Rapid diversification of sexual signals in Hawaiian Nesosydne planthoppers (Hemiptera: Delphacidae): the relative role of neutral and selective forces.

Changes in sexual signals have the potential to promote rapid divergence and reproductive isolation among populations of animals. Thus, identifying processes contributing to variation in signals is key to understanding the drivers of speciation. However, it is difficult to identify the processes initiating changes in signals in empirical systems because (1) the demographic history of populations under study is usually unclear, and (2) there is no unified hypothesis-testing framework for evaluating the simultaneous contribution of multiple processes. A unique system for study in the Hawaiian Islands, the planthopper species Nesosydne chambersi, offers a clear demographic context to disentangle these factors. By measuring variation in male vibratory sexual signals across different genetic populations on the island of Hawaii, we found that that multiple signal traits varied significantly between populations. We developed a mixed modelling framework to simultaneously test competing hypotheses about which processes contribute to changes in signal traits: genetic drift, sensory drive or reproductive character displacement. Our findings suggest that signal divergence proceeds along different axes for different signal traits under the influence of both neutral and selective processes. They are the first, to our knowledge, to document the relative importance of multiple processes on divergence in sexual signals.

Sterol metabolic constraints as a factor contributing to the maintenance of diet mixing in grasshoppers (Orthoptera: Acrididae).

Sterols are essential nutrients for all arthropods, including grasshoppers, but metabolic constraints may limit which sterols can support normal growth and development. In the firsts part of this study, a comparative experiment, which included five different species of grasshoppers (Orthoptera: Acrididae) representing three separate taxonomic groups, was performed to determine how widespread sterol metabolic constraints are within the Acrididae. Grasshoppers were reared on artificial diets containing sterols that differed in the position of double bonds within the sterol structure, and various life history traits were measured. Sterols with double bonds at position 7, within the sterol nucleus, and/or at position 22, on the cholestane side chain, failed to support development to the adult stage for any of the five species. In addition, grasshoppers reared on sterols with these configurations often had extended developmental times and reduced growth rates in the first and second stadium compared with grasshoppers reared on sitosterol or cholesterol diets. In the second half of this study, we examined how mixtures of suitable and unsuitable sterols influenced survival, growth, and development. Artificial foods containing mixtures of suitable and unsuitable sterols were fed to the highly polyphagous grasshopper Schistocerca americana. Results suggest that survival and performance of this grasshopper suffer as the concentration of unsuitable sterols increases and as the ratio of suitable to unsuitable sterols in the diet decreases. We review the literature to document variation in plant sterol profiles and propose that constraints on sterol metabolism may contribute to the maintenance of diet mixing in the Acrididae.

Phytosterol metabolism and absorption in the generalist grasshopper, Schistocerca americana (Orthoptera: Acrididae).

A series of experiments, using GLC, RP-HPLC, and GC-MS techniques, were performed to examine the metabolic fate and absorption of different dietary sterols in the grasshopper Schistocerca americana. In the first experiment, grasshoppers were reared on diets containing different sterols presented singly. Cholesterol was the dominant tissue sterol recovered from cholesterol and "soybean sitosterol" fed grasshoppers but among the grasshoppers fed diets with stigmasterol and spinach sterols (both unsuitable for growth and development), the amount of cholesterol recovered was not different from that of newly hatched grasshoppers. In the second experiment, grasshoppers were given diets containing mixtures of soybean sitosterol and stigmasterol and the metabolic fate of these dietary sterols was recorded. Results from this experiment suggest that the presence of an unsuitable dietary sterol does not interfere with cholesterol production from sitosterol. They also demonstrate that large quantities of unmetabolized dietary sterols with C-24 ethyl groups are recovered from grasshoppers fed diets containing stigmasterol. Finally, tissue sterol profiles of grasshoppers with and without their midguts were compared. Results suggest that the midgut is the major tissue where unmetabolized dietary sterols accumulate. How these sterol metabolic constraints impact development and survival is discussed as well as the impact they might have on grasshopper feeding behavior. Arch.

Post-ingestive feedbacks and associative learning regulate the intake of unsuitable sterols in a generalist grasshopper.

Behavioural studies of the grasshopper Schistocerca americana were undertaken to identify the mechanisms that regulate the intake of dietary sterols. In the first experiment, grasshoppers were allowed to feed on spinach, a plant containing only unsuitable sterols; immediately after this first meal, a suitable or unsuitable sterol was injected into the haemolymph. Grasshoppers injected with unsuitable sterols had second meals on spinach that were significantly shorter than those of grasshoppers injected with suitable sterols, indicating that unsuitable dietary sterols are detected post-ingestively. In the second experiment, grasshoppers were fed food containing only unsuitable sterols and were then presented with glass-fibre discs containing different concentrations of a suitable sterol or sucrose only (the control). The results suggest that grasshoppers do not use a direct feedback operating on mouthpart chemoreceptors to regulate their intake of suitable sterols. In the third experiment, grasshoppers were presented with artificial diets containing different sterols and flavours, and feeding was observed over a sequence of meals. The results from both the first and last experiments suggest a role for associative learning in regulating the intake of unsuitable sterols.

The nutritional significance of sterol metabolic constraints in the generalist grasshopper Schistocerca americana.

Sterols are essential nutrients for grasshoppers, as well as all other insects, but metabolic constraints can limit which phytosterols support normal growth and development. In the current study, the generalist grasshopper Schistocerca americana was used to address two questions related to grasshopper sterol nutrition: (1) how does sterol quantity influence growth and survival, and (2) how do mixtures of suitable and unsuitable sterols at different concentrations influence growth and survival? Results from the first experiment indicated that this grasshopper species had a minimum sterol requirement of 0.05% dry weight; as sterol quantity increased above this concentration, however, survival and performance were not enhanced. Results from the second experiment revealed two novel aspects of sterol nutrition in grasshoppers: (1) when suitable sterols were limiting, most individuals could not use unsuitable sterols to meet the minimum sterol requirement (i.e. no sparing occurred), and (2) above a certain threshold, unsuitable sterols were deleterious even when suitable sterols were present at a concentration that alone permits normal growth and development. We discuss these physiological findings in terms of how sterol metabolic constraints in grasshoppers might influence foraging.

Fio radiopaco para localização de pontes de safena / Radiopaque thread for localization of saphenous grafts

E apresentada uma tecnica simples e efetiva para marcacao do orificio de anastomose de pontes de safena na aorta. Consiste no aproveitamento do fio radiopaco que acompanha as gases cirurgicas comuns, que a fixado em torno da anastomose aortica