two contrasting view points

Most species are not driven Most species are not driven to extinction before genetic to extinction before genetic

factors impact themfactors impact them

Kristin DebordKristin DebordShaun FikeShaun Fike

Two contrasting view pointsTwo contrasting view points

Genetic factors do not affect Genetic factors do not affect extinction rates.extinction rates.

Genetic factors do affect extinctions Genetic factors do affect extinctions ratesrates

Factors Affecting Species Factors Affecting Species Population SizePopulation Size

Habitat lossHabitat loss Over exploitationOver exploitation Impact of introduced speciesImpact of introduced species pollutionpollution

Stochastic FactorsStochastic Factors

DemographicDemographic EnvironmentalEnvironmental Genetic stochastic factorsGenetic stochastic factors Natural catastrophesNatural catastrophes

Accumulation of inbreedingAccumulation of inbreeding

HHgg/H/H00 = [1-1/2(2N = [1-1/2(2Nee)])]gg = 1-F = 1-F

HHgg = heterozygosity @ generation = heterozygosity @ generation gg HH00= initial heterozygosity= initial heterozygosity NNee= long term effective population = long term effective population

sizesize F= inbreeding coefficient F= inbreeding coefficient

MethodsMethods

Conducted metaanalysis using IUCN- Conducted metaanalysis using IUCN- the World Conservation Union Red the World Conservation Union Red List threatened categorization List threatened categorization systemsystem

Methods cont.Methods cont.

Analyses were done on percentage Analyses were done on percentage differences in heterozygosity differences in heterozygosity between threatened and the nearest between threatened and the nearest related nonthreatened species or related nonthreatened species or group of species.group of species.

Analyses based on data for Analyses based on data for allozymes, microsatellites, and allozymes, microsatellites, and minisatellites.minisatellites.

Methods cont.Methods cont. Data from listed species were paired with Data from listed species were paired with

data of the same type from the most data of the same type from the most closely related species.closely related species.

Used observed or expected heterozygosityUsed observed or expected heterozygosity

If allozyme and microsatellite were If allozyme and microsatellite were

available for the same taxon, the available for the same taxon, the combined weighted average was used.combined weighted average was used.

Methods cont. (Major Taxa)Methods cont. (Major Taxa)

Plants were subdivided in to Plants were subdivided in to gymnosperms and angiosperms.gymnosperms and angiosperms.

Animals were divided into Animals were divided into invertebrates and vertebrates which invertebrates and vertebrates which were further subdivided into were further subdivided into poikilotherms, homeotherms, birds poikilotherms, homeotherms, birds and mammals.and mammals.

Null HypothesisNull Hypothesis

Genetic diversity of threatened taxa Genetic diversity of threatened taxa does not differ from that of non does not differ from that of non threatened taxa.threatened taxa.

Alternative HypothesisAlternative Hypothesis

Threatened taxa have less genetic Threatened taxa have less genetic diversity than comparable non diversity than comparable non threatened taxa.threatened taxa.

Data AnalysesData Analyses

The defining measure used was the The defining measure used was the percentage difference in percentage difference in heterozygosity.heterozygosity.

(100*(nonthreatened – threatened)/ (100*(nonthreatened – threatened)/ nonthreatened) or (100 * nonthreatened) or (100 * (nonthreatened- threatened)/ (nonthreatened- threatened)/ threatened)threatened)

Data analyses cont.Data analyses cont.

Wilcoxon’s signed ranked tests were Wilcoxon’s signed ranked tests were performed on the difference in performed on the difference in heterozygosity of each threatened heterozygosity of each threatened taxon compared with the most taxon compared with the most closely related available taxon or closely related available taxon or taxa not included in the IUCN Red taxa not included in the IUCN Red Lists.Lists.

Data analyses cont.Data analyses cont.

Tested for differences among the Tested for differences among the different Red List categories using different Red List categories using Kruskal-Wallis tests.Kruskal-Wallis tests.

ResultsResults

77% of the 170 threatened taxa had 77% of the 170 threatened taxa had lower heterozygosity than related lower heterozygosity than related nonthreatened taxa.nonthreatened taxa.

Results cont.Results cont.

Results cont.Results cont.

DiscussionDiscussion

A majority of the threatened taxa A majority of the threatened taxa showed lower genetic diversity than showed lower genetic diversity than related nonthreatened species.related nonthreatened species.

The mean difference was found to be The mean difference was found to be 35% and the median difference was 35% and the median difference was found to be 40%.found to be 40%.

Discussion cont.Discussion cont.

Taxa that do not currently show any Taxa that do not currently show any genetic impact may still experience genetic impact may still experience genetic impact prior to extinction.genetic impact prior to extinction.

Vulnerable taxa show a 10% Vulnerable taxa show a 10% probability of extinction within 100 probability of extinction within 100 years.years.

Discussion cont.Discussion cont.

It is unclear whether genetic factors It is unclear whether genetic factors have contributed to the current have contributed to the current threatened status of taxa in the threatened status of taxa in the study.study.

Reduced genetic diversity is a Reduced genetic diversity is a marker of reduced reproductive marker of reduced reproductive fitness, meaning that the extinction fitness, meaning that the extinction risk is elevated. risk is elevated.

Links Between Reduced Genetic Links Between Reduced Genetic Diversity and Extinction RiskDiversity and Extinction Risk

1.1. Reduced genetic diversity has been Reduced genetic diversity has been shown to reduce times to extinction. shown to reduce times to extinction.

2.2. The difference in heterozygosity is a The difference in heterozygosity is a measure of the inbreeding coefficient of measure of the inbreeding coefficient of a taxon.a taxon.

3.3. Computer projections show inbreeding Computer projections show inbreeding depression adversely affects extinction depression adversely affects extinction risk even when all other factors are risk even when all other factors are operating.operating.

When are genetic effects of lowered When are genetic effects of lowered diversity of sufficient magnitude that diversity of sufficient magnitude that

they must be managed?they must be managed?

Depends on inbreeding coefficient, Depends on inbreeding coefficient, effective population size, and number effective population size, and number of generationsof generations

It is also likely to vary among species It is also likely to vary among species in relation to population growth ratein relation to population growth rate

““No Genetic Impact” Doesn’t Apply No Genetic Impact” Doesn’t Apply to Most Threatened Taxato Most Threatened Taxa

1.1. Ratios of effective population sizes are Ratios of effective population sizes are lower than were assumed in 1988.lower than were assumed in 1988.

2.2. Impacts of interactions between genetic Impacts of interactions between genetic and other stochastic factors may have and other stochastic factors may have been underestimated.been underestimated.

3.3. Impacts of inbreeding depression were Impacts of inbreeding depression were likely underestimated.likely underestimated.

4.4. Overestimated effectiveness of natural Overestimated effectiveness of natural selection.selection.

ConclusionConclusion

Most threatened taxa have lower Most threatened taxa have lower genetic diversity than closely related genetic diversity than closely related nonthreatened taxa.nonthreatened taxa.

Most species are not driven to Most species are not driven to extinction before genetic factors extinction before genetic factors impact them.impact them.