Mahogany as a genetic resource

Newton, Adrian C.; Cornelius, J.P.; Baker, Peter S.; Gillies, Amanda; Hernández, M.; Ramnarine, S.; Mesén, J.F.; Watt, Allan D.

doi:10.1111/j.1095-8339.1996.tb02063.x

Cited by 17 publications

(13 citation statements)

References 18 publications

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“…For a greater range of species, and for longer periods, the extent and circumstances under which open grown trees present substandard germplasm for regeneration and planting needs more study. (Styles, 1972, Newton et al, 1996. The difficulty in defining a baseline from which to monitor change, and the virtual lack of studies, means that there is little evidence to back up the theory (Ledig, 1992).…”

Section: Future Research Prioritiesmentioning

confidence: 99%

Genetic resource impacts of habitat loss and degradation; reconciling empirical evidence and predicted theory for neotropical trees

et al. 2005

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The theoretical impacts of anthropogenic habitat degradation on genetic resources have been well articulated. Here we use a simulation approach to assess the magnitude of expected genetic change, and review 31 studies of 23 neotropical tree species to assess whether empirical case studies conform to theory. Major differences in the sensitivity of measures to detect the genetic health of degraded populations were obvious. Most studies employing genetic diversity (nine out of 13) found no significant consequences, yet most that assessed progeny inbreeding (six out of eight), reproductive output (seven out of 10) and fitness (all six) highlighted significant impacts. These observations are in line with theory, where inbreeding is observed immediately following impact, but genetic diversity is lost slowly over subsequent generations, which for trees may take decades. Studies also highlight the ecological, not just genetic, consequences of habitat degradation that can cause reduced seed set and progeny fitness. Unexpectedly, two studies examining pollen flow using paternity analysis highlight an extensive network of gene flow at smaller spatial scales (less than 10 km). Gene flow can thus mitigate against loss of genetic diversity and assist in long-term population viability, even in degraded landscapes. Unfortunately, the surveyed studies were too few and heterogeneous to examine concepts of population size thresholds and genetic resilience in relation to life history. Future suggested research priorities include undertaking integrated studies on a range of species in the same landscapes; better documentation of the extent and duration of impact; and most importantly, combining neutral marker, pollination dynamics, ecological consequences, and progeny fitness assessment within single studies. Keywords: fragmentation; gene flow; genetic diversity; inbreeding; neotropical trees; selective logging Introduction Anthropogenic destruction of tropical forests has dramatically increased in recent decades, and the threat to tropical ecosystems is well articulated (eg Bawa and Seidler, 1998;White et al, 1999;Trejo and Dirzo, 2000;Ghazoul and McLeish, 2001). For biodiversity, the single most important impact of these activities is loss of primary habitat (Lira et al, 2003). However, the degradation of habitat also leaves a lasting legacy with which biota must cope if they are to continue to survive. The need for a more integrative approach to this problem, which combines ecology and population genetics, is evident (Sih et al, 2000; Young and Clarke, 2000). For trees, degradation of primary habitat results from two main processes, fragmentation of forest into patches following clearance and disturbance of habitat following extraction processes, such as selective logging.Tropical trees are thought to be particularly vulnerable to the effects of habitat degradation due to their demographic and reproductive characteristics, including low density of occurrence, complex self-incompatible breeding systems, high rates of outcrossing ...

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Section: Future Research Prioritiesmentioning

confidence: 99%

Genetic resource impacts of habitat loss and degradation; reconciling empirical evidence and predicted theory for neotropical trees

et al. 2005

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“…For selectively exploited tropical tree species, genetic erosion can become an important consideration and sustainable production can be threatened if genetically determined wood quality or pest resistance characters are undermined (Newton et al, 1996). A genetic resource management strategy for such species needs to be based on research data examining the extent of genetic differentiation within and between populations, and on understanding the processes maintaining this variation.…”

Section: Introductionmentioning

confidence: 99%

“…Mahogany, Swietenia macrophylla King (Meliaceae, Swietenioideae), is one of the most important timber species in the world (Rodan et al, 1992), and overexploitation and high rates of deforestation have led to it becoming the focus of increased conservation concern (Newton et al, 1996). Mahogany matures to a large, deciduous tree able to reach heights of 40 m, a diameter of over 2 m and may live for several centuries.…”

Section: Introductionmentioning

confidence: 99%

Fine-scale genetic structure and gene flow within Costa Rican populations of mahogany (Swietenia macrophylla)

et al. 2003

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Fine-scale structure of genetic diversity and gene flow were analysed in three Costa Rican populations of mahogany, Swietenia macrophylla. Population differentiation estimated using AFLPs and SSRs was low (38.3 and 24%) and only slightly higher than previous estimates for Central American populations based on RAPD variation (20%). Significant finescale spatial structure was found in all of the surveyed mahogany populations and is probably strongly influenced by the limited seed dispersal range of the species. Furthermore, a survey of progeny arrays from selected mother trees in two of the plots indicated that most pollinations involved proximate trees. These data indicate that very little gene flow, via either pollen or seed, is occurring between blocks of mahogany within a continuous or disturbed forest landscape. Thus, once diversity is removed from a forest population of mahogany, these data suggest that recovery would be difficult via seed or pollen dispersal, and provides an explanation for mahogany's apparent susceptibility to the pressures of logging. Evidence is reviewed from other studies of gene flow and seedling regeneration to discuss alternative extraction strategies that may maintain diversity or allow recovery of genetic resources.

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“…The scattered stands provide the opportunity to directly assess the effect of fragmentation on the distribution of genetic variation within a tropical tree species. Listed in 1973 in Appendix II of the Convention on International Trade in Endangered Species (CITES), S. humilis has become the focus of increasing conservation concern and a strategy is required to define how remaining populations may be sustainably used and effectively conserved (Newton et al . 1996).…”

Section: Introductionmentioning

confidence: 99%

Genetic variation within a fragmented population ofSwietenia humilisZucc.

White¹,

Boshier

Powell³

1999

Molecular Ecology

121

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With large tracts of once continuous forest now modified by human use to leave reduced and highly fragmented stands of trees, the determination of the genetic consequences of forest fragmentation is a priority for ascertaining the conservation value of resultant stands, and in formulating sustainable management strategies. The levels and distribution of genetic diversity over 10 microsatellite loci were investigated within a fragmented population of the neotropical tree Swietenia humilis Zucc. High levels of genetic variation, typical of a highly outcrossing species, were found in all fragments at all loci (mean HE = 0.548). The majority of the variation was within rather than between fragments (RST = 0.032), giving high indirect estimates of gene flow (Nm = 8.9), probably reflecting the genetic structure of the trees present under more continuous forest. A high proportion of loci also showed significant departures from Hardy-Weinberg equilibrium with associated significant levels of FIS. The initial effects of fragmentation were, however, seen in the fragments through the loss of low-frequency alleles present in the continuous 'control' stand. The percentage of this allelic loss increased with a decrease in fragment size.

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Mahogany as a genetic resource

Cited by 17 publications

References 18 publications

Genetic resource impacts of habitat loss and degradation; reconciling empirical evidence and predicted theory for neotropical trees

Genetic resource impacts of habitat loss and degradation; reconciling empirical evidence and predicted theory for neotropical trees

Fine-scale genetic structure and gene flow within Costa Rican populations of mahogany (Swietenia macrophylla)

Genetic variation within a fragmented population ofSwietenia humilisZucc.

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