Allozyme variation and structure of the Canarian endemic palm tree Phoenix canariensis (Arecaceae): implications for conservation

The sweet tabaiba or there and back again: phylogeographical history of the Macaronesian Euphorbia balsamifera

BACKGROUND AND AIMS

Biogeographical relationships between the Canary Islands and north-west Africa are often explained by oceanic dispersal and geographical proximity. Sister-group relationships between Canarian and eastern African/Arabian taxa, the 'Rand Flora' pattern, are rare among plants and have been attributed to the extinction of north-western African populations. Euphorbia balsamifera is the only representative species of this pattern that is distributed in the Canary Islands and north-west Africa; it is also one of few species present in all seven islands. Previous studies placed African populations of E. balsamifera as sister to the Canarian populations, but this relationship was based on herbarium samples with highly degraded DNA. Here, we test the extinction hypothesis by sampling new continental populations; we also expand the Canarian sampling to examine the dynamics of island colonization and diversification.

METHODS

Using target enrichment with genome skimming, we reconstructed phylogenetic relationships within E. balsamifera and between this species and its disjunct relatives. A single nucleotide polymorphism dataset obtained from the target sequences was used to infer population genetic diversity patterns. We used convolutional neural networks to discriminate among alternative Canary Islands colonization scenarios.

KEY RESULTS

The results confirmed the Rand Flora sister-group relationship between western E. balsamifera and Euphorbia adenensis in the Eritreo-Arabian region and recovered an eastern-western geographical structure among E. balsamifera Canarian populations. Convolutional neural networks supported a scenario of east-to-west island colonization, followed by population extinctions in Lanzarote and Fuerteventura and recolonization from Tenerife and Gran Canaria; a signal of admixture between the eastern island and north-west African populations was recovered.

CONCLUSIONS

Our findings support the Surfing Syngameon Hypothesis for the colonization of the Canary Islands by E. balsamifera, but also a recent back-colonization to the continent. Populations of E. balsamifera from northwest Africa are not the remnants of an ancestral continental stock, but originated from migration events from Lanzarote and Fuerteventura. This is further evidence that oceanic archipelagos are not a sink for biodiversity, but may be a source of new genetic variability.

Population genetics data help to guide the conservation of palm species with small population sizes and fragmented habitats in Madagascar

BACKGROUND

The need to incorporate genetic data into conservation management decisions is increasingly recognised. However, many published studies represent a 'gold standard' of sampling, techniques, and analyses. Such rigour is often not possible with limited funding and resourcing available for developing plans for the increasing number of threatened species requiring conservation management. Two endemic palm species of the Itremo Massif in central Madagascar, Dypsis ambositrae and D. decipiens, are known to be threatened with extinction and conservation management for these species is a priority for the newly created protected area in the region.

METHODS

The genetic diversity of these two species was studied using the relatively low-cost and rapid AFLP technique. DNA fragments generated using three primer combinations were analysed for 20 and 50 individuals of the two species, respectively, from across their ranges.

RESULTS

Genetic diversity was relatively low for both species. The two sites where the highly restricted D. ambositrae grows were found to be genetically distinct (although overall heterozygosity was low). Despite having a much wider distribution and relatively large population, D. decipiens did not show clear geographical nor genetic groupings and had similarly low genetic heterozygosity to D. ambositrae.

DISCUSSION AND RECOMMENDATIONS

With so few individuals remaining in the wild and two genetically distinct subpopulations, it is recommended that both sites of D. ambositrae are conserved and that seed are collected from both for ex situ conservation and potential future reintroduction. It may be less important to focus resources on conserving or collecting ex situ material from all sites where D. decipiens is found, as the genetic diversity represented by each subpopulation is limited and increasing sampling may not protect significantly higher levels of genetic diversity. This study provides data that inform and support conservation decisions taken for both species within this region, and in the management of the newly designated Itremo Massif Protected Area, which covers most of the sites where these two species remain in the wild.

At risk of population decline? An ecological and genetic approach to the threatened palm species Butia eriospatha (Arecaceae) of Southern Brazil

To estimate the risk of population decline for the threatened palm species Butia eriospatha, we investigated the patterns of demography, natural regeneration, herbivory, and the levels of genetic diversity using 9 microsatellite loci from both adults and seedlings sampled from 4 populations in Southern Brazil (n = 330). Our results indicate that cattle grazing in B. eriospatha population areas severely affect their demographic structure. Three B. eriospatha populations showed a bimodal age structure made up of adult plants and seedlings and high rates (>77%) of livestock herbivory. For 1 population, we describe and quantify for the first time the occurrence of 6 ontogenetic stages for this threatened palm species. Populations of B. eriospatha showed high levels of genetic differentiation (F ST adult plants = 0.287, F ST seedlings = 0.175). The amount of observed heterozygosity differed significantly between small (H O = 0.329) and large populations (H O = 0.461), indicating that small populations can be more susceptible to genetic drift. With no recruitment and a mortality rate of 2.0%, we show that the populations investigated in this study would be at an extremely high risk of local extinction, with a greater than 50% reduction in the effective population size, in the next 40 years. Although this study highlights the importance of analyzing both population ecology parameters and genetic data to better understand the level of risk facing threatened species, we emphasize that policy actions are urgently needed for effective conservation of this vulnerable biological resource.

A review of the allozyme data set for the Canarian endemic flora: causes of the high genetic diversity levels and implications for conservation

Background and Aims Allozyme and reproductive data sets for the Canarian flora are updated in order to assess how the present levels and structuring of genetic variation have been influenced by the abiotic island traits and by phylogenetically determined biotic traits of the corresponding taxa; and in order to suggest conservation guidelines. Methods Kruskal-Wallis tests are conducted to assess the relationships of 27 variables with genetic diversity (estimated by A, P, Ho and He) and structuring (GST) of 123 taxa representing 309 populations and 16 families. Multiple linear regression analyses (MLRAs) are carried out to determine the relative influence of the less correlated significant abiotic and biotic factors on the genetic diversity levels. Key Results and Conclusions The interactions between biotic features of the colonizing taxa and the abiotic island features drive plant diversification in the Canarian flora. However, the lower weight of closeness to the mainland than of (respectively) high basic chromosome number, partial or total self-incompatibility and polyploidy in the MLRAs indicates substantial phylogenetic constraint; the importance of a high chromosome number is feasibly due to the generation of a larger number of linkage groups, which increase gametic and genotypic diversity. Genetic structure is also more influenced by biotic factors (long-range seed dispersal, basic chromosome number and partial or total self-incompatibility) than by distance to the mainland. Conservation-wise, genetic structure estimates (FST/GST) only reflect endangerment under intensive population sampling designs, and neutral genetic variation levels do not directly relate to threat status or to small population sizes. Habitat protection is emphasized, but the results suggest the need for urgent implementation of elementary reproductive studies in all cases, and for ex situ conservation measures for the most endangered taxa, even without prior studies. In non-endangered endemics, multidisciplinary research is needed before suggesting case-specific conservation strategies. The molecular information relevant for conservation should be conserved in a standardized format to facilitate further insight.

Molecular markers reveal no genetic differentiation between Myrica rivas-martinezii and M. faya (Myricaceae)

BACKGROUND AND AIMS

Myrica rivas-martinezii is a critically endangered endemic of the laurel forest of the Canary Islands and co-occurs very close to M. faya. Some authors suggest that M. rivas-martinezii and M. faya are two morphs of the same species, so molecular markers were used to estimate the levels and structuring of genetic variation within and among natural populations in order to evaluate genetic relationships between these two congeners.

METHODS

Six polymorphic microsatellite (simple sequence repeat, SSR) markers were used to determine the genetic diversity and the genetic relationship between both Myrica species.

KEY RESULTS

Most of the natural populations analysed were in Hardy-Weinberg equilibrium for both taxa. Analysis of molecular variance (AMOVA) for both species revealed that most of the genetic variability detected was contained within populations (92.48 and 85.91 % for M. faya and M. rivas-martinezii, respectively), which it is consistent with outcrossing and dioecious plants. Estimates of interpopulation genetic variation, calculated from F(ST) and G'(ST), were quite low in the two taxa, and these values did not increase substantially when M. rivas-martinezii and M. faya populations were compared. The UPGMA dendrogram based on Nei's genetic distance clustered the populations by their island origin, independently of taxon. In fact, the mixture of individuals of both taxa did not appreciably disrupt the intrapopulational genetic cohesion, and only 3.76 % variation existed between species.

CONCLUSIONS

All the results obtained using molecular markers indicate clearly that both taxa share the same genetic pool, and they are probably the same taxa. Considering that M. rivas-martinezii is classified as at risk of extinction, there should be a change of focus of the current management actions for the conservation of this putatively endangered Canarian endemic.