Age determination using the apodeme structure in adult screwworm flies (Cochliomyia hominivorax)

A method of age determination of adult screwworm flies is described and documented. This method uses the diurnal differences in the deposition of apodeme layers as a basis for counting the age in days since eclosion. The method is accurate to plus or minus one day, and can be determined on meterial that has been dried, pinned, frozen, or preserved in ethanol or other fixatives.     

Comparative analysis of DNA extraction methods to study the body surface microbiota of insects: A case study with ant cuticular bacteria

High‐throughput sequencing of the 16S rRNA gene has considerably helped revealing the essential role of bacteria living on insect cuticles in the ecophysiology and behaviour of their hosts. However, our understanding of host‐cuticular microbiota feedbacks remains hampered by the difficulties of working with low bacterial DNA quantities as with individual insect cuticle samples, which are more prone to molecular biases and contaminations. Herein, we conducted a methodological benchmark on the cuticular bacterial loads retrieved from two Neotropical ant species of different body size and ecology: Atta cephalotes (~15 mm) and Pseudomyrmex penetrator (~5 mm). We evaluated the richness and composition of the cuticular microbiota, as well as the amount of biases and contamination produced by four DNA extraction protocols. We also addressed how bacterial community characteristics would be affected by the number of individuals or individual body size used for DNA extraction. Most extraction methods yielded similar results in terms of bacterial diversity and composition for A. cephalotes (~15 mm). In contrast, greater amounts of artefactual sequences and contaminations, as well as noticeable differences in bacterial community characteristics were observed between extraction methods for P. penetrator (~5 mm). We also found that large (~15 mm) and small (~5 mm) A. cephalotes individuals harbour different bacterial communities. Our benchmark suggests that cuticular microbiota of single individual insects can be reliably retrieved provided that blank controls, appropriate data cleaning, and individual body size and functional role within insect society are considered in the experiment.     

紫外线阻断膜防控茄子害虫效果及对植株生长和果实品质的影响

【目的】紫外线阻断膜可以吸收光线中波长在380 nm以下的紫外光,从而影响昆虫的视觉反应,因此有望用于害虫防控。本研究旨在明确该项措施的可行性。【方法】以日光温室茄子Solanum melongena为作物对象,对紫外线阻断棚和使用普通棚膜的对照棚中3种主要害虫(西花蓟马Frankliniella occidentalis、烟粉虱Bemisia tabaci和桃蚜Myzus persicae)的发生情况进行了比较,分析了紫外线缺失对茄子植株生长和果实品质的影响。【结果】紫外线阻断棚中西花蓟马、烟粉虱和桃蚜的最大发生量均显著低于对照棚(P0.05),分别是对照棚中的44.3%,50.4%和37.5%;与对照棚相比,紫外线阻断棚中茄子株高偏高,但二者差异不显著(P0.05);紫外线阻断棚中茄子产量、果实重量和周长均降低,茄子果实颜色偏浅,果实中维生素C、可溶性糖、可滴定酸、粗脂肪和花青素含量下降(P0.05),Ca,K,Cu和Zn等矿物离子含量上升(P0.05)。【结论】本研究表明紫外线阻断技术可以显著抑制温室茄子上3种主要害虫的种群增长,但对茄子的生长和果实品质有一定影响。今后需要进一步研究该项技术在茄子品种和其他作物中的应用方式。     

Age and growth of the gulf toadfish Opsanus beta based on otolith increment analysis

In the present study, sagittal otoliths of confirmed male and female specimens of the gulf toadfish Opsanus beta that were collected monthly over the course of a year from Biscayne Bay, Florida, U.S.A. were analysed. The timing and frequency of O. beta spawning seasons are reported by examination of the gonado‐somatic index. The estimated ages of males and females ranged from < 1 year to 6 and 5 years, respectively. Strong sexual dimorphism in growth was apparent with von Bertalanffy parameter estimates for males of L_∞ = 393·8 mm, K = 0·30, t₀ = 0·36 and females of L_∞ = 201·1 mm, K = 0·79, t₀ = 0·47. Comparison with previously published growth trajectories of the more northerly distributed conspecific Opsanus tau showed that O. beta males had a higher growth rate. Female O. beta and O. tau growth trajectories appear similar, with an indication that the former becomes asymptotic at least a year before the latter. Results are discussed in the context of temperature regimes, reproductive energy allocation and waste urea excretion in the two species.     

Daily increments on the otoliths of larval and juvenile Coregonus spp., and their modification by environmental factors

The sagittal otoliths of pre- and posthatch embryos, larval, and juvenile coregonids (Coregonus spp.) were examined for growth increments. Under laboratory conditions, a check is formed on the day of hatching and subsequently one growth increment per day is deposited during at least 265 days. Under the experimental conditions of this study, the age of young coregonids can therefore be determined with high accuracy.In starving larvae, both increment width and ring contrast decrease during the first 10 days after hatching until daily increments are no longer recognizable. A change from one diet to another, alteration of the water temperature, or a short starvation period lead to the formation of characteristic ring patterns which appear on the otoliths within 1 to 3 days. These patterns are highly reproducible among all specimens of each treatment group and can therefore be used as intrinsic marks. They could be applied to hatchery-reared coregonids, thus providing a basis for judging the efficacy of stocking operations.     

Leaf cuticular waxes are arranged in chemically and mechanically distinct layers: evidence from Prunus laurocerasus L.

The composition and spatial arrangement of cuticular waxes on the leaves of Prunus laurocerasus were investigated. In the wax mixture, the triterpenoids ursolic acid and oleanolic acid as well as alkanes, fatty acids, aldehydes, primary alcohols and alcohol acetates were identified. The surface extraction of upper and lower leaf surfaces yielded 280 mg m ^{? 2} and 830 mg m ^{? 2}, respectively. Protocols for the mechanical removal of waxes from the outermost layers of the cuticle were devised and evaluated. With the most selective of these methods, 130 mg m ^{? 2} of cuticular waxes could be removed from the adaxial surface before a sharp, physically resistant boundary was reached. Compounds thus obtained are interpreted as ‘epicuticular waxes’ with respect to their localization in a distinct layer on the surface of the cutin matrix. The epicuticular wax film can be transferred onto glass and visualized by scanning electron microscopy. Prunus laurocerasus epicuticular waxes consisted entirely of aliphatic compounds, whereas the remaining intracuticular waxes comprised 63% of triterpenoids. The ecological relevance of this layered structure for recognition by phytotrophic fungi and herbivorous insects that probe the surface composition for sign stimuli is discussed.     

Growth of the clupeid fishes, Stolothrissa tanganicae and Limnothrissa miodon, in the Zambian waters of Lake Tanganyika

The age and growth of two endemic Lake Tanganyikan clupeid fishes, Stolothrissa tanganicae and Limnothrissa miodon , were estimated from analysis of otolith microstructure in specimens collected in Zambian waters from October to December 1990. Both species had relatively clear, concentric otolith increments which were believed to represent daily increments based on their similarity to daily increments found in some marine clupeid species. The growth rates estimated from length-at-age data were: for S. tanganicae, L_t = 104·0 (1 – exp (– 0.00512 ( t – 5·8))); for L. miodon, L_t = 155.4 (1 – exp (– 0.00236 ( t +8.1))). In most cases, the growth parameters obtained from otolith analyses generally agreed with those previously estimated from analyses of length-frequency distributions.     

Biological clocks as age estimation markers in animals: a systematic review and meta-analysis

Various biological attributes associated with individual fitness in animals change predictably over the lifespan of an organism. Therefore, the study of animal ecology and the work of conservationists frequently relies upon the ability to assign animals to functionally relevant age classes to model population fitness. Several approaches have been applied to determining individual age and, while these methods have proved useful, they are not without limitations and often lack standardisation or are only applicable to specific species. For these reasons, scientists have explored the potential use of biological clocks towards creating a universal age-determination method. Two biological clocks, tooth layer annulation and otolith layering have found universal appeal. Both methods are highly invasive and most appropriate for post-mortem age-at-death estimation. More recently, attributes of cellular ageing previously explored in humans have been adapted to studying ageing in animals for the use of less-invasive molecular methods for determining age. Here, we review two such methods, assessment of methylation and telomere length, describing (i) what they are, (ii) how they change with age, and providing (iii) a summary and meta-analysis of studies that have explored their utility in animal age determination. We found that both attributes have been studied across multiple vertebrate classes, however, telomere studies were used before methylation studies and telomere length has been modelled in nearly twice as many studies. Telomere length studies included in the review often related changes to stress responses and illustrated that telomere length is sensitive to environmental and social stressors and, in the absence of repair mechanisms such as telomerase or alternative lengthening modes, lacks the ability to recover. Methylation studies, however, while also detecting sensitivity to stressors and toxins, illustrated the ability to recover from such stresses after a period of accelerated ageing, likely due to constitutive expression or reactivation of repair enzymes such as DNA methyl transferases. We also found that both studied attributes have parentally heritable features, but the mode of inheritance differs among taxa and may relate to heterogamy. Our meta-analysis included more than 40 species in common for methylation and telomere length, although both analyses included at least 60 age-estimation models. We found that methylation outperforms telomere length in terms of predictive power evidenced from effect sizes (more than double that observed for telomeres) and smaller prediction intervals. Both methods produced age correlation models using similar sample sizes and were able to classify individuals into young, middle, or old age classes with high accuracy. Our review and meta-analysis illustrate that both methods are well suited to studying age in animals and do not suffer significantly from variation due to differences in the lifespan of the species, genome size, karyotype, or tissue type but rather that quantitative method, patterns of inheritance, and environmental factors should be the main considerations. Thus, provided that complex factors affecting the measured trait can be accounted for, both methylation and telomere length are promising targets to develop as biomarkers for age determination in animals.     

Otolith and somatic growth rates in Atlantic salmon parr, Salmo salar L: evidence against coupling

It is often assumed that otolith growth is in some way dependent on somatic growth (i.e. that the two processes are coupled). We examined the relationships between sagitta radius and fork length in 0+ Atlantic salmon parr that would subsequently smolt aged 1 + (UMG fish) or 2+ (LMG fish). Repeated measurements of fork lengths of individually marked parr, taken over a 211-day period from first feeding, were compared to sagitta radii on the same measuring dates (obtained by analysis of daily increments). The results showed that there was a linear relationship between fork length and otolith radius in UMG parr. However, this was not true for LMG parr. These fish enter a state of natural anorexia in their first autumn (despite excess food), but their otoliths continued to grow at the same rate despite the virtual cessation of somatic growth; they had therefore developed disproportionately large otoliths by the end of the study period. The relative growth rates of soma and otoliths first changed in LMG fish in late July/early August; this is the most precise estimate yet obtained of the timing of divergence in the developmental pathways of UMG and LMG parr. The rate of sagitta accretion was consistently lower in LMG parr, possibly indicating a lower metabolic rate in these fish. The results are discussed in relation to previous theories of the relationship between otolith and somatic growth.     

Validation of otolith daily increment formation for two temperate syngnathid fishes: the pipefishes Stigmatopora argus and Stigmatopora nigra

Otoliths were used for the first time to successfully validate the age of members of the family Syngnathidae: the spotted pipefish Stigmatopora argus and the wide-bodied pipefish Stigmatopora nigra. Otolith increments were deposited daily in (1) known-age juveniles ranging in age from 0 to 31 days and (2) adults that had been stained with alizarin complexone, and a hatch mark was found on all otoliths which represented day 0. Otolith increment validation will allow development of growth models for S. argus and S. nigra, essential to understanding and managing these exclusive seagrass species.     

The life cycle of Anguina agrostis: Post-embryonic growth of the second stage larva

The growth and development of the freshly hatched second stage larva (FHL₂) into the infective second stage “dauer” larva (DL₂) has been followed under field conditions and in callus tissue culture. A comparison of this development has been made between specimens originating from widely separated geographic regions. The FHL₂'s from Narrogin (Western Australia) are slightly shorter than those from Murray Bridge (South Australia) and have a mean length of 543 ± 55 μm compared with 580±51 μm. However, the lengths of the DL₂s from these areas are similar, having mean lengths of 841 ± 35 μm and 849 ±26 μm respectively. Furthermore stylet lengths in all these larvae are similar and are approx. 10 μm. Morphological changes associated with the transition from FHL₂ to DL₂ include thickening of the cuticle, a change in shape of the lateral alae associated with stretching and the synthesis of numerous lipid storage granules. Physiological changes include a marked increase in swimming activity and the ability to enter into an anhydrobiotic state. Growth from FHL₂ to DL₂ in Lolium multiflorum callus tissue culture took place within 9 days at 20°C. No moulting was observed and growth did not take place beyond the DL₂ stage under these conditions.     

Mechanics of growth pulsations as the basis of growth and morphogenesis in colonial hydroids

Growth and shaping in colonial hydroids (Hydrozoa, Cnidaria) are realized due to the functioning of special colony elements, growing tips located at the terminuses of branched colony body. Unlike in plants, the growing tips of colonial hydroids are sites of active cell movements related to morphogenesis and lacking proliferation. The activity of hydroid growing tips is expressed as growth pulsations: cyclic repetitions of their apex extensions and retractions. The parameters of growth pulsations are species specific and related to the shape of a forming element. Here, the succession of cell movements and changes in mutual arrangement within the growing tip are described in detail at all pulsation phases. The role of the inner cell layer in the tip activity was demonstrated for the first time. Relationships between the growing tip parameters, length and diameter, and pulsations are discussed. A scheme is proposed for cyclic processes in both epithelial layers. An explanation is provided for the two-step mode of growth pulsations with relative independence of the main phases. It was proposed that successive activities of the tip ecto-and endoderm serve as driving forces provided there is a hard outer skeleton. This scheme makes it possible to explain some patterns of growth and morphogenesis in colonial hydroids, such as gradually increasing growth rate of a new tip and its maximum growth rate, differences in the parameters of growth pulsations between shoot and stolon tips, shoot base inclination towards the stolon tip, etc., and provides a basis for further improvement of the model of morphogenesis in hydroids.     

Avian growth and development rates and age-specific mortality: the roles of nest predation and adult mortality

Previous studies have shown that avian growth and development covary with juvenile mortality. Juveniles of birds under strong nest predation pressure grow rapidly, have short incubation and nestling periods, and leave the nest at low body mass. Life-history theory predicts that parental investment increases with adult mortality rate. Thus, developmental traits that depend on the parental effort exerted (pre- and postnatal growth rate) should scale positively with adult mortality, in contrast to those that do not have a direct relationship with parental investment (timing of developmental events, e.g. nest leaving). I tested this prediction on a sample of 84 North American songbirds. Nestling growth rate scaled positively and incubation period duration negatively with annual adult mortality rates even when controlled for nest predation and other covariates, including phylogeny. On the contrary, neither the duration of the nestling period nor body mass at fledging showed any relationship. Proximate mechanisms generating the relationship of pre- and postnatal growth rates to adult mortality may include increased feeding, nest attentiveness during incubation and/or allocation of hormones, and deserve further attention.     

A salivary factor binds a cuticular protein and modulates biting by inducing morphological changes in the mosquito labrum

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Age and size at maturity: A quantitative review of diet‐induced reaction norms in insects

Optimality models predict that diet‐induced bivariate reaction norms for age and size at maturity can have diverse shapes, with the slope varying from negative to positive. To evaluate these predictions, we perform a quantitative review of relevant data, using a literature‐derived database of body sizes and development times for over 200 insect species. We show that bivariate reaction norms with a negative slope prevail in nearly all taxonomic and ecological categories of insects as well as in some other ectotherm taxa with comparable life histories (arachnids and amphibians). In insects, positive slopes are largely limited to species, which feed on discrete resource items, parasitoids in particular. By contrast, with virtually no meaningful exceptions, herbivorous and predatory insects display reaction norms with a negative slope. This is consistent with the idea that predictable resource depletion, a scenario selecting for positively sloped reaction norms, is not frequent for these insects. Another source of such selection—a positive correlation between resource levels and juvenile mortality rates—should similarly be rare among insects. Positive slopes can also be predicted by models which integrate life‐history evolution and population dynamics. As bottom‐up regulation is not common in most insect groups, such models may not be most appropriate for insects.     

Difference in cuticular transpiration and sclerophylly in juvenile and adult pine needles relates to the species-specific rates of development

Pinus species show remarkable ontogenetic differences in needle morphology (heterophylly) between juvenile and adult vegetative phases. This developmental shift may play an adaptative role in their success under diverse habitats. As a first step to know the functional differences between each vegetative phase, we compared water loss through the cuticles of juvenile and adult needles of 21-month-old nursery-grown seedlings of nine hard pine species. Cuticular transpiration (CT), calculated after complete stomatal closure, was obtained by leaf-drying curves, and was related to leaf, ontogenetic and climatic parameters. The rate of cuticular transpiration (RCT) between juvenile and adult needles differed across pine species, and in particular segregated the Mediterranean species Pinus canariensis and P. halepensis, from the Eurasian P. uncinata and introduced species P. radiata. For these species, RCT was always higher in juvenile needles. The different leaf and ontogenic parameters studied were correlated with the variation in RCT among the nine pine species. We discuss this relationship in the light of the species ecology. Besides their possible adaptive interpretation, these results suggest an underlying need to consider the ontogenetic heterophylly when assessing functional traits in hard pine seedlings, in particular those traits that govern water relations.     

An evaluation of two biochemical methods of age determination in insects (pteridines and lipofuscins) using the ant Polyrhachis sexpinosa Latrielle (Hymenoptera: Formicidae)

Accurate information on the age of wild-caught animals is valuable for a variety of areas, but can be particularly difficult to obtain for small holometabolous insects, whose body size is fixed at the time of pupal eclosion. A variety of chemical groups, such as lipofuscins and pteridines accumulate in body tissues through time and can be used to predict age in a variety of arthropod taxa. Here we use spectrofluorometry to confirm the presence of extractable levels of lipofuscins and pteridines in individual social insects (using the ant Polyrhachis sexpinosa Latrielle, average body size 25 mg, as an example) and evaluate their ability to predict age. Pteridine levels were independent of age but lipofuscin levels increased with age in a predictable manner ( r ² = 72.8%). Lipofuscin levels therefore represent a new method of age determination for social insects that should be applicable to both individual laboratory and wild-caught animals.     

A review of the biology and control of the vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae)

At the turn of the century, damage by Otiorhynchus sulcatus was sporadic and limited to small areas. Increasing horticultural intensification and the adoption of husbandry techniques favourable to the weevil, such as the use of polythene mulches, increased its pest status. The development of the early inorganic pesticides reduced the number of serious outbreaks of this pest and weevil control was further improved by the development of the persistent organochlorine insecticides in the 1940's. The banning of a number of the more persistent insecticides over recent years has now left the horticultural industry in a very vulnerable position. O. sulcatus is now a pest on a range of horticultural crops throughout the temperate regions of the world. Infestations are most common in Europe (where it originated) and the USA, and nearly 150 plants species have been identified as potential hosts to O. sulcatus. Damage is most frequently caused by the root feeding larval stage. Populations as low as one larva plant can kill sensitive species such as Cyclamen. Severe damage by the leaf feeding adults is less common, although low levels of damage or contamination by adults may be unacceptable in certain situations. There is one generation a year. Oviposition by the flightless parthenogenetic females occurs over the summer months with oviposition rates of c. 500 and 1200 eggs adult^-1for outdoor and laboratory populations, respectively. O. sulcatus mainly overwinters as larvae, although significant numbers of adults may survive in areas where winter temperatures are not too severe. A number of natural enemies, such as hedgehogs, frogs and predatory beetles, help to maintain O. sulcatus populations at a low level in natural environments, but they are less successful in intensive horticultural systems where persistent chemicals have been heavily relied on to maintain the population below the economic threshold level. Increasing environmental concern is now forcing growers to consider new pest control strategies. Controlled release formulations of non-persistent products, such as fonofos and chlorpyrifos, have shown potential as control agents for O. sulcatus larvae. Biological control agents, such as insect parasitic nematodes, have been developed commercially and new microbial control agents are in the process of development. Most of the new control products are directed towards control of O. sulcatus larvae. Adult vine weevils are nocturnal and a much more difficult target for the new control agents. It is likely that an integrated approach to pest control will be required to maintain O. sulcatus populations below their economic threshold level.