Texas field crickets (Gryllus texensis) use visual cues to place learn but perform poorly when intra- and extra-maze cues conflict.

Central place foraging field crickets are an ideal system for studying the adaptive value of learning and memory, but more research is needed on ecologically relevant cognition in these invertebrates. Here, we test the visuospatial place learning of Texas field crickets (Gryllus texensis) in a radial arm maze. Our study expands previous work on G. texensis cognition for accuracy measures and extends our previous findings on females to both sexes. Additionally, our study examines whether crickets use intra- or extra-maze cues to locate a food reward using a maze rotation that puts the cues in conflict. We found that male and female crickets improved performance over trials when measured by accuracy variables but not latency variables. Thigmotaxis negatively impacted performance in both sexes. In a reward-absent trial, both male and female crickets demonstrated place memory. When intra- and extra-maze cues conflicted during a rotation trial, crickets' performance was not better than chance. Our rotation results suggest that crickets may experience reciprocal overshadowing of conflicting cues - a result most often seen in other taxa with conflicting multi-modal cues. We conclude that crickets do not rely solely on: (1) a single-cue association, (2) route-following, or (3) their own scent cues to navigate the maze. Instead, male and female Texas field crickets seem to learn the location of the reward using a combination of proximal and distal cues. The possibility to test large numbers of wild-caught or laboratory-reared individuals opens the door to future investigations on the evolutionary ecology of visuospatial learning in these invertebrates.

Tests of the positive and functional allometry hypotheses for sexually selected traits in the Jamaican field cricket.

Sexually selected traits, including threat signals, have been shown to scale steeply positively with body size because their exaggeration maximizes honest signalling. However, the functional allometry hypothesis makes the opposite prediction for some weapons: because the biomechanics of force applied in their use may favor relatively smaller size, sexually selected weapons may exhibit negative allometry. Tests of these ideas in insects have largely focused on holometabolous species, whose adult body size is entirely dependent on nutrients acquired during the larval stage. In contrast, hemimetabolous insects may exhibit different patterns of allometry development because they forage throughout development, between successive moults. Here, we tested complementary and competing predictions made by the positive and functional allometry hypotheses, regarding intrasexually selected trait allometry in a hemimetabolous insect, the Jamaican field cricket (Gryllus assimilis). As expected, head width (a dominance and/or combat trait) was more positively allometric than non-sexually selected traits. In contrast, and consistent with the functional allometry hypothesis, mouthparts (weapons) were either isometric or negatively allometric. We also tested whether trait allometry responded to rearing diet by raising males on either a high protein diet or a high carbohydrate diet; we predicted stronger positive allometry under the high protein diet. However, diet did not influence allometry in the predicted manner. Overall, our results support the functional allometry hypothesis regarding sexually selected trait allometry and raise intriguing possibilities for integrating these ideas with recent paradigms for classifying intrasexually selected traits.

Teaching animal behavior online: A primer for the pandemic and beyond.

Behavior courses face numerous challenges when moving to an online environment, as has been made necessary by the COVID-19 pandemic. These challenges occur largely because behavior courses, like most organismal biology courses, often stress experiential learning through laboratories that involve live animals, as well as a lecture component that emphasizes formative assessment, discussion, and critical thinking. Although online behavior courses may be remote, they can still be interactive and social, and designed with inclusive pedagogy. Here, we discuss some of the key decisions that instructors should consider, provide recommendations, and point out new opportunities for student learning that stem directly from the move to online instruction. Specific topics include challenges related to generating an inclusive and engaging online learning environment, synchronous versus asynchronous formats, assignments that enhance student learning, testing format and execution, grade schemes, design of laboratory experiences including opportunities for community science, design of synthetic student projects, and workload balance for students and instructors. We designed this primer both for animal behavior instructors who need to quickly transition to online teaching in the midst of a pandemic, and for those facing such transitions in upcoming terms. Much of the manuscript's content should also be of general interest and value to instructors from all areas of organismal biology who are attempting to quickly transition to online teaching.

The effects of commonly used anaesthetics on colour measurements across body regions in the poeciliid fish, Girardinus metallicus.

The effects of common anaesthetics on the hue, saturation and brightness measurements of the poeciliid fish Girardinus metallicus were investigated in two experiments. For both experiments the coloration of four body regions was measured from digital images of the same males obtained under three conditions: (1) control (in a water-filled chamber); (2) anaesthetised with MS-222; and (3) anaesthetised with eugenol (clove oil). In experiment 1 anaesthetised fish were photographed out of water. In experiment 2 all photographs were taken in a water-filled chamber. Anaesthetics altered coloration in both experiments. In the more methodologically consistent experiment 2 we found significantly different hue, increased saturation and decreased brightness in anaesthetic v. control conditions, consistent with darkening caused by the anaesthetics. The body regions differed in coloration consistent with countershading but did not differentially change in response to anaesthesia. These findings suggest that photographing fish in a water-filled chamber without anaesthetic is preferable for obtaining digital images for colour analysis and that multiple body regions of fish should be measured when assessing coloration patterns meaningful in behavioural contexts, to account for the gradients caused by countershading. We are encouraged that some researchers employ such methods already and caution against using anaesthetics except when absolutely necessary for immobilisation.

Field Crickets Compensate for Unattractive Static Long-Distance Call Components by Increasing Dynamic Signalling Effort.

The evolution of multiple sexual signals presents a dilemma since individuals selecting a mate should pay attention to the most honest signal and ignore the rest; however, multiple signals may evolve if, together, they provide more information to the receiver than either one would alone. Static and dynamic signals, for instance, can act as multiple messages, providing information on different aspects of signaller quality that reflect condition at different time scales. While the nature of static signals makes them difficult or impossible for individuals to augment, dynamic signals are much more susceptible to temporary fluctuations in effort. We investigated whether male Texas field crickets, Gryllus texensis, that produce unattractive static signals compensate by dynamically increasing their calling effort. Our findings lend partial support to the compensation hypothesis, as males that called at unattractive carrier frequencies (a static trait) spent more time calling each night (a dynamic trait). Interestingly, this finding was most pronounced in males that called with attractive pulse characteristics (static traits) but did not occur in males that called with unattractive pulse characteristics. Males that signalled with unattractive pulse characteristics (duration and pause) spent less time calling through the night. Our correlative findings on wild caught males suggest that only males that signal with attractive pulse characteristics may be able to afford to pay the costs of both trait exaggeration and increased calling effort to compensate for poor carrier frequencies.

Male crickets adjust their aggressive behavior when a female is present.

Communication in nature often occurs within a broad social network, as signals can be perceived by other individuals beyond the primary intended receiver. Because signals often contain information about the signaller's quality, receivers other than the primary intended receiver may use this information in future interactions with the signaller. As a result, individuals who adjust their behavior depending on who is present may experience a selective advantage. The social environment can therefore have an important influence on the evolution of communication signals. We examined how the presence of a female audience influenced male aggressive behavior and post-contest victory displays in the Jamaican field cricket, Gryllus assimilis. We found a significant effect of female audience on aggressive interactions. When there was a female audience present, males were more likely to initiate and escalate fights, but they spent less time producing victory displays, compared to when there was no audience present. Our experiment suggests that the social environment is important in shaping the behavior of individuals during aggressive interactions.

Towards a synthesis of frameworks in nutritional ecology: interacting effects of protein, carbohydrate and phosphorus on field cricket fitness.

Phosphorus has been identified as an important determinant of nutrition-related biological variation. The macronutrients protein (P) and carbohydrates (C), both alone and interactively, are known to affect animal performance. No study, however, has investigated the importance of phosphorus relative to dietary protein or carbohydrates, or the interactive effects of phosphorus with these macronutrients, on fitness-related traits in animals. We used a nutritional geometry framework to address this question in adult field crickets (Gryllus veletis). Our results showed that lifespan, weight gain, acoustic mate signalling and egg production were maximized on diets with different P : C ratios, that phosphorus did not positively affect any of these fitness traits, and that males and females had different optimal macronutrient intake ratios for reproductive performance. When given a choice, crickets selected diets that maximized both lifespan and reproductive performance by preferentially eating diets with low P : C ratios, and females selected diets with a higher P : C ratio than males. Conversely, phosphorus intake was not regulated. Overall, our findings highlight the importance of disentangling the influences of different nutrients, and of quantifying both their individual and interactive effects, on animal fitness traits, so as to gain a more integrative understanding of their nutritional ecology.

How male sound pressure level influences phonotaxis in virgin female Jamaican field crickets (Gryllus assimilis).

Understanding female mate preference is important for determining the strength and direction of sexual trait evolution. The sound pressure level (SPL) acoustic signalers use is often an important predictor of mating success because higher sound pressure levels are detectable at greater distances. If females are more attracted to signals produced at higher sound pressure levels, then the potential fitness impacts of signalling at higher sound pressure levels should be elevated beyond what would be expected from detection distance alone. Here we manipulated the sound pressure level of cricket mate attraction signals to determine how female phonotaxis was influenced. We examined female phonotaxis using two common experimental methods: spherical treadmills and open arenas. Both methods showed similar results, with females exhibiting greatest phonotaxis towards loud sound pressure levels relative to the standard signal (69 vs. 60 dB SPL) but showing reduced phonotaxis towards very loud sound pressure level signals relative to the standard (77 vs. 60 dB SPL). Reduced female phonotaxis towards supernormal stimuli may signify an acoustic startle response, an absence of other required sensory cues, or perceived increases in predation risk.

Mating behavior and its morphological correlates in two color morphs of Girardinus metallicus (Pisces: Poeciliidae), a species previously thought not to exhibit courtship display.

Girardinus metallicus is a Cuban poeciliid fish whose social behavior has been little studied. The only account involves a colorless morph that is sexually monochromatic and does not exhibit courtship display. We describe the behavior of two other morphs (black and yellow) that exhibit sexual dichromatism. We observed courtship displays in black but not yellow males. Contrary to the pattern in most poeciliids, black males exhibit long gonopodia and courtship; typically, longer gonopodia evolve in species without courtship, because they facilitate coercive mating but circumvent female choice. We focused on the black morph to address whether morphological traits are favored by sexual selection. Larger males with longer gonopodia courted and attempted copulations more often. Black area was not associated with intersexual interactions, but was positively associated with aggressiveness. Dominant males attempted more copulations, consistent with the idea that black coloration may be a badge of status. Black males may possess long gonopodia because the gonopodium itself is a target of female choice. However, there was no difference in gonopodium length between black and yellow males, although the latter do not court. We discuss processes that may maintain the polymorphism and prospects for future studies in this intriguing system.

Body morphology, energy stores, and muscle enzyme activity explain cricket acoustic mate attraction signaling variation.

High mating success in animals is often dependent on males signalling attractively with high effort. Since males should be selected to maximize their reproductive success, female preferences for these traits should result in minimal signal variation persisting in the population. However, extensive signal variation persists. The genic capture hypothesis proposes genetic variation persists because fitness-conferring traits depend on an individual's basic processes, including underlying physiological, morphological, and biochemical traits, which are themselves genetically variable. To explore the traits underlying signal variation, we quantified among-male differences in signalling, morphology, energy stores, and the activities of key enzymes associated with signalling muscle metabolism in two species of crickets, Gryllus assimilis (chirper: <20 pulses/chirp) and G. texensis (triller: >20 pulses/chirp). Chirping G. assimilis primarily fuelled signalling with carbohydrate metabolism: smaller individuals and individuals with increased thoracic glycogen stores signalled for mates with greater effort; individuals with greater glycogen phosphorylase activity produced more attractive mating signals. Conversely, the more energetic trilling G. texensis fuelled signalling with both lipid and carbohydrate metabolism: individuals with increased ß-hydroxyacyl-CoA dehydrogenase activity and increased thoracic free carbohydrate content signalled for mates with greater effort; individuals with higher thoracic and abdominal carbohydrate content and higher abdominal lipid stores produced more attractive signals. Our findings suggest variation in male reproductive success may be driven by hidden physiological trade-offs that affect the ability to uptake, retain, and use essential nutrients, although the results remain correlational in nature. Our findings indicate that a physiological perspective may help us to understand some of the causes of variation in behaviour.

How age influences phonotaxis in virgin female Jamaican field crickets (Gryllus assimilis).

Female mating preference can be a dominant force shaping the evolution of sexual signals. However, females rarely have consistent mating preferences throughout their lives. Preference flexibility results from complex interactions of predation risk, social and sexual experience, and age. Because residual reproductive value should theoretically decline with age, older females should not be as choosy as younger females. We explored how age influences phonotaxis towards a standard mate attraction signal using a spherical treadmill (trackball) and a no-choice experimental protocol. Female Jamaican field crickets, Gryllus assimilis, were highly variable in their phonotaxis; age explained up to 64% of this variation. Females 10 days post imaginal eclosion and older oriented toward the mate attraction signal, with 10- and 13-day females exhibiting the greatest movement in the direction of the signal. Our study suggests 10- and 13-day old females would be most responsive when quantifying the preference landscape for G. assimilis sexual signals.

Adaptive plasticity in wild field cricket's acoustic signaling.

Phenotypic plasticity can be adaptive when phenotypes are closely matched to changes in the environment. In crickets, rhythmic fluctuations in the biotic and abiotic environment regularly result in diel rhythms in density of sexually active individuals. Given that density strongly influences the intensity of sexual selection, we asked whether crickets exhibit plasticity in signaling behavior that aligns with these rhythmic fluctuations in the socio-sexual environment. We quantified the acoustic mate signaling behavior of wild-caught males of two cricket species, Gryllus veletis and G. pennsylvanicus. Crickets exhibited phenotypically plastic mate signaling behavior, with most males signaling more often and more attractively during the times of day when mating activity is highest in the wild. Most male G. pennsylvanicus chirped more often and louder, with shorter interpulse durations, pulse periods, chirp durations, and interchirp durations, and at slightly higher carrier frequencies during the time of the day that mating activity is highest in the wild. Similarly, most male G. veletis chirped more often, with more pulses per chirp, longer interpulse durations, pulse periods, and chirp durations, shorter interchirp durations, and at lower carrier frequencies during the time of peak mating activity in the wild. Among-male variation in signaling plasticity was high, with some males signaling in an apparently maladaptive manner. Body size explained some of the among-male variation in G. pennsylvanicus plasticity but not G. veletis plasticity. Overall, our findings suggest that crickets exhibit phenotypically plastic mate attraction signals that closely match the fluctuating socio-sexual context they experience.

Playing to an audience: the social environment influences aggression and victory displays.

Animal behaviour studies have begun to incorporate the influence of the social environment, providing new opportunities for studying signal strategies and evolution. We examined how the presence and sex of an audience influenced aggression and victory display behaviour in field-captured and laboratory-reared field crickets (Gryllus veletis). Audience type, rearing environment and their interaction were important predictors in all model sets. Thus, audience type may impose different costs and benefits for competing males depending on whether they are socially experienced or not. Our results suggest that field-captured winners, in particular, dynamically adjust their contest behaviour to potentially gain a reproductive benefit via female eavesdropping and may deter future aggression from rivals by advertising their aggressiveness and victories.

Calling, courtship, and condition in the fall field cricket, Gryllus pennsylvanicus.

Theoretically, sexual signals should provide honest information about mating benefits and many sexually reproducing species use honest signals when signalling to potential mates. Male crickets produce two types of acoustic mating signals: a long-distance mate attraction call and a short-range courtship call. We tested whether wild-caught fall field cricket (Gryllus pennsylvanicus) males in high condition (high residual mass or large body size) produce higher effort calls (in support of the honest signalling hypothesis). We also tested an alternative hypothesis, whether low condition males produce higher effort calls (in support of the terminal investment hypothesis). Several components of long-distance mate attraction calls honestly reflected male body size, with larger males producing louder mate attraction calls at lower carrier frequencies. Long-distance mate attraction chirp rate dishonestly signalled body size, with small males producing faster chirp rates. Short-range courtship calls dishonestly reflected male residual mass, as chirp rate and pulse rate were best explained by a curvilinear function of residual mass. By producing long-distance mate attraction calls and courtship calls with similar or higher effort compared to high condition males, low condition males (low residual mass or small body size) may increase their effort in current reproductive success at the expense of their future reproductive success, suggesting that not all sexual signals are honest.

Phenotypic covariance structure and its divergence for acoustic mate attraction signals among four cricket species.

The phenotypic variance-covariance matrix (P) describes the multivariate distribution of a population in phenotypic space, providing direct insight into the appropriateness of measured traits within the context of multicollinearity (i.e., do they describe any significant variance that is independent of other traits), and whether trait covariances restrict the combinations of phenotypes available to selection. Given the importance of P, it is therefore surprising that phenotypic covariances are seldom jointly analyzed and that the dimensionality of P has rarely been investigated in a rigorous statistical framework. Here, we used a repeated measures approach to quantify P separately for populations of four cricket species using seven acoustic signaling traits thought to enhance mate attraction. P was of full or almost full dimensionality in all four species, indicating that all traits conveyed some information that was independent of the other traits, and that phenotypic trait covariances do not constrain the combinations of signaling traits available to selection. P also differed significantly among species, although the dominant axis of phenotypic variation (p(max)) was largely shared among three of the species (Acheta domesticus, Gryllus assimilis, G. texensis), but different in the fourth (G. veletis). In G. veletis and A. domesticus, but not G. assimilis and G. texensis, p(max) was correlated with body size, while p(max) was not correlated with residual mass (a condition measure) in any of the species. This study reveals the importance of jointly analyzing phenotypic traits.

How dietary phosphorus availability during development influences condition and life history traits of the cricket, Acheta domesticas.

Phosphorus is extremely limited in the environment, often being 10-20 times lower in plants than what invertebrate herbivores require. This mismatch between resource availability and resource need can profoundly influence herbivore life history traits and fitness. This study investigated how dietary phosphorus availability influenced invertebrate growth, development time, consumption, condition, and lifespan using juvenile European house crickets, Acheta domesticus L. (Orthoptera: Gryllidae). Crickets reared on high phosphorus diets ate more food, gained more weight, were in better condition at maturity, and contained more phosphorus, nitrogen, and carbon in their bodies at death than crickets reared on low phosphorus diets. There was also a trend for crickets reared on high phosphorus diets to become larger adults (interaction with weight prior to the start of the experiment). These findings can be added to the small but growing number of studies that reveal the importance of phosphorus to insect life history traits. Future research should explore the importance of dietary phosphorus availability relative to protein, lipid, and carbohydrate availability.

Multi-way multi-group segregation and diversity indices.

BACKGROUND: How can we compute a segregation or diversity index from a three-way or multi-way contingency table, where each variable can take on an arbitrary finite number of values and where the index takes values between zero and one? Previous methods only exist for two-way contingency tables or dichotomous variables. A prototypical three-way case is the segregation index of a set of industries or departments given multiple explanatory variables of both sex and race. This can be further extended to other variables, such as disability, number of years of education, and former military service. METHODOLOGY/PRINCIPAL FINDINGS: We extend existing segregation indices based on Euclidean distance (square of coefficient of variation) and Boltzmann/Shannon/Theil index from two-way to multi-way contingency tables by including multiple summations. We provide several biological applications, such as indices for age polyethism and linkage disequilibrium. We also provide a new heuristic conceptualization of entropy-based indices. Higher order association measures are often independent of lower order ones, hence an overall segregation or diversity index should be the arithmetic mean of the normalized association measures at all orders. These methods are applicable when individuals self-identify as multiple races or even multiple sexes and when individuals work part-time in multiple industries. CONCLUSIONS/SIGNIFICANCE: The policy implications of this work are enormous, allowing people to rigorously test whether employment or biological diversity has changed.

Normalized mutual entropy in biology: quantifying division of labor.

Division of labor is one of the primary adaptations of sociality and the focus of much theoretical work on self-organization. This work has been hampered by the lack of a quantitative measure of division of labor that can be applied across systems. We divide Shannon's mutual entropy by marginal entropy to quantify division of labor, rendering it robust over changes in number of individuals or tasks. Reinterpreting individuals and tasks makes this methodology applicable to a wide range of other contexts, such as breeding systems and predator-prey interactions.

Colony response to graded resource changes: an analytical model of the influence of genotype, environment, and dominance.

Successful social groups must respond dynamically to environmental changes. However, a flexible group response requires the coordination of many individuals. Here we offer a static analytical model that integrates variation in environment-based cues for performance of a task with genetically and environmentally based variation in individual responses, and predicts the resultant colony behavior for that task. We also provide formulae for computing effective number of alleles in a haplo-diploid colony founded by any number of parents. Variable colony resources combined with variation among worker phenotypes generate known patterns of colony flexibility, allowing us to explicitly test how the number of loci, dominance/codominance, and the phenotype's environment influences group response. Our model indicates that the number of loci strongly influences colony behavior. For one or two loci, the proportion of workers foraging for pollen remain constant over vast increases in colony pollen stores, but then drops dramatically when the pollen stores increase past a specific threshold. As the number of loci controlling pollen foraging increases, graded increases in pollen stores result in a graded drop in the proportion of the worker population foraging for pollen. The effect of number of alleles is less strong, a result we discuss in light of the fact that a low number of effective alleles are expected in a colony. Comparisons of our model with empirical honey bee (Apis mellifera) data indicate that worker foraging response to pollen stores is driven by one or two loci, each with dominant allelic effects. The growing body of evidence that genotype has strong effects on task performance in social insect colonies, and the variation in within-colony genetic diversity across social insect taxa, make our model broadly applicable in explaining social group coordination.

Temporally fluctuating selection of sex-limited signaling traits in the Texas field cricket, Gryllus texensis.

Gryllus texensis males produce acoustic mating signals and display extensive heritable variation in when and how much time they spend signaling throughout the night. The goal of this research is to elucidate the potential mechanism responsible for maintaining this heritable variation. Mating signals attract female crickets. In low-density spring populations females select males that signal most often; in high-density fall populations mating appears random with respect to signaling time. Mating signals also inadvertently attract acoustically orienting parasitoid flies; parasitoids are prevalent during the first half of the evening in the fall mating season. I hypothesized that mating signals are influenced by sex-limited temporally fluctuating selection. I predicted how mating signals would respond to this pattern of cyclical selection a priori, and then measured the sexual characters over four successive generations. I provide correlative evidence that mating signals appear to respond to sex-limited temporally fluctuating selection. These results indicate that sex-limited temporally fluctuating selection may play a role in the maintenance of variation in these sexual characters.