Evolution

Conservation Genetics of Freshwater Fish - A Review

In his , Conservation Genetics of Freshwater Fish , R .C . Vrijenhoek proposes that a better understanding of genetic markers in freshwater fish would be of use for the biological conservation of endangered fish species . He states that knowledge of historical patterns of gene flow can help to manage dispersal of anthropogenically fragmented populations ' and believes that by studying the genetic differences that occur in fish populations , biologists will be better equipped to design an effective management plan for the conservation of these endangered populations . He

says that various selectively neutral genetic markers can be used to provide an independent picture of historical processes that have occurred and shaped the genetic diversity within and among ' fish populations . This will help with management programs such as the restocking as you will be able to tell how long ago two populations diverged and compare the diversity within and among populations and see how genetically similar they are

Genetic data which can be utilized are F , the inbreeding coefficient which estimates how homozygous two individuals are with respect to their alleles Nc , which is the effective number of breeding adults in each generation . For a diverse and healthy population , Nc should be as high as possible , and F as low as possible , as if Nc becomes too low diversity is lost and never returns . Other genetic data that can also be used are HS , the average gene diversity , and DST , the average variance in allelic frequencies between populations . Together these two make up HT , the genetic diversity can also affected by complexities of stream and therefore DSR , the variance between tributaries within a river and DRT the variance between different rivers , are also calculated

An example of why genetic data should be considered is given in the stream-hierarchy model ' where fish occupying downstream portions of the Rio Mayo are shown to be genetically more similar to those in a neighboring river , than they are to those occupying the upstream portions of the same river . Without this knowledge , fish from the lower regions of the river may be relocated to the upstream regions by conservationists and this could wipe out regional differences that may have an adaptive value . Therefore management plans should be based genetic data and on estimates of gene flow . Gene flow is determined by estimating Nm , the number of migrants between populations per generation . Nm is a product of population size (N ) and the number of immigrants (m ) per generation . By then using a stepping stone model of dispersal , it is expected that gene flow between populations will decrease with distance

Vrijenhoek uses case studies of topminnows of the genus Poeciliopsis to assess the merits of various genetic approaches to biological conservation . His data were collected over 30 and as natural subdivision of the population is small , partially isolated subpopulations have allowed him to examine the effects that fragmentation has had on a formerly widespread and continuous fish population . One species is the endangered...