Identifying Populations for Conservation on the Basis of Genetic Markers

Abstract

To select candidate populations of wild species to be given priority for conservation, genetic criteria gained from the study of molecular markers may be useful. Traditionally, diversity measures such as expected heterozygosity or percentage of polymorphic loci have been considered. For conservation we propose instead that priority should be given to measures of allelic richness. To standardize the results of allelic richness across populations, we used the technique of rarefaction. This technique allows evaluation of the expected number of different alleles among equal-sized samples drawn from several different populations. We also show how the contribution of each population to total diversity can be partitioned into two components. The first is related to the level of diversity of the population and the second to its divergence from the other populations. For conservation purposes the uniqueness of a population-in terms of its allelic compositionmay be at least as important as its diversity level. These new descriptors are illustrated by means of isozyme and chloroplast DNA data obtained for an endangered tree species, the argan tree of Morocco ( Argania spinosa (L.) Skeels). With these analyses the conservation value of the argan tree populations, especially those of two isolates present in the north of the country, can be better appreciated. The methods proposed to identify priority areas for conservation of the genetic resources of the argan tree are compared to those sometimes advocated in the case of reserve design, where one of the goals is to maximize species richness. Identificacón de Poblaciones para su Conservación en Base a Marcadores GenéticosResumen: Los criterios genéticos obtenidos del estudio de marcadores moleculares podrían ser útiles para seleccionar poblaciones de vida silvestre como candidatos con prioridad para su conservación. Tradicionalmente se consideran medidas de la diversidad como son la heterocigocidad esperada, o el porcentaje de loci polimórficos. Para medidas de conservación, nosotros proponemos en su lugar que la prioridad se enfoque en medidas de riqueza alélica. Para estandarizar los resultados de riqueza alélica entre problaciones, utilizamos una técnica de vacuidad. Esta técnica permite evaluar el número esperado de alelos entre muestras de igual tamaño obtenidas de diferentes poblaciones. Mostramos como la contribución de cada población a la diversidad total puede ser repartida en dos componentes; el primero esta relacionado con el nivel de diversidad de la población y el segundo con su divergencia de las otras poblaciones. Para propósitos de conservación, la singularidad de una población (en forma de composición alélica) puede ser por lo menos tan importante como lo es su nivel de diversidad, Estos nuevos elementos descriptivos son ilustrados mediante el uso de datos de DNA de isozima y cloroplasto para una especie de árbol en peligro, el árbol argan de Morocco ( Argania spinosa (L.) Skeels). Con estos análisis, el valor de conservación de las poblaciones del árbol argan...

Assessing priorities for conservation in Tuscan cattle breeds using microsatellites

“…The results obtained were consistent across the methodologies used. Note that, for clarity, both positive contributions to diversity assessed using Petit et al (1998) and Caballero and Toro's (2002) methods indicate that the population excluded would be preferred for conservation. The two outgroup breeds (Asturiana de la Montañ a and Argentinean Creole) mainly based their contributions on the between-breed differentiation.…”

“…Note that, in contrast to the method of Caballero and Toro (2002), the assessment of diversity via rarefacted allelic richness (Petit et al, 1998) does not use the entire remaining dataset as the basis of computations but the individual breed; therefore, contributions to allelic richness explained by a group of breeds cannot be straightforwardly assessed. Pooling the breeds to be excluded as a single breed is only an approximation that assumes the risk of artificially inflating the diversity of the new-composite population.…”

“…Contributions of the breeds (or their combinations) to diversity were assessed, using the program MolKin, following Petit et al (1998) and Caballero and Toro (2002). The former method uses as a criterion the maintenance of the maximum overall Nei's (1987) gene diversity minimizing the overall molecular coancestry ð f T ; f W ; f B Þ, whereas the latter method assesses the contribution of the ith population to the total allelic richness (C T ; C W ; C B ).…”

“…Molecular techniques can be used to assess within-population genetic diversity and between-population differentiation and, therefore, make inferences on the degree of uniqueness of the analyzed populations. A number of approaches for quantifying genetic diversity have been proposed as tools for decision making in genetic conservation programs, including phylogenetic-like approaches such as that by Weitzman (1992) and Thaon d'Arnoldi et al (1998), those focusing on the maximization of the Nei's (1987) gene diversity (Eding and Meuwissen, 2001;Caballero and Toro, 2002) or the average number of alleles per locus (Petit et al, 1998; a These authors contributed equally to this work and shall share the first authorship.…”

“…From these, the latter two (Petit et al, 1998;Caballero and Toro, 2002) have the advantage of the explicit use of within-and betweenbreed diversity. This allows their use in assessment of the within-population impact of different selection policies (Á lvarez et al, 2009 and 2011).…”