Catasetum × sheyllae (Orchidaceae: Catasetinae), a new natural hybrid from Brazilian Amazon

Natural hybridization has often been recorded within certain genera of orchids, one of them is Catasetum. During a field study in a forest de igapó in Brazilian Amazon, a new natural hybrid was found, it is here described as Catasetum × sheyllae. Its morphological features, mainly the structures of the lip, are intermediate between those of its putative parent species, C. boyi and C. garnettianum, both observed in sympatry.

Patterns of Genomic Instability in Interspecific Yeast Hybrids With Diverse Ancestries

The genomes of hybrids often show substantial deviations from the features of the parent genomes, including genomic instabilities characterized by chromosomal rearrangements, gains, and losses. This plastic genomic architecture generates phenotypic diversity, potentially giving hybrids access to new ecological niches. It is however unclear if there are any generalizable patterns and predictability in the type and prevalence of genomic variation and instability across hybrids with different genetic and ecological backgrounds. Here, we analyzed the genomic architecture of 204 interspecific Saccharomyces yeast hybrids isolated from natural, industrial fermentation, clinical, and laboratory environments. Synchronous mapping to all eight putative parental species showed significant variation in read depth indicating frequent aneuploidy, affecting 44% of all hybrid genomes and particularly smaller chromosomes. Early generation hybrids with largely equal genomic content from both parent species were more likely to contain aneuploidies than introgressed genomes with an older hybridization history, which presumably stabilized the genome. Shared k-mer analysis showed that the degree of genomic diversity and variability varied among hybrids with different parent species. Interestingly, more genetically distant crosses produced more similar hybrid genomes, which may be a result of stronger negative epistasis at larger genomic divergence, putting constraints on hybridization outcomes. Mitochondrial genomes were typically inherited from the species also contributing the majority nuclear genome, but there were clear exceptions to this rule. Together, we find reliable genomic predictors of instability in hybrids, but also report interesting cross- and environment-specific idiosyncrasies. Our results are an important step in understanding the factors shaping divergent hybrid genomes and their role in adaptive evolution.

Aloe ×selmarii (Asphodelaceae subfam. Alooideae), a new nothospecies from South Africa, with A. davyana var. davyana and A. parvibracteata as parents

Aloe ×selmarii (Asphodelaceae subfam. Alooideae), a hybrid between A. davyana var. davyana and A. parvibracteata, is described. Although the natural distribution ranges of the parent species do not overlap, this nothospecies is often encountered as a result of the cultivation of A. parvibracteata outside its natural range, in areas where A. davyana var. davyana occurs naturally.

Phylogeographic reconstruction of the marbled crayfish origin

The marbled crayfish (Procambarus virginalis) is a triploid and parthenogenetic freshwater crayfish species that has colonized diverse habitats around the world. Previous studies suggested that the clonal marbled crayfish population descended as recently as 25 years ago from a single specimen of P. fallax, the sexually reproducing parent species. However, the genetic, phylogeographic, and mechanistic origins of the species have remained enigmatic. We have now constructed a new genome assembly for P. virginalis to support a detailed phylogeographic analysis of the diploid parent species, Procambarus fallax. Our results strongly suggest that both parental haplotypes of P. virginalis were inherited from the Everglades subpopulation of P. fallax. Comprehensive whole-genome sequencing also detected triploid specimens in the same subpopulation, which either represent evolutionarily important intermediate genotypes or independent parthenogenetic lineages arising among the sexual parent population. Our findings thus clarify the geographic origin of the marbled crayfish and identify potential mechanisms of parthenogenetic speciation.

Sorting out the muddle: taxonomy and nomenclature of Thymus ×porcii (Lamiaceae) and related nothotaxa, with comments on parent species delimitation

Thymus ×porcii is a natural hybrid between T. pannonicus and T. pulegioides, occurring within the co-occurrence range of its parental species in the forest and forest-steppe zones of Europe. Taxonomy and nomenclature of this hybrid present a longstanding puzzle due to the lack of critical evaluations of the original material as well as conflicting taxonomic interpretations of the parent taxa both at specific and intraspecific levels. The present paper attempts to clarify these issues, arguing against the synonymic treatment and/or consolidation of T. pannonicus and T. pulegioides, which is accepted in modern taxonomies apparently as a result of nomenclatural confusion related to T. pannonicus typification. Based on morphology and reported molecular data, it is proposed to treat T. pannonicus and T. pulegioides as separate species, each containing two varieties being well-distinguished by the presence or absence of leaf indumentum: T. pannonicus var. latifolius (glabrous leaves) and T. pannonicus var. pannonicus (pubescent leaves), and T. pulegioides var. pulegioides (glabrous leaves) and T. pulegioides var. vestitus (pubescent leaves). In view of such treatment, T. ×porcii is divided into three nothovarieties, representing natural crosses between different varieties of the parent species. Namely, in addition to the typical T. ×porcii nothovar. porcii [T. pannonicus var. latifolius × T. pulegioides var. pulegioides] (with T. ×pilisiensis and T. ×goginae as the taxonomic synonyms), we describe a new nothovariety T. ×porcii nothovar. calvariensis [T. pannonicus var. pannonicus × T. pulegioides var. pulegioides], and propose a new nomenclatural combination T. ×porcii nothovar. opizii [T. pannonicus × T. pulegioides var. vestitus] based on the previously published name T. ×opizii. On the basis of original material examination, two collections from BP are designated here as the lectotypes of T. ×porcii (≡ T. ×porcii nothovar. porcii) and T. ×pilisiensis respectively, and one specimen from PR is designated as the lectotype of T. ×opizii (≡ T. ×porcii nothovar. opizii). Main diagnostic traits of T. ×porcii nothovarieties and their parental taxa are compared and discussed.

Hybridization of Oxalis corniculata and O. dillenii in their non-native range

Many species have been introduced beyond their native ranges and many have become global weeds. Human mediated dispersal has removed the geographic isolation of these species, reversing millions of years of independent evolution. Examples are the Oxalis species in section Corniculatae where several species have become invasive. Here we characterize and formally describe a hybrid between O. dillenii and O. corniculata, which occurs spontaneously in Belgium and Japan. Oxalis corniculata is probably native to Japan, but both species are alien to Belgium and O. dillenii is native to North America. We formally name this hybrid as Oxalis × vanaelstii. Although this hybrid is sterile, it is nevertheless vigorous and perennial. Both parent species grow as weeds in gardens; therefore, it is likely to be more common than currently appreciated in countries where these species co-occur.

Extensive transgressive gene expression in a homoploid hybrid species

Hybridization is increasingly recognized as an important evolutionary force contributing novel variation for selection to act on. While mis-expression in F1 hybrids is well documented, how gene expression evolves in stabilized hybrid taxa and contributes novel variation remains an open question, especially for hybrid species without an increase in ploidy. As gene expression evolves in a stabilizing manner, break-up of co-evolved cis- and trans-regulatory elements could lead to transgressive patterns of gene expression in hybrids. Here, we address to what extent gonad gene expression has evolved in an old homoploid hybrid, Italian sparrow, Passer italiae. Through comparing the gene expression of parental species and F1 hybrids to that of the Italian sparrow, we find evidence for strongly transgressive expression in the Italian sparrow, with 22% of the testis genes exhibiting expression patterns outside the range of both parent species, compared to only 0.37% in the F1s. In contrast, Italian sparrow ovary expression was similar to that of one parent species, the house sparrow (P. domesticus). Moreover, the Italian sparrow testis transcriptome is 26.2 -26.6 times as diverged from those of the parent species compared to how divergent their transcriptomes are in spite of it being genetically intermediate. This highlights the potential for regulation of gene expression to produce novel variation following hybridization. Genes involved in energy production and protein synthesis are enriched in the subset that is over-dominantly expressed in Italian sparrow testis, suggesting that selection on key functions have molded the hybrid transcriptome.

Predictors of genomic differentiation within a hybrid taxon

ABSTRACTHybridization is increasingly recognized as an important evolutionary force. Novel genetic methods now enable us to address how the genomes of parental species are combined to build hybrid genomes. However, we still do not know the relative importance of contingencies, genome architecture and local selection in shaping hybrid genomes. Here, we take advantage of the genetically divergent island populations of Italian sparrow on Crete, Corsica and Sicily to investigate the predictors of genomic variation within a hybrid taxon. We test if differentiation is affected by recombination rate, selection, or variation in ancestry proportion from each parent species. We find that the relationship between recombination rate and differentiation is less pronounced within hybrid lineages than between the parent species, as expected if purging of minor parent ancestry in low recombination regions reduces the variation available for differentiation. In addition, we find that differentiation between islands is correlated with differences in selection in two out of three comparisons. Patterns of within-island selection are correlated across all islands, suggesting that shared selection may mould genomic differentiation. The best predictor of strong differentiation within islands is the degree of differentiation from house sparrow, and hence loci with Spanish sparrow ancestry may vary more freely. Jointly, this suggests that constraints and selection interact in shaping the genomic landscape of differentiation in this hybrid species.