José Gabriel Segarra-Moragues

Dated historical biogeography of the temperate Loliinae (Poaceae, Pooideae) grasses in the northern and southern hemispheres

Divergence times and biogeographical analyses have been conducted within the Loliinae, one of the largest subtribes of temperate grasses. New sequence data from representatives of the almost unexplored New World, New Zealand, and Eastern Asian centres were added to those of the panMediterranean region and used to reconstruct the phylogeny of the group and to calculate the times of lineage-splitting using Bayesian approaches. The traditional separation between broad-leaved and fine-leaved Festuca species was still maintained, though several new broad-leaved lineages fell within the fine-leaved clade or were placed in an unsupported intermediate position. A strong biogeographical signal was detected for several Asian-American, American, Neozeylandic, and Macaronesian clades with different affinities to both the broad and the fine-leaved Festuca. Bayesian estimates of divergence and dispersal-vicariance analyses indicate that the broad-leaved and fine-leaved Loliinae likely originated in the Miocene (13My) in the panMediterranean-SW Asian region and then expanded towards C and E Asia from where they colonized the New World. Further expansions in America (10-3.8My) showed a predominant migratory route from North to South (N America<-->the Andes<-->Patagonia). This late Tertiary scenario of successive colonizations and secondary polyploid radiations in the southern hemisphere from the northern hemisphere was accompanied by occasional transcontinental long-distance dispersal events between South America and New Zealand. Multiple Pliocene dispersal events (3.6-2.5My) from the near SW European and NW African continents gave rise to the Macaronesian Loliinae flora, while a more recent Pleistocene origin (2-1My) is hypothesized for the high polyploid lineages that successfully colonized newly deglaciated areas in both hemispheres.

The network structure of plant–arbuscular mycorrhizal fungi

Ecological network theory predicts that in mutualistic systems specialists tend to interact with a subset of species with which generalists interact (i.e. nestedness). Approaching plant-arbuscular mycorrhizal fungi (AMF) association using network analyses will allow the generality of this pattern to be expanded to the ubiquitous plant-AMF mutualism. Based on certain plant-AMF specificity recently suggested, networks are expected to be nested as a result of their mutualistic nature, and modular, with certain species interacting more tightly than others. Network analyses were used to test for nestedness and modularity and to compare the different contribution of plant and AMF to the overall nestedness. Plant-AMF networks share general network properties with other mutualisms. Plant species with few AMFs in their roots tend to associate with those AMFs recorded in most plant species. AMFs present in a few plant species occur in plant species sheltering most AMF (i.e. nestedness). This plant-AMF network presents weakly interlinked subsets of species, strongly connected internally (i.e. modularity). Both plants and AMF show a nested structure, although AMFs have lower nestedness than plants. The plant-AMF interaction pattern is interpreted in the context of how plant-AMF associations can be underlying mechanisms shaping plant community assemblages.

Population subdivision and genetic diversity in two narrow endemics of Antirrhinum L.

Genetic diversity and its partition within and among populations and families of two species of Antirrhinum L., A. charidemi Lange and A. valentinum F.Q., have been studied. Both species are narrow‐range endemics, self‐incompatible, ecologically specialized and form small isolated populations. Despite these similarities, the species differ markedly in the distribution of genetic diversity. In A. valentinum, 61.64% of the total variation was distributed among populations, whereas in A. charidemi it was only 8.55%. A. charidemi showed little population divergence (GST = 0.0542) relative to A. valentinum (GST = 0.4805). In neither species was within‐population genetic diversity correlated with population size, nor were there significant correlations between genetic and geographical distances. These results are discussed in relation to differences in flowering time and habitat continuity. They suggest that caution should be taken when making generalizations about levels of genetic variation and patterns of plant reproduction, life history and geographical distribution.

Burning phylogenies: Fire, molecular evolutionary rates, and diversification

Abstract Mediterranean-type ecosystems are among the most remarkable plant biodiversity “hot spots” on the earth, and fire has traditionally been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters, particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters—which did not agree with theoretical predictions—may occur if (1) the timing of the switch from seeding to resprouting (or vice versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems

Plant facilitation occurs between species differing in their associated arbuscular mycorrhizal fungi

Complementary beneficial effects of different arbuscular mycorrhizal fungi (AMF) can result in a more efficient exploitation of the soil nutrients available, thus influencing plant communities. Here, we hypothesize that plant-AMF specificity is mediated by phylogenetic constraints defining possible interactions, and that plant-AMF interaction patterns can influence plant-plant facilitation specificity. We reanalyzed previous data describing plant-plant and plant-AMF interaction at the community level to specifically test for a phylogenetic signal on plant and AMF interactions and for a relationship between plant-plant facilitation specificity and plant species differences in their AMF associates. Closely related AMF operational taxonomical units (OTUs) tend to interact with the same plant species, but there is not a significant signal in the interaction through the plant phylogeny. This indicates that the similarity in the AMF associates of two plant species is independent of their phylogenetic relatedness. Interestingly, plant-AMF interactions match plant facilitation specificity, with pairs of plant species recruiting more frequently under each other tending to have different AMF associates. An increment of AMF diversity in the rhizosphere, as a result of plant-AMF and plant-plant selectivity, is suggested as a potential driver of plant-plant facilitation. This study highlights the role of plant-AMF interactions in shaping plant community assemblages.

On the verge of extinction: genetics of the critically endangered Iberian plant species, Borderea chouardii (Dioscoreaceae) and implications for conservation management.

Borderea chouardii is a relictual and dioecious, strictly sexually reproducing, long‐living geophyte of the Dioscoreaceae family. Previous biological and demographic studies have indicated the existence of a uniformly distributed panmictic population of this taxon at the southernmost Spanish pre‐Pyrenean mountain ranges where it occurs in rather inaccessible crevices of a single limestone cliff. However, individuals of B. chouardii are spatially subdivided into two subpopulations located, respectively, on the upper and lower parts of the cliff, and vertically separated 150 m. Because of its extreme rarity, B. chouardii was the first Iberian taxon to have a specific conservation plan and has been included in several red lists under the category of critically endangered (CR). However, no previous attempts have been conducted to analyse the fine scale evolutionary mechanisms involved in its present microspatial distribution. Genetic diversity and population structure have been investigated through the analysis of neutral hypervariable markers such as simple sequence repeats (SSRs) and randomly amplified polymorphic DNAs (RAPDs) to unravel the impact of life history traits in the differentiation of the two subpopulations. Both types of molecular markers were unequivocal in distinguishing two genetically distinct groups of individuals corresponding to their spatial separation. However, SSRs detected a higher level of subpopulation differentiation (FST = 0.35, RST = 0.32) than RAPDs (FST = 0.21). SSR data indicated significant deviation from random dispersal of genes and genotypes between the two groups, suggesting that mating occurs mainly among individuals within subpopulations, thus, favouring the divergence between the two groups. This microevolutionary differentiation scenario might have been caused by a coupled effect of past genetic drift and reproductive isolation, as a result of strong glacial age bottlenecks and inefficient dispersal system of pollen and seeds, respectively. The identification of such genetic structure in this narrow endemic prompts a modification of the management strategies of its single extant population.

POSTFIRE RESPONSE AND GENETIC DIVERSITY IN ERICA COCCINEA: CONNECTING POPULATION DYNAMICS AND DIVERSIFICATION IN A BIODIVERSITY HOTSPOT

Understanding the processes of biological diversification is a central topic in evolutionary biology. The South African Cape fynbos, one of the major plant biodiversity hotspots out of the tropics, has prompted several hypotheses about the causes of generation and maintenance of biodiversity. Fire has been traditionally invoked as a key element to explain high levels of biodiversity in highly speciose fynbos taxa, such as the genus Erica. In this study, we have implemented a microevolutionary approach to elucidate how plant‐response to fire may contribute to explain high levels of diversification in Erica. By using microsatellite markers, we investigated the genetic background of seeder (fire‐sensitive) and resprouter (fire‐resistant) populations of the fynbos species Erica coccinea. We found higher within‐population genetic diversity and higher among‐population differentiation in seeder populations and interpreted these higher levels of genetic diversification as a consequence of the comparatively shorter generation times and faster population turnover in the seeder form of this species. Considering that genetic divergence among populations may be seen as the initial step to speciation, the parallelism between these results and the pattern of biodiversity at the genus level offers stimulating insights into understanding causes of speciation of the genus Erica in the Cape fynbos.

A Bayesian Approach for Discriminating Among Alternative Inheritance Hypotheses in Plant Polyploids: The Allotetraploid Origin of Genus Borderea (Dioscoreaceae)

Polyploidy is a common phenomenon occurring in a vast number of land plants. Investigations of patterns of inheritance and the origins of plants (i.e., autopolyploidy vs. allopolyploidy) usually involve cytogenetic and molecular studies of chromosome pairing, chromosome mapping, and marker segregation analysis through experimental crosses and progeny tests. Such studies are missing for most wild species, for which artificial crosses are difficult, not feasible, or unaffordable. We report here a Bayesian method to discriminate between alternative inheritance patterns in the two extant, tetraploid species of the monocot genus Borderea (Dioscoreaceae), which does not involve progeny array tests. Our approach is based on the screening of a large number of SSR genotypes, which were obtained from successful amplifications of 17 microsatellite regions in individuals of both B. chouardii and B. pyrenaica. We tested for tetrasomic vs. disomic modes of inheritance, using the Bayes factor test. Assignment of genotypes under both alternatives could be unequivocally done for 14 and 11 of the 17 studied microsatellite regions in B. chouardii and B. pyrenaica, respectively, totaling 9502 analyzed genotypes. The comparison of posterior probabilities for the two competing hypotheses across the surveyed loci clearly favored a disomic inheritance pattern. Linkage tests indicated that none of the studied SSR loci were in linkage disequilibrium, thus representing independent samples of the Borderea genome. These results, along with previous allozyme data, support the allotetraploid origin of this paleoendemic genus and reveal the lowest reported chromosome base number for the family of the yams.

Allozyme and chloroplast DNA variation in island and mainland populations of the rare Spanish endemic, Silene hifacensis (Caryophyllaceae)

Silene hifacensis is a narrowly endemicplant, restricted to a few small populations onlimestone cliffs in the Spanish province ofAlicante and on the Balearic island of Ibiza.The species was collected to extinction in itsoriginal mainland location by the early 20thcentury. Attempts have been made to reintroduceS. hifacensis to this area butconservation efforts are limited by a lack ofinformation on the geographic structure ofgenetic variation in the species. We usednuclear (allozyme) and chloroplast DNA (cpDNA)PCR/RFLP markers to investigate the structureof genetic variation in 2 mainland and 6 Ibizanpopulations. Levels of allozyme variation werelow, with a mean of 2 alleles per polymorphiclocus. Mean (over polymorphic loci) totalallozyme diversity (Htot) was 0.203 and meanwithin-population diversity (Hpop) was 0.085. Mostdiversity was explained by thebetween-population diversity component (Gpop.reg =57%). Both mainland populations showedallozyme fixation. Three composite cpDNAhaplotypes were identified. The first is uniqueto a mainland population that is alsoallozymically distinct from all the otherpopulations. The second haplotype is found inthe other mainland population and one Ibizanpopulation: these two populations areallozymically identical. The remaining Ibizanpopulations contain the third haplotype. Thegeographic distribution of allozymes and cpDNAhaplotypes is discussed in terms of populationhistory, dispersal and, speculatively, in termsof the possibility that there has beenundocumented translocation of material betweenpopulations.

Historical and biological determinants of genetic diversity in the highly endemic triploid sea lavender Limonium dufourii (Plumbaginaceae)

Microsatellite markers were used to evaluate the genetic diversity and population genetic structure in the critically endangered Limonium dufourii (Plumbaginaceae), a highly endemic triploid species from the coasts of eastern Spain. Sixty‐five alleles from 13 microsatellite regions were amplified in a sample of 122 individuals collected from the six extant populations. Microsatellite patterns were consistent with the triploid nature of L. dufourii. Alleles were unambiguously assigned to two different parental subgenomes in this hybrid species and the greater contribution of the diploid parental subgenome was confirmed. Eleven, 25 and 26 multilocus genotypes were recorded from the haploid, diploid and from the combined information of both subgenomes, respectively. Genetic diversity was mostly distributed among populations (72.06% of the total genetic variation). Genotypes from Marjal del Moro populations grouped into two highly structured clusters (88.41% of the total variance). The observed patterns of distribution of genetic diversity are interpreted to result from multiple hybridization events and isolation between populations. Threats to this species are mainly anthropogenic (urbanization and tourism pressure), although stochastic risks cannot be ignored. Therefore, in order to preserve extant genetic variation of L. dufourii, in situ strategies such as the preservation of its habitat are a high priority. Several recommendations in order to assist ex situ measures to guarantee the success of conservation strategies and maintain the relationships between individuals and populations are proposed.