Most species are not driven to extinction before genetic factors impact them Kristin Debord Shaun Fike

Two contrasting view points Two contrasting view points  Genetic factors do not affect extinction rates.  Genetic factors do affect extinctions rates

Factors Affecting Species Population Size  Habitat loss  Over exploitation  Impact of introduced species  pollution

Stochastic Factors  Demographic  Environmental  Genetic stochastic factors  Natural catastrophes

Accumulation of inbreeding H g /H 0 = [1-1/2(2N e )] g = 1-F  H g = generation g  H 0 = initial heterozygosity  N e = long term effective population size  F= inbreeding coefficient

Methods  Conducted metaanalysis using IUCN- the World Conservation Union Red List threatened categorization system

Methods cont.  Analyses were done on percentage differences in heterozygosity between threatened and the nearest related nonthreatened species or group of species.  Analyses based on data for allozymes, microsatellites, and minisatellites.

Methods cont.  Data from listed species were paired with data of the same type from the most closely related species.  Used observed or expected heterozygosity  If allozyme and microsatellite were available for the same taxon, the combined weighted average was used.

Methods cont. (Major Taxa)  Plants were subdivided in to gymnosperms and angiosperms.  Animals were divided into invertebrates and vertebrates which were further subdivided into poikilotherms, homeotherms, birds and mammals.

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

Alternative Hypothesis Alternative Hypothesis  Threatened taxa have less genetic diversity than comparable non threatened taxa.

Data Analyses  The defining measure used was the percentage difference in heterozygosity.  (100*(nonthreatened – threatened)/ nonthreatened) or (100 * (nonthreatened- threatened)/ threatened)

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

Data analyses cont.  Tested for differences among the different Red List categories using Kruskal-Wallis tests.

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

Results cont.

Discussion  A majority of the threatened taxa showed lower genetic diversity than related nonthreatened species.  The mean difference was found to be 35% and the median difference was found to be 40%.

Discussion cont.  Taxa that do not currently show any genetic impact may still experience genetic impact prior to extinction.  Vulnerable taxa show a 10% probability of extinction within 100 years.

Discussion cont.  It is unclear whether genetic factors have contributed to the current threatened status of taxa in the study.  Reduced genetic diversity is a marker of reduced reproductive fitness, meaning that the extinction risk is elevated.

Links Between Reduced Genetic Diversity and Extinction Risk 1. Reduced genetic diversity has been shown to reduce times to extinction. 2. The difference in heterozygosity is a measure of the inbreeding coefficient of a taxon. 3. Computer projections show inbreeding depression adversely affects extinction risk even when all other factors are operating.

When are genetic effects of lowered diversity of sufficient magnitude that they must be managed?  Depends on inbreeding coefficient, effective population size, and number of generations  It is also likely to vary among species in relation to population growth rate

“No Genetic Impact” Doesn’t Apply to Most Threatened Taxa “No Genetic Impact” Doesn’t Apply to Most Threatened Taxa 1. Ratios of effective population sizes are lower than were assumed in Impacts of interactions between genetic and other stochastic factors may have been underestimated. 3. Impacts of inbreeding depression were likely underestimated. 4. Overestimated effectiveness of natural selection.

Conclusion  Most threatened taxa have lower genetic diversity than closely related nonthreatened taxa.  Most species are not driven to extinction before genetic factors impact them.