POLYPLOIDY AND GENOME SIZE VARIATION IN PHLOX NANA (POLEMONIACEAE) FROM THE PECOS PLAINS OF NEW MEXICO AND THE DAVIS MOUNTAINS OF WEST TEXAS, U.S.A

• Published in: Journal of the Botanical Research Institute of Texas 2017-11, Vol.11 (2), p.351-362
• Main Authors: Ladner, Jamie, Mayfield, Mark H., Prather, L. Alan, Ferguson, Carolyn J.
• Format: Article
• Language: English
• Subjects: SYSTEMATICS
• ISSN: 1934-5259

Polyploidy is conspicuous in the genus Phlox, and some species exhibit variation in ploidy levels, or cytotypic variation. Diploid, tetraploid and hexaploid populations of P. nana occur across parts of the species distribution in the southwestern United States and northern Mexico. A recent study highlighted two areas for which ploidy level inferences were challenging: a population on the Pecos Plains of New Mexico ("Caprock") and the Davis Mountains region of West Texas. Plants in these areas were sampled and chromosome counts and flow cytometry methods were used to assess ploidy levels and genome sizes. Homoploid variation in genome size was unambiguously documented: the genome size of tetraploid plants from the Davis Mountains was significantly larger than that of plants from Caprock. The general condition of larger genome sizes for plants in the Davis Mountains explains previous difficulty in determining ploidy levels within the region. Most plants at the Caprock population appeared to be tetraploid (2n=28), but chromosome counts revealed variants, including some putative pentaploids. Within the Davis Mountains region, both diploid (2n=14) and tetraploid (2n=28) cytotypes were documented, with a parapatric distribution. Overall, this study clarifies patterns of cytotypic diversity in P. nana, highlights an example of infraspecific, homoploid genome size variation, and contributes to a framework for ongoing evolutionary investigation in this study system. La poliploidía es notable en el género Phlox, y algunas especies exhiben variación en sus niveles de ploidía, o variación cliotipica. Poblaciones diploides, tetraploides y hexaploides de P. nana ocurren en varias partes de la distribución de la especie en el suroeste de los Estados Unidos y el norte de México. Un estudio reciente destacó dos áreas para las cuales las inferencias del nivel de ploidía eran difíciles: una población en Pecos Plains de Nuevo México ("Caprock") y la región de Davis Mountains en el oeste de Texas. Se tomaron muestras de plantas en estas areas y se usaron recuentos de cromosomas y citometria de flujo para evaluar los niveles de ploidia y los tamaños del genoma. Se documentó sin ambigüedad la variación homoploide en el tamaño del genoma: el tamaño del genoma de las plantas tetraploides de Davis Mountains fue significativamente mayor que el de las plantas de Caprock. La condición generai de tamaños de genoma mayores para las plantas en Davis Mountains explica la dificultad previa