Final Molt Research Articles

Intraperitoneal development of the filarial nematode Brugia malayi in the Mongolian jird (Meriones unguiculatus)

In the present study, we describe intraperitoneal development of the FR3 strain of Brugia malayi in Mongolian jirds (Meriones unguiculatus). The third molt for male worms occurred between 4 and 7 days postinfection (dpi) and between 4 and 8 dpi for females. The fourth and final molt occurred between days 21 and 29 for males and 25 and 34 for females, considerably earlier than the times reported for subcutaneous infection models using cats and jirds. The timing of the third molt coincided largely with reports for subcutaneous Brugia pahangi infections of cats and jirds, but the final molt occurred considerably later and lasted longer than those reported for subcutaneous B. pahangi models. Spermatogenesis occurred by at least 50 dpi in adult males, and insemination of females likely occurred between 50 and 60 dpi. Microfilariae were observed in the uteri and ovejectors of adult females at 65 dpi.

Low temperature induces embryonic diapause in the spider mite, Eotetranychus smithi.

The spider mite, Eotetranychus smithi Pritchard & Baker (Acari: Tetranychidae), exhibits a facultative diapause that occurs at the egg stage. Diapause was induced by low temperatures alone (≤ 17.5°C) and averted by high temperatures (≥ 20°C). Photoperiod had little effect on diapause induction. This is the first example of temperature-induced diapause in spider mites. The diapause eggs became larger and darker (orange) than non- diapause eggs (white to pale yellow), suggesting that egg size and egg color are associated with diapause. When mites that were reared from eggs at 25°C and 16:8 L:D were transferred to 15°C and 16:8 L:D just after the start of the teleiochrysalis stage (the final molting stage before adulthood), all females laid non-diapause eggs during the first 30 days and then switched over to laying diapause eggs. The switch to diapause may be caused by the aging of mothers.

Predatory response to changes in camouflage in a sexually dimorphic jumping spider

Cryptic animals tend to spend most of their lives keeping still. The majority of predators, however, including those cryptically colored, are forced to move in order to find and approach their prey. For such predators visibility may be an important factor influencing predatory behavior. Therefore we can expect differences in the way they approach their prey on backgrounds with different camouflaging properties. To test this, we examined the behavior of Yllenus arenarius Menge 1868 (Araneae: Salticidae), a cryptically colored jumping spider, hunting leafhoppers on backgrounds matching and non-matching for the spiders. Juvenile and female Y. arenarius are cryptic on light sand, but males lose their cryptic coloration for this background after their final molt. We designed an experiment to determine if increased visibility of the spiders influenced their predatory behavior. We found that background color had a significant effect on jumping distance, approaching speed and predatory success. On the light background cryptic spiders attacked from closer distances, approached prey with faster speeds and had higher success than on the dark background. Differences in approaching speed between males before and after final molt suggest a combined effect of background color and ontogenetic change of body coloration on the predatory decisions of these male spiders.

Interacting Gears Synchronize Propulsive Leg Movements in a Jumping Insect

Gears are found rarely in animals and have never been reported to intermesh and rotate functionally like mechanical gears. We now demonstrate functional gears in the ballistic jumping movements of the flightless planthopper insect Issus. The nymphs, but not adults, have a row of cuticular gear (cog) teeth around the curved medial surfaces of their two hindleg trochantera. The gear teeth on one trochanter engaged with and sequentially moved past those on the other trochanter during the preparatory cocking and the propulsive phases of jumping. Close registration between the gears ensured that both hindlegs moved at the same angular velocities to propel the body without yaw rotation. At the final molt to adulthood, this synchronization mechanism is jettisoned.

Different paths to sexual size dimorphism in two praying mantids,Pseudomantis albofimbriataandHierodula majuscula

Sexual size dimorphism (SSD) is widespread among diverse animal taxa and has attracted the attention of evolutionary biologists for over a century. SSD is likely to be adaptive and the result of divergent selection on different size optima for males and females, given their different roles in reproduction. The developmental trajectory leading to SSD may help us to understand how selection acts on male and female size. Here, we describe the growth and development of two Australian praying mantids, Pseudomantis albofimbriata and Hierodula majuscula including the number of moults, time to adulthood, size at each moult, and the degree of SSD. While both species exhibit the common pattern of female-biased SSD, the number of moults required for individuals to reach adulthood differed between males and females and between species. Despite their larger adult size, P. albofimbriata females require fewer moults and less time than males to reach adulthood, but are significantly larger than males from the second instar onwards. In contrast, H. majuscula males reached adulthood in fewer moults, and less time than females, however males and females did not differ in size until females went through their final moult into adulthood. H. majuscula also required more time and more moults to reach adulthood than P. albofimbriata. We discuss these different developmental pathways in light of the existing knowledge of reproductive biology for each species. We also suggest that these differences may relate to the different phenologies that occur in strongly seasonal temperate environments compared with those in the tropics. This study provides evidence that SSD can result from two different patterns of growth and development in closely related species.

Postembryonic growth in two species of freshwater Ostracoda (Crustacea) shows a size-age sigmoid model fit and temperature effects on development time, but no clear temperature-size rule (TSR) pattern

Although the temperature-size rule is a widespread phenomenon that describes the impact of temperature on the intraspecific size of ectotherms, what determines the wide intrinsic variation in moult increment and the intermoult period within and between Crustacea species remains unknown. This work characterizes the growth of freshwater ostracods Chlamydotheca incisa and Strandesia bicuspis under different controlled temperatures and identifies growth patterns. Animals were collected from temporary ponds in Argentina. The experiment was done at two constant temperatures: 17 and 23 °C. The intermoult time and the time from hatching to the final moult were calculated. Three different growth regression equations were tested: von Bertalanffy and two sigmoidal models (Sigmoid and Gompertz). For both species, significant differences in the duration of each instar were found by comparing individuals grown at 17 and at 23 °C. A strong temperature effect was noted on intermoult time but not on growth factors. The best model selected for the size-age relationship was a sigmoid growth type, indicating accelerated growth in the earliest juvenile instars. These results challenge the widely-accepted application of nonsigmoidal growth models and are in agreement with recent analyses of growth patterns in aquatic invertebrates when early juvenile instars are considered.

Examination and revision of the larval life history of Microplitis croceipes (Hymenoptera: Braconidae)

Microplitis croceipes (Braconidae) is a solitary parasitoid of Heliothis virescens (Noctuidae), the tobacco budworm. The larva of M. crocepies develops within the abdominal cavity of its host while the host remains active. Larval development culminates with egression of the larva from its host, and subsequent cocoon spinning and pupation near the host’s body. Previous research indicated that M. croceipes larvae pass through three instars within the host, followed by egression and pupation. Head capsule measurements recorded in this study at several intervals during larval development revealed that the larvae of M. croceipes pass through five instars. The final molt, i.e. into the fifth instar, occurs during larval egression from the host, and the shed exuvium remains lodged in the egression wound, acting as a plug that prevents exsanguination of the host. The host remains alive through parasitoid pupation, and may play a defensive role guarding the parasitoid cocoon during its development to the adult stage.

Nephila female gigantism attained through post-maturity molting

Abstract Nephila are known for the greatest degrees of sexual size dimorphism among orb weaving spiders (Araneoidea) and thus among terrestrial animals. However, a meaningful quantification of the dimorphism is lacking and the proximate developmental mechanisms of female gigantism are poorly understood, being attributed solely to female delayed maturation. Here we show that females in the giant wood spider Nephila pilipes (Fabricius 1793) become giants through facultative post-maturity molting, a phenomenon resulting in female carapaces on average 4.27 times longer than males' (ranging from 3 to 6.4 times), and female mass averaging 125 times the male's (ranging from 28 to 502 times). Although the small males follow a typical developmental pathway and reach maturity with their final molt, the females mature at varying sizes and instars and then continue to grow by molting the entire exoskeleton except their genitals. The newly discovered phenomenon of additional, single-sex, adult, non-genital molting may...

Feather selection and replacement patterns demonstrate that Goldfinches Carduelis carduelis fix postjuvenile moult extent prior to moult initiation

Birds undergoing a partial moult have to make important decisions regarding moult extent, pattern and sequence. Moreover, since partial moults are usually subject to a great degree of individual variability, the mechanisms controlling and organising such moults can be particularly complex. In the present paper, I investigate the feather selection and replacement process involved in partial postjuvenile moult in the Goldfinch Carduelis carduelis. Moult patterns observed after moult completion indicate that birds select the feathers to be replaced according to a predetermined order of moult priorities. However, the sequence of feather replacement, both within and between feather tracts, differs markedly from this order of moult priorities, varying individually to be adjusted to the final moult extent. These results indicate that, prior to or at the beginning of moult, each bird fixes with precision which feathers will be replaced. These findings have important implications for the interpretation of partial and incomplete moult patterns and for our understanding of the underlying factors controlling moults.

Sexual receptivity varies according to female age in a Neotropical nuptial gift-giving spider

Abstract For many spiders, sex pheromones associated with female silk are important stimuli that elicit male searching and courtship behaviors. In that context, female sexual receptivity and chemical attractiveness can depend on age and reproductive status. In Paratrechalea ornata (Mello-Leitao 1943) (Araneae: Trechaleidae), males offer females a nuptial gift (a prey wrapped in silk) during courtship. Gift construction is elicited by the presence of female silk, and silk attractiveness is influenced by female age, increasing from 20 days after the female reaches adulthood. Our goal was to investigate whether female age affects female sexual receptivity and to discuss the relationship between receptivity and silk attractiveness. We exposed 26 virgin females, from 2 to 28 days after the final molt, to males offering a nuptial gift. Female sexual receptivity was age dependent and increased with adult female age. Females over 15 days from adulthood accepted more gifts than younger females, but the latency of ...

Caligus sclerotinosus (Copepoda: Caligidae), a serious pest of cultured red seabream Pagrus major (Sparidae) in Korea

Caligid copepods (Crustacea) known as sea lice are pests of cultured fish, causing serious diseases and economic losses in fish aquaculture worldwide. One species, Caligus sclerotinosus Roubal, Armitage & Rohde, 1983 (Caligidae), is considered a serious pest of the highly prized red seabream Pagrus major (Temminck and Schlegel, 1843) (Sparidae) cultured in Japan. Recently, in neighboring Korea, red seabream culture has intensified and almost replaced yellow tail culture. However, until now, there have been no reports on infection of this sea louse from red seabream in Korea. We surveyed 120 (20 fish per month) P. major from a sea ranched Tongyeong Marine Research Center aquaculture facility, Gyeongsangnamdo, Korea for six months in 2011 (June to November). We recorded severe infection by the sea louse C. sclerotinosus on the skin of P. major. Prevalence was 100%, mean intensity 7.06, maximum intensity 49, and minimum intensity 2. Adult females (624), males (219) and few chalimi (5) were observed and identified by their morphology. As an average of all our collections, less than 0.6% of individuals were chalimi. We suggest, therefore, that adults of C. sclerotinosus undergo ontogenetic host switching after their final moult. No infection of C. sclerotinosus was found on wild P. major collected from Tongyeong and Yeosu fish markets on the southern coast of Korea. Severe infection by this sea louse may cause secondary infections of the host. This copepod is already reported from Australia and Japan and hence, this is the first report from Korea. We expect this pest to have an impact on Korean red seabream fisheries equally serious to that being experienced in Japan.

Spinning behaviour and morphology of the spinning glands in male and female Aposthonia ceylonica (Enderlein, 1912) (Embioptera: Oligotomidae)

Embioptera (webspinners) are unique among insects in that juvenile and adults of both sexes spin silk. They possess spinning apparatuses in the basitarsomeres of their prothoracic legs, which they use to build galleries as habitat and protection. Embioptera are primitively social and cooperate in building the galleries. They also show sexual dimorphism that comprises modifications of the mandibles in males, the winglessness of the females and differences in the morphology of the forelegs. In the present investigation we address the correlation of spinning behaviour and sexual dimorphism in the spinning apparatus of Aposthonia ceylonica (Enderlein, 1912). To analyse spinning behaviour we conducted video observations of Ap. ceylonica in artificial habitats. We observed females and males alone as well as female–male pairs to cover possible effects of interactions between sexes. The morphology of the spinning apparatus was analysed and reconstructed using high resolution X-ray computed tomography (SRμCT). The observations show that during trials of 24h adult males and females produce similar amounts of silk per body weight, despite the fact that adult males do not feed, perhaps due to modifications of their mandibles related to courtship that interfere with feeding. Spinning glands in males are distinctly smaller than in females in absolute values, which reflect the general size difference in females and males. Despite their smaller body size, the volumes of reservoirs of spinning glands are larger in males in relative as well as in absolute values. Together with spinning behaviour and the amount of silk production, this indicates that males produce and store gland secretions in the large reservoirs prior to their final moult for later use.

Diaspidid (Hemiptera: Coccoidea) size plasticity as an adaptive life history trait

The size and fecundity of Hemiberlesia lataniae (Signoret) (Hemiptera: Diaspididae) on partially resistant and susceptible kiwifruit (Actinidia spp.) varieties was measured. The size ratio of mature H. lataniae grown on a partially resistant genotype, compared with those on a susceptible genotype, was 0.67-0.51 for 2nd instar exuviae area, 0.32 for adult body area and 0.18 for estimated body volume. The fertility ratio was 0.1, but the pre-oviposition period and the size of the crawlers were the same. Diaspidid scale insects' unusual ability to continue growing after the final moult appears to be a key feature allowing these insects to show extreme size plasticity while retaining the ability to reproduce even when very small. These observations challenge current theories of insect development that postulate the need to achieve a critical weight threshold before the final moult. We suggest that this strategy may have assisted the evolution of polyphagy within the Diaspididae.

Morph-specific differences in biochemical composition related to flight capability in the wing-polyphenic Sitobion avenae

Flight performance at various times after emergence in the alate morph and age-dependent changes in biochemical composition of winged and wingless morphs were evaluated in the wing-polyphenic aphid Sitobion avenae (Fabricius) (Hemiptera: Aphididae). Alates exhibited the highest flight activity at 18–36 h after adult emergence. Throughout the nymphal and adult development, the whole-body content of total lipid was significantly higher in the winged vs. wingless morph, whereas the content of water, soluble sugar, glycogen, phospholipid, and soluble protein showed significantly higher levels in the wingless vs. winged morph. There were no significant differences in the content of triglyceride and free fatty acid during nymphal and adult stages in both morphs. However, triglyceride content was significantly higher in the winged vs. wingless morph during adulthood. Differences in biochemical composition between morphs indicate that there is an energetic cost of flight capability. Our results from S. avenae adults showed that total lipid and triglyceride for the winged morph accumulated significantly to a maximum, and water content decreased significantly to a minimum, on days 1 and 2 after the final molt, exactly when the highest flight activity was reached. This study suggests that flight activity is associated with triglyceride and water content.

Genome-wide regulation of innate immunity by juvenile hormone and 20-hydroxyecdysone in the Bombyx fat body

BackgroundInsect innate immunity can be affected by juvenile hormone (JH) and 20-hydroxyecdysone (20E), but how innate immunity is developmentally regulated by these two hormones in insects has not yet been elucidated. In the silkworm, Bombyx mori, JH and 20E levels are high during the final larval molt (4 M) but absent during the feeding stage of 5th instar (5 F), while JH level is low and 20E level is high during the prepupal stage (PP). Fat body produces humoral response molecules and hence is considered as the major organ involved in innate immunity.ResultsA genome-wide microarray analysis of Bombyx fat body isolated from 4 M, 5 F and PP uncovered a large number of differentially-expressed genes. Most notably, 6 antimicrobial peptide (AMP) genes were up-regulated at 4 M versus PP suggesting that Bombyx innate immunity is developmentally regulated by the two hormones. First, JH treatment dramatically increased AMP mRNA levels and activities. Furthermore, 20E treatment exhibited inhibitory effects on AMP mRNA levels and activities, and RNA interference of the 20E receptor EcR-USP had the opposite effects to 20E treatment.ConclusionTaken together, we demonstrate that JH acts as an immune-activator while 20E inhibits innate immunity in the fat body during Bombyx postembryonic development.

Age-dependent changes in calling effort in the bell cricket Meloimorpha japonica

We investigated how male age and body weight influence male mating effort in the bell cricket Meloimorpha japonica. We adopted a longitudinal approach to study resource allocation to male mating effort (calling duration during 24 h) in the bell cricket. Calling durations and body weight of each male were measured at 7–8 days (young age), 14–15 days (middle age), and 22–25 days (old age) after the final molt. Calling duration increased between young and middle age. During the period between middle and old age, the amount of change in the calling duration was positively correlated with the body weight. The results suggested that older (i.e., low residual reproductive value) and better quality males invested more resources in mating effort.

Pre‐moult patterns of habitat use and moult site selection by Brent Geese Branta bernicla nigricans: individuals prospect for moult sites

In environments where habitat quality varies, the mechanism by which individuals assess and select habitats has significant consequences on their spatial distribution and ability to respond to environmental change. Each year, thousands of Black Brent Geese Branta bernicla nigricans migrate to the Teshekpuk Lake Special Area (TLSA), Alaska, to undergo a flightless wing‐moult. Over the last three decades, moulting Brent Geese have changed their distribution within the TLSA, redistributing from inland, freshwater wetlands towards coastal, brackish wetlands. To understand better the mechanism by which Brent Geese select a moult site, as well as reasons behind the long‐term shift of moulting distributions, we examined movements and habitat use of birds marked with GPS‐transmitters during the pre‐moult period. Brent Geese did not generally migrate directly to their moulting site during the pre‐moult period, defined as the time from arrival at the moulting grounds to the onset of flightlessness. Rather, individuals used an average of 3.7 ± 0.6 (se) wetland complexes and travelled a minimum of 95.14 ± 15.84 km during the pre‐moult period. Moreover, 69% of Brent Geese visited their final moult site only to leave and visit other sites before returning for the flightless moult. Brent Geese spent significant time in both inland freshwater and coastal estuarine habitats during the pre‐moult, irrespective of the habitat in which they ultimately moulted. Whereas previous research suggested that Brent Geese choose moult sites based largely upon the experience of previous years, our observations suggest a mechanism of moult site selection whereby Brent Geese ‘prospect’ for moult sites, visiting multiple potential moult sites across varied habitat types, presumably gathering information from each site and correspondingly using this information to choose an appropriate moult site. By allowing individuals to adjust their distributions in response to habitat quality cues that may change annually, such as forage type and availability, prospecting may have influenced the long‐term shift in moulting distributions of Brent Geese in the TLSA.

Collagenolytic activity related to metalloproteases (and serine proteases) in the fish parasite Hysterothylacium aduncum (Nematoda: Anisakidae)

Proteases play a vital role in both the life cycle of parasites and the parasite-host relationship and are considered important virulence factors. In the present study, the presence of proteases with collagenolytic activity was investigated in the fish nematode Hysterothylacium aduncum during in vitro development. Collagenolytic activity was found in all studied developmental stages of the nematode (third [L3] and fourth [L4] larval stages and adults). In L3, the activity was maximum at pH 6.5 and, in the other stages, at 7.0. Pepsin is known to favour in vitro development of the worm, but, in this study, collagenolytic activity was shown to be significantly greater when no pepsin was added to the culture medium (at pH 6.5, p = 0.011). At pH 7.0, most activity was observed in the immature adult, after the final moult, suggesting that the collagenolytic activity may be involved in remodelling of the cuticle and in sexual maturity. On the other hand, at pH 6.5, activity may be related to tissue migration by L3 within the host. Using specific inhibitors, it was demonstrated that most of the collagenolytic activity detected in all the developmental stages was due to metalloproteases (40 to 100%), although serine proteases were also detected in L4 and adults (10 to 30%).

Age-dependent cyclic locomotor activity in the cricket, Gryllus bimaculatus, and the effect of adipokinetic hormone on locomotion and excitability

Excitability and locomotor activity of male and female last instar larvae and adults of the two-spotted cricket are measured under crowded conditions, allowing the animals to interact with conspecifics during observations. Male and female last instar larvae display age-dependent cyclic patterns of activity with maxima during early to mid scotophase and minima during early photophase. A period of low locomotor activity without time of day-dependent cyclic changes starts 1 day before the final moult and lasts until 1 day after the moult. Then, both excitability and locomotor activity increase and become cyclic again within 2 or 3 days. The cyclic changes gradually dampen in adult females older than 6 days and finally cease. When injected into photophase larvae and adults, adipokinetic hormone (AKH) increases excitability and locomotor activity in a dose-dependent manner, whereas it has no such effect when injected into scotophase animals. Other behaviours (jumping, hind wing trembling) that mostly occur in scotophase crickets are also increased by injecting AKH into photophase crickets. We argue that AKH could be responsible for linking the endogenous clock output with the cyclic changes in locomotor activity. Furthermore, AKH may serve to synchronise metabolism and behaviour to optimise larval development and reproduction.

Caterpillar color patterns are determined by a two‐phase melanin gene prepatterning process: new evidence from tan and laccase2

The larval color patterns in Lepidoptera exhibit splendid diversity, and identifying the genes responsible for pigment distribution is essential to understanding color-pattern evolution. The swallowtail butterfly, Papilio xuthus, is a good candidate for analyzing marking-associated genes because its body markings change dramatically at the final molt. Moreover, the silkworm Bombyx mori is most suitable for identification of lab-generated color mutants because genome information and many color mutants are available. Here, we analyzed the expression pattern of 10 melanin-related genes in P. xuthus, and analyzed whether these genes were responsible for Bombyx larval color mutants. We found that seven genes correlated strongly with the stage-specific larval cuticular markings of P. xuthus, suggesting that, compared with Drosophila, more genes showed marking specificity in lepidopteran larvae. We newly found that the expression of both tan and laccase2 is strongly correlated with the larval black markings in both P. xuthus and B. mori. The results of F2 linkage analysis and mutant analysis strongly suggest that tan is the responsible gene for Bombyx larval color mutant rouge, and that tan is important in emphasizing black markings of lepidopteran larvae. Detailed comparison of temporal and spatial expression patterns showed that larval cuticular markings were regulated at two different phases. Marking-specific expression of oxidizing enzymes preceded the marking-specific expression of melanin synthesis enzymes at mRNA level, which is the reverse of the melanin synthesis step.