Dr. Karen Ober

 

Research

 

My primary interest is exploring molecular and morphological diversity in insects. Evolutionary history, molecular evolution, and developmental biology are critical in investigating the patterns and processes of morphological change and adaptations in groups of insects. Fundamental to my investigation of diversity and morphological and ecological change is seeking the evolutionary history of organisms. Beetles, in particular, offer a spectacular example of evolutionary success and diversification. They are a particularly good group of insects to examine the patterns and processes of morphological, ecological, and molecular change.

My research interests fall into two major areas: understanding evolution and relationships of major groups of beetles at deeper levels and understanding processes producing patterns of morphological diversity in insects. Insects are incredibly diverse, and they offer good models to study evolution and morphological adaptation. The broad array of adult insect morphologies are a direct result of the developmental pathways expressed in embryonic and larval development, and the timing and mode of this development. Most recently, I have been building on my interests in insect diversity and morphological innovations that have made this group so successful. I am using a comparative approach to uncover how developmental pathways and genetic mechanisms influence morphological evolution.

 

Welcome to the Ober Lab

 

Research in Insect Evolution

My primary interest is exploring molecular and morphological diversity in insects. Evolutionary history, molecular evolution, and developmental biology are critical in investigating the patterns and processes of morphological change and adaptations in groups of insects. Fundamental to my investigation of diversity and morphological and ecological change is seeking the evolutionary history of organisms. Beetles, in particular, offer a spectacular example of evolutionary success and diversification. They are a particularly good group of insects to examine the patterns and processes of morphological, ecological, and molecular change. My research interests fall into two major areas: understanding evolution and relationships of major groups of beetles at deeper levels and understanding processes producing patterns of morphological diversity in insects. Insects are incredibly diverse, and they offer good models to study evolution and morphological adaptation. The broad array of adult insect morphologies are a direct result of the developmental pathways expressed in embryonic and larval development, and the timing and mode of this development.

Evolution and Development of Insects

Most recently, I have been building on my interests in insect diversity and morphological innovations that have made this group so successful. I am using a comparative approach to uncover how developmental pathways and genetic mechanisms influence morphological evolution. I study developmental evolution of insect appendages and genes controlling body axis patterning to explore the genetic basis of morphological diversity. Diversification of insect segments and appendage structure and function were essential features of the evolutionary radiation of insects. Body segments and the appendages they bear have become specialized for feeding, walking, swimming, flying, and mating. How are developmental regulatory networks known to pattern particular aspects of morphology, such as appendages and body axes in Drosophila, modified in a related organism, Tribolium casteneum, an insect with a very different mode of development? And what is the role of positional information from genes in anterioposterior and dorsoventral axis formation? I study whether morphological evolution involves regulatory changes in otherwise conserved gene networks. I can ask what role such changes may play in the evolution of morphological diversity and whether developmental systems have properties that constrain or promote phylogenetic change.


Insects, and animals in general, set up the body axes early in development, using mechanisms that are paramount in directing the rest of morphogenesis. In Drosophila, and presumably other insects, morphogenesis results from progressive subdivision of the embryo along both the dorsoventral (D/V) and anterioposterior (A/P) axes. In addition, genes that direct segment boundaries and segment polarity are crucial in the spatial location of the head and thoracic appendages and especially in initiating appendage primordia. Proximodistal (P/D) axis patterning for appendages relies on positional information from the A/P and D/V axes for correct development. Segment polarity genes such as wingless (wg) and Engrailed (En) are involved in establishing the pattern of segments by refining the A/P axis and maintaining segmentation patterns. wg is expressed at the A/P compartment boundary in each segment in cells immediately anterior to the stripe of En gene product. Mutations in these genes lead to defects in A/P compartment boundaries and in downstream gene expression across Drosophila parasegments. Appendage primordia form at discrete A/P and D/V coordinates within particular segments in Drosophila. Unlike most insects, however, Drosophila appendages are formed from imaginal discs that differentiate during larval stages rather than developing appendages during embryogenesis. In addition, there are differences in the spatial and temporal regulation of axis patterning genes. Long germ band insects, like Drosophila, establish segments along the A/P axis in the entire germ band nearly simultaneously. In contrast, short germ band insects, like the red flour beetle Tribolium, add segments sequentially from anterior to posterior as the germ band elongates. Inferences about the evolution of insect axis, appendage development and regulatory networks employed in axis formation require an examination of genes purported to be important in the development of insects other than Drosophila in order to reveal the general developmental mechanisms underlying these phenomena.

Developmental gene expression studies have raised the possibility that despite substantial differences in embryology, many molecular aspects of axis and appendage patterning may be conserved. For example, wg expression in segmentally reiterated stripes is highly conserved across insect species as is wg expression along a ventral stripe in developing appendages. However, other developmental genes involved in axis patterning and appendage morphogenesis, such as decapentaplegic, snail, nubbin, and apterous, show a divergent pattern of gene expression between Tribolium and Drosophila.

 

Carabid Beetle Molecuar Systematics and Evolution

For my Ph.D. dissertation research, I combined molecular biology techniques and comparative morphological and ecological information to study the diversification, adaptations, and ecological evolution of a large group of ground beetles. I used DNA data from multiple genes and dense taxon sampling to infer the phylogeny of the largest ground beetle subfamily, Harpalinae (a group with over 19,000 species). The results of phylogenetic analyses revealed the boundaries and composition of Harpalinae and its sister group relationships. I also inferred the phylogenetic relationships of tribes within harpalines, focusing on the monophyly of several assemblages of tribes. Results from data simulations and parametric bootstrapping tests rejected the monophyly of several traditional assemblages and tribes. Among the surprising results from the phylogenetic analyses was strong support for the monophyly of a group of carabids, all obligate guests of ants and termites, previously thought to be unrelated. I plan to seek information on the rates and patterns of change in nuclear genes in beetles with the large molecular data sets I have collected. This work has inspired a preliminary investigation of the patterns left in molecular data of past rapid radiations in diverse lineages of organisms.


My work also investigated the evolution of arboreality in ground beetles. As one of the main life zones in tropical forests, the canopy holds crucial answer to the way in which forest ecosystems function. Studying the evolution and diversity of specialized tropical canopy carabids can give clues about what factors account for high arthropod diversity in tropical forests and the ecological and evolutionary pressures of arboreal adaptations. Investigation the evolution of arboreality in carabids may be an important step in understanding how other arthropod groups evolved adaptations to arboreal living. Models of ground beetle evolution and diversification have proposed unidirectional shifts into forest canopies. I used the phylogenetic hypothesis of harpaline relationships to examine the origins and losses of arboreality and morphological characters often associated with arboreality (e.g., modified leg characteristics, long body shape, etc.), as well as the direction and rate of change in habitat and morphological characters. Results indicated that arboreality and specialized morphological characters have evolved many times independently in harpalines and losses of these traits were common. Evidence for reversals back to ground dwelling contradicted the model of unidirectional habitat shifts previously proposed for carabid evolution. Modified leg characteristics, such as adhesive climbing setae on the legs, were found to be adaptations to arboreality.


Resulting from the large amount of molecular data collected for my dissertation research, I became increasingly interested in how molecules change through evolutionary time. I have investigated the molecular evolution and diversification of the Wnt gene family in metazoans and am currently exploring the changes in secondary structure in nuclear ribosomal RNAs in carabid beetles. I plan to seek information on the rates and patterns of change in nuclear genes in beetles with the large molecular data sets I have collected. This work has inspired a preliminary investigation of the patterns left in molecular data of past rapid radiations in diverse lineages of organisms.

 

 

 

Ober Lab Research Students

Monique Gallant '11 - Tribolium evolution and development

Evy Pratt '10 - Carabid biogeography

 

Ober Lab Student Alumni

Mike Tedaldi '10 - Ant microsatellites

Andrea Everheart '09 - Central MA insect biodiversity inventory

Tom Heider '09 - Molecular evolution and phylogenetics

Brian Hendrickson '09 - Tribolium evolution and development

Caitlin Griffin '08 - Tribolium evolution and development

Brian Matthews '07 - Carabid molecular systematics

Abbie Ferrieri '07 - Carabid biogeography

Krunal Patel '06 - Tribolium evolution and development

Sony Kuhn '06 - Carabid biogeography