Geographical Parthenogenesis Research Articles

Does ecology shape geographical parthenogenesis? Evidence from the facultatively parthenogenetic stick insect Megacrania batesii.

Closely related sexual and parthenogenetic species often show distinct distribution patterns, known as geographical parthenogenesis. Similar patterns, characterized by the existence of separate sexual and parthenogenetic populations across their natural range, can also be found in facultative parthenogens - species in which every female is capable of both sexual and parthenogenetic reproduction. The underlying mechanisms driving this phenomenon in nature remain unclear. Features of the habitat, such as differences in host-plant phenotypes or niche breadth, could favour sexual or asexual reproductive modes and thus help to explain geographical parthenogenesis in natural insect populations. Megacrania batesii is a facultatively parthenogenetic stick insect that displays geographical parthenogenesis in the wild. We aimed to explore whether sexual and parthenogenetic populations of M. batesii displayed niche differentiation or variations in niche breadth that could explain the separation of the two population types. To do this, we sampled host plants from across the range of M. batesii and quantified phenotypic traits that might affect palatability or accessibility for M. batesii, including leaf thickness, toughness, spike size and density, plant height, and chemical composition. We also quantified host-plant density, which could affect M. batesii dispersal. We found little evidence of phenotypic differences between host plants supporting sexual versus asexual M. batesii populations, and no difference in host-plant density or niche breadth between the two population types. Our results suggest that habitat parameters do not play a substantial role in shaping patterns of geographical parthenogenesis in wild populations of M. batesii. Instead, population sex ratio variation could result from interactions between the sexes or dispersal dynamics.

Taxonomy, ontogeny, and ecology of Tonnacypris stewarti (Daday 1908) comb. nov. (Ostracoda: Cyprididae) from Nam Co, Tibetan Plateau

Taxonomic clarification of Tonnacypris stewarti comb. nov. (= Herpetocypris stewarti), a non-marine ostracod first described by Daday in 1908, was required due to the existence of various synonyms without detailed morphological descriptions. Our study examined specimens from Mang-tsa, Nam Co (Tibetan Plateau) and Lake Band-e Amir (Afghanistan). We identified seven definitive synonyms (Herpetocypris stewarti Daday 1908, Ilyodromus estonicus Järvekülg 1960, Eucypris afghanistanensis Hartmann 1964, E. gyirongensis Yang 1982, E. rischtanica Schneider 1963 in Mandelstam & Schneider 1963, Tonnacypris estonica (Järvekülg 1960), and T. gyirongensis (Guo et al. 2016). After a detailed study of the morphology of valves and soft parts supplemented by a literature review, we propose combining the genus Tonnacypris with the specific epithet stewarti, resulting in the new name Tonnacypris stewarti. We documented the ontogenetic series of T. stewarti in surface sediment samples from Nam Co. Only female specimens were found, consistent with observations in Mongolia, where they were considered asexual populations. Sexual populations were reported from Afghanistan and the southern Tibetan Plateau, suggesting geographic parthenogenesis in the Palearctic region. Because of widely missing males, we explored the use of female genital lobes as a distinguishing feature for taxonomy. Considering current ecological knowledge, T. stewarti could serve as a (paleo)—bioindicator of cold, oligotrophic, and fresh to slightly brackish habitats, including rivers, lagoons, and lakes. This study emphasizes the importance of resolving taxonomic issues for future paleolimnological research. Moreover, our investigation highlights the potential use of sclerotized internal female genital lobes as distinctive characteristics for species differentiation, especially in asexual populations.

Plant kleptomaniacs: geographic genetic patterns in the amphi-apomictic Rubus ser. Glandulosi (Rosaceae) reveal complex reticulate evolution of Eurasian brambles.

Rubus ser. Glandulosi represents a unique model of geographic parthenogenesis on a homoploid (2n = 4x) level. We aim to characterize evolutionary and phylogeographic patterns in this taxon and shed light on the geographic differentiation of apomicts and sexuals. Ultimately, we aim to evaluate the importance of phylogeography in the formation of geographic parthenogenesis. R. ser. Glandulosi was sampled across its Eurasian range together with other co-occurring Rubus taxa (587 individuals in total). Double digest restriction-site associated DNA sequencing (ddRADseq) and modelling of suitable climate were employed for evolutionary inferences. Six ancestral species were identified that contributed to the contemporary gene pool of R. ser. Glandulosi. While sexuals were introgressed from R. dolichocarpus and R. moschus in West Asia and from R. ulmifolius agg., R. canescens and R. incanescens in Europe, apomicts were characterized by alleles of R. subsect. Rubus. Gene flow between sexuals and apomicts was also detected, as well as occasional hybridization with other taxa. We hypothesize that sexuals survived the last glacial period in several large southern refugia, whereas apomicts were mostly restricted to southern France from whence they quickly recolonized Central and Western Europe. The secondary contact of sexuals and apomicts was probably the principal factor that established geographic parthenogenesis in R. ser. Glandulosi. Sexual populations are not impoverished in genetic diversity along their borderline with apomicts and maladaptive population genetic processes likely did not shape the geographic patterns.

Distinct geographic parthenogenesis in spite of niche conservatism and a single ploidy level: A case of Rubus ser. Glandulosi (Rosaceae).

Asexual organisms often differ in their geographic distributions from their sexual relatives. This phenomenon, termed geographic parthenogenesis, has long been known, but the underlying factors behind its diverse patterns have been under dispute. Particularly problematic is an association between asexuality and polyploidy in most taxa. Here, we present a new system of geographic parthenogenesis on the tetraploid level, promising new insights into this complex topic. We used flow cytometric seed screen and microsatellite genotyping to characterise the patterns of distribution of sexuals and apomicts and genotypic distributions in Rubus ser. Glandulosi across its range. Ecological modelling and local-scale vegetation and soil analyses were used to test for niche differentiation between the reproductive groups. Apomicts were detected only in North-western Europe, sexuals in the rest of the range in Europe and West Asia, with a sharp borderline stretched across Central Europe. Despite that, we found no significant differences in ecological niches. Genotypic richness distributions suggested independence of the reproductive groups and a secondary contact. We argue that unless a niche differentiation (resulting from polyploidy and/or hybridity) evolves, the main factors behind the patterns of geographic parthenogenesis in plants are phylogeographic history and neutral microevolutionary processes, such as clonal turnover.

Clones on the run: The genomics of a recently expanded partially clonal species.

Why species that in their core areas mainly reproduce sexually become enriched with clones in marginal populations ("geographic parthenogenesis") remains unclear. Earlier hypotheses have emphasized that selection might promote clonality because it protects locally adapted genotypes. On the other hand, it also hampers recombination and adaptation to changing conditions. The aim of the present study was to investigate the early stages of range expansion in a partially clonal species and what drives an increase in cloning during such expansion. We used genome-wide sequencing to investigate the origin and evolution of large clones formed in a macroalgal species (Fucus vesiculosus) during a recent expansion into the postglacial Baltic Sea. We found low but persistent clonality in core populations, while at range margins, large dominant clonal lineages had evolved repeatedly from different sexual populations. A range expansion model showed that even when asexual recruitment is less favourable than sexual recruitment in core populations, repeated bottlenecks at the expansion front can establish a genetically eroded clonal wave that spreads ahead of a sexual wave into the new area. Genetic variation decreases by drift following repeated bottlenecks at the expansion front. This results in the emerging clones having low expected heterozygosity, which corroborated our empirical observations. We conclude that Baker's Law (clones being favoured by uniparental reproductive assurance in new areas) can play an important role during range expansion in partially clonal species, resulting in a complex spatiotemporal mosaic of clonal and sexual lineages that might persist during thousands of generations.

Dispersal and establishment traits provide a colonization advantage for a polyploid apomictic plant.

Apomictic plants (reproducing asexually through seed) often have larger ranges and occur at higher latitudes than closely related sexuals, a pattern known as geographical parthenogenesis (GP). Explanations for GP include differences in colonizing ability due to reproductive assurance and direct/indirect effects of polyploidy (most apomicts are polyploid) on ecological tolerances. While life history traits associated with dispersal and establishment also contribute to the potential for range expansion, few studies compare these traits in related apomicts and sexuals. We investigated differences in early life history traits between diploid-sexual and polyploid-apomictic Townsendia hookeri (Asteraceae), which displays a classic pattern of GP. Using lab and greenhouse experiments, we measured seed dispersal traits, germination success, and seedling size and survival in sexual and apomictic populations from across the range of the species. While theory predicts that trade-offs between dispersal and establishment traits should be common, this was largely not the case in T. hookeri. Apomictic seeds had both lower terminal velocity (staying aloft longer when dropped) and higher germination success than sexual seeds. While there were no differences in seedling size between reproductive types, apomicts did, however, have slightly lower seedling survival than sexuals. These differences in early life history traits, combined with reproductive assurance conferred by apomixis, suggest that apomicts achieve a greater range through advantages in their ability to both spread and establish.

Phylogeography of Eriotheca species complex: insights into the origin and range expansion of apomictic and polyploid trees in Neotropical Savannas.

Polyploidy and whole genome duplication are major evolutionary drivers in plants. Climate variations during the Pleistocene have influenced distribution and range expansion worldwide. Similar trends have been reported for Cerrado plants, but no attempt has been made to link phylogeography with ploidy and breeding changes. Thus, we aimed to (i) assess ploidy and genome size of Eriotheca estevesiae Carv.-Sobr., and compare it with E. pubescens (Mart.) Schott & Endl. (Both included into the Eriotheca Stellate Trichome Species Complex - ESTSC). (ii) Subsequently, we investigated their phylogeography to see whether genetic structure and range expansion trends were similar to those previously described for the Cerrado biome. Finally (iii), we discuss whether ESTSC phylogeographic patterns could be associated with geographic parthenogenesis processes. Common cytogenetic techniques and flow cytometry were used to confirm chromosome number and genome size of E. estevesiae. We used three cpDNA regions to analyse 14 ESTSC Cerrado populations, for which we also obtained ploidy level and breeding information. We investigated haplotype diversity, population structure and tested neutrality, aiming to reconstruct phylogeographic scenarios. We found three ploidy levels and eight cpDNA haplotypes in ESTSC, one shared by most populations. Haplotype and ploidy distribution corroborated that E. pubescens, the widely distributed polyploid and apomictic species, may have originated from northern diploid and probably sexual E. estevesiae. Matrilinear cpDNA links support the idea that apomixis and polyploidy in ESTSC may have allowed range expansion during the Pleistocene, in a process analogous to the geographic parthenogenesis described elsewhere.

Geographical Parthenogenesis in Alpine and Arctic Plants

The term "Geographical parthenogenesis" describes the phenomenon that asexual organisms usually occupy larger and more northern distribution areas than their sexual relatives, and tend to colonize previously glaciated areas. Several case studies on alpine and arctic plants confirm the geographical pattern, but the causal factors behind the phenomenon are still unclear. Research of the last decade in several plant families has shed light on the question and evaluated some of the classical evolutionary theories. Results confirmed, in general, that the advantages of uniparental reproduction enable apomictic plants to re-colonize faster in larger and more northern distribution areas. Associated factors like polyploidy seem to contribute mainly to the spatial separation of sexual and asexual cytotypes. Ecological studies suggest a better tolerance of apomicts to colder climates and temperate extremes, whereby epigenetic flexibility and phenotypic plasticity play an important role in occupying ecological niches under harsh conditions. Genotypic diversity appears to be of lesser importance for the distributional success of asexual plants. Classical evolutionary theories like a reduced pressure of biotic interactions in colder climates and hence an advantage to asexuals (Red Queen hypothesis) did not gain support from studies on plants. However, it is also still enigmatic why sexual outcrossing remains the predominant mode of reproduction also in alpine floras. Constraints for the origin of apomixis might play a role. Interestingly, some studies suggest an association of sexuality with abiotic stresses. Light stress in high elevations might explain why most alpine plants retain sexual reproduction despite other environmental factors that would favor apomixis. Directions for future research will be given.

Uniparentality: advantages for range expansion in diploid and diploid-autopolyploid species

AbstractUniparental reproduction, the capacity of an individual to produce offspring autonomously, is expected to facilitate range expansion of populations. Paspalum spp. reproduce uniparentally by sexual (self-fertility) and asexual (apomixis) reproduction and biparentally by sexual (self-sterility) reproduction. We evaluated the relationship between contrasting reproductive strategies (uni- and biparentality) and their impact on the colonizing ability and geographical range sizes of populations. We determined the cytotype composition of 16 populations of P. indecorum, P. cromyorhizon, P. pumilum and P. maculosum and assessed the sexual (self-fertile and self-sterile) and apomictic proportions by cyto-embryological analyses, fertility rates and seed flow cytometry. Data obtained regarding reproductive modes were compared to the distribution range of each cytotype and species. Sexual diploids with moderate degrees of self-fertility and mixed pollination syndromes showed wider distribution ranges than self-sterile diploids. In sexual diploids, increased rates of self-fertility relate to larger distribution areas. In agamic complexes, self-fertility reduces the differences in range sizes between biparental diploids and uniparental tetraploids. In such complexes, the range size of diploid cytotypes explains the range size and dispersal of apomictic tetraploids. Thus, uniparental reproduction via self-fertility and apomixis describes patterns of geographical parthenogenesis in South American species.

Diverged subpopulations in tropical Urochloa (Brachiaria) forage species indicate a role for facultative apomixis and varying ploidy in their population structure and evolution.

Urochloa (syn. Brachiaria) is a genus of tropical grasses sown as forage feedstock, particularly in marginal soils. Here we aimed to clarify the genetic diversity and population structure in Urochloa species to understand better how population evolution relates to ploidy level and occurrence of apomictic reproduction. We explored the genetic diversity of 111 accessions from the five Urochloa species used to develop commercial cultivars. These accessions were conserved from wild materials collected at their centre of origin in Africa, and they tentatively represent the complete Urochloa gene pool used in breeding programmes. We used RNA-sequencing to generate 1.1 million single nucleotide polymorphism loci. We employed genetic admixture, principal component and phylogenetic analyses to define subpopulations. We observed three highly differentiated subpopulations in U. brizantha, which were unrelated to ploidy: one intermixed with U. decumbens, and two diverged from the former and the other species in the complex. We also observed two subpopulations in U. humidicola, unrelated to ploidy; one subpopulation had fewer accessions but included the only characterized sexual accession in the species. Our results also supported a division of U. decumbens between diploids and polyploids, and no subpopulations within U. ruziziensis and U. maxima. Polyploid U. decumbens are more closely related to polyploid U. brizantha than to diploid U. decumbens, which supports the divergence of both polyploid groups from a common tetraploid ancestor and provides evidence for the hybridization barrier of ploidy. The three differentiated subpopulations of apomictic polyploid U. brizantha accessions constitute diverged ecotypes, which can probably be utilized in hybrid breeding. Subpopulations were not observed in non-apomictic U. ruziziensis. Sexual Urochloa polyploids were not found (U. brizantha, U. decumbens) or were limited to small subpopulations (U. humidicola). The subpopulation structure observed in the Urochloa sexual-apomictic multiploidy complexes supports geographical parthenogenesis, where the polyploid genotypes exploit the evolutionary advantage of apomixis, i.e. uniparental reproduction and clonality, to occupy extensive geographical areas.

Range of Occurrence of Bisexual and Parthenogenetic Populations of Labidostomma luteum (Acari: Prostigmata) in Europe

The current article describes an interesting case of geographic parthenogenesis among European mites from the Labidostommidae family (Acari: Prostigmata). In earlier publications on Labidostomma luteum Kramer, 1879, the authors pointed out that most of the populations of this species in Europe consisted of parthenogenetic females. Until now, populations of both sexes were known only in southwestern France. In the north–west areas, the number of males in the populations has gradually decreased, and in the populations found west of Paris there are no males at all. During the research project carried out in 2018, Błoszyk found the presence of populations which consisted of both sexes of the species in question near the town of Bény (60 km NE of Lion). This is the easternmost site of L. luteum in France where males have been found. All other known sites located east and north of the Bény–Paris line have only parthenogenetic females. Thus, this line can be considered as the boundary of L. luteum populations reproducing sexually. However, establishing the exact course of this range requires further research.

New records of the not-so-rare males of the parthenogenetic scorpion Tityus stigmurus (Thorell, 1876) (Scorpiones: Buthidae)

Parthenogenesis and sex-ratio bias may lead to erroneous assumptions concerning the natural history of some arachnids. To help address this issue, this study provides new data on the sex ratio and geographic distribution of sexual populations of the scorpion Tityus stigmurus (Thorell, 1876). Ultraviolet light lanterns were used to detect specimens during nocturnal searches performed in both urban and non-urban environments scattered thorough northeastern Brazil. Males of T. stigmurus were reported for 10 new localities, and although we did not find males in urban environments, non-urban populations presented near symmetrical sex ratios. Such results suggest that reproductive strategies in this species may be modulated by environmental conditions. Also, the general tendency of less biased sex ratios in non-urban environments reported here is in accordance with previous studies that indicated the occurrence of geographical parthenogenesis in this species. Thereby, we propose that sexual populations of T. stigmurus are less rare than previously reported.

Niche Shifts, Hybridization, Polyploidy and Geographic Parthenogenesis in Western North American Hawthorns (Crataegus subg. Sanguineae, Rosaceae)

We compare biogeographic and morphological parameters of two agamic complexes of western North American hawthorns so as to evaluate possible explanations of the differences in range between sexually reproducing taxa and their apomictic sister taxa. We have documented range, breeding system, morphology, leaf vascular architecture, and niche breadth in these hawthorns, for which phylogenetic relationships and ploidy levels are known. Species distribution data from herbarium specimens and online databases were analyzed in order to compare ranges and climate niches described by bioclimatic variables. Flow cytometry documented ploidy level and breeding system. Voucher specimens provided morphometric data that were analyzed using uni- and multivariate methods. Members of two black-fruited taxonomic sections of Crataegus subg. Sanguineae (sections Douglasianae, Salignae) have previously been identified as hybrids. They are presumptively self-fertile polyploids with pseudogamous gametophytic apomixis. Their morphologies, geographic ranges, and niche characteristics resemble those of their diploid, sexual parent or are intermediate between them and those of their other parent, one or both of two partially sympatric tetraploid apomicts in red-fruited C. subg. Americanae with much wider distributions. Comparing sections Douglasianae and Salignae suggests that geographic parthenogenesis (larger range sizes in apomicts, compared to sexually reproducing taxa) may have less to do with adaptation than it does with reproductive assurance in the pseudogamously apomictic and self-compatible hybrids. Greater climate niche breadth in allopolyploids compared to diploids similarly may be more due to parental traits than to effects of genome duplication per se.

Geographical parthenogenesis in the brown alga Scytosiphon lomentaria (Scytosiphonaceae): Sexuals in warm waters and parthenogens in cold waters.

Geographical parthenogenesis, a phenomenon where parthenogens and their close sexual relatives inhabit distinct geographical areas, has been considered an interesting topic in evolutionary biology. Reports of geographical parthenogenesis from land and freshwater are numerous, but this occurrence has been rarely reported from the sea. Brown algae are mostly marine and are thought to include numerous obligate parthenogens; still, little is known about the distribution, origin and evolution of parthenogens in this group. Here we report a novel pattern of geographical parthenogenesis in the isogamous brown alga Scytosiphon lomentaria. Sex ratio investigation demonstrated that, in Japan, sexual populations grew in the coast along warm ocean currents, whereas female-dominant parthenogenetic populations grew mainly in the coast along a cold ocean current. In the two localities where sexual and parthenogenetic populations were parapatric, parthenogens grew in more wave-exposed areas than sexuals. Population genetic and phylogenetic analyses, including those based on genome-wide single nucleotide polymorphism data, indicated that parthenogens have initially evolved at least twice and subsequent hybridizations between the parthenogens and sexuals have generated multiple new parthenogenetic lineages. The origin of the initial parthenogens is not clear, except that it would not be interspecies hybridization. Interestingly, we found that the production of sex pheromones, which attract male gametes, has been independently lost in the initial two parthenogenetic lineages. This parallel loss of the sexual trait may represent the direct origin of parthenogens, or the regressive evolution of a useless trait under asexuality.

Greater reproductive assurance of asexual plant compared with sexual relative in a low-density sympatric population: Experimental evidence for pollen limitation.

High reproductive assurance is regarded as a key advantage of uniparentally reproducing organisms for establishing a new population. This demographic benefit should especially be relevant for plants with autonomous apomixis, that is those which produce seeds completely independently from mates and pollinators. Indeed, many autonomous apomicts occupy larger distributional ranges when compared to their sexual relatives, showing geographical parthenogenesis patterns. However, uniparental reproduction advantage has only rarely been quantified in natural populations and results provided a mixed support, partly because allopatric sexual and asexual populations were exposed to different environmental and pollination conditions causing considerable between-population variation in the level of reproductive assurance. Here, we compared the level and stability of reproductive assurance between sexual self-incompatible and asexual autonomously apomictic plants of Hieracium alpinum (Asteraceae) cultivated in a sympatric low-density population with two levels of spatial clumping of sexual plants. Overall, we found that the realized seed set (i.e. proportion of well-developed seeds per capitulum) of asexuals was ca. 3 times greater than that of sexuals (83% vs. 27%), whereas the variance of this trait expressed as coefficient of variation was ca. 4 times smaller in asexuals compared with sexuals (19% vs. 83%). Solitary sexual plants had more than 2 times lower realized seed set when compared to clumps composed of two spatially close (20-30cm) sexual plants (13% vs. 34%). Our study provides experimental evidence for benefit of uniparental reproduction of asexuals in a sympatric situation when the availability of mates is limited. This, together with unpredictability of pollinator environment could provide autonomous apomicts with an ultimate demographic superiority during colonization reflected in geographical parthenogenesis observed in this species.

Phylogeography of the Poecilimon ampliatus species group (Orthoptera: Tettigoniidae) in the context of the Pleistocene glacial cycles and the origin of the only thelytokous parthenogenetic phaneropterine bush-cricket

Abstract Parthenogenetic lineages are known to rapidly colonize large areas that become available after glacial periods as parthenogenetic reproduction is beneficial over mating when the favorable season is very short. The only obligatory parthenogenetic species of the largest bush-cricket subfamily Phaneropterinae is Poecilimon intermedius. It belongs to the Anatolio-Balkan lineage Poecilimon ampliatus species group and in contrast has a remarkably broad distribution from Central Europe to China, following the pattern of geographical parthenogenesis. In this study we provide a systematic revision of the P. ampliatus group based on mitochondrial (ND2) and nuclear (ITS) phylogeny. We estimate divergence times by applying secondary calibration on the ND2 tree to test for congruence between recent splits in the group and the Pleistocene climatic oscillations. We use ecological niche modelling to analyze the ecological requirements of the parthenogenetic P. intermedius and its sexually reproducing sister species P. ampliatus. By projecting on the conditions during the Last Glacial Maximum we outline the suitable areas for both species during the glacial cycles and discuss range shifts in response to climate change. Based on all results we hypothesize that the drought-tolerant P. intermedius originated during the recent glaciations in the southwestern part of its current range and rapidly radiated in a northeastern direction. Its sister species P. ampliatus, which is adapted to higher levels of precipitation, remained in the western Balkans, where populations retreated to higher altitudes during warming.

Development of microsatellite markers for the geographically parthenogenetic stick insect Phraortes elongatus (Insecta: Phasmatodea).

Many plant and animal species exhibit geographic parthenogenesis, wherein unisexual (= parthenogenetic) lineages are more common in their marginal habitats such as high latitude or altitudes than their closely related bisexual counterparts. The Japanese stick insect, Phraortes elongatus (Thunberg) (Insecta: Phasmatodea), is known as a geographically parthenogenetic species due to the existence of both bisexual and unisexual populations. Here, we developed microsatellite markers to infer the genetic variation among populations of P. elongatus. Totally, 13 primer pairs were developed for the species, and they were tested on 47 samples collected from both a bisexual population and a unisexual population. All 13 loci were polymorphic in the bisexual population, whereas no loci were polymorphic in the unisexual population. The loss of variation in the unisexual population implies automixis with terminal fusion or gamete duplication as the mode of parthenogenesis. The markers developed in this study will be helpful for further comprehensive analysis of the genetic diversity and gene flow between bisexual and parthenogenetic lineages of P. elongatus.

Niche divergence contributes to geographical parthenogenesis in two dandelion taxa.

Many sexual‐asexual complexes show a distinct pattern where the asexuals have larger and more northerly ranges than closely related sexuals. A prime candidate to explain this so‐called “geographical parthenogenesis” is ecological niche divergence between the sexuals and asexuals. Modern niche modelling techniques allow testing niche divergence by directly comparing the niches of sexuals and asexuals. In this study, I use such techniques to perform range‐wide tests of whether nine bioclimatic variables, including annual mean temperature and annual precipitation, contribute to geographical parthenogenesis in two dandelion taxa: Taraxacum section Ruderalia and Taraxacum section Erythrosperma, which are both comprised of sexual diploids and asexual triploids. For both sections, I found evidence of niche divergence, though the exact nature of this divergence was different for the two sections. In section Ruderalia, the sexuals preferred warmer and wetter conditions, whereas in section Erythrosperma, the sexuals preferred dryer conditions. Using Species Distribution Modelling, consistent differences between the sexuals and asexuals were found when looking at the niche determinants: the variables that are most important for modelling the distribution. Furthermore, and in contrast with theoretical expectations that predict that the sexuals should have a wider niche, in section Erythrosperma the asexuals were found to have a wider niche than the sexuals. In conclusion, differences in niche optima, niche determinants, and niche width all contribute to the pattern of geographical parthenogenesis of these two dandelion taxa. However, the results also indicate that the exact causation of geographical parthenogenesis is not uniform across taxa.

Moving beyond assumptions: Polyploidy and environmental effects explain a geographical parthenogenesis scenario in European plants.

Geographical parthenogenesis (GP) describes the phenomenon that apomicts tend to have larger distribution areas and/or occur at higher altitudes or latitudes compared to sexual relatives. However, the complex effects of genome-wide heterozygosity, ploidy, reproduction mode (sexual vs. apomictic), and environment shaping GP of plants are still not well understood. We ascertained ploidy and reproduction mode by flow cytometry of 221 populations, and added genomic RADseq data (maximum 33,165 loci) of 80 taxa of the Ranunculusauricomus polyploid plant complex in temperate Europe. We observed 7% mainly diploid sexual, 28% facultative apomictic (mean sexuality 7.1%), and 65% obligate apomictic populations. Sexuals occupied a more southern, smaller distribution area, whereas apomicts expanded their range to higher latitudes. Within the complex, we detected three main genetic clusters and highly reticulate relationships. A genetically-informed path analysis using GLMMs revealed several significant relationships. Sexuality of populations (percent of sexual seeds) was higher in diploids compared to polyploids, associated with more petals, and similar between forests and open habitats. In contrast to other apomictic plant complexes, sexuality was mainly positively correlated to solar radiation and isothermality, which fits the southern distribution. We found up to three times higher heterozygosity in polyploids compared to diploids, and generally more heterozygous individuals in forests compared with open habitats. Interestingly, we revealed a previously unknown positive association between heterozygosity and temperature seasonality, suggesting a higher resistance of polyploids to more extreme climatic conditions. We provide empirical evidence for intrinsic and extrinsic factors shaping the GP pattern in a polyploid plant complex.

The Alternative Distribution of Related Earthworms Aporrectodea caliginosa and A. trapezoides (Oligochaeta, Lumbricidae) in Ukraine as a Case of Geographical Parthenogenesis

Geographical parthenogenesis describes phenomenon when parthenogenetic hybrid forms or species have larger distribution areas or higher abundance than their amphimictic parental species, especially in climatically unfavorable conditions. This phenomenon was studied in Ukraine for the pair species of earthworms Aporrectodea сaliginosa (Savigny, 1826) s. l. We found that the hermaphroditic amphimictic A. caliginosa clearly predominates in the northern and western regions, and the apomictic parthenogenetic A. trapezoides (Duges, 1828) in the southern and eastern regions with a continental arid climate. In the sample sets of A. сaliginosa–A. trapezoides group, usually one of the species sharply predominated, and the equality of their abundance was very rare. The reason for this fact is both the alternative geographical distribution and the ability of A. trapezoides to form populations in habitats unfavorable for A. caliginosa. In general, the situation in this group agrees with the classical model of geographic parthenogenesis and confirms the high adaptive potential of apomictic organisms. This fact once again raises the question of non-adaptive reasons for the exclusion of the apomictic reproduction in highly organized animals.