Systematics and morphology of Ischyrosonychini, with an investigation of color change in the Geiger tortoise beetle (Coleoptera: Chrysomelidae)
Shin, Chulwoo Cal
University of Kansas
Ecology & Evolutionary Biology
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The New World tribe Ischyrosonychini consists of 66 described species in seven genera. Seven genera in the tribe were traditionally recognized in three distinct tribes (Asterizini, Ischyrosonychini and Physonotini). However, the monophyly of Ischyrosonychini including three traditional tribes has been weakly supported. The monophyly of the tribe Ischyrosonychini and its phylogenetic relationship to other tortoise beetle tribes were tested by analysis of morphological characters. As a first step, two genera (Asteriza Chevrolat and Eurypedus Gistel) were revised. In the revision of the genus Asteriza (Chapter 1), the morphology of Asteriza was explored, two new species (A. blakeae Shin et al. and A. tainosa Shin et al.) were described, and the monophyly of Asteriza with four species was confirmed by a phylogenetic analysis based on morphological characters. In the revision of the genus Eurypedus (Chapter 2), E. thoni Barber was synonymized with E. peltoides (Boheman) because both species were described based on different colorations while other differences were demonstrated to merely represent intraspecific morphological variation. New diagnostic characters such as antennal notches on the ventral surface of the pronotum, the presence of head stridulatory file, and a projection of each antero-lateral region of the prosternum on the ventral surface of the pronotum were documented and illustrated. In addition, new host plants were reported for E. nigrosignatus (Boheman) and a distribution map was provided for two remaining species of Eurypedus (E. nigrosignatus and E. peltoides). Most locality data from the examined specimens and previously known distributions suggest that the distributions of the two species of Eurypedus are likely separated by the Amazon Basin. In Chapter 3, a phylogenetic analysis of tortoise beetles was conducted based on 155 morphological characters with 84 species representing 35 genera in 10 tribes. As a preceding step to the phylogenetic analysis, morphological terminology of tortoise beetles was reviewed using Physonota alutacea Boheman as an exemplar. Taxon sampling was focused on the historically recognized tribe Ischyrosonychini to test its monophyly and the validity of each genus within the group. The results indicate that the current tribe Ischyrosonychini should include only species of Cistudinella and Eurypedus, and the tribe Asterizini was resurrected to include Asteriza, Enagria, Eurypepla, Physonota, and Platycycla. In Asterizini, Enagria and Physonota were synonymized with Asteriza. With regard to tribal-level relationships, Asterizini and Ischyrosonychini formed a clade with Eugenysini, Goniocheniini, Mesomphaliini, and Omocerini. At the generic level, the monophyly of both Cistudinella and Eurypedus was confirmed. As new morphological characters, characters of the gastral spiculum on the aedeagus and of the head stridulatory file were introduced and used in the phylogenetic analysis. The distribution of terminal taxa of the Asterizini and Ischyrosonychini were mapped onto the resulting phylogeny. In Chapters 4 and 5, the biology of the Geiger Tortoise beetle (Eurypepla calochroma Blake) is documented with images from live specimens in South Florida. In Chapter 4, the whole life cycle (egg to adult) of E. calochroma is documented and illustrated. Two color morphotypes (green and brown) were observed in adults. The detailed morphology of elytral cuticular layers for the two morphotypes and differences between them were documented and illustrated by histology and scanning electron microscopy (SEM). The green individual possessed a thicker endocuticle with several layers and an endocuticular multi-layer reflector (EMLR), while these were lacking in brown individuals. It is suggested that the green coloration required the presence of an EMLR with hemolymph filling the spaces between its thin layers. In Chapter 5, the dorsal color change in green individuals of E. calochroma (green to blue) was observed as the response of visual and physical disturbances. The pattern of color change was documented and illustrated with images from live specimens. The internal staining of the elytra demonstrated that the EMLR was in contact with hemolymph. The EMLR was composed of over 40 thin layers and each layer nearly subequal in thickness; the dorsal layers were slightly thicker than the ventral ones, and the distance between the layers also appeared greater between the dorsal layers than between the ventral layers. The previously known causes of color change in tortoise beetles (freezing, pH, and physiology) were tested with E. calochroma. The mechanism of color change in E. calochroma is hypothesized as a structural change caused by a reduction in the amount of hemolymph within the elytra: when the hemolymph volume is reduced it decreases the distance between the thin layers in the EMLR and consequently causes reflection of shorter wavelength light. The hypothesized mechanism of the dorsal color change in E. calochroma was compared to the color change of another tortoise beetle species, Charidotella egregia (Boheman). Unlike the red dorsal color in C. egregia, which originates from red pigments in the epidermis, the blue coloration of E. calochroma originates from the EMLR. Thin-film theory (= hydraulic theory) was invoked to explain the proposed hypothesis.
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