes are not related to angiosperms. The "Mostly Male Theory" has a more genetic basis. Proponents of this theory point out that the gymnosperms have two very similar copies of the gene "LFY" while angiosperms only have one. Molecular clock analysis has shown that the other "LFY" paralog was lost in angiosperms around the same time as flower fossils become abundant, suggesting that this event might have led to floral evolution. According to this theory, loss of one of the "LFY" paralog led to flowers that were more male, with the ovules being expressed ectopically. These ovules initially performed the function of attracting pollinators, but sometime later, may have been integrated into the core flower. Plant secondary metabolites are low molecular weight compounds, sometimes with complex structures that have no essential role in primary metabolism. They function in processes such as anti-herbivory, pollinator attraction, communication between plants, allelopathy, maintenance of symbiotic associations with soil flora and enhancing the rate of fertilization.