L. Michael Romero

L. Michael Romero
Tufts University | Tufts · Department of Biology

Ph.D.

About

252
Publications
45,184
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21,425
Citations
Citations since 2016
59 Research Items
10298 Citations
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201620172018201920202021202202004006008001,0001,2001,400
201620172018201920202021202202004006008001,0001,2001,400
201620172018201920202021202202004006008001,0001,2001,400

Publications

Publications (252)
Article
Although stress can cause overall damage to the genome, it is currently unknown whether normal background damage to DNA varies throughout the annual cycle. If DNA damage did vary seasonally, it would have major implications on environmental-genomic interactions. We measured background DNA double-stranded breaks using the neutral comet assay in five...
Article
When animals are sick, their physiology and behavior change in ways that can impact their offspring. Research is emerging showing that infection risk alone can also modify the physiology and behavior of healthy animals. If physiological responses to environments with high infection risk take place during reproduction, it is possible that they lead...
Article
The relatively new technique of measuring corticosterone (cort) levels extracted from feathers provides a less invasive, more integrated method of assessing a bird's stress physiology. Current understanding is that cort is deposited into the feather via blood when the feather is replaced during molt. The blood supply in the feather is cut off when...
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Full-text available
One aspect of the Reactive Scope Model is wear-and-tear, which describes a decrease in an animal's ability to cope with a stressor, typically because of a period of chronic or repeated stressors. We investigated whether wear-and-tear due to chronic stress would accelerate a transition from phase II to phase III of fasting. We exposed house sparrows...
Article
There are complex interactions between an organism's microbiome and its response to stressors, often referred to as the “gut-brain axis;” however, the ecological relevance of this axis in wild animals remains poorly understood. Here, we used a chronic mild stress protocol to induce stress in wild-caught house sparrows (Passer domesticus), and compa...
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‘The Blob’, a mass of anomalously warm water in the Northeast Pacific Ocean peaking from 2014 to 2016, caused a decrease in primary productivity with cascading effects on the marine ecosystem. Among the more obvious manifestations of the event were seabird breeding failures and mass mortality events. Here, we used corticosterone in breast feathers...
Article
Glucocorticoids are popular hormones to measure in both biomedical and ecological studies of stress. Many assumptions used to interpret glucocorticoid results are derived from biomedical data on humans or laboratory rodents, but these assumptions often fail for wild animals under field conditions. We discuss five common assumptions often made about...
Article
Measuring corticosterone (Cort) in bird feathers has become increasingly popular as a non-invasive method of obtaining an integrated profile of Cort exposure during the period of feather replacement. Most studies use antibody-based assays to assess Cort levels in feathers [radioimmunoassays (RIA) or enzyme immunoassays (EIA)]. However, it is still...
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Full-text available
Physiological metrics are becoming popular tools for assessing individual condition and population health to inform wildlife management and conservation decisions. Corticosterone assays can provide information on how animals cope with individual and habitat-level stressors, and the recent development of feather assays is an exciting innovation that...
Article
Neophobia is an animal's avoidance of novelty. Animals tend to respond to novel objects by increasing their latency to approach the objects, and they eventually habituate after repeated exposure by attenuating this increased approach latency. Interestingly, the physiological stress response does not appear to have a causal link to neophobia, althou...
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Full-text available
As the world faces the health crisis of a global pandemic—with healthcare protocols in overhaul, and patients and care teams experiencing unprecedented levels of stress and unpredictability—we predict that current knowledge gaps in maternal health will inevitably have a lasting impact on the health of women giving birth now and in the near future....
Article
Although corticosterone (Cort) has been the predominant metric used to assess acute stress in birds, it does not always accurately reflect how an animal copes with a stressor. Downstream measurements may be more reliable. In the current study, we tested the hypothesis that acute increases in DNA damage could be used to assess stressor exposure. Stu...
Article
The field of stress physiology has rapidly expanded, particularly in those fields interested in identifying chronic stress in wild animals. Despite this expansion, stress remains difficult to assess and understand, due in large part to the temporal complexities of common stress measurement techniques. While the stress response happens on a short ti...
Article
Neophobia is a behavior characterized by a reluctance to approach novel objects. We measured neophobia in captive wild house sparrows (Passer domesticus) by comparing the time it took for hungry birds to approach their normal food dish compared to one that had been modified with a novel object. We tested the behavior of animals captured at differen...
Article
Wild animals brought into captivity frequently experience chronic stress and typically need a period of time to adjust to the conditions of captivity (restraint, artificial lighting, altered diet, human presence, etc.), to which they may never fully acclimate. Changes in mass, the hypothalamic–pituitary–adrenal axis and heart rate parameters have b...
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Full-text available
Wild animals are brought into captivity for many reasons-conservation, research, agriculture and the exotic pet trade.While the physical needs of animals are met in captivity, the conditions of confinement and exposure to humans can result in physiological stress. The stress response consists of the suite of hormonal and physiological reactions to...
Article
Animals often avoid novel objects, a behavior known as neophobia. We examined behavioral responses of captive European starlings to novel objects placed at their food dishes. Exposure occurred concurrently to food reintroduction following overnight fasting. Behavior was analyzed for 10 min via video recording. We expected an increase in avoidance b...
Article
Wild-caught European starlings (Sturnus vulgaris) were exposed to a learning task to determine whether heart rate (HR) and behavior responses to the learning activated the sympathetic nervous system. Birds learned to discriminate between images of opposite convexity (concave and convex) based on shading cues in a closed economy (food only available...
Article
Corticosterone is widely regarded to be the predominant glucocorticoid produced in amphibians. However, we recently described unusually low baseline and stress-induced corticosterone profiles in eastern hellbenders (Cryptobranchus alleganiensis alleganiensis), a giant, fully aquatic salamander. Here, we hypothesized that hellbenders might also prod...
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Full-text available
Synopsis Reference to glucocorticoids as “stress hormones” has been growing in prevalence in the literature, including in comparative and environmental endocrinology. Although glucocorticoids are elevated in response to a variety of stressors in vertebrate animals, the primary functions of glucocorticoids are not responding to stressors and they ar...
Article
For decades, researchers across disciplines have been captivated by classifying, diagnosing, and avoiding the consequences of chronic stress. Despite the vast body of literature this has generated, we still lack the ability to predict which individuals or populations may be susceptible to stress-related pathologies. One critical unanswered question...
Article
A number of studies have shown that chronic stress can negatively impact both physiology and behavior in a variety of organisms. What has yet to be extensively explored is whether these changes permanently alter an animal's functioning, or if they can be reversed. In this study, we used wild-caught house sparrows (Passer domesticus) to assess how r...
Article
The vertebrate stress response is considered to be a highly conserved suite of responses that are evolved to help animals survive noxious environmental stimuli. The two major pathways of the stress response include the catecholamine release that is part of the autonomic nervous system and comprises the immediate fight-or-flight response, and the sl...
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Investigations focusing on host–ectoparasite interactions in animals have revealed asymptomatic to severe health and fitness consequences suggesting that species mobilize different interspecific response mechanisms. Fewer studies, however, have examined intraspecific responses to ectoparasitic burdens. In this study, we analyzed host health and fit...
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All life requires the capacity to recover from challenges that are as inevitable as they are unpredictable. Understanding this resilience is essential for managing the health of humans and their livestock. It has long been difficult to quantify resilience directly, forcing practitioners to rely on indirect static indicators of health. However, meas...
Article
Acute psychological stress commonly occurs in young and older adults’ lives. Though several studies have examined the influence of stress on how young adults learn new information, the present study is the first to directly examine these effects in older adults. Fifty older adults (M age = 71.9) were subjected to either stress induction or a contro...
Article
Corticosterone does not change in consistent ways across species and contexts, making it challenging to use as an indicator of chronic stress. We assessed DNA damage as a potential metric that could be a more integrative stress measurement with direct links to health. We captured free-living house sparrows, took an immediate blood sample, and trans...
Article
Chronic stress has been extensively studied in both laboratory and field settings; however, a conclusive and consistent phenotype has not been reached. Several studies have reported attenuation of the hypothalamic–pituitary–adrenal axis during experiments intended to cause chronic stress. We sought to determine whether this attenuation could be ind...
Article
There is broad interest in determining repeatability of individual responses. Current methods calculate repeatability of individual points (initial and/or peak), time to peak value, or a single measure of the integrated total response (area under the curve), rather than the shape of the response profile. Repeatability estimates of response profiles...
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Full-text available
In birds, the use of corticosterone (Cort) implants is a frequent tool aimed at simulating systemic elevations of this hormone and studying effects on biological traits (e.g. physiology, morphology, behavior). This manipulation may alter adrenocortical function, potentially changing both baseline (BAS-Cort) and stress-induced (STRESS-Cort) plasma C...
Article
Changes in the environment related to inclement weather can threaten survival and reproductive success both through direct adverse exposure and indirectly by decreasing food availability. Glucocorticoids, released during activation of the hypothalamic-pituitary-adrenal axis as part of the stress response, are an important candidate for linking vert...
Article
The measurement of corticosterone levels in feathers (fCort) is gaining recognition as an effective means for describing links between stages of the annual cycle in birds. Many seabirds are especially good models for exploring these links, or carryover effects, due to their migratory behavior and reproductive investment in a single-egg clutch. Here...
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Despite decades of research, we still lack a complete understanding of what factors influence the transition of the necessary and adaptive acute stress response to what has become known as chronic stress. This gap in knowledge has illuminated the necessity for studies that examine the thresholds between these two sides of the stress response. Here,...
Article
Increased glucocorticoids cause a characteristic stress leukogram in mammalian taxa. It is assumed that avians exhibit a similar response, but to date, there have been no controlled studies to correlate serial endogenous corticosterone levels to hematologic values. An established flock of 18 Hispaniolan Amazon parrots ( Amazona ventralis) was used...
Article
Characterizing the health status and reproductive success of wild populations of sea turtles can be difficult; however, obtaining data to do this can provide important insight into the stability and long-term success of a population. This study examined the use of baseline corticosterone to assess reproductive success of a population of nesting log...
Article
The Common Degu (Octodon degus) is a small rodent endemic to central Chile. It has become an important model for comparative vertebrate endocrinology because of several uncommon life-history features - it is diurnal, shows a high degree of sociality, practices plural breeding with multiple females sharing natal burrows, practices communal parental...
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Full-text available
Repeated exposure to acute stressors causes dramatic changes in an animal's stress physiology and the cumulative effects are often called chronic stress. Recently we showed that short-term exposure to weather-related stimuli, such as temperature change, artificial precipitation, and food restriction, cause acute responses in captive European starli...
Chapter
Many free-living species show seasonal rhythms in baseline and stress-induced glucocorticoid release. Glucocorticoid titers, as well as glucocorticoid-binding proteins (CBG) and intracellular glucocorticoid receptors, vary with different life history stages over the course of the year. Concentrations are often highest during breeding. Seasonal gluc...
Article
The conditions of captivity can cause chronic stress in wild animals. Newly-captured animals may experience weight loss, elevated glucocorticoid hormones, increased heart rate, increased resting adrenomedullary activation, and an altered heart rate response to acute stressors. As captivity conditions persist, chronic stress may decrease as animals...
Article
El Niño Southern Oscillation events (ENSO) and the subsequent opposite weather patterns in the following months and years (La Niña) have major climatic impacts, especially on oceanic habitats, affecting breeding success of both land and sea birds. We assessed corticosterone concentrations from blood samples during standardized protocols of capture,...
Article
In birds, the steroid hormone corticosterone (CORT) increases in response to real or perceived threats to homeostasis. A long-term record of CORT exposure is recorded in feathers when the hormone is incorporated into the keratinized tissue, and then preserved when the mature feather is cut off from the blood supply. The opportunity to retrospective...
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Full-text available
Endocrinologists can make significant contributions to conservation biology by helping to understand the mechanisms by which organisms cope with changing environments. Field endocrine techniques have advanced rapidly in recent years and can provide substantial information on the growth, stress, and reproductive status of individual animals, thereby...
Article
We investigated the relation between environmental mercury exposure and corticosterone concentrations in free-living adult common loons (Gavia immer). We determined blood and feather mercury concentrations and compared them to testosterone, estradiol, and stress-induced plasma corticosterone concentrations. Although neither testosterone nor estradi...
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Full-text available
Visual signals of quality in offspring, such as plumage colour, should honestly advertise need and/or body condition, but links between nutritional status, physiological performance and the expression of colours are complex and poorly understood. We assess how food stress during rearing affected two physiological measures (T-cell mediated immune fu...
Article
Birds need to respond to weather changes quickly and appropriately for their own well-being and survival. The inability to respond appropriately to heat waves can be fatal to individual birds and can translate into large-scale mortality events. We investigated corticosterone (CORT) and heterophil∶lymphocyte (H∶L) ratio responses of budgerigars (Mel...
Article
We investigated the physiology of two closely related albatross species relative to their breeding strategy: black-browed albatrosses ( Thalassarche melanophris ) breed annually, while grey-headed albatrosses ( T. chrysostoma ) breed biennially. From observations of breeding fate and blood samples collected at the end of breeding in one season and...
Article
When wild animals are brought into captivity for the first time, they frequently develop chronic stress symptoms. Animals can develop glucocorticoid dysregulation or changes in the sympathetic nervous system over the course of the first week in captivity. By blocking the action of epinephrine and norepinephrine using α- or β-blockers, we hoped to r...
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Full-text available
Reactive scope predicts that all animals have an adaptive ability to respond to stressors in their environment, termed reactive homeostasis, and that only when an animal's response to stressful stimuli exceeds a certain threshold (homeostatic overload) will stress have pathological effects. While this framework has successfully helped interpret eff...
Article
The recently introduced technique of measuring corticosterone in feathers currently provides the longest-term measure of corticosterone in birds. This review examines the strengths, weaknesses, and unresolved technical issues of the feather corticosterone technique. Feather corticosterone's major strengths are that it provides: a retrospective asse...
Article
Maternal stress and care significantly affect offspring's future behavior and physiology. Studies in laboratory rats have shown that maternal stress decreases maternal care and that low rates of certain maternal behaviors cause offspring to develop hyperreactive stress responses. Plurally breeding rodents that practice communal care, such as degus...
Article
Neophobia, or the fear of novel objects, is a behavior that is often found in wild animals. Neophobia appears to be related to the physiological stress response because individuals with higher glucocorticoid responses to stress often are more neophobic. The relationship between the heart rate response and novelty, however, has not been tested in a...
Article
Chronic stress, potentially through the actions of corticosterone, is thought to directly impair the function of immune cells. However, chronic stress may also have an indirect effect by influencing allocation of energy, ultimately shifting resources away from the immune system. If so, the effects of chronic stress on immune responses may be greate...
Chapter
When thinking of stress in the wild, the authors picture a classic predator/prey scenario, a gazelle being chased across the savanna by a lion or something similar. At this basic level, the physiological and behavioral responses that are initiated when that gazelle perceives that lion are generally thought to be adaptive, helping the animal survive...
Article
Maternal stress and care significantly affect offspring’s future behavior and physiology. Studies in laboratory rats have shown that maternal stress decreases maternal care and that low rates of certain maternal behaviors cause offspring to develop hyperreactive stress responses. Plurally breeding rodents that practice communal care, such as degus...
Article
Full-text available
For many avian species, the decision to initiate breeding is based on information from a variety of environmental cues, including photoperiod, temperature, food availability, and social interactions. There is evidence that the hormone corticosterone may be involved in delaying the onset of breeding in cases where supplemental cues, such as low food...
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Although stress is usually associated with disease, the physiological and behavioral responses to stressors are critical mechanisms of resilience for healthy organisms. A recent workshop comprised of researchers who study healthy humans and both free-living and captive non-human animals identified a number of key roadblocks that are impeding progre...
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While livetrapping is a vital field research tool, it is not a completely unbiased method of sampling. Biased trapping arises during field endocrinological studies whenever hormone levels or response influence the probability of capture of a subject. We repeatedly captured wild, free-living adult degus (Octodon degus) from the same location over 12...
Article
Maternal stress can significantly affect offspring fitness. In laboratory rodents, chronically stressed mothers provide poor maternal care, resulting in pups with hyperactive stress responses. These hyperactive stress responses are characterized by high glucocorticoid levels in response to stressors plus poor negative feedback, which can ultimately...
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Full-text available
Arctic weather in spring is unpredictable and can also be extreme, so Arctic-breeding birds must be flexible in their breeding to deal with such variability. Unpredictability in weather conditions will only intensify with climate change and this in turn could affect reproductive capability of migratory birds. Adjustments to coping strategies are th...
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Full-text available
Because skin is an important physical barrier against pathogens, the ability to quickly and effectively heal wounds directly impacts an animal's health. The hormone corticosterone (CORT) has many complex effects on immune function and can slow wound healing. It has been suggested that CORT's role during wound healing may be to act as a "brake" on i...