The intrinsic rates of increase of insects of different sizes

ABSTRACT.

• 1 A negative relationship between intrinsic rate of increase, r, and body size has only clearly been shown using data for species drawn from a number of phyla and covering several orders of magnitude in size. Analyses for more closely related species are equivocal.
• 2 Data for ninety-one species of insects, from nine orders, were used to examine the correlation between intrinsic rate of increase and size.
• 3 Intrinsic rate of increase was negatively correlated with both length and weight across orders, but no relationship could be shown within orders.
• 4 Generation times were positively related to body size, but there was no relationship between net reproductive rate (R_Q) and size.
• 5 These results support the hypothesis that documented relationships between species size and colonization success in insects could be a consequence of the scaling of intrinsic rate of increase with size.

     

Activity budgets and use of enclosed space by wild boars (Sus scrofa) in captivity

This research was conducted on a captive group of eight wild boars: Four wildborn adults (one male and three females) and four piglets (one male and three females), born in captivity two months before the beginning of the study. They were housed in the Rome Zoo in a 1,000 sq m enclosure furnished with trees, mud pools, a water basin, and two small barns. Data on eight behavioral states (sleeping, resting, rooting, eating, walking, standing, scratching, and nursing) were collected by instantaneous sampling at 10-minute intervals. The spatial location of each subject was also noted, as well as closeness to conspecifics. Results showed that adults and piglets differed in their activity budgets. Activity patterns showed a significant correlation with the mean temperatures. Furthermore, there was a significant difference in the use of the exhibit areas between adults and piglets. This study suggests a social structure in which the core is constituted by females and their yearlings. The nonbreeding female has a more marginal position than the breeding ones. Finally, the male tends to be even more peripheral and solitary. Our results are partly consistent with the data obtained in studies on free-ranging wild boars (Mauget, 1980; Dardaillon, 1984).     

Covariance of adult size and development time in the parasitoid waspAphidius ervi in relation to the size of its host,Acyrthosiphon pisum

Summary Adult size (in terms of dry weight; DW) and development time (T _p ) of the solitary parasitoidAphidius ervi varied when reared in different nymphal instars of its host, apterous virginoparae of the pea aphid (Acyrthosiphon pisum). Parasitoid DW increased with an increase in the DW of the host at parasitization, from the first to the third aphid instar. Female wasps gained 1.1 times more in DW than their male counterparts in all four host classes, butT _p did not significantly differ between the sexes. Parasitoid DW was consistently more variable thanT _p . The two traits covaried positively with an increase in host size from the first to the third instar, but they varied independently in parasitoids from fourth-instar hosts. The host size (and stage) at the time of parasitization imposes constraints on the growth and development of immatureA. ervi that are reflected in the pattern of covariation between DW andT _p . When growing in aphids below a certain size threshold, parasitoids can maximize fitness by a trade-off between DW andT _p . Consequently, the assumption implicit in host-size models of parasitoid oviposition decisions — that females incur a relatively greater reduction in size (used as an index of fecundity) than males when developing in poor quality hosts — can be falsified.     

Labor specialization and the formation of markets for food in a Shipibo subsistence economy

Traditionally, the Shipibo economy was subsistence-based with shifting cultivation supplying calories, principally in the form of plantains and root crops, while fishing and hunting provided animal proteins to the diet. Some men, who recently began producing rice for sale in regional markets, now allocate less time to wild food procurement. Moreover, this trend has been accompanied by the nucleation of households, a growing cash market for agricultural labor, and the intravillage sale of faunal foods. This paper shows that with cash cropping, some Shipibo now freely distribute less food to others in relation to the amount they produce. To account for this change, a theory is developed based on time allocation and patterns of economic behavior reported throughout the Amazon. This theory is then applied to explain specialization and the formation of cash markets for food labor among the Shipibo.     

Transition time control analysis of a glycolytic system under different glucose concentrations. Control of transition time versus control of flux

Control and Response Coefficients of transition time have been determined in a rat liver glycolytic system under different glucose concentrations. Results have been compared with the Flux Control and Flux Response Coefficients measured in the same conditions, showing that transition time and flux are different responses of the system, subject to different regulation and control. Control Coefficients of flux and transition time show a very different profile in each condition of glucose concentration assayed. Ratio of Flux Control coefficients of glucokinase over phosphofructokinase at 5 and 20 mM glucose concentration changes from 3.2 to 0.5, while the same ratio in the case of Transition Time Control Coefficients moves from 0.6 to 0.93. Moreover, the absolute values of Transition Time Control Coefficients in glycolytic conditions are one order of magnitude bigger than in gluconeogenic conditions. Values of Response Coefficients also show that the transition time has a bigger sensitivity to changes in glucose concentration than the flux in all conditions assayed, but particularly in glycolytic ones.     

The time and egg budget of Leptopilina clavipes, a parasitoid of larval Drosophila

Abstract.

• 1 For the understanding of the influence of natural selection on the persistence of host selection behaviour in populations of Drosophila parasitoids it is important to know whether parasitoids will become time- or egg-limited. We investigated whether the Drosophila parasitoid Leptopilina clavipes (Hartig) meets egg- or time-limited conditions in the field.
• 2 To this end the following aspects of the parasitoid's life were studied: egg load at emergence, travelling velocity between patches, patch residence times, oviposition rates and life expectancy. Together with the results from earlier studies on host and patch distributions, this formed the input of a ‘Monte Carlo’ simulation model, in which the life history of an individual parasitoid can be traced.
• 3 The simulations revealed that under the conditions found in the field 12.9% of the parasitoid population is egg-limited. The model was also run for a number of scenarios which reflect ‘good’ or ‘bad’ circumstances. In most cases a significant proportion of the parasitoid population proved to be egg-limited.
• 4 For the measurement of travelling velocities and patch residence times a marking method, especially applicable to small-sized parasitoids such as L.clavipes, is described. Marking did not affect survival, host habitat location or host detection rate. Parasitoids were found to be attracted to the odour of fruit-bodies of Phallus impudicus, the most important breeding substrate of their hosts.

     

The parasitoidOoencyrtus nezarae (Hymenoptera: Encyrtidae) prefers hosts parasitized by conspecifics over unparasitized hosts

Summary Two laboratory experiments were conducted to examine the ovipositional preferences of the egg parasitoidOoencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) for parasitized and unparasitizedMegacopta punctatissimum Montandon (Hemiptera: Plataspidae). Females that had never oviposited or that had not oviposite for 3 days preferred recently parasitized hosts more than unparasitized hosts. The preference for recently parasitized hosts appeared to be mediated by the punctures in already parasitized hosts made by the ovipositor of the first female. Survival of the parasitoid progeny was lower in recently parasitized hosts than in unparasitized hosts. However, handling time of parasitized hosts was extremely short relative to that of unparasitized hosts, because the superparasitizing female could use the punctures made by the previous females. It is concluded that the females preferred the parasitized hosts over unparasitized hosts because the benefit of saving time and energy for drilling was more than the cost of progeny survival.     

Processing of behaviorally relevant temporal parameters of acoustic stimuli by single neurons in the superior olivary nucleus of the leopard frog

Summary Response characteristics of 130 single neurons in the superior olivary nucleus of the northern leopard frog (Rana pipiens pipiens) were examined to determine their selectivity to various behaviorally relevant temporal parameters [rise-fall time, duration, and amplitude modulation (AM) rate of acoustic signals. Response functions were constructed with respect to each of these variables. Neurons with different temporal firing patterns such as tonic, phasic or phasic-burst firing patterns, participated in time domain analysis in specific manners. Phasic neurons manifested preferences for signals with short rise-fall times, thus possessing low-pass response functions with respect to this stimulus parameter; conversely, tonic and phasic-burst units were non-selective and possessed all-pass response functions. A distinction between temporal firing patterns was also observed for duration coding. Whereas phasic units showed no change in the mean spike count with a change in stimulus duration (i.e., all-pass duration response functions), tonic and phasic-burst units gave higher mean spike counts with an increase in stimulus duration (i.e., primary-like high-pass response functions). Phasic units manifested greater response selectivity for AM rate than did tonic or phasic-burst units, and many phasic units were tuned to a narrow range of modulation rates (i.e., band-pass). The results suggest that SON neurons play an important role in the processing of complex acoustic patterns; they perform extensive computations on AM rate as well as other temporal parameters of complex sounds. Moreover, the response selectivities for rise-fall time, duration, and AM rate could often be shown to contribute to the differential responses to complex synthetic and natural sounds.Abbreviations SON superior olivary nucleus - DMN dorsal medullary nucleus - TS torus semicircularis - FTC frequency threshold curve - BF best excitatory frequency - PAM pulsatile amplitude modulation - SAM sinusoidal amplitude modulation - SQAM square-wave amplitude modulation - MTF modulation transfer function - PSTH peri-stimulus time histogram     

Factors influencing nitrate depletion in a rural stream

A mass balance procedure was used to analyze rates of nitrate depletion in three adjacent reaches of West Duffin Creek, Ontario, Canada. Daily nitrate losses in individual reaches were highly variable (0.5–24 kg N) during low and moderate stream flows in May–October, 1982–1985. Nitrate removal efficiency (nitrate loss as a % of nitrate input) showed a rapid exponential decline with increased nitrate inputs to each reach. Nitrate losses and nitrate removal efficiency also had a significant negative correlation with stream discharge. The association of large nitrate loads with high stream discharge reduced the nitrate removal capacity of the stream because of shorter residence times and a higher ratio of water volume to stream bed area. Water temperature exhibited a significant positive correlation with nitrate loss which may reflect increased denitrification at higher temperatures.Variations in nitrate losses and nitrate removal efficiency between the three reaches were highly influenced by differences in water residence time. Standarized nitrate losses with respect to water residence time revealed a longitudinal decline in nitrate depletion between the reaches which was associated with a downstream decrease in stream nitrate concentration and in the organic carbon content of fine textured sediments from pool habitats.     

Developmental rates of heterozygous and homozygous rainbow trout reared at three temperatures

The hatching distributions of rainbow trout (Salmo gairdneri) with different genotypes at eight loci are compared in two experiments with the same strain. Embryos were incubated at temperatures colder (5 and 8°C) and warmer (12°C) than normally experienced by these fish (9.5°C). At hatching, embryos were separated into five hatching groups representing the chronological order of hatching. There is no significant correlation between multilocus heterozygosity and hatching time at any temperature in either experiment. Fish in the middle of the hatching distribution had the highest average heterozygosity. In both experiments, heterozygotes at the majority of loci examined tended to hatch relatively later within the hatching distribution at 12°C than at both 5 and 8°C. Fish with different genotypes atPgm2 andCk1 showed significant differences in hatching time that were consistent between experiments.Ck1 heterozygotes hatched sooner than homozygotes at 8°C but later at 12°C.Pgm2 heterozygotes hatched later than homozygotes at all temperatures and significantly later in four of five cases. At the other loci examined, however, the relative hatching distributions of fish with particular genotypes were not significantly different or repeatable between experiments.This research was supported by National Science Foundation Grant BSR-8300039 awarded to Dr. Fred W. Allendorf. Moira M. Ferguson was supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada.