Molting Events Research Articles

Biology of <I>Symploce pallens</I> (Dictyoptera: Blattellidae)

Here, we describe the biology of a relatively new pest cockroach species in Southeast Asia, Symploce pallens (Stephens) (Dictyoptera: Blattellidae). S. pallens collected from Penang Island, Malaysia, were used for the biological parameter studies and were observed for molting and reproduction events. Nymphal development took 118.2 +/- 1.7 d, with a mean of 9.5 +/- 0.1 molts. The oothecal incubation period was 36.1 +/- 0.2 d. Females produced a mean of 16.0 +/- 10.2 oothecae, with mean 17.6 +/- 0.1 nymphs per ootheca. Nymphal survivorship per ootheca was 90.4%, and 90.7% of nymphs achieved adulthood. The sex ratio did not deviate from 1:1. The mean longevity of adult males and females was 309.3 +/- 7.6 and 322.6 +/- 14.8 d, respectively. In general, S. pallens exhibited higher oothecal production and longer nymphal development and longevity compared with the German cockroach, Blattella germanica (L.).

Catalogue of epidermal genes: Genes expressed in the epidermis during larval molt of the silkworm Bombyx mori

BackgroundThe insect cuticle is composed of various proteins and formed during the molt under hormonal regulation, although its precise composition and formation mechanism are largely unknown. The exhaustive catalogue of genes expressed in epidermis at the molt constitutes a massive amount of information from which to draw a complete picture of the molt and cuticle formation in insects. Therefore, we have catalogued a library of full-length cDNAs (designated epM) from epidermal cells during the last larval molt of Bombyx mori.ResultsOf the 10,368 sequences in the library, we isolated 6,653 usable expressed sequence tags (ESTs), which were categorized into 1,451 nonredundant gene clusters. Seventy-one clusters were considered to be isoforms or premature forms of other clusters. Therefore, we have identified 1,380 putative genes. Of the 6,653 expressed sequences, 48% were derived from 92 cuticular protein genes (RR-1, 24; RR-2, 17; glycine-rich, 29; other classes, 22). A comparison of epM with another epidermal EST data set, epV3 (feeding stage: fifth instar, day 3), showed marked differences in cuticular protein gene. Various types of cuticular proteins are expressed in epM but virtually only RR-1 proteins were expressed in epV3. Cuticular protein genes expressed specifically in epidermis, with several types of expression patterns during the molt, suggest different types of responses to the ecdysteroid pulse. Compared with other Bombyx EST libraries, 13 genes were preferentially included in epM data set. We isolated 290 genes for proteins other than cuticular proteins, whose amino acid sequences retain putative signal peptides, suggesting that they play some role in cuticle formation or in other molting events. Several gene groups were also included in this data set: hormone metabolism, P450, modifier of cuticular protein structure, small-ligand-binding protein, transcription factor, and pigmentation genes.ConclusionWe have identified 1,380 genes in epM data set and 13 preferentially expressed genes in epidermis at the molt. The comparison of the epM and other EST libraries clarified the totally different gene expression patterns in epidermis between the molting and feeding stages and many novel tissue- and stage-specifically expressed epidermal genes. These data should further our understanding of cuticle formation and the insect molt.

Juvenile hormone titers and caste differentiation in the damp-wood termite Hodotermopsis sjostedti (Isoptera, Termopsidae)

Termites are social insects, presenting morphologically distinct castes, performing specific tasks in the colony. The developmental processes underlying caste differentiation are mainly controlled by juvenile hormone (JH). Although many fragmentary data support this fact, there was no comparative work on JH titers during the caste differentiation processes. In this study, JH titer variation was investigated using a liquid chromatography-mass spectrometry (LC-MS) quantification method in all castes of the Japanese damp-wood termite Hodotermopsis sjostedti, especially focusing on the soldier caste differentiation pathway, which was induced by treatment with a JH analog. Hemolymph JH titers fluctuated between 20 and 720 pg/μl. A peak of JH was observed during molting events for the pseudergate stationary molt and presoldier differentiation, but this peak was absent prior to the imaginal molt. Soldier caste differentiation was generally associated with high JH titers and nymph to alate differentiation with low JH titers. However, JH titer rose in females during alate maturation, probably in relation to vitellogenesis. In comparison, JH titer was surprisingly low in neotenics. On the basis of these results in both natural and artificial conditions, the current model for JH action on termite caste differentiation is discussed and re-appraised.

Could krill schools significantly bias 234Th‐based carbon flux models?

To test the recent hypothesis that krill schools and their molting can hinder the accuracy of 234Th‐based particle flux models under specific conditions, radiotracer experiments were conducted with northern krill, Meganyctiphanes norvegica, to examine how 234Th uptake and release kinetics may affect residual 234Th concentrations in seawater. Krill rapidly took up 234Th from seawater, reaching a steady‐state concentration factor of ~180 in less than 1 week, and strongly retained the accumulated radionuclide until molting occurred. The nine molting events observed during the 18‐d experimental period indicated that ~50% of krill whole‐body 234Th activity was associated with the cast exoskeleton, and that a corresponding amount was rapidly adsorbed postecdysis on the newly formed cuticle. In regions characterized by the occurrence of high planktonic crustacean biomass, failure to link the presence of organisms with their effects on 234Th dynamics in the water column may induce significant biases (in some circumstances, up to one order of magnitude) in 234Th‐derived particulate organic carbon flux estimations or sediment trap efficiency calculations based on this method. However, because of the patchy distribution of dense aggregations of krill, the overall likelihood of such dramatic modeling artifacts is estimated to be relatively low (≤5% per sampling time).

The costs of autotomy and regeneration in animals: a review and framework for future research

Many organisms have the ability to shed an appendage (autotomy) to escape a predator or fouled molting event. Despite its immediate advantage on survivorship, autotomy can have important consequences for locomotion, foraging, survivorship, and/or reproduction. Thus, regeneration is a way that animals alleviate some of the costs associated with losing an appendage. Like autotomy, however, appendage regeneration can have important consequences for a variety of aspects of fitness; in a wide range of amphibians, reptiles, fishes, and arthropods, the allocation of resources to regenerate a lost appendage negatively affects somatic or reproductive growth. Previous research into the costs associated with regeneration has provided a strong framework to explore how trade-offs associated with regeneration may have influenced its evolution. However, all research to date describing the costs and benefits associated with autotomy and regeneration have compared individuals autotomizing and regenerating an appendage with individuals that have never lost an appendage. I suggest that for studies of the evolutionary significance of regeneration, an alternative comparison is between individuals experiencing autotomy without regeneration and individuals experiencing autotomy with regeneration. Future work in this direction promises new insights into the evolution of regenerative tendencies, as well as how regeneration may be influencing animal form and function.

Some considerations on calcium homeostasis in semi-terrestrial crabs

Calcium (Ca), deposited as CaCO 3 after molting events take place, indicates that Ca levels in semi-terrestrial crabs should be regulated at the dietary level as well as through whole animal net Ca flux. Two semi-terrestrial crabs found in salt marsh environments ( Sesarma rectum and Chasmagnathus granulata) were fed purified diets with variable Ca concentrations (0%, 2.22% and 6.66% Ca). Both animals displayed similar feeding strategies through consumption of higher amounts of the diet containing more Ca (6.66% Ca). Sesarma, a predominantly herbivore crab, ate more quantities of all the diets offered when compared to Chasmagnathus, a more carnivorous crab. Whole animal net fluxes of Ca over 5 days in Sesarma show that fluxes vary from 2.5 to 1.5 mmol kg −1 h −1, similar to values found earlier for a crayfish, Procambarus clarkii. However, the fluxes over 5 days did not decrease significantly compared to fluxes for the first day postmolt. Overall, semi-terrestrial crabs seem to maximize Ca influx through the gills and through dietary intake, a mineral that is known to have great importance for biomineralization in crustaceans.

Long-term recaptures of tagged Scyllarid lobsters ( Ibacus peronii) from the east coast of Australia

Ibacus peronii were captured, tagged and released off the east coast of Australia during 1993 and 1994 to study their patterns of growth and movements. Ten long-term recaptures have been reported since 1996, representing the longest recorded times at liberty for any tagged Scyllarid lobsters. Times at liberty for these 10 animals ranged between 1802 and 3417 days. Growth increments for all recaptured animals were within the ranges expected from shorter term recaptures, and all were recaptured from the same areas where they were tagged. These long-term recaptures reinforce previous conclusions on growth and movements of I. peronii, and are important in demonstrating to fishers and fishery managers that they are long-lived, do not move long distances and are susceptible to overfishing. The ratio of all recaptured tagged male and female I. peronii since 1993 was approximately 3:2. However, there were no differences in the recapture rates of males and females for small (less than 65 mm carapace length (CL)) and large (≥65 mm CL) individuals at tagging. The overall skewed recapture rate between sexes is likely to have been due to females being, on average, larger than males at the time of tagging and tag-loss being greater in these larger animals. These long-term recaptures show that, when properly inserted, the standard Hallprint T-bar tags used are retained through moulting events for many years.

Moulting growth of the Australian giant crab, Pseudocarcinus gigas

The growth of Australian giant crabs, Pseudocarcinus gigas, has not been previously studied. A tagging program was undertaken in four Australian states where the species is subject to commercial exploitation. Fishers reported a recapture sample of 1372 females and 383 males from commercial harvest, of which 190 females and 160 males had moulted at least once. Broad-scale modes of growth increment were readily identified and interpreted as 0 , 1 and 2 moults during time at large. Single-moult increments were normally distributed for six of seven data sets. Moult increments were constant with length for males and declined slowly for three of four female data sets. Seasonality of moulting in South Australia was inferred from monthly proportions captured with newly moulted shells. Female moulting peaked strongly in winter (June and July). Males moult in summer (November and December). Intermoult period estimates for P. gigas varied from 3 to 4 years for juvenile males and females (80–120 mm carapace length, CL), with rapid lengthening in time between moulting events to approximately seven years for females and four and a half years for males at legal minimum length of 150 mm CL. New moulting growth estimation methods include a generalization of the anniversary method for estimating intermoult period that uses (rather than rejects) most capture–recapture data and a multiple likelihood method for assigning recaptures to their most probable number of moults during time at large.

OBSERVATIONS ON THE TIMING OF MOULTING EVENTS IN THE CRAYFISH CAMBARUS ROBUSTUS GIRARD, 1852 (DECAPODA, CAMBARIDAE)

Cambarus robustus crayfish kept and monitored under constant summer-like photoperiod and temperature conditions in the laboratory did not moult during the winter months. The timing of the moulting events in the laboratory closely matched the timing of the corresponding types of moults in the field for adult Form I and Form II males, adult females, and juveniles of both sexes. The juveniles moulted during a less restricted period of time than the adults. The Form I to II adult male moults occurred only in the late fall, during a very narrow period. There is preliminary evidence that the timing of moulting in this northern, surface water crayfish species is governed by an endogenous circannual rhythm. This endogenous mechanism is capable of regulating the moulting cycle in C. robustus for long periods of time, even in the absence of any changes in external factors such as water temperature and photoperiod. Such a circannual endogenous rhythm would allow the crayfish to anticipate and prepare, both physiologically and behaviourally, for certain upcoming, predictable seasonal changes in the environment, such as the arrival of winter. Very large, and, presumably, very old individuals of this crayfish species can still moult successfully. The maximum life span of C. robustus may be greater than previous estimates have indicated.

Duration of Extended Parental Care in Marine Amphipods

ABSTRACT Several peracarid species provide parental care for their growing offspring after these have left the brood pouch of the female. In this study, I examined the duration of extended parental care in 3 soft-bottom dwelling amphipod species: the epibenthic suspension feeder Dyopedos monacanthus(Podoceridae), the burrow-dwelling filter-feeder Leptocheirus pinguis (Aoridae), and the burrow-dwelling deposit-feeder Casco bigelowi (Melitidae). Juvenile D. monacanthus remained on the mud whip of their mother for time periods of 10-20 days, maximally 27 days. Many juveniles left their mother before a second clutch was released onto her mud whip, indicating that factors other than the appearance of a second clutch limit the duration of care for the first clutch of juveniles. Juvenile L. pinguis left the burrow of their mother in distinct batches, usually after a molting event. Some juveniles remained in the burrow of their mother for 40-60 days. Juvenile C. bigelowi commonly remained in the burrow of their mother for >80 days, and departed over a period that lasted 20-40 days until all juveniles had left. A literature review revealed that in many epibenthic peracarids with extended parental care, juveniles usually remain with their mothers for about 3 weeks. Females of species that carry their offspring during parental care usually do not produce a second brood while carrying one brood, whereas females that do not carry but guard their offspring often produce a second brood while caring for the first brood. Duration of extended parental care is much more variable in tube-/burrow-dwelling species, lasting from minutes in some species up to 3 months in others. It is concluded that tube-/burrow-dwelling species have a higher potential for long-lasting (»20 days) extended parental care than epibenthic species. Ecological constraints, such as availability of space and food, predation, disturbance, and competition, are discussed as factors limiting the duration of extended parental care. It is hypothesized that the potential for extended parental care is high in marine peracarids, but advanced social behavior is restricted to species that are living in dwellings of biotic origin.

Use of Size–Frequency Data to Estimate the Age Composition of Crayfish Populations

Age-classes in crayfish populations can be determined from size–frequency data provided four tenets are adhered to: (1) only crayfish collected from areas of rock substrate are used; (2) trapping data are excluded; (3) species do not have longevities exceeding about 4 yr; and most importantly, (4) sample sizes are greater than about 200. Studies that have failed to follow these guidelines have met with limited success in dissecting mixed frequency distributions. Further, three validation procedures must be undertaken: (1) temporal replication within molting events to measure the precision of both data collection and size–frequency analysis; (2) corroboration with known-age crayfish from either field recaptures or laboratory molt increments; and (3) concordance with independent analysis of the mean size at onset of sexual maturity. When these checks support the size–frequency results, population age composition and analyses of rates of growth or mortality can be considered reliable.

Effects of precocene on intermoult length and ecdysteroid titres in relation to ovarian maturation in Thermobia domestica (Thysanura: Lepismatidae)

A topical application of precocene II (10 μg/♀) in adult females of the firebrat, Thermobia domestica, has anti-gonadotropic effects and also causes modifications of the intermoult length, the results varying according to the day of treatment. In non-treated females, which are normally inseminated at the beginning of each interecdysial period, this period can be divided into 2 parts separated by oviposition which takes place near the middle of the stadium (day 5). Treatment during the first part of a stadium generally induces slower growth of the vitellogenic oöcytes and/or slower resorption of these oöcytes, leading to a lengthening of this part of the stadium. The second part of the interecdysial period, marked by the pre-vitellogenic growth of the basal oöcytes and their preparation for yolk deposition, has a constant length of 4–5 days and always remains synchronized with the moulting events. Treatment after oviposition most often has no effect on the concerned stadium, but modifies the length of the following stadium. In females treated on day 5 the daily variations in the haemolymph ecdysteroid levels are similar to those of control females, but with a-day delay in the peak, corresponding to an equal delay of ecdysis. The present results are discussed in comparison with previously reported data concerning the effects of precocene on the corpora allata and on the titres of juvenile hormone.

Correlations between integument structure and ecdysteroid titers in fifth-stage nymphs of the tick, Ornithodoros moubata (Murray, 1877; sensu Walton, 1962)

The integument structure of fifth-stage nymphs of the tick Ornithodoros moubata was studied during the molting processes which are induced by the blood meal. In parallel, the ecdysteroid titers in hemolymph and in extracts from whole animals were determined by a radioimmunoassay (RIA). Between Days 2 and 3 after the meal (a.m.) a few procuticle lamellae were deposited and the mitotic period initiated. Ecdysteroid titers were low during the first 3 days a.m. They began to increase between Days 3 and 4 a.m. with the mitotic period ending. The titers rose sharply when apolysis and formation of the exuvial space took place (Day 4–5 a.m.). Highest ecdysteroid concentrations were measured during the deposition of the new epicuticle (Day 5–6 a.m.). Concomitant with the beginning of procuticle deposition and digestion of the old cuticle (Day 6 a.m.) the titers began to drop and reached low values again shortly before ecdysis (Day 9–10 a.m.). A preliminary chemical identification by thin-layer and high-performance liquid chromatography revealed that the majority of the RIA-positive ecdysteroids were composed of ecdysone and mainly ecdysterone. This was confirmed by gas chromatography of the silylated ecdysteroids. The results demonstrate that the titer changes in relation to the molting events in both ticks and insects appear to be very similar. It is thus likely that ecdysteroids are important in the control of tick molting.

"EXTRANUMERARY" CUTICLE DEPOSITION IN PIECES OF LARVAL INTEGUMENT TRANSPLANTED TO A PUPA IN THE SILKWORM BOMBY X MORI.

The author (Kato, 1973b) reported that in Bombyx mori, pieces of larval integument, if transplanted to a pupa, produced two layers of cuticle during the metamorphosis of the host pupa to an adult. In the present transplantation experiments, deposition of the two layers of cuticle was temporally examined to determine the timing of the two depositions, compared with the host's cuticle deposition, using 0-day-old fifth-instar or 1-day-old fourth-instar larvae as donors. In the transplant the first deposition occurred within 4 days of transplantation, with the second deposition at 6 to 8 days, while the host began cuticle deposition 6 days after receiving the transplant. These results show a failure of simultaneous deposition between the transplant and the host. These moulting events in the transplant, e.g., the fairly early appearance of the first cuticle and temporally-separated ecdyses, are discussed in view of the change of ecdysone titer in the host. Furthermore, the temporal pattern of cuticle deposition in the transplant appeared to have a definite relationship with the type of cuticle deposited.

The Molting Pattern in Trichinella spiralis. II. An Electron Microscope Study

Studies on the ultrastructure of Trichinella spiralis larvae revealed that molting did not occur during the intrauterine or intramuscular phases of development. Four molts were demonstrated during the intestinal phases of development, the sheaths of the second, third, and fourth being morphologically indistinguishable at the ultrastructural level. The cuticle of the intestine-infecting stage undergoes extensive transformation and differs greatly from that of the other stages. The development of this specialized cuticle probably represents an evolved adaptation for encapsulation and long survival in the muscles and later accommodation to conditions in the digestive tract of a new host. Studies with the light microscope failed to elucidate three aspects of molting in Trichinella spiralis: (1) the presence or absence of a molt during early development in the uterus of the parent worm, (2) details of morphogenesis of the cuticle during the period of growth and sexual differentiation in the muscles of the host, and (3) the question of whether the sheath of the second molt may be derived from the inner, granular layer of the sheath of the first molt. To resolve these three problems the present study of ultrastructure of the cuticle was done in conjunction with a similar study of its microstructure (Kozek, 1971). To establish the ultrastructural pattern of the molting events, attention was centered on the hypodermis and cuticle of all stages of larval development. MATERIALS AND METHODS Larvae and tissues were fixed at room or icewater temperature, in a 6% glutaraldehyde solution in Millonig's phosphate buffer at pH 7.5, for periods of 2 to 4 days. After fixation, the larvae were washed several times in a buffer-sucrose solution, and stored at about 4 C for later postfixation in a 1% solution of osmium tetroxide in Millonig's phosphate buffer for approximately 12 hr (at the same pH and temperature employed during the initial fixation). The larvae were then Received for publication 2 March 1971. * Portion of a dissertation submitted to the Graduate School of Tulane University in partial fullfillment of the requirements for the degree of Doctor of Philosophy. This study was supported by grants AI-04919 and AI-00002 from the NIH, U. S. Public Health Service. t Present address: Department of Microbiology, University of Chicago, 939 East 57th Street, Chicago, Illinois 60637. dehydrated in a graded series of ethanol and embedded in Epon 812 (Luft, 1961). The blocks were sectioned with glass knives on an LKB Ultratome III. Sections showing silver or silver-grey interference colors were picked up on formvarcoated grids, stained with uranyl acetate (Watson, 1958), combined with lead citrate (Reynolds, 1963), or with lead citrate only, and examined with a Philips 300 electron microscope operated at 60 or 80 kv.