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Abstract This essay analyzes a robust body of C and N stable isotopes from human and animal collagen and plant remains (n = 423) in the area of Lower Yangtze River dating to 8000–4300 cal. BP, combined with new isotopic data recovered from the Zhelin site in Shanghai, to explore the dietary differences between coastal region and the inland core area of the Liangzhu culture (5300–4300 cal. BP). Our findings suggest that the food variety of the peripheral inhabitants of the core area of the Liangzhu culture may became less diverse over time, while at the same time their reliance on a few domesticated species (rice and pigs) increased. It may be a result of the growing economic and cultural influence of the populations in the inland core Liangzhu area.

Objective The objective of the study was to identify the risk factors correlated with spontaneous preterm birth (SPTB) and iatrogenic preterm birth (IPTB), as well as to compare the pregnancy outcomes between SPTB and IPTB.Materials and methods A total of 1676 (343 SPTB, 144 IPTB and 1189 full-term control group) cases were collected from the International Peace Maternity & Child Health Hospital of Shanghai between August 2018 and October 2020. A case-control study was conducted to explore the risk factors and pregnancy outcomes of SPTB and IPTB.Results The study identified a set of risk factors for SPTB and IPTB, as well as differences in pregnancy outcomes. Reproductive tract infections and myoma of the uterus were the risk factors for SPTB (p

Abstract Noble and commoner in the medieval China capital of Chang’an (modern-day Xi’an) engaged in an intricately intertwined agricultural and pastoral economy. The period represents the peak of the integration of nomadic and agricultural populations in early China. Here we firstly reported human collagen δ 13C and δ 15N values for eight middle age nobles whose lifespans cover roughly a century (AD 503–604) and who include a Northern Zhou, Emperor Wu (北周武帝) and his consort, Empress A’shina (阿史那皇后). We also consider stable isotopic evidence from nine individuals in commoner burials in the Chang’an region, likewise dating to the sixth century. This century-long dietary profile provides direct archeological evidence for dietary variability at this core metropolitan population. Constructing a comparative model using existing historical human isotopic data (n = 1233) from northern China and its northern Steppe, we find a marked regional divergence in noble and commoner dietary patterns. We trace this back to the considerable variety of agricultural and pastoral dietary practices, likely pointing to different economic and geographic backgrounds of the individuals under study. We argue that a two-way relationship between shifting pastoral and agricultural practices was reflected to separate degrees at the elite and commoner level. This study offers an improved understanding of the multiplicity of dietary patterns and associated lifeways for the metropolitan societies of medieval northern China.

Abstract Previous genetic studies of pollinator wasps associated with a community of strangler figs (Ficus subgenus Urostigma, section Americana) in Central Panama suggest that the wasp species exhibit a range in host specificity across their host figs. To better understand factors that might contribute to this observed range of specificity, we used sticky traps to capture fig‐pollinating wasp individuals at 13 Ficus species, sampling at different phases of the reproductive cycle of the host figs (e.g., trees with receptive inflorescences, or vegetative trees, bearing only leaves). We also sampled at other tree species, using them as non‐Ficus controls. DNA barcoding allowed us to identify the wasps to species and therefore assign their presence and abundance to host fig species and the developmental phase of that individual tree. We found: (1) wasps were only very rarely captured at non‐Ficus trees; (2) nonetheless, pollinators were captured often at vegetative individuals of some host species; (3) overwhelmingly, wasp individuals were captured at receptive host fig trees representing the fig species from which they usually emerge. Our results indicate that wasp occurrence is not random either spatially or temporally within the forest and across these hosts, and that wasp specificity is generally high, both at receptive and vegetative host trees. Therefore, in addition to studies that show chemicals produced by receptive fig inflorescences attract pollinator wasps, we suggest that other cues (e.g., chemicals produced by the leaves) can also play a role in host recognition. We discuss our results in the context of recent findings on the role of host shifts in diversification processes in the Ficus genus.

AbstractThe Kazakhs of Xinjiang province are characterized by their nomadic lifestyle and patrilineal clan system. However, compared to Central Asian Kazakhs, a lack of Y chromosomal high-resolution analysis has hindered our understanding of the paternal history of modern Xinjiang Kazakhs.MethodsIn this study, we present the analysis of 110 Y-SNP data from 209 Altay Kazakhs and 201 Ili Kazakhs in Xinjiang, along with their previously reported 24 Y-STR loci data.Results and discussionWe found that the Y chromosome haplogroups exhibit greater diversity in Altay Kazakhs compared to Kazakhs in Kazakhstan, Russia, and other regions of China. Y-SNP-based PCA plots reveal that both the Altay and Ili Kazakhs are situated between the Turkic, Mongolia, and Tibeto-Burman clusters. The dominant haplogroup C2a1a3-F1918, which originated in northeast Asia during the Neolithic Age, accounts for nearly half of the Altay and Ili Kazakhs. The Y lineage network of C2a1a3-F1918 contained two subclusters. Approximately 60.6% of the Altay Kazakhs belong to the DYS448-23 subcluster, indicating their Kerey-Abakh ancestry. On the other hand, around three-quarters of the Ili Kazakhs belong to the DYS448-22 subcluster, suggesting their Kerey-Ashmaily heritage. Notably, the TMRCA ages of the DYS448-23 subcluster were calculated to be 289.4 ± 202.65 years, which aligns with the historical immigration of the Kerey clan back to the Altay Mountains after the defeat of the Dzungar by the Qing dynasty in the mid-18th century.

Summary: A high point of Tibetan Plateau (TP) civilization, the expansive Tubo Empire (618–842 AD) wielded great influence across ancient western China. However, whether the Tubo expansion was cultural or demic remains unclear due to sparse ancient DNA sampling. Here, we reported ten ancient genomes at 0.017- to 0.867-fold coverages from the Dulan site with typical Tubo archaeological culture dating to 1308–1130 BP. Nine individuals from three different grave types have close relationship with previously reported ancient highlanders from the southwestern Himalayas and modern core-Tibetan populations. A Dulan-related Tubo ancestry contributed overwhelmingly (95%–100%) to the formation of modern Tibetans. A genetic outlier with dominant Eurasian steppe-related ancestry suggesting a potential population movement into the Tubo-controlled regions from Central Asia. Together with archeological evidence from burial styles and customs, our study suggested the impact of the Tubo empire on the northeast edge of the TP involved both cultural and demic diffusion.

Han/non-Han interactions were engrained among the border regions of ancient Imperial China. Yet, little is known about either the genetic origins or the lifeways of these border peoples. Our study applies tools from ancient deoxyribonucleic acid (DNA) and stable isotope analysis to the study of a Han dynasty population at the Shichengzi site in modern-day Xinjiang. Isotopic analysis (δ13C and δ15N) of human (n = 8), animal (n = 26), and crop remains (n = 23) from Shichengzi indicated that dietary patterns among site inhabitants could be split among agro-pastoral and agricultural groups based on differences in the collagen 15N ratios. DNA analysis divided the four Shichengzi samples into two groups, with one group primarily harboring the ancient Northeast Asian (ANA) related ancestry, while the other showed a dominant Late Neolithic Yellow River (YR_LN) related ancestry. Both ancient DNA and stable isotope evidence point to the Northeast Asian origins of pastoralists and East Asian origins of Han agriculturalists, who, nonetheless, shared a single burial space at Shichengzi. This study thus provides clear evidence for the multiple origins and identities of populations across the porous border represented by the Han Empire and surrounding regions and proposes a new model for the interpretation of border culture in early Imperial China.

DNA barcoding technology is becoming an increasingly powerful tool in resolving issues of detailed species identification based on morphology, as commonly employed by museums. In the present study, we aimed to identify a stranded Bryde’s whale on Hainan Island, China by extracting DNA from a vertebra pre-treated by physical and/or chemical processes. Based on morphological characteristics, this Bryde’s whale was initially determined as Balaenoptera edeni. Then, DNA was efficiently extracted using ancient DNA techniques. The mitochondrial gene (COI) phylogenetic analysis further revealed that this museum whale specimen belonged to the sub-species B. e. edeni. This study provides a testable and rapid method for museum species verification, by using ancient DNA extraction methods to compensate the disadvantage of traditional DNA extraction methods that are difficult to extract valid DNA.

The relationship between archeological culture and ethnicity is invariably complex. This is especially the case for periods of national division and rapid inter-ethnic exchange, such as China’s Sixteen Kingdoms (304–439 CE) and Northern and Southern Dynasties (420–589 CE). Going by tomb shape and grave goods, the Foyemiaowan cemetery at Dunhuang exhibits a typical third–tenth century Han style. Despite this, the ethnic makeup of the Foyemiaowan population has remained unclear. We therefore analyzed 485 Y-chromosomal SNPs and entire mitochondrial genomes of 34 Foyemiaowan samples. Our study yielded the following discoveries: (1) principal component analysis revealed that the Foyemiaowan population was closely clustered with Tibeto-Burman populations on the paternal side and close to Mongolic-speaking populations on the maternal side; (2) lineage comparisons at the individual level showed that the Foyemiaowan population consisted of primarily Tibeto-Burman and Han Chinese related lineages (Oα-M117, 25%;Oβ-F46, 18.75%), partially Altaic speaking North Eurasian lineages (N-F1206, 18.75%) and a slight admixture of southern East Asian lineages (O1b1a2-Page59, 6.25%; O1b1a1-PK4, 3.13%). Similarly, the maternal gene pool of Foyemiaowan contained northern East Asian (A, 4.17%; CZ, 16.67%; D, 20.83%; G, 4.17%; M9, 4.17%), southern East Asian (B, 12.51%; F, 20.83%) and western Eurasian (H, 4.17%; J, 4.17%) related lineages; (3) we discovered a relatively high genetic diversity among the Foyemiaowan population (0.891) in our ancient reference populations, indicating a complex history of population admixture. Archeological findings, stable isotope analysis and historical documents further corroborated our results. Although in this period China’s central government had relinquished control of the Hexi Corridor and regional non-Han regimes became the dominant regional power, Foyemiaowan’s inhabitants remained strongly influenced by Han culture.

Despite decades of investigation, consensus has yet to be reached on when and where wheat replaced millet as the primary crop in the core regions of early Imperial China. Previous studies have suggested that wheat cultivation likely became widespread prior to or during the Han Dynasty (202 BC–AD 220). Here, we tested this hypothesis by applying archeobotanical tools to plant remains found in five pottery model granaries (cang) entombed in a newly excavated late Western Han burial at the Longzaocun cemetery in the Guanzhong Basin. This analysis allowed us to explore the extent of wheat expansion and agricultural strategies in the heartland of early dynastic China. Macro- and micro-botanical evidence shows that the Longzaocun residents consumed two kinds of crops: foxtail and common millet. Combining these findings with previous studies, we argue that millet-based multi-crop farming dominated the regional agricultural system during the Western Han Dynasty (202 BC-AD 8) and analyze the political and cultural motivations for the Han people’s usage on millet crops from the burial concepts and fiscal systems. Echoing previous studies, we argue that millets remained the most valuable subsistence food for inhabitants of the Loess Basins in the Han core, and that wheat was not cultivated on a large scale in this area during the Western Han Dynasty.

Figs and their wasp pollinators are a classic example of coevolution. By assembling and analysing genomes from across the Ficus clade, authors suggest that fig hybridization driven by pollinator host-switching in this obligate pollination system, is more common than previously thought.

The Hexi Corridor was an important arena for culture exchange and human migration between ancient China and Central and Western Asia. During the Han Dynasty (202 BCE–220 CE), subsistence strategy along the corridor shifted from pastoralism to a mixed pastoralist-agriculturalist economy. Yet the drivers of this transition remain poorly understood. In this study, we analyze the Y-chromosome and mtDNA of 31 Han Dynasty individuals from the Heishuiguo site, located in the center of the Hexi Corridor. A high-resolution analysis of 485 Y-SNPs and mitogenomes was performed, with the Heishuiguo population classified into Early Han and Late Han groups. It is revealed that (1) when dissecting genetic lineages, the Yellow River Basin origin haplogroups (i.e., Oα-M117, Oβ-F46, Oγ-IMS-JST002611, and O2-P164+, M134-) reached relatively high frequencies for the paternal gene pools, while haplogroups of north East Asian origin (e.g., D4 and D5) dominated on the maternal side; (2) in interpopulation comparison using PCA and Fst heatmap, the Heishuiguo population shifted from Southern-Northern Han cline to Northern-Northwestern Han/Hui cline with time, indicating genetic admixture between Yellow River immigrants and natives. By comparison, in maternal mtDNA views, the Heishuiguo population was closely clustered with certain Mongolic-speaking and Northwestern Han populations and exhibited genetic continuity through the Han Dynasty, which suggests that Heishuiguo females originated from local or neighboring regions. Therefore, a sex-biased admixture pattern is observed in the Heishuiguo population. Additionally, genetic contour maps also reveal the same male-dominated migration from the East to Hexi Corridor during the Han Dynasty. This is also consistent with historical records, especially excavated bamboo slips. Combining historical records, archeological findings, stable isotope analysis, and paleoenvironmental studies, our uniparental genetic investigation on the Heishuiguo population reveals how male-dominated migration accompanied with lifestyle adjustments brought by these eastern groups may be the main factor affecting the subsistence strategy transition along the Han Dynasty Hexi Corridor.

Microbial plant-soil feedbacks (PSF) are fundamentally important for plant diversity. The authors present a spatially explicit dynamic model that separates the effects of microbial mutualists and pathogens, thereby presenting a testable mechanistic framework to reconcile previously puzzling observations of the strength and direction of PSF with diversity maintenance.

As we continually reflect on the wars of the 20th century, identification of the remains of victims takes an increasingly prominent position in ongoing research. Existing work on the identification of human remains from 20th century wars primarily covers the determination of phenotypic characteristics, kinship and geographic origins, supporting the establishment of genetic information databases. Compared with standard forensic methods, DNA analyses have revealed greater effectiveness. The process of DNA analysis includes DNA extraction, genetic marker testing and data analysis. Protocols from ancient DNA research can be applied to degraded remains, and next-generation sequencing (NGS) techniques can compensate for shortcomings in the most commonly-used PCR-capillary electrophoresis typing. As it stands, wide-ranging inter-governmental and inter-institutional collaboration is necessary in order to set up NGS-based public databases, and thereby promote the identification of human remains and archaeological forensics.

Marine multicellular organisms host a diverse collection of bacteria, archaea, microbial eukaryotes, and viruses that form their microbiome. Such host-associated microbes can significantly influence the host's physiological capacities; however, the identity and functional role(s) of key members of the microbiome ("core microbiome") in most marine hosts coexisting in natural settings remain obscure. Also unclear is how dynamic interactions between hosts and the immense standing pool of microbial genetic variation will affect marine ecosystems' capacity to adjust to environmental changes. Here, we argue that significantly advancing our understanding of how host-associated microbes shape marine hosts' plastic and adaptive responses to environmental change requires (i) recognizing that individual host-microbe systems do not exist in an ecological or evolutionary vacuum and (ii) expanding the field toward long-term, multidisciplinary research on entire communities of hosts and microbes. Natural experiments, such as time-calibrated geological events associated with well-characterized environmental gradients, provide unique ecological and evolutionary contexts to address this challenge. We focus here particularly on mutualistic interactions between hosts and microbes, but note that many of the same lessons and approaches would apply to other types of interactions.

We describe a combinatorial formula for the coefficients when the dual immaculate quasisymmetric func- tions are decomposed into Young quasisymmetric Schur functions. We prove this using an analogue of Schensted insertion. We also provide a Remmel-Whitney style rule to generate these coefficients algorithmically.

Non-invasive bioluminescent imaging (NIBLI) of HIV-1 infection dynamics allows for real-time monitoring of viral spread and the localization of infected cell populations in living animals. In this report, we describe full-length replication-competent GFP and Nanoluciferase (Nluc) expressing HIV-1 reporter viruses from two clinical transmitted / founder (T/F) strains: TRJO.c and Q23.BG505. By infecting humanized mice with these HIV-1 T/F reporter viruses, we were able to directly monitor longitudinal viral spread at whole-animal resolution via NIBLI at a sensitivity of as few as 30-50 infected cells. Bioluminescent signal strongly correlated with HIV-1 infection and responded proportionally to virus suppression in vivo in animals treated daily with a combination antiretroviral therapy (cART) regimen. Longitudinal NIBLI following cART withdrawal visualized tissue-sites that harbored virus during infection recrudescence. Notably, we observed rebounding infection in the same lymphoid tissues where infection was first observed prior to ART treatment. Our work demonstrates the utility of our system for studying in vivo viral infection dynamics and identifying infected tissue regions for subsequent analyses.

Identifying the factors that influence the species diversity and distribution of ticks (Acari: Ixodida) across vertebrate host taxa is of fundamental ecological and medical importance. Host body size is considered one of the most important determinants of tick abundance, with larger hosts having higher tick burdens. The species diversity of tick assemblages should also be greater on larger-bodied host species, but empirical studies testing this hypothesis are lacking. Here, we evaluate this relationship using a comparative dataset of feeding associations from Panama between 45 tick species and 171 host species that range in body size by three orders of magnitude. We found that tick species diversity increased with host body size for adult ticks but not for immature ticks. We also found that closely related host species tended to have similar tick species diversity, but correcting for host phylogeny did not alter the relationships between host body size and tick species diversity. The distribution of tick species was highly aggregated, with approximately 20% of the host species harboring 80% of all tick species, following the Pareto principle or 20/80 Rule. Thus, the aggregated pattern commonly observed for tick burdens and disease transmission also holds for patterns of tick species richness. Our finding that the adult ticks in this system preferentially parasitize large-bodied host species suggests that the ongoing anthropogenic loss of large-bodied vertebrates is likely to result in host-tick coextinction events, even when immature stages feed opportunistically. As parasites play critical roles in ecological and evolutionary processes, such losses may profoundly affect ecosystem functioning and services.

The significance of symbioses between eukaryotic hosts and microbes extends from the organismal to the ecosystem level and underpins the health of Earth's most threatened marine ecosystems. Despite rapid growth in research on host-associated microbes, from individual microbial symbionts to host-associated consortia of significantly relevant taxa, little is known about their interactions with the vast majority of marine host species. We outline research priorities to strengthen our current knowledge of host-microbiome interactions and how they shape marine ecosystems. We argue that such advances in research will help predict responses of species, communities, and ecosystems to stressors driven by human activity and inform future management strategies.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

In the tropics, ticks parasitize many classes of vertebrate hosts. However, because many tropical tick species are only identifiable in the adult stage, and these adults usually parasitize mammals, most attention on the ecology of tick-host interactions has focused on mammalian hosts. In contrast, immature Neotropical ticks are often found on wild birds, yet difficulties in identifying immatures hinder studies of birds' role in tropical tick ecology and tick-borne disease transmission. In Panama, we found immature ticks on 227 out of 3,498 individually-sampled birds representing 93 host species (24% of the bird species sampled, and 13% of the Panamanian land bird fauna). Tick parasitism rates did not vary with rainfall or temperature, but did vary significantly with several host ecological traits. Likewise, Neotropical-Nearctic migratory birds were significantly less likely to be infested than resident species. Using a molecular library developed from morphologically-identified adult ticks specifically for this study, we identified eleven tick species parasitizing birds, indicating that a substantial portion of the Panamanian avian species pool is parasitized by a diversity of tick species. Tick species that most commonly parasitized birds had the widest diversity of avian hosts, suggesting that immature tick species are opportunistic bird parasites. Although certain avian ecological traits are positively associated with parasitism, we found no evidence that individual tick species show specificity to particular avian host ecological traits. Finally, our data suggest that the four principal vectors of Rocky Mountain Spotted Fever in the Neotropics rarely, if ever, parasitize Panamanian birds. However, other tick species that harbor newly-discovered rickettsial parasites of unknown pathogenicity are frequently found on these birds. Given our discovery of broad interaction between Panamanian tick and avian biodiversity, future work on tick ecology and the dynamics of emerging tropical tick-borne pathogens should explicitly consider wild bird as hosts.

Wind-borne pollinating wasps (Agaonidae) can transport fig (Ficus sp., Moraceae) pollen over enormous distances (> 100 km). Because of their extensive breeding areas, Neotropical figs are expected to exhibit weak patterns of genetic structure at local and regional scales. We evaluated genetic structure at the regional to continental scale (Panama, Costa Rica, and Peru) for the free-standing fig species Ficus insipida. Genetic differentiation was detected only at distances > 300 km (Jost´s Dest = 0.68 ± 0.07 & FST = 0.30 ± 0.03 between Mesoamerican and Amazonian sites) and evidence for phylogeographic structure (RST>>permuted RST) was only significant in comparisons between Central and South America. Further, we assessed local scale spatial genetic structure (SGS, d ≤ 8 km) in Panama and developed an agent-based model parameterized with data from F. insipida to estimate minimum pollination distances, which determine the contribution of pollen dispersal on SGS. The local scale data for F. insipida was compared to SGS data collected for an additional free-standing fig, F. yoponensis (subgenus Pharmacosycea), and two species of strangler figs, F. citrifolia and F. obtusifolia (subgenus Urostigma) sampled in Panama. All four species displayed significant SGS (mean Sp = 0.014 ± 0.012). Model simulations indicated that most pollination events likely occur at distances > > 1 km, largely ruling out spatially limited pollen dispersal as the determinant of SGS in F. insipida and, by extension, the other fig species. Our results are consistent with the view that Ficus develops fine-scale SGS primarily as a result of localized seed dispersal and/or clumped seedling establishment despite extensive long-distance pollen dispersal. We discuss several ecological and life history factors that could have species- or subgenus-specific impacts on the genetic structure of Neotropical figs.

It is increasingly recognized that macro-organisms (corals, insects, plants, vertebrates) consist of both host tissues and multiple microbial symbionts that play essential roles in their host’s ecological and evolutionary success. Consequently, identifying benefits and costs of symbioses, as well as mechanisms underlying them are research priorities. All plants surveyed under natural conditions harbor foliar endophytic fungi (FEF) in their leaf tissues, often at high densities. Despite producing no visible effects on their hosts, experiments have nonetheless shown that FEF reduce pathogen and herbivore damage. Here, combining results from three genomic, and two physiological experiments, we demonstrate pervasive genetic and phenotypic effects of the apparently asymptomatic endophytes on their hosts. Specifically, inoculation of endophyte-free (E-) Theobroma cacao leaves with Colletotrichum tropicale (E+), the dominant FEF species in healthy T. cacao, induces consistent changes in the expression of hundreds of host genes, including many with known defensive functions. Further, E+ plants exhibited increased lignin and cellulose content, reduced maximum rates of photosynthesis (Amax), and enrichment of nitrogen-15 and carbon-13 isotopes. These phenotypic changes observed in E+ plants correspond to changes in expression of specific functional genes in related pathways. Moreover, a cacao gene (Tc00g04254) highly up-regulated by C. tropicale also confers resistance to pathogen damage in the absence of endophytes or their products in host tissues. Thus, the benefits of increased pathogen resistance in E+ plants are derived in part from up-regulation of intrinsic host defense responses, and appear to be offset by potential costs including reduced photosynthesis, and endophyte metabolism of host tissues. Similar effects are likely in most plant-endophyte interactions, and should be recognized in the design and interpretation of genetic and phenotypic studies of plants.

Plants interact with each other, nutrients, and microbial communities in soils through extensive root networks. Understanding these below ground interactions has been difficult in natural systems, particularly those with high plant species diversity where morphological identification of fine roots is difficult. We combine DNA-based root identification with a DNA barcode database and above ground stem locations in a floristically diverse lowland tropical wet forest on Barro Colorado Island, Panama, where all trees and lianas >1 cm diameter have been mapped to investigate richness patterns below ground and model rooting distributions.DNA barcode loci, particularly the cpDNA locus trnH-psba, can be used to identify fine and small coarse roots to species. We recovered 33 species of roots from 117 fragments sequenced from 12 soil cores. Despite limited sampling, we recovered a high proportion of the known species in the focal hectare, representing approximately 14% of the measured woody plant richness. This high value is emphasized by the fact that we would need to sample on average 13 m(2) at the seedling layer and 45 m(2) for woody plants >1 cm diameter to obtain the same number of species above ground. Results from inverse models parameterized with the locations and sizes of adults and the species identifications of roots and sampling locations indicates a high potential for distal underground interactions among plants.DNA barcoding techniques coupled with modeling approaches should be broadly applicable to studying root distributions in any mapped vegetation plot. We discuss the implications of our results and outline how second-generation sequencing technology and environmental sampling can be combined to increase our understanding of how root distributions influence the potential for plant interactions in natural ecosystems.

Marine multicellular organisms host a diverse collection of bacteria, archaea, microbial eukaryotes, and viruses that form their microbiome. Such host-associated microbes can significantly influence the host's physiological capacities; however, the identity and functional role(s) of key members of the microbiome ("core microbiome") in most marine hosts coexisting in natural settings remain obscure. Also unclear is how dynamic interactions between hosts and the immense standing pool of microbial genetic variation will affect marine ecosystems' capacity to adjust to environmental changes. Here, we argue that significantly advancing our understanding of how host-associated microbes shape marine hosts' plastic and adaptive responses to environmental change requires (i) recognizing that individual host-microbe systems do not exist in an ecological or evolutionary vacuum and (ii) expanding the field toward long-term, multidisciplinary research on entire communities of hosts and microbes. Natural experiments, such as time-calibrated geological events associated with well-characterized environmental gradients, provide unique ecological and evolutionary contexts to address this challenge. We focus here particularly on mutualistic interactions between hosts and microbes, but note that many of the same lessons and approaches would apply to other types of interactions.

The significance of symbioses between eukaryotic hosts and microbes extends from the organismal to the ecosystem level and underpins the health of Earth's most threatened marine ecosystems. Despite rapid growth in research on host-associated microbes, from individual microbial symbionts to host-associated consortia of significantly relevant taxa, little is known about their interactions with the vast majority of marine host species. We outline research priorities to strengthen our current knowledge of host-microbiome interactions and how they shape marine ecosystems. We argue that such advances in research will help predict responses of species, communities, and ecosystems to stressors driven by human activity and inform future management strategies.

Identifying the factors that influence the species diversity and distribution of ticks (Acari: Ixodida) across vertebrate host taxa is of fundamental ecological and medical importance. Host body size is considered one of the most important determinants of tick abundance, with larger hosts having higher tick burdens. The species diversity of tick assemblages should also be greater on larger-bodied host species, but empirical studies testing this hypothesis are lacking. Here, we evaluate this relationship using a comparative dataset of feeding associations from Panama between 45 tick species and 171 host species that range in body size by three orders of magnitude. We found that tick species diversity increased with host body size for adult ticks but not for immature ticks. We also found that closely related host species tended to have similar tick species diversity, but correcting for host phylogeny did not alter the relationships between host body size and tick species diversity. The distribution of tick species was highly aggregated, with approximately 20% of the host species harboring 80% of all tick species, following the Pareto principle or 20/80 Rule. Thus, the aggregated pattern commonly observed for tick burdens and disease transmission also holds for patterns of tick species richness. Our finding that the adult ticks in this system preferentially parasitize large-bodied host species suggests that the ongoing anthropogenic loss of large-bodied vertebrates is likely to result in host-tick coextinction events, even when immature stages feed opportunistically. As parasites play critical roles in ecological and evolutionary processes, such losses may profoundly affect ecosystem functioning and services.