Asexual Origin Research Articles

Digest: Rare male offspring highlight an alternative pathway to obligate asexuality.

Obligate asexuality has arisen many times in eukaryotes, often related to the disrupted function of the core meiotic machinery. For obligately asexual lineages that evolve from facultatively asexual ancestors, there exists another possibility, namely altered regulation of preexisting asexual reproductive processes to produce obligate asexuality. These different pathways leave different signatures in properties of meiosis and recombination that could provide insights into the origin of asexuality. A new study by Molinier et al. (2023) investigates this problem and finds largely typical recombination rates during spermatogenesis of rare, asexually produced sons of obligately asexual Daphnia pulex, suggesting that regulation of reproduction, rather than disruption of meiosis, underpins obligate asexuality in Daphnia.

Comparative Genomics of Sex, Chromosomes, and Sex Chromosomes in Caenorhabditis elegans and Other Nematodes.

The nematode phylum has evolved a remarkable diversity of reproductive modes, including the repeated emergence of asexuality and hermaphroditism across divergent clades. The species-richness and small genome size of nematodes make them ideal systems for investigating the genome-wide causes and consequences of such major transitions. The availability of functional annotations for most Caenorhabditis elegans genes further allows the linking of patterns of gene content evolution with biological processes. Such gene-centric studies were recently complemented by investigations of chromosome evolution that made use of the first chromosome-scale genome assemblies outside the Caenorhabditis genus. This review highlights recent comparative genomic studies of reproductive mode evolution addressing the hybrid origin of asexuality and the parallel gene loss following the emergence of hermaphroditism. It further summarizes ongoing efforts to characterize ancient linkage blocks called Nigon elements, which form central units of chromosome evolution. Fusions between Nigon elements have been demonstrated to impact recombination and speciation. Finally, multiple recent fusions between autosomal and thesex-linked Nigon element reveal insights into the dynamic evolution of sex chromosomes across various timescales.

Population Genomic Analyses Suggest a Hybrid Origin, Cryptic Sexuality, and Decay of Genes Regulating Seed Development for the Putatively Strictly Asexual Kingdonia uniflora (Circaeasteraceae, Ranunculales).

Asexual lineages are perceived to be short-lived on evolutionary timescales. Hence, reports for exceptional cases of putative 'ancient asexuals' usually raise questions about the persistence of such species. So far, there have been few studies to solve the mystery in plants. The monotypic Kingdonia dating to the early Eocene, contains only K. uniflora that has no known definitive evidence for sexual reproduction nor records for having congeneric sexual species, raising the possibility that the species has persisted under strict asexuality for a long period of time. Here, we analyze whole genome polymorphism and divergence in K. uniflora. Our results show that K. uniflora is characterized by high allelic heterozygosity and elevated πN/πS ratio, in line with theoretical expectations under asexual evolution. Allele frequency spectrum analysis reveals the origin of asexuality in K. uniflora occurred prior to lineage differentiation of the species. Although divergence within K. uniflora individuals exceeds that between populations, the topologies of the two haplotype trees, however, fail to match each other, indicating long-term asexuality is unlikely to account for the high allele divergence and K. uniflora may have a recent hybrid origin. Phi-test shows a statistical probability of recombination for the conflicting phylogenetic signals revealed by the split network, suggesting K. uniflora engages in undetected sexual reproduction. Detection of elevated genetic differentiation and premature stop codons (in some populations) in genes regulating seed development indicates mutational degradation of sexuality-specific genes in K. uniflora. This study unfolds the origin and persistence mechanism of a plant lineage that has been known to reproduce asexually and presents the genomic consequences of lack of sexuality.

Polyembryony in citrus: does the largest embryo in the seed develop a nucellar seedling?

A generalized concept in the Citrus genus is that highly polyembryonic varieties produce only a small number of hybrids. Small zygotic embryos congregate primarily near the micropyle, while nucellar embryos organize near or away from the micropyle. In the present study, the authors determined the number of polyembryonic seeds, embryos per seed, and the largest embryo (LE) position in five citrus cultivars: C35 citrange, Volkamer lemon, Amblycarpa mandarin, Minneola tangelo, and Valencia orange. The percentage of nucellar seedlings obtained exclusively from the LE per seed was then calculated. The polyembryony percentage varied largely between genotypes, from 65 to 98 %, and the mean number of embryos ranged from 2.9 to 4.6. The chalaza contained up to 87 % of the LE. Out of 30 primers, 17 Simple sequence repeats [SSRs] (AG14, ATC09, CAT01, CCSM147, CCSM18, CCSM13, CCSM4, F2, F4, F6, GT03, TAA41, TAA45, TAA1, F7, F11 and TAA52) identified nucellar plants identical to the female parent (genetic similarity index [GSI] value ≥ 0.95). This study establishes for the first time the relationship between the sexual or asexual origin of seedlings derived from LE embryos isolated from seeds and the SSR primers described above. While the five citrus cultivars had high polyembryony levels, 30 % of the resulting plants differed from the female parent in C35 Citrange, 45 % in Volkamer lemon, 15 % in Amblycarpa mandarin, 15 % in Valencia orange, and 45 % in Minneola tangelo. The largest seedling is not always nucellar: in the five citrus species studied, the LE produces 55 to 85 % of the nucellar embryos.

Genome-Wide Allele-Specific Expression in Obligately Asexual Daphnia pulex and the Implications for the Genetic Basis of Asexuality.

Although obligately asexual lineages are thought to experience selective disadvantages associated with reduced efficiency of fixing beneficial mutations and purging deleterious mutations, such lineages are phylogenetically and geographically widespread. However, despite several genome-wide association studies, little is known about the genetic elements underlying the origin of obligate asexuality and how they spread. Because many obligately asexual lineages have hybrid origins, it has been suggested that asexuality is caused by the unbalanced expression of alleles from the hybridizing species. Here, we investigate this idea by identifying genes with allele-specific expression (ASE) in a Daphnia pulex population, in which obligate parthenogens (OP) and cyclical parthenogens (CP) coexist, with the OP clones having been originally derived from hybridization between CP D. pulex and its sister species, Daphnia pulicaria. OP D. pulex have significantly more ASE genes (ASEGs) than do CP D. pulex. Whole-genomic comparison of OP and CP clones revealed ∼15,000 OP-specific markers and 42 consistent ASEGs enriched in marker-defined regions. Ten of the 42 ASEGs have alleles coding for different protein sequences, suggesting functional differences between the products of the two parental alleles. At least three of these ten genes appear to be directly involved in meiosis-related processes, for example, RanBP2 can cause abnormal chromosome segregation in anaphase I, and the presence of Wee1 in immature oocytes leads to failure to enter meiosis II. These results provide a guide for future molecular resolution of the genetic basis of the transition to ameiotic parthenogenesis.

Genomic population structure of sympatric sexual and asexual populations in a parasitic wasp, Meteorus pulchricornis (Hymenoptera: Braconidae), inferred from six hundred single-nucleotide polymorphism loci.

In spite of the two-fold reproductive advantage, asexual reproduction is not common in nature, probably due to the associated genetic deterioration or reduced genetic variation. To understand how genetic diversity is maintained in existing asexual populations, we investigated the genetic diversity and population structure of sympatric sexual and asexual populations of a parasitic wasp, Meteorus pulchricornis, using 614 genome-wide single nucleotide polymorphisms. The genetic structures of the apomictic asexual populations were distinct, showing considerable genetic differentiation among them. Most of the asexual populations were highly differentiated from the sympatric sexual population; some asexual individuals could not be distinguished from members of the sexual population. Furthermore, significantly fewer multilocus genotypes were identified in the asexual populations (1-7) compared to the sexual population (42), which is consistent with their apomictic nature. The observed patterns of fixed heterozygous sites suggest that most asexual populations had the same evolutionary origin and have long since evolved individually; the detected gene flow between the sexual population and a few asexual population may indicate independent origins of asexuality. The potential role of occasional males in apomictic wasps is also discussed.

BioEssays 1/2021

The origins of asexuality in plants as well as animals have long puzzled researchers. In article 2000111, Diego Hojsgaard and Manfred Schartl integrate old ideas with recent molecular and genomic data and provide a single mechanistic model for this phenomenon. They highlight two usually overlooked conditions to understand the molecular nature of clonal organisms to explain asexuals' developmental diversity and biologically vague cases such as automixis and polyploidy.

Hybridization promotes asexual reproduction in Caenorhabditis nematodes.

Although most unicellular organisms reproduce asexually, most multicellular eukaryotes are obligately sexual. This implies that there are strong barriers that prevent the origin or maintenance of asexuality arising from an obligately sexual ancestor. By studying rare asexual animal species we can gain a better understanding of the circumstances that facilitate their evolution from a sexual ancestor. Of the known asexual animal species, many originated by hybridization between two ancestral sexual species. The balance hypothesis predicts that genetic incompatibilities between the divergent genomes in hybrids can modify meiosis and facilitate asexual reproduction, but there are few instances where this has been shown. Here we report that hybridizing two sexual Caenorhabditis nematode species (C. nouraguensis females and C. becei males) alters the normal inheritance of the maternal and paternal genomes during the formation of hybrid zygotes. Most offspring of this interspecies cross die during embryogenesis, exhibiting inheritance of a diploid C. nouraguensis maternal genome and incomplete inheritance of C. becei paternal DNA. However, a small fraction of offspring develop into viable adults that can be either fertile or sterile. Fertile offspring are produced asexually by sperm-dependent parthenogenesis (also called gynogenesis or pseudogamy); these progeny inherit a diploid maternal genome but fail to inherit a paternal genome. Sterile offspring are hybrids that inherit both a diploid maternal genome and a haploid paternal genome. Whole-genome sequencing of individual viable worms shows that diploid maternal inheritance in both fertile and sterile offspring results from an altered meiosis in C. nouraguensis oocytes and the inheritance of two randomly selected homologous chromatids. We hypothesize that hybrid incompatibility between C. nouraguensis and C. becei modifies maternal and paternal genome inheritance and indirectly induces gynogenetic reproduction. This system can be used to dissect the molecular mechanisms by which hybrid incompatibilities can facilitate the emergence of asexual reproduction.

Asexual reproduction and heterozygote selection in an Antarctic demosponge (Stylocordyla chupachus, Suberitida)

Antarctic bottoms harbor stable, benthic communities, subjected to low temperatures. Environmental stability may promote the asexual (clonal) reproduction of sponges to maintain adapted genotypes to those particular conditions. Stylocordyla chupachups forms patchy populations across the Antarctic continental shelf. Individuals are mostly similar in size without distinct cohorts, which indicates fast growth of the new recruits. Settlement of incubated (clonal?) functional sponges may accelerate sponge growth and success at early colonization phases. To analyze the weight of clonal reproduction in the species, a genetic study was performed on three close populations using eight polymorphic microsatellite loci that were designed from massive sequencing. The three study populations showed a relatively low genetic diversity and low loci polymorphism (from 2 to 6 alleles). The estimators of genetic structure, the Analysis of the Molecular Variance (AMOVA), and the presence of private alleles indicated low but significant structure between the populations. A relatively high rate of asexual reproduction (ca. 25% of the individuals) was detected. The program MLGsim found five identical multilocus genotypes (MLGs) with an asexual origin. An excess of heterozygotes (in five out of the eight loci genotyped) was found, which suggests a positive selection mechanism for heterozygotes. The relatively high rates of asexual reproduction may be the result of adaptation to the environmental stability, while heterozygote selection would help maintain some genetic diversity in the populations. S. chupachups has been reported to be one of the first sponge species recolonizing bare areas resulting from iceberg scouring, which indicates a high species fitness and adaptation to Antarctic bottoms. Two out of the three study populations showed bottleneck, which may indicate a recent founder effect and supports the pioneer nature of this species.

High genotypic diversity of the reef-building coral <i>Porites lobata</i> (Scleractinia: Poritidae) in Isla del Coco National Park, Costa Rica

The isolated Isla del Coco experiences periodic, extreme disturbances which devastate coral reefs surrounding the island. Scleractinian corals build the physical structure of the reef therefore ecosystem recovery relies on coral species recovery. Coral recruits can be of sexual or asexual origin, and the relative success of the two recruit types influences the speed and spread of recovery processes. Here we focus on the massive coral, Porites lobata, because it is the main reef-builder around Isla del Coco to describe the relative contribution of asexual and sexual recruits to population maintenance. P. lobata samples were collected using a spatially explicit random sampling design in three plots at Isla del Coco: Punta Ulloa (n=17), Bahía Weston (n=20) and Punta María (n=20) and samples were genotyped with 11 microsatellite markers. Additional sampling was conducted at three “coastal” sites near the Costa Rican mainland (Isla del Caño Biological Reserve): Caño1 (n=8), Caño2 (n=10), Caño5 (n=11) to compare the contributions of asexual and sexual recruits at Isla del Coco sites to coastal sites. Isla del Coco sites were characterized by small colony size (>60% of colonies <0.5m2) and high sexual reproduction. Sites were either mostly or entirely sexual,consisting of only unique genotypes (NG/N= 0.90-1.00; G O/GE=0.83-1.00; D=0.99-1.00). Although there were no significant differences in genetic diversity (number of alleles per locus, number of private alleles) or colony size between Isla del Coco and the coastal sites, the coastal sites exhibited a greater range of genotypic diversity from moderately asexual (NG/N=0.5; GO/GE=0.36; D=0.8) to purely sexual (NG/N=1.0; GO/GE=1.0; D=1.0). The mode of asexual reproduction in P. lobata is likely fragmentation of adult colonies rather than asexual larval production because ramets of P. lobata occurred close together and asexually produced larvae have not been reported in gonochoric broadcast spawners like P. lobata. Frequent sexual reproduction at Isla del Coco National Park might represent a resource for rapid recovery following extreme El Niño-Southern Oscillation (ENSO) disturbance events. In contrast, larger, asexuallyproduced fragments rather than smaller, sexually-produced larvae appear to have the advantage at some coastal sites. The high frequency of sexual reproduction at Isla del Coco indicates that not only are sexual partners available but also current conditions are favorable for the delivery of larvae and the rate of predation on small larval recruits must be moderate. Citation: Boulay, J.N., J. Cortés, J. Nivia-Ruiz & I.B. Baums. 2012. High genotypic diversity of the reef-building coral Porites lobata (Scleractinia: Poritidae) in Isla del Coco National Park, Costa Rica. Rev. Biol. Trop. 60 (Suppl. 3): 279-292. Epub 2012 Dec 01.

Chloroplast DNA sequencing and detailed microsatellite genotyping of all remnant populations suggests that only a single genet survives of the critically endangered plant Rehmannia japonica.

Rehmannia japonica (Thunb.) Makino ex T. Yamaz. is an endangered perennial herb species in Japan. Although earlier the Japanese considered it a variety of R. glutinosa, recent Japanese taxonomists have consistently regarded it as an independent species. According to the historical literature, Rehmannia japonica seems to have been known in China and Japan in the past. However, Chinese taxonomists do not recognize R. japonica at present. In Japan, only two populations are known, and although these populations flower every year, seed reproduction has not been observed. In this study, we aimed to reveal the phylogenetic relationships and levels of genetic diversity of R. japonica. A haplotype network based on two chloroplast DNA regions (trnL-trnF and rps16) showed that the sequences of R. japonica were distinguishable by three or four sites of indels from the most closely related species, R. chingii, consistent with the separate species status of R. japonica. An analysis of genetic diversity using twelve microsatellite loci showed that all of the ramets of R. japonica collected from two geographically isolated populations had an identical multilocus genotype, including identical heterozygous genotypes at six loci. This result indicated asexual origin of all sampled ramets. This study also suggests that the absence of sexual reproduction of R. japonica is explained by self-incompatibility combined with only a single genet remaining in the R. japonica populations.

Asexual origin of brooding in the sea anemones Actinia equina and A. schmidti: molecular evidence from the Portuguese shore

ABSTRACTReproduction by sexual or asexual viviparity is a common phenomenon in some anemone species. In this short communication, the origin of the brooded young of Actinia equina and A. schmidti from the Portuguese shore was investigated. DNA was extracted from 56 brooding adult Actinia sp. and the nuclear gene that codes for the 28S ribosomal subunit was sequenced. Species identity was then assessed using GenBank. In total, 50 individuals were A. schmidti, five were A. equina and one had a hybrid origin. Three adult anemones (the hybrid, one A. equina and one A. schmidti) possessed two different 28S sequences and so their offspring was selected for further analysis using the same molecular procedure. Each brooded polyp was found to possess the exact same sequence as its parent, strongly suggesting the asexual origin of broods in A. equina and A. schmidti.

Hybridization and the Origin of Contagious Asexuality in Daphnia pulex.

Hybridization plays a potentially important role in the origin of obligate parthenogenesis (OP) in many organisms. However, it remains controversial whether hybridization directly triggers the transition from sexual reproduction to obligate asexuality or a hybrid genetic background enables asexual species to persist. Furthermore, we know little about the specific genetic elements from the divergent, yet still hybridizing lineages responsible for this transition and how these elements are further spread to create other OP lineages. In this study, we address these questions in Daphnia pulex, where cyclically parthenogenetic (CP) and OP lineages coexist. Ancestry estimates and whole-genome association mapping using 32 OP isolates suggest that a complex hybridization history between the parental species D. pulex and D. pulicaria is responsible for the introgression of a set of 647 D. pulicaria single nucleotide polymorphism alleles that show perfect association with OP. Crossing experiments using males of OP lineages and females of CP lineages strongly support a polygenic basis for OP. Single-sperm analyses show that although normal meiotic recombination occurs in the production of haploid sperm by males of OP lineages, a significant proportion of such sperm are polyploid, suggesting that the spread of asexual elements through these males (i.e., contagious asexuality) is much less efficient than previously envisioned. Although the current Daphnia genome annotation does not provide mechanistic insight into the nature of the asexuality-associated alleles, these alleles should be considered as candidates for future investigations on the genetic underpinnings of OP.

When sexual meets apomict: genome size, ploidy level and reproductive mode variation of Sorbus aria s.l. and S. austriaca (Rosaceae) in Bosnia and Herzegovina.

Allopolyploidy and intraspecific heteroploid crosses are associated, in certain groups, with changes in the mating system. The genus Sorbus represents an appropriate model to study the relationships between ploidy and reproductive mode variations. Diploid S. aria and tetraploid apomictic S. austriaca were screened for ploidy and mating system variations within pure and sympatric populations in order to gain insights into their putative causalities. Flow cytometry was used to assess genome size and ploidy level among 380 S. aria s.l. and S. austriaca individuals from Bosnia and Herzegovina, with 303 single-seed flow cytometric seed screenings being performed to identify their mating system. Pollen viability and seed set were also determined. Flow cytometry confirmed the presence of di-, tri- and tetraploid cytotype mixtures in mixed-ploidy populations of S. aria and S. austriaca. No ploidy variation was detected in single-species populations. Diploid S. aria mother plants always produced sexually originated seeds, whereas tetraploid S. austriaca as well as triploid S. aria were obligate apomicts. Tetraploid S. aria preserved sexuality in a low portion of plants. A tendency towards a balanced 2m : 1p parental genome contribution to the endosperm was shared by diploids and tetraploids, regardless of their sexual or asexual origin. In contrast, most triploids apparently tolerated endosperm imbalance. Coexistence of apomictic tetraploids and sexual diploids drives the production of novel polyploid cytotypes with predominantly apomictic reproductive modes. The data suggest that processes governing cytotype diversity and mating system variation in Sorbus from Bosnia and Herzegovina are probably parallel to those in other diversity hotspots of this genus. The results represent a solid contribution to knowledge of the reproduction of Sorbus and will inform future investigations of the molecular and genetic mechanisms involved in triggering and regulating cytotype diversity and alteration of reproductive modes.

Determinación histológica de regenerantes de Euchile mariae (Ames) Withner, (Orchidaceae), obtenidos a partir de protocormos cultivados in vitro

From the germination of seeds of Euchile mariae in modified MS medium, the formation of pro- tocorms was achieved. Once these reached an average size from 2 to 5 mm long and the formation of his first leaf primordium, they were used like explants to induce a morphogenetic response. Through in vitro culture of top and bottom protocorms sections, were obtained differentiated structures from asexual origin. Their morphology was similar to protocorms obtained from the germination of seeds, in this way we call them protocorm like bodies (PLB’s). Through of the histological analysis of these structures it was possible to reveal that these PLB’s turned out to be somatic embryos. The histochemical tests demonstrate the pres- ence of cellular contents like: proteins, lipids and starch; both in the cells of the embryos as well as in the cells of initial tissues.

Production and rooting of cordia - Cordia trichotoma (Vell.) Arrab. ex Steud. mini-cuttings collected from ministumps of asexual and seminal origin

This study aimed to evaluate the production of cordia (Cordia trichotoma) ministumps of seminal and asexual origin, as well as the effect of the naphthaleneacetic acid (NAA) on the rooting of mini-cutitings. Seedlings and plantlets from rooted cuttings were pruned to form a clonal mini-hedge. The ministumps were fertirrigated with three concentrations of nutrient solution and they were evaluated for survival and production of mini-cuttings. The mini-cuttings were or not treated with 1000mg L-1 of NAA and planted in substrate for rooting. The mini-cuttings were evaluated for the percentages of survival and rooting, and number and total length of roots after 30 days of cultivation. There was no difference in survival and number of mini-cuttings obtained from seminal or asexual ministumps. Mini-cuttings from ministumps of asexual origin showed higher rooting capability. The use of 1000mg L-1 NAA did not increase the rooting percentage of cordia mini-cuttings.

Range-wide genetic analysis reveals limited structure and suggests asexual patterns in the rare forbSenecio macrocarpus

Genetic diversity and recombination underlie the long-term persistence and evolution of species and are strongly influenced by population size, breeding system and plant longevity. Here, we study genetic structure in the rare Senecio macrocarpus in southeastern Australia to guide current conservation practices. Thirteen neutral microsatellite markers and two chloroplast regions were used to survey the 20 known S. macrocarpus populations and one sympatric S. squarrosus population, a morphologically similar species. All markers showed severe excess or deficit of heterozygotes and linkage disequilibrium was significant. Microsatellite markers revealed 100 multi-locus genotypes (MLGs) from 523 S. macrocarpus individuals and a further 4 MLGs from 27 S. squarrosus individuals. MLGs varied in frequency and distribution. At the extremes, one MLG was found 108 times across the sampling region and 66 MLGs were found once. The MLGs of all 38 seedlings genotyped were identical to their seed parents implying an asexual origin. Chloroplast regions showed little variation within S. macrocarpus but differed from S. squarrosus. Chromosome counts for S. macrocarpus revealed the same ploidy level as S. squarrosus (2n = 6x = 60) and pollen–ovule ratios were typical of erechthitoid Senecio species showing self-compatibility. Results suggest that establishment of small populations occur primarily from one extensive source population with indications that both apomixis and selfing may be contributing to its reproduction cycle. We suggest that this species may contribute to future evolutionary processes despite limited genotypic variation and restricted distribution. Its conservation will safeguard evolutionary processes that might occur through occasional outcrossing and hybridization events between sympatric species. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 256–269.

Marginal coral populations: the densest known aggregation of Pocillopora in the Galápagos Archipelago is of asexual origin

Coral populations at distributional margins frequently experience suboptimal and variable conditions. Recurrent El Nino-Southern Oscillation (ENSO) warming events have caused extensive mortality of reef-building corals in the Eastern Pacific, and particularly impacted branching pocilloporid corals in the Galapagos Islands. Pocillopora spp. were previously more common and formed incipient reefs at several locations in the Archipelago but now occur as scattered colonies. Here, we report an unusually concentrated aggregation of colonies and evaluate their current genetic diversity. In particular we focus on a large population of 1614 live Pocillopora colonies found in a volcanic lagoon along the southern shore of Isabela Island. Forty seven colonies were sampled, primarily using a spatially explicit sampling design, and all colonies belonged to Pocillopora mitochondrial open reading frame lineage type 3a. Typing of additional Pocillopora samples (n = 40) from three other islands indicated that this stand is the only known representative of type 3a in the Galapagos Islands. The Isabela Pocillopora type 3a colonies harbored Symbiodinium ITS-2 clade C1d. Multilocus genotyping (n = 6 microsatellites) capable of resolving individual clones indicated that this stand is monogenotypic and thus the high density of colonies is a result of asexual reproduction, likely via fragmentation. Colony size distribution, while imperfect, suggested the stand regrew from remnant colonies that survived the 1997/98 ENSO event but may postdate the 1982/83 ENSO. The community of Pocillopora colonies at Isabela is of particular ecological value due to its high density and support of associated organisms such as fish and benthic invertebrates. The Galapagos Pocillopora corals will continue to provide insights into the genetic structure and population dynamics of marginal coral populations.

Efectos de la gestión selvícola pasada y presente sobre la diversidad genética actual y futura de Quercus pyrenaica Willd. en Sierra Nevada

Valbuena-Carabana, M., Gil, L. 2014. Assessing past and present management effects on current and future levels of genetic diversity in Quercus pyrenaica Willd. in Sierra Nevada. Ecosistemas 23(2):90-98. Doi.: 10.7818/ECOS.2014.23-2.12 Quercus pyrenaica Willd. is a Mediterranean and western European oak species widely distributed in the Iberian Peninsula. Its profuse resprouting ability from the entire root system was made use of in traditional management practices, especially as coppices for firewood and charcoal production and less frequently as open woodland for cattle grazing. The abandonment of traditional management evidences the general degradation sate of these woodlands –growing stagnation, stem top drying and lack of seed production–, and causes of such degradation were theoretically attributed to the exhaustion of clonal clumps and to the lack of genetic diversity. Nevertheless, the recent survey by means of nuclear microsatellites markers of several oak woodlands, included these hereby presented, allowed to discard such hypothesis. Lack of relation between forest structure (coppice vs. open woodlands) and the asexual or sexual origin of trees, and the high heterogeneity in clonal sizes hinders to predict the current clonal structure of woodlands based on their forest structure. The present study analyses the conservation state of genetic resources in a territory intensively used by man along the history evidencing the important resilience of the species to traditional coppicing. The study shows the effect of past forest management (coppicing and maintaining open woodlands) and the most commonly applied treatment in the present (coppice thinning with standards) on the current genetic diversity and clonal structure in three plots of the same oak woodland having different forest structures at Sierra Nevada National Park. Moreover, the potential evolution of genetic diversity is evaluated through the analyses of the juvenile cohort in each plot. Although, in the adult cohort, coppices bear higher levels of genetic diversity, the asexual origin of their juvenile class may limit the genetic diversity in the future. On the contrary, in the open woodland, the sexual origin from seeds of the juvenile class will potentially increase genetic diversity in the future.

Difference in reproductive strategies of two scleractinian corals (branching vs massive) along the west coast of Mexico

This study addressed the relative contribution of sexual and asexual reproduction to the genetic composition of populations of two scleractinian corals, Pocillopora damicornis and Porites panamensis, off the west coast of mainland Mexico. Reproductive indexes showed that P. damicornis reproduced both sexually and asexually; P. panamensis reproduced sexually, but colonies with an asexual origin were also observed (10–30%). Asexual reproduction is usually attributed to fragmentation caused by hurricanes; however, no significant association between reproductive index values and frequency of hurricanes was observed for either species. Environmental conditions in the Gulf of California seem to be more favorable for sexual reproduction in both species than other parts of the west coast of Mexico. This study contributes baseline information of differences in sexual and asexual reproduction in massive and branching corals.