Competition in phenotypically variable and uniform populations of the tadpole shrimp Triops longicaudatus (Notostraca: Triopsidae)

Summary Life-history parameters (growth, reproduction, and survival) were measured from one genetically heterogeneous and three homogeneous populations of tadpole shrimp (Triops longicaudatus) raised under three competitive levels: 5, 10, and 16 shrimp per 38-1 aquarium. Comparisons were made between the homogeneous populations (three monomorphic selfing lines) and a heterogeneous population (a mixture of the three lines) to test for increased productivity in genetically variable populations, a prediction of the tangled bank hypothesis for a short-term advantage to sexual reproduction. In most comparisons, the mixture of inbred lines performed better than expected from their individual performances in pure cultures but did not outperform the best performing line in any comparison. Decomposition of the mixed culture's performance into performances of the component inbred lines showed that not all lines experienced release from competition in the mixed culture. No genotype X environment interaction was found for any of the three fitness correlates, indicating that all three lines performed similarly under the three competitive conditions. These results provide little support for the tangled bank hypothesis and suggest that the levels of heterogeneity necessary for detectable resource partitioning in these shrimp may involve factors not considered in this study.     

Laboratory studies of factors affecting egg hatch of triops longicaudatus (LeConte) (Notostraca : Triopsidae)

Egg hatch was greatest (78.33%) for eggs not previously desiccated. A reduction in numbers hatched occurred as the relative humidity at which they were dried decreased. Some eggs hatched (0.67–79.33%) at pH levels of 3.10–10.01 with the highest hatch at pH 5.60. Water temperature greatly affected egg hatch. No hatch occurred until temperatures were above 14°C. A constant 29°C significantly inhibited hatching. Egg hatch increased 13.00 to 43.42% as salinity decreased from 2200 to 9.24 micromhos/cm. As little as 13 mm of flooded soil covering the eggs prevented them from hatching for 14 days. Eighteen percent hatch resulted when soil and eggs were redistributed to a 1 mm soil layer. Egg samples from the same parent, even though treated similarly, often hatched at greatly varying rates and only rarely was hatching 100% within a replication.     

Toxicity and effects of mosquito larvicides methoprene and surface film (Agnique® MMF) on the development and fecundity of the tadpole shrimp Triops newberryi (Packard) (Notostraca: Triopsidae)

We investigated the interactions of tadpole shrimp, a mosquito biological control agent, with the juvenile hormone analog methoprene and a monomolecular surface film. In laboratory assays, the tadpole shrimp (TPS) Triops newberryi (Packard) was able to tolerate high concentrations of methoprene without negative impacts on its growth, longevity, and fecundity when exposed to 1 to 10 mg/liter, or 90–900 fold, of the IE₉₀ levels against a laboratory colony of Culex quinquefasciatus Say. The same held true in field trials when the habitats were treated with Altosid® Liquid Larvicide (Altosid® LL, 5% methoprene) at 0.3–1.2 liters/ha. or 1–4 fold of the label rates for mosquito control. However, some significant impacts on the TPS occurred when they were exposed to Agnique® Monomolecular Film (Agnique® MMF) at the label rates for mosquito control ranging from 1.89–9.45 liters/ha. under laboratory and field conditions. To avoid the negative impact of Agnique MMF on tadpole shrimp, it appears that 1.89 liters/ha. would be the maximum rate when Agnique MMF is used to control mosquitoes in the habitats where the TPS is employed as a biological control agent, or prevailing in the aquatic habitats with potential for suppressing mosquito larval populations.     

Evidence of cross-fertilization in a gonochoric population of the tadpole shrimp Triops numidicus (Crustacea: Branchiopoda: Notostraca)

Cross-fertilization was evident in a gonochoric population of the notostracan Triops numidicus, in which a thick, hard eggshell had been suspected of preventing the sperm from reaching the egg. Most of the eggs from copulated females hatched into larvae, but the eggs from virgin females did not develop. In the larvae, paternal DNA fragments were detected by AFLP. In histological sections, several spermatozoa were found in the shell of newly oviposited eggs in the brood pouches of copulated females, suggesting that the shell was still soft enough to be penetrated by spermatozoa. These results showed that copulation and subsequent fertilization achieved by penetration of sperm through the newly deposited eggshell were indispensable for the normal development of the eggs.     

Draft genomes and genomic divergence of two Lepidurus tadpole shrimp species (Crustacea,Branchiopoda, Notostraca)

Crustaceans of the order Notostraca (Branchiopoda) are distributed worldwide and are known for the remarkable morphological stasis between their extant and Permian fossil species. Moreover, these crustaceans show relevant ecological traits and a wide range of reproductive strategies. However, genomic studies on notostracans are fairly limited. Here, we present the genome sequences of two notostracan taxa, Lepidurus arcticus and Lepidurus apus lubbocki. Taking advantage of the small genome sizes (~0.11 pg) of these taxa, genomes were sequenced for one individual per species with one run on the Illumina HiSeq X platform. We finally assembled 73.2 Mbp (L. arcticus) and 90.3 Mbp (L. apus lubbocki) long genomes. Assemblies cover up to 84% of the estimated genome size, with a gene completeness >97% for both genomes. In total, 13%–16% of the assembled genomes consist of repeats, and based on read mapping, L. apus lubbocki shows a significantly lower transposable element content than L. arcticus. The analysis of 2,376 orthologous genes indicates an ~7% divergence between the two Lepidurus taxa, with a nucleotide substitution rate significantly lower than that of Daphnia taxa. K_a/K_s analysis suggests purifying selection in both branchiopod lineages, raising the question of whether the low substitution rate of Lepidurus is correlated with morphological conservation or is linked to specific biological traits. Our analysis demonstrates that, in these organisms, it is possible to obtain high‐quality draft genomes from single individuals with a relatively low sequencing effort. This result makes Lepidurus and Notostraca interesting models for genomic studies at taxonomic, ecological and evolutionary levels.     

Reproduction, molting, and growth of two Mexican uniparental forms of the tadpole shrimp Triops (Branchiopoda: Notostraca) under a recirculating culture system

Two forms (here called short and long) of the tadpole shrimp Triops from the Baja California peninsula (Mexico) exhibit interesting features for aquacultural purposes; rapid growth, early maturation (six days) and uniparental reproduction via cysts (i.e. drought-resistant dormant eggs). The use of Triops for aquaculture depends on the standard production of viable cysts. Basic information on the reproductive potential of Triops is scarce. Using a recirculating system, we studied, through two culture tests, the cyst production, frequency of molting, and growth rate of the two Mexican forms. For each form, individual data were obtained from five specimens in Test 1 over 15 days, and from 10 specimens in Test 2 over 20 days. Hatching response of cysts produced in Test 1 was also studied. The short-form showed a high fecundity depositing groups of cysts from the ovisacs several times a day. The mean cyst production per day was 156–306 (Test 1 & 2), and the mean total cyst production was 2028 (range 728–3193) (Test 1), and 5821 (range 4136–7554) (Test 2). The maximum number of cysts deposited by one short-form individual in a day was 1231 (Test 2). The reproductive performance of the long-form was poor. The mean cyst production per day was only 4.2–7.9 (Test 1 & 2). The short-form molted every 2.5–2.8 days and the long-form molted every 2.8–3.7 days. The mean growth rate calculated from the standard length (mm d^–1) of the short-form was 0.43–0.84 (Test 1 & 2), and in the long-form the values were 0.84–1.25 (Test 1 & 2). The poor cyst production of the long-form may be explained by inadequate food resources that did not fulfill the nutritional requirements for reproduction. Given its prolific uniparental reproduction (vs. biparental reproduction), the short-form Triops appears as a good potential candidate for aquaculture.     

Factors affecting contributions of the tadpole shrimp,Lepidurus packardi,to its oversummering egg reserves

The phenology and reproductive biology of the tadpole shrimp, Lepidurus packardi, which inhabits temporary annual pools in northern California, U.S.A., were investigated to identify factors affecting its contributions to its egg reserves that oversummer in the dried pond sediments. Field observations throughout 2 seasons revealed the nearly continuous presence of juveniles, indicating multiple generations, and a predominance of males during the mid to late stages of the pond. Observation of the first oviposition, and dissections revealed that sexual maturation occurred in shrimp 10–12 mm carapace length. Fecundity increased with size, but was drastically reduced in parasitized individuals. Metacercariae of an echinostome fluke caused parasitic castration in 53% of the population by mid-season. In the laboratory, oversummered eggs collected from dried pond sediments hatched within 17 days, when incubated at 10 °C. Eggs laid in the laboratory hatched within 25 days at 10 °C, without prior dehydration, but hatching was reduced at higher temperatures.     

Studies on the biology of Argas (A.) reflexus (Fabricius, 1794) (Acari: Ixodida: Argasidae). 2. Effect of alternating temperatures on embryonic development and egg hatch.

The paper presents the results of observations on the effect of temperature alterations between 9 degrees C and 30 degrees C every 6 and 12 hours, respectively, on the embryonic development and egg hatch of Argas (A.) reflexus. No effect of the frequency of temperature changes on the percentage of egg mortality, embryo mortality, abnormal egg hatching, or egg hatching into morphologically normal larvae was observed. The experiments showed that in changes temperature have a particularly detrimental effect on the eggs prior to blastulation.     

Triops ssp. [Notostraca: Triopsidae] for the biological control agents of weeds in rice paddies in Japan

Tadpole shrimps,Triops spp. are aquatic crustaceans which appear in rice paddies a few days after the flooding and ploughing. They are pioneer animals and have a life cycle adapted to irregularly disturbed habitats. In this regard they have many similarities in ecological characteristics with the annual plant weeds in the paddy fields despite belonging to quite different taxonomic groups. Tadpole shrimps control weeds by consuming their seedlings and by scratching the soil surface thereby pulling up weed seedlings while searching for food and egg laying sites. They are omnivorous and damage a wide range of weed species. However, the injurious effects on rice seedlings are avoided through the transplanting process, commonly practised in Japan. Biological control of weeds withTriops spp. in paddy fields is practised in certain localities in Japan and scientific studies are beginning to develop more practical techniques.

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Résumé Les crevettes têtards,Triops spp sont des crustacés aquatiques qui se manifestent dans les rizières quelques jours après la mise en eau et le labour. Ce sont des animaux pionniers dont le cycle est adapté à des habitats perturbés irrégulièrement. A cet égard ils ont beaucoup de caractéristiques écologiques semblables à celles des mauvaises herbes annuelles dans les rizières malgré leur appartenance à des groupes taxonomiques très différents. Ces crevettes détruisent les mauvaises herbes en consommant les plantules et en grattant la surface du sol pour la recherche de leur nourriture et de lieux de ponte, de sorte que les jeunes plants se trouvent arrachés. Elles sont polyphages et attaquent un grand nombre d'espèces de mauvaises herbes. Cependant, les dégats aux plantules de riz sont évités du fait du repiquage, couramment pratiqué au Japon. La lutte biologique contre les mauvaises herbes à l'aide deTriops spp dans les rizières est réalisée dans certaines localités du Japon et des recherches sont entreprises pour développer davantage leur utilisation pratique.

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This study was supported in part by the grants from the Japanese Ministries of Education, and Agriculture and Forestry.     

Temperature effects on egg development of the rosy apple aphid and forecasting of egg hatch

The development of Dysaphis plantaginea (Pass.) (Homoptera: Aphididae) winter eggs was studied at six different constant temperatures ranging from 7.5 to 16.5 °C in order to improve the basis for phenological forecasts in early spring. The mortality was generally low at temperatures below 13.5 °C but increased considerably at 16.5 °C. The effect of temperature on development rates could be described with linear regression within the temperature range under study. The lower temperature threshold for development was estimated to be 4.0 °C and the thermal constant 140 day‐degrees. A time‐varying distributed delay approach was used to establish a temperature driven phenology model for winter egg hatch of D. plantaginea considering the intrinsic variability in development time. The model parameters such as temperature‐dependent development times and corresponding variances were quantified based on the experimental data. When compared with independent observations on egg hatch under semifield conditions, the model gave satisfactory validation results. It can be used as forecasting tool for the optimal timing of monitoring and control measures for D. plantaginea in early spring.     

Influence of soil moisture on egg cold hardiness in the migratory locust Locusta migratoria (Orthoptera: Acridiidae)

Abstract.  The present study investigates the influence of environmental moisture on cold hardiness of the migratory locust, Locusta migratoria . The water content of locust eggs kept in soil at 30 °C varies according to the moisture content of the substrate. In turn, it can significantly affect the supercooling point of locust eggs (range from −26 to −14.8 °C) and the mortality when exposed to subzero temperatures. Environmental moisture influences the supercooling capacity of eggs and their survival at low temperature. When locust eggs of the same water content are exposed to subzero temperatures under different soil moistures, their mortality varies between short-time exposure and long-time exposure at subzero temperatures. Given a short-time exposure, mortality in wet soil is lower than in dry soil due to the buffering effect of soil water against temperature change. The pattern of egg mortality is reversed after long-time exposure at low temperature, suggesting that inoculative freezing may be an important mortality factor. It is suggested that interactions between soil moisture and low temperature can influence the cold hardiness of locust eggs, and partial dehydration is beneficial to over-wintering eggs of the migratory locust.     

Effect of soil moisture on bioremediation of chlorophenol-contaminated soil

A chlorophenol-contaminated soil was tested for the biodegradability in a semi-pilot scale microcosm using indigenous microorganisms. More than 90% of 4-chlorophenol and 2,4,6-trichlorophenol, initially at 30 mg kg^–1, were removed within 60 days and 30 mg pentachlorophenol kg^–1 was completely degraded within 140 days. The chlorophenols were degraded more effectively under aerobic condition than under anaerobic condition. Soil moisture had a significant effect with the slowest degradation rate of chlorophenols at 25% in the range of 10–40% moisture content. At 25–40%, the rate of chlorophenol degradation was directly related to the soil moisture content, whereas at 10–25%, it was inversely related. Limited oxygen availability through soil agglomeration at 25% moisture content might decrease the degradation rate of chlorophenols.     

The apple sawfly, Hoplocampa testudinea: egg development and forecasting of egg hatch

The effect of temperature on egg development of the apple sawfly Hoplocampa testudinea Klug was studied under controlled conditions. Based on a linear model describing the relationship between temperature and developmental rates a thermal threshold of 6.9 °C and a thermal constant of 85 day-degrees were established. The experimental results were used to expand and parameterise an existing phenology model to include egg development and hatching of first instar larvae. The model thus became a valuable forecasting tool not only for adult emergence and the optimal monitoring period but also for egg hatch and the best timing of control measures against first instar larvae. The model was validated by comparing predictions with independent observations on egg-laying and subsequent hatching of first instar larvae under semi-field conditions.     

环境因子对真水狼蛛胚胎发育的影响

研究了温度、相对湿度和光照时间对真水狼蛛（Pirata piraticus）胚胎发育的影响。结果表明,温度不仅影响真水狼蛛胚胎发育的全过程,也对胚胎发育的各阶段有影响,在20℃-35℃范围内,随着温度的升高,胚胎发育加快,卵的发育起点温度为11.9℃,低温下,卵的孵化整齐度高温下要高,28℃时,孵化率最高。为探讨真水狼蛛胚胎发育的影响因子和合适条件,考虑温度、相对湿度和光照时间3个因子的综合作用,按照二次正交旋转组合设计的要求安排实验,得出了影响胚胎发育历期、胚胎成形率和孵化率的二次回归模型,并分析了其影响因子,利用孵化率的回归模型,得到了真水狼蛛卵孵化的最优条件为温度为27℃-28.5℃,相对湿度为94％－97％,光照时间为14－17h。     

Comparative genomics of tadpole shrimps (Crustacea,Branchiopoda, Notostraca): Dynamic genome evolution against the backdrop of morphological stasis

This analysis presents five genome assemblies of four Notostraca taxa. Notostraca origin dates to the Permian/Upper Devonian and the extant forms show a striking morphological similarity to fossil taxa. The comparison of sequenced genomes with other Branchiopoda genomes shows that, despite the morphological stasis, Notostraca share a dynamic genome evolution with high turnover for gene families' expansion/contraction and a transposable elements content comparable to other branchiopods. While Notostraca substitutions rate appears similar or lower in comparison to other branchiopods, a subset of genes shows a faster evolutionary pace, highlighting the difficulty of generalizing about genomic stasis versus dynamism. Moreover, we found that the variation of Triops cancriformis transposable elements content appeared linked to reproductive strategies, in line with theoretical expectations. Overall, besides providing new genomic resources for the study of these organisms, which appear relevant for their ecology and evolution, we also confirmed the decoupling of morphological and molecular evolution.     

Embryonic development of orchard leafrollers and the forecasting of egg hatch

The development time of eggs of three of the most noxious leafrollers found in Northeuropean orchards, Spilonota ocellana (Denis & Schiffermüller), Archips podana (Scopoli), and Pandemis heparana (Denis & Schiffermüller) (Lepidoptera: Tortricidae) was recorded in the laboratory at five constant temperatures between 14 and 25°C. In this range, developmental rates of the three species did not differ significantly. While the flight periods of these species overlap largely, a single algorithm could be used to devise optimal spraying time(s) for the three species.