Upset in response to a Sibling’s partner’s infidelities

Using data collected from people with at least one brother and one sister, and consistent with an evolutionary perspective, we find that older men and women (a) are more upset by a brother’s partner’s sexual infidelity than by her emotional infidelity and (b) are more upset by a sister’s partner’s emotional infidelity than by his sexual infidelity. There were no effects of participant sex or sex of in-law on upset over a sibling’s partner’s infidelities, but there was an effect of participant sex on reports of upset over one’s own partner’s infidelities. The results suggest that the key variable among older participants is the sex of the sibling or, correspondingly, the sex of the sibling’s partner, as predicted from an evolutionary analysis of reproductive costs, and not the sex of the participant, as predicted from a socialization perspective. Discussion offers directions for future work on jealousy.     

Gender differences in sexual jealousy: Adaptionist or social learning explanation?

It has often been speculated, and some evidence suggests, that men and women differ in the elicitation of jealousy: Men appear to be more likely than women to become upset over threats to sexual exclusivity; whereas women are more likely than men to react negatively to potential loss of partner time and attention. Both adaptionist and traditional social learning theories have been used to explain these apparent gender differences. In the present article we outline both explanations and review the relevant psychological literature on gender differences in the elicitation of jealousy. We propose that the difference in men's and women's psychological mechanisms for elicitation of jealousy is best characterized (at least in this culture) as a greater sensitivity among men to cues indicative of possible sexual infidelity rather than greater emotional upset in response to the occurence of extradyadic sex on the part of one's mate. We also provide data testing a traditional social learning explanation for the elicitation of jealousy. Results of a survey administered to college students (N = 223) demonstrate the subtle nature of gender differences in the elicitation of jealousy within this culture. Men and women were most likely to differ (in the hypothesized directions) when items pertained to concern over a partner's potential extradyadic sex rather than to reactions to sexual infidelity that is suspected to have already occurred. Although men reported placing more value on sexual activity within dating relationships and women reported placing more value on emotional intimacy, these ratings of relationship rewards did not explain the gender differences in reported jealousy. Results failed to support a traditional social learning explanation of jealousy and are discussed with regard to evolutionary theory and directions for future research.     

Sex (similarities and) differences in friendship jealousy

Friendships provide material benefits, bolster health, and may help solve adaptive challenges. However, a recurrent obstacle to sustaining those friendships—and thus enjoying many friendship-mediated fitness benefits—is interference from other people. Friendship jealousy may be well-designed for helping both men and women meet the recurrent, adaptive challenge of retaining friends in the face of such third-party interference. Although we thus expect several sex similarities in the general cognitive architecture of friendship jealousy (e.g., it is attuned to friend value), there are also sex differences in friendship structures and historical functions, which might influence the inputs of friendship jealousy (e.g., the value of any one friendship). If so, we should also expect some sex differences in friendship jealousy. Findings from a reanalysis of previously-published data and a new experiment, including both U.S. student and adult community participants (N = 993), provide initial support for three predicted sex differences: women (versus men) report greater friendship jealousy at the prospective loss of best friends to others, men (versus women) report greater friendship jealousy at the prospective loss of acquaintances to others, and men's (but not women's) friendship jealousy is enhanced in the context of intergroup contests.     

Sex differences (and similarities) in jealousy: The moderating influence of infidelity experience and sexual orientation of the infidelity

Past demonstrations of sex differences in jealousy have generally employed Buss et al.'s [Psychol. Sci. 3 (1992) 251] forced-choice methodology, a limitation criticized by DeSteno and Salovey [Psychol. Sci. 7 (1996) 367]. The present studies address this criticism by demonstrating the sex difference using both forced-choice and continuous measures of jealousy. In addition, the results distinguish two important moderators of the sex difference: infidelity experience, in which male victims and female perpetrators of infidelity reported greater distress in response to a sexual infidelity, and sexual orientation of the infidelity, in which the sex difference disappears completely when an infidelity carries no risk of conception because an opposite-sex partner has become involved with a same-sex lover.     

The impact of slow stomatal kinetics on photosynthesis and water use efficiency under fluctuating light

Dynamic light conditions require continuous adjustments of stomatal aperture. The kinetics of stomatal conductance (g_s) is hypothesized to be key to plant productivity and water use efficiency (WUE). Using step-changes in light intensity, we studied the diversity of light-induced g_s kinetics in relation to stomatal anatomy in five banana genotypes (Musa spp.) and modeled the impact of both diffusional and biochemical limitations on photosynthesis (A). The dominant A limiting factor was the diffusional limitation associated with g_s kinetics. All genotypes exhibited a strong limitation of A by g_s, indicating a priority for water saving. Moreover, significant genotypic differences in g_s kinetics and g_s limitations of A were observed. For two contrasting genotypes, the impact of differential g_s kinetics was further investigated under realistic diurnally fluctuating light conditions and at the whole-plant level. Genotype-specific stomatal kinetics observed at the leaf level was corroborated at whole-plant level by transpiration dynamics, validating that genotype-specific responses are still maintained despite differences in g_s control at different locations in the leaf and across leaves. However, under diurnally fluctuating light conditions the impact of g_s speediness on A and intrinsic (_iWUE) depended on time of day. During the afternoon there was a setback in kinetics: absolute g_s and g_s responses to light were damped, strongly limiting A and impacting diurnal _iWUE. We conclude the impact of differential g_s kinetics depended on target light intensity, magnitude of change, g_s prior to the change in light intensity, and particularly time of day.     

Sexual jealousy as a facultative trait: Evidence from the pattern of sex differences in adults from China and the United States

Across two studies, 716 and 308 undergraduate students from the United States and mainland China, respectively, were administered a series of measures on jealousy, emotional responses to partner infidelity, family background, and personality. Across both studies for the U.S. and Chinese samples, a higher proportion of males than females reported more distress to a partner's imagined sexual infidelity than to emotional infidelity, whereas a higher proportion of females than males reported more distress to a partner's emotional infidelity than to sexual infidelity, consistent with theoretical expectations and previous empirical research. However, a much higher proportion of U.S. males and females reported more distress to sexual infidelity than their same-sex Chinese peers, suggesting that the tendency toward sexual jealousy might be facultatively influenced by sexual permissiveness in the general culture. The overall pattern of results is considered in terms of individual and contextual differences in the expression of jealousy, as well as in terms of the emotional and behavioral responses associated with jealousy reactions.     

Morbid Jealousy and Sex Differences in Partner-Directed Violence

Previous research suggests that individuals diagnosed with morbid jealousy have jealousy mechanisms that are activated at lower thresholds than individuals with normal jealousy, but that these mechanisms produce behavior that is similar to individuals with normal jealousy. We extended previous research documenting these similarities by investigating sex differences in partner-directed violence committed by individuals diagnosed with morbid jealousy. The results support some of our predictions. For example, a greater percentage of men than women diagnosed with morbid jealousy used physical violence, attempted to kill, and actually killed their partners, and used their hands rather than an object to kill their partners. These results replicate results generated for individuals with normal jealousy. Discussion addresses implications of the current research and highlights directions for future research on the psychology of morbid jealousy.

An integrative study of facultative personality calibration

The theory of facultative calibration, which explains personality differences as responses to variation in other phenotypic traits of individuals, received mixed results throughout the last years. Whereas there is strong evidence that individual differences in human behavior are correlated with the self-perception of other traits, it still needs to be questioned whether they are also adjusted to objective differences in body condition (i.e. formidability). In two independent studies (N₁?=?119 men and 124 women, N₂?=?165 men) we tested hypotheses of facultative personality calibration in an integrative way, assessing various outcomes of previous studies in the same samples (including Anger Proneness, Extraversion, Neuroticism, Narcissism, Shyness, Vengefulness, and Sociosexual Orientation). Formidability was derived from assessments of physical strength and various anthropometric measures from full-body 3D scans and paired with measures of self-perceived and other-rated physical attractiveness (based on rotating morphometric 3D body models and facial photographs). We could replicate positive correlations with self-perceived attractiveness across outcomes, though these were not corroborated by more objective assessments of attractiveness: an effect of other-rated attractiveness was clearly not supported in our results for either sex, regardless of the personality outcome. Anthropometric measures and physical strength were also largely unrelated to personality, with the exception of Extraversion, Utility of Personal Aggression, and Sociosexual Orientation. While the two samples differed in their results for domain-level Extraversion, at least the Extraversion facets Activity and Assertiveness were related to strength and masculinity in men. For Sociosexual Orientation the results of our two samples varied more substantially, a positive association was only present in Study 2. Future studies need to clarify whether formidability, potentially an indicator of genetic quality for males, enhances their orientation and success in short-term mating. Furthermore we propose longitudinal twin-difference studies as means to evaluate the theory of personality recalibration in a more controlled manner.     

Mate selection criteria: A pilot study

Open-ended questions were used to investigate mate selection criteria among male and female medical students (n = 40). Striking sex differences emerged in this sample's preferences concerning spouses' relative earning power and occupational status, partners' physical attractiveness, and the marital division of labor. The results supported the hypotheses: Increasing socioeconomic status (SES) of women does not eliminate and may not even reduce traditional sex differences in mate selection criteria and marital goals. Increasing the SES of women tends to increase their socioeconomic standards for mates, thereby reducing their pool of acceptable partners; increasing men's SES tends to enlarge their pool of available acceptable partners. Based on these interviews and pertinent literature, closed-ended questions were developed and administered to female (n = 212) and male (n = 170) undergraduates. Highly significant sex differences emerged in this sample; these sex differences mirrored those found among the medical students. The methodological implications of these results are discussed.     

Demographic patterns of human antibody levels to Simulium damnosum s.l. saliva in onchocerciasis-endemic areas: An indicator of exposure to vector bites

BackgroundIn onchocerciasis endemic areas in Africa, heterogenous biting rates by blackfly vectors on humans are assumed to partially explain age- and sex-dependent infection patterns with Onchocerca volvulus. To underpin these assumptions and further improve predictions made by onchocerciasis transmission models, demographic patterns in antibody responses to salivary antigens of Simulium damnosum s.l. are evaluated as a measure of blackfly exposure.Methodology/Principal findingsRecently developed IgG and IgM anti-saliva immunoassays for S. damnosum s.l. were applied to blood samples collected from residents in four onchocerciasis endemic villages in Ghana. Demographic patterns in antibody levels according to village, sex and age were explored by fitting generalized linear models. Antibody levels varied between villages but showed consistent patterns with age and sex. Both IgG and IgM responses declined with increasing age. IgG responses were generally lower in males than in females and exhibited a steeper decline in adult males than in adult females. No sex-specific difference was observed in IgM responses.Conclusions/SignificanceThe decline in age-specific antibody patterns suggested development of immunotolerance or desensitization to blackfly saliva antigen in response to persistent exposure. The variation between sexes, and between adults and youngsters may reflect differences in behaviour influencing cumulative exposure. These measures of antibody acquisition and decay could be incorporated into onchocerciasis transmission models towards informing onchocerciasis control, elimination, and surveillance.     

No evidence for sexual dimorphism of facial width-to-height ratio in four large adult samples

Sexual dimorphism in physical appearance may be an important cue in both intra- and intersex competition. Recently, the facial width-to-height ratio (fWHR) has been proposed as a novel sexually dimorphic morphologic measure, with men suggested to have a higher fWHR than women. Currently, however, the status of fWHR as a sexually dimorphic trait is unclear. Here we tested for sexual dimorphism in fWHR, as well as in three additional, previously reported facial measures, in four (three Caucasian and one African) independent samples. In three of the four samples, no significant sex differences in fWHR were observed. In one sample, males showed a significantly lower (rather than higher) fWHR than females (this effect was no longer significant after controlling for body mass index). By contrast, significant and large sex differences were observed in all four samples for each of the three previously validated facial metrics, namely, (a) lower face/face height, (b) cheekbone prominence, and (c) face width/lower face height. These results provide strong evidence against the claim that fWHR, at least as measured from the surface of the face, is sexually dimorphic.     

Biological and molecular responses of Chironomus riparius (Diptera,Chironomidae) to herbicide 2,4-D (2,4-dichlorophenoxyacetic acid)

2,4-Dichlorophenoxyacetic acid (2,4-D) is an agricultural contaminant found in rural ground water. It remains to be determined whether neither 2,4-D poses environmental risks, nor is the mechanism of toxicity known at the molecular level. To evaluate the potential ecological risk of 2,4-D, we assessed the biological parameters including the survival rate, adult sex ratio of emerged adults, and mouthpart deformities in Chironomus riparius after long-term exposure to 2,4-D. The larvae were treated with 0.1, 1 or, 10 μg L^? 1 of 2,4-D for short- and long-term exposure periods. The sex ratio was changed in C. riparius exposed to only 10 μg L^? 1 of 2,4-D, whereas mouthpart deformities were observed as significantly higher in C. riparius exposed to 0.1 μg L^? 1 of 2,4-D. Survival rates were not significantly affected by 2,4-D. Furthermore, we evaluated the molecular and biochemical responses of biomarker genes such as gene expression of heat shock proteins (HSPs), ferritins and glutathione S-transferases (GSTs) in C. riparius exposed to 2,4-D for 24 h. The expressions of HSP70, HSP40, HSP90 and GST levels in C. riparius were significantly increased after exposure to a 10 μg L^? 1 concentration of 2,4-D, whereas ferritin heavy and light chain gene expressions were significantly increased at all concentrations of 2,4-D exposure. Finally, these results may provide an important contribution to our understanding of the toxicology of 2,4-D herbicide in C. riparius. Moreover, the 2,4-D-mediated gene expressions may be generated by 2,4-D is the causative effects on most probable cause of the observed alterations. These biological, molecular and morphological parameters and the measured parameters can be used to monitor 2,4-D toxicity in an aquatic environment.     

Wear Fast,Die Young: More Worn Teeth and Shorter Lives in Iberian Compared to Scottish Red Deer

Teeth in Cervidae are permanent structures that are not replaceable or repairable; consequently their rate of wear, due to the grinding effect of food and dental attrition, affects their duration and can determine an animal''s lifespan. Tooth wear is also a useful indicator of accumulative life energy investment in intake and mastication and their interactions with diet. Little is known regarding how natural and sexual selection operate on dental structures within a species in contrasting environments and how these relate to life history traits to explain differences in population rates of tooth wear and longevity. We hypothesised that populations under harsh environmental conditions should be selected for more hypsodont teeth while sexual selection may maintain similar sex differences within different populations. We investigated the patterns of tooth wear in males and females of Iberian red deer (Cervus elaphus hispanicus) in Southern Spain and Scottish red deer (C. e. scoticus) across Scotland, that occur in very different environments, using 10343 samples from legal hunting activities. We found higher rates of both incisor and molar wear in the Spanish compared to Scottish populations. However, Scottish red deer had larger incisors at emergence than Iberian red deer, whilst molars emerged at a similar size in both populations and sexes. Iberian and Scottish males had earlier tooth depletion than females, in support of a similar sexual selection process in both populations. However, whilst average lifespan for Iberian males was 4 years shorter than that for Iberian females and Scottish males, Scottish males only showed a reduction of 1 year in average lifespan with respect to Scottish females. More worn molars were associated with larger mandibles in both populations, suggesting that higher intake and/or greater investment in food comminution may have favoured increased body growth, before later loss of tooth efficiency due to severe wear. These results illustrate how independent selection in both subspecies, that diverged 11,700 years BP, has resulted in the evolution of different longevity, although sexual selection has maintained a similar pattern of relative sex differences in tooth depletion. This study opens interesting questions on optimal allocation in life history trade-offs and the independent evolution of allopatric populations.     

Sex ratios and sex-biased infection behaviour in the entomopathogenic nematode genus Steinernema

In experimentally infected insects, the sex ratio of first generation nematodes of five species of Steinernema was female-biased (male proportion 0.35-0.47). There was a similar female bias when the worms developed in vitro (0.37-0.44), indicating that the bias in these species is not due to a lower rate of infection by male infective juveniles (IJs). Experimental conditions influenced the proportion of males establishing in insects, indicating that male and female IJs differ in their behaviour. However, there was no evidence that males are the colonising sex in any species, contrary to what has previously been proposed. Time of emergence from the host in which the nematodes had developed influenced sex ratios in experimental infections. In three species (Steinernema longicaudum, Steinernema glaseri and Steinernema kraussei), early emerged nematodes had a higher proportion of males than those that emerged later, with the reverse trend for Steinernema carpocapsae and Steinernema feltiae. In a more detailed in vitro study of S. longicaudum, the proportion of males was similar whether or not the nematodes passed through the developmentally arrested IJ stage, indicating that the female bias is not due to failure of males to exit this stage. The sex ratio in vitro was independent of survival rate from juvenile to adult, and was female-biased even when all juveniles developed, indicating that the bias is not explained by failure of males to develop to adults. The female-biased sex ratio characteristic of Steinernema populations appears to be present from at least the early juvenile stage. We hypothesise that the observed female bias is the population optimal sex ratio, a response to cycles of local mate competition experienced by nematodes reproducing within insect hosts interspersed with periods of outbreeding with less closely related worms following dispersal.     

Gadd45g Is Essential for Primary Sex Determination,Male Fertility and Testis Development

In humans and most mammals, differentiation of the embryonic gonad into ovaries or testes is controlled by the Y-linked gene SRY. Here we show a role for the Gadd45g protein in this primary sex differentiation. We characterized mice deficient in Gadd45a, Gadd45b and Gadd45g, as well as double-knockout mice for Gadd45ab, Gadd45ag and Gadd45bg, and found a specific role for Gadd45g in male fertility and testis development. Gadd45g-deficient XY mice on a mixed 129/C57BL/6 background showed varying degrees of disorders of sexual development (DSD), ranging from male infertility to an intersex phenotype or complete gonadal dysgenesis (CGD). On a pure C57BL/6 (B6) background, all Gadd45g^−/− XY mice were born as completely sex-reversed XY-females, whereas lack of Gadd45a and/or Gadd45b did not affect primary sex determination or testis development. Gadd45g expression was similar in female and male embryonic gonads, and peaked around the time of sex differentiation at 11.5 days post-coitum (dpc). The molecular cause of the sex reversal was the failure of Gadd45g^−/− XY gonads to achieve the SRY expression threshold necessary for testes differentiation, resulting in ovary and Müllerian duct development. These results identify Gadd45g as a candidate gene for male infertility and 46,XY sex reversal in humans.     

Fatty acid composition and content in chironomid species at various life stages dominating in a saline Siberian lake

This paper studies the fatty acid (FA) composition and content of essential polyunsaturated fatty acids (PUFAs) in the biomass of larvae and adults of chironomids from the saline Shira Lake. Species of different genera significantly differ in their larvae FA composition and essential PUFA content, and they also occupy different ecological niches: Chironomus species with a low PUFA content (0.2–0.3 mg g^–1 of wet weight) inhabit a deepwater zone of the lake, while Glyptotendipes barbipes species that were richer in PUFA (2.3 mg g^–1 of wet weight) dwell in the littoral of the lake. The biochemical differences are likely related to different feeding spectra of these taxa and can also be explained by the phylogenetic factor. A comparison does not find differences in the PUFA content in larvae and adults in the samples of the same species G. barbipes; i.e., we do not confirm the data on an increase in the content of these acids during the metamorphosis of chironomids. Thus, the data on the PUFA content in larvae can be used in calculations of PUFA fluxes through chironomid emergence from water bodies; however, the taxonomic affiliation of the emerged chironomids should be taken into consideration due to the high variability in the PUFA content in Chironomidae species.     

Autosomal sex-associated co-methylated regions predict biological sex from DNA methylation

Sex is a modulator of health that has been historically overlooked in biomedical research. Recognizing this knowledge gap, funding agencies now mandate the inclusion of sex as a biological variable with the goal of stimulating efforts to illuminate the molecular underpinnings of sex biases in health and disease. DNA methylation (DNAm) is a strong molecular candidate for mediating such sex biases; however, a robust and well characterized annotation of sex differences in DNAm is yet to emerge. Beginning with a large (n = 3795) dataset of DNAm profiles from normative adult whole blood samples, we identified, validated and characterized autosomal sex-associated co-methylated genomic regions (sCMRs). Strikingly, sCMRs showed consistent sex differences in DNAm over the life course and a subset were also consistent across cell, tissue and cancer types. sCMRs included sites with known sex differences in DNAm and links to health conditions with sex biased effects. The robustness of sCMRs enabled the generation of an autosomal DNAm-based predictor of sex with 96% accuracy. Testing this tool on blood DNAm profiles from individuals with sex chromosome aneuploidies (Klinefelter [47,XXY], Turner [45,X] and 47,XXX syndrome) revealed an intimate relationship between sex chromosomes and sex-biased autosomal DNAm.     

Morphometric traits and sexual dimorphisms do not strongly differentiate populations of Zeravshan juniper (Juniperus seravschanica Kom.) in Kyrgyzstan

Intra- and among-population variations of Juniperus seravschanica were morphologically examined in eight populations originating from elevations of 1300–2200 m a.s.l. in Kyrgyzstan. Eleven traits of needles and cones were studied on 70 vouchers. In addition, height, diameter, stem form, and sex of 172 trees were recorded in the field in order to test whether male trees invest more in vegetative growth than females and if sex ratio is shaped by (limited) environmental resources. Morphological differences among populations were small, but needle length, width and thickness were statistically different. However, differences based on needle traits were independent from geographical, altitudinal and environmental distances. In sharp contrast to studies in other Juniperus species, sex ratio in J. seravschanica was strongly female biased (3.5 females : 1 male). Moreover, no correlation between the habitat conditions and the sex ratio was detected, suggesting that within the altitudinal range of this species, females occur more frequently. This has implications for sustainable use and the conservation of J. seravschanica populations. It is likely, that due to the higher investment of male individuals in vegetative growth males are more exploited than females. An average effective population size of 70% of the respective census suggests that conservation measures and non-selective logging regimes are required to allow reproduction and a natural regeneration of this species.     

Sex,Diet, and the Social Environment: Factors Influencing Hair Cortisol Concentration in Free-Ranging Black Bears (Ursus americanus)

Increasingly, measures of glucocorticoid levels (e.g., cortisol), key components of the neuroendocrine stress axis, are being used to measure past hypothalamic-pituitary-adrenal (HPA) activity to index psychological and physiological stress exhibited by wildlife for assessing individual and population-level well-being. However, many intrinsic and extrinsic factors affect HPA activity in animals. Using American black bears (Ursus americanus; n = 116) as an ecological model and hair cortisol concentration (HCC) as an integrative measure of past HPA activity, we evaluated the influence of diet, sex and the social environment on black bear HCC in a free-ranging population that spanned adjoining ecoregions with differing densities of potential conspecific and heterospecific competitors. HCC varied by sex, with female HCC ranging from 0.6 to 10.7 pg/mg (median = 4.5 ± 1.2 mean absolute deviation [MAD]) and male HCC ranging from 0.5 to 35.1 pg/mg (median = 6.2 ± 2.6 MAD). We also observed a three-way interaction among sex, δ¹⁴C and ecoregion, which may indicate that some differences in HCC between female and male black bears results from variability in the nutritional needs of larger-bodied males relative to smaller-bodied females, slight differences in food resources use between ecoregions as well as sex-based differences regarding the social environment. Once we understand what drives sex-specific differences in HCC, HCC may aid our understanding of the physiological responses by bears and other wildlife to diverse environmental challenges.     

Nonlinear analysis of heart rate variability for evaluating the growing pig stress response to an acute heat episode

Heart rate variability (HRV) is a proxy measure of autonomic function and can be used as an indicator of swine stress. While traditional linear measures are used to distinguish between stressed and unstressed treatments, inclusion of nonlinear HRV measures that evaluate data structure and organization shows promise for improving HRV interpretation. The objective of this study was to evaluate the inclusion of nonlinear HRV measures in response to an acute heat episode. Twenty 12- to 14-week-old growing pigs were individually housed for 7 days and acclimated to thermoneutral conditions (20.35°C ± 0.01°C; 67.6% ± 0.2% RH) before undergoing one of the two treatments: (1) thermoneutral control (TN; n = 10 pigs) or (2) acute heat stress (HS; n = 10 pigs; 32.6°C ± 0.1°C; 26.2% ± 0.1% RH). In Phase 1 of the experimental procedure (P1; 60 min), pigs underwent a baseline HRV measurement period in thermoneutral conditions before treatment [Phase 2; P2; 60 min once gastrointestinal temperature (T_g) reached 40.6°C], where HS pigs were exposed to heated conditions and TN pigs remained in thermoneutral conditions. After P2, all pigs were moved back to thermoneutral conditions (Phase 3; P3; 60 min). During each phase, T_g data were collected every 5 min and behavioural data were collected to evaluate the amount of time each pig spent in an active posture. Additionally, linear (time and frequency domain) and nonlinear [sample entropy (SampEn), de-trended fluctuation analysis, percentage recurrence, percentage determinism (%DET), mean diagonal line length in a recurrence plot] HRV measures were quantified. Heat stressed pigs exhibited greater T_g (P = 0.002) and spent less time in an active posture compared to TN pigs during P2 (P = 0.0003). Additionally, low frequency to high frequency ratio was greater in HS pigs during P3 compared to TN pigs (P = 0.02). SampEn was reduced in HS pigs during P2 (P = 0.01) and P3 (P = 0.03) compared to TN pigs. Heat stressed pigs exhibited greater %DET during P3 (P = 0.03) and tended to have greater %DET (P = 0.09) during P2 than TN pigs. No differences between treatments were detected for the remaining HRV measures. In conclusion, linear HRV measures were largely unchanged during P2. However, changes to SampEn and %DET suggest increased heat stress as a result of the acute heat episode. Future work should continue to evaluate the benefits of including nonlinear HRV measures in HRV analysis of swine heat stress.