Thomas Eisner - US grants

The study deals with the chemical mechanisms whereby insects interact with organisms in their environment. Particular attention is being given to glandular substances that insects produce for protection against predators or for communication with conspecifics. The substances are being studied from the chemical, biochemical, and ecological points of view, in hopes of clarifying both their basic and applied significance.

Herbivore-induced defense in plants is well documented, but field evidence that these induced changes protect plants is lacking. The damage-induced increases in leaf alkaloid content in wild tobacco will be studied. Currently enough mechanistic information on the workings of this induced defense system to propose a field test of its ecological significance is available. With a previously tested experimental design that involves artificially damaging two groups of wild Nicotiana repanda plants growing in south-Texas, hormonally supressing the alkaloidal respose in one group, measuring the amount of natural herbivory sustained by induced and suppressed plants and their respective alkaloid coantents, the following three questions will be addressed: 1) are these damage-induced alkaloid levels functioning as an antiherbivore defense? 2) is this induced- defense costly in terms of reproductive output? and 3) is there variation in herbivory between different populations of wild tobacco, and is this variation correlated with variation in the benefit (reduced herbivory) and cost (reproductive costs) of this induced defense? This project is one of the few field studies of induced plant resistance which simultaneously measures both leaf chemistry and herbivore performance. Moreover, it is the first time the efficacy of an induced defense has been studied by inhibiting the defense in damaged plants, and the first project to measure the reproductive cost of defense.

The investigators will study the chemical mechanisms involved in the interactions between insects from the southern cone region and organisms in their environment. Their study will include the characterization of the chemical structure and biological function of substances that insects use for defense against predators, communication with conspecifics, protection of progeny and location of food. Structure elucidation will be attained by modern chromatographic (GC, HPLC) and spectroscopic (NMR, MS, IR) techniques. Biological functions will be studied by electrophysiological techniques (EAG) and field and laboratory bioassays, including predation tests for defensive substances and wind tunnel studies for volatile semiochemicals. The study will focus on species likely to produce new natural products of pharmacological value, as well as on certain local pests.

Dissertation Research: Inducible Defenses and Plasticity in Tadpoles: Chracterization of Chemical Alarm Cues

Dr. Thomas Eisner & Jacqualine Grant

Many organisms go about their daily business unprepared for danger. However, some can anticipate hazards by cueing in on the environmental stimuli that presage peril. In the gray treefrog (Hyla versicolor) chemical alarm cues are released from the skin of injured tadpoles. These cues induce morphological and behavioral changes in conspecific tadpoles, changes that improve their ability to withstand future attacks. Specifically, the induction involves enlargement of the tailfin, and a simultaneous color change of the fin from nearly translucent to a mottled red and black. In its transformed state, the tadpole is said to be less vulnerable, because the gaudy tail deflects attacks away from the body itself. The transformed tadpole is also less active and, as a result, less conspicuous. The ecology of this phenomenon has received much attention, but so far the mediating chemicals remain unknown. This dissertation research is focused on characterizing those substances that trigger inducible defenses in gray treefrog tadpoles. The results will shed light on the evolution and ecology of morphological and behavioral plasticity.

Phenotypic and genetic benefits of polyandry in an arctiid moth (Utetheisa ornatrix)



Thomas Eisner



Female insects are frequently promiscuous. Given that a single male can provide sufficient sperm to fertilize a female's entire complement of eggs, why do females take multiple partners?



An obvious possibility is that they are thereby able to avoid the pitfalls of inbreeding. Whether or not they actually give preference to males of disparate genetic makeup, implying that they are able to compare sets of sperm, is a question that can be answered by determining the degree of inbreeding of insects in natural populations.


The moth Utetheisa ornatrix offers the opportunity to look into these unknowns. The female of the moth can take as many as 23 partners in her 2-3 weeks of existence. Mating incidence can be determined by counting the sperm sac remnants in the female's mating chamber, and degree of relatedness of the individuals in the population can be assessed by microsatellite analyses. Degree of relatedness is usually ignored in studies of insects. In Utetheisa the ascertainment of genetic affinities could cast light on the determinant selective processes that molded the reproductive behavior of Utetheisa, and could lay the groundwork for similar inquiries with other insects.