Chromosome number variation and evolution in Neotropical Leguminoseae (Mimosoideae) from northeastern Brazil

• Published in: Genetics and molecular research 2012-01, Vol.11 (3), p.2451-2475
• Main Authors: Santos, E C X R, Carvalho, R, Almeida, E M, Felix, L P
• Format: Article
• Language: English
• Subjects: Brazil; Cell Nucleus - genetics; Chromosomes, Plant - genetics; Evolution, Molecular; Fabaceae - genetics; Genetic Variation; Interphase - genetics; Species Specificity; Tropical Climate
• ISSN: 1676-5680; 1676-5680
• DOI: 10.4238/2012.June.27.1

Most members of the subfamily Mimosoideae have pantropical distributions, variable habits, and a basic chromosome number x = 13. We examined karyotypic evolution of 27 species of this subfamily occurring principally in northeastern Brazil by examining chromosomes stained with Giemsa. All of the species had semi-reticulated interphase nuclei and early condensing segments in the proximal region of both chromosome arms. The basic number x = 13 was the most frequent, with 2n = 2x = 26 in 19 of the species, followed by 2n = 4x = 52 and 2n = 6x = 78. However, the three species of the genus Calliandra had the basic number x = 8, with 2n = 2x = 16, while Mimosa cordistipula had 2n = 4x = 32. The karyotypes were relatively symmetrical, although bimodality was accentuated in some species, some with one or two acrocentric pairs. As a whole, our data support earlier hypotheses that the Mimosoideae subfamily has a basic number of x = 13 and underwent karyotypic evolution by polyploidy. However, x = 13 seems to be a secondary basic number that originated from an ancestral stock with x₁ = 7, in which polyploidy followed by descending disploidy gave rise to the current lineages with x = 13. Another lineage, including current representatives of Calliandra with x = 8, may have arisen by ascending disploidy directly from an ancestral monoploid stock with x₁ = 7.