Gene Flow and Genetic Variability in Cave and Surface Populations of the Mexican Tetra, Astyanax mexicanus (Teleostei: Characidae)
We estimated genetic diversity in cave (hypogean) and surface (epigean) populations of the Mexican Tetra, Astyanax mexicanus, using RAPDs and microsatellites. By either measure, genetic diversity was significantly lower in hypogean than in epigean populations, although there was considerable variability in both classes. We examined three factors potentially influencing genetic diversity among hypogean populations: relative population size, cave isolation, and the presence of eyed fish in the cave. Of the three, only the presence of epigean forms within the caves correlated with increased genetic diversity in cave populations. This suggests that increased genetic diversity of A. mexicanus cave populations reflects introgression of alleles from surface populations. Estimation of migration rates among populations using microsatellites supported this conclusion and also suggested that alleles can move among cave and surface populations more easily than from cave to cave.Abstract
Astyanax mexicanus localities in the Sierra de el Abra region, Mexico. Cave localities: 1 = Molino; 2 = Vásquez; 3 = Pachón; 4 = Yerbaniz; 5 = Subterráneo; 6 = Curva; 7 = Toro; 8 = Chica. Surface fish localities: 4 = Yerbaniz; 5 = Subterráneo; 9 = Arroyo Sarco; 10 = km 70; 11 = km 16; 12 = km 285
Rates of migration among populations of A. mexicanus in northeast Mexico. Compare with Fig. 1. Rectangles (Areas) correspond to regions of surface drainage while ovals correspond to cave populations. Area 1 represents the region to the west of the Sierra de Colmena; Area 2 represents the region between the Colmena and the Sierra de el Abra; Area 3 represents the coastal plain east of the Sierra de el Abra. The arrows represent directions of migration and the thicknesses are proportional to the rates estimated by analysis with Migrate
Contributor Notes
Cave Biology Research Group, Department of Biology, New York University, New York, New York 10003. Current address: (KP) University of Texas, Department of Biology, Arlington, Texas 76001. (RB) rb4@nyu.edu Send reprint requests to RB.