Background Evolution Research Articles

Breaking the Hybrid Myth of Paphiopedilum wenshanense: Double Bifurcated Divergence Followed by Adaptive Introgression Formed a Morphological Intermediate.

Species with intermediate phenotypes are usually hypothesised to have originated from hybrid speciation. However, other mechanisms, such as double bifurcated speciation with introgression may create the same phenotypes. Clarifying the underlying process generating the observed intermediate morphology is important for conservation efforts, as it provides insights into the species' evolutionary background and adaptability. Here, we utilised genome-wide single nucleotide polymorphism data to test evolutionary history models for Paphiopedilum wenshanense Z. J. Liu & J. Yong Zhang, an orchid species that is widely considered to be a hybrid with intermediate morphology of other two closely related species, P. concolor Pfitzer and P. bellatulum Pfitzer, distributed in Indochina. Our results rejected the hybrid speciation hypothesis and ascribed the intermediate floral phenotypes of P. wenshanese to introgression from P. concolor after it diverged from P. bellatulum during the last glacial maximum. Excluding the geographic covariate, the current genetic mixing rate of P. wenshanense from P. concolor is stronger in the south part of its range and is associated with precipitation in the early summer, indicating that population divergence in P. wenshanense is being driven by adaptive introgression. These genetic patterns also correspond to the observed floral variation across P. wenshaense populations. The introgression from P. concolor, along with the intermediate and varying floral morphologies, may expand the ecological opportunities for P. wenshanense, providing an explanation for why high genetic diversity has been maintained despite a high level of inbreeding and small census population size. Our study provides a framework for future research to investigate the characteristics and underlying mechanisms of intermediate morphologies in general.

Cell type census in cerebral cortex reveals species-specific brain function and connectivity

The cerebral cortex contains a diverse array of functional regions that are conserved across species, such as primary somatosensory and primary visual cortex. However, despite this conservation, these regions exhibit different connectivity and functions in various species. It is hypothesized that these differences arise from distinct cell types within the conserved regions. To uncover these species-specific differences, investigating gene expression at the cellular level can reveal unique cell types. In this review, we highlight recent research on the molecular mechanisms that govern the formation of specific cell types in the rodent primary somatosensory cortex. Furthermore, we explore how these conserved molecular mechanisms are observed across different brain regions in various species. These findings offer new insights into the diversity and evolutionary background of neural circuit formation in the mammalian cortex.

Unraveling enigmatic disjunctions: Population genetic analysis points to independent origins of rare rhododendrons in the Rhododendron keiskei complex (Ericaceae)

AbstractUnraveling species boundaries is pivotal for evolutionary biology and conservation endeavors. However, it proves challenging in instances where recent speciation is intertwined with complex demographic histories and natural selection processes. The Rhododendron keiskei complex, an evergreen rhododendron distributed in East Asia, consists of a widespread variety (R. keiskei var. keiskei) and a more restricted R. keiskei var. hypoglaucum. Intriguingly, the latter is exceptionally rare yet displays a disjunction that spans approximately 1100 km. This study aimed to elucidate the evolutionary backgrounds of the enigmatic disjunctions of R. keiskei var. hypoglaucum and to propose species delimitation within the species complex. An integrative approach, combining genomic data (MIG‐seq and GBS‐derived SNPs) with Scanning Electron Microscopy analysis of leaf microstructures was adopted in this study. Phylogenetic analyses revealed significant divergence among the studied rhododendrons. Genetic demographic analyses favored the population models that assumed non‐monophyly of two disjunct populations of R. keiskei var. hypoglaucum indicating their independent origins. Recent gene flow between the widespread R. keiskei var. keiskei and “var. hypoglaucum” populations were limited due to geographic and habitat isolation factors, even in areas where their distributions overlap. Detailed morphological assessments detected distinctions between morphologically similar “var. hypoglaucum” populations based on leaf microstructures and flowering habits. Our study has shown that the apparent disjunctions of rare rhododendrons are more likely attributed to morphological convergence, possibly due to similar environmental selections in unrelated taxa. The finding highlights the importance of an integrative approach for resolving taxonomic challenges in plant species complexes.

Rethinking the Roles of the Social Determinants of Health in Bystander Intervention for Partner Violence Among College Students

Willingness to intervene as an effective bystander is critical in preventing partner violence and fostering safety among college students. Informed by the Social Determinants of Health framework, this conceptual paper provides an overview of the background and historical evolution of bystander intervention and invites a rethinking of how various factors impact bystander intervention for partner violence among college students by highlighting the roles of (1) economic factors and education, (2) sexual beliefs, myths, and media, (3) gender values and norms, (4) environmental factors, (5) college students at risk, (6) social support network and access to services, (7) acculturation and familiarity with the U.S. culture, and (8) cost-benefit analyses. We also discuss potential practice, research, and policy implications. Understanding the Social Determinants of Health is instrumental in addressing the root cause of intersecting health disparities, which is vital in preventing violence, encouraging bystander intervention, and creating a safer community.

Ecdysteroid-dependent molting in tardigrades.

Although molting is a defining feature of the most species-rich animal taxa-the Ecdysozoa, including arthropods, tardigrades, nematodes, and others1,2-its evolutionary background remains enigmatic. In pancrustaceans, such as insects and decapods, molting is regulated by the ecdysteroid (Ecd) hormone and its downstream cascade (Figure1A, see also the text).3,4,5 However, whether Ecd-dependent molting predates the emergence of the arthropods and represents an ancestral machinery in ecdysozoans remains unclear. For example, involvement of the Ecd hormone in molting regulation has been suggested only in some parasitic nematodes outside of arthropods,6,7 and insect Ecd synthesis and receptor genes are lacking in some ecysozoan lineages (FigureS1A).8,9,10 In this study, we investigated the role of Ecd in the molting process of the tardigrade Hypsibius exemplaris. We show that the endogenous Ecd level periodically increases during the molting cycle of H.exemplaris. The pulse treatment with exogenous Ecd induced molting, whereas an antagonist of the Ecd receptor suppressed the molting. Our spatial and temporal gene expression analysis revealed the putative regulatory organs and Ecd downstream cascades. We demonstrate that tardigrade molting is regulated by the Ecd hormone, supporting the ancestry of Ecd-dependent molting in panarthropods. Furthermore, we were able to identify the putative neural center of molting regulation in tardigrades. This region may be homologous to the neural center in the protocerebrum of pancrustaceans and represent an ancestral state of panarthropods. Together, our results suggest that Ecd-dependent molting evolved in the early-late Ediacaran, 22-76 million years earlier than previously suggested.11.

Exploring the Effectiveness and Specific Teaching Methods of English Etymology in Expanding Mental Lexicon for College Students

English etymology, as a discipline that studies the origin and development of words, reveals the intrinsic connection and meaning of vocabulary by tracing the historical background, etymology and semantic evolution of words, which not only helps learners to understand the deeper meaning of vocabulary, but also expands and builds their English mental lexicon effectively, thus helping students achieve effective vocabulary enhancement in a short time. The purpose of this paper is to discuss the role of English etymology in the construction and expansion of mental lexicon, analyze its actual teaching methods, and demonstrate its application and effect in educational practice.

Bank vole genomics links determinate and indeterminate growth of teeth

BackgroundContinuously growing teeth are an important innovation in mammalian evolution, yet genetic regulation of continuous growth by stem cells remains incompletely understood. Dental stem cells responsible for tooth crown growth are lost at the onset of tooth root formation. Genetic signaling that initiates this loss is difficult to study with the ever-growing incisor and rooted molars of mice, the most common mammalian dental model species, because signals for root formation overlap with signals that pattern tooth size and shape (i.e., cusp patterns). Bank and prairie voles (Cricetidae, Rodentia, Glires) have evolved rooted and unrooted molars while retaining similar size and shape, providing alternative models for studying roots.ResultsWe assembled a de novo genome of Myodes glareolus, a vole with high-crowned, rooted molars, and performed genomic and transcriptomic analyses in a broad phylogenetic context of Glires (rodents and lagomorphs) to assess differential selection and evolution in tooth forming genes. Bulk transcriptomics comparisons of embryonic molar development between bank voles and mice demonstrated overall conservation of gene expression levels, with species-specific differences corresponding to the accelerated and more extensive patterning of the vole molar. We leverage convergent evolution of unrooted molars across the clade to examine changes that may underlie the evolution of unrooted molars. We identified 15 dental genes with changing synteny relationships and six dental genes undergoing positive selection across Glires, two of which were undergoing positive selection in species with unrooted molars, Dspp and Aqp1. Decreased expression of both genes in prairie voles with unrooted molars compared to bank voles supports the presence of positive selection and may underlie differences in root formation.ConclusionsOur results support ongoing evolution of dental genes across Glires and identify candidate genes for mechanistic studies of root formation. Comparative research using the bank vole as a model species can reveal the complex evolutionary background of convergent evolution for ever-growing molars.

Detection prospects of gravitational waves from SU(2) axion inflation

We study detection prospects of a gravitational-wave background (GWB) sourced by SU(2) gauge fields considering all possible observational constraints. More precisely, we consider bounds set by cosmic microwave background measurements, primordial black hole overproduction, as well as backreaction of the gauge fields on the background evolution. Gravitational-waves data from the first three observing runs of the LIGO-Virgo-KAGRA Collaboration show no evidence for a GWB contribution from axion inflation. However, we are able to place conservative constraints on the parameters of the SU(2) inflation with current data. We investigate conditions on the inflationary potential that would lead to a detectable signal that evades astrophysical and cosmological constraints and discuss detection prospects for third generation networks. Published by the American Physical Society 2024

Phenotypic and Transcriptomic Analysis Revealed a Lack of Risk Perception by Native Tadpoles Toward Novel Non-Native Fish.

The introduction of alien species poses a serious threat to native biodiversity, and mountain lake systems in the southwest of China are particularly vulnerable to the introduction of non-native fish. The prey naivety hypothesis states that native species may not be able to recognize novel introduced species due to a lack of common evolutionary background and therefore become easy targets, so the impacts of non-native fish on mountain endemic amphibians need to be urgently assessed. In an ex-situ experiment, we exposed the tadpoles of the Chaochiao Brown Frog (Rana chaochiaoensis), endemic to western China, to kairomones of both native and translocated fish species, and their phenotypic and genetic response patterns were compared. The results revealed significant phenotypic plasticity responses in total length (TOL), tail length (TL), and tail muscle width (TW) of tadpoles induced by native fish kairomone, while tadpoles exposed to translocated fish kairomone exhibited weaker phenotypic changes. At the transcriptional level, the number of differently expressed genes (DEGs) in the native fish treatment was 3.1-fold (liver) and 52.6-fold (tail muscle) higher than in the translocated fish treatment, respectively. There were more unique DEGs in the native fish treatment, primarily enriched in terms and pathways related to stress response, energy metabolism, and muscle development. The study revealed a lack of risk perception by native tadpoles toward novel non-native fish, providing new evidence for the prey naivety hypothesis from both phenotypic and molecular perspectives. Future conservation efforts should prioritize assessing the impacts of non-native fish on alpine and subalpine threatened and narrowly distributed amphibians. Additionally, prevention, early warning, monitoring, and removal of non-native fish should be carried out as soon as possible.

Climate change scenarios predict reduction in suitable habitats and range shifts for Ophiocordyceps sinensis (Berk.) in Hindu Kush Himalaya

The Hindu Kush Himalayan region has seen a faster pace of anthropogenic climate warming than the global average during the last 50 years. Since 1980s this region is experiencing intense climatic events notably elevation-dependent warming. Given its unique evolutionary background, rich variety of species, and significant endemism, it is crucial to comprehend the effects of climate change on species distributions in this area. Of particular interest are the fungi, which have been the subject of much fewer studies on how they will respond to climate change, despite the fact that they may have a significant role in the functioning and stability of ecosystems. We therefore selected Ophiocordyceps sinensis an alpine fungus species for predicting the effects of climate change on its distribution in Hindu Kush Himalaya. Regarded as one of the most expensive natural resources used in oriental medicine, Ophiocordyceps and its surrounding habitats are under threat from various ecological and anthropogenic factors. We used Species Distribution Modeling software Maxent 3.3.4 and a set of uncorrelated climatic (temperature and precipitation) and topographical (elevation, slope and aspect) variables at a spatial resolution of 2.5 arc minutes to model the suitable habitats. To predict the future distribution of O. sinensis we used future climate data from BCCCSM2- HR global circulation model for three emission scenarios of the shared socioeconomic pathways (SSPs) (SSP126, SSP245 and SSP585). Maxent model predicted current and future habitats with high accuracy. Current potential distribution map of O. sinensis shows that high suitability areas occur in India, China, Nepal and Bhutan. Prediction maps under all three scenarios showed a large reduction in suitable habitats as compared to current climatic conditions. Analysis of range change reveals that species exhibits both range expansion and range contraction under climate change scenarios. Range contraction is noticeably more than range expansion causing overall reduction in the suitable habitats occupied by O. sinensis. ‘Centroid Range Shift’ analysis revealed potential suitable habitats will shift to South-West direction under all future scenarios with almost overlapping centroids.

Gravitational waves driven by holographic dark energy

In this paper, we have studied the effects of holographic dark energy on the evolution of gravitational waves. The background evolution of gravitational waves in a flat FRW universe is considered and studied in the presence of various holographic dark energy models. The perturbation equations governing the evolution of the gravitational waves have been constructed and solutions are obtained. These solutions are studied in detail to get a proper understanding of the characteristics of the gravitational waves in the presence of holographic dark energy. The work can be a significant tool in studying different dark energy models comparatively using the features of the gravitational wave evolution.

Exploring the pre-inflationary dynamics in loop quantum cosmology with a DBI scalar field

Loop quantum cosmology is a symmetry-reduced application of loop quantum gravity. The theory predicts a bounce for the universe at the Planck scale and resolves the singularity of standard cosmology. The dynamics is also governed by an effective Hamiltonian, which predicts a modified Friedmann equation containing the quadratic terms of the energy density. The term plays an essential role in the high energy regime, but the equations return to the standard form in the low energy regime. The evolution of the universe in the pre-inflationary period is studied in the framework of loop quantum cosmology, where the DBI scalar field is assumed to be the dominant component of the universe. Using the numerical method, we provide the evolution of the DBI field. The background evolution shows that there are three phases as: bouncing phase, transition phase and slow-roll inflationary phase. There is also a short period of super-inflation just at the beginning of the bounce phase. The field first climbs the potential and then reaches the turning point where ϕ̇ disappears and the potential energy becomes the dominant part of the energy density. This is the time when the slow roll inflation begins and the field slowly rolls down the potential. The results indicate that there are a few e-fold expansions in the bounce phase, about N = 3.5–4, and the universe experiences about N = 59 e-fold expansions in the slow-roll inflation phase.

Untangling poikilohydry and desiccation tolerance: evolutionary and macroecological drivers in ferns.

Poikilohydry describes the inability of plants to internally regulate their water content (hydroregulation), whereas desiccation tolerance (DT) refers to plants ability to restore normal metabolic functions upon rehydration. The failure to clearly separate these two adaptations has impeded a comprehensive understanding of their unique evolutionary and ecological drivers. Unlike bryophytes and angiosperms, these adaptations in ferns are sometimes uncorrelated, offering a unique opportunity to navigate their intricate interplay. We classified ferns into two syndromes: the Hymenophyllum-type (H-type), encompassing species with filmy leaves lacking stomata that experience extreme poikilohydry and varying degrees of DT, and the Pleopeltis-type (P-type), consisting of resurrection plants with variable hydroregulation but high DT. The H-type evolved during globally cool Icehouse periods, as an adaptation to low light levels in damp, shady habitats, and currently prevails in wet environments. Conversely, the P-type evolved predominantly under Greenhouse periods as an adaptation to periodic water shortage, with most extant species thriving in warm, seasonally dry habitats. Out study underscores the fundamental differences between poikilohydry and DT, emphasizing the imperative to meticulously differentiate and qualify the strength of each strategy as well as their interactions, as a basis for understanding the genetic and evolutionary background of these ecologically crucial adaptations.

Cosmology of dark energy radiation

In this work, we quantify the cosmological signatures of dark energy radiation—a novel description of dark energy, which proposes that the dynamical component of dark energy is comprised of a thermal bath of relativistic particles sourced by thermal friction from a slowly rolling scalar field. For a minimal model with particle production emerging from first principles, we find that the abundance of radiation sourced by dark energy can be as large as ΩDER=0.03, exceeding the bounds on relic dark radiation by three orders of magnitude. Although the background and perturbative evolution of dark energy radiation are distinct from Quintessence, we find that current and near-future cosmic microwave background and supernova data will not distinguish these models of dark energy. We also find that our constraints on all models are dominated by their impact on the expansion rate of the Universe. Considering extensions that allow the dark radiation to populate neutrinos, axions, and dark photons, we evaluate the direct detection prospects of a thermal background comprised of these candidates consistent with cosmological constraints on dark energy radiation. Our study indicates that a resolution of ∼6 meV is required to achieve sensitivity to relativistic neutrinos compatible with dark energy radiation in a neutrino capture experiment on tritium. We also find that dark matter axion experiments lack sensitivity to a relativistic thermal axion background, even if enhanced by dark energy radiation, and dedicated search strategies are required to probe new parameter space. We derive constraints arising from a dark photon background from oscillations into visible photons, and find that viable parameter space can be explored with the late dark energy radiation experiment. Published by the American Physical Society 2024

Effects of neutrino-ultralight dark matter interaction on the cosmic neutrino background

Ultralight dark matter interacting with sterile neutrinos would modify the evolution and properties of the cosmic neutrino background through active-sterile neutrino mixing. We investigate how such an interaction would induce a redshift dependence in neutrino masses. We highlight that cosmological constraints on the sum of neutrino masses would require reinterpretation due to the effective mass generated by neutrino-dark matter interactions. Furthermore, we present an example where such interactions can alter the mass ordering of neutrinos in the early Universe, compared to what we expect today. We also address the expected changes in the event rates in a PTOLEMY-like experiment, which aims to detect the cosmic neutrino background via neutrino capture and discuss projected constraints. Published by the American Physical Society 2024

Interacting ultralight dark matter and dark energy and fits to cosmological data in a field theory approach

The description of dark matter as a pressure-less fluid and of dark energy as a cosmological constant, both minimally coupled to gravity, constitutes the basis of the concordanceΛCDM model. However, the concordance model is based on using equations of motion directly for the fluids with constraints placed on their sources, andlacks an underlying Lagrangian. In this work, we propose a Lagrangian model of two spin zero fields describing dark energy and dark matter with an interaction term between the two along with self-interactions. We study the background evolution of the fields as well as their linear perturbations, suggesting an alternative to ΛCDM with dark matter and dark energy being fundamental dynamical fields. The parameters of the model are extracted using a Bayesian inference tool based on multiple cosmological data sets which include those of Planck (with lensing), BAO, Pantheon, SH0ES, and WiggleZ. Using these data, we set constraints on the dark matter mass and the interaction strengths. Furthermore, we find that the model is able to alleviate the Hubble tension for some data sets while also resolving the S 8 tension.

Model-independent reconstruction of f(T) and f(R) gravity

In this paper, we revisit the model-independent reconstruction of f(T) and f(R) gravity at the cosmological background and linear matter density perturbation levels respectively via Gaussian process by using the currently available cosmic observations, which consist Pantheon+ SNe Ia samples, observed Hubble parameter H(z) and the redshift space distortion fσ8(z)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f\\sigma _8(z)$$\\end{document} data points. For the f(T) gravity, we find the reconstructed form of f(T) from the background and perturbation levels cannot match each other well in 1σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma $$\\end{document} regions, it might imply the tension between the background and perturbation evolutions. For the f(R) gravity, due to the existence of an extra degree for freedom F˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\dot{F}}$$\\end{document}, the form of f(R) can be reconstructed by the addition of the growth rate function. The results show that the reconstructed form of f(R) might be viable in the redshift range of z<0.75\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z<0.75$$\\end{document} based on the currently available cosmic observations, for filling the requirement of f,R>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_{,R}>0$$\\end{document} and f,RR>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_{,RR}>0$$\\end{document} to avoid a tachyonic instability and be ghosts free in theory.

Honeybee Nutrition: Physiological and Ecological Insights

Bees play a vital role in global agriculture through their pollination services; however, their populations have declined over the past three decades due to various stress, including nutritional deficits stemming from habitat loss and alteration. ​This review emphasizes the critical need for understanding bee nutrition, which is essential for overcoming these declines.​ With their evolutionary background alongside flowering plants, bees have adapted to a herbivorous diet primarily consisting of floral nectar and pollen. Nectar provides the energy necessary for flight and other metabolic processes, while pollen supplies essential proteins, fats and micronutrients. Foraging behaviors vary among bee species and are influenced by environmental factors and the genetic composition of the colony. Honey bees exhibit complex social structures where worker bees gather nectar, pollen and water, each contributing to the nutritional needs of the colony. The transformation of collected nectar into honey and pollen into bee bread illustrates bees unique food storage strategies, providing vital nutrition to larvae and adult workers. Additionally, understanding the nutritional processes involved in larval development and royal jelly production sheds light on caste differentiation and overall colony health. This comprehensive view on bee nutrition underscores its significance for future conservation strategies.

The 21-cm signal during the end stages of reionization

ABSTRACT During the epoch of reionization (EoR), the 21-cm signal allows direct observation of the neutral hydrogen (H i) in the intergalactic medium (IGM). In the post-reionization era, this signal instead probes H i in galaxies, which traces the dark matter density distribution. With new numerical simulations, we investigated the end stages of reionization to elucidate the transition of our Universe into the post-reionization era. Our models are consistent with the latest high-redshift measurements, including ultraviolet (UV) luminosity functions up to redshift $\simeq$8. Notably, these models consistently reproduced the evolution of the UV photon background, which is constrained from Lyman-$\alpha$ absorption spectra. We studied the dependence of this background on the nature of photon sinks in the IGM, requiring mean free path of UV photons to be $\sim$10 comoving-megaparsecs (cMpc) during the EoR that increases gradually with time during late stages ($z\lesssim 6$). Our models revealed that the reionization of the IGM transitioned from an inside-out to an outside-in process when the Universe is less than 0.01 per cent neutral. During this epoch, the 21-cm signal also shifted from probing predominantly the H i in the IGM to that in galaxies. Furthermore, we identified a statistically significant number of large neutral islands (with sizes up to 40 cMpc) persisting until very late stages ($5 \lesssim z \lesssim 6$) that can imprint features in Lyman-$\alpha$ absorption spectra and also produce a knee-like feature in the 21-cm power spectrum.

No time to derive: unraveling total time derivatives in in-in perturbation theory

The in-in formalism provides a way to systematically organize the calculation of primordial correlation functions. Although its theoretical foundations are now firmly settled, the treatment of total time derivative interactions, incorrectly trivialized as “boundary terms”, has been the subject of intense discussions and conceptual mistakes. In this work, we demystify the use of total time derivatives — as well as terms proportional to the linear equations of motion — and show that they can lead to artificially large contributions cancelling at different orders of the in-in operator formalism. We discuss the treatment of total time derivative interactions in the Lagrangian path integral formulation of the in-in perturbation theory, and we showcase the importance of interaction terms proportional to linear equations of motion. We then provide a new route to the calculation of primordial correlation functions, which avoids the generation of total time derivatives, by working directly at the level of the full Hamiltonian in terms of phase-space variables. Instead of integrating by parts, we perform canonical transformations to simplify interactions. We explain how to retrieve correlation functions of the initial phase-space variables from the knowledge of the ones after canonical transformations. As an important first application, we find the explicit sizes of Hamiltonian cubic interactions in single-field inflation with canonical kinetic terms and for any background evolution, straight in terms of the primordial curvature perturbation and its canonical conjugate momentum, as well as the corresponding ones in the tensor sector, and the ones mixing scalars and tensors. We also briefly comment on quartic interactions. Our results are important for performing complete calculations of exchange diagrams in inflation, such as the (scalar and tensor) exchange trispectrum and the one-loop power spectrum. Being already written in a form amenable to characterize quantum properties of primordial fluctuations, they also promise to shed light on the non-linear dynamics of quantum states during inflation.