Research Projects
- 1. Evolution of a Novel Ovipositional Behavior in the Neotropical Leafhopper Tribe Proconiini (Insecta: Hemiptera: Cicadellidae)
- Dietrich, C. H., Rakitov, R. A. , Takiya D. M.
- Support: NSF DEB0089671 (to C. H. Dietrich)
The discovery of a unique oviposition behavior in certain Neotropical leafhoppers of the tribe Proconiini provides an opportunity to examine the evolutionary steps involved in the acquisition of a complex set of correlated behavioral, morphological, and physiological traits within a phylogenetic context. Unlike other leafhoppers, which insert their eggs into plant tissues without covering the ovipositional scars, some proconiine species cover the scars or exposed egg masses with brochosomes, ultramicroscopic excretory particles produced by specialized cells of the Malpighian tubules (MT). In other leafhoppers brochosomes are used only as a protective coat of the integument; thus, the use of this secretory material in oviposition seems to be an evolutionary novelty. Three ontogenetically independent structures involved in this novel behavior--brochosomes, hindlegs, and tegmina (forewings)--show corresponding modifications that are markedly expressed in females and poorly, or not expressed in males, suggesting that sexual dimorphism was derived by modification of originally monomorphic traits. Each trait exhibits gradient-like variation from unspecialized to highly specialized conditions among proconiine taxa, possibly reflecting a temporal succession in the evolution of the syndrome. - The project has two main objectives: 1. To estimate the phylogenetic relationships among proconiine leafhoppers using DNA sequence data. 2. To examine the evolution of various behavioral, morphological and physiological traits associated with the unique ovipositional syndrome.
- Development of a robust estimate of proconiine phylogeny based on molecular data will enable us to address several questions including: (1) Have the syndrome and its individual components arisen more than once in the group? (2) Did acquisition of all components of the syndrome coincide, or were they acquired in a stepwise progression? (3) What was the key innovation, if any? (4) Did acquisition of the new syndrome facilitate speciation?
- Picture: Female Acrogonia sp. from Guatemala displays reserves of brochosomes to be used in oviposition on its forewings.
- 2. Composition and Properties of Brochosomes
- Rakitov, R. A.
- Support: no current support
- The poor knowledge of the composition of brochosomes is a stumbling block in understanding the development, function, and evolution of this unique biomaterial. The project involves development of techniques for the isolation of brochosomes, and the biochemical characterization of this material. The methods include microfiltration, centrifugation, scanning and transmission electron microscopy, electrophoresis, and other methods of protein chemistry.
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A transmission electron micrograph of a whole brochosome
SDS-PAGE gel stained with Coumassie: molecular weight standards (left) and a brochosome sample (right)
- 3. Homoplastic evolution of a stereotyped behavior and associated structural and physiological traits in the leafhopper genus Cuerna (Insecta: Hemiptera, Cicadellidae)
- Rakitov R. A., Dietrich C. H.
- Loss of ancestral traits and trait complexes is a pervasive aspect of the evolutionary process, but its causes, mechanisms, consequences, and the possibility of restoration of the lost traits are still poorly understood. The current project aims to explore the patterns of repeated decay and loss of a stereotyped maternal behavior in the North American leafhopper genus Cuerna as a model of the regressive evolution of a complex biological function at the species level. In some of the 31 known species of the genus, females display an ancestral egg-powdering behavior, coating the egg nests with a layer of specialized Malpighian tubule products and displaying a suite of corresponding physiological and structural modifications, while in other species no such behavior is observed. Preliminary phylogenetic analyses suggested that egg-powdering has been lost or lost-and-restored within the genus multiple times. In the three years of the project the investigators will collect detailed comparative data on the egg-laying behavior and associated specializations of the external morphology and the Malpighian tubules for every species of Cuerna. Then, they will analyze these in the context of a detailed DNA-based phylogeny of the genus to address the following questions: Did the changes of particular traits proceed as quantum leaps or gradually? Do morphological, behavioral, and physiological traits display similar evolutionary plasticity? Did they change in a certain order? Did any restorations of lost egg-powdering occur in the evolution of Cuerna? What were the most likely causes of the losses? The study will also result in a taxonomic revision of the genus, which currently contains a number of poorly defined species. The study will contribute to management of economically important species of Cuerna by providing identification aids, as well as behavioral and physiological data for improved integrated pest management. An interactive key to species of Cuerna, complete with bionomical and distribution data, will be served on-line. The project will also provide training for a graduate student in the systematics, molecular phylogenetics, and evolutionary biology of insects.
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"Powdering" species of Cuerna:
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striata
alba
arida
obtusa
balli
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"Non-powdering" species of Cuerna:
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costalis
obesa
kaloostiani
gladiola
sayi