Impacts of caffeine on fathead minnow behaviour and physiology.

Pollution from regularly used substances such as pharmaceuticals, cleaning agents, and even food and beverages is an increasing problem in the environment. Caffeine, a commonly ingested stimulant, is one such contaminant that has been detected in aquatic environments worldwide. Yet, little is known about how ecologically relevant concentrations of caffeine influence the morphology, behaviour, and physiology of exposed organisms. To address this knowledge gap, we exposed fathead minnow (Pimephales promelas) to three caffeine treatments: a freshwater control (nominal: 0 ng/L), a low (nominal: 1,000 ng/L) and high environmentally relevant dose (nominal: 10,000 ng/L), for 35 days. We tested the learning abilities, anxiety, metabolic rates, and morphological features of exposed vs. control fish. Caffeine exposure did not affect the ability of fish to learn but did influence anxiety levels. Over the course of repeated anxiety testing, unexposed control fish visited a black square more often while fish exposed to low levels of caffeine did not, potentially indicating that these fish remained in a more anxious state. While caffeine did not impact metabolism, fish growth, or body size, it was associated with lower liver investment-although this response was only observed in our low caffeine treatment. Overall, our results suggest that even relatively low concentrations of caffeine may impact the liver size and anxiety of exposed fish, but further research is needed to assess how extended exposure to caffeine impacts fitness. Given the increase in anthropogenic contaminants in aquatic environments, it is important that we continue to investigate their effects on the organisms exposed to them.

Impacts of Exposure to Ultraviolet Radiation and an Agricultural Pollutant on Morphology and Behavior of Tadpoles (Limnodynastes tasmaniensis).

Amphibians are the most threatened vertebrate class globally. Multiple factors have been implicated in their global decline, and it has been hypothesized that interactions between stressors may be a major cause. Increased ultraviolet (UV) radiation, as a result of ozone depletion, has been identified as one such stressor. Exposure to UV radiation has been shown to have detrimental effects on amphibians and can exacerbate the effects of other stressors, such as chemical pollutants. Chemical pollution has likewise been recognized as a major factor contributing to amphibian declines, particularly, endocrine-disrupting chemicals. In this regard, 17ß-trenbolone is a potent anabolic steroid used in the agricultural industry to increase muscle mass in cattle and has been repeatedly detected in the environment where amphibians live and breed. At high concentrations, 17ß-trenbolone has been shown to impact amphibian survival and gonadal development. In the present study, we investigated the effects of environmentally realistic UV radiation and 17ß-trenbolone exposure, both in isolation and in combination, on the morphology and behavior of tadpoles (Limnodynastes tasmaniensis). We found that neither stressor in isolation affected tadpoles, nor did we find any interactive effects. The results from our 17ß-trenbolone treatment are consistent with recent research suggesting that, at environmentally realistic concentrations, tadpoles may be less vulnerable to this pollutant compared to other vertebrate classes. The absence of UV radiation-induced effects found in the present study could be due to species-specific variation in susceptibility, as well as the dosage utilized. We suggest that future research should incorporate long-term studies with multiple stressors to accurately identify the threats to, and subsequent consequences for, amphibians under natural conditions. Environ Toxicol Chem 2024;43:1615-1626. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Leveraging AI to improve evidence synthesis in conservation.

Systematic evidence syntheses (systematic reviews and maps) summarize knowledge and are used to support decisions and policies in a variety of applied fields, from medicine and public health to biodiversity conservation. However, conducting these exercises in conservation is often expensive and slow, which can impede their use and hamper progress in addressing the current biodiversity crisis. With the explosive growth of large language models (LLMs) and other forms of artificial intelligence (AI), we discuss here the promise and perils associated with their use. We conclude that, when judiciously used, AI has the potential to speed up and hopefully improve the process of evidence synthesis, which can be particularly useful for underfunded applied fields, such as conservation science.

Transhumeral prosthesis use affects upper body kinematics and kinetics.

BACKGROUND: Transhumeral (TH) limb loss leads to loss of body mass and reduced shoulder range of motion. Despite most owning a prosthesis, prosthesis abandonment is common. The consequence of TH limb loss and prosthesis use and disuse during gait may be compensation in the upper body, contributing to back pain or injury. Understanding the impact of not wearing a TH prosthesis on upper body asymmetries and spatial-temporal aspects of gait will inform how TH prosthesis use and disuse affects the body. RESEARCH QUESTION: Does TH limb loss alter upper body asymmetries and spatial-temporal parameters during gait when wearing and not wearing a prosthesis compared to able-bodied controls? METHODS: Eight male TH limb loss participants and eight male control participants completed three gait trials at self-selected speeds. The TH limb loss group performed trials with and without their prosthesis. Arm swing, trunk angular displacement, trunk-pelvis moment, and spatial-temporal aspects were compared using non-parametric statistical analyses. RESULTS: Both TH walking conditions showed greater arm swing in the intact limb compared to the residual (p≤0.001), resulting in increased asymmetry compared to the control group (p≤0.001). Without the prosthesis, there was less trunk flexion and lateral flexion compared to the control group (p≤0.001). Maximum moments between the trunk and pelvis were higher in the TH group than the control group (p≤0.05). Spatial-temporal parameters of gait did not differ between the control group and either TH limb loss condition. SIGNIFICANCE: Prosthesis use affects upper body kinematics and kinetics, but does not significantly impact spatial-temporal aspects of gait, suggesting these are compensatory actions. Wearing a prosthesis helps achieve more normative upper body kinematics and kinetics than not wearing a prosthesis, which may help limit back pain. These findings emphasize the importance of encouraging at least passive use of prostheses for individuals with TH limb loss.

Evaluating the Efficacy of Time for Living and Caring: An Online Intervention to Support Dementia Caregivers' Use of Respite.

Background and Objectives: Respite, defined as time away from caregiving, is the most requested type of caregiver support. Time for Living and Caring (TLC) is a virtual coaching "app" that helps caregivers schedule and plan their respite time-use. The objectives of this analysis are: (1) to assess the efficacy of the TLC intervention on respite time-use and on caregiver well-being and (2) to identify the key features of the intervention that serve as the likely mechanism of action. Research Design and Methods: A sample of dementia caregivers (n = 163, 79% female, 84% White, 6% Hispanic, average age 62) were randomized into one of two intervention delivery methods. Intervention efficacy was evaluated using pre/post-comparisons of respite time-use and an additive "dosing" model that estimated unique parameters associated with the exposure to each specific intervention component. Results: Both immediate and delayed-attention groups reported increased respite time. They also improved in their ability to plan and perceive benefit from their respite time-use over the 16-week intervention period. At 8 weeks, the immediate group did not change in anxiety, whereas the delayed group worsened (p < .001). At 16 weeks, the groups were similar in their anxiety levels. By the 20-week follow-up period, when neither group had access to TLC, both experienced an increase in anxiety. Discussion and Implications: TLC is a promising intervention that may support caregivers' well-being, by helping them schedule and plan their respite to maximize its benefit. The provision of weekly coaching seems to be the intervention component (mechanism) associated with caregiver outcomes. Clinical Trial Registration: NCT03689179.

Sexual Selection Increases Male Behavioral Consistency in Drosophila melanogaster.

AbstractSexual selection has been suggested to influence the expression of male behavioral consistency. However, despite predictions, direct experimental support for this hypothesis has been lacking. Here, we investigated whether sexual selection altered male behavioral consistency in Drosophila melanogaster-a species with both pre- and postcopulatory sexual selection. We took 1,144 measures of locomotor activity (a fitness-related trait in D. melanogaster) from 286 flies derived from replicated populations that have experimentally evolved under either high or low levels of sexual selection for >320 generations. We found that high sexual selection males were more consistent (decreased within-individual variance) in their locomotor activity than male conspecifics from low sexual selection populations. There were no differences in behavioral consistency between females from the high and low sexual selection populations. Furthermore, while females were more behaviorally consistent than males in the low sexual selection populations, there were no sex differences in behavioral consistency in high sexual selection populations. Our results demonstrate that behavioral plasticity is reduced in males from populations exposed to high levels of sexual selection. Disentangling whether these effects represent an evolved response to changes in the intensity of selection or are manifested through nongenetic parental effects represents a challenge for future research.

Dissemination innovation: Using found poetry to return study results to patients and partners facing cancer.

Objective: Investigators should return study results to patients and families facing cancer to honor their research contributions. We created a found poem from transcripts of sexual and gender minority (SGM) couples facing cancer and returned it to study participants. Methods: Participants were randomized to receive the found poem in text, text and audio, audio, or video format, completed dissemination preferences and emotion questionnaires, and open-ended questions about their experience receiving the poem. Results: Participants preferred the format they received (n = 15, 75.0%), with text-only and combined text and audio formats evoking the greatest number of emotions (n = 13 each). The following categories and subcategories were identified: dyadic experiences (support, strength, depth, durability); dissemination preferences (timing, method); emotion (positive, negative); utility of the found poem (affirming; fostering reflection; not useful or inaccurate, and sense of community). SGM participants utilized positive emotion, affirming, and a sense of community with greater frequency than non-SGM participants. Conclusion: Innovative approaches to dissemination are acceptable; providing choices in how and when participants receive results may increase engagement; and SGM versus non-SGM groups may describe dyadic experiences differently. Innovation: Returning study results via found poetry is an innovative way to honor research participants facing cancer.

The Impact of Design Factors on User Behavior in a Virtual Hospital Room to Explore Fall Prevention Strategies.

OBJECTIVES: Falls in hospitals pose a significant safety risk, leading to injuries, prolonged hospitalization, and lasting complications. This study explores the potential of augmented reality (AR) technology in healthcare facility design to mitigate fall risk. BACKGROUND: Few studies have investigated the impact of hospital room layouts on falls due to the high cost of building physical prototypes. This study introduces an innovative approach using AR technology to advance methods for healthcare facility design efficiently. METHODS: Ten healthy participants enrolled in this study to examine different hospital room designs in AR. Factors of interest included room configuration, door type, exit side of the bed, toilet placement, and the presence of IV equipment. AR trackers captured trajectories of the body as participants navigated through these AR hospital layouts, providing insights into user behavior and preferences. RESULTS: Door type influenced the degree of backward and sideways movement, with the presence of an IV pole intensifying the interaction between door and room type, leading to increased sideways and backward motion. Participants displayed varying patterns of backward and sideways travel depending on the specific room configurations they encountered. CONCLUSIONS: AR can be an efficient and cost-effective method to modify room configurations to identify important design factors before conducting physical testing. The results of this study provide valuable insights into the effect of environmental factors on movement patterns in simulated hospital rooms. These results highlight the importance of considering environmental factors, such as the type of door and bathroom location, when designing healthcare facilities.

Pairing automated exercise coaching with patient-reported symptom monitoring: A way to nudge exercise uptake during cancer treatment?

INTRODUCTION: Symptoms during cancer treatment cause burden, diminished physical functioning, and poor quality of life. Exercise is recommended during treatment to mitigate symptoms; however, interventions are difficult to translate into clinical care due to the lack of patient uptake and clinical implementation barriers. We evaluated the uptake, acceptability, and impact of an automated ePRO exercise module triggered by three patient-reported symptoms: nausea/vomiting, fatigue, and anxiety, during chemotherapy. METHODS: We conducted a secondary analysis of an exercise module intervention imbedded in the cancer symptom monitoring and management platform, Symptom Care at Home (SCH). Utilizing behavioral economics principles, the exercise module was triggered when any of the three symptoms were reported. Once triggered, participants were coached on exercise benefits for symptom reduction and then offered the opportunity to set weekly exercise goals plus tracking of the goal outcomes and receive further encouragement. We examined uptake, exercise goal setting and attainment, and symptom impact. RESULTS: Of 180 SCH participants receiving the SCH intervention, 170 (94.4%) triggered the exercise module and 102 of the 170 (60%) accepted the module, setting goals on average for 6.3 weeks. Of 102 participants, 82 (80.4%) achieved one or more exercise goals, exercising on average 79.8 min/week. Participants who achieved a higher proportion of goals had statistically significant lower overall symptom severity and lower severity of the triggered symptom. CONCLUSION: An automated mHealth exercise coaching intervention, aimed to nudge those receiving chemotherapy to initiate an exercise routine had significant uptake, is acceptable and may reduce symptom severity. TRIAL REGISTRATION: NCT01973946.

Sexual selection and speciation in the Anthropocene.

Anthropogenic change threatens global biodiversity by causing severe ecological disturbance and extinction. Here, we consider the effects of anthropogenic change on one process that generates biodiversity. Sexual selection (a potent evolutionary force and driver of speciation) is highly sensitive to the environment and, thus, vulnerable to anthropogenic ecological change. Anthropogenic alterations to sexual display and mate preference can make it harder to distinguish between conspecific and heterospecific mates or can weaken divergence via sexual selection, leading to higher rates of hybridization and biodiversity loss. Occasionally, anthropogenically altered sexual selection can abet diversification, but this appears less likely than biodiversity loss. In our rapidly changing world, a full understanding of sexual selection and speciation requires a global change perspective.

Travel Distance Between Participants in US Telemedicine Sessions With Estimates of Emissions Savings: Observational Study.

BACKGROUND: Digital health and telemedicine are potentially important strategies to decrease health care's environmental impact and contribution to climate change by reducing transportation-related air pollution and greenhouse gas emissions. However, we currently lack robust national estimates of emissions savings attributable to telemedicine. OBJECTIVE: This study aimed to (1) determine the travel distance between participants in US telemedicine sessions and (2) estimate the net reduction in carbon dioxide (CO2) emissions attributable to telemedicine in the United States, based on national observational data describing the geographical characteristics of telemedicine session participants. METHODS: We conducted a retrospective observational study of telemedicine sessions in the United States between January 1, 2022, and February 21, 2023, on the doxy.me platform. Using Google Distance Matrix, we determined the median travel distance between participating providers and patients for a proportional sample of sessions. Further, based on the best available public data, we estimated the total annual emissions costs and savings attributable to telemedicine in the United States. RESULTS: The median round trip travel distance between patients and providers was 49 (IQR 21-145) miles. The median CO2 emissions savings per telemedicine session was 20 (IQR 8-59) kg CO2). Accounting for the energy costs of telemedicine and US transportation patterns, among other factors, we estimate that the use of telemedicine in the United States during the years 2021-2022 resulted in approximate annual CO2 emissions savings of 1,443,800 metric tons. CONCLUSIONS: These estimates of travel distance and telemedicine-associated CO2 emissions costs and savings, based on national data, indicate that telemedicine may be an important strategy in reducing the health care sector's carbon footprint.

No effect of testosterone or sexual ornamentation on telomere dynamics: A case study and meta-analyses.

Life-history theory predicts that reproductive investments are traded-off against self-maintenance. Telomeres, the protective caps on the ends of chromosomes, offer a promising avenue for assessing life-history trade-offs, as they shorten in response to stressors and are predictive of the remaining lifespan. In males, testosterone frequently mediates life-history trade-offs, in part, through its effects on sexual ornamentation, which is an important aspect of reproductive investment. However, studies of within-individual associations between telomere dynamics and sexual ornamentation are limited in number and have produced mixed results. Furthermore, most such studies have been observational, making it difficult to discern the nature of any causal relationship. To address this, we used short-acting testosterone implants in free-living male superb fairy-wrens (Malurus cyaneus) to stimulate the production of a sexual ornament: early moult into a costly blue breeding plumage. We found no evidence that elevated testosterone, and the consequent earlier moult into breeding plumage, accelerated telomere shortening. We therefore followed up with a systematic review and two meta-analyses (28 studies, 54 effect sizes) exploring the associations between telomeres and (1) testosterone and (2) sexual ornamentation. In line with our experimental findings, neither meta-analysis showed an overall correlation of testosterone or sexual ornamentation with telomere length or telomere dynamics. However, meta-regression showed that experimental, compared to observational, studies reported greater evidence of trade-offs. Our meta-analyses highlight the need for further experimental studies to better understand potential responses of telomere length or telomere dynamics to testosterone or sexual ornamentation.

Size dependent antipredator responses in a fish-shrimp mutualism.

For prey, taking refuge from predators has obvious fitness benefits but may also be costly by impinging on time and effort available for feeding or attracting mates. The antipredator responses of refuge-seeking animals are therefore predicted to vary strategically depending on how threatening they perceive the risk. To test this, we studied the impacts of a simulated predatory threat on the antipredator responses of wild sandy prawn-gobies (Ctenogobiops feroculus) that co-inhabit burrows with Alpheus shrimp (family Alpheidae) in a mutualistic relationship. We exposed goby-shrimp pairs, repeatedly on three separate occasions, to an approaching threat and measured the antipredator behaviours of both partners. We found that re-emerging from the burrow took longer in large compared to small fish. Moreover, quicker re-emergence by small-but not medium or large-sized gobies-was associated with an earlier flight from the approaching threat (i.e. when the threat was still further away). Finally, the goby and shrimp sharing a burrow were matched in body size and their risk-taking behaviour was highly dependent on one another. The findings contribute to our understanding of how an individual's phenotype and perception of danger relates to its risk-taking strategy, and how mutualistic partners can have similar risk sensitivities.

Extended physiological proprioception is affected by transhumeral Socket-Suspended prosthesis use.

The objective of this study was to define targeted reaching performance without visual information for transhumeral (TH) prosthesis users, establishing baseline information about extended physiological proprioception (EPP) in this population. Subjects completed a seated proprioceptive targeting task under simultaneous motion capture, using their prosthesis and intact limb. Eight male subjects, median age of 58 years (range 29-77 years), were selected from an ongoing screening study to participate. Five subjects had a left-side TH amputation, and three a right-side TH amputation. Median time since amputation was 9 years (range 3-54 years). Four subjects used a body-powered prosthetic hook, three a myoelectric hand, and one a myoelectric hook. The outcome measures were precision and accuracy, motion of the targeting hand, and joint angular displacement. Subjects demonstrated better precision when targeting with their intact limb compared to targeting with their prosthesis, 1.9 cm2 (0.8-3.0) v. 7.1 cm2 (1.3-12.8), respectively, p = 0.008. Subjects achieved a more direct reach path ratio when targeting with the intact limb compared to with the prosthesis, 1.2 (1.1-1.3) v. 1.3 (1.3-1.4), respectively, p = 0.039 The acceleration, deceleration, and corrective phase durations were consistent between conditions. Trunk angular displacement increased in flexion, lateral flexion, and axial rotation while shoulder flexion decreased when subjects targeted with their prosthesis compared to the intact limb. The differences in targeting precision, reach patio ratio, and joint angular displacements while completing the targeting task indicate diminished EPP. These findings establish baseline information about EPP in TH prosthesis users for comparison as novel prosthesis suspension systems become more available to be tested.

Comparison of recruitment methodologies for clinical trials: Results from the time for living and caring (TLC) intervention study.

BACKGROUND: Recruiting participants for research studies is a critical yet challenging task. Community-engaged recruitment strategies have gained prominence as effective means to engage diverse populations and ensure the representativeness of study samples. This case study aims to investigate the cost and effectiveness of various recruitment methods in enhancing research participation. METHODS: A comparative approach was employed to assess the outcomes of five different recruitment strategies used in the Time for Living & Caring (TLC) research study. Data on recruitment success, participant demographics, and retention rates were collected and analyzed using descriptive statistics, including ANOVA and Chi-squares, to statistically compare the outcomes associated with 5 different recruitment methodologies. The recruitment methodologies included two community-engaged strategies (community partner referral and community-based recruiters), a clinical database, social media, and word-of-mouth referral. CONCLUSION: The meta-data used to build this methodological case study describe different recruitment methodologies that may be used for clinical trials. This data-driven evaluation provides examples and considerations for researchers when developing budgets and proposals for future clinical trials. The primary finding is that there are tradeoffs in terms of cost, time, labor, and ultimately the representativeness of the sample, based on the type of recruitment methodology chosen.

A Secondary Data Analysis of Technology Access as a Determinant of Health and Impediment in Social Needs Screening and Referral Processes.

Introduction: Although health systems increasingly integrate social needs screening and referrals into routine care, the effectiveness of these interventions and for whom they work remains unclear. Methods: Patients (N=4,608) seen in the emergency department were screened for social needs (e.g., transportation, housing, food) and offered an opportunity to receive outreach from community service specialists. Results: Among 453 patients with 1 or more social needs who requested assistance, outreach specialists connected with 95 (21.0%). Patients preferred to be contacted through their telephone (n=21, 60.2%), email (n=126, 28.0%), someone else's telephone (n=30, 6.7%), or first by telephone followed by email (n=23, 5.1%). Preferred contact method varied by patient age; endorsement of unmet transportation, housing, and utility needs; receipt of service outreach; and differences in emergency department utilization from the 6 months before the index visit to the 6 months after. Conclusions: Because limited access to a stable telephone or internet connection may prevent patients from connecting with resource referrals, social needs interventions may not benefit the most underserved populations who are at the highest risk of negative health outcomes. Future research should investigate whether communication preferences are an important indicator of needs and how to adapt social needs screening and referral processes so that they are more accessible to populations who may experience more frequent disruptions in methods utilized for digital communication.

Using Digital Inequality Framework to Evaluate a Technology-Delivered Intervention for Caregivers: Age, Education, and Computer Proficiency.

Objectives: Using "digital inequality" as a conceptual framework, this study evaluates the feasibility and usability of a technology-delivered intervention (an "app") for Alzheimer's and related dementia family caregivers. Time for Living and Caring (TLC) is an on-line intervention that provides virtual coaching and self-administered education and resources. Methods: A sample of family caregivers (n = 163) used the tool for 16 weeks, which included completing the Computer Proficiency Questionnaire (CPQ-12) at baseline. Analyses investigate the relationship between age, CPQ scores, intervention use, appraisal, and caregiver outcomes. Results: Age was inversely associated with CPQ; however, CPQ scores did not have a significant relationship with participant's self-perceived benefits or intervention appraisal. Computer Proficiency Questionnaire scores provided insight regarding research feasibility, with lower scores associated with greater odds of discontinuing engagement. Discussion: CPQ-12 scores can be used as a screening tool to identify those who may need additional support to engage with and benefit from technology-delivered interventions.

Convergent genomic signatures associated with vertebrate viviparity.

BACKGROUND: Viviparity-live birth-is a complex and innovative mode of reproduction that has evolved repeatedly across the vertebrate Tree of Life. Viviparous species exhibit remarkable levels of reproductive diversity, both in the amount of care provided by the parent during gestation, and the ways in which that care is delivered. The genetic basis of viviparity has garnered increasing interest over recent years; however, such studies are often undertaken on small evolutionary timelines, and thus are not able to address changes occurring on a broader scale. Using whole genome data, we investigated the molecular basis of this innovation across the diversity of vertebrates to answer a long held question in evolutionary biology: is the evolution of convergent traits driven by convergent genomic changes? RESULTS: We reveal convergent changes in protein family sizes, protein-coding regions, introns, and untranslated regions (UTRs) in a number of distantly related viviparous lineages. Specifically, we identify 15 protein families showing evidence of contraction or expansion associated with viviparity. We additionally identify elevated substitution rates in both coding and noncoding sequences in several viviparous lineages. However, we did not find any convergent changes-be it at the nucleotide or protein level-common to all viviparous lineages. CONCLUSIONS: Our results highlight the value of macroevolutionary comparative genomics in determining the genomic basis of complex evolutionary transitions. While we identify a number of convergent genomic changes that may be associated with the evolution of viviparity in vertebrates, there does not appear to be a convergent molecular signature shared by all viviparous vertebrates. Ultimately, our findings indicate that a complex trait such as viviparity likely evolves with changes occurring in multiple different pathways.

Pharmaceutical pollution alters the cost of bacterial infection and its relationship to pathogen load.

The relationship between pathogen proliferation and the cost of infection experienced by a host drives the ecology and evolution of host-pathogen dynamics. While environmental factors can shape this relationship, there is currently limited knowledge on the consequences of emerging contaminants, such as pharmaceutical pollutants, on the relationship between a pathogen's growth within the host and the damage it causes, termed its virulence. Here, we investigated how exposure to fluoxetine (Prozac), a commonly detected psychoactive pollutant, could alter this key relationship using the water flea Daphnia magna and its bacterial pathogen Pasteuria ramosa as a model system. Across a variety of fluoxetine concentrations, we found that fluoxetine shaped the damage a pathogen caused, such as the reduction in fecundity or intrinsic growth experienced by infected individuals, but with minimal change in average pathogen spore loads. Instead, fluoxetine modified the relationship between the degree of pathogen proliferation and its virulence, with both the strength of this trade-off and the component of host fitness most affected varying by fluoxetine concentration and host genotype. Our study underscores the potential for pharmaceutical pollution to modify the virulence of an invading pathogen, as well as the fundamental trade-off between host and pathogen fitness, even at the trace amounts increasingly found in natural waterways.

Mitochondrial genetic variation as a potential mediator of intraspecific behavioural diversity.

Mitochondrial genes play an essential role in energy metabolism. Variation in the mitochondrial DNA (mtDNA) sequence often exists within species, and this variation can have consequences for energy production and organismal life history. Yet, despite potential links between energy metabolism and the expression of animal behaviour, mtDNA variation has been largely neglected to date in studies investigating intraspecific behavioural diversity. We outline how mtDNA variation and interactions between mitochondrial and nuclear genotypes may contribute to the expression of individual-to-individual behavioural differences within populations, and why such effects may lead to sex differences in behaviour. We contend that integration of the mitochondrial genome into behavioural ecology research may be key to fully understanding the evolutionary genetics of animal behaviour.