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Population genetic diversity and fitness in multiple environments.

Markert JA, Champlin DM, Gutjahr-Gobell R, Grear JS, Kuhn A, McGreevy TJ, Roth A, Bagley MJ, Nacci DE - BMC Evol. Biol. (2010)

Bottom Line: The combined effects of reduced average fitness and increased variability contributed to increased extinction rates for very low diversity populations.More modest losses of genetic diversity resulted in measurable decreases in population fitness; AFLP markers did not always detect these losses.However when AFLP markers indicated lost genetic diversity, these losses were associated with reduced population fitness.

View Article: PubMed Central - HTML - PubMed

Affiliation: U.S. Environmental Protection Agency, Narragansett, RI, USA. jeffreymarkert@gmail.com

ABSTRACT

Background: When a large number of alleles are lost from a population, increases in individual homozygosity may reduce individual fitness through inbreeding depression. Modest losses of allelic diversity may also negatively impact long-term population viability by reducing the capacity of populations to adapt to altered environments. However, it is not clear how much genetic diversity within populations may be lost before populations are put at significant risk. Development of tools to evaluate this relationship would be a valuable contribution to conservation biology. To address these issues, we have created an experimental system that uses laboratory populations of an estuarine crustacean, Americamysis bahia with experimentally manipulated levels of genetic diversity. We created replicate cultures with five distinct levels of genetic diversity and monitored them for 16 weeks in both permissive (ambient seawater) and stressful conditions (diluted seawater). The relationship between molecular genetic diversity at presumptive neutral loci and population vulnerability was assessed by AFLP analysis.

Results: Populations with very low genetic diversity demonstrated reduced fitness relative to high diversity populations even under permissive conditions. Population performance decreased in the stressful environment for all levels of genetic diversity relative to performance in the permissive environment. Twenty percent of the lowest diversity populations went extinct before the end of the study in permissive conditions, whereas 73% of the low diversity lines went extinct in the stressful environment. All high genetic diversity populations persisted for the duration of the study, although population sizes and reproduction were reduced under stressful environmental conditions. Levels of fitness varied more among replicate low diversity populations than among replicate populations with high genetic diversity. There was a significant correlation between AFLP diversity and population fitness overall; however, AFLP markers performed poorly at detecting modest but consequential losses of genetic diversity. High diversity lines in the stressful environment showed some evidence of relative improvement as the experiment progressed while the low diversity lines did not.

Conclusions: The combined effects of reduced average fitness and increased variability contributed to increased extinction rates for very low diversity populations. More modest losses of genetic diversity resulted in measurable decreases in population fitness; AFLP markers did not always detect these losses. However when AFLP markers indicated lost genetic diversity, these losses were associated with reduced population fitness.

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Population fitness, estimated with Median Population Size (A), Last Census size (B), and Reproductive Index (C). Paired box plots define the median and middle two quantiles in stressful (left) and permissive environments (right). Lower case letters unite groups that are not statistically distinguishable using post-hoc tests (Tukey's HSD) at α = 0.05.
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Figure 1: Population fitness, estimated with Median Population Size (A), Last Census size (B), and Reproductive Index (C). Paired box plots define the median and middle two quantiles in stressful (left) and permissive environments (right). Lower case letters unite groups that are not statistically distinguishable using post-hoc tests (Tukey's HSD) at α = 0.05.

Mentions: Abundance after three weeks of culture under permissive conditions (Phase 1) was significantly correlated with nominal genetic diversity level (Spearman's ρ = 0.68, p < 0.0001, Table 3). Final population sizes increased from 12 individuals at the start of the experiment to an average of 18.6 individuals in the low diversity lines (1x) and to 79.3 individuals in the highest diversity populations (AMX). All treatments differed from each other, except 6x and 8x. Variance was unequal among treatments (p = 0.0244) with the coefficient of variation inversely related to genetic diversity (Table 3, Figure 1).


Population genetic diversity and fitness in multiple environments.

Markert JA, Champlin DM, Gutjahr-Gobell R, Grear JS, Kuhn A, McGreevy TJ, Roth A, Bagley MJ, Nacci DE - BMC Evol. Biol. (2010)

Population fitness, estimated with Median Population Size (A), Last Census size (B), and Reproductive Index (C). Paired box plots define the median and middle two quantiles in stressful (left) and permissive environments (right). Lower case letters unite groups that are not statistically distinguishable using post-hoc tests (Tukey's HSD) at α = 0.05.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2927917&req=5

Figure 1: Population fitness, estimated with Median Population Size (A), Last Census size (B), and Reproductive Index (C). Paired box plots define the median and middle two quantiles in stressful (left) and permissive environments (right). Lower case letters unite groups that are not statistically distinguishable using post-hoc tests (Tukey's HSD) at α = 0.05.
Mentions: Abundance after three weeks of culture under permissive conditions (Phase 1) was significantly correlated with nominal genetic diversity level (Spearman's ρ = 0.68, p < 0.0001, Table 3). Final population sizes increased from 12 individuals at the start of the experiment to an average of 18.6 individuals in the low diversity lines (1x) and to 79.3 individuals in the highest diversity populations (AMX). All treatments differed from each other, except 6x and 8x. Variance was unequal among treatments (p = 0.0244) with the coefficient of variation inversely related to genetic diversity (Table 3, Figure 1).

Bottom Line: The combined effects of reduced average fitness and increased variability contributed to increased extinction rates for very low diversity populations.More modest losses of genetic diversity resulted in measurable decreases in population fitness; AFLP markers did not always detect these losses.However when AFLP markers indicated lost genetic diversity, these losses were associated with reduced population fitness.

View Article: PubMed Central - HTML - PubMed

Affiliation: U.S. Environmental Protection Agency, Narragansett, RI, USA. jeffreymarkert@gmail.com

ABSTRACT

Background: When a large number of alleles are lost from a population, increases in individual homozygosity may reduce individual fitness through inbreeding depression. Modest losses of allelic diversity may also negatively impact long-term population viability by reducing the capacity of populations to adapt to altered environments. However, it is not clear how much genetic diversity within populations may be lost before populations are put at significant risk. Development of tools to evaluate this relationship would be a valuable contribution to conservation biology. To address these issues, we have created an experimental system that uses laboratory populations of an estuarine crustacean, Americamysis bahia with experimentally manipulated levels of genetic diversity. We created replicate cultures with five distinct levels of genetic diversity and monitored them for 16 weeks in both permissive (ambient seawater) and stressful conditions (diluted seawater). The relationship between molecular genetic diversity at presumptive neutral loci and population vulnerability was assessed by AFLP analysis.

Results: Populations with very low genetic diversity demonstrated reduced fitness relative to high diversity populations even under permissive conditions. Population performance decreased in the stressful environment for all levels of genetic diversity relative to performance in the permissive environment. Twenty percent of the lowest diversity populations went extinct before the end of the study in permissive conditions, whereas 73% of the low diversity lines went extinct in the stressful environment. All high genetic diversity populations persisted for the duration of the study, although population sizes and reproduction were reduced under stressful environmental conditions. Levels of fitness varied more among replicate low diversity populations than among replicate populations with high genetic diversity. There was a significant correlation between AFLP diversity and population fitness overall; however, AFLP markers performed poorly at detecting modest but consequential losses of genetic diversity. High diversity lines in the stressful environment showed some evidence of relative improvement as the experiment progressed while the low diversity lines did not.

Conclusions: The combined effects of reduced average fitness and increased variability contributed to increased extinction rates for very low diversity populations. More modest losses of genetic diversity resulted in measurable decreases in population fitness; AFLP markers did not always detect these losses. However when AFLP markers indicated lost genetic diversity, these losses were associated with reduced population fitness.

Show MeSH
Related in: MedlinePlus