Showing papers by "Ryan L. Earley published in 2019"

Fixed or flexible? Winner/loser effects vary with habitat quality in a parasitoid wasp

Abstract: Prior experience of fighting affects the outcome of subsequent contests, with prior winners being more likely to win and prior losers being more likely to lose a future encounter. These winner and loser effects have been shown in numerous species but have usually been tested in only one set of conditions. However, if such effects are not fixed but context dependent, we can expect their strength to change according to the situation. In particular, their magnitude could covary with other factors, such as those influencing contestants’ fighting abilities or the value they place on the contested resource, which in turn are known to influence contest behaviors and outcomes. Here, we tested the effect that prior experience of resource availability had on the expression of winner and loser effects in Eupelmus vuilleti, a parasitoid wasp fighting for hosts on which to lay their eggs. We showed that a loser effect was observable only when females experienced a habitat rich in hosts (hence placed low value on the contested individual host) but not when they were deprived of hosts (leading to individual hosts having high value). Contrary with a prior study, no clear winner effect was observed. These results suggest that the strength of winner and loser effects are context dependent in E. vuilleti, and interactions with other factors can either accentuate or attenuate the effects. Our data further raise the question of whether the intensity of the first encounter, not only its outcome, influences the behavioral decisions of individuals during a subsequent contest. A previous victory can increase the chance of winning a subsequent fight, while a prior defeat can increase the chance of losing. Such winner and loser effects have been shown in numerous species but have usually been studied in only one set of conditions. We show that the strength of these effects can be context dependent, such that they are accentuated or attenuated when experience interacts with factors such as habitat quality. Our data further raise the question of whether the intensity of the first encounter (how “hard” it was to win or lose), not just the outcome, influences behavioral decisions during subsequent contests.

Evolutionary genetic integration of behavioural and endocrine components of the stress response

Abstract: The vertebrate stress response comprises a suite of behavioural and physiological traits that must be functionally integrated to ensure organisms cope adaptively with acute stressors. The expectation that natural selection has favoured functional integration leads to a prediction of genetic integration: genetic variation in the stress response should include covariation between its component behavioural and physiological traits. Despite the implications of such genetic integration for our understanding of human and animal health, as well as evolutionary responses to natural and anthropogenic stressors, formal quantitative genetic tests of this prediction are lacking. Here we demonstrate that Trinidadian guppies (Poecilia reticulata) show genetic variation in a suite of behavioural and physiological components of the acute stress response, and that these are indeed integrated into a single major axis of genetic variation. This axis appears to reflect continuous variation in the magnitude of integrated stress responsiveness, rather than variation in 9coping style9 (a verbal model that postulates equal levels of stress responsiveness will manifest differently across individuals). The genetic integration we find here could either facilitate or constrain evolutionary responses to selection, depending upon the extent to which the direction of selection aligns with this single major axis of genetic covariation among stress response traits. Such integration also suggests that, while stress-related disease typically arises from physiological components of the stress response, selection on the genetically correlated behavioural responses to stress could offer a viable non-invasive route to the improvement of health and welfare in captive animal populations through artificial selection.

Prolonged survival out of water is linked to a slow pace of life in a self-fertilizing amphibious fish

Abstract: Metabolic rate and life-history traits vary widely both among and within species, reflecting trade-offs in energy allocation, but the proximate and ultimate causes of variation are not well understood. We tested the hypothesis that these trade-offs are mediated by environmental heterogeneity, using isogenic strains of the amphibious fish Kryptolebias marmoratus that vary in the amount of time each can survive out of water. Consistent with pace of life theory, the strain that survived air exposure the longest generally exhibited a 'slow' phenotype, including the lowest metabolic rate, largest scope for metabolic depression, slowest consumption of energy stores and least investment in reproduction under standard conditions. Growth rates were fastest in the otherwise slow strain, however. We then tested for fitness trade-offs between 'fast' and 'slow' strains using microcosms where fish were held either with constant water availability or under fluctuating conditions where water was absent for half of the experiment. Under both conditions the slow strain grew larger and was in better condition, and under fluctuating conditions the slow strain produced more embryos. However, the fast strain had larger adult population sizes under both conditions, indicating that fecundity is not the sole determinant of population size in this species. We conclude that genetically based differences in the pace of life of amphibious fish determine survival duration out of water. Relatively slow fish tended to perform better under conditions of limited water availability, but there was no detectable cost under control conditions. Thus, pace of life differences may reflect a conditionally neutral instead of antagonistic trade-off.

Genetic integration of the stress response

Abstract: The stress response is a product of selection for an integrated suite of behavioural and physiological traits that facilitate coping with acute stressors. As such, genetic variation in the stress response is expected to reflect genetic variation in, and genetic covariation among, its behavioural and physiological components. Such genetic integration among stress response components has yet to be formally demonstrated using multivariate quantitative genetics, despite its profound implications for optimising human and animal health and understanding the responses of wild populations to natural and anthropogenic stressors. Here we use a laboratory population of wild-derived Trinidadian guppies (Poecilia reticulata) to determine levels of genetic variation in behavioural and physiological components of the acute stress response, and to establish whether such variation is integrated into a single major axis of genetic (co)variation. First, using a novel method to characterise behavioural components of the stress response from a widely used Open Field Trial paradigm, we find genetic variation in, and genetic covariation among, behavioural parameters that characterise movement patterns under stress. Second, we find a strong genetic component to variation in both the endocrine response to a confinement stressor and the rate at which this response attenuates following repeated exposures to the stressor. Finally, we show that these behavioural and physiological components of the stress response align on a major axis of genetic (co)variation as predicted, suggesting correlational selection in the past has led to genetic integration. This genetic integration could either facilitate or constrain future responses to selection, depending upon the extent to which the direction of selection aligns with this major axis of genetic covariation among stress response traits. This genetic integration also suggests that, while stress-related disease typically arises from physiological stress responses, selection on the genetically correlated behavioural responses could offer a viable non-invasive route to the genetic improvement of health and welfare in captive animal populations.

How individual and relative size affect participation in territorial defense and cortisol levels in a social fish.

Abstract: For many species, behaviors such as territory defense and parental care are energetically costly, but are nonetheless can provide substantial fitness gains. In systems in which both parents provide parental care, each of the parents benefits from exhibiting (or having their partner exhibit) these behaviors. However, in many cases, costs and benefits differ between parents due to factors such as size or sex. Different intruder types may also impose different costs on parents. Predatory intruders might consume offspring, whereas conspecifics might threaten the social status of a parent, or provide benefits as a potential group joiner or mate. Responses to these intrusions may also be associated with variation in individual stress responses. We investigated associations among male and female sizes, and the interaction between these, with defense against conspecific and heterospecific territorial intruders by members of successfully breeding pairs in the cichlid fish Neolamprologus pulcher. We also investigated whether cortisol levels were associated with size or participation in territory defense because each may be a cause or consequence of individual variation in the stress response. We found that females paired with large males performed fewer defensive behaviors than females paired with smaller males. Males paired with relatively large females had higher baseline cortisol levels than those paired with smaller females. Collectively, individual characteristics such as size have consequences for each individual's behavior, and also influence the behavior, and endocrine state of social partners.

Does Body Shape in Fundulus Adapt to Variation in Habitat Salinity

Abstract: Understanding the ecological pressures that generate variation in body shape is important because body shape profoundly affects physiology and overall fitness. Using Fundulus, a genus of fish that exhibits considerable morphological and physiological variation with evidence of repeated transitions between freshwater and saltwater habitats, we tested whether habitat salinity has influenced the macroevolution of body shape at different stages in development. After accounting for phylogenetic inertia, we find that body shape deviates from the optimal streamlined shape in a manner consistent with different osmoregulatory pressures exerted by different salinity niches at every stage of ontogeny that we examined. We attribute variation in body shape to differential selection for osmoregulatory efficiency because: (1) saline intolerant species developed body shapes with relatively low surface areas more conducive to managing osmoregulatory demands and (2) inland species that exhibit high salinity tolerances have body shapes similar to saline tolerant species in marine environments.

Development of G: a test in an amphibious fish.

Abstract: Heritable variation in, and genetic correlations among, traits determine the response of multivariate phenotypes to natural selection. However, as traits develop over ontogeny, patterns of genetic (co)variation and integration captured by the G matrix may also change. Despite this, few studies have investigated how genetic parameters underpinning multivariate phenotypes change as animals pass through major life history stages. Here, using a self-fertilizing hermaphroditic fish species, mangrove rivulus (Kryptolebias marmoratus), we test the hypothesis that G changes from hatching through reproductive maturation. We also test Cheverud's conjecture by asking whether phenotypic patterns provide an acceptable surrogate for patterns of genetic (co)variation within and across ontogenetic stages. For a set of morphological traits linked to locomotor (jumping) performance, we find that the overall level of genetic integration (as measured by the mean-squared correlation across all traits) does not change significantly over ontogeny. However, we also find evidence that some trait-specific genetic variances and pairwise genetic correlations do change. Ontogenetic changes in G indicate the presence of genetic variance for developmental processes themselves, while also suggesting that any genetic constraints on morphological evolution may be age-dependent. Phenotypic correlations closely resembled genetic correlations at each stage in ontogeny. Thus, our results are consistent with the premise that-at least under common environment conditions-phenotypic correlations can be a good substitute for genetic correlations in studies of multivariate developmental evolution.

Cryptic Male Phenotypes in the Mangrove Rivulus Fish, Kryptolebias marmoratus

Abstract: Alternative male phenotypes exist in many species and impact mating system dynamics, population genetics, and mechanisms of natural and sexual selection that operate within a population. We report on the discovery of a cryptic male phenotype in the mangrove rivulus fish (Kryptolebias marmoratus), one of only two self-fertilizing hermaphroditic vertebrates. In this androdiecious species, males are infrequent, often making up less than 5% of a population; and they have historically been described as having an orange color and lacking or having a very faded outline of the well-defined caudal eyespot (ocellus) that is obvious in hermaphrodites. The cryptic male we describe varies subtly from the hermaphrodite phenotype, without visible orange pigmentation on the body and retention or only minor fading of the ocellus. This male morph was identified by a loss of a defined melanistic "fingerprinting" on the caudal fin seen in hermaphrodites, not previously used as diagnostic for hermaphrodites, and replaced by a diffuse deposition of pigment across the fin. Individuals were identified as male with 85.7% accuracy when using these criteria. We report that in nine populations, spanning three geographically distinct regions in Florida, across two and a half years, 0.3% of the 6057 mangrove rivulus collected exhibited this cryptic male phenotype and were confirmed to have testes via dissection. Overall, 2.3% of the animals were male (normal and cryptic phenotypes), and cryptic males represented 12.9% of all males collected. Even a minor increase in individuals identified as male in a species where males make up such a small portion of the population can have important implications for population genetics. Opportunities for outbreeding are likely enhanced, which has significant evolutionary ramifications.

Comparison of Lactate and Electromyographical Thresholds After an Exercise Bout.

Abstract: Snarr, RL, Esco, MR, Tolusso, DV, Hallmark, AV, Earley, RL, Higginbotham, JC, Fedewa, MV, and Bishop, P. Comparison of lactate and electromyographical thresholds after an exercise bout. J Strength Cond Res 33(12): 3322-3331, 2019-The electromyographical threshold (EMGT) has been previously validated as a means to predict the work rate at which lactate threshold (LT) occurs. The reliability of these measures has yet to be examined after a bout of exercise. The purpose was to determine the agreement between electromyography (EMG) and LT after a 30-minute bout of steady-state aerobic exercise. Participants completed 2 graded exercise tests (GXT) on a cycle ergometer separated by 30 minutes of steady-state exercise. Blood lactate was measured the last 45 seconds of each stage during both GXTs, whereas EMG of the vastus lateralis was monitored continuously. Individual agreement demonstrated that pre-exercise and post-exercise LT occurred at the same work rate in 2 of 10 participants, whereas EMGT occurred at the same work rate in 6 of 10 participants. Results showed no mean difference between work rates for LT or EMG threshold for the pre-exercise GXT, but LT was significantly lower (p < 0.01) than EMGT during the post-exercise GXT. Post-GXT LT work rates were also determined to be significantly lower than pre-GXT LT (p = 0.034), whereas no differences existed in EMG thresholds. Although both LT and EMGT testing may display similar properties, they are not interchangeable. The physiological responses to increasing exercise intensity between La and EMG signaling seem to be associated, and their interaction may not be cause-effect. Because of poor individual agreement, caution should be used when determining LT through the use of EMG. Further research is needed to determine the ability of these 2 metrics to prescribe training intensities.