Protein synthesis by intracellular symbionts in two closely interrelated aphid species

An aphid endosymbiont in vivo synthesizes symbionin almost exclusively which is not produced in vitro by the same symbiont. While symbionin produced by the endosymbiont of the pea aphid is an acidic protein with a molecular weight of 63,000, that by the symbiont of the kondo aphid, the closest relative to the former, is a distinct, less acidic, molecule. While the two endosymbionts in vivo in old insects synthesize about 11 protein species in common, they produce many different proteins when incubated extracellularly.     

Survival, growth, and reproduction of two aphid species on sucrose solutions containing host or non-host honeydews

Aphids, like most phloem-feeding insects, commonly exhibit a high degree of host specificity. Plant-specific chemical compounds are likely to serve as important host selection cues for monophagous aphids and such substances could be present in aphid honeydew. Apterous virginoparae ofMyzus persicae (Sulzer) andPhorodon humuli (Schrank) were reared on a buffered sucrose solution containing various aphid honeydews or a mixture of amino acids. In two separate experiments, the host-specificP. humuli (hop aphid) could grow and reproduce only on diets containing honeydew collected from hop (Humulus lupulus L.).M. persicae (the green peach aphid, GPA) did not perform well on diets containing hop honeydew, perhaps because hop is a poor GPA host. Honeydew collected from preferred GPA host plants rape,Brassica napus L., and jimsonweed,Datura stramonium L., allowed GPA growth and reproduction. Hop aphids, however, performed poorly on rape and jimsonweed honeydew diets. Bell pepper,Capsicum annuum L., honeydew supported neither the hop aphid nor GPA. The study of aphid honeydew components may contribute towards a more complete understanding of host preference and selection phenomena in aphids.     

Effect of pH on survival,reproduction, egg viability and growth rate of five closely related rotifer species

In the laboratory we examined the effect of pH (5–10 with one interval) on survival, reproduction, egg viability and growth rate (intrinsic growth rate—r _m and population growth rate—r) of five Brachionus rotifer species (B. calyciflorus, B. quadridentatus, B. urceolaris, B. patulus and B. angularis). The pH was shown to exert a major influence on egg viability and growth rate (r _m and r) for each species. The age-specific survivorship curves within a species were not significantly different at pH 6–10. The optimal pH for each species is near-neutral pH (pH 6–8), and the fecundity decreased as the pH deviated from these values. For each Brachionus species, there was no significant difference between age-specific fecundity curves at pH 7 and 8. At acid pH (pH 5 or 6) higher egg mortality was observed for each species. The r _m and population r of the five Brachionus species incubated at different pHs were significantly influenced by pH. The pH supporting the highest r _m or r was obtained at pH 6–8, but varied due to species. In this study B. urceolaris and B. patulus could tolerate a broad range of pH, while the populations of B. calyciflorus, B. quadridentatus and B. angulari declined at acid conditions.     

Comparing resource exploitation and allocation of two closely related aphid parasitoids sharing the same host

Species belonging to the same guild (i.e. sharing the same resources) can reduce the negative effects of resource competition through niche partitioning. Coexisting species may differ in their resource exploitation and in the associated allocation of nutrients, depending on their resource niche. Trade-offs in nutrient allocation, such as between reproduction and survival, or between early and late reproduction, are moderated by the abundance and distribution of resources. In this study we investigate differences in larval resource exploitation and adult reproductive strategy of two sympatric aphid parasitoids sharing a common host. The habitat specialist Aphidius rhopalosiphi and the generalist Aphidius avenae occur in cereal crops of Western Europe, where both species attack the major host resource: the grain aphid Sitobion avenae. For this purpose, we measured their acquisition of capital lipid resources, their age-specific fecundity and reproductive effort, their life span and their metabolic rate. We found that these species do not differ neither in larval lipid accumulation nor in the number of eggs at emergence and the timing of egg production, but diverge in other adult reproductive strategies. The rate of adult egg production was higher in A. rhopalosiphi than A. avenae, but at the expense of producing smaller eggs. Throughout adult life, reproductive effort was higher in A. avenae, perhaps facilitated by its higher metabolic rate than A. rhopalosiphi. The divergence between species in life history syndromes likely reflects their adaptations to their resource niche. A high egg production probably allows the specialist A. rhopalosiphi to exploit more S. avenae individuals in cereal crops, while the generalist A. avenae because of its variety of hosts, maximizes the investment per egg but at the expense of a lower lifespan. Our results suggest that differential resource allocation may be a more common pattern that promotes coexistence of species within a guild.     

Exploring species limits in two closely related Chinese oaks

BACKGROUND: The species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches. METHODOLOGY/PRINCIPAL FINDINGS: Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species. MAIN CONCLUSIONS/SIGNIFICANCE: All results based on SSRS and AFLPS reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors.     

The effect of temperature on reproduction in three species of cyclopoid copepods

Megacyclops viridis (Jurine), Macrocyclops albidus (Jurine), and Acanthocyclops vernalis (Fischer) were raised in the laboratory at six temperatures (5, 8, 10, 12, 15 and 20°) and fed a mixture of ciliates (Paramecium caudatum and Colpidium campylum). Data were taken on clutch size, embryonic development time, interclutch period, time to first clutch, sex ratio and longevity.Clutch size, time to first clutch, embryonic development time, interclutch period and longevity are inversely related to temperature. The ratio of males to females in a cohort is independent of temperature.     

亚致死剂量杀虫剂对两种蚜虫翅型、发育和生殖的影响

【目的】研究亚致死剂量杀虫剂对桃蚜Myzuspersicae(Sulzer)和萝卜蚜Lipaphiserysimi(Kaltenbach)翅型、发育和生殖的影响。【方法】采用叶片浸渍法测定了7种杀虫剂对两种蚜虫的毒力,并计算了实验所需的亚致死浓度LC10;采用微虫笼法测定了7种杀虫剂对桃蚜和萝卜蚜翅型分化、发育和生殖的影响。【结果】在20℃下,烯啶虫胺延长了桃蚜的发育历期;噻虫啉显著增加了桃蚜的产仔数量。在25℃,噻虫啉显著降低萝卜蚜有翅蚜比例;噻虫啉、吡虫啉、阿维菌素和烯啶虫胺延长了萝卜蚜发育历期;噻虫啉、阿维菌素、烯啶虫胺、啶虫脒和噻虫嗪显著降低了萝卜蚜产仔数量。【结论】亚致死剂量的杀虫剂对桃蚜和萝卜蚜的发育历期及产仔数量均有影响,但仅对萝卜蚜的翅型比例产生影响,对桃蚜的翅型分化比例无显著影响。     

The use of electrophoresis in the separation of two closely related species of terrestrial slugs

The pattern of variation of non-specific esterases, revealed by the use of disc electrophoresis, was used in an investigation of the specific difference between Limax flavus and L. pseudoflavus. The isozyme patterns were used to differentiate between the two taxa both qualitatively and quantitatively. The results were in agreement with the results from studies of the variation in the morphology of the distal portions of the genitalia and of external body colouration and patterning. The biochemical methods allowed a rapid estimation of the difference between the two taxa and were more precise than the use of colour variation.     

Effect of hymexazol on growth and reproduction of low temperature Phytophthora species

The effect of hymexazol (3-hydroxy-5-methylisoxazole or HMI) on growth and reproduction of low temperature Phytophthora species with growth maxima under 30 °C, was studied on clarified V-8 juice agar medium at 50 g/ml and 5 g/ml. HMI severely inhibited growth of P. infestons, P. phaseoli, P. porri and P. syringae, retarded the growth of P. hibernalis and P. lateralis but enhanced the growth of P. fragariae and P. ilicis. Phytophthora cactorum and P. pseudotsugae with a maximal temperature of 30 °C were moderately inhibited.HMI reduced or prevented sporangial production on agar medium by P. cactorum, P. hibernalis, P. ilicis, P. infestons, P. lateralis, P. phaseoli, P. porri and P. primulae, and suppressed chlamydospore formation in P. porri and to a lesser extent, P. lateralis. The production of sex organs was prevented by HMI in P. phaseoli, P. porri, and P. syringae, reduced in P. hibernalis and P. ilicis but unaffected in P. cactorum, P. primulae and P. psuedotsugae.     

Developmental characteristics of two closely related species of Allonemobius and their hybrids

Summary Two species of ground crickets, Allonemobius fasciatus (from Corvallis, 44.3 N) and A. socius (from Gainesville, 30.3 N), and their hybrids were compared for nymphal development, wing form, and embryonic diapause. A. fasciatus matured more rapidly at a short photoperiod than at a long photoperiod and also than A. socius which showed no developmental response to photoperiod. The proportion of long-winged forms varied with nymphal photoperiod greatly in A. fasciatus but slightly in A. socius. A. fasciatus laid only diapause eggs, while A. socius responded to a long parental photoperiod and a high incubation temperature by averting diapause. A. fasciatus showed temperature-dependent shift of the diapause stage butA. socius entered diapause only at the early stage. These differences are related to their voltinism and distribution.Reciprocal crosses between the two species produced viable hybrids. In development rate, female hybrids were intermediate between their parents while male hybrids were closer to their mothers, suggesting that the development rate is controlled primarily by the X chromosome. Overdominance occurred in wing form; reciprocal crosses produced either higher or lower proportions of long-winged forms than their parents. Diapause of F1 hybrid embryos was determined only by the female parent and the paternal effect appeared in F2 embryos.     

Homology of Balbiani Ring DNA in two closely related Chironomus species

Cytogenetic analysis indicates that Balbiani Ring 2 (BR 2) in the two sibling species Chironomus tentans and Chironomus pallidivittatus arises from identifically banded segments in the salivary gland polytene chromosomes, although chromosomal rearrangements have occurred. In situ hybridization of BR 2 RNA to the polytene chromosomes of each individual species, as well as their F1 hybrids, reveals that the repetitious BR 2 DNA in the two species has, within the limits of the technique, retained identity of nucleotide sequences and degree of repetition. The DNA of the naturally expressed BR 1 and BR 3 in both species and that ot the galactose induced BR 6 in C. pallidivittatus did not hybridize with BR 2 RNA, indicating that these BR's are different from BR 2 with regard to sequence content.     

Respiration rates of two closely related species of carabids in Australia

Abstract The respiration rates of Notonomus gravis (Chaudoir) and N.philippi (Newman) (Coleoptera: Carabidae) were measured at temperatures between 10°C and 45°C. Mature males of both species had higher respiration rates than mature females. There was no difference between the rates of teneral male and female beetles at 30°C. The difference in respiration rates between the sexes is attributed to the maternal behaviour, and decreased surface activity, of mature females.     

Characterization of microsatellite loci in two closely related Lissotriton newt species

We have developed eight di- and tetranucleotide Lissotriton microsatellite markers. Eight loci were polymorphic in the palmate newt Lissotriton helveticus and six were polymorphic in the smooth newt L. vulgaris. Polymorphism detected in 33 and 37 individuals per species ranged from 3 to 15 alleles. These markers are suitable for the investigation of population structure, genetic variation and taxonomic identification in the two focal species, and may also be of use in other Lissotriton–Triturus species.     

The effect of nutrient stress on development and reproduction in an aphid

To investigate the influence of nutritional quality on reproduction in the rose-grain aphid (Metopolophium dirhodum, Wlk.), it was reared on barley seedlings of different nutritional quality or starved either during the last instar or the first few days of adulthood. Their reproductive performance was studied by analysing the gonadal status of teneral adults and by scoring the number of offspring. Metopolophium dirhodum was very tolerant of starvation in the fourth instar with most surviving (97%) to adulthood. During starvation the embryos continued to grow but the fat content of the soma declined by nearly 50%. Aphids starved in the fourth instar and control animals matured at the same time and produced a similar number of offspring in the first three weeks. However, the fecundity of aphids reared throughout their larval development on a plant of low nutritional quality was significantly lower. Aphids starved during the fourth instar were able to compensate for their loss in weight by an increased growth rate relative to the controls after transfer to a high quality plant. Early experience of nutritional stress is more important in determining reproductive performance than nutritional stress in the last larval instar. Aphids transferred from a high to a low quality plant showed a high mortality and a lower reproductive output. Thus fecundity was not always correlated with teneral weight but with host plant condition during larviposition. Metopolophium dirhodum showed a very flexible reproductive strategy when subjected to nutritional stress.

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Zusammenfassung Für Untersuchungen über den Einfluß von Nahrungsqualität auf die Reproduktion wurde die Bleiche Getreideblattlaus, Metopolophium dirhodum (Wlk.), auf jungen Gerstenpflanzen verschiedener Qualität bzw. ohne Nahrung während des letzten Larvenstadiums oder in den ersten Tagen als Imagines gehalten. Als Maß für die Reproduktionsfähigkeit wurden die Gonaden von frischgehäuteten L4-Larven und Adulten analysiert und die Zahl der Nachkommen bestimmt. Metopolophium dirhodum erwies sich als sehr widerstandsfähig gegenüber Nahrungsentzug während des vierten Larvenstadiums, da die meisten Tiere (97%) diese Behandlung bis zum Adultstadium überlebten. Die Embryos wuchsen und entwickelten sich, während der Fettgehalt des Somas um fast 50% abnahm. Tiere, die gehungert hatten und Kontrolltiere führten die Imaginalhäutung zum gleichen Zeitpunkt durch und produzierten gleich viele Nachkommen in den ersten drei Wochen. Larven, die gehungert hatten, konnten ihren Gewichtsverlust durch eine verstärkte Nahrungsaufnahme nach der Übertragung auf eine kräftige Pflanze ausgleichen. Die Wirkung von Nahrungsstreß auf die Reproduktion ist am Anfang der Larvalentwicklung höher als im letzten Larvenstadium, denn die Reproduktionsrate von Blattläusen, die während der gesamten Larvalentwicklung auf Pflanzen niedriger Qualität gehalten worden waren, war signifikant geringer. Blattläuse, die von einer Pflanze hoher auf eine niedriger Qualität umgesetzt wurden, hatten eine hohe Mortalitätsrate und genauso viele Nachkommen wie Tiere, deren Nahrungsqualität gleichbleibend gering war. Die Reproduktionsrate war also nicht immer mit dem Gewicht von frischgehäuteten Müttern korreliert, sondern im wesentlichen von der Qualität der Wirtspflanze während der Reproduktionsphase abhängig. Metopolophium dirhodum zeigte unter Nahrungsstreß eine sehr flexible Reproduktionsstrategie.

     

Short-term effects of two aphid species on plant growth and root respiration of three leguminous species

The short-term effects of cowpea aphids ( Aphis craccivora Koch) and pea aphids ( Acyrthosiphon pisum Harris), both Homoptera: Aphididae, on plant growth and respiration of excised, intact roots of cowpea [ Vigna unguiculata (L.) Walp. cv. Caloona], broadbean ( Vicia faba L. cv. Aquadulce) and garden pea ( Pisum sativum L. cv. Victory Freezer) seedlings were investigated, but not all plant-aphid combinations were used. Plant and root mean relative growth rates were significantly reduced within 10 days in the infested plants. Rates of total root respiration were was also significantly reduced in all infested plants within 10 days, presumably because of the reduced availability of translocate to the roots. The contribution of the cytochrome pathway to root respiration was significantly greater in control than in infested plants. The activity and engagement of the alternative respiratory pathway was also greater in control plants, and was absent in infested plants after 10 days infestation in all cases but one. These data indicate that the roots of aphid-infested plants were more efficient, in terms of energy conversion, than their respective controls.     

Overwintering of the sycamore aphid, Drepanosiphum platanoidis

Spatial and temporal aspects of overwintering in the holocyclic sycamore aphid Drepanosiphum platanoidis (Schrank) (Homoptera: Callaphididae) were investigated. Eggs of D. platanoidis were principally laid on trunks and branches of Acer pseudoplatanusL., at considerable distances from the buds. Trunks with rough bark, followed by branches with moderate roughness supported more overwintering eggs than the relatively exposed smooth surfaces of twigs and terminal buds. Eggs were aggregated on rough bark. Aspect had no effect on the number of eggs laid. Experimental manipulations varying ovipara densities showed intra-specific competition among oviparae for optimal oviposition sites. Overwintering egg mortality was a function of time, with the greatest mortality rate occurring in late winter. Egg mortality varied from 80.4% to 76.9% on trunks and 83.0% to 65.9% on branches in 1996 and 1997.     

Flower-visiting insect communities on two closely related Rhododendron species flowering in different seasons

To determine the effects of flowering season on the community structure and dynamics of flower visitors, I examined annual and hourly variation in flower-visiting insects on two Rhododendron species in a deciduous secondary forest in central Japan. Rhododendron reticulatum flowers from late March to mid-April, whereas R. macrosepalum flowers from late April to late May. Bagged and hand-pollination experiments indicated that outcrossing by flower visitors was important for the pollination of both R. reticulatum and R. macrosepalum. Pollinator and pollen limitation were detected in both Rhododendron species, although the extent of both differed between the two species. The flowers of both Rhododendron species were visited by insects of diverse taxa, including Hymenoptera, Diptera and Lepidoptera. The composition of flower visitors differed between R. reticulatum and R. macrosepalum, although a few species visited both of them. The beefly Bombylius major (Diptera: Bombyliidae) most frequently visited R. reticulatum, whereas the bumblebee Bombus ardens ardens (Hymenoptera: Apidae) most frequently visited R. macrosepalum. Hourly changes in the number of flower visitors also differed between R. reticulatum and R. macrosepalum; insects visited R. reticulatum flowers less frequently in the morning than in the afternoon, whereas insect visitations to R. macrosepalum flowers did not differ between morning and afternoon. Differences in both insect community structure and hourly changes of visitations between the two Rhododendron species occurred annually and may be related to the life history of the abundant visitor species as well as flowering phenology.     

The joint allele-frequency spectrum in closely related species

We develop the theory for computing the joint frequency spectra of alleles in two closely related species. We allow for arbitrary population growth in both species after they had a common ancestor. We focus on the case in which a single chromosome is sequenced from one of the species. We use classical diffusion theory to show that, if the ancestral species was at equilibrium under mutation and drift and a chromosome from one of the descendant species carries the derived allele, the frequency spectrum in the other species is uniform, independently of the demographic history of both species. We also predict the expected densities of segregating and fixed sites when the chromosome from the other species carries the ancestral allele. We compare the predictions of our model with the site-frequency spectra of SNPs in the four HapMap populations of humans when the nucleotide present in the Neanderthal DNA sequence is ancestral or derived, using the chimp genome as the outgroup.