MOCZEK LAB RESEARCH


Overview

Beetle Horns and Horned Beetles- Unique and Diverse
Current Research Objectives


I: OVERVIEW

Our research focuses on a central question in biology: how do novel complex traits originate and diversify in nature? In particular, we are interested in the ecological, developmental, and genetic mechanisms, and the interactions between them, that enable and channel evolutionary innovation and diversification. To tackle these issues from a variety of perspectives and at different levels of biological organization we use approaches ranging from evolutionary developmental genetics and ecological genomics to comparative endocrinology and behavioral ecology. While most of our work has focused on the innovation and diversification embodied by horned beetles and beetle horns we have recently begun to develop additional model organisms for study, including fireflies and their mesmerizing lanterns, or photic organs, and treehoppers and their exuberant helmets. Below we first provide a brief summary of the biology of our main study organisms: horned beetles in the genus Onthophagus, followed by a summary of our current research foci.

 


II: BEETLE HORNS AND HORNED BEETLES- UNIQUE AND DIVERSE

Beetle horns and horned beetles combine several characteristics that make them outstanding models for studying the origin and diversification of novel traits (Moczek 2006a). (1) Beetle horns are large structures, often dominating the phenotype of their bearers. (2) Beetle horns function as weapons in male combat, thus playing a major role in the behavioral ecology of individuals and populations. (3) Beetle horns are inordinately variable within sexes, between sexes, and between species, including differences in number, size, shape and location. (4) Beetle horns are influenced in their expression by both genetic and environmental factors, ranging from absence of environmental sensitivity to complete determination by nutritional conditions. In some cases, both extremes of environmental sensitivity can be found in different horn types expressed by the same individual. (5) Beetle horns lack obvious homology to structures in other insects. In other words, beetle horns are not just modified antennae or mouthparts, instead horns were “invented” by beetles in addition to traditional appendages and now provide their bearers with an important new function: a weapon used in male-male competition. (6) Work in our lab over the past 4 years has substantially increased the experimental tool box available for the most diverse group of horned beetles – the genus Onthophagus. As detailed below, this tool box now allows us to explore molecular, genetic, genomic, hormonal, and behavioral components of horn formation. Combined with the tremendous diversity in horn phenotypes that exists among closely related individuals and species we are now in a position to identify the genetic, developmental, and physiological mechanisms, and the interactions between them, that underlie horns and horn diversity, as well as the ecological components that shape this diversity in natural populations (reviewed in Kijimoto et al 2012).

III: CURRENT RESEARCH OBJECTIVES

Overview: Our main objective is to better understand what needs to come together genetically, developmentally, and ecologically for major complex traits to originate and diversify. We mostly use beetle horns and horned beetles as a microcosm to explore this issue, and detailed below are the current objectives of this effort. Highlighted towards the end of this section are our recent attempts to establish additional groups of organisms and classes of novel traits – fireflies and their bioluminescent lanterns and treehoppers and their extravagant helmets – to begin exploring which, if any, common themes exist in the mechanics of innovation and diversification in nature.

Specifically, our research program has 7 major foci:

(1) The origin of novelty: Beetle horns are evolutionary novelties. Our research asks: which genetic and developmental processes regulate the formation of horns during development? What are the similarities and differences between these processes and those used in the making of other, more traditional traits in insects?

(2)The origin and diversification of sexual dimorphism:Sexual dimorphism is widespread among horned beetles and highly variable, ranging from modest to extreme to sex-reversed depending on species and focal trait. Our research asks: which developmental processes enable sex-specific development of horns compared to other traits? How have these processes been modified to permit the dramatic diversification of sexual dimorphisms among horned beetles?

(3) The origin and diversification of environment-sensitive development:Horned beetle development is influenced by environmental conditions, in particular nutrition (Fig. 2). Depending on species, sex, and trait this influence can be minimal, gradual, or extreme. Our research asks: which developmental processes enable nutrition-sensitive development? How did these processes originate and diversify?

(4) The role of ecological and social conditions in developmental evolution: The function of beetle horns is embedded within a rich behavioral and social context. At the same time, development and evolution of horns do not occur in isolation, but instead interact with those of others traits, which in turn function in their own contexts. Our research asks: how do ecological and social conditions shape developmental evolution in horned beetles and vice versa? What role have these interdependencies played in the diversification of horned beetles?

(5) Beetle horns and horned beetles as tools to address longstanding questions in comparative arthropod morphology and evolution. Because of their developmental and evolutionary “connected-ness” to other traits, studies into beetle horns can provide insights into longstanding questions in comparative morphology. For example, our research asks:  what can we learn from the positioning of head horns about the patterning and origin of the insect head, a fundamental yet largely unresolved issue in arthropod evolution?

(6) Innovation is arguably the most defining property of evolution, but the nature of innovation has remained elusive. Our research asks: What, if any, are the common themes in innovation in nature? What properties and processes enable or bias innovation across diverse taxa and trait classes?

(7) The learning and teaching of complex traits. Related to my research into complex trait evolution I engage in a NSF funded collaboration with researches at IU’s School of Education and ask:  How do young children learn and understand complex systems, self organization, and emergent properties? What are effective means to engage young children in systems learning and comprehension? [see section D below for details]

(B) PROGRESS TO DATE
1. The origin of novelty     To date, our research has shown that the origin of beetle horns was made possible through a rich combination of pre-existing developmental-genetic mechanisms that have been recruited into a new developmental context (rev. in Kijimoto et al. 2012). While the details of these results were often surprising (i.e. the particular combination of genes and pathways, or time and place of their activation) the general result confirms a well-established theme in Evolutionary Developmental Biology: novel traits do not require new genes or developmental pathways to come into being, but instead arise from recruitment, and possibly rewiring, of already existing developmental machinery into new contexts. (ii) In addition, our studies unearthed tremendous, and surprising, variation in these properties between morphs, sexes, populations and species (Moczek and Nagy 2005, Moczek et al. 2006a; Moczek 2006a,b; Shelby et al. 2007; Moczek and Rose 2009; Wasik et al. 2010; Wasik and Moczek 2011, 2012;). Combined, these results contradict the common notion that ancient developmental pathways should be evolutionarily entrenched given their importance in the regulation of basic aspects of animal architecture and thus resistant to the acquisition of novel functions. Instead, our findings illustrate that regulatory processes whose functions are otherwise highly conserved retain the capacity to acquire additional functions. Second, our results suggest that little phylogenetic distance is necessary for the evolution of sex- and species-specific differences in these functions. This raises the possibility that the interactions between inputs and outputs of otherwise highly conserved developmental pathways can diversify on the level of populations and species with unexpected ease (Moczek 2012). Third, many of the developmental differences seen between species have striking parallels in sexual dimorphisms or male dimorphisms, which raises the possibility that the developmental capacity to generate macroevolutionary differences may originate well within species, between sexes, and – fueled by developmental plasticity – across alternative morphs (Moczek 2009b).

2. The origin and diversification of sexual dimorphism    (i) Work in the lab has shown that a variety of developmental mechanisms associated with the regulation of appendage patterning and growth are differentially employed in the sex-specific growth of beetle horns, such as signaling via Juvenile Hormone (Shelby et al. 2007), proximodistal-axis patterning genes (Moczek and Rose 2009), hox genes (Wasik et al. 2010) as well as genes in the wingless-, tgfβ- and insulin-signaling pathways (Wasik and Moczek 2011, 2012; Snell-Rood et al. 2012).   (ii) Starting in 2008 we have begun to use genomic approaches to better characterize the developmental-genetic underpinnings of sexually dimorphic development and its evolution. This effort yielded a first understanding of sex-specific differences in transcription profiles as a function of body region, tissue type, and species (Kijimoto et al. 2009; Choi et al. 2010; Snell-Rood et al. 2010a).  (iii) These same efforts identified a rich set of candidate genes underlying the regulation of sex-dependent development shared among, as well as unique to, specific body regions. We are now following up on these results with focused analyses of select candidate pathways, such as programmed cell death and ecdysteroid-signaling (Kijimoto et al. 2010) and the role of doublesex in the mediation of sex-specific development (Kijimoto et al. 2012).

3. The origin and diversification of nutrition-sensitive development in horned beetles    We first used comparative morphological and histological approaches (Moczek 2006, 2007) to better understand where (i.e. in which tissue) and when (i.e. exactly which developmental stage)  developmental responses to nutritional variation occur. We then utilized our first-generation genomic resources to characterize the developmental-genetic underpinnings of nutritional plasticity and plasticity evolution (Kijimoto et al 2009; Choi et al. 2010; Snell-Rood et al. 2010a). This work provided the first evidence to date for any organism with pronounced developmental plasticity that documented that transcription profiles among alternative morphs can be as divergent as those observed among sexes, suggestive of similar degrees of developmental, and perhaps evolutionary, decoupling (Snell-Rood et al. 2010a). Furthermore, we found that the (dis)similarity of transcription profiles among morphs and sexes changed dramatically with body region, tissue types, and species. (ii) These same efforts also identified numerous candidate pathways possibly underlying the regulation and diversification of nutritional sensitivity. While many of these studies are ongoing, several have already yielded important and in part completely unexpected results: (a) For example, our investigation into insulin signaling provided the first insights to date into how the relative sizes of multiple growing organs may be regulated and integrated during horned beetle development (Snell-Rood & Moczek 2012). (b) Our investigation into the role of methylation as an epigenetic mechanism in the regulation of nutrition-responsive development has documented for the first time that horned beetles possess the complete molecular machinery to differentially methylate DNA during development and do so in association with nutritional conditions (Choi et al. 2010; Snell-Rood et al. 2012). (c) The perhaps most surprising results of this effort has been the implication of doublesex (dsx) in the regulation of nutrition-dependent development, the same transcription factor examined above in the context of sex-specific development. Our data show that dsx not only mediates the expression of sex-specific traits, but has been coopted to facilitate the expression of nutritionally-cued phenotypes within sexes (Kijimoto et al. 2012, NSF Research Highlight).

4. The role of ecological and social conditions in developmental evolution           To provide a solid understanding of the behavioral context within which horned beetle function we first documented the existence of alternative reproductive tactics in males (Moczek and Emlen 1999, 2000) and females (Moczek and Cochrane 2006), measured the costs and benefits of horn possession (Moczek and Emlen 2000), and explored the role of paternal and maternal behavior in offspring development and performance (Moczek 1998, 1999). We also took advantage of several geographically isolated populations of horned beetles and began to explore the behavioral and social mechanisms that bring about divergences in horn formation on the level of populations (Moczek et al. 2002; Moczek 2003, Moczek and Nijhout 2003), and the hormonal mechanisms that mediate such divergences (Moczek and Nijhout 2002).

            More recent work has focused on the role of parental investment in buffering offspring development against environmental and genetic perturbations, including the deleterious effects of novel mutations. Work with former postdoc Emilie Snell-Rood explores the degree to which parental investment can mask genetic variation in populations and release it under periods of stress, enabling rapid evolutionary responses in the face of rapid ecological changes (Snell-Rood and Moczek, in review).

            Other foci include the role of developmental tradeoffs as important guides of developmental and morphological evolution. For example (i) honors student Brittany Shepherd documented that the formation of long horns during development of large males may result in reduced muscle development and compromises the later ability to effectively thermoregulate in the face of temperature fluctuations (Shepherd et al. 2008). Similarly, (ii) we found that the development of horns trades off with the development of primary sexual traits such as the copulatory organ: populations or species whose social conditions force them to invest more into horns end up investing less into copulatory organs and vice versa (Parzer and Moczek 2008; Macagno et al. 2011). This later trade-off is particularly intriguing as changes in copulatory organ size in insects are generally thought to play a major role in the formation of new species, and we are currently investigating the developmental underpinnings of this trade-off as well as its behavioral consequences.

5. Beetle horns and horned beetles as tools to address longstanding questions in comparative arthropod morphology and evolution   Beetle horns embody uniqueness and novelty. At the same time they are integrated components of larger structures, such as the head, or utilize similar developmental processes as traditional appendages such as mouthparts. Through this connectedness the study of horned beetle evodevo can provide insights into the developmental evolution of other traits, including some that have thus far stubbornly resisted a analysis. For example, (i) the diversification of mouthparts has played a central role in the evolutionary and ecological success of insects (Grimaldi & Engel 2005). We have learned a great deal about the roles of appendage patterning genes in mouthpart development of two insect models with highly derived mouthparts, the fruit fly Drosophila and the plant sucking bug Oncopeltus, yet know little about the regulation of the presumed ancestral mouthpart type, as represented by beetles (Angelini & Kaufman 2004). Re-analyzing individuals generated for our horn studies we recently published the first functional genetic analysis of adult mouthpart development in a beetle, including the first functional analysis in any insect of the development of the labrum, an enigmatic mouthpart whose evolutionary origins are especially debated (Simonnet and Moczek 2012). We are now expanding this effort to other appendages (legs, antennae) and in particular male copulatory organs. (ii) Ongoing work focuses on the developmental mechanisms that position horns on the dorsal surface of the head, and how this positioning machinery has diversified during the radiation of horned beetles. As a byproduct this effort generates important insights into how the insect head is patterned, a long-standing and contentiously debated issue (reviewed in Grimaldi & Engel 2005).

6. Development of (a) fireflies and (b) treehoppers as new model systems for studying the evolution of novel, complex traits

(i) Over the past three years graduate student Matt Stansbury has begun to develop regional firefly species into a possible model system. Fireflies are beetles famous for their bioluminescent displays, produced by an organ, called the lantern, which is unique to these organisms and unlike anything known from other insects. This organ is diverse within and between species, and much like the horns of horned beetles represents a complex evolutionary novelty that fireflies invented during their evolutionary history, enabling a key novel function in the process, in this case the production of nightly flash patterns used in courtship. Using expression and RNAi-mediated gene function analysis we have begun to piece together a first understanding of the developmental regulation of lantern formation.

(ii) Postdoctoral associate Teiya Kijimoto has begun to develop regional treehoppers into a possible complimentary model system. Treehoppers are small, plant sucking insects famous for their dramatic elaboration of the thorax into a “helmet”. This structure functions in a variety of ecological contexts and has undergone extreme diversification. Our goal is to explore the developmental-genetic origins treehopper helmets, and the ecological conditions that have shaped their diversity. So far we have been able to rear and experimentally manipulate 2 species of treehopper in the lab, have cloned several candidate genes, and executed the first successful RNAinterference-mediated knockdowns in treehoppers.

D. The Science of Teaching and Learning: Developing novel approaches to teach and learn complex systems through embodied play and computer simulations

Our research emphasis on the biology of insects and complex traits has permitted me to engage in a very different, but nevertheless incredibly stimulating collaboration, with two colleagues at IU’s School of Education, Drs. Kylie Peppler and Joshua Danish. Our work is designed to test and, ultimately, overcome current paradigms for our understanding of how young children learn and understand complex systems, self organization, and emergent properties. Most generally, we assume that young children cannot understand such systems as it is already difficult for adults to comprehend how order, organization, or efficiency emerge out of the seemingly random interactions of a large number of component parts and in the absence of a central organizer (e.g. the internet, whole-body physiology, food webs, global economy, etc.). In a pilot study, our work has generated sufficient data to demonstrate that (a) young children are completely capable to quickly understand complex systems and to apply this knowledge in practice, but (b) to achieve such an understanding learning strategies must be employed that take advance of children’s natural tendencies to make sense of the work around them. Specifically, we focused our analyses on complex biological systems, in particular honey bee foraging behavior, where order and efficiency on the level of a hive emerge from the seemingly random interactions on thousands of individually foraging and interacting bees. In addition, we have recently branched into additional systems, such as biological food webs. To do so we focus on the power of (a) computer simulations presented on smart boards where children – using an outside perspective – manipulate system properties (such as the nature of interactions between individual bees, or nature and patterns of resource availability in the field) – and form predictions on how the system should behave, which are then tested immediately. Second, we utilize (b) embodied play approaches, i.e. in our case children wear computer enhanced bee costumes and through guided play experience honey bee foraging behavior from a first-person perspective: children become bees who interact, whose costume computers keep track of the type and frequency of these interactions (i.e. number of visits to electronically enhanced flowers that did or did not have a chance to refill with nectar yet), and whose social interactions (e.g. whether or not bees are allowed to talk or gesture to each other) determine the efficiency of the hive (i.e. the classroom, working together) as a whole. This  collaboration is currently funded by a multi-year grant from NSF’s Cyber Learning Initiative.