Genetic variation in larval period and pupal mass in an aphidophagous ladybird beetle (Harmonia axyridis) reared in different environments

Abstract Genetic trade‐offs for host plant use are hypothesized to facilitate the diversification of insect populations through specialization to their host plants. Previous studies mainly estimated the architecture of genetic variances and covariances in herbivorous species with discrete and limited types of host species. In contrast to herbivores, the relative abundance of resources for predatory species fluctuates in time and space, causing a more unpredictable encounter with prey species. The ecological characteristics of resource use might result in a differential mode of selection for herbivorous and predatory species, which could be reflected in a differential genetic architecture of developmental traits such as the duration of larval stage (henceforth referred to as larval period) and size of pupa (measured as pupal weight). This paper presents results from a study on the genetic architecture of larval period and pupal mass of an aphidophagous ladybird beetle, Harmonia axyridis Pallas, in different resource environments. Beetles reared on Acyrthosiphon pisum (Harris) showed a shorter developmental period and a heavier pupal mass than their siblings on Aphis craccivora Koch or on artificial diet, while the average larval period and pupal mass on A. craccivora and the artificial diet were similar. Further analyses of the genetic architecture suggest that the developmental traits on the two aphid species are genetically correlated, while there are only weak or no genetic correlations between these two traits on the two aphid preys and the artificial diet. Thus, the results suggest that the patterns of genotypic relationships between developmental traits differ from the phenotypic ones. The effects of past selection on the genetic architecture and the possible cause of the genetic correlation are discussed, as well as consequences for mass rearing for biological control.     

Life‐cycle variation,including female production by virgin females in Frankliniella occidentalis (Thysanoptera: Thripidae)

The influence of three different temperatures on developmental time and sex ratio was investigated in the bisexual Thysanoptera species Frankliniella occidentalis. Increasing temperatures decreased developmental time and induced a more female biased sex ratio. Remarkably, there are second instars with a prolonged developmental time requiring the same number of hours as the shortest developmental time from egg to adult. Arrhenotokous reproduction in this species is based on haplodiploidy, with virgin females producing male offspring exclusively. However, at all three temperatures tested, about 0.5% of offspring from unfertilized eggs were females. The presence of Wolbachia could not be detected in Western flower thrips and can be excluded as influencing reproduction in this species.     

EVOLUTION OF DEVELOPMENTAL PROGRAMS IN VOLVOX (CHLOROPHYTA)1

The volvocine green algal genus Volvox includes ～20 species with diverse sizes (in terms of both diameter and cell number), morphologies, and developmental programs. Two suites of characters are shared among distantly related lineages within Volvox. The traits characteristic of all species of Volvox—large (>500) numbers of small somatic cells, much smaller numbers of reproductive cells, and oogamy in sexual reproduction—have three or possibly four separate origins. In addition, some species have evolved a suite of developmental characters that differs from the ancestral developmental program. Most multicellular volvocine algae, including some species of Volvox, share an unusual pattern of cell division known as palintomy or multiple fission. Asexual reproductive cells (gonidia) grow up to many times their initial size and then divide several times in rapid succession, with little or no growth between divisions. Three separate Volvox lineages have evolved a reduced form of palintomy in which reproductive cells are small and grow between cell divisions. In each case, these changes are accompanied by a reduction in the rate of cell division and by a requirement of light for cell division to occur. Thus, two suites of characters—those characteristic of all Volvox species and those related to reduced palintomy—have each evolved convergently or in parallel in lineages that diverged at least 175 million years ago (mya).     

Thermal attributes of Chrysomya species

The correct identification of forensically important arthropods for post‐mortem interval estimation is crucial, as the rate of larval development can vary substantially between species. The identification of forensically important blowflies of the genus Chrysomya (Diptera: Calliphoridae) may be hampered by their close morphological similarities, especially as immatures. The aim of this study was to establish whether genetically closely related blowfly species would share similar developmental profiles. This could permit the application of developmental data to a number of closely related species, including those for which thermodevelopmental studies are lacking. If Australian Chrysomya were found to share developmental profiles, identification of the blowfly specimen to a level beyond genus may not be necessary, or at least it may not be necessary to distinguish morphologically similar sister species. The three Chrysomya species studied were collected from the same geographical location (Cairns, Australia), reducing the effects of acclimation and population‐level genetic variation. The experimental conditions in this study were virtually identical, which enabled direct comparisons to be made among the species. Blowfly larval lengths were obtained for 24‐hourly intervals at constant temperatures of 25, 30, and 35 °C. The thermal preferences of newly‐hatched feeding larvae were determined by their positions on a temperature gradient apparatus. This study established that all three species investigated differed significantly in their developmental profiles, despite the genetic closeness of the sister species Chrysomya megacephala (Fabricius) and Chrysomya saffranea (Bigot). Because of this, genetic distance was not considered to be a useful factor for predicting thermodevelopment profiles of closely related species within a genus, and highlights the necessity for correct species identification.     

Developmental specificity and evolution of the acid phosphatase isozymes of Triticum aestivum and its progenitor species

The tissue and developmental specificities of the acid phosphatase (ACPH) isozymes of Triticum aestivum and its progenitor species T. turgidum and T. tauschii have been determined and compared using the zymogram technique. Tissue and/or developmental variation in relative staining intensity, suggestive of variation in the quantity of active enzyme present, was observed for each of the seven major isozymes expressed. Isozymes homologous to each of the major isozymes of the hexaploid were detected in one or the other of the progenitor species. No difference in the pattern of developmental or tissue specificity was observed between the species for any isozyme. However, ACPH-4, encoded by Acph4, a structural gene linked to chromosome 4A, differs in electrophoretic mobility between T. aestivum and T. turgidum, indicating that divergence has occurred between these species at the Acph4 locus since the origin of the hexaploid. The molecular weight of each of five ACPH isozymes of the hexaploid was determined to be approximately 58,000. This finding, plus the results of the developmental study and the earlier demonstration that the structural genes for six isozymes (including four of those whose molecular weight was determined) are linked to homoeologous chromosomes, provides evidence in support of the suggestion that the ACPH structural genes of hexaploid wheat are homoeologously related.Technical article No. 12233 of the Texas Agricultural Experiment Station. Adapted from a dissertation submitted to the Graduate College, Texas A&M University, by M. A. T. in partial fulfillment of the requirements for the Ph.D. in genetics.     

Models of development for blowfly sister species Chrysomya chloropyga and Chrysomya putoria

Abstract Developmental curves for the sister species Chrysomya chloropyga (Wiedemann, 1818) and Chrysomya putoria (Wiedemann, 1830) (Diptera: Calliphoridae) were established at eight and 10 different constant temperatures, respectively, using developmental landmarks and body length as measures of age. The thermal summation constants (K) and developmental threshold (D₀) were calculated for five developmental landmarks using a previously described method. Isomorphen and isomegalen diagrams were also constructed for the purpose of estimating postmortem intervals (PMIs). Chrysomya chloropyga had an average developmental threshold value (D₀) of 10.91 °C (standard error [SE] = 0.94 °C, n = 5), significantly lower than that of C. putoria (13.42 °C, SE = 0.45 °C, n = 5) (paired t‐test: t = ? 4.63, d.f. = 8, P < 0.00). Similarly, K values for C. chloropyga were larger than those for C. putoria for all developmental events except onset of the wandering phase. These are the first data that can be used to calculate minimum PMIs and predict population growth of C. chloropyga and C. putoria in Africa; the data indicate that developmental data for one of these species cannot be used as surrogate data for the sister species.     

Relative toxicity of three wheat herbicides to two species of Coccinellidae

Abstract On the High Plains of the USA, herbicides specific for broad-leaf weeds are regularly applied to winter wheat in the early spring, sometimes late enough to coincide with the colonization of fields by cereal aphids and their natural enemies. We tested the toxicity of three such herbicides, Ally (Dupont), Rave (Syngenta) and 2,4-D ester (generic), to neonate larvae of two coccinellid species important in cereal aphid biocontrol, Coleomegilla maculata DeGeer and Hippodamia convergens Guérin-Méneville. Topical treatment of larvae with 2,4-D resulted in 25% and 60% mortality in the two species, respectively, with surviving C. maculata larvae experiencing a 5% increase in developmental time. No significant effects were noted for the other two materials, save for a 2.5% increase in developmental time for C. maculata larvae exposed to Rave. No material caused significant mortality in either species when larvae were fed on prey (Schizaphis graminum Rondani) treated with herbicide 24 h earlier, although 2,4-D reduced developmental time slightly in C. maculata. When herbicide applications are delayed enough in spring to coincide with aphid activity in wheat, farmers can reduce the risk of disrupting biological control by selecting an alternative to 2,4-D.     

Postembryonic development of Phyllodiaptomus blanci (Guerne & Richard, 1896) (Copepoda,Calanoida)

All the postembryonic developmental instars of Phyllodiaptomus blanci (Guerne & Richard, 1896), reared in the laboratory, are described and illustrated. The larval affinities of this species vis-a-vis certain other diaptomid species are mentioned.     

Variance and covariance of ovipositional rates and developmental rates in the Phytoseidae (Acari: Mesostigmata): a phylogenetic consideration

Variance and covariance of ovipositional rates and developmental rates in the Phytoseiidae were analysed using comparative methods which consider phylogenetic effects. Nested analysis of variance showed that mean ovipositional rates and developmental rates of phytoseiid mites varied significantly between subfamilies, among genera within subfamilies, among subgenera within genera and among species within subgenera. For example, the mean ovipositional rate (eggs per day) was higher in the Amblyseiinae (2.04) than in the Phytoseiinae (1.39) and within the Amblyseiinae, it was higher in the genus Phytoseiulus (2.66) than in Amblyseius (1.80). Regressions using mean values of subgenera or higher taxa to account for phylogenetic effects showed significant correlation between mean ovipositional rates and developmental rates. The implications of this analysis for selecting species for future comparative analysis of phytoseiid life history variation are discussed.     

Developmental stability in hybrids between the sibling species pair,Drosophila melanogaster and Drosophila simulans

Drosophila melanogaster and its sibling species D. simulans were hybridized in the laboratory to test the hypothesis that developmental homeostasis in hybrids between two species having no prior gene flow would be significantly reduced. Developmental stability was assessed by measuring fluctuating asymmetry for three bilateral traits: sternopleural chaetae, wing length, and fronto-orbital plus frontal chaetae. Male F₁ hybrids showed no decrease in developmental stability compared to males of parental species. Female hybrids showed significant fluctuating asymmetry compared to other flies. The results are discussed with respect to ideas about coadaptation and gene flow based upon previous studies of hybrid developmental stability.     

Balbiani rings and puffs of the polytene chromosomes of Drosophila auraria

Drosophila auraria and its sibling species, D. biauraria, D. triauraria, and D. quadraria are unique among Drosophila species in that their salivary gland chromosomes exhibit Balbiani rings. In this report we present a cytological map of D. auraria and information on the developmental profiles of its puffs and Balbiani rings. Information is presented on the existence of tandem inverted duplications involving the Balbiani ring regions and other regions of the chromosomes, and data are given concerning the puffing patterns of the duplicated bands. Possible homologies between puffs of D. melanogaster and D. auraria and certain differences between the two species in the developmental sequences of the active loci are discussed.     

The dietary relationships of Tribolium castaneum (Herbst) with microfungi

The ecology of Tribolium castaneum (Herbst) outside of grain storage facilities is poorly known. However, high densities of T. castaneum adults are known to infest stored cotton seeds (Gossypium hirsutum (L.)) in Queensland, Australia, despite the absence of stored food products in the immediate vicinity. Previous studies suggest that the beetles are attracted to the fungal colonies growing on the residual fibres that remain on the cotton seeds after ginning, but the specifics of this remain unclear, even as to the species of fungi involved. In the current study, 14 fungal species were isolated from stored cotton seeds collected from four sites in Queensland. The feeding preferences of the adult beetles and the developmental success of the larvae were recorded for each fungal species. Gut analyses of T. castaneum adults, after exposure in no-choice feeding tests, showed that the beetles will feed on any one of the 14 fungal species when exposed (over 14 days) to cotton seeds that had been inoculated with one particular fungal species. The developmental success of the larvae varied depending on the fungal species, with most fungal species supporting only low levels of successful development (<30%). Tests with each fungal species and the volatiles they release revealed that neither adult nor larval survival was significantly affected by the presence of any particular fungal isolate. These results indicate that T. castaneum will feed on a variety of fungal species but that none of the tested fungal species on its own provides a good larval diet for T. castaneum.     

Germination and regeneration mechanisms in Mediterranean degenerate forests

Abstract. Germination and developmental behaviour during juvenile stages are of importance in relation to succession mechanisms acting on plant communities. This is particularly so in the Mediterranean region, where the climatic summer drought causes stress. We investigated and compared germination and development of four tree species in two parts of the French Mediterranean region where the original dominant tree species (Quercus pubescens) has been largely replaced by Quercus ilex in the southern part, and Castanea sativa in the northern part. Observed differences in germination rates and developmental behaviour, especially shootroot ratio and the role of water supply, suggest that other species may eventually replace the current dominant species.     

DEVELOPMENTAL INSTABILITY AND HIGH MERISTIC COUNTS IN INTERSPECIFIC HYBRIDS OF SALMONID FISHES

Interspecific hybrids have been proposed to have reduced developmental stability in comparison to their parental species because the parental genomes have not undergone selection for the maintenance of developmental stability when they occur together. We present data from four interspecific hybrids of salmonid fishes that support this view. Natural hybrids of bull trout (Salvelinus confluentus) with brook trout (Salvelinus fontinalis) and laboratory hybrids of rainbow trout (Salmo gairdneri) with Yellowstone (Salmo clarki bouvieri), westslope (S. c. lewisi), and coastal (S. c. clarki) cutthroat trout all have higher levels of fluctuating asymmetry than either of their parental species raised in the same environment. Thus, the hybrids have reduced developmental stability. The hybrids do not have meristic counts intermediate to the counts of the parental species. The hybrids usually have counts as high as the species with the higher count for those characters that differ between the parental species and often have higher counts for those characters that do not differ between the parental species. We suggest that the tendency for interspecific hybrids to have high meristic counts may be related to differences between the species in the length and timing of the developmental periods during which the counts of the characters are determined.     

Regulation of flower organogenesis: Phytohormone control of mRNA populations during sexual differentiation inMercurialis annua L.

Some general data on the genetic control and the possibilities of regulation of developmental paths inDrosophila are furnished. The insights to be gained from this insect will surely have implications that extend far beyond the fruit-fly. For example, in plants, developmental programs for floral organs, implying specific proteins are known. Developmental mutants in which mutate alleles control developmental programs for flowering were also selected in several species (Zea, Pisum, Sorghum, Cucumis, Mercurialis). Chemicals, especially phytohormones interfering with these programs are discussed. The case of sexual differentiation ofMercurialis is discussed in more detail. In this species, sex organs are controlled by sex determination genes and by auxins (male) and cytokinins (female). Flowers of each sex can be characterized by specific mRNA populations. They were evidenced by translationin vitro in a cell-free system of the various kinds of mRNAs [poly(A), non poly(A), polysomes]. The feminisation of genetic males by cytokinins induces the mRNA population of female type. Evidence concerning the implications of cytokinins in protein synthesis before translation level is presented. This is also probably true for auxins, although direct evidence is lacking.     

ONTOGENETIC STUDIES OF FLORETS IN POA (GRAMINEAE): ALLOMETRY AND HETEROCHRONY

Species distinctions in grasses are based on differences in sizes of parts, particularly floral parts, and on differences in distribution of hairs; both sets of characters are apparently subject to repeated parallel evolution. Developmental studies of florets in the genus Poa reveal that there are only two developmental trajectories for lemma length relative to anther length (a measure of time to maturity): either lemma growth is continuous with anther growth, or the lemma reaches its adult size well before the anthers do. The tuft of long, cobweb-like hairs on the callus of many species forms early in lemma development, as might be expected for a character that marks a large group of species. The five possible patterns of hair distribution on the lemma itself represent stages of a single developmental pathway; differences between species presumably reflect differences in timing of onset or truncation of the developmental program (heterochrony).     

Comparative study on the gametophyte morphology and development of three paramo species of Jamesonia (Pteridaceae,Polypodiopsida)

The sexual phase of three species of Jamesonia (J. imbricata, J. rotundifolia and J. scammaniae) has been studied, from spore germination to gametangia formation, with special attention to the morphological development of prothalli. This is the first work to deal with gametophytes of species in this genus. All three species have trilete, tetrahedrical spores that germinate following the Vittaria type. The developmental pattern of J. imbricata and J. rotundifolia is intermediate between the Adiantum and Ceratopteris types, as the initial mitotic activity is assumed by an obconical apical cell, substituted later by a lateral meristem. In J. scammaniae, no apical cell or lateral meristem is formed, so the prothalli remain ameristic throughout the developmental process. Adult gametophytes are naked and variable in shape, in the same species ranging from typical cordate prothalli to irregularly lobed forms. Gametangia of normal shape and size was observed in both J. imbricata and J. rotundifolia, but not in J. scammaniae. Apogamy could be expected to occur in the genus, a phenomenon to be examined in the future. Comparisons are made with known species of related genera and results are discussed from an ecological perspective in the paramo environment.     

Demographic population structure of a leafy epixylic hepatic Anastrophyllum hellerianum (Nees ex Lindenb.) R.M.Schust

Understanding the population processes is central when assessing proper conservation acts, especially in the case of species which inhabit temporal and patchy substrates, such as decaying wood. In epixylic bryophytes, however, only little is known of the demographic population structure and within-population dynamics. In this study on a leafy epixylic hepatic, Anastrophyllum hellerianum (Nees ex Lindenb.) R.M.Schust., a set of demographic traits is investigated, including colony area and size, proportions of the sterile, gemmiparous or sexual developmental stages, the shoot size class distribution among the developmental stages, and numbers of asexual propagules present on the shoots. The estimates of mortality are assessed on the basis of the proportions of dead shoots found in the colonies. The size distribution within the developmental stages of this species shows that a certain threshold size is required for both asexual and sexual reproduction. The shoot size is negatively correlated with density, whereas the numbers of asexual gemmae and the proportions of developmental stages are not affected by shoot density. Furthermore, provisional estimates are calculated for the transitions from early developmental stages to reproductively mature stages. The results indicate that the initial phases of the gametophyte development are the most vulnerable.     

Ontogeny of skull size and shape changes within a framework of biphasic lifestyle: a case study in six <Emphasis Type="Italic">Triturus</Emphasis> species (Amphibia,Salamandridae)

As with many other amphibians, Triturus species are characterized by a biphasic life cycle with abrupt changes in the cranial skeleton during metamorphosis. The post-metamorphic shape changes of the cranial skeleton were investigated using geometric morphometric techniques in six species: Triturus alpestris, T. vulgaris, T. dobrogicus, T. cristatus, T. carnifex, and T. karelinii. The comparative analysis of ontogenetic trajectories revealed that these species have a conserved developmental rate with divergent ontogenetic trajectories of the ventral skull shape that mainly reflect phylogenetic relatedness. A striking exception in the ontogenetic pattern was possibly found in T. dobrogicus, characterized by a marked increase in the developmental rate compared to the other newt species. The size-related shape changes explained a large proportion of shape change during post-metamorphic growth within each species, with marked positive allometric growth of skull elements related to foraging.     

Stage-based mortality of grassland grasshoppers (Acrididae) from wandering spider (Lycosidae) predation

Mortality rates in insects, including grasshoppers (Acrididae), are often stage- or size-specific. We estimated stage-specific mortality rates for three common grasshopper species from a Nebraska (USA) sandhills grassland (Ageneotettix deorum, Melanoplus sanguinipes and Phoetaliotes nebrascensis), and partitioned the impact due to wandering spider predation from remaining sources. Survivorship was estimated for multiple developmental stages (3rd instar through adult) under experimental conditions that either prevented or permitted predation from free-living, wandering spiders (primarily Schizocosa species). Total stage-specific mortality, including spider predation, examined over the period of single stages was greatest for the youngest stages (91% for 3rd instar, 73% for 4th instar, 63.5% for 5th instar and 30.4% for adults). For the developmental stages considered and averaged for all species, the contribution to total mortality from spider predation over the 10-d period (approximately the length of a developmental stage) ranged from 17% for 3rd instar nymphs to 23% for 4th and 5th instars, and an undetectable level for adults. While spiders may depress grasshopper numbers, contributions from spider predation to grasshopper population dynamics are uncertain.