Cambios en la longitud cromosómica total en tres poblaciones de Prosopis laevigata (Fabaceae). Implicaciones genecológicas y evolutivas

Abstract

A CYTOGENETIC ANALYSIS WAS MADE ON THREE PROSOPIS LAEVIGATA (WILL..) M.C. JOHNST. (MESQUITE) POPULATION SAMPLES, TWO LOCATED AT INTERTROPICAL LATITUDES AND ONE IN A TEMPERATE LATITUDE IN MEXICO. THE AIM WAS TO COMPARE THEIR MITOTIC AND MEIOTIC CHROMOSOMES IN ORDER TO KNOW THE POSSIBLE RELATIONSHIPS AMONG AN ECO-GEOGRAPHIC GRADIENTS (LATITUDE) AND VARIATIONS IN THE TOTAL CHROMOSOMIC LENGTH, IN ORDER TO ESTABLISH IF THE RELATIONSHIPS REPRESENT A FUNCTIONAL CHARACTERS AND TO ANALYZE THEIR IMPORTANCE IN THE DIFFERENTIATION AND EVOLUTION OF THE SPECIES, AND THUS UNDERSTAND THEIR PRESENT ECO-GEOGRAPHICAL DISTRIBUTION. THE SAMPLED INTERTROPICAL SITES WERE TEHUACAN VALLEY (18° 29'N) IN PUEBLA STATE AND ACTOPAN VALLEY(20º 16'N) IN HIDALGO STATE AND, IN THE TEMPERATE ZONE, BERMEJILLO (25° 49'N) IN DURANGO STATE. THE MITOTIC STUDIES WERE MADE IN ROOT APICES FROM THREE-DAY GERMINATED SEEDS; THE MEIOTIC ONES IN POLLEN MOTHER CELLS FROM IMMATURE ANTHERS FOLLOWING STANDARD TECHNIQUES. THE COMPARATIVE EVALUATION WAS MADE FROM PHOTOGRAPHS AT THE SAME SCALE. RESULTS SHOW A CHROMOSOME NUMBER OF 2N=28 IN ALL POPULATIONS, WITH SIGNFICATIVE DIFFERENCES (ANOWA A=0.01 AND USD, TUCKEY) IN THE TOTAL CHROMOSOMIC LENGTH, IN 2 CELLS, IN THE BERMEJILLO POPULATION WITH RESPECT TO THE TEHUACAN AND ACTOPAN ONES;IN BOTH LENGTHS THE LARGEST CHROMOSOME LENGTH WAS FOUND IN THE BERMEJILLO POPULATION AND THE SMALLEST IN THE ACTOPAN SAMPLE. THIS SUGGESTS: 1) A GENOTYPIC DIFFERENTIATION CORRELATED WITH LATITUDE, AND MORE PRECISELY WITH CYCLIC CHANGES IN THE ENVIRONMENT OF THE POPULATION AND ITS ECOGEOGRAPHY; IN EFFECT, A SMALLER DNA CONTENT PROMOTES SHORT CELLULAR CYCLES AND BRIEF PHENOLOGIC ACTIVITY PERIODS, 2) AN EVIDENCE FAVORING CHROMOSOME REMODELING BY INTERSPECIFIC HYBRIDIZATION WITH P. GLANDULOSA, REPORTED FROM MEXICO. FINALLY, IT IS POSTULATED AS AN EXPLANATORY HYPOTHESIS THAT, WHEN A PLANT SPECIES MIGRATES FROM INTERTROPICAL SITES TO MORE COMPLEX HABITATS, WHEN A PLANT SPECIES MIGRATES FROM INTERTROPICAL SITES TO MORE COMPLEX HABITATS, BY STATIONALITY AND OTHER CYCLIC PROCESSES, ASSOCIATED WITH TEMPERATURE LATITUDES, ITS DNA CONTENT TENDS TO INCREASE IN ORDER TO HAVE A LARGER ANSWER REPERTORIE OF GENETIC OR ONTOGENIC ORIGIN, TO FACE A LARGER VARIABILITY IN THE NEW ENVIRONMENT. IF THIS IS CORRECT, IT WOULD INDICATE THAT P. LAEVIGATA DEVELOPED, AS A SPECIES, IN THE CENTER-SOUTH OF THE MEXICAN PLATEAU, GRADUALLY COLONIZING THE NORTH FOLLOWING THE EVOLUTIONARY TREND OF GENETIC INFORMATION ACCUMULATION.