‘Absolute steepness’ of ramps as an essential cue for auditory pattern recognition by a grasshopper (Orthoptera; Acrididae; Chorthippus biguttulus L.)

Male grasshoppers of the species Chorthippus biguttulus react to female songs with a characteristic turn towards the female. The probability of turning towards female song models was used to evaluate those parameters which are essential for a signal to be interpreted as female song.

1. The shape of sound pulses turned out to be most decisive; pulses with ramps rising gradually over 3 and more ms were efficient (Figs. 2, 3), whereas rectangularly modulated pulses evoked only weak responses and only when pulse intervals were between 3 and 5 ms (Fig. 2). The decline of a pulse did not influence its efficiency (Fig. 3). In particular, pulses with sudden onsets and gradual declines were as weakly effective as rectangularly modulated ones and thus remarkably less effective than pulses with ramp-like onsets (Fig. 4).
2. Intensity tuning curves suggest, that the absolute steepness of ramps (expressed as μbar/ms) is detected by the grasshopper nervous system (Figs. 6, 7), possibly by processing the delay in excitation onset of at least two receptor types differing in threshold sensitivity.
3. The sawtooth shape of pulses in female signals is suggested to be adaptive with respect to directional hearing.

     

Do extra‐pair paternities provide genetic benefits for female blue tits Parus caeruleus?

A large body of theories on extra-pair paternity (EPP) in birds has proposed four main "genetic" hypotheses to explain this behaviour: the "good genes" hypothesis, the genetic diversity hypothesis, the genetic compatibility hypothesis and the fertility insurance hypothesis. Empirical tests have been scarce, mainly because high sample sizes are difficult to collect. We have tested these hypotheses in three Mediterranean populations of blue tits Parus caeruleus in which 50–68% of the broods contained extra-pair young. Results showed that the distribution of extra-pair young among broods was not random, and that survival to fledging of extra-pair young was higher than that of their within-pair sibs. These results support the idea of genetic effects benefiting extra-pair young. However, comparison of cuckolded and cuckolding males showed no significant difference in their body size, age, survival or relatedness with their paired females, and offspring morphometrics did not differ between extra-pair and within-pair young. We conclude that none of the genetic hypotheses can explain fully the high level of extra-pair paternity, at least in our populations of Mediterranean blue tits. We suggest that direct ecological benefits of EPP for females should be tested more often in correlative as well as experimental approaches.     

Discrimination abilities for nutrients: which difference matters for choosy birds and why?

Fine-tuned discrimination abilities are a prerequisite for optimal diet theory (ODT) and the concept of nutrient regulation as alternative models of food choice. These abilities have rarely been determined, and neither has been applied to frugivorous consumers. We investigated nutrient choices of four tanagers (Tachyphonus cristatus, Dacnis cayana, Chlorophanes spiza and Cyanerpes nitidus) for different lipid or carbohydrate concentrations, and determined discrimination abilities by reducing in steps the difference between two foods ranging from 2.5 to 12%. Three species detected differences in sugar concentrations of only 1% and differences in lipid content of 2%. Hence, frugivorous tanagers were able to select the more rewarding food based on fine-scale differences in nutritional content. Tanagers also consumed more carbohydrates than proteins or lipids in isocaloric trials, but were indifferent to equicaloric solutions of 20% of either glucose or sucrose. In contrast to foods with low sugar contents, intake of foods high in lipids or carbohydrates was limited to a protein intake of 0.75 g/7 h. Lipid and carbohydrates were treated as though they were interchangeable nutrients for birds at low, but not at high, sugar concentrations. Furthermore, the tanagers discriminated foods containing the same amount of protein but differing in the type of protein. Preference for boviserine serum albumin (BSA) over casein was not related to moult. We supplemented the food consisting of casein with the essential amino acid cysteine to match cysteine concentrations of BSA. The birds then consumed more of the casein food than of the cysteine-supplemented casein food. Overall, the birds' consistent choices in the experiments with foods of different energy density are interpretable by both ODT and the nutrient regulation theory. However, only the latter accounts for the birds' choices of isocaloric foods differing in macro- or micronutritional content. Models of food selection should therefore focus on nutrient geometry and consumer-specific requirements. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Metabolic syndrome: which definition for what treatment(s)?

Metabolic syndrome is asymptomatic and results from the increasing prevalence of obesity. Although several definitions exist and complicate its diagnosis, metabolic syndrome is characterized by the clustering of moderate troubles of glucose, lipid metabolism, body weight, hypertension and vascular inflammation ; the synergy between 3 of them triggers type 2 diabetes, atherosclerosis and associated clinical events. Whatever the age but particularly in adolescence, the prevalence of metabolic syndrome is high ; beyond lifestyle interventions, the available treatments address essentially a single risk factor and an unmet medical need persists. The reduction of cardiovascular events in secondary prevention has been demonstrated for some antidiabetic, hypolipidemic and antihypertensive agents but any difference in efficacy between populations with and without metabolic syndrome has yet to be established. The approval of metabolic syndrome as a specific therapeutic target would need the characterization of its pathogenic mechanism, a clearer guidance for definition and diagnosis, and the clinical proof of concept of a novel molecule displaying multifactorial impacts. Some new mechanistic approaches are discussed and may represent a breakthrough particularly if positive results of Field and Proactive clinical studies related to PPARs are disclosed soon.     

Does cladode inclination restrict microhabitat distribution for Opuntia puberula (Cactaceae)?

In contrast with other Opuntia species, most of the cladodes of Opuntia puberula have a horizontal position. This study explores whether the horizontal cladodes are an adaptive trait to increase light interception in the understory or are a neutral trait, and if this characteristic may prevent its distribution in full sun habitats. Cladode inclination angle and its effect on light interception, cladode temperature, and carbon gain are characterized, and anatomical and physiological traits of upper and lower cladode surfaces are described. Inclination angle was under 50° for 95% of the cladodes, and the frequency of low inclination angles increases as light availability decreases. Nocturnal acid accumulation increased with total daily PPFD intercepted, but no significant differences were detected between typical horizontal cladodes and the few vertical cladodes. Chlorophyll content differed in the upper and lower surfaces of horizontal cladodes; however, chlorenchyma thickness, stomatal conductance, and nocturnal acid accumulation were similar between surfaces. The horizontal position of O. puberula cladodes, which is anatomically determined, restricts it to shaded habitats, where the plants do not overheat, but seems to have no effect on carbon gain.     

Is there a sex-phenotype association for esterase D (EC 3.1.1.1)?

Recently, a significant sex distortion of the esterase D locus segregation, both in Portugal and Germany, was reported. In contrast to these puzzling results, data on around 1,200 informative northeastern Brazilian individuals did not show any signs of a sex-phenotype association (chi 2 = 0.35). The joint analysis of this sample together with that of the previous report showed that, although the pooled material presented a significant sex distortion (p less than 0.05), the heterogeneity was also high (p less than 0.05) as to discourage any generalization based upon the European findings. Moreover, since the present sample is almost 3 times larger than the pooled European one, the whole picture suggests strongly that there is no segregation distortion attributed to sex, at this locus.     

Effects of parasitic infection on mate sampling by female wild turkeys (Meleagris gallopavo): should infected females be more or less choosy?

Investigations of parasite-mediated sexual selection have concentratedon the effects of parasites on males. Differences in femalesusceptibility to parasitic infection may also cause variationin reproductive behavior. I propose two alternative hypothesesto explain how infected females may alter their mate samplingbehavior. In the first hypothesis, infected females sample fewerprospective mates because chronic parasitic infection imposesenergetic costs that limit the time and calories that a femalecan expend in mate searching. A novel alternative hypothesisis that females recognize their own susceptibility to infectionand thus invest more time searching for a male phenotype thatindicates he offers genes complementary to her genome. In recombination,these good genes would allow her offspring to better resistparasites despite their mother's susceptibility. I examinedthe mate sampling behavior of experimentally infected wild turkeyhens when presented with an array of males, and compared themto control hens. Infected females did not invest more time assessingindividuals, did not wait longer to choose a male, nor werethey less likely to solicit during the trial. They did differfrom control females in that they visited more males beforesoliciting copulation and exhibited different preference functionsfor snood length. These results suggest that females are notso energetically restricted by latent coccidia infection thatthey must hurry to find a mate. Instead, it appears that infectedfemales assess a larger set of males as prospective mates, perhapsto increase the opportunity to obtain complementary genes forparasite resistance.     

Is maximum sustainable yield independent of body size for mammals (and others)?

Summary Provided carrying capacity (K) for non-primate mammals scales with the –0.75 power of adult body weight (W), MSY (in weight) should be approximately one-sixth ofC, whereC is defined byK =CW^–0.75.     

Gaze direction - a cue for hidden food in rooks (Corvus frugilegus)?

Other individual's head- and eye-directions can be used as social cues indicating the presence of important events. Among birds, ravens and rooks have been shown to co-orient with conspecifics and with humans by following their gaze direction into distant space and behind visual screens. Both species use screens to cache food in private; also, it had been suggested that they may rely on gaze cues to detect hidden food. However, in an object-choice task, ravens failed to do so, and their competitive lifestyle may have prevented them from relying on these cues. Here we tested closely related and cooperative rooks. Food was hidden in one of two cups and the experimenter gazed at the baited cup. In a second experiment, we aimed to increase the birds’ motivation to choose correctly by increasing the investment needed to obtain the reward. To do so, the birds had to pull on a string to obtain the cup. Here, the birds as a group tended to rely on gaze cues. In addition, individual birds quickly learned to use the cue in both experiments. Although rooks may not use gaze cues to find hidden food spontaneously, they may quickly learn to do so.     

Indirect evidence that guarded quiescent deutonymph females invest energy to attract conspecific males in the Kanzawa spider mite (Acari: Tetranychidae)?

Because only the first mating results in fertilization in Tetranychus kanzawai (Acari: Tetranychidae), adult males guard quiescent deutonymph females (i.e., precopulatory mate guarding). A previous study reported that quiescent deutonymph females guarded by a male attract more conspecific males than solitary females and then hypothesized that guarded females release more chemical signals than solitary ones to attract males. Quiescent deutonymph females do not feed. If the hypothesis is appropriate, guarded females should invest energy in attracting males at the expense of investment in other activities, such as egg production. Therefore, we compared oviposition rates immediately after adult emergence between guarded females and solitary females. On the first day, the oviposition rate of guarded females was lower than that of solitary females. On the second day, however, there was no significant difference between female groups. These results suggest that guarded females invest energy in activities other than egg production before adult emergence and that the energetic cost is easily recoverable. We believe that our finding indirectly supports the hypothesis that guarded females release more chemical signals than solitary females to attract conspecific males.     

Out of South America? Additional evidence for a southern origin of melanopline grasshoppers

Molecular phylogenetic methods provide a useful tool for critically evaluating competing biogeographic hypotheses. This paper focuses on conjectures at the intercontinental level. An earlier phylogeographic study of the grasshopper subfamily Melanoplinae examined relationships among taxa occupying the Americas and Eurasia. The objective was to test which of three scenarios best described the subfamily's origins and patterns of intercontinental movement. It was tentatively proposed that the melanopline grasshoppers evolved somewhere in the Americas and spread to the Old World. The present article, by including additional Neotropical species, not only upholds that conjecture, but is able to identify South America as the site of origin. Phylogenetic analysis indicates a direction of dispersal: South America-->North America-->Eurasia, that is opposite to what was previously believed. This study also provides, for the first time, a preliminary molecular phylogeny of selected South American melanopline genera.     

Indirect selection on female extra-pair reproduction? Comparing the additive genetic value of maternal half-sib extra-pair and within-pair offspring

One specific hypothesis explaining the evolution of extra-pair reproduction (EPR) by socially monogamous females is that EPR is under indirect selection because extra-pair offspring (EPO) sired by extra-pair males have higher additive genetic value for fitness than the within-pair offspring (WPO) a female would have produced had she solely mated with her socially paired male. This hypothesis has not been explicitly tested by comparing additive genetic value between EPO and the WPO they replaced. We show that the difference in additive genetic breeding value (BV) between EPO and the WPO they replaced is proportional to the genetic covariance between offspring fitness and male net paternity gain through EPR, and estimate this covariance with respect to offspring recruitment in free-living song sparrows (Melospiza melodia). Recruitment and net paternity gain showed non-zero additive genetic variance and heritability, and negative genetic covariance. Opposite to prediction, EPO therefore had lower BV for recruitment than the WPO they replaced. We thereby demonstrate an explicit quantitative genetic approach to testing the hypothesis that EPR allows polyandrous females to increase offspring additive genetic value, and suggest that there may be weak indirect selection against female EPR through reduced additive genetic value for recruitment of EPO versus WPO in song sparrows.