Population Genetic Consequences of Small Population Size: Implications for Plant Conservation

Ellstrand, Norman C.; Elam, Diane R.

doi:10.1146/annurev.es.24.110193.001245

Cited by 2,152 publications

(1,128 citation statements)

References 98 publications

(26 reference statements)

Supporting

Mentioning

1,031

Contrasting

Unclassified

Order By: Relevance

“…Em pequena população, como parece ser a de O. mexiae, a deriva genética e a endogamia podem resultar em mudanças na diversidade genética e na adaptabilidade dos indivíduos (Ellstrand & Elam 1993). Segundo esses autores, a deriva genética resulta em perda de heterozigosidade e de eventual fixação de alelos, além do aumento da diferenciação entre populações.…”

Section: Resultsunclassified

Sistema reprodutivo de Oxypetalum mexiae Malme (Asclepiadaceae), espécie endêmica de Viçosa, MG, Brasil, em perigo de extinção

Vieira

Grabalos

2003

Acta Bot. Bras.

View full text Add to dashboard Cite

RESUMO -(Sistema reprodutivo de Oxypetalum mexiae Malme (Asclepiadaceae), espécie endêmica de Viçosa, MG, Brasil, em perigo de extinção). São reportados resultados de polinização aberta (flores expostas aos polinizadores), em indivíduos de O. mexiae de população natural, e de polinizações manuais (polinização cruzada e autopolinização), em indivíduos cultivados. Essa espécie ocorre na Reserva Florestal Mata do Paraíso, fragmento de floresta com cerca de 195ha e cuja vegetação original faz parte da unidade fitogeográfica de Floresta Atlântica. O. mexiae é trepadeira de grandes dimensões, que cresce na borda da mata, acompanhando curso d'água. É espécie autocompatível, mas autopolinização espontânea não ocorre por razões morfológicas. Sementes de frutos resultantes da xenogamia (40%) e autogamia (50%) apresentaram alta viabilidade (respectivamente, 99 e 100%). A frutificação, em população natural, foi nula, indicando que essa espécie apresenta limitação reprodutiva. Essa limitação é imposta pelo baixo nível de polinização, que restringe o número de frutos produzidos, e pela herbivoria, que impede que os frutos em desenvolvimento alcancem a maturidade. O baixo nível de polinização pode estar relacionado à fragmentação do hábitat. Além disso, há limitação na distribuição e abundância de O. mexiae imposta pelo hábitat. Palavras-chave -autocompatibilidade, baixa frutificação, fragmentação de hábitat, OxypetalumABSTRACT -(Breeding system of Oxypetalum mexiae Malme (Asclepiadaceae), an endemic and endangered species of Viçosa, Minas Gerais, Brazil). Results of open-pollination (exposed flowers), in natural population, and cross and self-pollination, in cultivated individuals, are reported in O. mexiae. This species occurs at the Reserva Florestal Mata do Paraíso, a forest fragment with 195ha, whose original vegetation is part of the phytogeographic unit of the Atlantic forest. O. mexiae is a climbing species of great dimension, which grows at the wood border, following the water flow. It is self-compatible, but spontaneous self-pollination does not occur for morphological reasons. Seeds of xenogamous (40%) and autogamous (50%) fruit sets presented a high viability (respectively, 99 and 100%). No fruit was produced in natural population, indicating that this species presents reproductive limitation. This limitation is imposed by a low level of pollination, which restricts the number of fruit-set, and herbivory, which impedes the developing fruits to reach maturation. The low level of pollination may be related to habitat fragmentation. Besides, O. mexiae habitat may further limit its distribution and abundance.

show abstract

Section: Resultsunclassified

Sistema reprodutivo de Oxypetalum mexiae Malme (Asclepiadaceae), espécie endêmica de Viçosa, MG, Brasil, em perigo de extinção

Vieira

Grabalos

2003

Acta Bot. Bras.

View full text Add to dashboard Cite

show abstract

“…In addition to the number of mating individuals, N e is affected by sex ratio, variation in reproductive success, age structure, migration and other demographic factors. It is an extremely relevant metric in conservation biology, with low N e leading to inbreeding and reduced genetic diversity (Ellstrand and Elam, 1993). See Charlesworth (2009) for a primer on N e , and Wang (2005) for a review of estimation methods.…”

Section: Introductionmentioning

confidence: 99%

Estimating contemporary effective population size in non-model species using linkage disequilibrium across thousands of loci

2016

View full text Add to dashboard Cite

Contemporary effective population size (N e ) can be estimated using linkage disequilibrium (LD) observed across pairs of loci presumed to be selectively neutral and unlinked. This method has been commonly applied to data sets containing 10-100 loci to inform conservation and study population demography. Performance of these N e estimates could be improved by incorporating data from thousands of loci. However, these thousands of loci exist on a limited number of chromosomes, ensuring that some fraction will be physically linked. Linked loci have elevated LD due to limited recombination, which if not accounted for can cause N e estimates to be downwardly biased. Here, we present results from coalescent and forward simulations designed to evaluate the bias of LD-based N e estimates (N e ). Contrary to common perceptions, increasing the number of loci does not increase the magnitude of linkage. Although we show it is possible to identify some pairs of loci that produce unusually large r 2 values, simply removing large r 2 values is not a reliable way to eliminate bias. Fortunately, the magnitude of bias inN e is strongly and negatively correlated with the process of recombination, including the number of chromosomes and their length, and this relationship provides a general way to adjust for bias. Additionally, we show that with thousands of loci, precision ofN e is much lower than expected based on the assumption that each pair of loci provides completely independent information. Heredity (Wright, 1931), which determines the rate of evolutionary change due to genetic drift and informs the equilibrium level of genetic variation and the effectiveness of selection. N e is often much lower than census size (Frankham, 1995), demonstrating that simply counting individuals is insufficient to predict rates of evolutionary change. In addition to the number of mating individuals, N e is affected by sex ratio, variation in reproductive success, age structure, migration and other demographic factors. It is an extremely relevant metric in conservation biology, with low N e leading to inbreeding and reduced genetic diversity (Ellstrand and Elam, 1993). See Charlesworth (2009) for a primer on N e , and Wang (2005) for a review of estimation methods.Populations with smaller N e undergo more genetic drift than larger populations. This genetic drift randomly generates associations between alleles at different loci, known as linkage (or gametic) disequilibrium (LD) at a rate inversely proportional to N e . As a result, measures of LD between independently-segregating loci can be used to provide an estimate of N e (Sved, 1971;Hill, 1981;Waples, 1991). Over the past decades, many studies have leveraged data sets consisting of a few dozen loci for genetic estimates of N e (Luikart et al., 2010). While these studies continue to be useful, especially for long-running

show abstract

“…This population may have been small for a long period and must have experienced both loss and genetic reorganization, which was expected due to genetic drift (Ellstrand & Elam, 1993). The factors responsible for the low diversity should be related to the geographic distance and the lack of connection between this area and other areas in Porto Murtinho (Figure 1).…”

Section: Discussionmentioning

confidence: 99%

“…The inbreeding coefficient significantly differed from zero in P. rubriflora only for the area in Nioaque; the AAL area revealed little disturbance. Because AAL contains a small population and is geographically isolated, stronger evidence of inbreeding was expected, especially in the biparental data and in terms of its structure due to limitations in pollen flow and seed dispersal (Ellstrand & Elam, 1993). …”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, these new allele frequencies contribute to increased differentiation among populations. Smaller populations trend toward increased individual homozygosity and inbreeding depression, which tends to reduce fitness and affect the fertility and survival of individuals (Charlesworth & Willis, 2009), especially for noninbred species (Ellstrand & Elam, 1993). …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Genetic structure of twoProsopisspecies in Chaco areas: A lack of allelic diversity diagnosis and insights into the allelic conservation of the affected species

Alves

Sartori

Zucchi

et al. 2018

Ecology and Evolution

View full text Add to dashboard Cite

The Gran Chaco is the largest continuous region of the South American dry forest, spanning Argentina, Paraguay, Bolivia, and Brazil. Prosopis rubriflora and Prosopis ruscifolia are typical tree species of chaquenian area forests, which have been subjected to continuous fragmentation caused by cattle raising. This study evaluated P. rubriflora and P. ruscifolia in areas with varying levels of disturbance. We investigated the contemporary genetic diversities of both species in areas with distinct anthropogenic disturbances. Even with a lower heterozygote frequency, disturbed areas can provide important storage for alleles, allowing the maintenance of diversity. The genetic diversity of P. rubriflora was surprisingly similar to that of P. ruscifolia (H e = 0.59 and H e = 0.60, respectively) even with very different distribution ranges of both species. However, P. ruscifolia exhibited a higher intrapopulation fixation index than P. rubriflora. P. rubriflora showed evidence of bottlenecking in 64% of the sampled areas, while P. ruscifolia showed such evidence in 36% of the sampled areas. Additionally, P. rubriflora had two distinct populations due to its disjunctive geographic distribution, whereas P. ruscifolia had a single population that exhibited few signs of population structure in some areas, possibly due to the main pollinators presenting a short range of dispersion. Our results suggest that 42 Chaco areas should be conserved to retain the minimum of 500 individuals necessary to maintain genetic diversity for 100–1,000 generations. This study improves our understanding of these two Prosopis species and provides information for the conservation of their genetic diversities.

show abstract

Population Genetic Consequences of Small Population Size: Implications for Plant Conservation

Cited by 2,152 publications

References 98 publications

Sistema reprodutivo de Oxypetalum mexiae Malme (Asclepiadaceae), espécie endêmica de Viçosa, MG, Brasil, em perigo de extinção

Sistema reprodutivo de Oxypetalum mexiae Malme (Asclepiadaceae), espécie endêmica de Viçosa, MG, Brasil, em perigo de extinção

Estimating contemporary effective population size in non-model species using linkage disequilibrium across thousands of loci

Genetic structure of twoProsopisspecies in Chaco areas: A lack of allelic diversity diagnosis and insights into the allelic conservation of the affected species

Contact Info

Product

Resources

About