Relationships between population density, fine-scale genetic structure, mating system and pollen dispersal in a timber tree from African rainforests

Abstract

Owing to the reduction of population density and/or the environmental changes it induces, selective logging could affect the demography, reproductive biology and evolutionary potential of forest trees. This is particularly relevant in tropical forests where natural population densities can be low and isolated trees may be subject to outcross pollen limitation and/or produce low-quality selfed seeds that exhibit inbreeding depression. Comparing reproductive biology processes and genetic diversity of populations at different densities can provide indirect evidence of the potential impacts of logging. Here, we analysed patterns of genetic diversity, mating system and gene flow in three Central African populations of the self-compatible legume timber species Erythrophleum suaveolens with contrasting densities (0.11, 0.68 and 1.72 adults per ha). The comparison of inbreeding levels among cohorts suggests that selfing is detrimental as inbred individuals are eliminated between seedling and adult stages. Levels of genetic diversity, selfing rates (∼16%) and patterns of spatial genetic structure (Sp ∼0.006) were similar in all three populations. However, the extent of gene dispersal differed markedly among populations: the average distance of pollen dispersal increased with decreasing density (from 200 m in the high-density population to 1000 m in the low-density one). Overall, our results suggest that the reproductive biology and genetic diversity of the species are not affected by current logging practices. However, further investigations need to be conducted in low-density populations to evaluate (1) whether pollen limitation may reduce seed production and (2) the regeneration potential of the species.

Gene dispersal via seeds and pollen and their effects on genetic structure in the facultative-apomictic Neotropical tree Aspidosperma polyneuron

“…Similar results have been found in other studies on tree species (Bittencourt and Sebbenn, 2007;Duminil et al, 2016;Degen and Sebbenn, 2014). Null alleles can also affect the parentage analysis due to homozygotehomozygote mismatches between offspring and parents, resulting in no assignment of parents for some individuals and overestimates in seed and pollen flow (Chybicki and Burczyk, 2010).…”

“…The difference between plots may be attributed to the low population density in plot-1 (9.8 trees/ha). Population density may affect gene dispersal by influencing insect behavior and the restricting the movement of wind (Duminil et al, 2016). Pollen dispersal is affected by the distance between conspecifics and wind seed dispersal is affected by forest density, determined not only by the density of the studied species, but by other trees in the area as well.…”

“…To test the statistical significance of SGS, the spatial position of individuals was permuted 1000 times. The standard error of Sp was estimated by -b k(SE) /1-θ 1 , where b k(SE) is the standard error of b k , estimated by jackknifing among loci (Finger et al, 2012).…”

Genetic rescue by distant trees mitigates qualitative pollen limitation imposed by fine‐scale spatial genetic structure

“…Specifically, we investigated the following hypotheses: (a) kinship will be higher among trees within each spatial cluster than among trees from different clusters. Although empirical support is increasingly being found for long-distance pollen dispersal in insect-pollinated plants (Castilla et al, 2017;Duminil et al, 2016;Ismail et al, 2012;Monthe, Hardy, Doucet, Loo, & Duminil, 2017), short-distance pollen dispersal is still an important component of pollen dispersal kernels and may lead to the deposition of pollen from genetically related donors and contribute to qualitative pollen limitation (Aizen & Harder, 2007). Although fruit set can be initiated despite low-quality (i.e., genetically related) pollen, most of these inbred fruits are expected to abort during the development process (Aizen & Harder, 2007;Herlihy & Eckert, 2004).…”

Environmental effects on fine‐scale spatial genetic structure in four Alpine keystone forest tree species

“…Despite several recent FSGS studies (e.g., Duminil et al, 2016;Fajardo, Torres-D ıaz, & Till-Bouttraud, 2016;Sork, Smouse, Grivet, & Scofield, 2015;Torroba-Balmori et al, 2017), the effects of environmental factors on spatial genetic structure within populations are yet to be investigated. Different nonexclusive processes could contribute to environmental effects on FSGS, being climate effects of particular relevance in Alpine species, where spring phenology is triggered by climate factors and not by photoperiod (Zohner, Benito, Svenning, & Renner, 2016).…”