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TRANSPLANT Résumé de rapport

Project ID: EVK2-CT-1999-00004
Financé au titre de: FP5-EESD
Pays: Netherlands

Inbreeding depression experiments

The crossing experiments aimed at assessing the effects of inbreeding depression on fitness traits in different plant species occurring in fragmented landscapes in Europe. In general, inbreeding depression reduces fitness traits (e.g. seed production, seed germination, plant growth and survival) and therefore weakens plant populations, fact that may increase the extinction risks of plant populations. Fragmentation reduces population size and increases isolation between populations, increasing the probability of inbreeding, reducing gene flow, and therefore increasing inbreeding depression. Inbreeding depression is mostly caused by the effect of recessive deleterious mutations that are expressed when individual plants self-fertilize or mate with close relatives (biparental inbreeding).

The plant species used in the crossing experiments differ in mating system (self-compatible, mixed-mating system and self-incompatible), longevity (short- and long-lived), and dispersal ability (good and poor dispersers). These three life-history traits may have an important effect on the response of plants to inbreeding depression and subsequently on the viability of populations. Populations of self-compatible, long-lived plants with dispersal ability could cope with high levels of inbreeding whereas populations of self-incompatible, short-lived plants without dispersal ability could dramatically be affected. The study plant species were: Succisa pratensis (mixed-mating system, long-lived, poor disperser), Scabiosa columbaria (mixed-mating system, short-lived, poor disperser), Tragopogon pratensis (self-compatible, short-lived, good disperser), Hypochaeris radicata (self-incompatible, long-lived, good disperser), and Leontodon autumnalis (self-incompatible, long-lived, good disperser).

The effects of inbreeding depression were analyzed on all life-cycle traits, from seed set (i.e. the proportion of ovules that set seed) to flowering of resulting plants. In general, results show that seed production is greatly affected by inbreeding depression for all species except Tragopogon pratensis. Seed production determines recruitment and represents a very important trait for the maintenance of populations. In fact, populations are no viable in the long term if recruitment fails or is strongly limited. The fact that seed production in Tragopogon pratensis was not affected by inbreeding is explained by the species’ self-compatibility system.

As a result, populations of plant species with self-incompatible or mixed-mating systems might significantly reduce recruitment if inbreeding increases as a result of decreasing population size. The second important result was that dispersal was not affected by inbreeding depression. Hence, the dispersal potential of plant species of study was not reduced by genetic factors. Migration could buffer the effects of inbreeding depression on recruitment if dispersal is effective in connecting plant populations in a fragmented landscape. This mostly applies to good dispersers (Tragopogon pratensis, Hypochaeris radicata and Leontodon autumnalis), whereas poor dispersers (Succisa pratensis and Scabiosa columbaria) would have less chance to renovate the genetic load of the populations due to migration events. It must be noted, however, that poor dispersers are long-lived species. Thus, populations can persist for long periods of time during which the opportunities for long-distance dispersal events would increase.

Finally, inbreeding depression effects on life-cycle traits are being included into demographic models to test the demographic implications of inbreeding depression. The study species used is Succisa pratensis. Results indicate that the species can cope with low levels of inbreeding, but under high levels of inbreeding depression, fragmented isolated populations can go extinct in 40 years. Conservation plans devoted to preserve plant populations in fragmented landscapes should take into account measures to prevent the genetic deterioration of populations and to avoid high levels of inbreeding depression. Re-introductions of plants from other populations seem to be an effective measure to restore the genetic variability of fragmented populations.

Informations connexes


Joop OUBORG, (Senior lecturer)
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