Reproduction and larval development of two sympatric Pseudopolydora species (Annelida: Spionidae) in Japan

Pseudopolydora cf. kempi and Pseudopolydora cf. reticulata, which are morphologically similar, are sympatric in Gamo Lagoon, near Sendai on the Pacific eastern coast of Honshu, Japan. Reproduction, larval development, and larval morphology of these two species were compared. The larval developmental pattern of P. cf. kempi was determined to be short-term planktonic with lecithotrophy and adelphophagy, whereas that of P. cf. reticulata was long-term planktonic with planktotrophy. The number of embryos per capsule differed between the two species: 0–16 for P. cf. kempi and 62–405 for P. cf. reticulata. Nurse eggs were only found for P. cf. kempi. The results of this study suggest that some previous studies attributed to P. kempi may have been to P. cf. reticulata or to another species in this complex.     

Evolution and development of scyphozoan jellyfish

Scyphozoan jellyfish, or scyphomedusae, are conspicuous members of many ocean ecosystems, and have large impacts on human health and industry. Most scyphomedusae are the final stage in a complex life cycle that also includes two intermediate stages: the larval planula and benthic polyp. In species with all three life‐cycle stages, the metamorphosis of a polyp into a juvenile scyphomedusa (ephyra) is termed strobilation, and polyps can produce one ephyra (termed monodisc strobilation) or many ephyrae (termed polydisc strobilation). In contrast to species with planula, polyp and medusa stages, a handful of scyphozoan species possess modified life cycles with reduced or absent stages. The evolutionary patterns associated with strobilation and life‐cycle type have not been thoroughly investigated, and many studies of ephyra development and strobilation induction are not yet synthesized. Herein, I place the development of scyphomedusae in an evolutionary context. I first review the current evolutionary hypotheses for Scyphozoa. Next, I review what is known about scyphomedusa development across a broad diversity of species, including the first signs of strobilation, the formation of strobila segments, and the morphogenesis of ephyrae. I then review cases where the canonical scyphozoan life cycle has been modified, and take advantage of phylogenetic hypotheses to place these observations in an evolutionary context. I show that the evolution of monodisc strobilation occurred at least twice, and that the loss of intermediate life‐cycle stages occurred several times independently; by contrast, the reduction of the medusa stage appears to have occurred within a single clade. I then briefly review the major natural cues of strobilation induction. Finally, I summarize what is currently known about the molecular mechanisms of strobilation induction and ephyra development. I conclude with suggestions for future directions in the field.     

The ontogeny of Pseudis platensis (Anura,Hylidae): Heterochrony and the effects of larval development on postmetamorphic life

Recent studies have described the giant tadpole, delayed metamorphic transformations, and absence of postmetamorphic growth of the skeleton of Pseudis Platensis. These features address questions about derived patterns of life cycles and the role of the heterochrony during the metamorphosis in anurans. Using anatomical methods, we provide new data on the development of reproductive, digestive and integument systems, and age inference obtained from ontogenetic series of Pseudis platensis. Our results indicate that at the end of metamorphosis, the adult skin is completely differentiated, including the calcified dermal layer; the testis has seminiferous tubules with spermatogonia, spermatocytes, and spermatids; ovarian sacs present previtellogenic ova; and the adult digestive tract is fully formed. The froglets differ from adults only in being unable to reproduce. The entire life cycle of P. platensis can occur in 4 years. In the first year, larval development, growth to adult size, and gonad differentiation are completed. Long larval development rather than size of the tadpoles seems to be involved in the absence of juvenile stages. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

幼虫密度对草地螟生长发育及繁殖的影响

为了明确幼虫密度对草地螟Loxostege sticticalis种群增长的影响, 对室内条件下（温度22±1℃, RH 70%±5%, 光周期16L∶ 8D）不同幼虫密度[1, 10, 20, 30和40头/瓶（650 mL）］饲养的草地螟生长发育及繁殖进行了研究。结果表明: 幼虫密度对草地螟幼虫体色、 发育历期和存活率, 以及蛹重和成虫生殖等有显著影响。随着幼虫密度的增加, 幼虫体色黑化程度呈增强趋势, 幼虫密度大于10头/瓶时的体色黑化值均显著大于幼虫密度为1头/瓶时的体色黑化值（P<0.05）。20头/瓶的幼虫和蛹历期最短, 且随幼虫密度的增加而显著延长（P<0.05）。幼虫存活率以10头/瓶最高, 其他幼虫密度的幼虫存活率显著较低（P<0.05）。蛹重以1头/瓶的最重, 并随幼虫密度增加而显著下降（P<0.05）。成虫产卵量和交配率分别以1和20头/瓶的幼虫密度最高, 幼虫密度升高则产卵量、 交配率逐渐降低。成虫产卵历期随着幼虫密度的增加逐渐缩短。雌、 雄蛾寿命分别以10和20头/瓶幼虫密度时最长, 幼虫密度过高时雌雄蛾寿命又显著缩短（P<0.05）。生命表分析表明, 幼虫密度对草地螟种群增长指数有显著影响, 以10头/瓶幼虫密度的种群增长指数最高, 幼虫密度过高或过低时种群增长指数下降。据此认为, 幼虫密度是影响草地螟种群增长的重要因子之一。     

Laboratory investigations on larval development,motility and settlement of white weed ( Sertularia cupressina L.) – in view of its assumed decrease in the Wadden Sea

There are indications from various studies that the formerly extensive fields of the hydroid colonies of Sertularia cupressina ('white weed') in the subtidal zone of the German part of the Wadden Sea have now completely disappeared. These fields were harvested year after year by the white weed fisheries for many decades, until the early 1970s. However, this exploitation is not likely to have caused the decrease, since it was given up for economic reasons at a time when the fields still existed. In search for other causes, laboratory experiments were carried out which revealed: (a) The motility of the larvae is of the order of only a few millimeters. The larvae seem to be dispersed in the Wadden Sea by tidal currents, (b) Settlement is possible on different kinds of hard substrate, even on grains of sand. This implies that settlement will be successful only on a substrate which is not displaced by the currents and which does not become intermittently covered by sediments such as shells and stones. The substrate is not actively selected by the larvae. The response to settle seems to be triggered by hydrodynamic conditions. (c) Most larvae settled within 12 hours of hatching, but most planulae started metamorphosis a few days after settling which indicated that the larvae had been in different stages of development at the time of release from the acrocyst. The results are discussed in the context of the hydrodynamic changes, as well as the changes in water quality and fishing effort of white-weed fisheries and shrimping in the Wadden Sea in the course of the century. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of feeding structures in larval fish with different life histories: winter flounder and Atlantic cod

The size at which feeding structures developed and shifts in head proportions occurred, differed between Atlantic cod Gadus morhua and winter flounder Pseudopleuronectes americanus. The sequence and timing of the development of feeding structures may not be dependent on size, but may occur because they are necessary to meet specific requirements offish larvae feeding in the plankton. In early larval stages development of feeding structures was similar in number and type and was necessary for first-feeding in both species. In later stages, significant differences between species occurred in the timing of the development of feeding structures. In cod differentiation of new structures and changes in head proportions occurred at about two-thirds of the way through larval life, which coincided with an increase in growth. In flounder changes in feeding morphology did not occur during the symmetrical larval stage, but occurred only after metamorphosis to the asymmetrical demersal juvenile stage. Differences between cod and flounder in the size at which feeding structures develop may reflect life history adaptations expressed in the duration of the pelagic larval stage, as well as differences in juvenile habitat and feeding ecology.     

Ancestral Role of Ecdysis-Related Neuropeptides in Animal Life Cycle Transitions

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幼虫密度对甜菜夜蛾生长发育与繁殖的影响

为了研究甜菜夜蛾Spodoptera exigua(Hübner)幼虫的密度对其发育及繁殖的影响,本实验观察了5种幼虫密度下（1,5,10,20,30头/瓶）,幼虫发育和成虫繁殖情况。结果表明：幼虫和蛹历期、存活率和蛹重均差异显著。幼虫和蛹历期均以20头/瓶的最短,1头/瓶的最长,其余随幼虫密度增加而延长;幼虫至蛹存活率以10头/瓶的最高,其余随幼虫密度增加而降低;1头/瓶的蛹最重,显著高于其他密度的,其余随幼虫密度增加而下降。尽管密度间成虫羽化率和产卵前期均无显著差异,但成虫产卵量、寿命和畸形率差异显著。1头/瓶的产卵量最多,其次为10头/瓶的,其余随幼虫密度增加而减少,30头/瓶的产卵量显著少于其他密度的; 密度在1～20头/瓶范围内,雌蛾寿命均较短,显著短于30头/瓶的,而雄蛾寿命以5头/瓶的最短,显著短于其他密度的（10头/瓶除外）,10头/瓶的次之,其余密度间差异不显著;不同幼虫密度下羽化的成虫畸形率差异显著,10头/瓶的最低,其余随幼虫密度增加而升高; 生命表结果表明甜菜夜蛾在10头/瓶下世代存活率和种群增长指数均最高,幼虫密度过低或过高均不利于种群增长;世代存活率（S）和种群增长指数（I）与幼虫密度之间的关系均呈抛物线关系：S =－0.2087x²+2.5694x+211.52 (R²=0.88),I=－0.0552x²+0.9166x+54.168 (R²=0.95)。结果提示幼虫密度影响甜菜夜蛾种群动态的重要生态因子之一。     

The timing of oviposition and larval growth by two tephritid fly species in relation to host-plant development

Abstract. 1. The relationships between the timing of oviposition, larval establishment and host development were studied in the tephritids Tephritis bardanae (Schrank) and Cerajocera tussilaginis (Fab.) which attack flowerheads of Arctium minus (Hill) Bernh. (Compositae).
2. T. bardanae laid eggs in small sized flowerheads that were at an early stage of development, and appeared to use the external dimensions of the head as an oviposition cue. In contrast, C. tussilaginis females laid eggs into heads that were near to flowering and the timing of their attack was most closely related to particular lengths of florets and achenes inside the head. Both tephritids apparently recognized suitable heads by comparing aspects of their own body size with the size of particular flowerhead structures.
3. Individual heads were suitable for oviposition for a period of 10–11 days for both species, but the periods of susceptibility to each species did not overlap.
4. Attack by T. bardanae was timed to exploit the flowering phase of flowerhead development. Larval establishment and early development were synchronized with increasing nutrient availability occurring during the rapid growth of the florets and achenes before and during anthesis.
5. In contrast, the later attack by C. tussilaginis was timed to exploit the seed maturation phase of head development. Individual C. tussilaginis larvae operated as highly specialized 'achene parasites', utilizing the influx of nutrients into single achenes after fertilization.
6. Larvae of both tephritids induced abnormal host-tissue growth, but oviposition in both species was timed primarily to synchronize larval development with natural periods of high nutrient availability inside flowerheads, rather than with the presence of tissues suitable for gall induction.     

Effects of larval energetic resources on life history and adult allocation patterns in a caddisfly (Trichoptera: Phryganeidae)

Abstract 1. How populations respond to environmental change depends, in part, on the connection between environmental variance during early life stages and its effect on subsequent life‐history traits. For example, environmental variation during the larval stage can influence the life histories of organisms with complex life cycles by altering the amount of time spent in each stage of the life cycle as well as by altering allocation to life‐history traits during metamorphosis. 2. The effects of larval energetic resources on developmental timing, adult mass, fecundity, mating success, and allocation to adult body structures (thorax, abdomen, wings) were examined in an aquatic caddisfly (Agrypnia deflata Milne, Trichoptera: Phryganeidae). Larval energetic reserves were manipulated by removing larval cases just prior to pupation. In the first experiment, cases of all individuals were removed just prior to pupation; experimental individuals were required to build a new case whereas control individuals were allowed to re‐enter their case without building. In the second experiment, energy differences were maximised between the two treatments by supplementing the larval diet of the control group and removing cases and not supplementing the diet of the experimental group. 3. Male and female development time, adult mass, and female fecundity were not influenced by case removal or diet supplementation. In contrast, allocation to adult body parts indicated a trade‐off between abdominal and thoracic mass among case‐removal females, suggesting that, under larval resource stress, females adjust resource allocation during metamorphosis to alleviate potential negative impacts on clutch size. In addition, latency to copulation increased when cases were removed, indicating larval resource stress could influence male mating success. 4. This study suggests that, under larval energetic stress, the negative impacts on female reproduction might be mitigated by re‐allocating resources during metamorphosis, whereas male allocation strategies might not be as flexible as female strategies.     

Different egg-associated and larval development characteristics of Macrobrachium jelskii and Macrobrachium amazonicum (Arthropoda: Crustacea) in a Venezuelan continental lagoon

Summary

In Venezuela, M. jelskii and M. amazonicum are both found living in fresh waters and sometimes share the same habitat. The respective patterns of development of the two species have been compared, with reference to such parameters as egg size and number, duration and number of larval stages, and body length of the first zoea. Development of M. jelskii exhibits features characteristic of fresh water species, whereas that of M. amazonicum has features usually associated with brackish water species.     

Correlated responses to selection for faster development and early reproduction in Drosophila: the evolution of larval traits

Studies on selection for faster development in Drosophila have typically focused on the trade-offs among development time, adult weight, and adult life span. Relatively less attention has been paid to the evolution of preadult life stages and behaviors in response to such selection. We have earlier reported that four laboratory populations of D. melanogaster selected for faster development and early reproduction, relative to control populations, showed considerably reduced preadult development time and survivorship, dry weight at eclosion, and larval growth rates. Here we study the larval phase of these populations in greater detail. We show here that the reduction in development time after about 50 generations of selection is due to reduced duration of the first and third larval instars and the pupal stage, whereas the duration of the second larval instar has not changed. About 90% of the preadult mortality in the selected populations is due to larval mortality. The third instar larvae, pupae, and freshly eclosed adults of the selected populations weigh significantly less than controls, and this difference appears during the third larval instar. Thereafter, percentage weight loss during the pupal stage does not differ between selected and control populations. The minimum amount of time a larva must feed to subsequently complete development is lower in the selected populations, which also exhibit a syndrome of reduced energy expenditure through reduction in larval feeding rate, larval digging and foraging activity, and pupation height. Comparison of these results with those observed earlier in populations selected for adaptation to larval crowding and faster development under a different protocol from ours reveal differences in the evolved traits that suggest that the responses to selection for faster development are greatly affected by the larval density at which selection acts and on details of the selection pressures acting on the timing of reproduction.     

Knockdown of specific cuticular proteins analogous to peritrophin 3 genes disrupt larval and ovarian development in Bactrocera dorsalis (Diptera: Tephritidae)

Cuticular proteins (CPs) are critical components of the insect cuticle and play important roles in maintaining normal insect development and defense against various environmental stresses. The oriental fruit fly (Bactrocera dorsalis) is one of the most destructive pests worldwide, and its eight CPs analogous to peritrophin 3 (BdCPAP3) family genes have been identified in our previous study. In the present study, we further explored the possible roles of CPAP3 genes in B. dorsalis development. Each sequence of BdCPAP3 genes contained three conserved ChtBD2 (chitin-binding) domains. Spatial and temporal expression patterns revealed that the four BdCPAP3 genes (BdCPAP3-A1, B, E, and E2) might play important roles in larval pupariation of B. dorsalis. Moreover, treatment with a juvenile hormone analog (methoprene) significantly restricted expression of these four CPAP3 genes, whereas treatment with 20-hydroxy-ecdysone induced expression. The RNA interference (RNAi) results revealed that down-regulated CPAP3 genes led to significant delay of pupariation, and injection of dsBdCPAP3-E into 5-d-old B. dorsalis larvae caused approximately 40% mortality. Interestingly, we also confirmed that BdCPAP3-D2 was involved in B. dorsalis ovarian development. This study showed that some specific CPAP3 genes had crucial roles in B. dorsalis development, and these CP genes could be used as potential targets to control this pest via RNAi.     

Egg production, hatching rates, and abbreviated larval development of Campylonotus vagans Bate, 1888 (Crustacea: Decapoda: Caridea), in subantarctic waters

Early life history patterns were studied in the caridean shrimp, Campylonotus vagans Bate, 1888, from the subantarctic Beagle Channel (Tierra del Fuego). As a consequence of very large egg size (minimum 1.4 mm), fecundity was low, ranging from 83 to 608 eggs per female (carapace length [CL] 11-22.5 mm). Egg size increased continuously throughout embryonic development, reaching prior to hatching about 175% of the initial diameter. Due to low daily numbers of larval release, hatching of an egg batch lasted for about 2-3 weeks. The complete larval and early juvenile development was studied in laboratory cultures fed with Artemia sp. nauplii. At 7.0±0.5 °C, development from hatching to metamorphosis lasted for about 6 weeks. It comprised invariably two large zoeal stages and one decapodid, with mean stage durations of 12, 17, and 15 days, respectively. Larvae maintained without food survived on average for 18 days (maximum: 29 days), but did not reach the moult to the zoea II stage. Size increments at ecdysis were low in all larval stages (2.1-3.9%), indicating partial utilisation of internal energy reserves. A clearly higher increment (14%) was observed in the moult from the first to the second juvenile stage. Low fecundity, large size of eggs and larvae, an abbreviated mode of larval development, high larval survival rates during absence of food, demersal behaviour of the early life history stages, and an extended hatching period with low daily release rates are interpreted as adaptations to conditions typically prevailing in subantarctic regions, namely low temperatures (causing long durations of development) in combination with a pronounced seasonality in plankton production (i.e., short periods of food availability).     

Evolution of poecilogony from planktotrophy: cryptic speciation, phylogeography, and larval development in the gastropod genus Alderia

Poecilogony, a rare phenomenon in marine invertebrates, occurs when alternative larval morphs differing in dispersal potential or trophic mode are produced from a single genome. Because both poecilogony and cryptic species are prevalent among sea slugs in the suborder Sacoglossa (Gastropoda: Opisthobranchia), molecular data are needed to confirm cases of variable development and to place them in a phylogenetic context. The nominal species Alderia modesta produces long-lived, feeding larvae throughout the North Atlantic and Pacific, but in California can also produce short-lived larvae that metamorphose without feeding. We collected morphological, developmental, and molecular data for Alderia from 17 sites spanning the eastern and western Pacific and North Atlantic. Estuaries south of Bodega Harbor, California, contained a cryptic species (hereafter Alderia sp.) with variable development, sister to the strictly planktotrophic A. modesta. The smaller Alderia sp. seasonally toggled between planktotrophy and lecithotrophy, with some individuals differing in development but sharing mitochondrial DNA haplotypes. The sibling species overlapped in Tomales Bay, California, but showed no evidence of hybridization; laboratory mating trials suggest postzygotic isolation has arisen. Intra- and interspecific divergence times were estimated using a molecular clock calibrated with geminate sacoglossans. Speciation occurred about 4.1 million years ago during a major marine radiation in the eastern Pacific, when large inland embayments in California may have isolated ancestral populations. Atlantic and Pacific A. modesta diverged about 1.7 million years ago, suggesting trans-Arctic gene flow was interrupted by Pleistocene glaciation. Both Alderia species showed evidence of late Pleistocene population expansion, but the southern Alderia sp. likely experienced a more pronounced bottleneck. Reduced body size may have incurred selection against obligate planktotrophy in Alderia sp. by limiting fecundity in the face of high larval mortality rates in warm months. Alternatively, poecilogony may be an adaptive response to seasonal opening of estuaries, facilitating dispersal by long-lived larvae. An improved understanding of the forces controlling seasonal shifts in development in Alderia sp. may yield insight into the evolutionary forces promoting transitions to nonfeeding larvae.     

梨小食心虫蛹重对成虫繁殖力和寿命及下一代幼虫发育的影响

【目的】本文旨在明确营养状况不同造成的梨小食心虫Grapholitha molesta(Busck)雌、雄蛹重量差异对其羽化的成虫产卵量、产卵期、寿命及下一代(F1)幼虫发育的影响。【方法】室内条件下,通过不同的饲养方法,获得个体重量不同的梨小食心虫雌、雄蛹,待其羽化交配后,记录其产卵量、产卵时间和成虫寿命;卵孵化前后,分别测量卵和初孵幼虫大小,计算卵孵化率,统计幼虫发育历期。【结果】雌蛹重量对梨小食心虫的成虫产卵量影响显著,其重量与产卵量呈正相关(y=15.505x-59.292);同一条件下,雌蛹与雄蛹重量也呈正相关(y=0.823x-0.538)。同时,雌蛹重量对成虫产卵期影响也较大,蛹重大的个体羽化的雌虫比蛹重小的个体羽化的雌虫产卵高峰期提前1 d;较重、中等和较轻蛹羽化出的雌虫个体每天产卵量高于10粒/雌的时间分别为9~10,7和5~6 d;产卵量高于5粒/雌的时间分别为12~13,9和6~7 d。而雄蛹重量对产卵量、雄成虫寿命影响没有明显影响。较轻的蛹羽化的雌成虫寿命比较重蛹羽化的雌成虫短2~3 d;而雄蛹重量对其羽化的雄成虫寿命影响没有明显规律。雌、雄蛹重量对其羽化成虫的卵孵化率、卵和初孵幼虫的大小影响均不显著,对F_1幼虫发育历期影响也不显著。【结论】梨小食心虫雌蛹重对羽化成虫的产卵量和产卵期等影响显著,田间防治时应注意在不同条件下完成发育的个体,尤其是雌虫,由于营养差异引起的个体大小对随后种群增长的影响。     

Chiton myogenesis: perspectives for the development and evolution of larval and adult muscle systems in molluscs.

We investigated muscle development in two chiton species, Mopalia muscosa and Chiton olivaceus, from embryo hatching until 10 days after metamorphosis. The anlagen of the dorsal longitudinal rectus muscle and a larval prototroch muscle ring are the first detectable muscle structures in the early trochophore-like larva. Slightly later, a ventrolaterally situated pair of longitudinal muscles appears, which persists through metamorphosis. In addition, the anlagen of the putative dorsoventral shell musculature and the first fibers of a muscular grid, which is restricted to the pretrochal region and consists of outer ring and inner diagonal muscle fibers, are generated. Subsequently, transversal muscle fibers form underneath each future shell plate and the ventrolateral enrolling muscle is established. At metamorphic competence, the dorsoventral shell musculature consists of numerous serially repeated, intercrossing muscle fibers. Their concentration into seven (and later eight) functional shell plate muscle bundles starts after the completion of metamorphosis. The larval prototroch ring and the pretrochal muscle grid are lost at metamorphosis. The structure of the apical grid and its atrophy during metamorphosis suggests ontogenetic repetition of (parts of) the original body-wall musculature of a proposed worm-shaped molluscan ancestor. Moreover, our data show that the "segmented" character of the polyplacophoran shell musculature is a secondary condition, thus contradicting earlier theories that regarded the Polyplacophora (and thus the entire phylum Mollusca) as primarily eumetameric (annelid-like). Instead, we propose an unsegmented trochozoan ancestor at the base of molluscan evolution.