33 results on '"Erin A. McCullough"'
Search Results
2. The life history of
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Erin L, McCullough, Emma, Whittington, Akanksha, Singh, Scott, Pitnick, Mariana F, Wolfner, and Steve, Dorus
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Male ,Proteomics ,Life Cycle Stages ,Sexual Behavior, Animal ,Proteome ,Reproduction ,Seminal Plasma Proteins ,Animals ,Drosophila ,Female ,Genitalia ,Spermatozoa - Abstract
SignificanceIn species with internal fertilization, sperm spend an important part of their lives within the female. To examine the life history of the sperm during this time, we used semiquantitative proteomics and sex-specific isotopic labeling in fruit flies to determine the extent of molecular continuity between male and female reproductive tracts and provide a global catalog of sperm-associated proteins. Multiple seminal fluid proteins and female proteins associate with sperm immediately after mating. Few seminal fluid proteins remain after long-term sperm storage, whereas female-derived proteins constitute one-fifth of the postmating sperm proteome by then. Our data reveal a molecular "hand-off" from males to females, which we postulate to be an important component of sperm-female interactions.
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- 2022
3. The life history of Drosophila sperm involves molecular continuity between male and female reproductive tracts
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Erin L. McCullough, Emma Whittington, Akanksha Singh, Scott Pitnick, Mariana F. Wolfner, and Steve Dorus
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endocrine system ,Multidisciplinary ,urogenital system ,reproductive and urinary physiology - Abstract
Significance In species with internal fertilization, sperm spend an important part of their lives within the female. To examine the life history of the sperm during this time, we used semiquantitative proteomics and sex-specific isotopic labeling in fruit flies to determine the extent of molecular continuity between male and female reproductive tracts and provide a global catalog of sperm-associated proteins. Multiple seminal fluid proteins and female proteins associate with sperm immediately after mating. Few seminal fluid proteins remain after long-term sperm storage, whereas female-derived proteins constitute one-fifth of the postmating sperm proteome by then. Our data reveal a molecular “hand-off” from males to females, which we postulate to be an important component of sperm–female interactions.
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- 2022
4. Cost of an elaborate trait: a trade-off between attracting females and maintaining a clean ornament
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Chun-Chia Chou, Patricia R. Y. Backwell, and Erin L McCullough
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0106 biological sciences ,0303 health sciences ,animal structures ,Biology ,biology.organism_classification ,Trade-off ,010603 evolutionary biology ,01 natural sciences ,Fiddler crab ,03 medical and health sciences ,Mate choice ,Sexual selection ,Trait ,Animal Science and Zoology ,Marketing ,Ecology, Evolution, Behavior and Systematics ,030304 developmental biology - Abstract
Many sexually selected ornaments and weapons are elaborations of an animal’s outer body surface, including long feathers, colorful skin, and rigid outgrowths. The time and energy required to keep these traits clean, attractive, and in good condition for signaling may represent an important but understudied cost of bearing a sexually selected trait. Male fiddler crabs possess an enlarged and brightly colored claw that is used both as a weapon to fight with rival males and also as an ornament to court females. Here, we demonstrate that males benefit from grooming because females prefer males with clean claws over dirty claws but also that the time spent grooming detracts from the amount of time available for courting females. Males, therefore, face a temporal trade-off between attracting the attention of females and maintaining a clean claw. Our study provides rare evidence of the importance of grooming for mediating sexual interactions in an invertebrate, indicating that sexual selection has likely shaped the evolution of self-maintenance behaviors across a broad range of taxa.
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- 2020
5. Exploratory Activities for Understanding Evolutionary Relationships Depicted by Phylogenetic Trees: United but Diverse
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Erin L. McCullough, Alaina Weinsztok, Lauren Verdeflor, Steve Dorus, and Jason R. Wiles
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0106 biological sciences ,Phylogenetic tree ,Process (engineering) ,media_common.quotation_subject ,05 social sciences ,050301 education ,Tree of life ,010603 evolutionary biology ,01 natural sciences ,Agricultural and Biological Sciences (miscellaneous) ,Data science ,Article ,Education ,Cladogram ,Component (UML) ,Active learning ,ComputingMilieux_COMPUTERSANDEDUCATION ,General Agricultural and Biological Sciences ,0503 education ,Diversity (politics) ,media_common - Abstract
Evolution explains both the unity and the diversity of all organisms, and developing students' ability to represent and communicate evolutionary relationships is an important component of a complete biology education. We present a series of student-centered, exploratory activities to help students develop their tree-thinking skills. In these activities, students use complementary phenotypic and molecular data to explore how to build phylogenetic trees and interpret the evolutionary relationships they represent. This learning module is designed to engage students in the process of science, provide them with active learning experiences using online bioinformatics tools, and foster their appreciation for the evolutionary connections across the tree of life.
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- 2020
6. China's domestic and foreign influence in the global cobalt supply chain
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Erin A. McCullough, Andrew L. Gulley, and Kim B. Shedd
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Economics and Econometrics ,Sociology and Political Science ,business.industry ,020209 energy ,Supply chain ,chemistry.chemical_element ,02 engineering and technology ,Foreign direct investment ,010501 environmental sciences ,Management, Monitoring, Policy and Law ,01 natural sciences ,Refinery ,Agricultural economics ,chemistry ,0202 electrical engineering, electronic engineering, information engineering ,Production (economics) ,Business ,China ,Law ,Commodity (Marxism) ,Cobalt ,0105 earth and related environmental sciences ,Downstream (petroleum industry) - Abstract
In addition to increasing interest in the supply risk of minerals produced in China, there is also concern that China's efforts to mitigate its own mineral supply risk—through overseas foreign direct investment—may limit mineral availability for other countries in the short-term (due to production capacity constraints). However, little is publicly known about the quantity of global mineral production that is subject to Chinese ownership influence or how this influence may mitigate China's exposure to mineral commodity supply risk. In this analysis, we estimate China's ownership-share of foreign production for cobalt mine and intermediate materials (in the year 2016), as well as the net import reliance of China's cobalt refinery industry—which is then adjusted to reflect China's ownership share of foreign production. First, we find that China's foreign cobalt ownership is predominantly in the Democratic Republic of the Congo, the largest source of cobalt mine and intermediate imports for China's growing cobalt refinery industry. Second, overseas foreign direct investment provided China with ownership influence over roughly 29% of its cobalt mine and intermediate imports in 2016—which may have reduced the supply risk exposure of China's refinery industry from a net import reliance of 97% (on cobalt mine and intermediate materials) to an adjusted net import reliance of 68%. Third, China's global production share jumps from 2% to 14% (for cobalt mine material) and from 11% to 33% (for cobalt intermediate material) when China's ownership-share of foreign production is added to China's domestic production share. Fourth, over time China's foreign direct investment appears to have targeted facilities with progressively larger cobalt production capacities. Finally, China's global production share increases as cobalt material moves downstream (i.e. mine, 14%; intermediate, 33%; refined, 50% in 2016). If a primary motivation of China's Going Out Strategy is to secure natural resources, then China's global production share may be reserved for Chinese manufacturers. As a result, this analysis indicates that—for countries outside China—concerns related to critical mineral availability and supply risk may not be confined to minerals produced in China.
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- 2019
7. Critical minerals: A review of elemental trends in comprehensive criticality studies
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Erin A. McCullough and Sarah M. Hayes
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Economics and Econometrics ,Sociology and Political Science ,Computer science ,020209 energy ,Context (language use) ,02 engineering and technology ,010501 environmental sciences ,Management, Monitoring, Policy and Law ,01 natural sciences ,Data science ,Variety (cybernetics) ,Criticality ,0202 electrical engineering, electronic engineering, information engineering ,Geographic regions ,Law ,0105 earth and related environmental sciences - Abstract
Mineral criticality is a subjective concept that has evolved throughout history. An abundance of literature on this topic has been published over the last decade, encompassing a variety of criteria and methodologies. To our knowledge, this work is the first large-scale effort to organize and analyze recent comprehensive criticality studies in order to determine if a consensus exists within the global community as to which elements are critical. Here, we set aside methodological differences and analyze the results of 32 comprehensive nonfuel mineral criticality studies that evaluate at least 10 elements. Of the 56 elements or elemental groups evaluated, the three most commonly identified as critical in these studies are the rare-earth elements (REE), the platinum-group metals (PGM), and indium. Most of the studies also identify tungsten, germanium, cobalt, niobium, tantalum, gallium, and antimony as critical. These results are consistent with the 11 most recent studies, published post-2014, which also identify bismuth as critical. Furthermore, the same elements identified in the complete dataset, except antimony, were designated as critical when normalized by geographic region. Magnesium was also deemed critical. Elements may be identified consistently as critical for several reasons; similarities in methodologies, which embody evolving perceptions of risk, or changing national and institutional priorities. This work compiles a large number of recent criticality studies in an effort to define a consensus of currently critical materials, essentially defining the modern criticality paradigm, which is valuable when interpreting an individual perspective in more global context.
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- 2018
8. The role of claw color in species recognition and mate choice in a fiddler crab
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Daniela M. Perez, Miranda L. Dyson, Tony Curran, Erin L McCullough, and Patricia R. Y. Backwell
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Claw ,animal structures ,genetic structures ,Lizard ,Zoology ,Biology ,biology.organism_classification ,Fiddler crab ,Intraspecific competition ,body regions ,Mate choice ,Animal ecology ,biology.animal ,Animal Science and Zoology ,Stabilizing selection ,Ecology, Evolution, Behavior and Systematics ,Hue - Abstract
Abstract Many animal signals are brightly colored and convey information about species identity as well as information about individual conspecifics. Colorful bird and lizard signals have received much attention, and many studies have related specific spectral properties of these signals to variation in mating success and territory defense. Far less attention has been given to invertebrates even though there are spectacularly colorful species. The enlarged claw of the male banana fiddler crab Austruca mjoebergi, for example, is bright yellow and contrasts vividly against the mudflat substrate. It is used in waving displays to attract females and in male territory defense and combat. Claw color varies among males in the degree of “yellowness,” ranging very pale yellow to orange. In this study, we examined female responses to claw color variation in two-choice tests using robotic crabs. We found that although females strongly discriminate against colors that fall outside the natural range of intensity, hue, and chroma, they show no consistent preferences for different claw colors within the natural range, and no single component of claw color (hue, chroma, or intensity) independently affected female choices. Using three-choice tests, we also showed that female preferences induce stabilizing selection on male claw color. We conclude that, although claw color is sufficient to facilitate species recognition, it is unlikely to be used in intraspecific mate choice to provide information about male quality. Significance statement Fiddler crabs are often brightly colored, are visually orientated animals, and have a highly complex social system. Despite this, there are few studies that have looked at the role of color in species recognition and mate choice in these animals. In this study, we use robotic crabs with painted claws to determine the role of claw color in species recognition and mate choice in the banana fiddler crab, Austruca mjoebergi. We found that color is important in conspecific mate recognition but the variation among males in claw “yellowness” is unlikely to be used by females in intraspecific mate choice decisions.
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- 2020
9. Population density mediates the interaction between pre‐ and postmating sexual selection
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Erin L. McCullough, Bruno A. Buzatto, and Leigh W. Simmons
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Male ,0106 biological sciences ,0301 basic medicine ,Zoology ,Onthophagus taurus ,Context (language use) ,010603 evolutionary biology ,01 natural sciences ,Population density ,03 medical and health sciences ,Genetics ,Animals ,Mating ,Sperm competition ,Ecology, Evolution, Behavior and Systematics ,Selection (genetic algorithm) ,Population Density ,biology ,Mating Preference, Animal ,biology.organism_classification ,humanities ,Coleoptera ,030104 developmental biology ,Fertilization ,Sexual selection ,Female ,Genetic Fitness ,General Agricultural and Biological Sciences ,Scramble competition ,Microsatellite Repeats - Abstract
When females mate with more than one male, sexual selection acts both before and after mating. The interaction between pre- and postmating episodes of selection is expected to be context dependent, but few studies have investigated how total sexual selection changes under different ecological conditions. We examined how population density mediates the interaction between pre- and postmating sexual selection by establishing replicate populations of the horned dung beetle Onthophagus taurus at low, medium, and high densities, and then using microsatellite-based parentage analyses to measure male fitness. We found that mating success and fertilization success were positively correlated at all three densities, but the strength of the correlation decreased with increasing density. We also found a shift from negative to positive linear selection on testes mass as density increased, and opposing selection on weapons and testes at high densities. These patterns suggest that the importance of postmating processes increases with increasing population density, which reduces the selective advantage of weapons for premating contest competition, and increases the selective advantage of large ejaculates for postmating sperm competition. We expect that density-dependent selection on testes mass has contributed to the phenotypic variation observed between natural populations of O. taurus that differ in density.
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- 2018
10. Assessment of critical minerals: updated application of an early-warning screening methodology
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Nedal T. Nassar and Erin A. McCullough
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Warning system ,Natural resource economics ,Chemistry ,020209 energy ,Economics, Econometrics and Finance (miscellaneous) ,02 engineering and technology ,010501 environmental sciences ,Market dynamics ,01 natural sciences ,Annual change ,Mineral resource classification ,Environmental protection ,0202 electrical engineering, electronic engineering, information engineering ,Volatility (finance) ,Social Sciences (miscellaneous) ,0105 earth and related environmental sciences - Abstract
Increasing reliance on non-renewable mineral resources reinforces the need for identifying potential supply constraints before they occur. The US National Science and Technology Council recently released a report that outlines a methodology for screening potentially critical minerals based on three indicators: supply risk (R), production growth (G), and market dynamics (M). This early-warning screening was initially applied to 78 minerals across the years 1996 to 2013 and identified a subset of minerals as “potentially critical” based on the geometric average of these indicators—designated as criticality potential (C). In this study, the screening methodology has been updated to include data for 2014, as well as to incorporate revisions and modifications to the data, where applicable. Overall, C declined in 2014 for the majority of minerals examined largely due to decreases in production concentration and price volatility. However, the results vary considerably across minerals, with some minerals, such as gallium, recording increases for all three indicators. In addition to assessing magnitudinal changes, this analysis also examines the significance of the change relative to historical variation for each mineral. For example, although mined nickel’s R declined modestly in 2014 in comparison to that of other minerals, it was by far the largest annual change recorded for mined nickel across all years examined and is attributable to Indonesia’s ban on the export of unprocessed minerals. Based on the 2014 results, 20 minerals with the highest C values have been identified for further study including the rare earths, gallium, germanium, rhodium, tantalum, and tungsten.
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- 2017
11. Benefits of polyandry: Molecular evidence from field‐caught dung beetles
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Bruno A. Buzatto, Erin L. McCullough, and Leigh W. Simmons
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Male ,0106 biological sciences ,0301 basic medicine ,Genotype ,Offspring ,media_common.quotation_subject ,Onthophagus taurus ,Biology ,010603 evolutionary biology ,01 natural sciences ,Sexual Behavior, Animal ,03 medical and health sciences ,Genetics ,Animals ,Mating ,Sperm competition ,reproductive and urinary physiology ,Ecology, Evolution, Behavior and Systematics ,media_common ,Reproduction ,biology.organism_classification ,Spermatozoa ,Coleoptera ,030104 developmental biology ,Female sperm storage ,Onthophagus ,Evolutionary biology ,Sexual selection ,behavior and behavior mechanisms ,Female ,Genetic Fitness ,Microsatellite Repeats - Abstract
When females mate with multiple males, they set the stage for postcopulatory sexual selection via sperm competition and/or cryptic female choice. Surprisingly little is known about the rates of multiple mating by females in the wild, despite the importance of this information in understanding the potential for postcopulatory sexual selection to drive the evolution of reproductive behaviour, morphology and physiology. Dung beetles in the genus Onthophagus have become a laboratory model for studying pre- and postcopulatory sexual selection, yet we still lack information about the reproductive behaviour of female dung beetles in natural populations. Here, we develop microsatellite markers for Onthophagus taurus and use them to genotype the offspring of wild-caught females and to estimate natural rates of multiple mating and patterns of sperm utilization. We found that O. taurus females are highly polyandrous: 88% of females produced clutches sired by at least two males, and 5% produced clutches with as many as five sires. Several females (23%) produced clutches with significant paternity skew, indicating the potential for strong postcopulatory sexual selection in natural populations. There were also strong positive correlations between the number of offspring produced and both number of fathers and paternity skew, which suggests that females benefit from mating polyandrously by inciting postcopulatory mechanisms that bias paternity towards males that can sire more viable offspring. This study evaluates the fitness consequences of polyandry for an insect in the wild and provides strong evidence that female dung beetles benefit from multiple mating under natural conditions.
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- 2017
12. Global Trends in Mineral Commodities for Advanced Technologies
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Erin A. McCullough, Steven M. Fortier, Christine L. Thomas, and Amy C. Tolcin
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Sustainable development ,National security ,business.industry ,Natural resource economics ,Supply chain ,Corporate governance ,010501 environmental sciences ,010502 geochemistry & geophysics ,01 natural sciences ,Mineral resource classification ,Supply and demand ,Commerce ,Geological survey ,Economics ,Volatility (finance) ,business ,0105 earth and related environmental sciences ,General Environmental Science - Abstract
The U.S. Geological Survey National Minerals Information Center (NMIC) is the U.S. Government agency tasked with the collection, analysis, and dissemination of information on the production, consumption, import, export, and other measures of the flows of non-fuel mineral commodities of importance to the U.S. economy and national security. The NMIC and its agency predecessors have maintained a database of this information, collected and published annually, dating back to the beginning of the twentieth century. Time series analysis of annual information from the NMIC provides the opportunity to identify trends in the supply chains of the minerals and metals which are increasingly in demand for advanced technologies. The identification of trends in data for net import reliance, country concentration of production, global demand, price volatility, and other measures, when combined with world governance indicators, can be used to focus attention on individual mineral commodities where supply chain restrictions may develop. Specific examples for U.S. net import reliance, global tantalum primary mining, and mineral criticality screening are presented to illustrate the utility of time series analysis of trends in mineral commodity supply and demand, the types of data required, and the limitations of currently available information.
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- 2017
13. Staying cool: the importance of shade availability for tropical ectotherms
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Chun-Chia Chou, Megan L. Head, Erin L. McCullough, Patricia R. Y. Backwell, Sophie Johns, Daniela M. Perez, R. Gardner, and Kecia A. Kerr
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0106 biological sciences ,Time budget ,Ecology ,05 social sciences ,Global warming ,Biology ,biology.organism_classification ,010603 evolutionary biology ,01 natural sciences ,Fiddler crab ,Austruca mjoebergi ,Animal ecology ,Ectotherm ,0501 psychology and cognitive sciences ,Animal Science and Zoology ,050102 behavioral science & comparative psychology ,Mating ,Ecology, Evolution, Behavior and Systematics - Abstract
Understanding how organisms mitigate the impacts of climate warming is one of the biggest challenges facing modern-day biologists. For tropical ectotherms, staying cool is critical for avoiding thermal stress, so individuals that are able to maintain territories in cool microhabitats are likely to gain fitness advantages. This study evaluated the importance of shade availability in the tropical fiddler crab, Austruca mjoebergi, by investigating temperature variation and behavioral responses (distribution, activity level, and time budget) in sun-exposed and shaded microhabitats. We found that the daily temperatures in sun-exposed microhabitats were significantly higher than in shady microhabitats, and that more male crabs held territories in the shade. Shaded males were active on the sediment surface for longer periods each day, allowing more time for feeding and more opportunities to detect mate-searching females. The greater number of males resident in the shade, and shorter distances between male neighbors in the shade, suggested that there was less available space for individuals to move into the shaded microhabitats. The behavioral differences between sun- and shade-living residents are likely to have consequences for male fitness. We highlight the importance of shade in providing thermal refugia for tropical ectotherms. The impact of climate warming on tropical organisms could be less dire if individuals are able to access shade. Shade can offer thermal refugia for tropical organisms that may have important consequences for both behavior and fitness. Relatively low and stable temperatures in shaded areas allow male fiddler crabs to remain on the surface for longer compared to sun-exposed males, allowing for longer feeding periods and more mating opportunities.
- Published
- 2019
14. Muscle mass drives cost in sexually selected arthropod weapons
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Erin L. McCullough, Ummat Somjee, Gregory I. Holwell, Anthony J. R. Hickey, Romain P. Boisseau, Devin M. O'Brien, Douglas J. Emlen, Meghan Duell, Erin C. Powell, Christina J. Painting, and Sarah Solie
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0106 biological sciences ,Evolution ,Sexual Behavior ,Biology ,Computer security ,computer.software_genre ,Muscle mass ,010603 evolutionary biology ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,03 medical and health sciences ,Animals ,Arthropods ,030304 developmental biology ,General Environmental Science ,0303 health sciences ,General Immunology and Microbiology ,Muscles ,fungi ,General Medicine ,social sciences ,Metabolic cost ,humanities ,Phenotype ,Metabolic rate ,population characteristics ,Weapons ,General Agricultural and Biological Sciences ,computer - Abstract
Sexually selected weapons often function as honest signals of fighting ability. If poor-quality individuals produce high-quality weapons, then receivers should focus on other, more reliable signals. Cost is one way to maintain signal integrity. The costs of weapons tend to increase with relative weapon size, and thereby restrict large weapons to high-quality individuals who can produce and maintain them. Weapon cost, however, appears to be unpredictably variable both within and across taxa, and the mechanisms underlying this variation remain unclear. We suggest variation in weapon cost may result from variation in weapon composition—specifically, differences in the amount of muscle mass directly associated with the weapon. We test this idea by measuring the metabolic cost of sexually selected weapons in seven arthropod species and relating these measures to weapon muscle mass. We show that individuals with relatively large weapon muscles have disproportionately high resting metabolic rates and provide evidence that this trend is driven by weapon muscle mass. Overall, our results suggest that variation in weapon cost can be partially explained by variation in weapon morphology and that the integrity of weapon signals may be maintained by increased metabolic cost in species with relatively high weapon muscle mass.
- Published
- 2019
15. Pronounced Postmating Response in the Drosophila Female Reproductive Tract Fluid Proteome
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Scott E. Erdman, Erin L. McCullough, Steve Dorus, Emma Whittington, Scott Pitnick, Caitlin E. McDonough-Goldstein, and Sharleen M. Buel
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Male ,endocrine system ,Proteome ,biology ,Translation (biology) ,Genitalia, Female ,Saccharomyces cerevisiae ,Proteomics ,biology.organism_classification ,Biochemistry ,Sperm ,Analytical Chemistry ,Cell biology ,Sexual Behavior, Animal ,Drosophila melanogaster ,Gene expression ,Animals ,Drosophila Proteins ,Female ,Molecular Biology ,Gene ,Sperm motility - Abstract
Fertility depends on the progression of complex and coordinated postmating processes within the extracellular environment of the female reproductive tract (FRT). Molecular interactions between ejaculate and FRT proteins regulate many of these processes, including sperm motility, migration, storage, and modification, along with concurrent changes in the female. Although extensive progress has been made in the proteomic characterization of male-derived components of sperm and seminal fluid, investigations into the FRT have remained more limited. To achieve a comparable level of knowledge regarding female-derived proteins that comprise the reproductive environment, we utilized semiquantitative mass spectrometry-based proteomics to study the composition of the FRT tissue and, separately, the luminal fluid, before and after mating in Drosophila melanogaster. Our approach leveraged whole-fly isotopic labelling to delineate female proteins from those transferred male ejaculate proteins. Our results revealed several characteristics that distinguish the FRT fluid proteome from the FRT tissue proteome: (1) the fluid proteome is encoded by genes with higher overall levels of FRT gene expression and tissue specificity, including many genes with enriched expression in the fat body, (2) fluid-biased proteins are enriched for metabolic functions and (3) the fluid exhibits pronounced postmating compositional changes. The dynamic mating-induced proteomic changes in the FRT fluid informs our understanding of secretory mechanisms of the FRT, serves as a foundation for establishing female contributions to the ejaculate-female interactions that regulate fertility and highlights the importance of applying proteomic approaches to characterize the composition and dynamics of the FRT environment.
- Published
- 2021
16. Selection on male physical performance during male–male competition and female choice
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Leigh W. Simmons and Erin L. McCullough
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0106 biological sciences ,0301 basic medicine ,Ecology ,media_common.quotation_subject ,Onthophagus taurus ,Biology ,Mating system ,biology.organism_classification ,010603 evolutionary biology ,01 natural sciences ,Sexual dimorphism ,Courtship ,03 medical and health sciences ,030104 developmental biology ,Mate choice ,Sexual selection ,Animal Science and Zoology ,Mating ,Scramble competition ,Ecology, Evolution, Behavior and Systematics ,Demography ,media_common - Abstract
Male contest competition and female choice are key features of the mating systems of many species, and whole-organism performance may be targeted by both mechanisms given the dynamic body movements required during fighting and courtship displays. Using the dimorphic horned dung beetle Onthophagus taurus as a model system, we tested whether physical performance was important in determining a male’s victory in fights, and whether successful fighters were preferred by females as mates. We found that physical strength, horn length, and body mass were significant predictors of male fighting success, but males that won fights were not more attractive to females. Rather, females preferred males that delivered a high courtship rate, which was not correlated with strength, horn length, or body mass, but previously has been shown to be genetically correlated with body condition. The fact that there was no relationship between fighting success and mating success suggests that selection on traits favored by male–male competition and female choice can act relatively independently in this species, although both mechanisms appear to favor traits (strength and courtship, respectively) that are linked to a male’s ability to acquire and allocate resources for mass gain. Future work is needed to determine the relative contributions of these processes to the total strength of sexual selection acting on male phenotypes.
- Published
- 2016
17. Emerald ash borer and the urban forest: Changes in landslide potential due to canopy loss scenarios in the City of Pittsburgh, PA
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Jeffery Bergman, Daniel J. Bain, Erin Pfeil-McCullough, and Danielle Crumrine
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Hydrology ,Canopy ,Environmental Engineering ,biology ,Environmental engineering ,Poison control ,Landslide ,Pennsylvania ,biology.organism_classification ,Risk Assessment ,Pollution ,Coleoptera ,Geospatial predictive modeling ,Emerald ash borer ,Fraxinus ,Urban forest ,Spatial ecology ,Cohesion (geology) ,Animals ,Environmental Chemistry ,Environmental science ,Cities ,Waste Management and Disposal ,Landslides - Abstract
Emerald ash borer is expected to kill thousands of ash trees in the eastern U.S. This research develops tools to predict the effect of ash tree loss from the urban canopy on landslide susceptibility in Pittsburgh, PA. A spatial model was built using the SINMAP (Stability INdex MAPping) model coupled with spatially explicit scenarios of tree loss (0%, 25%, 50%, and 75% loss of ash trees from the canopy). Ash spatial distributions were estimated via Monte Carlo methods and available vegetation plot data. Ash trees are most prevalent on steeper slopes, likely due to urban development patterns. Therefore, ash loss disproportionately increases hillslope instability. A 75% loss of ash resulted in roughly 800 new potential landslide initiation locations. Sensitivity testing reveals that variations in rainfall rates, and friction angles produce minor changes to model results relative to the magnitude of parameter variation, but reveal high model sensitivity to soil density and root cohesion values. The model predictions demonstrate the importance of large canopy species to urban hillslope stability, particularly on steep slopes and in areas where soils tend to retain water. To improve instability predictions, better characterization of urban soils, particularly spatial patterns of compaction and species specific root cohesion is necessary. The modeling framework developed in this research will enhance assessment of changes in landslide risk due to tree mortality, improving our ability to design economically and ecologically sustainable urban systems.
- Published
- 2015
18. Variation in the allometry of exaggerated rhinoceros beetle horns
- Author
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Devin M. O'Brien, Erin L. McCullough, Douglas J. Emlen, and Kimberly J. Ledger
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Sexual dimorphism ,biology ,Ecology ,Horn (anatomy) ,Stag beetle ,Sexual selection ,Giraffe weevil ,Animal Science and Zoology ,Rhinoceros ,Allometry ,biology.organism_classification ,Ecology, Evolution, Behavior and Systematics ,Dynastinae - Abstract
Exaggerated horns are a characteristic feature of many male rhinoceros beetles. We surveyed and compared the scaling relationships of these sexually selected weapons for 31 Dynastinae species with different degrees of horn exaggeration. We found that nearly all rhinoceros beetle species were male dimorphic, that the allometric slope of major males was consistently shallower than the slope of minor males, and that the decrease in slope was greatest among species with the most exaggerated horns. These patterns are consistent with the curved allometries of stag beetle mandibles and giraffe weevil rostra, and suggest that the depletion of developmental resources is a general phenomenon limiting the continued exaggeration of insect weapons. The dimorphisms in horn morphology are expected to correspond to behavioural differences between major and minor males, but little is still known about the mating tactics of most rhinoceros beetle species. Future studies on the relative benefits and performance of horns during male–male combat are needed to fully understand the diversity of horn allometries and the evolution of exaggerated structures.
- Published
- 2015
19. Seasonal drivers of chemical and hydrological patterns in roadside infiltration-based green infrastructure
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Erin M. Copeland, Angela R. Mullins, Daniel J. Bain, Sarah M. Lavin, Kristina G. Hopkins, and Erin Pfeil-McCullough
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Hydrology ,Environmental Engineering ,010504 meteorology & atmospheric sciences ,Water table ,Stormwater ,010501 environmental sciences ,Infiltration (HVAC) ,01 natural sciences ,Pollution ,Nutrient ,Evapotranspiration ,Trench ,Environmental Chemistry ,Green infrastructure ,Waste Management and Disposal ,Groundwater ,0105 earth and related environmental sciences - Abstract
Infiltration-based green infrastructure has become a popular means of reducing stormwater hazards in urban areas. However, the long-term effects of green infrastructure on the geochemistry of roadside environments are poorly defined, particularly given the considerable roadside legacy metal contamination from historic industrial activity and vehicle emissions (e.g., Pb). Most current research on green infrastructure geochemistry is restricted to time periods of less than a year or limited sets of chemical species. This further limits our understanding of systems that evolve over time and are subject to seasonal variability. Between 2016 and 2018, two infiltration trenches in Pittsburgh, PA, were monitored to determine infiltration rates and dissolved nutrient and metal content. The trench water was analyzed to characterize seasonal patterns in both trench function and chemistry. Shifting patterns in infiltration rate and geochemical activity show trends corresponding with seasonal changes. Trench function is dependent on the local water table, with the highest infiltration rates occurring when evapotranspiration is active and groundwater elevation is low. Two seasonal chemical patterns were identified. The first is driven by road salt application in the winter and interaction of the salt pulse increase Pb and Cu concentrations. The second is driven by the formation of summer reducing environments that increase dissolved Fe and Mn. These findings suggest that chemical and hydrological activity in infiltration-based green infrastructure varies seasonally and may remobilize legacy contamination.
- Published
- 2020
20. Draft critical mineral list—Summary of methodology and background information—U.S. Geological Survey technical input document in response to Secretarial Order No. 3359
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Graham W. Lederer, Nedal T. Nassar, Erin A. McCullough, Joseph Gambogi, Steven M. Fortier, and Jamie Brainard
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Transport engineering ,Background information ,Order (business) ,Geological survey ,Environmental science - Published
- 2018
21. Variation in cross-sectional horn shape within and among rhinoceros beetle species
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Kimberly J. Ledger, Talia Y. Moore, and Erin L. McCullough
- Subjects
Prothorax ,Ecology ,Sexual selection ,Functional morphology ,Rhinoceros ,Microcomputed tomography ,Body size ,Biology ,biology.organism_classification ,Ecology, Evolution, Behavior and Systematics ,Horn structure ,Dynastinae - Abstract
Sexual selection has equipped male rhinoceros beetles with large horns on their head and prothorax to aid in battle over access to females. Horns are used to pry and dislodge opponents from resource sites that attract females, so an optimal horn should be able both to withstand the high stresses imposed during fights, and to resist deflection in response to these loads. We examined the cross-sectional morphology of horns using microcomputed tomography scanning to determine how horn structure changes with horn length to withstand the different fighting loads. Specifically, we measured the second moment of area of horns within and among rhinoceros beetle species to assess whether changes in cross-sectional morphology accompany changes in body size in order to maintain high strength and stiffness during fights. We find that the second moment of area of horns increases with body size both intra-specifically and inter-specifically, and that these relationships closely fit those predicted if horns have been selected to be strong and stiff fighting structures. Our results therefore support the hypothesis that rhinoceros beetle horns are structurally adapted for combat. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 00: 000–000.
- Published
- 2015
22. Honeybees Use Celestial and/or Terrestrial Compass Cues for Inter-Patch Navigation
- Author
-
Rudolf Jander, Daniel A. Najera, and Erin L. McCullough
- Subjects
Honey Bees ,Communication ,business.industry ,Compass ,Foraging ,Representation (systemics) ,Animal Science and Zoology ,Biology ,business ,Ecology, Evolution, Behavior and Systematics - Abstract
Foraging honeybees (Apis mellifera) are well known to fly straight from the hive, their primary hub, to distal goals as well as between familiar feeding sites. More recently, it was shown that a distal feeding site may be used as a secondary hub. If not fully satiated, the foraging bee may decide to depart the first feeding site in a new compass direction straight to one of many other feeding sites (inter-patch foraging). Using a recently developed recording method, we discovered that the chosen departure direction at a secondary hub can be guided exclusively by either celestial or terrestrial compass cues. Given our data, we draw two theoretical inferences. First, the bees must be capable of learning and remembering multiple, spatially distinct, navigation vectors between the hive and among multiple feeding sites. Second, this documented and useful representation of multiple navigation vectors between multiple, identified target locations logically implies composite place-vector mapping, stored in long-term memory.
- Published
- 2014
23. Evaluating the costs of a sexually selected weapon: big horns at a small price
- Author
-
Douglas J. Emlen and Erin L. McCullough
- Subjects
Public economics ,Horn (anatomy) ,Ecology ,media_common.quotation_subject ,Cheating ,Ornaments ,Rhinoceros ,Biology ,Sexual selection ,Animal Science and Zoology ,Quality (business) ,Trypoxylus dichotomus ,Ecology, Evolution, Behavior and Systematics ,media_common - Abstract
A major assumption of sexual selection theory is that ornaments and weapons are costly. Such costs should maintain the reliability of ornaments and weapons as indicators of male quality, and therefore explain why choosy females and rival males pay attention to these traits. However, honest signalling may not depend on costs if the penalty for cheating is sufficiently high, a situation that is likely to be true for most weapons because they are frequently tested during combat. We examined and summarized the costs of producing and carrying giant horns in the rhinoceros beetle, Trypoxylus dichotomus. Remarkably, we found no evidence for fitness costs. Previously we found that horns do not impair flight performance, and here we found that horns did not stunt the growth of other body structures or weaken the beetles' immune response. Finally, and most importantly, horns did not reduce male survival in the field. Collectively, our results provide strong evidence that the exaggerated horns of T. dichotomus are surprisingly inexpensive. We discuss why weapons may be inherently less costly than ornaments, and suggest that the lack of fitness costs offers a simple, yet unexpected, explanation for why rhinoceros beetle horns are both elaborate and diverse.
- Published
- 2013
24. Sensilla Density Corresponds to the Regions of the Horn Most Frequently Used During Combat in the Giant Rhinoceros Beetle Trypoxylus dichotomus (Coleoptera: Scarabaeidae: Dynastinae)
- Author
-
Robert A. Zinna and Erin L. McCullough
- Subjects
Scarabaeidae ,Sensory input ,Horn (anatomy) ,Ecology ,Insect Science ,Functional significance ,Rhinoceros ,Biology ,biology.organism_classification ,Trypoxylus dichotomus ,Sensillum ,Dynastinae - Abstract
In the Japanese horned beetle, Trypoxylus dichotomus (L.), males have a long forked head horn that they use in fights with other males over access to sap sites that attract females. Because of the high risk of injury from these contests, males should assess the fighting potential of their rivals before escalating to direct combat. Indeed, male rhinoceros beetles only escalate to intense fighting when matched with equal-sized rivals. Males often tap their opponents with their head horn before and during fights, so it is likely that beetles assess the size of their competitors via sensory input from their horns. Here, we used scanning electron microscopy to examine the density and distribution of sensory hairs along the length of the males’ horn. To assess the potential functional significance of variation in hair density, we combined our microscopy observations with a behavioral analysis of how males use their horns during fights. We found a strong correlation between the density of sensory hairs and the regions of the horns that were used most during combat. The distal tips of the horns had the highest hair density, and were also the region of the horn most frequently in contact with an opponent. Given the shaft and socket morphology of these hairs, which is the characteristic morphology of mechanoreceptors, we expect that they provide mechanosensory input. Thus, although beetle horns are often described as dedicated weapons, our results suggest that the head horns of T. dichotomus also play an important sensory role.
- Published
- 2013
25. Interpatch foraging in honeybees—rational decision making at secondary hubs based upon time and motivation
- Author
-
Rudolf Jander, Erin L. McCullough, and Daniel A. Najera
- Subjects
Forage (honey bee) ,Logical operations ,Decision Making ,Foraging ,Experimental and Cognitive Psychology ,Machine learning ,computer.software_genre ,Rational planning model ,Cognition ,Homing Behavior ,Time of day ,Conditional logic ,Animals ,Ecology, Evolution, Behavior and Systematics ,Motivation ,Communication ,Cognitive map ,business.industry ,Distal site ,Feeding Behavior ,Bees ,Geography ,Time Perception ,Artificial intelligence ,business ,computer - Abstract
For honeybees, Apis mellifera, the hive has been well known to function as a primary decision-making hub, a place from which foragers decide among various directions, distances, and times of day to forage efficiently. Whether foraging honeybees can make similarly complex navigational decisions from locations away from the hive is unknown. To examine whether or not such secondary decision-making hubs exist, we trained bees to forage at four different locations. Specifically, we trained honeybees to first forage to a distal site "CT" 100 m away from the hive; if food was present, they fed and then chose to go home. If food was not present, the honeybees were trained to forage to three auxiliary sites, each at a different time of the day: A in the morning, B at noon, and C in the afternoon. The foragers learned to check site CT for food first and then efficiently depart to the correct location based upon the time of day if there was no food at site CT. Thus, the honeybees were able to cognitively map motivation, time, and five different locations (Hive, CT, A, B, and C) in two spatial dimensions; these are the contents of the cognitive map used by the honeybees here. While at site CT, we verified that the honeybees could choose between 4 different directions (to A, B, C, and the Hive) and thus label it as a secondary decision-making hub. The observed decision making uncovered here is inferred to constitute genuine logical operations, involving a branched structure, based upon the premises of motivational state, and spatiotemporal knowledge.
- Published
- 2012
26. Using Radio Telemetry to Assess Movement Patterns in a Giant Rhinoceros Beetle: Are There Differences Among Majors, Minors, and Females?
- Author
-
Erin L. McCullough
- Subjects
Sexual dimorphism ,Entomology ,Horn (anatomy) ,Animal ecology ,Ecology ,Insect Science ,Biological dispersal ,Zoology ,Rhinoceros ,Mating ,Biology ,Trypoxylus dichotomus ,Ecology, Evolution, Behavior and Systematics - Abstract
The Japanese horned beetle Trypoxylus dichotomus is a peculiar example of a maledimorphic species that does not exhibit any alternative reproductive tactics. Typically, differences in male morphology correspond to marked differences in mating behaviors (Dominey 1984; Gross 1996). Large males tend to adopt aggressive, territorial tactics to attract and secure females, while small or otherwise inferior males try to mate via sneak or satellite tactics, or by dispersing away from dominant males (reviewed in Oliveira et al. 2008). Alternative reproductive tactics are expected to favor distinct male morphologies, because exaggerated weapons that confer fighting advantages to dominant males should impair dispersal and sneaking capabilities (Moczek and Emlen 2000; Madewell and Moczek 2006). Although alternative reproductive tactics have been described in a number of dimorphic beetle species (Eberhard 1982; Rasmussen 1994; Emlen 1997; Moczek and Emlen 2000), T. dichotomus major and minor males apparently do not have distinct mating behaviors. Large major males have a long, branched head horn and short, sharp thoracic horn that they use to pry rival males away from sap sites that attract females. Small minor males have short head and thoracic horns, yet they engage in direct combats with other males just as readily as major males, and do not fight in qualitatively different ways (Hongo 2003). Even though minor males engage in sneak-like behaviors, major males also sneak copulations, and the only male that is known to have successfully mated after sneaking was a major male (Hongo 2007). J Insect Behav (2013) 26:51–56 DOI 10.1007/s10905-012-9334-8
- Published
- 2012
27. Costs of elaborate weapons in a rhinoceros beetle: how difficult is it to fly with a big horn?
- Author
-
Erin L. McCullough, Paul R. Weingarden, and Douglas J. Emlen
- Subjects
Muscle size ,Wing ,Ecology ,Horn (anatomy) ,Sexual selection ,Flight speed ,Zoology ,Animal Science and Zoology ,Ornaments ,Rhinoceros ,Biology ,Muscle mass ,Ecology, Evolution, Behavior and Systematics - Abstract
The giant horns of rhinoceros beetles exemplify the extreme morphologies that can result from sexual selection. Ornaments and weapons help males obtain mates but may also impose fitness costs. Intuitively, exaggerated sexually selected traits should impair locomotion, yet compensatory morphologies often make it difficult to detect locomotor costs. Here, we tested whether horns of the rhinoceros beetle Trypoxylus dichotomus impair flight and whether males compensate by developing larger wings or flight muscles. Contrary to our expectation that horns are costly for flight, males flew as fast as females, and among males, horn length was not correlated with flight speed or distance flown. We found some evidence for compensations in the male flight apparatus; males had relatively larger wings and flight muscles than females, and males with long horns for their body size had larger wings than males with relatively short horns. Flight muscle mass, however, was unaffected by horn length. We conclude that T. dichotomus horns may have been costly in the past and led to morphological compensations in wing and flight muscle size, but they do not currently impose significant flight costs. Fitness costs are a central tenet of sexual selection theory, and the large horns of rhinoceros beetles are expected to impose particularly strong costs on locomotion. Given our finding that T. dichotomus horns are surprisingly easy to carry, future work will be needed to identify the potential costs that have been important in shaping the evolution of elaborate horn morphologies. Key words: compensations, costs, flight, horns, rhinoceros beetles, sexual selection. [Behav Ecol]
- Published
- 2012
28. The research bias is unfortunate but also unsurprising: a comment on Tinghitella et al
- Author
-
Douglas J. Emlen and Erin L. McCullough
- Subjects
0106 biological sciences ,05 social sciences ,0501 psychology and cognitive sciences ,Animal Science and Zoology ,050102 behavioral science & comparative psychology ,Biology ,010603 evolutionary biology ,01 natural sciences ,Ecology, Evolution, Behavior and Systematics ,Epistemology - Published
- 2018
29. Photoperiod-dependent floral reversion in the natural allopolyploid Arabidopsis suecica
- Author
-
Chanel P. Clark, Kirsten M. Wright, Wayne L. Rickoll, Aurelia Alvarez, Erin L. McCullough, and Andreas Madlung
- Subjects
Time Factors ,Physiology ,Photoperiod ,Meristem ,Arabidopsis ,Reversion ,Flowers ,Plant Science ,Biology ,Polyploidy ,Gene Expression Regulation, Plant ,Botany ,Gene ,reproductive and urinary physiology ,Regulator gene ,Regulation of gene expression ,photoperiodism ,Genetics ,Arabidopsis Proteins ,fungi ,food and beverages ,Phenotype ,Inflorescence ,Mutation ,Homeotic gene - Abstract
Flower reversion is the result of genetic or environmental effects that reverse developmental steps in the transition from the vegetative to the reproductive phase in plants. Here, we describe peculiar floral abnormalities, homeotic conversions, and flower reversion in several wild-type accessions of the natural allopolyploid Arabidopsis suecica. Microscopy was used to illustrate the phenotype in detail and we experimented with varying photoperiod lengths to establish whether or not the phenotype was responsive to the environment. We also profiled the transcriptional activity of several floral regulator genes during flower reversion using real-time PCR. We showed that the frequency of floral reversion was affected by day length and the position of the flower along the inflorescence axis. In reverting flowers we found unusual gene expression patterns of floral promoters and inflorescence maintenance genes, including lower mRNA levels of AGAMOUS-LIKE-24 (AGL-24), APETALA1 (AP1), and SHORT VEGETATIVE PHASE (SVP), and higher mRNA levels of SUPRESSOR OF CONSTANS1 (SOC1) compared with normal flowers. We conclude that the floral reversion frequency in A. suecica is susceptible to photoperiod changes, and that the floral abnormalities coincide with the competing expression of floral promoters and floral repressors in reverting floral tissue.
- Published
- 2010
30. Structural adaptations to diverse fighting styles in sexually selected weapons
- Author
-
Erin L. McCullough, Douglas J. Emlen, and Bret W. Tobalske
- Subjects
Male ,Engineering ,Competitive Behavior ,media_common.quotation_subject ,Finite Element Analysis ,Adaptation, Biological ,Poison control ,Rhinoceros ,Diversification (marketing strategy) ,Computer security ,computer.software_genre ,Models, Biological ,Sex Factors ,Species Specificity ,Sex factors ,Form and function ,medicine ,Animals ,media_common ,Horns ,Multidisciplinary ,business.industry ,Aggression ,fungi ,social sciences ,Biological Sciences ,Biological Evolution ,humanities ,Coleoptera ,Sexual selection ,population characteristics ,Female ,medicine.symptom ,business ,computer ,Cognitive psychology ,Diversity (politics) - Abstract
The shapes of sexually selected weapons differ widely among species, but the drivers of this diversity remain poorly understood. Existing explanations suggest weapon shapes reflect structural adaptations to different fighting styles, yet explicit tests of this hypothesis are lacking. We constructed finite element models of the horns of different rhinoceros beetle species to test whether functional specializations for increased performance under species-specific fighting styles could have contributed to the diversification of weapon form. We find that horns are both stronger and stiffer in response to species-typical fighting loads and that they perform more poorly under atypical fighting loads, which suggests weapons are structurally adapted to meet the functional demands of fighting. Our research establishes a critical link between weapon form and function, revealing one way male–male competition can drive the diversification of animal weapons.
- Published
- 2014
31. Heightened condition-dependent growth of sexually selected weapons in the rhinoceros beetle, Trypoxylus dichotomus (Coleoptera: Scarabaeidae)
- Author
-
Laura Corley Lavine, Douglas J. Emlen, Hiroki Gotoh, Erin L. McCullough, and A. Johns
- Subjects
Scarabaeidae ,Male ,Larva ,Sex Characteristics ,Ecology ,Rhinoceros ,Ornaments ,Plant Science ,Biology ,biology.organism_classification ,Biological Evolution ,Coleoptera ,Sexual Behavior, Animal ,Sexual selection ,External genitalia ,Animals ,Animal Science and Zoology ,Female ,Selection, Genetic ,Trypoxylus dichotomus ,Corticosterone ,Condition dependent - Abstract
Synopsis The exaggerated weapons and ornaments of sexual selection are condition-dependent traits that often grow to exaggerated proportions. The horns of male rhinoceros beetles are extremely sensitive to the larval nutritional environment and are used by rival males in combat over access to females. In contrast to horns, other parts of the body, such as wings, eyes, and legs, scale proportionally with body size, whereas others, such as males’ external genitalia, are invariant with body size, regardless of nutrition. We document how body parts of the Asian rhinoceros beetle, Trypoxylus dichotomus, exhibit plasticity and constraint in response to nutritional condition. We discuss the implications of these results for the evolution of condition-dependent and condition-independent traits in animals.
- Published
- 2014
32. Elaborate horns in a giant rhinoceros beetle incur negligible aerodynamic costs
- Author
-
Erin L. McCullough and Bret W. Tobalske
- Subjects
Male ,Sex Characteristics ,General Immunology and Microbiology ,Reproductive success ,Horn (anatomy) ,Ecology ,Body Weight ,Zoology ,Ornaments ,Rhinoceros ,Total body ,General Medicine ,Aerodynamics ,Biology ,Biological Evolution ,General Biochemistry, Genetics and Molecular Biology ,Coleoptera ,Drag ,Sexual selection ,Flight, Animal ,Animals ,Female ,General Agricultural and Biological Sciences ,Research Articles ,General Environmental Science - Abstract
Sexually selected ornaments and weapons are among nature's most extravagant morphologies. Both ornaments and weapons improve a male's reproductive success; yet, unlike ornaments that need only attract females, weapons must be robust and functional structures because they are frequently tested during male–male combat. Consequently, weapons are expected to be particularly costly to bear. Here, we tested the aerodynamic costs of horns in the giant rhinoceros beetle,Trypoxylus dichotomus. We predicted that the long, forked head horn would have three main effects on flight performance: increased body mass, an anterior shift in the centre of mass and increased body drag. We found that the horns were surprisingly lightweight, and therefore had a trivial effect on the male beetles' total mass and mass distribution. Furthermore, because beetles typically fly at slow speeds and high body angles, horns had little effect on total body drag. Together, the weight and the drag of horns increased the overall force required to fly by less than 3 per cent, even in the largest males. Because low-cost structures are expected to be highly evolutionarily labile, the fact that horns incur very minor flight costs may have permitted both the elaboration and diversification of rhinoceros beetle horns.
- Published
- 2013
33. Mechanical limits to maximum weapon size in a giant rhinoceros beetle
- Author
-
Erin L. McCullough
- Subjects
Male ,Structural failure ,Zoology ,Rhinoceros ,Biology ,General Biochemistry, Genetics and Molecular Biology ,Animals ,Maximum size ,Operations management ,Trypoxylus dichotomus ,Research Articles ,Horns ,General Environmental Science ,Sex Characteristics ,General Immunology and Microbiology ,Horn (anatomy) ,General Medicine ,Biological evolution ,Mating Preference, Animal ,Biological Evolution ,Biomechanical Phenomena ,Coleoptera ,Phenotype ,nervous system ,Sexual selection ,Female ,General Agricultural and Biological Sciences - Abstract
The horns of giant rhinoceros beetles are a classic example of the elaborate morphologies that can result from sexual selection. Theory predicts that sexual traits will evolve to be increasingly exaggerated until survival costs balance the reproductive benefits of further trait elaboration. InTrypoxylus dichotomus, long horns confer a competitive advantage to males, yet previous studies have found that they do not incur survival costs. It is therefore unlikely that horn size is limited by the theoretical cost–benefit equilibrium. However, males sometimes fight vigorously enough to break their horns, so mechanical limits may set an upper bound on horn size. Here, I tested this mechanical limit hypothesis by measuring safety factors across the full range of horn sizes. Safety factors were calculated as the ratio between the force required to break a horn and the maximum force exerted on a horn during a typical fight. I found that safety factors decrease with increasing horn length, indicating that the risk of breakage is indeed highest for the longest horns. Structural failure of oversized horns may therefore oppose the continued exaggeration of horn length driven by male–male competition and set a mechanical limit on the maximum size of rhinoceros beetle horns.
- Published
- 2014
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