Abstract
We estimated the genetic variability of nine fish species from the Brazilian upper Paraná River floodplain (Astyanax altiparanae, Hoplias malabaricus, Leporinus lacustris, Loricariichthys platymetopon, Parauchenipterus galeatus, Pimelodus maculatus, Rhaphiodon vulpinus, Roeboides paranensis and Serrasalmus marginatus) based on data for 36 putative allozyme loci obtained using corn starch gel electrophoresis of 13 enzymatic systems: aspartate aminotransferase (EC 2.6.1.1), acid phosphatase (EC 3.1.3.2), esterase (EC 3.1.1.1), glycerol-3-phosphate dehydrogenase (EC 1.1.1.8), glucose-6-phosphate dehydrogenase (EC 1.1.1.49), glucose-6-phosphate isomerase (EC 5.3.1.9), Iditol dehydrogenase (EC 1.1.1.14), isocitrate dehydrogenase - NADP+ (EC 1.1.1.42), L-lactate dehydrogenase (EC 1.1.1.27), malate dehydrogenase (EC 1.1.1.37), malate dehydrogenase-NADP+ (EC 1.1.1.40), phosphoglucomutase (EC 5.4.2.2) and superoxide dismutase, (EC 1.15.1.1). The mean expected heterozygosity varied from zero to 0.147. When data from the literature for 75 species of tropical fish were added to the nine species of this study, the heterozygosity values differed significantly among the groups of different reproductive strategies. The highest mean heterozygosity was for the non-migratory without parental care, followed by the long-distance migratory, and the lowest mean was for the non-migratory with parental care or internal fecundation.
Highlights
The reactions that species offer to environmental selective pressures is reflected in their physiological strategies, which can reduce maintenance energy, increase the efficiency of energy acquisition and, optimize reproductive efficiency
The calculated genetic variability values for each species are presented in Table 3, from which it can be seen that the greatest frequency of polymorphic loci, average number of alleles per locus and heterozygosity were obtained for A. altiparanae, followed by H. malabaricus
All loci were in Hardy-Weinberg equilibrium (HWE) for L. lacustris, L. platymetopon, P. maculatus, R. vulpinus and R. paranensis
Summary
The reactions that species offer to environmental selective pressures is reflected in their physiological strategies, which can reduce maintenance energy, increase the efficiency of energy acquisition and, optimize reproductive efficiency. The success of such strategies may be estimated by the individual ability of being genetically present in the offspring (Agostinho and Júlio Jr., 1999). Nevo (1988) analyzed the relationship between heterozygosity and ecological and biological features such as climate (arctic, temperate and tropical), geographic range (wide, narrow, endemic), habitat type (underground, terrestrial, aquatic), habitat range (specialist, generalist) aridity (arid, sub-arid, sub-humid, mesic with a moderate or well-balanced moisture supply) and territoriality (territorial, non-territorial) in 1,111 species (vertebrates, invertebrates, and plants) and concluded that environmental heterogeneity is the major factor in maintaining and structuring genetic diversity in natural populations. Several authors have tried to explain the mechanisms which maintain genetic variability in natural populations. Nevo (1988) analyzed the relationship between heterozygosity and ecological and biological features such as climate (arctic, temperate and tropical), geographic range (wide, narrow, endemic), habitat type (underground, terrestrial, aquatic), habitat range (specialist, generalist) aridity (arid, sub-arid, sub-humid, mesic with a moderate or well-balanced moisture supply) and territoriality (territorial, non-territorial) in 1,111 species (vertebrates, invertebrates, and plants) and concluded that environmental heterogeneity is the major factor in maintaining and structuring genetic diversity in natural populations. Ward et al (1994) compared the heterozygosity of marine, freshwater and anadromous (fish which live mostly in the sea but breed in fresh water) fish and concluded that marine fish have greater genetic variability than the other types. Heithaus and Laushman (1997) investigated the effects of ecology, life history and water quality on genetic variation of three stream-dwelling fish species and revealed that the genetic variability tends to decrease as species become more ecologically specialized
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