Summary
Due to human activities, populations of many species have become small and isolated. In this situation they become subject to genetic drift and inbreeding, resulting in loss of genetic variation, an increase in homozygosity, and possibly a decrease in viability (inbreeding depression). This process, here referred to as genetic erosion, may significantly increase the extinction probability of populations or even species, and is therefore currently an important issue in conservation biology. The research presented here aimed to determine the occurrence, extent, and significance of genetic erosion in natural populations of Scabiosa columbaria and Salvia pratensis, two species that are considered endangered in The Netherlands.
We observed decreased levels of both allozyme variation and phenotypic variation in the smaller populations of both species, indicating the occurrence of substantial genetic drift. Experiments that compared outcrossed progeny to selfed progeny showed a severe reduction in fitness for many fitness components, while on the other hand crosses between different populations revealed substantial heterosis. This proved that in both species there is potentially sufficient genetic load to cause inbreeding depression when populations become small. In contrast to expectation, no correlation between population size and the level of inbreeding depression due to selfing was observed, suggesting that purging of genetic load had not (yet) occurred in the small populations. This most probably indicates that the small populations had become small only recently. To evaluate the possible future consequences of the observed amount of genetic load, data on inbreeding depression were integrated with demographic data and the environmental variance in transition models. These computer simulations showed that most populations, both small and large, have a high probability of becoming extinct in the near future, and also that inbreeding depression did significantly increase this extinction probability of populations, except of those populations that, due to the high environmental stochasticity, already had a very high extinction chance in the absence of inbreeding depression. Implications of the results for possible management measures and future research are discussed.
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Bijlsma, R., Ouborg, N.J., van Treuren, R. (1994). On genetic erosion and population extinction in plants: A case study in Scabiosa columbaria and Salvia pratensis . In: Loeschcke, V., Jain, S.K., Tomiuk, J. (eds) Conservation Genetics. EXS, vol 68. Birkhäuser, Basel. https://doi.org/10.1007/978-3-0348-8510-2_21
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DOI: https://doi.org/10.1007/978-3-0348-8510-2_21
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