Search

Farming of fungi by ants, termites, or beetles has led to ecologically successful societies fueled by industrial‐scale food production. Another type of obligate insect agriculture in Fiji involves the symbiosis between the ant Philidris nagasau and epiphytes in the genus Squamellaria (Rubiaceae) that the ants fertilize, defend, harvest, and depend on for nesting. All farmed Squamellaria form tubers (domatia) with preformed entrance holes and complex cavity networks occupied by P. nagasau. The inner surface of the domatia consists of smooth‐surfaced walls where the ants nest and rear their brood, and warty‐surfaced walls where they fertilize their crop by defecation. Here, we use RNA sequencing to identify gene expression patterns associated with the smooth versus warty wall types. Since wall differentiation occurred in the most recent common ancestor of all farmed species of Squamellaria, our study also identifies genetic pathways co‐opted following the emergence of agriculture. Warty‐surfaced walls show many upregulated genes linked to auxin transport, root development, and nitrogen transport consistent with their root‐like function; their defense‐related genes are also upregulated, probably to protect these permeable areas from pathogen entry. In smooth‐surfaced walls, genes functioning in suberin and wax biosynthesis are upregulated, contributing to the formation of an impermeable ant‐nesting area in the domatium. This study throws light on a number of functional characteristics of plant farming by ants and illustrates the power of genomic studies of symbiosis., We performed the first transcriptomic analysis of the newly discovered obligate farming symbiosis involving ants farming plants. Our analyses reveal a number of candidate genes associated with the differentiation of the plant tissue for ant nesting and fertilization.

PREMISE State‐sponsored weather stations became ubiquitous by the 1880s, yet many old climate data and phenological observations still need to be digitized and made accessible. METHODS We here make available flowering times for 450 species of herbs and shrubs gathered in 1844 by Carl Friedrich Philipp von Martius (1794–1868), director of the Munich Botanical Garden. The data formed part of the world’s third‐oldest phenological monitoring network as we explain in a brief overview of the history of such networks. Using data from one of the world’s oldest continuously functioning weather stations, Hohenpeißenberg, we relate temperature to flowering in three species with short flowering times and herbarium collections made since 1844 within the city’s perimeter, namely, Anemone patens, A. pulsatilla, and Arum maculatum. RESULTS Mean advances in flowering dates were 1.3–2.1 days/decade or 3.2–4.2 days/1°C warming. These advances are in keeping with similar advances in other European herbs during more recent periods. CONCLUSIONS Future studies might use the 1844 flowering data made available here as a source of information on the availability of particular flowers for specialized pollinators including insects looking for oviposition sites, such as the Psychoda flies that become trapped in Arum inflorescences. Another use of Martius’s 1844 data would be their incorporation into larger‐scale analyses of flowering in southern‐central Europe., American Journal of Botany, 108 (4), ISSN:1914-2016, ISSN:0002-9122

Hundreds of land plant lineages have independently evolved separate sexes in either gametophytes (dioicy) or sporophytes (dioecy), but 43% of all dioecious angiosperms are found in just 34 entirely dioecious clades, suggesting that their mode of sex determination evolved a long time ago. Here, we review recent insights on the molecular mechanisms that underlie the evolutionary change from individuals that each produce male and female gametes to individuals specializing in the production of just one type of gamete. The canonical model of sex chromosome evolution in plants predicts that two sex-determining genes will become linked in a sex-determining region (SDR), followed by expanding recombination suppression, chromosome differentiation and, ultimately, degeneration. Experimental work, however, is showing that single genes function as master regulators in model systems, such as the liverwort Marchantia and the angiosperms Diospyros and Populus. In Populus, this type of regulatory function has been demonstrated by genome editing. In other systems, including Actinidia, Asparagus and Vitis, two coinherited factors appear to independently regulate female and male function, yet sex chromosome differentiation has remained low. We discuss the best-understood systems and evolutionary pathways to dioecy, and present a meta-analysis of the sizes and ages of SDRs. We propose that limited sexual conflict explains why most SDRs are small and sex chromosomes remain homomorphic. It appears that models of increasing recombination suppression with age do not apply because selection favours mechanisms in which sex determination depends on minimal differences, keeping it surgically precise.

The increase in managed honeybees (Apis mellifera) in many European cities has unknown effects on the densities of wild bees through competition. To investigate this, we monitored honeybees and non-honeybees from 01 April to 31 July 2019 and 2020 at 29 species of plants representing diverse taxonomic and floral-functional types in a large urban garden in the city of Munich in which the same plant species were cultivated in both years. No bee hives were present in the focal garden, and all bee hives in the adjacent area were closely monitored by interviewing the relevant bee keepers in both 2019 and 2020. Honeybee numbers were similar in April of both years, but increased from May to July 2020 compared to 2019. The higher densities correlated with a significant increase in shifts from wild bee to honeybee visits in May/June/July, while visitor spectra in April 2019 and 2020 remained the same. Most of the species that experienced a shift to honeybee visits in 2020 were visited mostly or exclusively for their nectar. There were no shifts towards increased wild bee visits in any species. These results from a flower-rich garden have implications for the discussion of whether urban bee keeping might negatively impact wild bees. We found clear support that high honeybee densities result in exploitative competition at numerous types of flowers.

In 1917, sex chromosomes in plants were discovered in a liverwort with hetermorphic U and V chromosomes. Such heteromorphy is unexpected because, unlike the XY chromosomes in diploid-dominant plants, in haploid-dominant plants the female U and the male V chromosomes experience largely symmetrical potential recombination environments. Here we use molecular cytogenetics and super-resolution microscopy to study Frullania dilatata, a liverwort with one male and two female sex chromosomes. We applied a pipeline to Illumina sequences to detect abundant types of repetitive DNA and developed FISH probes to microscopically distinguish the sex chromosomes. We also determined the phenotypic population sex ratio because biased ratios have been reported from other liverworts with heteromorphic sex chromosomes. Populations had male-biased sex ratios. The sex chromosomes are monocentric, and of 14 probes studied (eight satellites, five transposable elements and one plastid region), four resulted in unique signals that differentiated the sex chromosomes from the autosomes and from each other. One FISH probe selectively marked the centromeres of both U chromosomes, so we could prove that during meiosis each U chromosome associates with one of the opposite telomeres of the V chromosome, resulting in a head-to-head trivalent. The similarity of the two U chromosomes to each other in size and in their centromere FISH signal positions points to their origin via a non-disjunction event (aneuploidy), which would fit with the general picture of sex chromosomes rarely crossing-over and being prone to suffer from non-disjunction.

Bees require suitably close foraging and nesting sites to minimize travel time and energy expenditure for brood provisioning. Knowing foraging distances in persistent (‘healthy’) populations is therefore crucial for assessing harmful levels of habitat fragmentation. For small bees, such distances are poorly known because of the difficulty of individual tagging and problems with mark-recapture approaches. Using apiarist’s number tags and colour codes, we marked 2689 males and females of four oligolectic and two polylectic species of Osmiini bees (Megachilidae, genera Chelostoma, Heriades, Hoplitis, Osmia) with body lengths of 6 to 15 mm. The work was carried out in 21 ha-large urban garden that harbours at least 106 species of wild bees. Based on 450 re-sightings, mean female flight distances ranged from 73 to 121 m and male distances from 59 to 100 m. These foraging distances suggest that as a rule of thumb, flower strips and nesting sites for supporting small solitary bees should be no further than 150 m apart.

Previous work has shown that among 428 species of bees occurring in Germany, decline or extinction over the past 40 years have been correlated with late-season emergence and restricted habitats, while other factors, such as pollen specialization, body size, nesting sites, and sociality, played no role in models that included a phylogeny of these bees. Doing best are spring-flying, city-dwelling species. Building on these results, we here investigate changes in bee diversity from the 1990s to 2018 at three protected sites within the city perimeter of Munich, focusing on the correlates of flight season (spring or summer), flight duration (in months), and number of habitats (one or two vs. three to six). Local species pools were assessed against the total species pool from 1795 onwards. Twenty years ago, 150 species were present at one or more of the sites, while in 2017/2018, this was true of 188 species, with the increase at two sites being of similar proportion. In two of the three areas, broad habitat use was positively correlated with persistence. Flight season or duration had no statistical effect. These results underscore the function of urban protected sites in bee conservation and imply that summer food shortages, which negatively affect bees in agricultural areas, play no role in urbanized regions so that late-season flight is not an extinction handicap.

AIM: Trees need to avoid frost damage to their young leaves by leafing out after the occurrence of the last frost, yet they also need to start photosynthesis early in the season to achieve sufficient growth. This trade‐off leads to the hypothesis that ‘safety margins’ against spring frost should become shorter, the longer the winter duration, perhaps reaching an asymptotic limit where frost damage would occur in most years. Physiologically, shorter safety margins in high‐latitude ecotypes might be achieved by lower degree‐day requirements for leaf‐out, compared to low‐latitude ecotypes. LOCATION: Europe. TIME PERIOD: 1902–2009. MAJOR TAXA STUDIED: Temperate trees. METHODS: Using herbarium collections of Acer platanoides, Carpinus betulus, Fagus sylvatica and Prunus spinosa made over 108 years at 40° to 60° N latitude, we related historic leaf‐out dates to winter and spring temperatures (chilling and degree‐days), winter duration, and date of last frost occurrence in the relevant years and locations. RESULTS: In all species, frost safety margins decreased towards high‐latitude regions with long winters, with each day increase in winter duration reducing frost safety margins by 0.48 days in Fagus and 0.32–0.21 days in Prunus, Acer and Carpinus. These latitudinal differences correlate with northern ecotypes’ shorter degree‐day requirements for leaf‐out. MAIN CONCLUSIONS: The decline in spring frost safety margins in regions with long winters supports the new hypothesis that species may reach their geographic range limit where they ‘bump up’ against experiencing regular frost injury to their young leaves. Larger datasets are necessary to further corroborate our hypothesis and future efforts should thus be directed toward increasing the latitudinal range of existing phenological databases.

Background and Aims Unlike other nuclear genes in eukaryotes, rDNA genes (5S and 35S loci) are present in numerous copies per cell and, when stained, can therefore provide basic information about genome organization. In tracheophytes (vascular plants), they are usually located on separate chromosomes, the so-called S-type organization. An analysis of 1791 species of land plants suggested that S-type arrays might be ancestral in land plants, while linked (L-type) organization may be derived. However, no outgroup and only a handful of ferns and bryophytes were included. Methods We analysed genome sizes and the distribution of telomere, 5S and 35S rDNA FISH signals in up to 12 monoicous or dioicous species of liverworts from throughout a phylogeny that includes 287 of the 386 currently recognized genera. We also used the phylogeny to plot chromosome numbers and the occurrence of visibly distinct sex chromosomes. Key Results Chromosome numbers are newly reported for the monoicous Lejeunea cavifolia and for females of the dioicous Scapania aequiloba. We detected sex-related differences in the number of rDNA signals in the dioicous Plagiochila asplenioides and Frullania dilatata. In the latter, the presence of two UU chromosomes in females and additional 5S-35S rDNA loci result in a haploid genome 0.2082 pg larger than the male genome; sex-specific genome differences in the other dioicous species were small. Four species have S-type rDNA, while five species have mixed L-S rDNA organization, and transitions may have occurred multiple times, as suggested by rDNA loci not being conserved among closely related species of Pellia. All species shared an Arabidopsis-like telomere motif, and its detection allowed verification of the chromosome number of Radula complanata and chromosome rearrangements in Aneura pinguis and P. asplenioides, the latter also showing sex-specific interstitial telomere repeats. Conclusions The S and L rDNA arrangements appear to have evolved repeatedly within liverworts, even in the same species. Evidence for differential accumulation of rDNA between the sexes so far is limited.

Diverse forms of cultivation have evolved across the tree of life. Efficient farming requires that the farmer deciphers and actively promotes conditions that increase crop yield. For plant cultivation, this can include evaluating tradeoffs among light, nutrients, and protection against herbivores. It is not understood if, or how, nonhuman farmers evaluate local conditions to increase payoffs. Here, we address this question using an obligate farming mutualism between the ant Philidris nagasau and epiphytic plants in the genus Squamellaria that are cultivated for their nesting sites and floral rewards. We focused on the ants' active fertilization of their crops and their protection against herbivory. We found that ants benefited from cultivating plants in full sun, receiving 7.5-fold more floral food rewards compared to shade-cultivated plants. The higher reward levels correlated with higher levels of crop protection provided by the ants. However, while high-light planting yielded the greatest immediate food rewards, sun-grown crops contained less nitrogen compared to shade-grown crops. This was due to lower nitrogen input from ants feeding on floral rewards instead of insect protein gained from predation. Despite this tradeoff, farming ants optimize crop yield by selectively planting their crops in full sun. Ancestral state reconstructions across this ant-plant clade show that a full-sun farming strategy has existed for millions of years, suggesting that nonhuman farmers have evolved the means to evaluate and balance conflicting crop needs to their own benefit.

Coriariaceae comprise only Coriaria , a genus of shrubs with nine species in Australasia (but excluding Australia), five in the Himalayas, Taiwan, the Philippines, and Japan, one in the Mediterranean, and one ranging from Patagonia to Mexico. The sister family, Corynocarpaceae, comprises five species of evergreen trees from New Guinea to New Zealand and Australia. This distribution has long fascinated biogeographers as potential support for Wegener's theory of continental drift, with alternative scenarios invoking either Antarctic or Beringian range expansions. Here, we present the discovery of pollen grains from Early Campanian (ca. 82 Mya) deposits in Antarctica, which we describe as Coriaripites goodii sp. nov., and newly generated nuclear and plastid molecular data for most of the family's species and its outgroup. This greatly expands the family's fossil record and is the so far oldest fossil of the order Cucurbitales. We used the phylogeny, new fossil, and an Oligocene flowering branch assigned to a small subclade of Coriaria to generate a chronogram and to study changes in chromosome number, deciduousness, and andromonoecy. Coriaria comprises a Northern (NH) and a Southern Hemisphere (SH) clade that diverged from each other in the Paleocene (ca. 57 Mya), with the SH clade reaching the New World once, through Antarctica, as supported by the fossil pollen. While the SH clade retained perfect flowers and evergreen leaves, the NH clade evolved andromonoecy and deciduousness. Polyploidy occurs in both clades and points to hybridization, matching weak species boundaries throughout the genus.

To combat the loss of flower-rich meadows, many cities are supporting greening measures, including the creation of flower strips. To assess the effectiveness of these measures in supporting flower-visiting insects, their faunas need to be compared to the background fauna at various distances from the flower strips. To meet this goal, we quantified the bee faunas of nine 1000 m2-large and newly established flower strips in the city of Munich, all planted with a regional seed mix, and compared them to the fauna recorded between 1997 and 2017 within 500, 1000, and 1500 m from the respective strip. The 68 species recorded during the flower strips’ first season represent 21% of the 324 species recorded for Munich since 1795 and 29% of the 232 species recorded between 1997 and 2017. Non-threatened species are statistically over-represented in the strips, but pollen generalists are not. These findings illustrate the conservation value of urban flower strips for common species that apparently quickly discover this food source. To our knowledge, this is the first quantitative assessment of the speed and distance over which urban flower strips attract wild bees.

Although hybridization plays a large role in speciation, some unknown fraction of hybrid individuals never reproduces, instead remaining as genetic dead-ends. We investigated a morphologically distinct and culturally important Chinese walnut, Juglans hopeiensis, suspected to have arisen from hybridization of Persian walnut (J. regia) with Asian butternuts (J. cathayensis, J. mandshurica, and hybrids between J. cathayensis and J. mandshurica). Based on 151 whole-genome sequences of the relevant taxa, we discovered that all J. hopeiensis individuals are first-generation hybrids, with the time for the onset of gene flow estimated as 370,000 years, implying both strong postzygotic barriers and the presence of J. regia in China by that time. Six inversion regions enriched for genes associated with pollen germination and pollen tube growth may be involved in the postzygotic barriers that prevent sexual reproduction in the hybrids. Despite its long-recurrent origination and distinct traits, J. hopeiensis does not appear on the way to speciation.

When flowers provide nectar, they can count on visits, and potential pollen transport, by many kinds of nectar-drinking animals. Yet, some flowers instead offer fatty oils that certain specialized bees gather with their forelegs. A recent study reveals how such a switch occurred and may have contributed to the formation of a new species.

Squamellaria is a genus of epiphytic Rubiaceae which has been domesticated by ants on the Fiji islands. One species is on the verge of extinction.

Persian walnut (Juglans regia) is cultivated worldwide for its high-quality wood and nuts, but its origin has remained mysterious because in phylogenies it occupies an unresolved position between American black walnuts and Asian butternuts. Equally unclear is the origin of the only American butternut, J. cinerea. We resequenced the whole genome of 80 individuals from 19 of the 22 species of Juglans and assembled the genome of its relatives Pterocarya stenoptera and Platycarya strobilacea. Using phylogenetic-network analysis of single-copy nuclear genes, genome-wide site pattern probabilities, and Approximate Bayesian Computation, we discovered that J. regia (and its landrace J. sigillata) arose as a hybrid between the American and the Asian lineages and that J. cinerea resulted from massive introgression from an immigrating Asian butternut into the genome of an American black walnut. Approximate Bayesian Computation modeling placed the hybrid origin in the late Pliocene, ∼3.45 My, with both parental lineages since having gone extinct in Europe.

Cytogenetic studies in bryophytes have been limited by the difficulty of obtaining sufficient dividing nuclei and by the absence of modern protocols. The technical difficulties stem from the plants’ small size and lack of roots and pollen mother cells, the main sources of cells in division in vascular plants. In bryophytes instead, tiny sporophytes, antheridia, or phyllid meristems must be used to obtain meiotic or mitotic chromosome spreads. We here describe the preparation of such spreads from phyllids, antheridia, and sporophytes in several species of liverworts and compare available protocols with or without prefixation treatments. We also provide illustrated step-by-step instructions. The three prefixation agents (including colchicine) that we tested failed to improve synchronization of cell divisions. Young sporophytes were the best source of diploid synchronized cells, while antheridia were the best source of haploid cells. For meiotic nuclei, a short fixation of capsule tissue at the right developmental stage with 45% acetic acid sufficed to conserve the DNA for cytological investigations, while for mitotic nuclei, fixation in 3:1 ethanol/glacial acetic acid for a longer period (4–24 h) worked well.

The date palm, Phoenix dactylifera, has been a cornerstone of Middle Eastern and North African agriculture for millennia. It was first domesticated in the Persian Gulf, and its evolution appears to have been influenced by gene flow from two wild relatives, P. theophrasti, currently restricted to Crete and Turkey, and P. sylvestris, widespread from Bangladesh to the West Himalayas. Genomes of ancient date palm seeds show that gene flow from P. theophrasti to P. dactylifera may have occurred by ∼2,200 years ago, but traces of P. sylvestris could not be detected. We here integrate archeogenomics of a ∼2,100-year-old P. dactylifera leaf from Saqqara (Egypt), molecular-clock dating, and coalescence approaches with population genomic tests, to probe the hybridization between the date palm and its two closest relatives and provide minimum and maximum timestamps for its reticulated evolution. The Saqqara date palm shares a close genetic affinity with North African date palm populations, and we find clear genomic admixture from both P. theophrasti, and P. sylvestris, indicating that both had contributed to the date palm genome by 2,100 years ago. Molecular-clocks placed the divergence of P. theophrasti from P. dactylifera/P. sylvestris and that of P. dactylifera from P. sylvestris in the Upper Miocene, but strongly supported, conflicting topologies point to older gene flow between P. theophrasti and P. dactylifera, and P. sylvestris and P. dactylifera. Our work highlights the ancient hybrid origin of the date palms, and prompts the investigation of the functional significance of genetic material introgressed from both close relatives, which in turn could prove useful for modern date palm breeding., Molecular Biology and Evolution, 38 (10), ISSN:0737-4038, ISSN:1537-1719

Wild relatives or progenitors of crops are important resources for breeding and for understanding domestication. Identifying them, however, is difficult because of extinction, hybridization, and the challenge of distinguishing them from feral forms. Here, we use collection-based systematics, iconography, and resequenced accessions of Citrullus lanatus and other species of Citrullus to search for the potential progenitor of the domesticated watermelon. A Sudanese form with nonbitter whitish pulp, known as the Kordofan melon (C. lanatus subsp. cordophanus), appears to be the closest relative of domesticated watermelons and a possible progenitor, consistent with newly interpreted Egyptian tomb paintings that suggest that the watermelon may have been consumed in the Nile Valley as a dessert by 4360 BP. To gain insights into the genetic changes that occurred from the progenitor to the domesticated watermelon, we assembled and annotated the genome of a Kordofan melon at the chromosome level, using a combination of Pacific Biosciences and Illumina sequencing as well as Hi-C mapping technologies. The genetic signature of bitterness loss is present in the Kordofan melon genome, but the red fruit flesh color only became fixed in the domesticated watermelon. We detected 15,824 genome structural variants (SVs) between the Kordofan melon and a typical modern cultivar, "97103," and mapping the SVs in over 400 Citrullus accessions revealed shifts in allelic frequencies, suggesting that fruit sweetness has gradually increased over the course of watermelon domestication. That a likely progenitor of the watermelon still exists in Sudan has implications for targeted modern breeding efforts.

Our study showed that increases in seasonal productivity drive earlier autumn senescence of temperate trees. Norby argues that this finding is contradicted by observations from free-air CO 2 enrichment (FACE) experiments, where elevated CO 2 has been found to delay senescence in some cases. We provide a detailed answer showing that the results from FACE studies are in agreement with our conclusions.

Limits to the growing season The length of the growing season in temperate forests has been increasing under recent climate change because of earlier leaf emergence and later leaf senescence. However, Zani et al. show that this trend might be reversed as increasing photosynthetic productivity begins to drive earlier autumn leaf senescence (see the Perspective by Rollinson). Using a combination of experimental, observational, and modeling studies based on European forest trees, the researchers conclude that leaf senescence will advance by 3 to 6 days by the end of the 21st century rather than lengthening by 1 to 3 weeks as current phenological models have predicted. In turn, this predicted phenological pattern will limit the capacity of temperate forests to mitigate climate change through carbon uptake. Science , this issue p. 1066 ; see also p. 1030

Natural history collections are leading successful large-scale projects of specimen digitization (images, metadata, DNA barcodes), thereby transforming taxonomy into a big data science. Yet, little effort has been directed towards safeguarding and subsequently mobilizing the considerable amount of original data generated during the process of naming 15,000–20,000 species every year. From the perspective of alpha-taxonomists, we provide a review of the properties and diversity of taxonomic data, assess their volume and use, and establish criteria for optimizing data repositories. We surveyed 4113 alpha-taxonomic studies in representative journals for 2002, 2010, and 2018, and found an increasing yet comparatively limited use of molecular data in species diagnosis and description. In 2018, of the 2661 papers published in specialized taxonomic journals, molecular data were widely used in mycology (94%), regularly in vertebrates (53%), but rarely in botany (15%) and entomology (10%). Images play an important role in taxonomic research on all taxa, with photographs used in >80% and drawings in 58% of the surveyed papers. The use of omics (high-throughput) approaches or 3D documentation is still rare. Improved archiving strategies for metabarcoding consensus reads, genome and transcriptome assemblies, and chemical and metabolomic data could help to mobilize the wealth of high-throughput data for alpha-taxonomy. Because long-term—ideally perpetual—data storage is of particular importance for taxonomy, energy footprint reduction via less storage-demanding formats is a priority if their information content suffices for the purpose of taxonomic studies. Whereas taxonomic assignments are quasifacts for most biological disciplines, they remain hypotheses pertaining to evolutionary relatedness of individuals for alpha-taxonomy. For this reason, an improved reuse of taxonomic data, including machine-learning-based species identification and delimitation pipelines, requires a cyberspecimen approach—linking data via unique specimen identifiers, and thereby making them findable, accessible, interoperable, and reusable for taxonomic research. This poses both qualitative challenges to adapt the existing infrastructure of data centers to a specimen-centered concept and quantitative challenges to host and connect an estimated \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$ \le $\end{document}2 million images produced per year by alpha-taxonomic studies, plus many millions of images from digitization campaigns. Of the 30,000–40,000 taxonomists globally, many are thought to be nonprofessionals, and capturing the data for online storage and reuse therefore requires low-complexity submission workflows and cost-free repository use. Expert taxonomists are the main stakeholders able to identify and formalize the needs of the discipline; their expertise is needed to implement the envisioned virtual collections of cyberspecimens. [Big data; cyberspecimen; new species; omics; repositories; specimen identifier; taxonomy; taxonomic data.]

While the importance of mutualisms across the tree of life is recognized, it is not understood why some organisms evolve high levels of dependence on mutualistic partnerships, while other species remain autonomous or retain or regain minimal dependence on partners. We identify four main pathways leading to the evolution of mutualistic dependence. Then, we evaluate current evidence for three predictions: ( a) Mutualisms with different levels of dependence have distinct stabilizing mechanisms against exploitation and cheating, ( b) less dependent mutualists will return to autonomy more often than those that are highly dependent, and ( c) obligate mutualisms should be less context dependent than facultative ones. Although we find evidence supporting all three predictions, we stress that mutualistic partners follow diverse paths toward—and away from—dependence. We also highlight the need to better examine asymmetry in partner dependence. Recognizing how variation in dependence influences the stability, breakdown, and context dependence of mutualisms generates new hypotheses regarding how and why the benefits of mutualistic partnerships differ over time and space.

About 15,000 angiosperms are dioecious, but the mechanisms of sex determination in plants remain poorly understood. In particular, how Y chromosomes evolve and degenerate, and whether dosage compensation evolves as a response, are matters of debate. Here, we focus on Coccinia grandis, a dioecious cucurbit with the highest level of X/Y heteromorphy recorded so far. We identified sex-linked genes using RNA sequences from a cross and a model-based method termed SEX-DETector. Parents and F1 individuals were genotyped, and the transmission patterns of SNPs were then analyzed. In the &gt, 1300 sex-linked genes studied, maximum X-Y divergence was 0.13&ndash, 0.17, and substantial Y degeneration is implied by an average Y/X expression ratio of 0.63 and an inferred gene loss on the Y of ~40%. We also found reduced Y gene expression being compensated by elevated expression of corresponding genes on the X and an excess of sex-biased genes on the sex chromosomes. Molecular evolution of sex-linked genes in C. grandis is thus comparable to that in Silene latifolia, another dioecious plant with a strongly heteromorphic XY system, and cucurbits are the fourth plant family in which dosage compensation is described, suggesting it might be common in plants.

Some ~15.000 angiosperms are dioecious, but mechanisms of sex determination in plants remain poorly understood. In particular, how Y chromosomes evolve and degenerate, and whether dosage compensation evolves as a response, are matters of debate. Here we focus on Coccinia grandis, a dioecious cucurbit with the highest level of X/Y heteromorphy recorded so far. We identified sex-linked genes using RNA sequences from a cross and a model-based method termed SEX-DETector. Parents and F1 individuals were genotyped and the transmission patterns of SNPs then analysed. In the >1300 sex-linked genes studied, X-Y divergence was 0.13 - 0.17, and substantial Y degeneration is implied by an average Y/X expression ratio of 0.63 and an inferred gene loss on the Y of ~40%. We also found reduced Y gene expression being compensated by elevated expression of corresponding genes on the X and an excess of sex-biased genes on the sex chromosomes. Molecular evolution of sex-linked genes in C. grandis is thus comparable to that in Silene latifolia, another dioecious plant with a strongly heteromorphic XY system, and cucurbits are the fourth plant family in which dosage compensation is described, suggesting it might be common in plants.

Ongoing global warming is causing phenological shifts that affect photosynthesis and growth rates in temperate woody species. However, the effects of seasonally uneven climate warming-as is occurring in much of Europe, where the winter/spring months are warming twice as fast than the summer/autumn months-on autumn growth cessation (completion of overwintering buds) and leaf senescence, and possible carry-over effects between phenophases, remain under-investigated. We conducted experiments in which we exposed saplings of canopy and understory species to 4 °C warming in winter/spring, summer/autumn, or all year to disentangle how the timing of bud break, bud set completion, and leaf senescence is affected by seasonally uneven warming. All-year warming led to significantly delayed leaf senescence, but advanced bud set completion; summer/autumn warming only delayed leaf senescence; and winter/spring warming advanced both bud set and senescence. The non-parallel effects of warming on bud completion and leaf senescence show that leaf senescence alone is an inadequate proxy for autumn growth cessation in trees and counterintuitively suggest that continued uneven seasonal warming will advance cessation of primary growth in autumn, even when leaf senescence is delayed. Phenological responses to warming treatments (earlier spring onset, later autumn senescence) were more than twice as high in understory species than in canopy species, which can partly be explained by the absence of carry-over effects among phenophases in the former group. This underscores the need to consider differences among plant functional types when forecasting the future behaviour of ecosystems.

The ability to rapidly generate and share molecular, visual, and acoustic data, and to compare them with existing information, and thereby to detect and name biological entities is fundamentally changing our understanding of evolutionary relationships among organisms and is also impacting taxonomy. Harnessing taxonomic data for rapid, automated species identification by machine learning tools or DNA metabarcoding techniques has great potential but will require their review, accessible storage, comprehensive comparison, and integration with prior knowledge and information. Currently, data production, management, and sharing in taxonomic studies are not keeping pace with these needs. Indeed, a survey of recent taxonomic publications provides evidence that few species descriptions in zoology and botany incorporate DNA sequence data. The use of modern high-throughput (-omics) data is so far the exception in alpha-taxonomy, although they are easily stored in GenBank and similar databases. By contrast, for the more routinely used image data, the problem is that they are rarely made available in openly accessible repositories. Improved sharing and re-using of both types of data requires institutions that maintain long-term data storage and capacity with workable, user-friendly but highly automated pipelines. Top priority should be given to standardization and pipeline development for the easy submission and storage of machine-readable data (e.g., images, audio files, videos, tables of measurements). The taxonomic community in Germany and the German Federation for Biological Data are researching options for a higher level of automation, improved linking among data submission and storage platforms, and for making existing taxonomic information more readily accessible.

Orchids are globally distributed, a feature often attributed to their tiny dustlike seeds. They were ancestrally terrestrial but in the Eocene expanded into tree canopies, with some lineages later returning to the ground, providing an evolutionarily replicated system. Because seeds are released closer to the ground in terrestrial species than in epiphytic ones, seed traits in terrestrials may have been under selective pressure to increase seed dispersal efficiency. In this study, we test the expectations that seed airspace-a trait known to increase seed flotation time in the air-is (i) larger in terrestrial lineages and (ii) has increased following secondary returns to a terrestrial habit. We quantified and scored 20 seed traits in 121 species and carried out phylogenetically informed analyses. Results strongly support both expectations, suggesting that aerodynamic traits even in dust seeds are under selection to increase dispersal ability, following shifts in average release heights correlated with changes in habit.

Phenological mismatch results when interacting species change the timing of regularly repeated phases in their life cycles at different rates. We review whether this continuously ongoing phenomenon, also known as trophic asynchrony, is becoming more common under ongoing rapid climate change. In antagonistic trophic interactions, any mismatch will have negative impacts for only one of the species, whereas in mutualistic interactions, both partners are expected to suffer. Trophic mismatch is therefore expected to last for evolutionarily short periods, perhaps only a few seasons, adding to the difficulty of attributing it to climate change, which requires long-term data. So far, the prediction that diverging phenologies linked to climate change will cause mismatch is most clearly met in antagonistic interactions at high latitudes in the Artic. There is limited evidence of phenological mismatch in mutualistic interactions, possibly because of strong selection on mutualists to have co-adapted phenological strategies. The study of individual plasticity, population variation, and the genetic bases for phenological strategies is in its infancy. Recent work on woody plants revealed the large imprint of historic climate change on temperature, chilling, and day-length thresholds used by different species to synchronize their phenophases, which in the Northern Hemisphere has led to biogeographic phenological regions in which long-lived plants have adapted to particular interannual and intermillennial amplitudes of climate change.

Botanical gardens represent artificial, but stable environments. With this premise, we analyzed the Munich Botanical Garden's bee fauna in 1997/1999 and again in 2015/2017. The garden covers 20 ha, uses no bee-relevant insecticides, has a protected layout, and on three sides abuts protected areas. Outdoors, it cultivates some 10,871 species/subspecies, many suitable as pollen and nectar sources for bees. The first survey found 79 species, the second 106, or 55% of the 192 species recorded for Munich since 1990. A Jackknife estimate for the second survey suggests 115 expected species. Classifying bees according to their thermal preferences (warm habitats, cool habitats, broad preferences, or unknown) revealed that 15 warm-loving species were gained (newly found), two lost (no longer found), and 12 retained, but only one cool-loving species was gained, three lost, and none retained, which multinomial models show to be significant differences. Of the 62 retained species, 27 changed in abundance, with 18 less frequent and nine more frequent by 2017 than they had been in 1997/1999. Retention, gain, or loss were unconnected to pollen specialization and Red List status of bee species. Between 1997 and 2017, average temperatures in Munich have increased by 0.5 °C, and climate warming over the past century is the most plausible explanation for the directional increase in warm-loving and the decrease in cool-adapted species. These results highlight the potential of botanic gardens with their artificially diverse and near-pesticide-free floras as systems in which to investigate climate change per se as a possible factor in shifting insect diversity.

Aim: Winteraceae comprise c.130 species in seven genera, with the greatest species diversity in the Pacific (Pseudowintera, Zygogynum), Australia (Bubbia, Tasmannia), New Guinea (Belliolum, Bubbia, Zygogynum, Tasmannia) and Madagascar (Takhtajania). Only Drimys occurs in South America. Because of their Cretaceous leaves, wood and pollen fossils, and their lack of xylem vessels, Winteraceae throw light on early angiosperm evolution. We describe a Winteraceae pollen tetrad from the Paleocene of Greenland, review the family's fossil record and palaeogeography and document its current climate preferences. Location: Worldwide. Methods: Extant and fossil pollen were studied with light and scanning electron microscopy. Molecular phylogenetic and character mapping approaches were used to infer the evolution of pollen characters, and 37,842 collections from the Global Biodiversity Information Facility were used to infer the climate and vegetation types occupied by today's Winteraceae and to compare them to the Paleocene climate and vegetation of Greenland as inferred from the fossil record of other families. Results: Winteraceae are the only flowering plants with persistent, acalymmate tetrads composed of ulcerate grains with a distinct reticulate sculpturing. The tetrad described here as Pseudowinterapollis agatdalensis Grimsson & Zetter spec. nov. comes from Agatdalen valley in western Greenland and dates to the Early Paleocene, Danian, 64-62Ma. It shows the complete character suite of modern Winteraceae and overlaps the LM characters of the three previously known Pseudowinterapollis species from Australia, New Zealand and South Africa. The palaeoflora of the Agatdal Formation consisted of a mixed deciduous-evergreen forest resembling habitats where Winteraceae occur today. Main conclusions: Macro- and microfossil records of Winteraceae extend back to the Upper Cretaceous in both Laurasia and Gondwana, and the family's biogeography, like that of its sister family, Canellaceae, cannot be understood by focusing only on southern Gondwana. Winteraceae instead were part of broadleaved forests in Paleocene and Eocene North American and Greenland and may have reached Europe via the North Atlantic Land Bridge, explaining Eocene Winteraceae wood in northern Germany.

Watermelons are among the most important vegetable crops worldwide, but targeted breeding is hindered by problems with Citrullus taxonomy. Here we clarify nomenclature and species relationships in Citrullus, its chromosome numbers, and the likely geographic region of watermelon domestication. We correct an erroneous chromosome count in recent literature, provide a count for an understudied species, and data on chromosome numbers for the entire genus. We also use a nuclear/plastid locus phylogeny to summarize data on Citrullus sexual systems, loss of tendrils, life history, and geographic ranges. Key insights from new sequences are that (i) material of C. vulgaris var. "colocynthoides", collected by Schweinfurth in Egypt in 1882 represents the colocynth, C. colocynthis, and (ii) the citron or bitter watermelon, C. amarus, is indeed a separate species, not a subspecies of the dessert watermelon. Schweinfurth's varietal name, a nomen nudum, has been widely used for seeds as old as 5400 BP, and it now needs to be investigated whether these seeds are colocynths, watermelon or a hybrid. To help improve Citrullus taxonomy and nomenclature, we allocate some 50 scientific names to seven biological species, tabulate chromosome counts, and provide notes on misidentified germplasms traceable by accession numbers. More wild-collected herbarium-verified material from northeast Africa is urgently needed, especially given the discovery of Russian breeders that populations of wild "cordophanus" from Sudan are closer to the cultivated watermelon than are any other wild populations so far known.

Between 1836 and 1840, Jan Vilém Helfer collected thousands of insects, birds and plants in Burma, the Andaman Islands and the Mergui Archipelago, with many first records from these regions. His botanical specimens are preserved in Prague, Kew, Calcutta and many other herbaria. Yet no account has been published of his itinerary, and the volume of his collections has not previously been appreciated. We bring together the available data on Helfer, reconstruct his itinerary and the two routes by which his plants were distributed, and explain the different numbering systems used on the labels of Helfer's duplicates. Based on what his widow transferred to the Czech National Museum in Prague, Helfer collected almost 48,000 beetles, 609 bird skins, 14 mammal skins, 508 Lepidoptera, and 6,086 herbarium specimens or collections. His diaries and his wife's account of their travels have allowed us to reconstruct his itinerary, and we have generated new labels for 305 collections, most of which have two or three duplicates. Helfer's Burmese and Andaman herbarium contains some of the first records of economically important plants in which he was particularly interested.

Herbarium specimens deposited in publicly accessible collections are the basis for all scientific names because only permanent specimens can be re-studied by independent researchers, the very essence of science. Re-investigations may be done with morphological, chemical, genomic, computer-tomographic, or other methods. Based on new herbarium material, I here provide a name for the Xishuangbanna gourd, a plant long cultivated in Yunnan because of its large non-bitter fruits, rich in β-carotene. Genome re-sequencing of numerous accessions has shown that this cucumber mutant is closer to Cucumis sativus var. sativus than is the wild bitter-fruited progenitor C. sativus var. hardwickii, and two dozen studies have further clarified the genetics of key traits, including pulp color, fruit shape, and flowering times. Morphological and molecular diagnoses of the new variety are provided and museum-quality specimens have been distributed to the World’s major herbaria.

Trait matching between the Madagascan orchid Angraecum sesquipedale, with a nectar spur of 33 cm, and a hawkmoth with a tongue almost as long has fascinated biologists since Darwin, who saw only flowers but correctly predicted the moth pollinator. This moth, Xanthopan morgani praedicta, was described from museum specimens in 1903 and documented as the pollinator in photographs and film in 1992 and 2004. However, Madagascar harbours c. 30 species of long-spurred orchids and seven species of long-tongued hawkmoths, and mutualisms between moths and 'Angraecum and other deep tubular flowers' (Darwin, 1862: p. 202) probably involve a network of interacting species. We infer the evolutionary time over which Madagascan sphingids and Angraecum have interacted, based on an orchid phylogeny that includes 62 of 144 Angraecum species on Madagascar and a moth phylogeny with all nine Madagascan Sphinginae. Clock models using either rate- or fossil-based calibrations imply that the Madagascan subspecies X. morgani praedicta and the African morgani diverged 7.4 +/- 2.8 Mya, which overlaps the divergence of An. sesquipedale from its sister, Angraecum sororium, namely 7.5 +/- 5.2 Mya;since both have extremely long spurs, long spurs probably existed before that. The phylogenies moreover show that several long-tongued moths and long-spurred orchids probably coevolved on Madagascar since the mid-Miocene, although field data on the moths' levels of polyphagy and pollen transport are lacking.

The three bryophyte lineages have longy-lived gametophytes that are either bisexual, producing both male- and female gametes, or sexually specialized and then producing only one type of gamete. Phylogenies suggest repeated evolutionary switches between these systems, implying that bryophyte sex chromosomes may have been gained and lost repeatedly. How this occurred is poorly understood, even though plant sex chromosomes were first discovered in liverworts. We explain how the sex chromosomes of haploid-dominant organisms are distinct from the better-studied X-Y and Z-W systems in the tree of life, summarise what is known about their distribution and genetic composition, and present new cytogenetic data for Frullania dilatata and Plagiochila asplenioides, the former with two U chromosomes and one V chromosome, the latter with one U chromosome and two V chromosomes; male and female C-values in F. dilatata are correspondingly asymmetric (the C-value of P. asplenioides is only known for female nuclei). So far, there is a lack of high-throughput sequencing, quantification, and in situ study of the repetitive DNA, organellar DNA, and transposable elements, and it is therefore not known what causes the size difference of U and V chromosomes from the autosomes or each other. Heterochromatin was also first discovered in bryophytes, but its function in their sex regulation has not been addressed. Studies of bryophyte sex chromosomes with combined cytogenetic and genomic approaches are fundamental for fuller understanding of s sex chromosome evolution across the tree of life.

Our understanding of the evolution of plant sex chromosomes is increasing rapidly due to high-throughput sequencing data and phylogenetic and molecular-cytogenetic approaches that make it possible to infer the evolutionary direction and steps leading from homomorphic to heteromorphic sex chromosomes. Here, we focus on four species of Coccinia, a genus of 25 dioecious species, including Coccinia grandis, the species with the largest known plant Y chromosome. Based on a phylogeny for the genus, we selected three species close to C. grandis to test the distribution of eight repetitive elements including two satellites, and several plastid and mitochondrial probes, that we had previously found to have distinct accumulation patterns in the C. grandis genome. Additionally, we determined C-values and performed immunostaining experiments with (peri-)centromere-specific antibodies on two species (for comparison with C. grandis). In spite of no microscopic chromosomal heteromorphism, single pairs of chromosomes in male cells of all three species accumulate some of the very same repeats that are enriched on the C. grandis Y chromosome, pointing to either old (previous) sex chromosomes or incipient (newly arising) ones, that is, to sex chromosome turnover. A 144-bp centromeric satellite repeat (CgCent) that characterizes all C. grandis chromosomes except the Y is highly abundant in all centromeric regions of the other species, indicating that the centromeric sequence of the Y chromosome diverged very recently.

Aim Partners in co-evolutionary interactions must be ecologically interdependent and at least at some stage have matching traits and more or less overlapping ranges. As co-evolution is a process, neither the mutual dependence nor the trait and range matching are expected to be static or perfect. Here we investigate the extent of evolutionary flexibility in tight pollination mutualisms between hummingbirds and plants, ranging from straight-billed species to sicklebills. Location The Americas. Methods The five considered pollination mutualisms are between the following hummingbird and plant species: Calypte anna and Ribes speciosum (Grossulariaceae); Basilinna xantusii and Arbutus peninsularis (Ericaceae); two species of Sephanoides and Tristerix aphyllus/corymbosus (Loranthaceae); two species of Eutoxeres and 34 species of curved-corolla Centropogon (Campanulaceae); and six species of Oreotrochilus and seven species of Chuquiraga (Asteraceae). While ecological interdependence and trait matching in these mutualisms are well established, geographic occurrence data and molecular clock-based ages for the 10 clades were newly compiled. Results We found matching bird and plant stem ages in two of the five systems and (much) older bird than plant ages in the other three. The implied adaptation of plant populations to already existing hummingbird species fits with the modelled distributions. In three of the systems, the ranges of the plants overlap those of their pollinators by > 90%; conversely, the range overlap between the bird species and the plant species they pollinate is much less than that. Surprisingly, the age mismatch was greatest in the Eutoxeres/Centropogon system, in spite of the perfect morphological fit among bills and corollas, illustrating the evolutionary flexibility of these mutualisms and the apparently rapid ‘addition’ of further plant species. Main conclusions These findings illuminate the macroevolutionary assembly of hummingbird/plant mutualisms, which has been highly dynamic, even in specialized systems with perfect morphological trait fitting.

Premise The proportion of woody dicots with toothed leaves increases toward colder regions, a relationship used to reconstruct past mean annual temperatures. Recent hypotheses explaining this relationship are that (1) leaves in colder regions are thinner, requiring thick veins for support and water supply, with the resulting craspedodromous venation leading to marginal teeth (support–supply hypothesis) or that (2) teeth are associated with the packing of leaf primordia in winter buds (bud‐packing hypothesis). Methods We addressed these hypotheses by examining leaf thickness, number of primordia in buds, growing season length (mean annual temperature, MAT), and other traits in 151 deciduous woody species using georeferenced occurrences and a Bayesian model controlling for phylogeny. We excluded evergreen species because longer leaf life spans correlate with higher leaf mass per area, precluding the detection of independent effects of leaf thickness on leaf‐margin type. Results The best model predicted toothed leaves with 94% accuracy, with growing season length the strongest predictor. Neither leaf thickness nor number of leaves preformed in buds significantly influenced margin type, rejecting the support–supply and bud‐packing hypotheses. Conclusions A direct selective benefit of leaf teeth via a carbon gain early in the spring as proposed by Royer and Wilf (2006) would match the strong correlation between toothed species occurrence and short growing season found here using Bayesian hierarchical models. Efforts should be directed to physiological work quantifying seasonal photosynthate production in toothed and nontoothed leaves., American Journal of Botany, 106 (11), ISSN:1914-2016, ISSN:0002-9122

Domestication of the watermelon (Citrullus lanatus) has alternatively been placed in South Africa, the Nile valley, or more recently West Africa, with the oldest archeological evidence coming from Libya and Egypt. The geographic origin and domestication of watermelons has therefore remained unclear. Using extensive nuclear and plastid genomic data from a 3,560-year-oldCitrullusleaf from a mummy’s sarcophagus and skimmed genomes for representatives of the seven extant species ofCitrullus, we show that modern cultivars and the ancient plant uniquely share mutations in a lycopene metabolism gene (LYCB) affecting pulp color and a stop codon in a transcription factor regulating bitter cucurbitacin compounds. This implies that the plant we sequenced had red-fleshed and sweet fruits and that New Kingdom Egyptians were cultivating domesticated watermelons. The genomic data also identify extant Sudanese watermelons with white, sweet pulp as the closest relatives of domesticated watermelons.Significance statementWith some 197.8 million tons in 2017, watermelon,Citrullus lanatus, is among the World’s most important crops, yet its area of origin and domestication have remained unclear, with competing hypotheses favoring South Africa, West Africa, Central Africa, or the Nile valley. We generated extensive nuclear and plastid genomic data from a 3500-year-old leaf from a Pharaonic sarcophagus and performed genome skimming for representatives of all otherCitrullusspecies to compare key genes involved in fruit bitterness and color. White-fleshed, non-bitter melons from southern Sudan are the closest relatives of domesticated watermelon, and the ancient genome shares unique alleles with a red-fleshed, non-bitter domesticated form (but no wild forms), implying that 18thDynasty Egyptians were cultivating domesticated watermelon by 3500 years ago.

Photoperiod is only an important leaf-out regulator for woody plants in areas with short winters and in lineages that derive from lower latitudes. Consequently, photoperiod constraint on range expansion should be limited to these areas and species. The relative roles of temperature and day length in driving spring leaf unfolding are known for few species, limiting our ability to predict phenology under climate warming1,2. Using experimental data, we assess the importance of photoperiod as a leaf-out regulator in 173 woody species from throughout the Northern Hemisphere, and we also infer the influence of winter duration, temperature seasonality, and inter-annual temperature variability. We combine results from climate- and light-controlled chambers with species’ native climate niches inferred from georeferenced occurrences and range maps. Of the 173 species, only 35% relied on spring photoperiod as a leaf-out signal. Contrary to previous suggestions, these species come from lower latitudes, whereas species from high latitudes with long winters leafed out independent of photoperiod. The strong effect of species’ geographic–climatic history on phenological strategies complicates the prediction of community-wide phenological change.

Lobelioideae comprise about 1200 species in 30 genera worldwide and include famous cases of parallel evolution in the "giant rosette" lobelias occurring in East Africa, Hawaii, and Bhutan. To date, no phylogeny has included the Himalayan giant lobelia, and its age and phylogenetic distance from the Hawaiian and African giant species (the latter in the same section as the Bhutan species) are therefore unknown. Asian Lobelioideae in general have received little attention, partly because of the difficult access to material. Here we use nuclear and plastid markers of Lobelioideae (with worldwide sampling) to test the monophyly of the section that includes most Asian lobelias, and we then use a reduced concatenated matrix to resolve the position of Lobelia nubigena from Bhutan and of the likewise cold-adapted lowland species L. sessilifolia. Most sequences come from herbarium material. Lobelia nubigena diverged from its Asian lowland relatives 13.8 (12.6-15) million years ago (about the time of the Bhutan Himalaya orogeny), and in an unexpected twist, L. sessilifolia is the sister species to a huge Glade (ca. 265 species) that comprises African, South American, Asian, and the entire Hawaiian Lobelioideae radiation. The African and Hawaiian high-elevation lobelias in our sample are younger than L. nubigena, although the time when gigantism evolved in this species cannot be precisely inferred. Our results support the previously hypothesized Asian origin of (1) the Hawaiian Lobelioideae, (2) Southeast Asian islands lobelias, and (3) the African Lobelia-Rynchopetalum group, which also reached South America.

Some of the World's most valuable crops, including watermelon, honey melon, cucumber, squash, zucchini and pumpkin, belong to the family Cucurbitaceae. We review insights on their domestication from new phylogenies, archaeology and genomic studies. Ancestral state estimation on the most complete Cucurbitaceae phylogeny to date suggests that an annual life cycle may have contributed to domestication. Domestication started c. 11 000 years ago in the New World and Asia, and apparently more recently in Africa. Some cucurbit crops were domesticated only once, others multiple times (e.g. melon from different Asian and African populations). Most wild cucurbit fruits are bitter and nonpalatable to humans, and nonbitterness of the pulp apparently was a trait favoured early during domestication, with genomic data showing how bitterness loss was achieved convergently. The genetic pathways underlying lycopene accumulation, red or orange pulp colour, and fruit size and shape are only just beginning to be understood. The study of cucurbit domestication in recent years has benefitted from the increasing integration of archaeological and genomic data with insights from herbarium collections, the most efficient way to understand species' natural geographic ranges and climate adaptations.

True agriculture - defined by habitual planting, cultivation, harvesting and dependence of a farmer on a crop - is known from fungi farmed by ants, termites or beetles, and plants farmed by humans or ants. Because farmers supply their crops with nutrients, they have the potential to modify crop nutrition over evolutionary time. Here we test this hypothesis in ant/plant farming symbioses. We used field experiments, phylogenetic-comparative analyses and computed-tomography scanning to investigate how the evolution of farming by ants has impacted the nutrition of locally coexisting species in the epiphytic genus Squamellaria (Rubiaceae). Using isotope-labelled mineral and organic nitrogen, we show that specialised ants actively and exclusively fertilise hyperabsorptive warts on the inner walls of plant-formed structures (domatia) where they nest, sharply contrasting with nitrogen provisioning by ants in nonfarming generalist symbioses. Similar hyperabsorptive warts have evolved repeatedly in lineages colonised by farming ants. Our study supports the idea that millions of years of ant agriculture have remodelled plant physiology, shifting from ant-derived nutrients as by-products to active and targeted fertilisation on hyperabsorptive sites. The increased efficiency of ant-derived nutrient provisioning appears to stem from a combination of farming ant behaviour and plant 'crop' traits.

PREMISE Parasitic plants with large geographic ranges, and different hosts in parts of their range, may acquire horizontally transferred genes (HGTs), which might sometimes leave a footprint of gradual host and range expansion. Cynomorium coccineum, the only member of the Saxifragales family Cynomoriaceae, is a root holoparasite that occurs in water-stressed habitats from western China to the Canary Islands. It parasitizes at least 10 angiosperm families from different orders, some of them only in parts of its range. This parasite therefore offers an opportunity to trace HGTs as long as parasite-host pairs can be obtained and sequenced. METHODS By sequencing mitochondrial, plastid, and nuclear loci from parasite-host pairs from throughout the parasite's range and with prior information from completely assembled mitochondrial and plastid genomes, we detected 10 HGTs of five mitochondrial genes. RESULTS The 10 HGTs appear to have occurred sequentially as C. coccineum expanded from East to West. Molecular-clock models yield Cynomorium stem ages between 66 and 156 Myr, with relaxed clocks converging on 66-67 Myr. Chinese Sapindales, probably Nitraria, were the first source of transferred genes, followed by Iranian and Mediterranean Caryophyllales. The most recently acquired gene appears to come from a Tamarix host in the Iberian Peninsula. CONCLUSIONS Data on HGTs that have accumulated over the past 15 years, along with this discovery of multiple HGTs within a single widespread species, underline the need for more whole-genome data from parasite-host pairs to investigate whether and how transferred copies coexist with, or replace, native functional genes.