Genetics of neotropical fish: from chromosomes to populations

Abstract

The Neotropical freshwater fish fauna is very rich--according to the most recent catalogue 71 families and 4,475 species have been described. However, only a small amount of general information is available on the composition of Neotropical marine fishes. In Brazil, 1,298 marine species have been recorded. General analysis of available cytogenetic and population genetic data clearly indicates research has been mainly concentrated on freshwater fishes. Thus, today, cytogenetic information is available for 475 species of Characiformes, 318 species of Siluriformes, 48 species of Gymnotiformes, 199 freshwater species that do not belong to the superorder Ostariophysi, and only 109 species of marine fishes. For the species studied, only about 6% have sex chromosomes and about 5% have supernumerary or B chromosomes. A review of the cytogenetic studies shows that these data have provided valuable information about the relationships between fish groups, the occurrence of cryptic species and species complexes, the mechanism of sex determination and sex chromosome evolution, the distribution of nucleolus organizer regions, the existence supernumerary chromosomes, and the relationship between polyploidy and evolution. In relation to populations in Neotropical marine waters, the studies have shown the presence of cryptic species, which has important implications for fishery management. Different levels of genetic structuring can be found among Neotropical freshwater migratory fish species. This raises important implications for fish population genetic diversity and consequently its sustainable utilization in inland fisheries and aquaculture, specifically for conservation of ichthyo-diversity and survival.

Genetic analysis of five sedentary fish species in middle Laranjinha River (upper Paraná River basin): A case study

“…F statistics (Wright, 1978) or their analogs are measurements of the hierarchical levels of structure within and between populations (Piorski et al, 2008;Oliveira et al, 2009). In the present study, relatively low levels of genetic structure, i.e., F ST /ϕ ST values smaller than 0.05 (Wright, 1978;Excoffier et al, 1992), were found in four species but not S. insculpta (Table 2).…”

“…Genetic diversity studies in neotropical ichthyofauna have focused on species with a long history of reproductive displacement (Piorski et al, 2008;Oliveira et al, 2009). The effects on these species are often related to the immediate impacts of the construction of dams, which often affect migration routes and, therefore, gene flow within and between populations.…”

“…Considering the genetic similarity between the fish sampled upstream and downstream of the Corredeira Dam, and that only P. microstoma was captured in the fish ladder, other factors must influence the maintenance of gene flow. Most studies on population genetic structure in neotropical freshwater fish focus on the effects of large dams (Oliveira et al, 2009). Large geographic barriers tend to impose greater difficulties on fish movements and may result in complete interruption of gene flow (Agostinho et al, 2008).…”

“…These changes influence the reproduction, distribution, and vulnerability of populations to stochastic processes related to loss of genetic diversity (Slatkin, 1985;Piorski et al, 2008;Oliveira et al, 2009). The upper Paraná River basin is one of the most studied watersheds in South America.…”

Ichthyofauna of tributaries of the Vermelho River, upper Paraguay River basin, region of Rondonópolis, state of Mato Grosso, Brazil

“…Thus, in recent decades, groups focusing on the study of fish have increased greatly. Current inventories, studies in systematics, ecology, reproduction, cytogenetics, molecular biology, among others, have been published (Reis et al 2003;Lowe-McConnell, 1999;Oliveira et al 2009;among others). However, such studies have focused more on southern and southeastern Brazil, where the largest number of researchers is concentrated.…”