Faced with adverse conditions, such as winter in temperate regions or hot and dry conditions in tropical regions, many insect species enter a state of diapause, a period of dormancy associated with a reduction or arrest of physical activity, development, and reproduction. Changes in common physiological pathways underlie diapause phenotypes in different insect species. However, most transcriptomic studies of diapause have not simultaneously evaluated and compared expression patterns in different tissues. Honey bees (Apis mellifera) represent a unique model system to study the mechanisms underpinning diapause. In winter, honey bees exhibit a classic diapause phenotype, with reduced metabolic activity, increased physiological nutritional resources, and altered hormonal profiles. However, winter bees actively heat their colony by vibrating their wing muscles; thus, this tissue is not quiescent. Here, we evaluated the transcriptional profiles of flight muscle tissue and fat body tissue (involved in nutrient storage, metabolism and immune function) of winter bees. We also evaluated two behavioral phenotypes of summer bees: nurses, which exhibit high nutritional stores and low flight activity, and foragers, which exhibit low nutritional stores and high flight activity. We found winter bees and nurses have similar fat body transcriptional profiles compared to foragers, whereas winter bees and foragers have similar flight muscle transcriptional profiles compared to nurses. Additionally, differentially expressed genes were enriched in diapause-related GO terms. Thus, honey bees exhibit tissue-specific transcriptional profiles associated with diapause, laying the groundwork for future studies evaluating the mechanisms, evolution, and consequences of this tissue-specific regulation.

Early-life telomere length (TL) is associated with fitness in a range of organisms. Little is known about the genetic basis of variation in TL in wild animal populations, but to understand the evolutionary and ecological significance of TL it is important to quantify the relative importance of genetic and environmental variation in TL. In this study, we measured TL in 2746 house sparrow nestlings sampled across 20 years and used an animal model to show that there is a small heritable component of early-life TL (h2=0.04), but with a strong component of maternal inheritance. Variation in TL among individuals was mainly driven by environmental (year) variance, but also brood and parental effects. We did not find evidence for a negative genetic correlation underlying the observed negative phenotypic correlation between TL and structural body size. Thus, TL may evolve independently of body size and the negative phenotypic correlation is likely to be caused by non-genetic environmental effects. We further used genome‐wide association analysis to identify genomic regions associated with TL variation. We identified several putative genes underlying TL variation; these have been inferred to be involved in oxidative stress, cellular growth, skeletal development, cell differentiation and tumorigenesis in other species. Together, our results show that TL is a lowly heritable, polygenic trait which is strongly affected by environmental conditions in a free-living bird.

Madagascar’s Central Highlands are largely composed of grasslands, interspersed with patches of forest. The pre-human extent of these grasslands is a topic of vigorous debate, with conventional wisdom holding that they are anthropogenic in nature and emerging evidence supporting that grasslands were a component of the pre-human Central Highlands vegetation. Here, we shed light on the temporal dynamics of Madagascar’s vegetative composition by conducting a population genomic investigation of Goodman’s mouse lemur (Microcebus lehilahytsara; Cheirogaleidae). These small-bodied primates occur both in Madagascar’s eastern rainforests and in the Central Highlands, which makes them a valuable indicator species. Population divergences among forest-dwelling mammals can serve as a proxy for habitat fragmentation and patterns of post-divergence gene flow can reveal potential migration corridors consistent with a wooded grassland mosiac. We used RADseq data to infer phylogenetic relationships, population structure, demographic models of post-divergence gene flow, and population size change through time. These analyses offer evidence that open habitats are an ancient component of the Central Highlands, and that wide-spread forest fragmentation occurred naturally during a period of decreased precipitation near the last glacial maximum. Models of gene flow suggest that migration across the Central Highlands has been possible from the Pleistocene through the recent Holocene via riparian corridors. Notably, though our findings support the hypothesis that Central Highland grasslands predate human arrival, we also find evidence for human-mediated population declines. This highlights the extent to which species imminently threatened by human-mediated deforestation may be more vulnerable from paleoclimatic changes.

Any random genetic change is more likely to impair than improve fitness, a situation that owes to the fact that contemporary genotypes bear a history of having been shaped by natural selection for a very long time. Most mutations are thus deleterious and generate a genetic load that can be difficult to handle in small populations and increase the risk of extinction. We used functional annotation and evolutionary conservation scores to study deleterious variation in 200+ genomes from the highly inbred Scandinavian wolf population, founded by only three wolves and suffering from inbreeding depression, and neighboring populations in northern Europe. The masked load was high in Russia and Finland with deleterious alleles segregating at lower frequency than neutral variation. Genetic drift in the Scandinavian population led to the loss of ancestral alleles and fixation of deleterious variants. The per-individual realized load increased with the extent of inbreeding and reached several hundred homozygous deleterious genotypes in protein-coding genes, and a total of more than 50,000 homozygous deleterious genotypes in the genome. Arrival of immigrants gave a temporary genetic rescue effect with ancestral alleles re-entering the population and moving deleterious alleles into heterozygote genotypes. However, in the absence of permanent connectivity inbreeding has then again led to the exposure of deleterious mutations. These observations provide genome-wide insight into the character of genetic load and genetic rescue at the molecular level, and in relation to population history. They emphasize the importance of securing gene flow in the management of endangered populations.

An accurate inference of the chronological and biological age of individuals is fundamental to population ecology and our understanding of ageing itself, its evolution and the biological processes that affect or even cause ageing. In humans, epigenetic clocks based on the DNA methylation (DNAm) at selected CpG sites correlate highly with chronological age. Discrepancies between the inferred epigenetic and known chronological age predict morbidity and mortality, and therefore epigenetic clocks are thought to reflect biological age. Recently, a growing number epigenetic clocks in non-model organisms have been developed towards a diverse array of purposes in commercial, conservation and ageing research. Here we review those studies and conduct the first meta-analysis to assess the effects of different aspects of experimental protocol on the accuracy of epigenetic clocks for non-model species. Our analysis reveals higher coefficients of determination (R2) of chronological age for epigenetic clocks based on the HorvathMammalMethylChip4, compared to other DNAm quantification approaches. No dependence of (R2) was detected for the number of CpG sites in a clock; the sample size; the number or kind of tissue(s) used; the class of animals; or whether captive or wild animals were sampled to infer the epigenetic clocks. We further conclude that epigenetic clocks can predict chronological age with relatively high accuracy, suggesting great potential for the field of ecological epigenetics. We therefore encourage further research on the topic of ecological epigenetics in relation to ageing and, perhaps more importantly, discuss the potential of employing DNAm to assess key traits other than age.

Stony coral tissue loss disease (SCTLD) remains an unprecedented disease outbreak due to its high mortality rate and rapid spread throughout Florida’s Coral Reef and wider Caribbean. A collaborative effort is underway to evaluate disease intervention strategies that mitigate the spread of SCTLD across coral colonies and reefs. We conducted an in-situ experiment in Southeast Florida to assess molecular responses among SCTLD-affected Montastraea cavernosa pre- and post-application of the most widely-used intervention method, CoreRx Base 2B with amoxicillin. Through Tag-Seq gene expression profiling of apparently healthy, diseased, and treated corals, we identified modulation of metabolomic and immune pathways following antibiotic treatment. In a complementary ex-situ disease challenge experiment, we exposed nursery-cultured M. cavernosa and Orbicella faveolata fragments to SCTLD-affected donor corals to compare transcriptomic profiles among clonal individuals from unexposed controls, those exposed and displaying disease signs, and corals exposed and not displaying disease signs. Suppression of metabolic functional groups and activation of stress gene pathways as a result of SCTLD exposure were apparent in both species. Amoxicillin treatment led to a ‘reversal’ of the majority of gene pathways implicated in disease response, suggesting potential recovery of corals following antibiotic application. In addition to increasing our understanding of molecular responses to SCTLD, we provide resource managers with transcriptomic evidence that disease interventions with antibiotics appear to be successful and may help to modulate coral immune responses to SCTLD. These results contribute to feasibility assessments of intervention efforts following disease outbreaks and improved predictions of coral reef health in Southeast Florida.

Coral reefs are losing coral cover across the globe largely as a result of a rise in seawater temperatures that trigger coral bleaching and induce coral mortality. How coral reefs will respond to climate change will be a function of genetic variation and how it is partitioned among species. A critical initial step is to accurately delineate species and quantify their physiological potential to cope with heat stress. Cryptic species, morphologically indistinguishable but genetically different ones, typically harbor distinct physiological variation and respond differently to climatic changes. A dominant Caribbean reef builder severely affected by climate change is the mountainous star coral, Orbicella faveolata. Recently, Dziedzic et al. (2019) reported genetic variation in the physiological response to thermal stress in a single population of this species, suggesting that variation within populations will allow these corals to adapt to rising ocean temperatures. We reanalyzed their data and found multiple cryptic lineages rather than a single panmictic population, with only one of the lineages being heat-tolerant. Our finding of hidden lineages within a threatened species highlights the varying extinction risks faced by these independently evolving groups, especially when the prospects of survival under warmer oceans seem favorable for a few of them only.

Accurate and testable species delimitation hypotheses are essential for measuring, surveying and managing biodiversity. Today, taxonomists often rely on mitochondrial DNA barcoding to complement morphological species delimitations. Although COI barcoding has largely proven successful in assisting identifications for most animal taxa, there are nevertheless numerous cases where mitochondrial barcodes do not necessarily reflect the species history. For instance, what is regarded as one single species can be associated with two distinct DNA barcodes, which can point either to cryptic diversity or to deep within-species mitochondrial divergences with no reproductive isolation. In contrast, two or more species can share barcodes, for instance due to mitochondrial introgression. These intrinsic limitations of mitochondrial DNA barcoding can only be addressed with nuclear genomic markers, which are expensive, labour intensive, poorly repeatable, and often require high-quality DNA. To overcome these limitations, we examined the use of ultraconserved nuclear genetic elements (UCEs) as a quick and robust genomic approach to address such problematic cases of species delimitation. This genomic method was assessed using six different bee species complexes suspected to harbour cryptic diversity, mitochondrial introgression, or mitochondrial paraphyly. The sequencing of UCEs recovered between 686 and 1860 homologous nuclear loci and provided explicit species delimitation hypotheses in all investigated species complexes. These results provide strong evidence for the suitability of UCEs as a fast method for species delimitation even in recently diverged lineages. Furthermore, this study provided the first conclusive evidence for both mitochondrial introgression among distinct species, and mitochondrial paraphyly within a single bee species.

A recent Molecular Ecology editorial made a proactive statement of support for the “Nagoya Protocol” and the principle of benefit-sharing (Marden et al. 2020) by requiring authors to provide a “Data Accessibility and Benefit‐Sharing Statement” in their articles. Here, we encourage another step that enables Indigenous communities to provide their own definitions and aspirations for access and benefit-sharing alongside the author’s “Statement”. We invite the Molecular Ecology research community to use Biocultural-, Traditional Knowledge-, and Cultural Institution Notices to help Indigenous communities gain visibility within our research structures. Notices are one of the tools offered by the Biocultural Labels Initiative (part of the Local Contexts system) designed specifically for researchers and institutions. The Notices are highly visible, machine-readable icons that signal the Indigenous provenance of genetic resources, and rights of Indigenous communities to define the future use of genetic resources and derived benefits. The Notices invite collaboration with Indigenous communities and create spaces within our research systems for them to define the provenance, protocols, and permissions associated with genetic resources using Labels. Authors contributing to Molecular Ecology can apply Notices to their articles by providing the persistent unique identifier and an optional use-statement associated with the Notice in their “Data Accessibility and Benefit‐Sharing Statement”. In this way, our research community has an opportunity to accelerate support for the principles of the Nagoya Protocol, to alleviate concerns regarding Indigenous Data Sovereignty and equitable outcomes, and to build better relationships with Indigenous collaborators to enhance research, biodiversity, and conservation outcomes.

There is ample evidence that macroscopic animals form geographic clusters termed as zoogeographic realms (zones), whereas distributions of species of microscopic animals are still poorly understood. The common view has been that micrometazoans, thanks to their putatively excellent dispersal abilities, are subject to the ‘Everything is Everywhere but environment selects’ hypothesis (EiE). One of such groups, <1 mm in length, are limnoterrestrial water bears (Tardigrada), which can additionally enter cryptobiosis that should further enhance their potential for long distance dispersion (e.g. by wind). However, an increasing number of studies, including the most recent phylogeny of a eutardigrade genus Milnesium, seem to question the general applicability of the EiE hypothesis to tardigrade species. Nevertheless, all the Milnesium phylogenies published to date were based on a limited number of populations, which are likely to falsely suggest limited geographic ranges. Thus, in order to comprehensively test the EiE hypothesis, here, we considerably enlarged the Milnesium dataset both taxonomically and geographically, and we analysed it in tandem with climate type and reproductive mode. Additionally, we time-calibrated our phylogeny to align it with major geological events. Our results show that, although cases of long distance dispersal are present, they seem to be rare and mostly ancient. Overall, Milnesium species are restricted to single zoogeographic realms, which suggests that these tardigrades have limited dispersal abilities. Finally, our results also suggest that the breakdown of Gondwana may influenced the evolutionary history of Milnesium. In conclusion, phylogenetic relationships within the genus seem to be determined mainly by paleogeography.

While hybridisation has long been recognised as an important natural phenomenon in evolution, the conservation of taxa subject to introgressive hybridisation from domesticated forms is a subject of intense debate. Hybridisation of the Scottish wildcat, the UK’s sole extant native felid, with the domestic cat is a good example in this regard. We develop a modelling framework to determine the timescale and mode of introgression using approximate Bayesian computation (ABC). Applying the model to ddRAD-seq data from 129 individuals, genotyped at 6,546 loci, we show that a population of wildcats genetically distant from domestic cats is still present in Scotland, though these individuals are found almost exclusively within the captive breeding program. Most wild-living cats sampled were introgressed to some extent. Additionally, we evaluate the effectiveness of current methods that are used to classify hybrids. We show that an optimised 35 SNP panel is a better predictor of the ddRAD-based hybrid score in comparison with a morphological method.

Heterogeneous seascapes and strong environmental gradients in coastal waters are expected to influence adaptive divergence, particularly in species with large population sizes where selection is expected to be highly efficient. However, these influences might also extend to species characterized by strong social structure, natal philopatry and small home ranges. We implemented a seascape genomic study to test this hypothesis in Indo-Pacific bottlenose dolphins (Tursiops aduncus) distributed along the environmentally heterogeneous coast of southern Australia. The datasets included oceanographic and environmental variables thought to be good predictors of local adaptation in dolphins and 8,081 filtered single nucleotide polymorphisms (SNPs) genotyped for individuals sampled from six different bioregions. From a neutral perspective, population structure and connectivity of the dolphins were generally influenced by habitat type and social structuring. Genotype-environment association analysis identified 241 candidate adaptive loci and revealed that sea surface temperature and salinity gradients influenced adaptive divergence in these animals at both large- (1,000s km) and fine-scales (<100 km). Enrichment analysis and annotation of candidate genes revealed functions related to sodium-activated ion transport, kidney development, adipogenesis and thermogenesis. The findings of spatial adaptive divergence and inferences of putative physiological adaptations challenge previous suggestions that marine megafauna is most likely to be affected by environmental and climatic changes via indirect, trophic effects. Our work contributes to conservation management of coastal bottlenose dolphins subjected to anthropogenic disturbance and to efforts of clarifying how seascape heterogeneity influences adaptive diversity and evolution in small cetaceans.

Barriers to gene flow (BGF) play a pivotal role in the dynamics of population genetics promoting genetic differentiation, thus, are inexorably associated with the development and maintenance of phylogeographic structure. Phylogeographic structure resulting from BGF represents data that help the management of natural genetic resources, aiding in the recognition of areas of conservation interest. Several geographic and oceanographic processes found along the Brazilian coast have been proposed as BGF. However, no consensus exist identifying which of them represents the most important in shaping biodiversity. Therefore, this study provides a synthesis of the scientific literature on Brazilian marine phylogeography and used published data to build datasets that allowed us apply linear (lm) and generalized additive models (gam) to identify spatially congruent phylogeographic breaks among marine species (as areas of high BGF frequency occurrence). Lm identified a significant negative correlation between the occurrence of BGF and latitude, suggesting that population in the tropics are genetically more structured than in higher latitudes. This result bears strong association with the latitude species diversity gradient observed worldwide. Gam identified Cape São Roque (05° 28’ S) as the main BGF for populations with continuous distribution along the Brazilian coast. Cape São Roque is located near the center point region where the South Equatorial Current splits into the northward North Brazil Current and the southward Brazil Current. This study represents the first literature synthesis of Brazil’s marine phylogeography and provides a novel explicit quantitative approach to comparative phylogeography.

Genomes retain evidence of the demographic history and evolutionary forces that have shaped populations. Across island systems, contemporary patterns of genetic diversity reflect complex population demography, including colonisation events, bottlenecks, gene flow and genetic drift. Here, we investigate whether island founder events have prolonged effects on genome-wide diversity and runs of homozygosity (ROH) distributions, using whole genome resequencing from six populations across three archipelagos of Berthelot’s pipit (Anthus berthelotii) - a passerine which has undergone island speciation relatively recently. Pairwise sequential Markovian coalescent (PSMC) analyses estimated divergence from its sister species approximately two million years ago. Results indicate that all Berthelot’s pipit populations had shared ancestry until approximately 50,000 years ago, when the Madeiran archipelago populations were founded, while the Selvagens were colonised within the last 8,000 years. We identify extensive long ROH (>1 Mb) in genomes in the most recently colonised populations of Madeira and Selvagens which have experienced sequential island founder events and population crashes. Population expansion within the last 100 years may have eroded long ROH in the Madeiran archipelago, resulting in a prevalence of short ROH (<1 Mb). Extensive long and short ROH in the Selvagens reflects strong recent inbreeding, small contemporary effective population size and past bottleneck effects, with as much as 37.7% of the autosomes comprised of ROH >250 kb in length. These findings highlight the importance of demographic history, as well as selection and genetic drift, in shaping contemporary patterns of genomic diversity across diverging populations.

An exhaustive assessment of biodiversity is a major challenge of ecological research, and molecular approaches such as the metabarcoding of environmental DNA are boosting our ability to perform biodiversity inventories. Are we actually able to assess the whole community, to unravel the intricate interactions between organisms and the impacts of global changes on the different trophic levels? The majority of metabarcoding papers published in the last years used just one or two markers and analyzed a limited number of taxonomic groups. Nevertheless, approaches are emerging that might allow “all-taxa biological inventories”. Exhaustive biodiversity assessments can be attempted by combining a large number of specific primers, by exploiting the power of universal primers, or by combining specific and universal primers to obtain good information on key taxa while limiting the overlooked biodiversity. Multiplexes of primers and shotgun sequencing may provide a better coverage of biodiversity compared to standard metabarcoding, but still require major methodological advances. We identify the strengths and limitations of different approaches, and suggest new development lines that might improve broad scale biodiversity analyses in the near future.

Holocentric organisms, unlike typical monocentric organisms, have kinetochore activity distributed along almost the whole length of the chromosome. Because of this, chromosomal rearrangements through fission and fusion are more likely to become fixed in holocentric species, which may account for their extraordinary rates of chromosome evolution. Genome synteny has been reported to be conserved in animals with holocentric chromosomes despite high rates of chromosome rearrangements. Comparing genomes of Carex species and a genome of a distantly related Cyperaceae we have characterised conserved vs. rearranged genome regions across pairs of species that range in time since divergence between 2 and 50 million years. We have compared a C. scoparia genome with a linkage map of the same species to study rearrangements at a population level and suppression of recombination patterns. We found a surprisingly conserved genome synteny even between very distantly related species and extraordinarily high rates of chromosome evolution in genus Carex. Comparing the distribution of repetitive DNA and gene density between conserved and rearranged genomic regions, we found repetitive DNA to be related to holocentromeres and as well as rearranged regions of the genome. This evidence of extremely conserved synteny in sedges and the massive events of chromosome fission and fusion found across the evolution of genus Carex suggests the presence of common genomic hotspots of chromosome evolution related to repetitive DNA.

Deciduous forests form the dominant natural vegetation of Europe today, but were restricted to small refugia during Pleistocene cold stages, implying an evolutionary past shaped by recurrent range contractions and expansions. Cold-stage forest refugia were probably widespread in southern and central Europe, with the northwestern Balkan Peninsula being of particular importance. However, the actual number and location of deciduous forest refugia, as well as the connections between them, remain disputed. Here, we address the evolutionary dynamics of the deciduous forest understorey species Euphorbia carniolica as a proxy for past forest dynamics. To do so, we obtained genomic and morphometric data from populations representing the species' entire range, investigated phylogenetic position and intraspecific genetic variation, tested explicit demographic scenarios and applied species distribution models. Our data support two disjoint groups linked to separate refugia on the northwestern and central Balkan Peninsula. We find that genetic differentiation between groups started in the early Pleistocene via vicariance, suggesting a larger distribution in the past. Both refugia acted as sources for founder events to the southeastern Alps and the Carpathians, whereas the latter were likely colonized before the last cold stage. In line with traditional views on the pre-Pleistocene origin of many southeastern European deciduous forest species, the origin of E. carniolica was dated to the late Pliocene. The fact that E. carniolica evolved at a time when a period of continuous forestation was ending in much of Eurasia provides an interesting biogeographical perspective on the past links between Eurasian deciduous forests and their biota.

Anthropogenic impact and loss of genetic diversity threaten more than 50% of raptors. These threats are particularly pronounced for island- endemic species, which occupy small areas, making them more vulnerable to rapid environmental changes. The Reunion harrier (Circus maillardi) is a typical example of the challenges encountered by island- endemic species. In this study, we characterize genetic variation at near-neutral and coding loci to test the historical impact of human activity on harrier populations, and evaluate their (mal)adaptive potential. We observed low but significant genetic differentiation between populations on the West and North-East sides of the island, echoing observations in other endemic species. Inbreeding was significant, with a substantial fraction of samples being first or second-degree relatives. Historical effective population sizes have declined from ~3000 to 300 individuals in the past 1000 years, with a more recent drop ~100 years ago consistent with human activity. Based on our simulations and comparisons with a close relative (Circus melanoleucos), this demographic history may have allowed purging of the most deleterious variants, but is unlikely to have allowed the purging of mildly deleterious variants. Our study provides an example of the massive impact that human activity may have on the genetic diversity and adaptive potential of island populations, and calls for urgent action to closely monitor the reproductive success of such endemic populations, in association with genetic studies.