Population type can influence the magnitude of inbreeding depression in Clarkia concinna (Onagraceae) |
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Authors: | Martha J Groom Todd E Preuninger |
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Institution: | (1) Department of Zoology, North Carolina State University, Raleigh, U.S.A. |
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Abstract: | Fragmented populations may face high risk of extinction due to the deleterious consequences of increased inbreeding or of
genetic drift in small and isolated populations. Theories on the mechanisms of inbreeding depression predict that the severity
of inbreeding depression can eventually decrease in populations that persistently inbreed, and hence populations that are
isolated through habitat fragmentation might experience a decrease in inbreeding depression over time. In this study, we tested
this hypothesis using the patchily distributed, outcrossing annual plant, Clarkia concinna concinna (Onagraceae), which naturally experiences many fragmentation effects. We collected seeds from isolated and central subpopulations
and created artificially inbred and outcrossed lines. Progeny from these crosses were planted into the field and greenhouse
and assayed for fitness traits over the course of a growing season. Overall, inbreeding depression was substantial, ranging
as high as 0.76 (for cumulative fitness in the field), and significant for plant height, fecundity, and above-ground biomass
in all experiments. No inbreeding depression was detected for germination or survival rates in the greenhouse experiments,
but in the field, survival was significantly depressed for inbred progeny. There was no evidence to support our hypothesis
that increased inbreeding in isolated populations would lead to the purging of deleterious alleles and a decrease in the severity
inbreeding depression. The most likely hypothesis to explain our results is that purging is not occurring more strongly in
the isolated populations due to details of a number of genetic factors (e.g., selection against deleterious alleles is inconsistent
or insufficient, or drift has caused fixation of deleterious alleles in these populations). This study supports the view that
even when inbreeding depression is predicted to be less problematic, it may still be an important force influencing the fitness
of populations.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Clarkia concinna concinna heterosis inbreeding depression purging |
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