Genetic consequences of anthropogenic disturbances and population fragmentation in Acacia senegal

Long-distance gene flow in Acacia senegal: Hope for disturbed and fragmented populations

Even though pollen and seed dispersals are some of the important factors that determine tree species survival across landscapes, gene dispersal data of important tropical dryland tree species such as Acacia senegal that are undergoing various population disturbances remain scarce. Understanding patterns of gene dispersal in these ecosystems is important for conservation, landscape restoration and tree improvement. We investigated pollen and seed mediated gene flow in two A. senegal populations of contrasting state (less disturbed and heavily undisturbed) using nine microsatellites and 128 genotyping-by-sequencing single nucleotide polymorphism (SNPs) multilocus genotypes of two growth stages (juvenile and adult trees) and their spatial locations. We performed parentage assignments using likelihood approach and undertook spatial genetic structure (SGS) analyses for the two growth stages through correlation among kinship coefficients and geographical distances between pair of individuals. The SNPs showed higher resolving power and assignment rates than microsatellites; however, a combination of the two marker-types improved the assignment rate and provided robust parentage assessments. We found evidence of long-distance (up to 210 m) pollination events for both populations; however, the majority of seed dispersal was found closer to the putative maternal parent. On average, parentage analysis showed high amounts of pollen (40%) and seed (20%) immigration in both populations. Significant positive SGS was found only for the adult cohorts in the less disturbed population for distance classes 20 and 40 m, indicating historical short-distance seed dispersals. Our results suggest long-distance gene flow within the species and we recommend conservation of remnant and isolated populations or individual trees to promote genetic connectivity.

Climate change will disproportionally affect the most genetically diverse lineages of a widespread African tree species

Global climate change is proceeding at an alarming rate with major ecological and genetic consequences for biodiversity, particularly in drylands. The response of species to climate change may differ between intraspecific genetic groups, with major implications for conservation. We used molecular data from 10 nuclear and two chloroplast genomes to identify phylogeographic groups within 746 individuals from 29 populations of Senegalia senegal, a savannah tree species in sub-Saharan Africa. Three phylogroups are identified corresponding to Sudano-Sahelian, Zambezian and Southern African biogeographic regions in West, East and Southern Africa. Genetic diversity was highest in Southern and Zambesian and lowest in the Sudano-Sahelian phylogroups. Using species distribution modeling, we infer highly divergent future distributions of the phylogroups under three climate change scenarios. Climate change will lead to severe reductions of distribution area of the genetically diverse Zambezian (- 41-- 54%) and Southern (- 63-- 82%) phylogroups, but to an increase for the genetically depauperate Sudano-Sahelian (+ 7- + 26%) phylogroups. This study improves our understanding of the impact of climate change on the future distribution of this species. This knowledge is particularly useful for biodiversity management as the conservation of genetic resources needs to be considered in complementary strategies of in-situ conservation and assisted migration.

The impact of anthropogenic disturbances on the genetic diversity of terrestrial species: A global meta-analysis

Human activities are primarily responsible for habitat loss and changes in natural environments around the world. It has been suggested that populations inhabiting human-modified landscapes experience reduced gene flow, inbreeding depression, and loss of alleles due to genetic drift. However, empirical evidence shows the contrasting effects of anthropogenic disturbances on the genetic diversity of species. We performed a meta-analysis of 61 studies that compared the genetic diversity of plant and/or animal populations in disturbed and more preserved areas (316 paired comparisons) to investigate the genetic responses to different disturbance types. There is a negative effect (effect size: -0.45; 95% confidence interval: -0.61, -0.29) of disturbances on genetic diversity, in which the most detrimental effects are caused by the loss of connectivity and forest cover. The methodological approach can explain part of the heterogeneity among the genetic responses detected by primary studies: (a) studies using the number of effective alleles did not detect genetic erosion, while all other indices revealed negative responses to disturbances; and (b) only studies performed with transferred or a combination of transferred and specific microsatellites detected negative responses. The effects on animal populations are more detrimental than in plant populations. Only plant species with a shrub life form, self-incompatible reproductive systems, and biotic pollination and seed dispersal showed negative responses to disturbances. Despite heterogeneity among studies, there is an overall negative effect of disturbances on genetic diversity, which indicates that remaining populations inhabiting human-modified landscapes have reduced evolutionary potential and are prone to local extinction.

Quantitative and Qualitative Genetic Studies of Some Acacia Species Grown in Egypt

The objective of the current work is to study the genetic differentiation between Acacia species growing in Egypt as plant genetic resources based on morphological, biochemical, and molecular markers. The 20 replicates of Acacia tree collected from four localities from Egypt were A. tortilis ssp. raddiana and A. farnesiana (Siwa Oasis and Borg El-Arab City), A. stenophylla, A. sclerosperma (Marsa Matroh City), and A. saligna (Abis Station Farm, Alexandria). The results based on the previous markers indicated highly significant differences between Acacia species, confirming the hypothesis of the possibility of using morphological, biochemical, and molecular parameters in species identification. Qualitative characteristics results indicated some similarities and differences that are taxonomically important for comparing taxonomical grouping with morphological data for the genetic description of Acacia species. The activities of antioxidant enzymes have been studied intensively and the results provide strong similarities between the Acacia species (69%), between A. raddiana (Siwa and Borg Al-Arab) and A. saligna, followed by all Acacia species (50%). Finally, the molecular studies showed that a total of 563 amplification fragments, 190 fragments were monomorphic, and 373 fragments were polymorphic. The highest number of amplification fragments (21) was detected with OPB-20 primer, while OPA-20 showed seven amplification fragments; the average number was 13.09. The results indicated that Acacia species exhibit high genetic differentiation, helpful in the future for genetic improvement programs. The novelty of the current study is highlighting the importance of plant genetic resources in Egypt and using different techniques to measure the differentiation between these species.