Institut de Recerca de la Biodiversitat de la Universitat de Barcelona

Comprehensive knowledge of the effects of disturbances on biodiversity is crucial for conservation and management, not least because ecosystems with low biodiversity may be the most vulnerable. In rivers, the role of disturbance in shaping aquatic biodiversity has mainly focused on floods. Perennial rivers (PRs) often flood, whereas intermittent rivers (IRs) flood, stop flowing and dry. Despite the recent and significant increase in research on IRs, controversy remains about whether they are more or less biodiverse than PRs. Our aim was to determine (Q1) if PRs and IRs differ in biodiversity and (Q2) if the direction and magnitude of the differences (effect sizes) are related to environmental (climate, season, habitat, longitudinal zonation and anthropogenic disturbance) and/or biological factors (taxonomic group). We conducted a meta‐analysis on 44 published studies of PR and IR biodiversity that had replicated data. We applied random effects models to the data to obtain weighted mean effect sizes for differences between PRs and IRs, and their confidence intervals, by first considering all studies and then by splitting studies into groups on the basis of the above factors. We found that biodiversity was significantly higher in PRs than in IRs (Q1). We also detected significant differences (PRs> IRs) in studies of macroinvertebrates, in those conducted within arid and temperate climates, dry and wet sampling seasons, headwaters, and regions subject to different levels of anthropogenic disturbance (Q2). Our meta‐analysis suggests that the expected increase in the prevalence of IRs in certain regions of the world due to global change could result in a decrease in freshwater biodiversity. To better manage and preserve aquatic biodiversity under future global change scenarios and to avoid potential ecosystem consequences of biodiversity loss, conservation efforts should be targeted towards those environmental conditions or taxonomic groups with significant differences (PRs > IRs).

Within the free-living platyhelminths, the triclads, or planarians, are the best-known group, largely as a result of long-standing and intensive research on regeneration, pattern formation and Hox gene expression. However, the group's evolutionary history has been long debated, with controversies ranging from their phyletic structure and position within the Metazoa to the relationships among species within the Tricladida. Over the the last decade, with the advent of molecular phylogenies, some of these issues have begun to be resolved. Here, we present an up-to-date summary of the main phylogenetic changes and novelties with some comments on their evolutionary implications. The phylum has been split into two groups, and the position of the main group (the Rhabdithophora and the Catenulida), close to the Annelida and the Mollusca within the Lophotrochozoa, is now clear. Their internal relationships, although not totally resolved, have been clarified. Tricladida systematics has also experienced a revolution since the implementation of molecular data. The terrestrial planarians have been demonstrated to have emerged from one of the freshwater families, giving a different view of their evolution and greatly altering their classification. The use of molecular data is also facilitating the identification of Tricladida species by DNA barcoding, allowing better knowledge of their distribution and genetic diversity. Finally, molecular phylogenetic and phylogeographical analyses, taking advantage of recent data, are beginning to give a clear picture of the recent history of the Dugesia and Schmidtea species in the Mediterranean.

Hepatitis E virus (HEV) is a hepatotropic virus, endemic in Europe where it infects humans and animals, with domestic pigs and wild boars as main reservoirs. The number of HEV-infected cases with unknown source of infection increases in Europe. There are human HEV strains genetically similar to viruses from domestic pigs, and zoonotic transmission via consumption of uncooked pork meat has been shown. Due to continuous growth of the wild boar populations in Europe, another route may be through direct or indirect contacts with wild boars. In the Collserola Natural Park near Barcelona, Spain, the wild boars have spread into Barcelona city. In Sweden, they are entering into farmlands and villages. To investigate the prevalence of HEV and the risk for zoonotic transmissions, the presence of antibodies against HEV and HEV RNA were analysed in serum and faecal samples from 398 wild boars, 264 from Spain and 134 from Sweden and in sera from 48 Swedish patients with HEV infection without known source of infection. Anti-HEV was more commonly found in Spanish wild boars (59% vs. 8%; p < 0.0001) while HEV RNA had similar prevalence (20% in Spanish vs. 15% in Swedish wild boars). Seven Swedish and three Spanish wild boars were infected with subtype 3f, and nine Spanish with subtype 3c/i. There were three clades in the phylogenetic tree formed by strains from wild boars and domestic pigs; another four clades were formed by strains from humans and wild boars. One strain from a Spanish wild boar was similar to strains from chronically infected humans. The high prevalence of HEV infections among wild boars and the similarity between wild boar HEV strains and those from humans and domestic pigs indicate that zoonotic transmission from wild boar may be more common than previously anticipated, which may develop into public health concern.

BACKGROUND: We present the draft genome sequence of Dysdera silvatica, a nocturnal ground-dwelling spider from a genus that has undergone a remarkable adaptive radiation in the Canary Islands. RESULTS: The draft assembly was obtained using short (Illumina) and long (PaciBio and Nanopore) sequencing reads. Our de novo assembly (1.36 Gb), which represents 80% of the genome size estimated by flow cytometry (1.7 Gb), is constituted by a high fraction of interspersed repetitive elements (53.8%). The assembly completeness, using BUSCO and core eukaryotic genes, ranges from 90% to 96%. Functional annotations based on both ab initio and evidence-based information (including D. silvatica RNA sequencing) yielded a total of 48,619 protein-coding sequences, of which 36,398 (74.9%) have the molecular hallmark of known protein domains, or sequence similarity with Swiss-Prot sequences. The D. silvatica assembly is the first representative of the superfamily Dysderoidea, and just the second available genome of Synspermiata, one of the major evolutionary lineages of the "true spiders" (Araneomorphae). CONCLUSIONS: Dysderoids, which are known for their numerous instances of adaptation to underground environments, include some of the few examples of trophic specialization within spiders and are excellent models for the study of cryptic female choice. This resource will be therefore useful as a starting point to study fundamental evolutionary and functional questions, including the molecular bases of the adaptation to extreme environments and ecological shifts, as well of the origin and evolution of relevant spider traits, such as the venom and silk.

Bycatch mortality in longline fisheries is considered the main threat at sea for numerous seabird species. These incidental catches occur worldwide, but mortality levels are mainly determined by the specific traits of the fishery operating in each area and the feeding behaviour and local abundance of seabirds. In the Mediterranean, demersal artisanal longliners are known to catch several seabirds, but bycatch rates and the main factors influencing both the probability and the level of seabird bycatch are poorly known. From 2011 to 2015 we conducted 220 trips onboard demersal longline vessels of the Balearic Sea, aiming to study their interaction with seabirds, as well as to understand the detailed procedures of the fishery and the factors that might influence seabird bycatch. Additionally, we recorded bird catches reported by fishermen. We found an average overall bycatch rate of 0.58 birds per 1000 hooks (0.13-1.37, 95% CI), which would imply a conservative estimate ranging from 274 to 2198 seabirds caught annually on demersal longliners in the study area. The most affected species were the 3 endemic and threatened Scopoli's, Balearic and Mediterranean shearwaters of the Mediterranean (Calonectris diomedea, Puffinus mauretanicus and P. yelkouan, respectively), likely due to their highly aggregative behaviour and diving capabilities. Overall, the main factors influencing bycatch risk were season and time of day. Other influential factors were bait type, wind conditions, gear configuration (specifically, distance between weights), proximity to the breeding colony and the number of hooks. This study shows that mortality caused by demersal longliners is high and may be jeopardizing the viability of the shearwater populations. Therefore, the identification and implementation of mitigation measures is urgently required.

The term “migratory” refers to animals performing yearly round-trips between breeding grounds and post-breeding areas, whereas the term “sedentary” refers to those remaining the whole year in their breeding grounds. However, migration is a complex and varying phenomenon governed by genetic and environmental factors, particularly in species with wide distribution ranges. Here we describe and classify the seasonal movement patterns of 71 little bustards Tetrax tetrax, an endangered Palearctic steppe bird, radio- and satellite-tracked in the Iberian Peninsula. Four major movement patterns were identified, with 89% of little bustards behaving as migrants, among which 75% (summer migrants and summer-winter migrants) performed their first movement after breeding during the summer (mainly between May and July), whereas 14% (winter migrants) left their breeding sites in autumn (mainly between September and November). The remaining 11% were strictly sedentary. On average, summer migration started on June 14th, and winter migration on October 3rd, while pre-breeding migration started on March 23rd. Summer migration occurred in most Iberian regions, although it was mainly found in semiarid Mesomediterranean areas. Winter migration occurred only in the northern half of the Peninsula, being the only pattern found in Subatlantic and highland areas. All winter migrants wintered in Thermomediterranean localities of southern Iberia. The sedentary pattern was found only in the Semiarid Mesomediterranean and Thermomediterranean sectors. This is a good example of complex intraspecific variation in the migratory behaviour of a species that occupies a diverse range of environments. The variability of movement patterns of Iberian little bustards is much greater than previously thought and should be taken into account in conservation programmes for the species.

BACKGROUND: Predicted genetic consequences of asexuality include high intraindividual genetic diversity (i.e., the Meselson effect) and accumulation of deleterious mutations (i.e., Muller's Ratchet), among others. These consequences have been largely studied in parthenogenetic organisms, but studies on fissiparous species are scarce. Differing from parthenogens, fissiparous organisms inherit part of the soma of the progenitor, including somatic mutations. Thus, in the long term, fissiparous reproduction may also result in genetic mosaicism, besides the presence of the Meselson effect and Muller's Ratchet. Dugesiidae planarians show outstanding regeneration capabilities, allowing them to naturally reproduce by fission, either strictly or combined with sex (facultative). Therefore, they are an ideal model to analyze the genetic footprint of fissiparous reproduction, both when it is alternated with sex and when it is the only mode of reproduction. RESULTS: In the present study, we generate and analyze intraindividual cloned data of a nuclear and a mitochondrial gene of sexual, fissiparous and facultative wild populations of the species Dugesia subtentaculata. We find that most individuals, independently of their reproductive strategy, are mosaics. However, the intraindividual haplotype and nucleotide diversity of fissiparous and facultative individuals is significantly higher than in sexual individuals, with no signs of Muller's Ratchet. Finally, we also find that this high intraindividual genetic diversity of fissiparous and facultative individuals is composed by different combinations of ancestral and derived haplotypes of the species. CONCLUSIONS: The intraindividual analyses of genetic diversity point out that fissiparous reproduction leaves a very special genetic footprint in individuals, characterized by mosaicism combined with the Meselson effect (named in the present study as the mosaic Meselson effect). Interestingly, the different intraindividual combinations of ancestral and derivate genetic diversity indicate that haplotypes generated during periods of fissiparous reproduction can be also transmitted to the progeny through sexual events, resulting in offspring showing a wide range of genetic diversity and putatively allowing purifying selection to act at both intraindividual and individual level. Further investigations, using Dugesia planarians as model organisms, would be of great value to delve into this new model of genetic evolution by the combination of fission and sex.

Studying the feeding ecology of seabirds is important not only to understand basic aspects of their ecology and threats but also for the conservation of marine ecosystems. In this regard, tropical seabirds have been relatively neglected, and in particular the trophic ecology of tropicbirds is scarcely known. We combined GPS tracking, environmental variables and sampling of regurgi tates during incubation and brooding to understand the feeding ecology of red-billed tropicbirds Phaethon aethereus as well as how foraging strategies may change between 2 contrasting marine envi ronments: a coastal island in the Canary Current upwelling (Iles de la Madeleine) and an oceanic island in the middle of the south Atlantic (St Helena). Tropicbirds breeding on the Iles de la Madeleine headed west, foraging on and beyond the shelf slope, probably to associate with subsurface predators which bring pelagic fish close to the surface. Birds from St Helena showed a greater foraging effort and a strong attraction to areas with the greatest species richness of Scombridae, possibly due to a greater difficulty in finding prey in the oligotrophic oceanic waters. Tropicbirds ranged much beyond the extension of the protected areas around their colonies, indicating that current protected areas are insufficient for these populations. We found no evidence to suspect direct mortality of tropicbirds in regional fisheries, but overexploitation of small epipelagic fish and tuna may decrease feeding opportunities and lead to competition with fisheries. The substantial differences in foraging behaviour demonstrated by individuals from both colonies indicates that caution should be taken when extrapolating foraging patterns of tropical seabirds breeding in contrasting oceanographic environments.

Climate change is altering the water cycle globally, increasing the frequency and magnitude of floods and droughts. An outstanding question is whether biodiversity responses to hydrological disturbance depend on background climatic context – and if so, which contexts increase vulnerability to disturbance. Answering this question requires comparison of organismal responses across environmental gradients. However, opportunities to track disturbed communities against an undisturbed baseline remain rare. Here we gathered a global dataset capturing responses of aquatic invertebrate communities to river drying, which includes 112 sites spanning a gradient of climatic aridity. We measured the effects of river drying on taxonomic richness and temporal β‐diversity (turnover and nestedness components). We also measured the relative abundance of aquatic invertebrates with strategies that confer resilience (or resistance) to drying. Contrary to our expectations, we found that taxonomic richness recovered from drying similarly across the aridity gradient. The turnover component of β‐diversity (i.e. species replacements over time) largely accounted for differences in community composition before versus after drying. However, increasing aridity was associated with greater nestedness‐driven compositional changes at intermittent sites – that is, after drying communities became subsets of those before drying. These results show that climatic context can explain variation in community responses to the same hydrological disturbance (drying), and suggest that increased aridity will constrain biodiversity responses at regional scales. Further consideration of the climatic context in hydroecological research may help improve predictions of the local impacts of hydrological disturbance by identifying climate regions where communities are more (or less) sensitive to extremes, including river drying events.

The rates of species and trait diversification vary across the Tree‐of‐Life and over time. Whereas species richness and clade age generally are decoupled, the correlation of accumulated trait diversity of clades (trait disparity) with clade age remains poorly explored. Total trait disparity may be coupled with clade age if the growth of disparity (disparification) within and across clades is continuous with time in an additive niche expansion process (linear‐cumulative model), or alternatively if the rate of trait disparification varies over time and decreases as ecological space becomes gradually saturated (disparity‐dependent model). Using a clock‐calibrated phylogenetic tree for 143 freshwater macroinvertebrate families and richness and trait databases covering &gt; 6400 species, we measured trait disparity in 18 independent clades that successively transitioned to freshwater ecosystems and analyzed its relation with clade age. We found a positive correlation between clade age and total disparity within clades, but no relationship for most individual traits. Traits unique to freshwater lifestyle were highly variable within older clades, while disparity in younger clades shifted towards partially terrestrial lifestyles and saline tolerance to occupy habitats previously inaccessible or underutilized. These results argue that constraints from incumbent lineages limit trait disparity in younger clades that evolved for filling unoccupied regions of the trait space, which suggests that trait disparification may follow a disparity‐dependent model. Overall, we provide an empirical pattern that reveals the potential of the disparity‐dependent model for understanding fundamental processes shaping trait dynamics across the Tree‐of‐Life.

Speciation is a continuous and complex process shaped by the interaction of numerous evolutionary forces. Despite the continuous nature of the speciation process, the implementation of conservation policies relies on the delimitation of species and evolutionary significant units (ESUs). Puffinus shearwaters are globally distributed and threatened pelagic seabirds. Due to remarkable morphological status the group has been under intense taxonomic debate for the past three decades. Here, we use double digest Restriction-Site Associated DNA sequencing (ddRAD-Seq) to genotype species and subspecies of North Atlantic and Mediterranean Puffinus shearwaters across their entire geographical range. We assess the phylogenetic relationships and population structure among and within the group, evaluate species boundaries, and characterise the genomic landscape of divergence. We find that current taxonomies are not supported by genomic data and propose a more accurate taxonomy by integrating genomic information with other sources of evidence. Our results show that several taxon pairs are at different stages of a speciation continuum. Our study emphasises the potential of genomic data to resolve taxonomic uncertainties, which can help to focus management actions on relevant taxa, even if they do not necessarily coincide with the taxonomic rank of species.

Adaptive sex allocation has frequently been studied in sexually size dimorphic species, but far less is known about patterns of sex allocation in species without pronounced sexual size dimorphism. Parental optimal investment can be predicted under circumstances in which sons and daughters differ in costs and/or fitness returns. In common terns Sterna hirundo , previous studies suggest that sons are the more costly sex to produce and rear. We investigated whether hatching and fledging sex ratio and sex‐specific chick mortality correlated with the ecological environment (laying date, clutch size, hatching order and year quality) and parental traits (condition, arrival date, experience and breeding success), over seven consecutive years. Population‐wide sex ratios and sex‐specific mortality did not differ from parity, but clutch size, mass of the father, maternal breeding experience and to some extent year quality correlated with hatching sex ratio. The proportion of sons tended to increase in productive years and when the father was heavier, suggesting the possibility that females invest more in sons when the environmental and the partner conditions are good. The proportion of daughters increased with clutch size and maternal breeding experience, suggesting a decline in breeding performance or a resources balance solved by producing more of the cheaper sex. No clear patterns of sex‐specific mortality were found, neither global nor related to parental traits. Our results suggest lines for future studies on adaptive sex allocation in sexually nearly monomorphic species, where adjustment of sex ratio related to parental factors and differential allocation between the offspring may also occur.

The diversification of modern birds has been shaped by a number of radiations. Rapid diversification events make reconstructing the evolutionary relationships among taxa challenging due to the convoluted effects of incomplete lineage sorting (ILS) and introgression. Phylogenomic data sets have the potential to detect patterns of phylogenetic incongruence, and to address their causes. However, the footprints of ILS and introgression on sequence data can vary between different phylogenomic markers at different phylogenetic scales depending on factors such as their evolutionary rates or their selection pressures. We show that combining phylogenomic markers that evolve at different rates, such as paired-end double-digest restriction site-associated DNA (PE-ddRAD) and ultraconserved elements (UCEs), allows a comprehensive exploration of the causes of phylogenetic discordance associated with short internodes at different timescales. We used thousands of UCE and PE-ddRAD markers to produce the first well-resolved phylogeny of shearwaters, a group of medium-sized pelagic seabirds that are among the most phylogenetically controversial and endangered bird groups. We found that phylogenomic conflict was mainly derived from high levels of ILS due to rapid speciation events. We also documented a case of introgression, despite the high philopatry of shearwaters to their breeding sites, which typically limits gene flow. We integrated state-of-the-art concatenated and coalescent-based approaches to expand on previous comparisons of UCE and RAD-Seq data sets for phylogenetics, divergence time estimation, and inference of introgression, and we propose a strategy to optimize RAD-Seq data for phylogenetic analyses. Our results highlight the usefulness of combining phylogenomic markers evolving at different rates to understand the causes of phylogenetic discordance at different timescales. [Aves; incomplete lineage sorting; introgression; PE-ddRAD-Seq; phylogenomics; radiations; shearwaters; UCEs.].

Understanding the capacity of ecological systems to withstand and recover from disturbances is a major challenge for ecological research in the context of environmental changes. Past research has mostly focused on the local effects of disturbances on biodiversity recovery, while alterations of inter‐patch connectivity induced by disturbances have received comparatively less attention. Here, we investigated the effect of disturbances on local biodiversity recovery within metacommunities. Our specific focus was on drying river networks, which are characterised by a high variability of patch connectivity. We found marked variations of local biodiversity recovery among sites and among groups of organisms with contrasting dispersal modes, which were explained by the amount of patch connectivity loss due to drying events. Local communities of flying organisms recovered more efficiently from drying events than organisms with strictly aquatic dispersal due to the capacity of the former group to overcome hydrological connectivity loss. As a general rule, loss of patch connectivity decreases community recovery, regardless of patch location in the river network, dispersal mode or drying spatial extent. The relationship between patch connectivity loss and community recovery we found in river networks is general and applicable to any spatial network with a high variability of patch connectivity.

Three new diterpenes named gersemiols A-C (1-3) and a new eunicellane diterpene, eunicellol A (4), have been isolated together with the known sesquiterpene (+)-α-muurolene (5) from the Arctic soft coral Gersemia fruticosa. The name gersemiane was assigned to the rare and unnamed diterpene skeleton of compounds 1-3 corresponding to 4-isopropyl-1,5,8a-trimethyltetradecahydrophenanthrene. The chemical structures were elucidated on the basis of extensive spectroscopic analysis (HR-ESIMS, 1D and 2D NMR) as well as coupling constant calculations for the determination of the relative configurations. All compounds were tested for their antimicrobial activity against several bacteria and fungi and eunicellol A was found to exhibit moderate and selective antibacterial activity.

Hundreds of thousands of seabirds die annually as a result of being bycaught in longline fisheries, and these rates are unsustainable for many seabird populations worldwide. To understand effects at the population level, it is essential to assess sex-and age-biased mortalities, since uneven mortalities may exacerbate bycatch impacts. In the Mediterranean, bycatch is the main cause of population declines for the 3 endemic shearwater species (Scopoli's Calonectris diomedea, Balearic Puffinus mauretanicus and Mediterranean shearwater P. yelkouan), but little is known about population biases of the birds caught in longliners. From 2003 to 2015, we collected 639 shearwater carcasses from Spanish longliners operating in the north-western Mediterranean, determined their age and sex and examined their spatial and temporal patterns and the origin of ringed birds. Most shearwaters caught in longliners were adults, but the proportion of immatures and subadults increased in the late breeding period. Adult Scopoli's shearwaters were mostly caught around the breeding colonies. In contrast, all Puffinus birds were caught on the Iberian shelf. Catches of Scopoli's shearwaters were male-biased, particularly during the prelaying period and close to the breeding colonies. Catches of Puffinus shearwaters were also malebiased during the pre-laying period, but adult catches were female-biased during chick-rearing. Ring recoveries revealed that most birds were ringed in the nearby Balearic Islands, but some Scopoli's shearwaters ringed in France and Italy were also caught during their migration, indicating that the impacts of the Spanish longliners extend well beyond the Spanish colonies. The adult-biased and sex-biased mortality found in this study may aggravate bycatch impacts on populations and highlights the urgent need for conservation action.

Drosophila subobscura is a paleartic species of the obscura group with a rich chromosomal polymorphism. To further our understanding on the origin of inversions and on how they regain variation, we have identified and sequenced the two breakpoints of a polymorphic inversion of D. subobscura--inversion 3 of the O chromosome--in a population sample. The breakpoints could be identified as two rather short fragments (∼300 bp and 60 bp long) with no similarity to any known transposable element family or repetitive sequence. The presence of the ∼300-bp fragment at the two breakpoints of inverted chromosomes implies its duplication, an indication of the inversion origin via staggered double-strand breaks. Present results and previous findings support that the mode of origin of inversions is neither related to the inversion age nor species-group specific. The breakpoint regions do not consistently exhibit the lower level of variation within and stronger genetic differentiation between arrangements than more internal regions that would be expected, even in moderately small inversions, if gene conversion were greatly restricted at inversion breakpoints. Comparison of the proximal breakpoint region in species of the obscura group shows that this breakpoint lies in a small high-turnover fragment within a long collinear region (∼300 kb).

Feather mites are useful models for studying speciation due to their high diversity and strong degree of host specialization. However, studies to date have focused on the evolution of higher-level mite taxa while much hidden diversity likely occurs at the level of host genera and species. In this study, we examined the diversity and evolution of feather mites infesting six sympatric seabird species from six genera, breeding in the Cape Verde archipelago. We report 32 feather mite morphospecies categorized into ten genera and three families, of which nine correspond to new, undescribed species. Molecular data corroborated morphological species descriptions, except for two morphologically-cryptic, but genetically distinct mite lineages related to Zachvatkinia oceanodromae and Laminalloptes simplex. Using these communities, we then applied a co-structure approach to test the contribution of ectosymbiont and host factors in driving feather mite evolution. Most seabird species hosted specific and unique feather mite species, even under sympatric conditions, and in general, feather mite species exhibited strong host-driven genetic structure. However, patterns of genetic differentiation were variable. That is, some mite species are more generalist than others and mite lineages/haplotypes can be shared by related seabird species. Interestingly, host-specific mites (eg., Zachvatkinia spp.) tend to display much higher intra-specific diversity compared to more generalist mites (eg., Microspalax and Plicatalloptes spp.). We discuss ectosymbiont and host life-history traits that might generate these patterns, such as host dispersal and breeding behavior and/or mite spatial and trophic specialization. Our findings highlight both the vast and largely unrecognized diversity of avian feather mites on seabirds, and the intrinsic complexity of the ecological processes underlying the evolution of these ectosymbionts.

The increasing levels of heavy metals derived from human activity are poisoning marine environments, threating zooplankton and ocean food webs. To protect themselves from the harmful effects of heavy metals, living beings have different physiological mechanisms, one of which is based on metallothioneins (MTs), a group of small cysteine-rich proteins that can bind heavy metals counteracting their toxicity. The MT system of urochordate appendicularians, an ecologically relevant component of the zooplankton, remained, however, unknown. In this work, we have characterized the MTs of the appendicularian species Oikopleura dioica, revealing that O. dioica has two MT genes, named OdMT1 and OdMT2, which encode for Cys-rich proteins, the former with 72 amino acids comparable with the small size MTs of other organisms, but the second with 399 amino acids representing the longest MT reported to date for any living being. Sequence analysis revealed that OdMT2 gene arose from a duplication of an ancestral OdMT1 gene followed by up to six tandem duplications of an ancestral repeat unit (RU) in the current OdMT2 gene. Interestingly, each RU contained, in turn, an internal repeat of a 7-Cys subunit (X3CX3CX2CX2CX3-6CX2CXCX), which is repeated up to 12 times in OdMT2. Finally, ICP-AES analyses of heterologously expressed OdMT proteins showed that both MTs were capable to form metal-complexes, with preference for cadmium ions. Collectively, our results provide the first characterization of the MT system in an appendicularian species as an initial step to understand the zooplankton response to metal toxicity and other environmental stress situations.

ABSTRACT The avocado, Persea americana , is a fruit crop of immense importance to Mexican agriculture with an increasing demand worldwide. Avocado lies in the anciently-diverged magnoliid clade of angiosperms, which has a controversial phylogenetic position relative to eudicots and monocots. We sequenced the nuclear genomes of the Mexican avocado race, P. americana var. drymifolia , and the most commercially popular hybrid cultivar, Hass, and anchored the latter to chromosomes using a genetic map. Resequencing of Guatemalan and West Indian varieties revealed that ∼39% of the Hass genome represents Guatemalan source regions introgressed into a Mexican race background. Some introgressed blocks are extremely large, consistent with the recent origin of the cultivar. The avocado lineage experienced two lineage-specific polyploidy events during its evolutionary history. Although gene-tree/species-tree phylogenomic results are inconclusive, syntenic ortholog distances to other species place avocado as sister to the enormous monocot and eudicot lineages combined. Duplicate genes descending from polyploidy augmented the transcription factor diversity of avocado, while tandem duplicates enhanced the secondary metabolism of the species. Phenylpropanoid biosynthesis, known to be elicited by Colletotrichum (anthracnose) pathogen infection in avocado, is one enriched function among tandems. Furthermore, transcriptome data show that tandem duplicates are significantly up- and down-regulated in response to anthracnose infection, whereas polyploid duplicates are not, supporting the general view that collections of tandem duplicates contribute evolutionarily recent “tuning knobs” in the genome adaptive landscapes of given species. SIGNIFICANCE STATEMENT Avocado is a nutritious, economically important fruit species that occupies an unresolved position near the earliest evolutionary branchings of flowering plants. Our nuclear genome sequences of Mexican and Hass variety avocados inform ancient evolutionary relationships and genome doublings, the admixed nature of Hass, and provide a look at how pathogen interactions have shaped avocado’s more recent genomic evolutionary history.