It comprises 155–320 species mainly distributed in Mexico ( Reppenhagen, 1992 Guzmán et al., 2003 Hunt et al., 2006 Hernández and Gómez-Hinostrosa, 2015 Villaseñor, 2016). Mammillaria is the most diverse genus within the Cactaceae family. Therefore, we attempt to provide elements to this discussion in plant evolution, studying the root development of Mammillaria species. macro-evolutionary divergence has been indirectly addressed in the determinate primary growth of the root apex, a highly conserved trait in the subfamily Cactoideae ( Shishkova et al., 2013 Rodriguez-Alonso et al., 2018) in which the timeframe of this apex determination is correlated with environmental factors, within and between species ( Martino et al., 2018) however, the number of species and accessions are low to draw conclusions about the nature of evolutionary divergence. One of the few examples is the case of cacti, in which the comparison of micro- vs. Despite the relevance of the question for the understanding of evolution and development of breeding strategies, in plants, to our knowledge there are very few comprehensive cases where these ideas have been tested at the morphological or genetic level. This is because regardless of their adaptive value, phenotypic differentiation has been suggested to be frequently rapid, and random in direction, involving the evolution of gene regulation, pleiotropy, epistasis and canalization ( Davis and Gilmartin, 1985), which in turn could result in different nature of the variation within and between species. On the other hand, it has been argued that morphological divergence between species is often non-adaptive, as compared to variation within species. Furthermore, in model species such as Drosophila, it has been experimentally shown that the genetic variation explaining divergent pigmentation patterns among species, are shared with the genetic variation displayed within species ( Wittkopp et al., 2009). This possibility has been tested in some organisms such as crocodiles, in which intraspecific crane variation (a highly robust trait) spans half of the extant species ( Okamoto et al., 2015). One possibility is that the macroevolutionary outcomes are the result of the cumulative microevolutionary processes, so the footprint of microevolution can be seen at higher levels of taxonomic divergence. These phenotypic outcomes at different evolutionary time-scales can be interpreted as macroevolution being the cumulative outcome of microevolutionary phenotypic divergence, such as the one observed in Mammillaria accessions and species.Ī long standing debate in evolutionary biology is whether the nature of macroevolutionary change can be explained based on the principles and processes of microevolution. When plants were grown in controlled environments, we found that the variation in root architecture observed at the intra-specific level, partially recapitulates the variation observed at the inter-specific level. Finally, we compared these patterns of variation to what is found in a set of Mammillaria species belonging to different Series (diverging for the last 8 million years). Then we compare this variation to closely related species within the Series Supertexta in Mammillaria (diverging for the last 2.1 million years) in which M. First, we show the patterns of variation in natural variants of the species Mammillaria haageana. Here we show the patterns of root architecture development in a gradient of divergent lineages, from populations to species in Mammillaria. Genetic mechanisms controlling root development are well-understood in plant model species, and emerging frontier research is currently dissecting how some of these mechanisms control root development in cacti.
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