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- Genetic structure at range edge: Low diversity and high inbreeding in Southeast Asian mangrove (Avicennia marina) populationsPublication . ARNAUD-HAOND, Sophie; Teixeira, Sara; Massa, S. I.; Billot, C.; Saenger, P.; Coupland, G.; Duarte, C. M.; Serrão, EsterUnderstanding the genetic composition and mating systems of edge populations provides important insights into the environmental and demographic factors shaping species’ distribution ranges. We analysed samples of the mangrove Avicennia marina from Vietnam, northern Philippines and Australia, with microsatellite markers. We compared genetic diversity and structure in edge (Southeast Asia, and Southern Australia) and core (North and Eastern Australia) populations, and also compared our results with previously published data from core and southern edge populations. Comparisons highlighted significantly reduced gene diversity and higher genetic structure in both margins compared to core populations, which can be attributed to very low effective population size, pollinator scarcity and high environmental pressure at distribution margins. The estimated level of inbreeding was significantly higher in northeastern populations compared to core and southern populations. This suggests that despite the high genetic load usually associated with inbreeding, inbreeding or even selfing may be advantageous in margin habitats due to the possible advantages of reproductive assurance, or local adaptation. The very high level of genetic structure and inbreeding show that populations of A. marina are functioning as independent evolutionary units more than as components of a metapopulation system connected by gene flow. The combinations of those characteristics make these peripheral populations likely to develop local adaptations and therefore to be of particular interest for conservation strategies as well as for adaptation to possible future environmental changes.
- Polymorphic microsatellite DNA markers in the mangrove tree Avicennia albaPublication . Teixeira, Sara; ARNAUD-HAOND, Sophie; Duarte, C. M.; Serrão, EsterLike most species of mangrove trees of the genus Avicennia , A. alba is widely distributed among tropical and subtropical coasts around the world. Mangroves play an essential role in ecosystem dynamics but are reported to be regressing as human pressure increases on coastal zones. Hypervariable genetic markers are useful for population genetics studies, to estimate the level of impact and the populations potential for recovery. Microsatellite markers for A. alba were obtained by screening a partial genomic library enriched for micro-satellite dinucleotide repeats. Among 20 primer pairs defined, six amplified polymorphic microsatellites with a satisfying level of variability.
- Genetic recolonization of mangrove: Genetic diversity still increasing in the Mekong delta 30 years after Agent OrangePublication . ARNAUD-HAOND, Sophie; Duarte, C. M.; Teixeira, Sara; Massa, S. I.; Terrados, J.; Tri, N. H.; Hong, P. N.; Serrão, EsterThe widespread use of Agent Orange (a mixture of phenoxyl herbicides) over Southern Vietnam by US Forces led to the decimation of mangrove forests in the Mekong Delta. Mangrove trees Avicennia alba were sampled across the Mekong Delta; their age was assessed using models based on internode growth and samples were genotyped for 6 microsatellite loci. The evolution of genetic diversity over time elapsed since local extinction was reconstructed and compared with the genetic diversity of an unaffected population from Thailand. The results show that genetic diversity of the A. alba population is still increasing in the Mekong Delta 3 decades after the end of the Vietnam War, but is reaching an asymptotic level that is comparable to the adjacent non-affected population of Thailand. This might be a sign of genetic recovery, but may also reveal a limitation, either of genetic enrichment due to current predominance of auto-recruitment or of demographic increase due to intraspecific competition in this pioneer species. In any case, these results, although encouraging, demonstrate that genetic recovery after complete or almost complete population depletion continues over a longer time-scale than apparent demographic recovery.