Histology and microscopic anatomy of the thyroid gland during the larval development of Pseudis platensis (Anura,Hylidae)

Several hormones regulate anuran larval development, most notably thyroid hormones (THs). In anurans, metamorphosis fails when the thyroid gland is absent or inactivated, resulting in giant tadpoles. Larval gigantism occurs naturally in neotropical frogs of the genus Pseudis as a result of a prolonged larval period. Its thyroid function is poorly investigated and the focus of this study. We describe qualitative and quantitative variations in larval development for field-captured specimens of Pseudis platensis and compare those to the development of two sympatric species, Phyllomedusa sauvagii and Pithecopus azureus, which have small tadpoles and a shorter larval period. We describe morphological changes in the thyroid glands of larval and adult specimens. In contrast to other species with similar ecological requirements, P. platensis exhibits distinct glandular activity. During premetamorphosis, there was little or no thyroid activity, a period in which the tadpole reached 70% of its maximum size. Development and degree of activity of the thyroid gland determine the duration of the early stages of the larval period. Thyroid gland histology in tadpoles appears to correlate with the TH activity, and in turn with the diversity in anuran life history transitions.     

Early life‐history of the spiny siganid Siganus spinus (Linnaeus 1758) inferred from otolith microstructure

Juveniles of the spiny siganid Siganus spinus were sampled from three sources in April, May and June 2008 for a study of its early life‐history through otolith microstructure analysis. Specimens were obtained from bagnet catches in off‐reef sites and seine nets in seagrass beds operating in Lagonoy Gulf, Philippines, and from the guts of skipjack tuna Katsuwonus pelamis caught by hand‐line in an offshore area about 72 km east of the mouth of the gulf. The core, hatch ring, first feeding rings, and settlement increment of spiny siganid were identified and their widths measured. Mean daily otolith ages were 20.6, 22.1 and 21.7 of specimens from the gut, off‐reef site and seagrass bed, respectively. Sagittae of the youngest (17‐, 18‐ and 19‐day‐old) specimens from the tuna gut do not have settlement marks. Planktonic larval duration is 17 days. Most settlement (59%) occurred at the 20th increment on the evidence of its highest reduction in width and lessening of opacity. During the settlement process the juveniles swim from the fringing coral reefs to the seaweed beds then finally to the seagrass beds, wherein settlement volume is highest on or about the new moon date. The short, pelagic larval duration and restricted settlement timed on or 1–2 days near the new moon are integral elements in the settlement strategy of the fish.     

Coexistence of three differentDrosophila species by rescheduling their life history traits in a natural population

We present evidence for coexistence of three differentDrosophila species by rescheduling their life history traits in a natural population using the same resource, at the same time and same place.D. ananassae has faster larval development time (DT) and faster DT(egg-fly) than other two species thus utilizing the resources at maximum at both larval and adult stages respectively. Therefore,D. ananassae skips the interspecific competition at preadult stage but suffers more from intraspecific competition. However,D. melanogaster andD. biarmipes have rescheduled their various life history traits to avoid interspecific competition. Differences of ranks tests for various life history traits suggest that except for DT(egg-pupa), the difference of ranks is highest for the combination ofD. melanogaster andD. ananassae for all other life history traits. This difference is maintained by tradeoffs between larval development time and pupal period and between pupal period and DT(egg-pupa) inD. ananassae.     

Effects of larval density and feeding rates on larval life history traits in Anopheles gambiae s.s. (Diptera: Culicidae)

Mosquito larval habitat determines the fitness, survivorship, fecundity, and vector capacity of emerging adults. We manipulated larval density and food provisioning in the laboratory to determine their effects on a number of life history parameters of Anopheles gambiae. Larval mortality was positively correlated with larval density. In addition, increased density skewed sex ratios that favored females.     

Early life history of kitsune-mebaru,sebastes vulpes (scorpaenidae), in the sea of japan

The larval and juvenile stages of kitsune-mebaru,Sebastes vulpes, based on 50 wild specimens collected in, the Sea of Japan, are described and illustrated, and some ecological aspects of the early life history (feeding, horizonal distribution and habitat shift) included. Preflexion larvae became extruded between 3.9–4.6 mm body length (BL) and notochord flexion occurred between 4.7–7.1 mm BL. Transformation from postflexion larvae to pelagic juventiles occurred between 13–17 mm BL. Compared with other rockfish species,S. vulpes is deep-bodied, throughout both larval and, juvenile stages. Larval and juvenileS. vulpes inhabit mainly coastal water surface layer (usually on the continental shelf), but do not occur offshore region (northwest of Oki Islands). Although someS. vulpes juveniles are associated with drifting seaweed, such clumps are not indispensable habitats for any stages. Surface-to-benthie migration of juveniles occurs at about 25 mm BL. Preflexion and flexion larvae feed mainly on copepod nauplii, and postflexion, transforming larvae and pelagic juveniles mainly on calanoid copepodites (Parracalanus parvus).     

Life history,distribution and molecular phylogenetics of the Upward-Mouth Spikefish Atrophacanthus japonicus (Teleostei: Tetraodontiformes: Triacanthodidae)

Ninety-six juvenile specimens (37–54 mm standard length; L_S) of the rarely collected Upward-Mouth Spikefish Atrophacanthus japonicus (Triacanthodidae) were obtained from the stomachs of three Yellowfin Tuna Thunnus albacares collected off Guam in the Mariana Islands in the central Pacific Ocean. These specimens extend the range of A. japonicus eastward into Oceania. We review the systematic characters of the monotypic genus Atrophacanthus and present colour photographs of freshly collected specimens. The diet of the juvenile specimens of A. japonicus consisted of thecosome pteropods and foraminiferans. We present a range map of A. japonicus based on all known specimens and show that specimen size is related to whether specimens were collected in the pelagic zone or on the bottom. Our results support that, compared to all other Triacanthodidae, A. japonicus has an unusually extended pelagic larval and juvenile period, up to 54 mm L_S, before settling to the bottom as adults. Lastly, we provide a multilocus phylogeny addressing the phylogenetic placement of Atrophacanthus based on eight of 11 triacanthodid genera and six genetic markers. Our results reveal that Atrophacanthus is the sister group of Macrorhamphosodes and they provide new insights about the evolutionary history of the family.     

Association of insect life stages using DNA sequences: the larvae of Philodytes umbrinus (Motschulsky) (Coleoptera: Dytiscidae)

Abstract. Insect life stages are known imperfectly in many cases, and classifications are based often on only one or a few semaphoronts of a species. This is unfortunate as information in alternative life stages often is useful for scientific study. Although recent examples of DNA in taxonomy have emphasized the identification of indistinguishable species, such sequence data facilitate the association of life history stages and hold considerable promise in phylogenetic analysis, evolutionary studies, diagnostics, etc. These concepts are discussed here and an example is provided from diving beetles (Dytiscidae: Coleoptera). Three unknown larval specimens of an apparent species of Laccophilinae collected in Namibia were associated with the species Philodytes umbrinus (Motschulsky) using DNA sequence data. An 806-bp portion of the gene cytochrome oxidase I was sequenced from the unknown larvae. Several identified adult specimens of species of Laccophilinae from Namibia were also sequenced, including two P. umbrinus specimens and specimens from four Laccophilus Leach species. Additional species of Laccophilus from other areas of the world also were sequenced, as were specimens of Agabetes acuductus (Harris), Australphilus saltus Watts, Neptosternus boukali Hendrich & Balke and a species of Laccodytes Régimbart. Parsimony analysis resulted in two most parsimonious trees with the unknown larva unambiguously resolved in a group with both adult specimens of P. umbrinus (bootstrap value = 100%). The average pairwise p-distance between the unknown larva and adult P. umbrinus specimens averaged 0.09% (0–0.14%), compared with an average divergence between other conspecifics in the analysis of 0.24% (0–0.82%) and an overall average divergence between species of 13.49% (1.90–19.86%). Based on this, the unknown larvae were assigned to P. umbrinus. The larvae are diagnosed and described and their relationship with other Laccophilinae is discussed.     

江西上三叠统安源组叶肢介一新属*

香溪叶肢介亚科(Xiangxiellinae)以壳瓣胎壳较大、壳上具有一条或两条短脊为特征,包括两个属:原单脊叶肢介属(ProtomonocarinaTasch,1962)和香溪叶肢介属(XiangxiellaShen,1976)。该亚科化石广布于世界各地,最早出现于我国晚石炭世,三叠纪末消失。本文建立的新属叉脊叶肢介(Dicerestheriagen.nov.),以胎壳上具有两条呈“人”字形向前后分叉的、粗壮的短脊为特征,与香溪叶肢介的构造特征最为接近。推测新属壳瓣胎壳脊的形成与闭壳肌附着引起的壳瓣变异或与生态环境变化有关。化石产于江西抚州崇礼县礼陂煤矿,上三叠统安源组徐坊段。湘赣一带安源组为一套含煤地层,属于滨海、近海、沼泽沉积区,产半咸水类型的双壳类,时代认为卡尼及早诺利期。植物化石Ptiozamites–Anthrophyopsis组合是诺利期的代表,适宜于热带、亚热带气候,滨海环境生长的群落。因此推测新属是一个生活在炎热、潮湿的热带-亚热带气候近海沼泽环境的类型。     

Comparative post-hatching ontogeny of Pseudoplatystoma reticulatum (Eigenmann & Eigenmann 1889) and Leiarius marmoratus (Gill, 1870) and their hybrid

Ontogenetic studies of the eggs and larvae of fish can provide information on the initial life history and biology of a species, are important for taxonomic and evolutionary studies, and for cultivation in captivity. The aim of this study was to analyze and describe the main morphological differences in the larval ontogeny of Pseudoplatystoma reticulatum, Leiarius marmoratus, and its hybrid (♀ P. reticulatum × ♂ L. marmoratus), as well as to identify characteristics that can identify the species and their hybrid at the larvae and juvenile stages. 205 L. marmoratus, 210 P. reticulatum, and 205 hybrid specimens were analyzed, all of which were obtained through induced reproduction. Analyses were performed from hatching to 30 days post-hatching. 19 morphometric and 5 meristic characteristics were evaluated, in addition to chromatophore shape and distribution. The specimens were classified into two life periods: Larval (stages: yolk sac, pre-flexion, flexion, and post-flexion) and Juvenile. Newly hatched larvae were transparent, poorly developed, and had a scarcity of chromatophores. During the early stages of larval development, the three groups showed similarities in appearance and proportional dimensions. However, at both the end of the post-flexion stage and at the juvenile period when individuals were approximately 2 cm long, it was possible to differentiate between hybrids and their parental species by their morphometric, meristic, and pigment characteristics. The hybrid, despite occupying an intermediate position in relationship to its parents, exhibited a shape and size more similar to P. reticulatum, its maternal parent.     

Unexpected deep-sea fish species on the Porcupine Bank (NE Atlantic): Biogeographical implications

Four specimens corresponding to three rare deep-water fish species were caught on the Porcupine Bank (Northeast Atlantic) in September 2019. These catches include the new northernmost records of Azores rockling Gaidropsarus granti and deep-water dab Poecilopsetta beanii in the Atlantic Ocean and the second record of the latter species in its eastern zone. Three of the specimens were retained and their molecular identification also allowed the Cataetyx alleni DNA barcode to be obtained for the first time. The appearance of P. beanii, a West Atlantic species, in its eastern zone is discussed in relation to a possible phenomenon of transoceanic drift in the larval stage.     

Utilization of larval and pupal detritus by Aedes aegypti and Aedes albopictus

The utilization of detritus sources by mosquito larvae during development may significantly affect adult life history traits and mosquito population growth. Many studies have shown invertebrate carcasses to be an important detritus source in larval habitats, but little is known regarding how invertebrate carcasses are utilized by mosquito larvae. We conducted two studies to investigate the rate of detritus consumption and its effect on larval development and life history traits. Overall, we found that Aedes aegypti and Aedes albopictus larvae rapidly consumed larval detritus, while pupal detritus was consumed at a significantly slower rate. We also found that the consumption of larval detritus significantly increased larval survivorship and decreased male development time but did not significantly influence female development time or pupal cephalothorax length for either sex. Our results suggest that the direct consumption of larval detritus can support the production of adults in larval habitats that lack allochthonous detritus inputs or where such organic inputs are insufficient. These studies indicate that different forms of invertebrate detritus are utilized in distinct ways by mosquito larvae, and therefore different forms of invertebrate detritus may have distinct effects on larval development and adult life history traits.     

Winter feeding leads to a shifted phenology in the browntail moth Euproctis chrysorrhoea on the evergreen strawberry tree Arbutus unedo

• 1 The browntail moth Euproctis chrysorrhoea is a highly polyphagous univoltine forest pest. Although its young larvae usually overwinter in diapause from early autumn to the beginning of spring, winter larval feeding has been reported when this species feeds on the evergreen woody shrub strawberry tree Arbutus unedo.
• 2 The present study investigated life‐history traits of four populations of E. chrysorrhoea feeding on A. unedo, including phenology of the different life stages, larval feeding activity and diapause incidence. By modelling the relationship between larval size and host plant leaf persistence, elevation and mean annual temperature, we also studied larval development in ten populations of this species sampled from a range of geographical locations in Spain, from both A. unedo and deciduous hosts.
• 3 The results obtained revealed that on A. unedo, E. chrysorrhoea phenology has shifted: from October to March, A. unedo larvae doubled their size, whereas, on deciduous Ulmus minor and Quercus faginea, larval size did not change. General linear models demonstrated that such differences were not related to environmental variables. We also found that on A. unedo larval feeding was arrested for 2 months, with this period representing a true diapause.
• 4 The results obtained in the present study suggest that E. chrysorrhoea populations are phenologically adapted to their local host plants, and that the presence of foliage is a key element in the phenological shift reported on A. unedo. These results may have implications with respect to the formation of E. chrysorrhoea host races.

     

A Theoretical Approach to Study the Evolution of Aggregation Behavior by Larval Codling Moth, <Emphasis Type="BoldItalic">Cydia pomonella</Emphasis> (Lepidoptera: Tortricidae)

Pupation site-seeking larvae of the codling moth, Cydia pomonella, aggregate in response to aggregation pheromone produced by cocoon-spinning conspecific larvae. Larvae that pupate in an aggregation rather than in solitude may experience a lower rate of parasitism by the parasitoid Mastrus ridibundus. Additionally, adults eclosing from a larval aggregation may encounter mates more rapidly at the site of eclosion (on-site) than away from that site (off-site). We employed an evolutionary simulation to determine the effect of several ecological parameters on the evolution of larval aggregation behavior. These parameters included (i) the probability of mate encounter off-site; (ii) the time available for finding a mate; and (iii) the population density of parasitoids and their rate of larval parasitism. The model predicts that larval aggregation behavior is selected for when the probability of off-site mate encounter is low, the time to locate mates is short, and egg-limited parasitoids are at high population levels. We also show that aggregations reduce the risk of parasitism through dilution effects. The parameters found to favour the evolution of larval aggregation behavior are consistent with life history traits exhibited by C. pomonella.     

Larval width as indicator of growth rate and effect of larval classification on final body composition and flesh quality in cultured gilthead seabream (Sparus aurata,L.)

The objective of this study was evaluating the effects on the growth rate and flesh quality of separating larvae according to their larval width in cultured gilthead seabream (Sparus aurata, L.). Progeny from two broodstocks (A and B) were divided into two groups according to larval width: heads (being the larger specimens) and tails. After 18 months both groups were analysed to evaluate growth, carcass traits and proximal composition. The head specimens reached a larger size and showed a greater level of well‐being and degree of nourishment. Total body and fillet composition in general were found to be as expected for this species. Some differences were found in total body composition between head and tail specimens in both batches, and in the fillet composition in batch B (higher fat and lower moisture content in the head specimens). Sensory analyses were carried out using untrained panelists, who were unable to distinguish between the head and tail samples in batch A, whereas differences were noticeable in batch B. Samples from the head group were judged to be tastier and juicier, a consequence of their higher fat content. Hence, fish separation according to larval width is an effective tool to separate progeny into slow and fast growing groups, whereas the total body and fillet analyses and a sensory test ensure that the selection does not generate negative effects on the product quality.     

Prey Capture Ecology of the Cubozoan Carukia barnesi

Adult Carukia barnesi medusae feed predominantly on larval fish; however, their mode of prey capture seems more complex than previously described. Our findings revealed that during light conditions, this species extends its tentacles and ‘twitches’ them frequently. This highlights the lure-like nematocyst clusters in the water column, which actively attract larval fish that are consequently stung and consumed. This fishing behavior was not observed during dark conditions, presumably to reduce energy expenditure when they are not luring visually oriented prey. We found that larger medusae have longer tentacles; however, the spacing between the nematocyst clusters is not dependent on size, suggesting that the spacing of the nematocyst clusters is important for prey capture. Additionally, larger specimens twitch their tentacles more frequently than small specimens, which correlate with their recent ontogenetic prey shift from plankton to larval fish. These results indicate that adult medusae of C. barnesi are not opportunistically grazing in the water column, but instead utilize sophisticated prey capture techniques to specifically target larval fish.     

Occurrence of additional Zoea-VI larvae in the mud crab, Scylla paramamosain (Estampador), reared in the laboratory

Mud crabs, Scylla spp. , are commercially important in many Indo-Pacific countries. The larval development of mud crabs has been reported previously as five zoeal and one megalopal stages. This paper reports larval rearing experiments that revealed variability in larval developmental stages in the mud crab Scylla paramamosain, one of four mud crab species. In addition to normal five zoeal stages, an alternative pathway of developing through six zoeal stages was observed for the crab. There were evidences suggested that the appearance of the additional Zoea-VI larvae was associated with unfavourable dietary conditions, including poor quality of diet, inadequate quantity of dietary supply and a period of starvation for newly hatched larvae. Based on exuviae and larval specimens, the morphology of the additional Zoea-VI larvae was described.     

Growth of larval and juvenile Diaphus theta (Pisces: Myctophidae) in the transitional waters of the western North Pacific

Diaphus theta is one of the most common myctophid fish species in the subarctic and transitional waters of the North Pacific. The growth of larval and juvenile D. theta was investigated using sagittal otolith increment analysis of specimens caught in transitional waters of the western North Pacific. Samples taken over a 24-h period demonstrated that otoliths exhibited daily growth cycles, allowing accurate determination of age. Calcification of the incremental zone of otoliths took place only at night, suggesting that the formation cycle of the increment of juvenile D. theta was different from that of shallow-water fishes and would be related to their diel vertical migration. The relationships between standard length (SL) and daily growth increment (D) were expressed as linear equations: SL = 2.65 + 0.141D (r ² = 0.942) for larvae of 5.1–9.6 mm SL and SL = 3.54 + 0.129D (r ² = 0.933) for juveniles of 13.7–27.6 mm SL. The growth rates were 0.14 mm d⁻¹ in larvae and 0.13 mm d⁻¹ in juveniles; this is slow compared with tropical or subtropical mycto-phid species, in which growth occurs at about twice these rates. The larval period, including the metamorphic stage, was long compared with species at lower latitudes and was estimated to be 71 days. The slow growth rate and long period of larval stage of D. theta would be the life history pattern of high-latitudinal species adapted to a low-temperature habitat. Received: March 23, 2001 / Revised: July 5, 2001 / Accepted: July 19, 2001