Revisão cromossômica das espécies da tribo Andropogoneae (Poaceae: Panicoideae) e suas contribuições para a evolução do grupo

Abstract

This dissertation explores the chromosomal evolution of species in the tribe Andropogoneae, which belongs to the family Poaceae, one of the largest families of angiosperms with approximately 11,783 species. The tribe Andropogoneae is diverse and complex, containing 1,224 species organized into 14 subtribes and 92 genera, predominantly in pantropical grasslands. A detailed search of the literature and databases was conducted to obtain chromosomal information for 230 species of the tribe and related tribes. The phylogenetic tree of Andropogoneae by Welker et al. (2020), based on complete plastome sequencing, was used to analyze chromosomal evolution. The reconstruction of the ancestral chromosomal number was performed using the methodology of Angulo et al. (2022), employing MrModeltest software to select the evolutionary model (GTR+G+I) and Bayesian inference for reconstructing the phylogenetic tree, with character optimization carried out in Mesquite. The results revealed 46 chromosomal number variations (2n), ranging from 2n = 8 to 2n = 140, with 30% of the species showing polyploidy. The chromosomal number 2n = 20 was identified as the ancestral state for most internal nodes of the tree, while higher chromosomal numbers were found in more recently divergent taxa. This suggests multiple events of polyploidization and other chromosomal changes throughout evolution. For the subtribe Andropogoninae, the analysis confirmed the predominance of 2n = 20, indicating it may be the ancestral chromosomal number for many genera. The research highlights the need for more chromosomal data to fill important gaps, allowing for a more complete understanding of chromosomal diversity and evolutionary mechanisms within the Andropogoneae tribe. Future studies should focus on collecting and analyzing additional data to clarify the evolutionary dynamics and processes shaping chromosomal variation in this tribe.