Relationship of Genetic Variation to Population Size in Wildlife

Abstract

Genetic diversity is one of three levels of biological diversity requiring conservation. Genetic theory predicts that levels of genetic variation should increase with effective population size. Sould (19 76) compiled the first convincing evidence that levels of genetic variation in wildlife were related to population size, but this issue remains controversial. The hypothesis that genetic variation is related to population size leads to the following predictions: (1) genetic variation within species should be related to population size; (2) genetic variation within species should be related to island size; (3) genetic variation should be related to population size within taxonomic groups; (4) widespread species should have more genetic variation than restricted species; (5) genetic variation in animals should be negatively correlated with body size; (6) genetic variation should be negatively correlated with rate of chromosome evolution; (7) genetic variation across species should be related to population size; (8) vertebrates should have less genetic variation than invertebrates or plants; (9) island populations should have less genetic variation than mainland populations; and (10) endangered species should have less genetic variation than nonendangered species. Empirical observations support all these hypotheses. There can be no doubt that genetic variation is related to population size, as Sould proposed. Small population size reduces the evolutionary potential of wildlife species. La Relaci6n Entre la Variacion Gen~tica y el Tamafio Poblacional en Vida SilvestreRestmaen: La diversidad gendtica es uno de los tres niveles de diversidad biol6gica que requieren ser conservados. La teoria gendtica predice que los niveles de variaci6n gendtica se incrementan con el tamar~o de la poblaci6n efectiva. Soul# (1976) reuni6 la primera evldencia convincente de que los niveles de variaci6n gendtica en la fauna silvestre se relacionaban con el tama~o de sus poblaciones. Sin embargo, este tema sigue siendo controversial. La hip6tesls de que la variaci6n gen~tica se relaciona con el tama~o poblacional conduce alas siguientes predicciones (1) la variaci6n gendtica intraespecifica debe relacionarse con el tama~o de la poblaci6n, (2) la variaci6n gen~tica intraespecifica debe relacionarse con el tama~o de la isle, (3) la variaci6n gen~tica debe relacionarse con el tama~o poblacional dentro de grupos taxon6micos, (4) especies ampliamente distribuldas deben tener mayor variaci6n gen~tica que especies de distn'buci6n restringida, (5) la variaci6n gen#tica en animales debe tener una correlaci6n negative con el tama~o del cuerpo, (6) la vari-aci6n gendtica debe correlacionarse negativamente con la tasa de evoluci6n cromos6mica, (7) la variaci6n gen~tica intraespecifica debe relacionarse con el tama~o de la poblaci6n, (8) los vertebrados deben tener menos variaci6n gen~tica que los invertebrados o plantas, (9) poblaciones insulares deben tener menos vari-aci6n gendtica que poblaciones continentales, (10) especies amenazadas deben ten...

Rivers shape population genetic structure in Mauritia flexuosa (Arecaceae)

“…Although these observations remain to be tested explicitly, our patterns of high diversity are also consistent with the hypothesis that large population sizes of this species have been maintained by continuous activities of human cultivation, likely for thousands of years (Levis et al., 2017). As a result, outcrossing would be favored by human tending and a high number of reproductive individuals would be maintained, resulting in a higher effective population size and thus higher genetic variation (Frankham, 1996). …”

Individual genetic diversity correlates with the size and spatial isolation of natal colonies in a bird metapopulation

“…At the population level, low genetic diversity is suspected to reduce the ability of populations to respond to novel and changing environmental conditions ( Willi et al 2006) and compromise their long-term viability (Saccheri et al 1998;Westemeier et al 1998;Nieminen et al 2001;Spielman et al 2004;Frankham 2005). The level of genetic variation within a population depends on a balance between mutation, natural selection, genetic drift, inbreeding and gene flow, the last four factors being closely linked to the size and spatial isolation of populations (Frankham 1996;Hedrick 2000). Thus, it is not very surprising that the study of the genetic and demographic consequences of small population size and isolation is of central concern in both population and conservation biology ( Frankham 1996;Amos & Balmford 2001).…”

“…The level of genetic variation within a population depends on a balance between mutation, natural selection, genetic drift, inbreeding and gene flow, the last four factors being closely linked to the size and spatial isolation of populations (Frankham 1996;Hedrick 2000). Thus, it is not very surprising that the study of the genetic and demographic consequences of small population size and isolation is of central concern in both population and conservation biology ( Frankham 1996;Amos & Balmford 2001).…”

Relatedness and polyandry of sixgill sharks, Hexanchus griseus, in an urban estuary

“…This is more pronounced in slow growing, long lived species such as sixgills. For populations in decline or under diverse and ever intensifying pressures, such as more than half the known shark species, understanding and ultimately conserving the genetic variability of the population may increase its ability to withstand environmental changes or anthropogenic stressors (Frankham 1996;Keller and Waller 2002). …”

“…Genetic diversity of a species is a fundamental concern to conservation biologists because it is the basic tool allowing populations to adapt to environmental changes, novel situations and to rebound from population bottlenecks (Frankham 1996). There are few in-depth genetic diversity studies using microsatellite neutral nuclear markers in large shark species.…”