Onthophagus Taurus Research Articles

Can Sexual Selection Drive the Evolution of Sperm Cell Structure?

Sperm cells have undergone an extraordinarily divergent evolution among metazoan animals. Parker recognized that because female animals frequently mate with more than one male, sexual selection would continue after mating and impose strong selection on sperm cells to maximize fertilization success. Comparative analyses among species have revealed a general relationship between the strength of selection from sperm competition and the length of sperm cells and their constituent parts. However, comparative analyses cannot address causation. Here, we use experimental evolution to ask whether sexual selection can drive the divergence of sperm cell phenotype, using the dung beetle Onthophagus taurus as a model. We either relaxed sexual selection by enforcing monogamy or allowed sexual selection to continue for 20 generations before sampling males and measuring the total length of sperm cells and their constituent parts, the acrosome, nucleus, and flagella. We found differences in the length of the sperm cell nucleus but no differences in the length of the acrosome, flagella, or total sperm length. Our data suggest that different sperm cell components may respond independently to sexual selection and contribute to the divergent evolution of these extraordinary cells.

Dung beetles show metabolic plasticity as pupae and smaller adult body size in response to increased temperature mean and variance

Though organisms may use thermal plasticity to cope with novel temperature regimes, our understanding of plastic responses is limited. Research on thermal plasticity has traditionally focused on the response of organisms to shifts in mean temperatures. However, increased temperature variation can have a greater impact on organismal performance than mean temperature alone. In addition, thermal plasticity studies are often designed to investigate plasticity in response to more extreme temperatures despite the fact that organisms make physiological adjustments to diurnal temperature fluctuations that they experience. Using pupae of the dung beetle Onthophagus taurus, we investigated the potential for plasticity in response to increasing temperature mean and variance using thermal regimes that were well within the species critical thermal limits. We reared 40 beetles from egg to pupae (n = 20) or adults (n = 20) at one of nine incubation treatments, including all combinations of three mean temperatures (22, 24, 26 °C) and three amplitudes of fluctuation (±2, ±4, ±8 °C). To measure thermal plasticity of pupae, we quantified CO2 production across a range of temperatures (i.e., 15, 20, 25, and 30 °C) for 20 beetles per treatment. The relationship between CO2 production and temperature provides an estimate of energetic costs at a given temperature (i.e., using the intercept) and thermal sensitivity (i.e., using the slope). We reared the remaining O. taurus in each treatment (n = 20) to adulthood and then recorded mass (g) to determine body size, a proxy for fitness. Pupae exhibited thermal plasticity in response to the additive and interactive effects of temperature mean and variance. Pupae reared in the warmest and most variable treatment (26 ± 8 °C) showed the greatest decrease in overall metabolism compared to all other treatments, and adult beetles from this treatment (26 ± 8 °C) were also significantly smaller than adult beetles from any other treatment. We found that both temperature mean and variance contributed to thermal plasticity of pupae and had consequences for adult body size, a trait related to dung beetle fitness. Importantly, the temperatures we used in our treatments are not extreme and are likely well below the critical thermal maxima of the species, demonstrating that organisms can make adjustments to temperatures they experience across diurnal or seasonal timescales.

Signals of selection beyond bottlenecks between exotic populations of the bull-headed dung beetle, Onthophagus taurus.

Colonization of new environments can lead to population bottlenecks and rapid phenotypic evolution that could be due to neutral and selective processes. Exotic populations of the bull-headed dung beetle (Onthophagus taurus) have differentiated in opposite directions from native beetles in male horn-to-body size allometry and female fecundity. Here we test for genetic and transcriptional differences among two exotic and one native O. taurus populations after three generations in common garden conditions. We sequenced RNA from 24 individuals for each of the three populations including both sexes, and spanning four developmental stages for the two exotic, differentiated populations. Identifying 270,400 high-quality single nucleotide polymorphisms, we revealed a strong signal of genetic differentiation between the three populations, and evidence of recent bottlenecks within and an excess of outlier loci between exotic populations. Differences in gene expression between populations were greatest in prepupae and early adult life stages, stages during which differences in male horn development and female fecundity manifest. Finally, genes differentially expressed between exotic populations also had greater genetic differentiation and performed functions related to chitin biosynthesis and nutrient sensing, possibly underlying allometry and fecundity trait divergences. Our results suggest that beyond bottlenecks, recent introductions have led to genetic and transcriptional differences in genes correlated with observed phenotypic differences.

Incipient hybrid inferiority between recently introduced, diverging dung beetle populations

AbstractUnderstanding why and how certain clades emerge as speciation hotspots is a fundamental objective of evolutionary biology. Here we investigate divergences between exotic Onthophagus taurus, a dung beetle introduced into the USA and Australia in the 1970s, as a potential model for the widespread recent speciation events characterizing the genus Onthophagus. To do so, we hybridized O. taurus derived from Eastern US (EUS) and Western Australian (WA) populations, and assessed fitness-relevant trait expression in first- and second-generation hybrids. We found that dams invest more in offspring provisioning when paired with a sire from the same population, and that WA dams crossed with EUS sires produce smaller and lighter F1 hybrids, with an unexpectedly male-biased sex ratio. Furthermore, fewer F2 hybrids with vertically inherited WA cytoplasm and microbiome emerged compared with WA backcrosses with WA cytoplasm/microbiome, suggesting that combinations of nuclear genome, cytoplasm and/or microbiome may contribute to hybrid viability. Lastly, we document a dominance of WA genotypes over body size at the point of inflection between minor and major male morphs, a trait of significance in mate competition, which has diverged remarkably between these populations. We discuss our results in light of the evolutionary ecology of onthophagine beetles and the role of developmental evolution in clade diversification.

Impact of dung beetle activity on the quality of water percolating through Allophanic soil

Dung beetles are described as key ecosystem service providers. Because of ecosystem benefits from their activity, approval has been granted to import dung-burying beetles for release into pasture systems in New Zealand. Concerns remain, however, about the impact of dung beetle tunnelling and burying activity on the leaching of contaminants through soil. To assess the quality of water leaching from soil cores containing dung beetles, a trial was conducted using 12 intact Allophanic soil core lysimeters under in situ soil moisture and temperature regimes. Four lysimeters received dung and beetles (Geotrupes spiniger and Onthophagus taurus), four received dung and no beetles and four (controls) received no dung and no beetles. The quality of water was assessed by monitoring leachate samples for Escherichia coli and total N and P for 6 months. Key findings of the study were that concentrations of E. coli, N and P leaching through the lysimeters treated with dung beetles were not significantly different from soils without dung beetles. In addition, where dung was buried there was a significant decrease in E. coli and total N and P in surface soil compared with the lysimeters receiving dung only. Results from this study suggest dung beetle tunnelling and burying activity does not negatively impact the quality of water leaching through Allophanic soil.

Don't stand so close to me: Microbiota-facilitated enemy release dynamics in introduced Onthophagus taurus dung beetles.

Microbial symbionts can influence their hosts in stunningly diverse ways. Emerging research suggests that an underappreciated facet of these relationships is the influence microbes can have on their host's responses to novel, or stressful, environmental conditions. We sought to address these and related questions in populations resulting from the recent introduction and subsequent rapid range expansion of Onthophagus taurus dung beetles. Specifically, we manipulated both microbial communities and rearing temperature to detect signatures of developmental and life history differentiation in response to the local thermal conditions in two populations derived from the southern most (Florida) and northern most (Michigan) extremes of the exotic Eastern U.S. range of O. taurus. We then sought to determine the contributions, if any, of host‐associated microbiota to this differentiation. We found that when reared under common garden conditions individuals from Florida and Michigan populations differed significantly in developmental performance measures and life history traits, consistent with population divergence. At the same time, and contrary to our predictions, we failed to find support for the hypothesis that animals perform better if reared at temperatures that match their location of origin and that performance differences may be mediated by host‐associated microbiota. Instead, we found that microbiome swapping across host populations improved developmental performance in both populations, consistent with enemy release dynamics. We discuss the implications of our results for our understanding of the rapid spread of exotic O. taurus through the Eastern United States and the significance of symbiosis in host responses to novel environmental conditions more broadly.

Sampling Efficacy and Survival Rates of Labarrus pseudolividus (Coleoptera: Scarabaeidae) and Onthophagus taurus (Coleoptera: Scarabaeidae) Using Flotation and Sieve-Separation Methodology.

Understanding collection methodologies and their limitations are essential when targeting specific arthropods for use in habitat restoration, conservation, laboratory colony formation, or when holistically representing local populations using ecological surveys. For dung beetles, the most popular collection methodology is baited traps, followed by light traps and unbaited flight-intercept traps during diversity surveys. A less common collection method, flotation, is assumed to be laborious and messy, and so only a handful of papers exist on its refinement and strengths. Our purpose was threefold: First, we tested the recovery and survival rates of Labarrus (=Aphodius) pseudolividus (Balthasar) and Onthophagus taurus (Schreber) when floating beetle-seeded dung pats to determine potential collection and safety issues. We collected 72.4 and 78% of the seeded L. pseudolividus and O. taurus, respectively, with >95% survival rating. Second, we developed a flotation-sieving technique that enables users to rapidly collect and passively sort dung beetles with less time and effort. Specifically, we often collected 50–100 g of wild dung beetles within a couple of hours of gathering dung and sorted them in a couple more by allowing dung beetles to sort themselves by size within a series of sieves; Third, we reviewed flotation-based advantages and disadvantages in comparison to other methodologies.

DISTRIBUSI VERTIKAL KOMUNITAS KUMBANG KOTORAN Scarabaeidae DI HABITAT TAMAN NASIONAL GUNUNG SALAK

Scarabaeidae dung beettles is a bioindicator through its function as decomposer, Scrabaeidae maintains the balance of environmental conditions that represented by the variation community structures. A study of Scarabaeidae was conducted to observe the variation of community structures related to different heights (900, 1400 dan 2000 masl) in Salak Halimun Mountains National Park (TNGHS), West Java. Pit Fall Dung Trap method was applied in a belt transect paralele with tracking line. In every height , there were 5 traps created with 10 meters distance among each other. In addition, the study also measured main abiotic paramters, such as type of susbtrate, soil acidity, soil temperature that presumed to have strong influence in establishment of the communities. The result showed that there was a variation in community structures related to different heights. In 900 masl, diversity index (H’) was 0.80 which caterogised as low, in 1400 masl, H’= 1,29 (middle) and H’=0,84 (low) was found in the 2000 masl. The community structures of Scarabaeidae in TNGHS were made up by genus of Onthophagus dan Copris that conssits of 4 (four) spesies, they were O. taurus, O. semicupreus, O. babirussoides dan Copris punctulatus. Onthophagus taurus considered as dominant species that filled 60 % or 339 individual of the communities. Meanwhile, Onthopagus babirussoides can be considered as rare species which only 8% been caught during study.

Dung beetle species introductions: when an ecosystem service provider transforms into an invasive species.

Dung beetle introduction programmes were designed to accelerate exotic livestock dung degradation and to control dung breeding pestiferous flies and livestock parasites. The introduction programmes provided exotic dung beetle species with an opportunity to cross natural barriers and spread beyond their native range. There are no reports that explain what probable adaptation mechanisms enable particular dung beetle species to be the most successful invader. Here we identify the morphological, biological, physiological, ecological and behavioural attributes of the four most widespread and successful dung beetle species in introduced areas on a global scale in relation to the assumption that these species are different from other exotic and native dung beetles. We have recognised Digitonthophagus gazella (Fabricius), Onthophagus taurus (Schreber), Euoniticellus intermedius (Reiche) and Aphodius fimetarius (Linnaeus) as the most successful invaders based on their spread, predominance, distribution range and the reports of invasion. Each of these four species has different natural history traits that increase their fitness making them successful invaders. D. gazella has high fecundity and spreading ability, can instantly locate and colonise fresh and nutritious dung, and has a broad thermal window. O. taurus has morphological plasticity, high fecundity, high brood survival rate due to bi-parenting, and is adapted to extreme thermal and moisture conditions. E. intermedius has remnant-dung feeding abilities, a wide thermal window, functioning best at upper-temperature levels, and successful breeding and survival abilities at extremely low soil moisture conditions. A. fimetarius is small-sized, has high breeding and dispersal abilities, and is adapted to lower thermal and upper moisture extremes and variable soil conditions. Discussed here are perspectives on adaptive attributes of dung beetle species that are important to consider during their selection for redistributions. We have elaborated on the fitness and success characteristics of the four species individually. Further, we recommend a prior-introduction baseline monitoring of native dung beetle assemblages so as to evaluate the future impact of exotic dung beetle introductions on the recipient ecosystem.

Carbon Neutral: The Failure of Dung Beetles (Coleoptera: Scarabaeidae) to Affect Dung-Generated Greenhouse Gases in the Pasture.

Research suggests dung beetles can churn, aerate, and desiccate dung in ways that influence the dung and soil microbes producing greenhouse gases (GHGs). We examined the impacts of the tunneling beetle, Onthophagus taurus (Schreber), and the dwelling beetle, Labarrus pseudolividus (Balthasar), on the carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emitted from pasture-laid bovine dung as well as their sum-total (CO2 + CH4 + N2O) effect on global warming, or their carbon dioxide equivalent (CO2e). Despite dung beetles potential effects on CH4 and N2O, the existing literature shows no ultimate CO2e reductions. We hypothesized that more dung beetles would degrade pats faster and reduce CO2e, and so we increased the average dung beetle biomass per dung volume 6.22× above previously published records, and visually documented any dung damage. However, the time effects were 2–5× greater for any GHG and CO2e (E = 0.27–0.77) than dung beetle effects alone (E = 0.09–0.24). This suggests that dung beetle communities cannot adequately reduce GHGs unless they can accelerate dung decomposition faster than time alone.

Phenotypic plasticity but no adaptive divergence in cuticular hydrocarbons and desiccation resistance among translocated populations of dung beetles

Translocated populations must adapt to their new environment to survive. A key aspect of survival for insects is the maintenance of water balance. It is thought that insects can adapt to dry environments by adjusting their cuticular hydrocarbon (CHC) profile to reduce water loss, though there is limited empirical support for this, and studies generally focus on other roles of CHCs, such as chemical communication. We tested for phenotypic adaptation in introduced populations of the Mediterranean dung beetle Onthophagus taurus, which have become established along a climatic gradient from dry northern to wet southern locations in southwestern Australia. We compared CHC profiles and desiccation resistance between northern and southern populations of the species. To quantify desiccation resistance, we measured both the rate of weight loss and time until death in beetles incubated at 35 °C. We tested for associations between these measures of desiccation resistance and CHC profiles, which were obtained through gas chromatography mass spectrometry. The abundance of CHCs was positively associated with desiccation resistance, and individuals that underwent the desiccation treatment produced a greater quantity of several CHC compounds indicating their ability to plastically adjust their CHC profile in response to desiccation stress. However, northern populations did not produce more CHCs than southern populations, and southern populations were better able to tolerate desiccation. Our results suggest that CHCs are an important component of desiccation resistance in O. taurus. However, the lack of evidence for local adaptation to the drier northern climate suggests there may be constraints to increasing desiccation resistance, and demonstrates the importance of considering local environmental conditions before translocating populations to new locations.

Evolution and plasticity of morph-specific integration in the bull-headed dung beetle Onthophagus taurus.

Developmental and evolutionary processes underlying phenotypic variation frequently target several traits simultaneously, thereby causing covariation, or integration, among phenotypes. While phenotypic integration can be neutral, correlational selection can drive adaptive covariation. Especially, the evolution and development of exaggerated secondary sexual traits may require the adjustment of other traits that support, compensate for, or otherwise function in a concerted manner. Although phenotypic integration is ubiquitous, the interplay between genetic, developmental, and ecological conditions in shaping integration and its evolution remains poorly understood. Here, we study the evolution and plasticity of trait integration in the bull‐headed dung beetle Onthophagus taurus which is characterized by the polyphenic expression of horned (‘major’) and hornless (‘minor’) male morphs. By comparing populations subject to divergent intensities of mate competition, we tested whether mating system shifts affect integration of traits predicted to function in a morph‐specific manner. We focussed on fore and hind tibia morphology as these appendages are used to stabilize major males during fights, and on wings, as they are thought to contribute to morph‐based differences in dispersal behavior. We found phenotypic integration between fore and hind tibia length and horn length that was stronger in major males, suggesting phenotypic plasticity in integration and potentially secondary sexual trait compensation. Similarly, we observed that fore tibia shape was also integrated with relative horn length. However, although we found population differentiation in wing and tibia shape and allometry, populations did not differ in integration. Lastly, we detected little evidence for morph differences in integration in either tibia or wing shape, although wing allometries differed between morphs. This contrasts with previous studies documenting intraspecific differentiation in morphology, behavior, and allometry as a response to varying levels of mate competition across O. taurus populations. We discuss how sexual selection may shape morph‐specific integration, compensation, and allometry across populations.

Maternal and larval niche construction interact to shape development, survival, and population divergence in the dung beetle Onthophagus taurus.

Through niche construction, organisms modify their environments in ways that can alter how selection acts on themselves and their offspring. However, the role of niche construction in shaping developmental and evolutionary trajectories, and its importance for population divergences and local adaptation, remains largely unclear. In this study, we manipulated both maternal and larval niche construction and measured the effects on fitness-relevant traits in two rapidly diverging populations of the bull-headed dung beetle, Onthophagus taurus. We find that both types of niche construction enhance adult size, peak larval mass, and pupal mass, which when compromised lead to a synergistic decrease in survival. Furthermore, for one measure, duration of larval development, we find that the two populations have diverged in their reliance on niche construction: larval niche construction appears to buffer against compromised maternal niche construction only in beetles from Western Australia, but not in beetles from the Eastern United States. We discuss our results in the context of rapid adaptation to novel conditions and the role of niche construction therein.

Rapid differentiation of plasticity in life history and morphology during invasive range expansion and concurrent local adaptation in the horned beetle Onthophagus taurus.

Understanding the interplay between genetic differentiation, ancestral plasticity, and the evolution of plasticity during adaptation to environmental variation is critical to predict populations' responses to environmental change. However, the role of plasticity in rapid adaptation in nature remains poorly understood. We here use the invasion of the horned beetle Onthophagus taurus in the United States during the last half century to study the contribution of ancestral plasticity and post-invasion evolution of plastic responses in rapid population differentiation. We document latitudinal variation in life history and morphology, including genetic compensation in development time and body size, likely adaptive responses to seasonal constraints in the North. However, clinal variation in development time and size was strongly dependent on rearing temperature, suggesting that population differentiation in plasticity played a critical role in successful adaptation on ecological timescales. Clinal variation in wing shape was independent of ancestral plasticity, but correlated with derived plasticity, consistent with evolutionary interdependence. In contrast, clinal variation in tibia shape aligned poorly with thermal plasticity. Overall, this study suggests that post-invasion evolution of plasticity contributed to range expansions and concurrent adaptation to novel climatic conditions.

Genome-based analysis reveals a novel SNMP group of the Coleoptera and chemosensory receptors in Rhaphuma horsfieldi

Through an exhaustive homology-based approach, coupled with manual efforts, we annotated and characterized 128 sensory neuron membrane proteins (SNMPs) from genomes and transcriptomes of 22 coleopteran species, with 107 novel candidates. Remarkably, we discovered, for the first time, a novel SNMP group, defined as Group 4 based on the phylogeny, sequence characteristics, gene structure and organization. The lineage-specific expansions in SNMPs occurred mainly in the family Scarabaeidae, harboring 12 representatives in Onthophagus taurus as a typical gene duplication and the most massive set of SNMPs in insects to date. Transcriptome sequencing of Rhaphuma horsfieldi resulted in the yields of approximately 611.9 million clean reads that were further assembled into 543,841 transcripts and 327,550 unigenes, respectively. From the transcriptome, 177 transcripts encoding 84 odorant (ORs), 62 gustatory (GRs), 20 ionotropic (IRs), and 11 ionotropic glutamate (iGluRs) receptors were identified. Phylogenetic analysis classified RhorORs into six groups, RhorGRs into four subfamilies, and RhorIRs into 10 conserved antennal IRs and one divergent IRs. Expression profiles revealed that over 80% of chemosensory genes were specifically or highly transcribed in antennae or tarsi, suggestive of their olfactory and/or gustatory roles. This study has greatly complemented the resources for chemosensory genes in the cerambycid beetles, and most importantly, identifies a novel group of SNMPs in Coleoptera.

Endophytes matter: Variation of dung beetle performance across different endophyte-infected tall fescue cultivars

Traditional tall fescue cultivar, Kentucky 31, possesses a wild-type endophyte strain that produces several bioactive compounds including the ergot alkaloid, ergovaline, known to cause cattle toxicity and effects on insects. Novel cultivars, BarOptima PLUS E34, Jesup MaxQ, and Texoma MaxQ II, possess different endophyte strains that do not have negative effects on cattle but still protect from insect grazing. Our study investigated if different cultivars have different effects on insect dung decomposers such as dung beetles and determined if ergovaline could be detected in cow dung. Ergovaline at 0.04 and 0.27 μg/g was detected only from Kentucky 31 dung samples from 2017 and 2018 collections, respectively. From the 2017 dung collection, we tested Onthophagus taurus oviposition substrate preferences for each cultivar versus dung from uninfected pasture and also larval survival and development for each dung-type. From the 2018 dung collection, O. taurus and Digitonthophagus gazella oviposition substrate preferences, larval survival and development were tested for Texoma MaxQ II versus Kentucky 31 dung-types. Among the four cultivars, for making brood-balls O. taurus preferred dung from Texoma MaxQ II while dung from Kentucky 31 and BarOptima PLUS E34 were avoided. Both beetle species preferred dung from Texoma MaxQ II versus Kentucky 31 pasture. Larval survival was not affected by dung-type with the 2017 samples. However, with the 2018 samples both beetle species had reduced larval survival on Kentucky 31 than on Texoma MaxQ II brood-balls. Development time for O. taurus was shorter for larvae from Texoma MaxQ II versus Kentucky 31 or uninfected dung brood-balls. Adult mass was not affected in the 2017 collection but was reduced in 2018 Kentucky 31 samples when compared with Texoma MaxQ II. Finally, dung beetles can differentiate dung from pastures with different tall fescue cultivars. Novel cultivar, Texoma MaxQ II, provides more benefits for dung beetles. Pasture renovations with Texoma MaxQ II may improve pasture ecology by enhancing dung beetle populations.

Warming effects on dung beetle ecosystem services: brood production and dung burial by a tunnelling dung beetle,Onthophagus taurus(Coleoptera: Scarabaeidae), is reduced by experimental warming

AbstractDung beetles provide economically valuable ecosystem services to agriculture. Dung beetles are also sensitive to climate change, which may impact on the services that they provide. Using climate‐controlled chambers, we investigated the potential effects of climate change on the performance of a tunnelling dung beetle,Onthophagus taurus. Over two trials, we exposed beetles to a +0°C, +2°C or +4°C increase in diurnally fluctuating field recorded temperatures and measured survival, pat departure, reproduction (brood number and size) and dung burial by beetles. Temperature treatment did not affect pat departure behaviour. Relative to the control +0°C chambers, beetle survival was higher in the +2°C chambers, but there was no difference in survival between the +0°C and +4°C chambers. In Trial 1, brood number was reduced in both the +2°C and +4°C chambers, relative to the +0°C chambers. In Trial 2, brood number was significantly reduced relative to control chambers in the +2°C chambers only. Temperature did not affect brood size. Across temperature treatments, there was a significant, positive relationship between brood number and dung burial. However, trends in brood production with temperature were not mirrored by dung burial; the only reduction in dung burial was found in the warmest treatment of Trial 2. Our results suggest that initially, warming may not substantially reduce dung burial byO. taurus; however, ecosystem services may be impacted if lower brood production eventually reduces beetle numbers. Studies such as ours identify the vulnerabilities of ecosystem service providers to climate change and in doing so are an essential first step in the management of ecosystem services under future warming.

Notch signaling patterns head horn shape in the bull-headed dung beetle Onthophagus taurus.

Size and shape constitute fundamental aspects in the description of morphology. Yet while the developmental-genetic underpinnings of trait size, in particular with regard to scaling relationships, are increasingly well understood, those of shape remain largely elusive. Here we investigate the potential function of the Notch signaling pathway in instructing the shape of beetle horns, a highly diversified and evolutionarily novel morphological structure. We focused on the bull-headed dung beetle Onthophagus taurus due to the wide range of horn sizes and shapes present among males in this species, in order to assess the potential function of Notch signaling in the specification of horn shape alongside the regulation of shape changes with allometry. Using RNA interference-mediated transcript depletion of Notch and its ligands, we document a highly conserved role of Notch signaling in general appendage formation. By integrating our functional genetic approach with a geometric morphometric analysis, we find that Notch signaling moderately but consistently affects horn shape, and does so differently for the horns of minor, intermediate-sized, and major males. Our results suggest that the function of Notch signaling during head horn formation may vary in a complex manner across male morphs, and highlights the power of integrating functional genetic and geometric morphometric approaches in analyzing subtle but nevertheless biologically important phenotypes in the face of significant allometric variation.

Life stages differ in plasticity to temperature fluctuations and uniquely contribute to adult phenotype in Onthophagus taurus dung beetles.

Adaptive thermal plasticity allows organisms to adjust their physiology to cope with fluctuating environments. However, thermal plasticity is rarely studied in response to thermal variability and is often measured in a single life stage. Plasticity in response to thermal variability likely differs from responses to constant temperature or acute stress. In addition, life stages likely differ in their plasticity, and responses in one stage may be affected by the experiences in a previous stage. Increasing the resolution with which we understand thermal plasticity in response to thermal variation across ontogeny is crucial to understanding how organisms cope with the thermal variation in their environment and to estimating the capacity of plasticity to mitigate costs of rapid environmental change. We wanted to know whether life stages differ in their capacity for thermal plasticity under temperature fluctuations. We reared Onthophagus taurus dung beetles in either low or high temperature fluctuation treatments and quantified thermal plasticity of metabolism of pupae and adults. We found that adults were thermally plastic and pupae were not. Next, we tested whether the plasticity observed in the adult life stage was affected by the thermal conditions during development. We again used low and high temperature fluctuation treatments and reared individuals in one condition through all egg to pupal stages. At eclosion, we switched half of the individuals in each treatment to the opposite fluctuation condition and, later, measured thermal plasticity of metabolism in adults. We found that temperature conditions experienced during the adult stage, but not egg to pupal stages, affect adult thermal plasticity. However, temperature fluctuations during development affect adult body size, suggesting that some aspects of the adult phenotype are decoupled from previous life stages and others are not. Our data demonstrate that life stages mount different responses to temperature variability and uniquely contribute to the adult phenotype. These findings emphasize the need to broadly integrate the life cycle into studies of phenotypic plasticity and physiology; doing so should enhance our ability to predict organismal responses to rapid global change and inform conservation efforts.

Serotonin differentially affects morph-specific behavior in divergent populations of a horned beetle

AbstractAssociations between animal weapons and corresponding aggressive behaviors are among the most characteristic features of species, yet at the same time their co-expression is itself often strongly dependent on context, such as male condition or population ecology. Yet the mechanisms that modulate associations between aggression, morphology, and biological context remain poorly understood. The biogenic amine serotonin has been shown to regulate a wide range of aggressive and morph-specific behaviors in diverse insect species. However, the extent to which serotonin may coordinate the expression of behavior with morphology across biological contexts remains unclear. In this study, we pharmacologically increased serotonin biosynthesis in males of the polyphenic beetle, Onthophagus taurus, and assessed how this manipulation affects both aggressive and non-aggressive behaviors in alternative fighter and sneaker morphs, as well as in males derived from two rapidly diverging populations characterized by disparate levels of competition for mates. We find (i) that enhancing serotonin biosynthesis increases most measures of aggressive behaviors, but influences only a subset of nonaggressive behaviors, (ii) that similar serotonin-mediated behavioral changes manifest in both morphs within populations more often than just a single morph, and (iii) that males derived from the two focal populations have diverged in their behavioral responsiveness to serotonin up-regulation. Collectively, our study suggests that serotonin signaling plays a critical role in the regulation of male behavior and its evolution, including in the context of rapid, short-term population divergence.