Effects of cucumber mosaic virus‐infected chilli plants on non‐vector Bemisia tabaci (Hemiptera: Aleyrodidae)

Plant virus infections are known to alter host plant attractiveness and suitability for insect herbivores.This study was conducted to determine how cucumber mosaic virus (CMV)-infected chilli plants affect the fitness and settling preferences ofnonvector whitefly,Bemisia tabaci adults under dual-choice conditions with volatile organic compounds analyzed using solid phase microextraction coupled with gas chromatography-mass spectrometry (GC-MS).Results showed that the presence of CIVIV in chilli plants substantially affects the settling preferences of the B.tabaci,which preferred to settle on noninfected plants.Duration of the egg stage and the longevity and fecundity of adult B.tabaci on CMV-infected chilli plants were not markedly different from those on noninfected chilli plants.In contrast,the developmental time from egg to adult was significantly reduced in CMV-infected chilli plants compared to the noninfected plants.The results also showed that CMV-infected chilli plants released significantly more linalool and phenylacetaldehyde than noninfected plants.Overall,it was suggested that the behavioral response of B.tabaci might be modified by CMV-infected plants,which alter the release of specific headspace volatiles.Based on these results,the modification of plant volatile profiles may help in enhancing the effectiveness of biological control and the protection of crop plants against B.tabaci.     

The evolution of the phenotypic covariance matrix: evidence for selection and drift in Melanoplus

Phenotypic variation in trait means is a common observation for geographically separated populations. Such variation is typically retained under common garden conditions, indicating that there has been evolutionary change in the populations, as a result of selection and/or drift. Much less frequently studied is variation in the phenotypic covariance matrix (hereafter, P matrix), although this is an important component of evolutionary change. In this paper, we examine variation in the phenotypic means and P matrices in two species of grasshopper, Melanoplus sanguinipes and M. devastator. Using the P matrices estimated for 14 populations of M. sanguinipes and three populations of M. devastator we find that (1) significant differences between the sexes can be attributed to scaling effects; (2) there is no significant difference between the two species; (3) there are highly significant differences among populations that cannot be accounted for by scaling effects; (4) these differences are a consequence of statistically significant patterns of covariation with geographic and environmental factors, phenotypic variances and covariances increasing with increased temperature but decreasing with increased latitude and altitude. This covariation suggests that selection has been important in the evolution of the P matrix in these populations Finally, we find a significant positive correlation between the average difference between matrices and the genetic distance between the populations, indicating that drift has caused some of the variation in the P matrices.     

A physiological perspective on the response of body size and development time to simultaneous directional selection

Natural selection typically acts on multiple traits simultaneously.Quantitative genetics provides the theory for predicting theresponse to selection of multiple traits and predicts symmetricalresponses to selection (the response to upward selection onboth traits is equal to their response to downward selection).In reality, however, the response to simultaneous selectionon two traits is often asymmetrical. We provide a physiology-basedframework to explain the asymmetrical response to simultaneousselection on two important life history traits: body size anddevelopment time. The tobacco hornworm, Manduca sexta, is particularlywell suited for such a study, as the physiological control ofbody size and development time is well known in this species.Three physiological factors control both life history traitsin M. sexta: growth rate, the critical weight that measuresthe timing of the onset of the cessation of juvenile hormonesecretion (which initiates the processes leading to pupation)and the time interval between the critical weight and secretionof the molting hormone 20-hydroxyecdysteroid (the interval tocessation of growth, ICG). Asymmetry in the response to simultaneousselection on the two life history traits is due to the differenttypes of selection acting on the three physiological factors.The critical weight and ICG are always under synergistic selectionwhen both focal traits are selected in the same direction andunder antagonistic selection when the focal traits are selectedin opposite directions. Growth rate follows the opposite pattern.We propose a general model to explain the asymmetric responseto simultaneous selection. This model emphasizes the importanceof physiological processes in understanding evolutionary responsesto selection and the control of complex traits.     

The evolution of offspring size and number: a test of the Smith-Fretwell model in three species of crickets

Most models of parental investment in offspring assume a trade-off between propagule size and number, and an increasing concave down function relating offspring fitness to propagule size. In this study, we test these two fundamental assumptions, using three closely related species of crickets, Gryllus firmus, G. veletis, and G. pennsylvanicus. Egg weight, 35-day fecundity and 35-day egg biomass were estimated in a population of each species, and the relationships between these reproductive traits and date of egg laying and body size were estimated. The relationships between egg weight and offspring survival were also sought for eggs buried at different depths, soil moistures, and soil types (G. firmus and G. veletis), as well as in the field (G. pennsylvanicus). A trade-off between egg weight and 35-day fecundity was revealed in a multivariate analysis taking into account among-species variation in egg weight and body size. Independent of the environmental conditions affecting the eggs, a positive correlation existed between the number of larvae that emerged from the soil and propagule weight in each species. Therefore, these findings provide partial support for the assumptions considered in the models mentioned above. A single optimal egg size was favored in two out of the three sets of conditions in which the functions relating egg weight to larval survival could be derived. The conditions encountered by the eggs, however, influenced the average survival of the larvae, as well as the shape of the relationship between egg weight and offspring survival. This suggests that cricket eggs frequently face heterogeneous environments with respect to egg and hatchling survival; the implication of habitat heterogeneity on the evolution of an optimal egg size is considered. The relationships between the reproductive components and female age and size, as well as between egg size and variation in cricket life-history, are discussed in an ecological and evolutionary context.     

The evolution of flightlessness: Is history important?

Summary Though most birds and insects are capable of flight (volant) some species are flightless. In this paper I test the hypothesis that phylogenetic constraints have played a role in the evolution of flightlessness. If speciation occurred after the evolutionary transition to flightlessness, inferences concerning the importance of particular aspects of the environment on the probability of the evolution of flightlessness may be statistically spurious because of the inflation of the sample size. Among birds, ratites and penguins illustrate the phenomenon of considerable speciation subsequent to the transition to the evolution of flightlessness. In contrast, the rails represent a group in which each flightless species probably represents a separate evolutionary transition. There are many more flightless insect species than bird species and several orders are monomorphically flightless, the sometimes enormous speciation within the order following and possibly being a consequence of the evolution of flightlessness. While it can be shown in insects that flightlessness has evolved independently many times, there are at least as many cases in which the question cannot be resolved. Therefore, in both birds and insects phylogenetic effects should not be ignored, for the number of evolutionary transitions may be much less than the number of species. The effect of incorporating phylogenetic (or at least taxonomic) constraints into the analysis of habitat factors associated with flightlessness is considered.     

Nearshore abundance of zooplankton in relation to shoreline configuration and mechanisms involved

Zooplankton abundance was examined in relation to shorelineconfiguration. Four embayments (0.15, 1.5, 4 and 7 km opening)were each divided into three zones, corresponding to regionsinside, outside and downstream. A portion of straight coast[{small tilde}12 km, Sainte-Flavie (SF)] was also divided intothree zones. Only the largest embayment was sampled in 1993,but all embayments and SF were sampled in 1994. In 1993, zooplanktonabundance was significantly higher within the embayinent thanin external zones for six of seven dates. Zones inside the fourembayments had generally higher zooplankton abundance than zonesexternal to the embayments in 1994, but the opposite was observedduring the first of two sampling dates for the largest embayments.No definite pattern was observed among zones along SF. Fourhypotheses could explain the higher abundance of zooplanktoninside embayments. Three were tested using meroplankton (M)/holoplankton(H) ratios. The M/H ratios confirmed hypotheses of retentionand local production of meroplanktonic larvae inside embayments.Zooplankton abundance was lower inside than in zones externalto embay ments only twice, and wind direction may have beenresponsible for these results. No embayment size effect on zooplanktonabundance was detected. The patchy distribution of zooplanktonmay increase the difficulty of observing an effect of embaymentsize on zooplankton abundance.     

Broadening the taxonomic scope of coral reef palaeoecological studies using ancient DNA

Marine environments face acute pressures from human impacts, often resulting in substantial changes in community structure. On the inshore Great Barrier Reef (GBR), palaeoecological studies show the collapse of the previously dominant coral Acropora from the impacts of degraded water quality associated with European colonization. Even more dramatic impacts can result in the replacement of corals by fleshy macroalgae on modern reefs, but their past distribution is unknown because they leave no fossil record. Here, we apply DNA metabarcoding and high‐throughput sequencing of the 18S rDNA gene on palaeoenvironmental DNA (aeDNA) derived from sediment cores at two sites on Pandora Reef (GBR), to enhance palaeoecological studies by incorporating key soft‐bodied taxa, including macroalgae. We compared temporal trends in this aeDNA record with those of coral genera derived from macrofossils. Multivariate analysis of 12 eukaryotic groups from the aeDNA community showed wide variability over the past 750 years. The occurrence of brown macroalgae was negatively correlated only with the dominant coral at both sites. The occurrence of coralline and green macroalgae was positively correlated with only the dominant coral at one of the sites, where we also observed a significant association between the whole coral community and the occurrence of each of the three macroalgae groups. Our results demonstrate that reef sediments can provide a valuable archive for understanding the past distribution and occurrence of important soft‐bodied reef dwellers. Combining information from fossils and aeDNA provides an enhanced understanding of temporal changes of reefs ecosystems at decadal to millennial timescales.