Elaboration and ultrastructural changes in the pore canal system of the mineralized cuticle of Carcinus maenas during the moulting cycle

Two basic structural components are concerned in the elaboration of the pore canal system in the mineralized cuticle of the decapod crab Carcinus maenas: tubular cytoplasmic extensions originating from epidermis and vertical fibres. These components are present from the moment the first procuticular materials of the new cuticle are laid down but their organization varies according to a precise schedule during the further moult cycle stages. Cytoplasmic extensions form a complicated branching system connecting the epidermal layer with all regions of the cullcular compartment, at least transitorily. During the moult cycle the prolongation of this cellular system appears to result from two concomitant but opposite phenomena. Before ecdysis the growth of cell extensions in the proximal cuticular layers prevails over their regression at the distal level. During the post-moult period these phenomena are reversed in importance so that the pore canal system is without cytoplasmic material as soon as intermoult starts. The depositing of vertical fibres takes place in close contact with the proximal cell extension plasma membrane, which never bears dense plaques. As moult stages progress, they are gradually organized into twisted sheaths that persist throughout the intermoult. Incidentally, some fibres invade the pore canal lumen freed from cell extensions. Some aspects regarding the fine organization, the chemical composition and the functional significance of both epidermal tubular extensions or vertical fibres are also discussed in the light of previous investigations carried out on crustaceans and in other arthropods.     

Spinneret Microstructure of the Silk Spinning Apparatus in the Crab Spider, Misumenops tricuspidatus (Araneae: Thomisidae)

The silk spinning apparatus in the crab spider, Misumenops tricuspidatus was studied with the field emission scanning electron microscope (FESEM) and the main microstructural characteristics of the silk glands are presented. In spite of the fact that the crab spiders do not spin webs to trap a prey, they also have silk apparatus even though the functions are not fully defined. The crab spider, Misumenops tricuspidatus possesses only three types of silk glands which connected through the typical spinning tubes on the spinnerets. The spinning apparatus of Misumenops closely corresponds to that of wandering spiders such as jumping spiders or wolf spiders except some local variations. Anterior spinnerets comprise 2 pairs of the ampullates and 48 (±5) pairs of pyriform glands. Another 2 pairs of ampullate glands and nearly 20 (±3) pairs of aciniform glands were connected on the middle spinnerets. Additional 50 (±5) pairs of the aciniform glands were connected on the posterior spinnerets. The aggregate glands and the flagelliform glands which have the function of sticky capture thread production in orb‐web spiders as well as the tubuliform glands for cocoon production in females were not developed at both sexes of this spider, characteristically.     

Moult of the giant petrels Macronectes halli and M. giganteus at South Georgia

Moult scores were collected from colour-ringed individuals of known reproductive status of the two species of giant petrel, Macronectes halli and M. giganteus , at Bird Island, South Georgia between 1978–81.
Both species showed a substantial overlap between breeding and wing-moult, unlike most other Southern Ocean seabirds. Males started moult before females and both sexes of M. giganteus moulted at an earlier stage of the breeding cycle than M. halli , which breeds six weeks earlier than its congener.
Changes in moult rate during the breeding season are documented for both species, with Id. halli showing a rapid increase as the chick nears fledging. Male M. giganteus show a notably different pattern to the other three species-sex groups, starting moult much earlier (at egg-laying), with greater individual synchrony and usually suspending primary moult throughout the main chick growth period, whereas only two male M. halli and no females of either species suspended moult. Differences in pattern, timing and rate of moult are interpreted in terms of availability of food resources and the competing energy demands of other activities, especially chick-rearing.
Completion of primary moult could not be observed in the field but was estimated using data frcsm non-breeding birds and failed breeders; the latter started a rapid moult almost immediately they failed. In both sexes of both species moult is probably concluded at least by early winter.
The general pattern of moult in giant petrels at Bird Island is contrasted with that of other populations and species of Southern Ocean seabirds. It is suggested that the unusually extensive overlap between breeding and moult in giant petrels is a consequence of the very abundant and easily available summer food supplies (especially carrion) and the much diminished winter resources, favouring a completion of moult by the beginning of the winter.     

Crab spiders (Thomisidae) attract insect flower‐visitors without UV signalling

1. Crab spiders (Thomisidae) indirectly affect insect flower‐visitor and flowering plant interactions by consuming and altering the behaviour of insects. 2. Although one expects insect flower‐visitors to avoid crab spiders actively, some crab spider species are known to attract flower‐visitors. Crab spiders may use UV signalling to lure potential prey to the flowers they occupy. 3. In the present study, a field experiment was conducted to examine the effects of crab spiders occupying three prairie plant species for the insect flower‐visitor community. Pollinating insects were significantly attracted to inflorescences with crab spiders compared to inflorescences without crab spiders for two plant species, and herbivorous insects were attracted to inflorescences with crab spiders for one of these plant species. The two flowering plant species with increased pollinator visitation showed increased seed weights for plants with crab spiders, indicating crab spider presence indirectly increased pollination. 4. To test the UV signalling hypothesis, inflorescences with crab spiders of one plant species were observed under both a UV‐blocking plastic and a clear plastic control. Contrary to our prediction, flower‐visitors were not more likely to land on inflorescences under the clear plastic; the UV signalling hypothesis was not supported. Other unknown explanations underlie prey attraction to inflorescences with crab spiders.     

The effect of colour variation in predators on the behaviour of pollinators: Australian crab spiders and native bees

1. Australian crab spiders exploit the plant–pollinator mutualism by reflecting UV light that attracts pollinators to the flowers where they sit. However, spider UV reflection seems to vary broadly within and between individuals and species, and we are still lacking any comparative studies of prey and/or predator behaviour towards spider colour variation. 2. Here we looked at the natural variation in the coloration of two species of Australian crab spiders, Thomisus spectabilis and Diaea evanida, collected from the field. Furthermore, we examined how two species of native bees responded to variation in colour contrast generated by spiders sitting in flowers compared with vacant flowers. We used data from a bee choice experiment with D. evanida spiders and Trigona carbonaria bees and also published data on T. spectabilis spiders and Austroplebeia australis bees. 3. In the field both spider species were always achromatically (from a distance) undetectable but chromatically (at closer range) detectable for bees. Experimentally, we showed species‐specific differences in bee behaviour towards particular spider colour variation: T. carbonaria bees did not show any preference for any colour contrasts generated by D. evanida spiders but A. australis bees were more likely to reject flowers with more contrasting T. spectabilis spiders. 4. Our study suggests that some of the spider colour variation that we encounter in the field may be partly explained by the spider's ability to adjust the reflectance properties of its colour relative to the behaviour of the species of prey available.     

Moult cycle and growth of the crab Halicarcinus planatus (Brachyura, Hymenosomatidae) in the Beagle Channel, southern tip of South America

The crab Halicarcinus planatus is the only hymenosomatid crab that inhabits the southern tip of South America and is the only decapod species that reproduces twice a year in the Beagle Channel. In this article, we study the moult cycle in the field (moult frequency, analysis of size frequency distribution) and linked it with growth studied in the laboratory (absolute and per cent growth increment, Hiatt function). Hiatt functions were similar for males and females. Moult frequency was seasonal: in early austral spring and in austral summer. In females, the pubertal moult is the terminal moult, whereas males continue moulting after attaining the size of morphometric maturity. Moult increment was highly variable. The relationship between absolute moult increment and crab size was described by a quadratic function. Per cent growth increment decreased with size, and relationships were different for each sex: linear for females and quadratic for males. Seven and eight modal groups explained the size frequency distributions for females and males from the field, respectively, and revealed the existence of two cohorts of recruits per year. Further modal analysis was mainly hampered by the high variability of size increment that could make any moulting individual fall in its own or one of two following modal groups. The antagonism between growth and reproduction was evident in small males. We hypothesize that the terminal pubertal moult is an advantageous feature that allows females to maximize their investment in reproduction after their terminal moult, which allows this species to have two spawnings per year.     

Spider movement, UV reflectance and size, but not spider crypsis, affect the response of honeybees to Australian crab spiders

According to the crypsis hypothesis, the ability of female crab spiders to change body colour and match the colour of flowers has been selected because flower visitors are less likely to detect spiders that match the colour of the flowers used as hunting platform. However, recent findings suggest that spider crypsis plays a minor role in predator detection and some studies even showed that pollinators can become attracted to flowers harbouring Australian crab spider when the UV contrast between spider and flower increases. Here we studied the response of Apis mellifera honeybees to the presence of white or yellow Thomisus spectabilis Australian crab spiders sitting on Bidens alba inflorescences and also the response of honeybees to crab spiders that we made easily detectable painting blue their forelimbs or abdomen. To account for the visual systems of crab spider's prey, we measured the reflectance properties of the spiders and inflorescences used for the experiments. We found that honeybees did not respond to the degree of matching between spiders and inflorescences (either chromatic or achromatic contrast): they responded similarly to white and yellow spiders, to control and painted spiders. However spider UV reflection, spider size and spider movement determined honeybee behaviour: the probability that honeybees landed on spider-harbouring inflorescences was greatest when the spiders were large and had high UV reflectance or when spiders were small and reflected little UV, and honeybees were more likely to reject inflorescences if spiders moved as the bee approached the inflorescence. Our study suggests that only the large, but not the small Australian crab spiders deceive their preys by reflecting UV light, and highlights the importance of other cues that elicited an anti-predator response in honeybees.     

Foraging at a safe distance: crab spider effects on pollinators

1. The ability of pollinating insects to discover and evade their predators can affect plant–pollinator mutualisms and have cascading ecosystem effects. Pollinators will avoid flowers with predators, but it is not clear how far away they will move to continue foraging. If these distances are relatively small, the impact of predators on the plant–pollinator mutualism may be lessened. The plant could continue to receive some pollination, and pollinators would reduce the time and energy needed to search for another patch. 2. A native crab spider, Xysticus elegans, was placed on one cluster in a small array of Baccharis pilularis inflorescence clusters, and the preferred short‐range foraging distances of naturally visiting pollinators was determined. 3. Nearly all pollinator taxa (honey bees, wasps, other Hymenoptera, and non‐bombyliid flies) spent less time foraging on the predator cluster. 4. The key result of this study is that inflorescences within 90 mm of the crab spider were avoided by visiting honey bees and wasps, which spent three‐ and 18‐fold more time, respectively, foraging on more distant flower clusters. 5. Whether honey bees can use olfaction to detect spiders was then tested, and this study provides the first demonstration that honey bees will avoid crab spider odour alone at a food source.     

Crab spiders deter insect visitations to slickspot peppergrass flowers

Insects visiting the flowers of slickspot peppergrass, Lepidium papilliferum (Brassicaceae), risk predation by crab spiders, Misumena vatia (Thomisidae). In a field study conducted at two sites in southwestern Idaho, 7.5±2.7% of L. papilliferum plants (range 0–30%, N=16 surveys of up to 40 randomly selected plants) harbored a crab spider. However, through 205 minutes of observations at plants with a spider, only 15 predation attempts were observed, with only 3 of those being successful. Despite the relatively low incidence of predation by crab spiders, an experiment revealed that the number of insects visiting L. papilliferum flowers was significantly lower at plants that harbored a crab spider than at plants free of spiders. In another experiment, floral visits increased significantly following the removal of crab spiders from individual plants. The deterrent effect of spiders was not due to a disproportionate avoidance response by certain types of insects; all insect families included in our analysis showed decreases in visitations to flowers when spiders were present, although none of these differences were statistically significant at the individual level. We found no significant change in the duration of visits to plants harboring a spider, implying either that the visitors were oblivious to the predator's presence, or that they were aware of the predator but kept their distance. Our study is one of a growing number to find a decrease in floral visits in response to predators, suggesting that the phenomenon is more widespread than was previously recognized.     

External parasite infestation depends on moult-frequency and age in Antarctic krill (<Emphasis Type="Italic">Euphausia superba</Emphasis>)

Levels of infestation by the suctorian Ephelota sp. were determined in Antarctic krill taken in the north-eastern region of the Scotia sea, close to the island of South Georgia. Individuals caught in summer between 2002 and 2004 were measured for body length, eye diameter, moult stage, sex, sexual maturity and number of suctorian parasites. All krill samples were found to contain at least two modal size-classes and the complete range of maturity- and moult stages. Sample analysis for the different characters identified moult stage as an important determinant of infestation by Ephelota sp., with 66% of those about to moult (pre-moult individuals) being infested compared with 0% of post-moult individuals. Multiple Correspondence Analysis also identified a strong link between age and degree of suctorian infestation with large-eyed (and hence old) males having very high numbers of suctorian bodies. Moulting is costly in terms of energy and vulnerability, but it is believed that krill moult at relatively high rates throughout their life to facilitate growth and “shrinkage”. Here, we demonstrate that the control of external parasitism is also a major advantage of moulting at high frequency. The capacity of krill to maintain a high moult rate decreases with age, leading to older krill enduring higher parasitic loads.     

Rapid moult among palaearctic passerines in West Africa- an adaptation to the oncoming dry season?

Moult of some palaearctic migrant passerines was studied at a wintering site in northern Ghana, West Africa. We present data on moult pattern and estimated moult duration for a sample of species. Savi's Warbler Locustella luscinioides , Woodchat Shrike Lanius senator and probably Grasshopper Warbler Locustella naevia deviated from the ordinary descendent moult sequence. Different measures of moult speed (moult speed of retrapped individuals, growth of individual feathers, wing raggedness and first date of completion of moult) showed unexpectedly rapid moult among individuals of several species, notably the Great Reed Warbler Acrocephalus arundinaceus and the Sedge Warbler A. schoenobaenus. The rapid moult might be an adaptation to a limited period of abundant food which comes to an end at the beginning of the dry season.     

Moult Strategies Affect Age Differences in Autumn Migration Timing in East Mediterranean Migratory Passerines

Adult passerines renew their flight feathers at least once every year. This complete moult occurs either in the breeding areas, just after breeding (summer moult), or, in some long-distance migratory species, at the non-breeding areas, after arrival to the southern wintering area at the end of autumn migration (winter moult). The aim of this study was to relate moult strategies with the DMD, the difference in median migration date, through Israel, between juveniles and adults. Our data on autumn migration timing in juveniles and adults was based on ringing data of 49,125 individuals belonging to 23 passerine species that breed in Europe and Western Asia and migrate through Israel. We found that DMD was associated with moult timing. In all species that perform a winter moult, adults preceded juveniles during autumn. Among migrants who perform a summer moult, we found evidence of both migration timing patterns: juveniles preceding adults or adults preceding juveniles. In addition, in summer moulters, we found a significant, positive correlation between mean breeding latitude and DMD. Although previous studies described that moult duration and extent can be affected by migration, we suggest that moult strategies affect both migration timing and migration strategy. These two moult strategies (summer or winter moult) also represent two unique migration strategies. Our findings highlight the evolutionary interplay between moult and migration strategies.     

Age, sex, and condition as predictors of moult and the efficacy of a novel fur-clip technique for individual marking of the European badger (Meles meles)

The European badger ( Meles meles ) moults once a year. In our study site in lowland England, pelage replacement of the guard hairs and a protracted period of fur growth (follicular anagen) occur between May and early November, with a peak in July. The precise timing of the moult depends on the age and condition of the badger. Yearling badgers undergo moult significantly earlier than adults. Adult females that have lactated, moult significantly later than other classes of adult, delaying the moult until autumn which corresponds to an annual period of food abundance. Lactation was significantly associated with poor condition in these badgers. It was not possible to determine whether delayed moult was due to poor condition per se , or due to some other physiological consequence of lactation, e.g. hormonal changes. We hypothesize that delay of moult in laclating/poor condition individuals has the adaptive consequence of delaying the metabolic costs of pelage replacement from a time of energy deficit until a time of relative plenty.
These findings are of practical importance to a novel solution to the problem of individually marking badgers during observational studies. The technique involves clipping the dark band near the tips of the badger's guard hairs to reveal the white under-fur and produce patterning of the coat. The highly contrasting marks were well suited to visual identification during observations under low light and infra-red illumination, and they allowed a large number of individuals (over 80 in our study) to be distinctively marked. The mark persists until the badger undergoes its single annual moult, or until three months of the active phase of fur growth have passed. Clip marks on adults made in late August had the greatest longevity, with 80% still visible after nine months. Though clipping had no significant effect on body condition in our study site, it should be cautiously applied with individuals in poor condition or in cold climates.     

Negative Correlation between Ant and Spider Abundances in the Canopy of a Bornean Tropical Rain Forest

In tropical rain forests, high canopy trees have diverse and abundant populations of ants and spiders. However, accessing high trees and their fauna remains difficult; thus, how ants and spiders interact in the canopy remains unclear. To better understand the interspecific interactions between these two dominant arthropod groups, we investigated their spatial distributions at the canopy surface in a tropical rain forest in Borneo. We sampled ants and spiders six times between 2009 and 2011 by sweeping with an insect net at the tree crown surfaces of 190 emergent or tall (≥20 m in height) trees. We collected 438 ant individuals belonging to 94 species and 1850 spider individuals (1630 juveniles and 220 adults) belonging to 142 morphospecies (adults only) from a total of 976 samples. The fact that we collected four times more spider individuals than ant individuals suggests that fewer ants forage at the tree crown surface than previously thought. The number of spider individuals negatively correlated with the number of ant individuals and the number of ant species, indicating significant exclusivity between ant and spider spatial distributions at the tree crown surface. Niche‐overlap between the two taxa confirmed this observation. Although our data do not address the causes of these spatial distributions, antagonistic interspecific interactions such as interference behaviors and intra‐guild predation are ecological mechanisms that give rise to exclusive spatial distributions.     

Post-juvenile and post-breeding moult of Savi's Warblers Locustella luscinioides in Portugal

We describe the sequence and extent of the complex and little understood post-juvenile and post-breeding moults of Savi's Warblers Locustella luscinioides . In contrast to previous studies, the post-juvenile moult occurred in at least 44% of the birds, 5% of which moulted some or all tertials and greater coverts. The timing of overlap between the filling and the post-juvenile moults, and the fact that later-moulting birds had no post-juvenile moult, strongly suggests that the moult extent is dependent on fledging date. From July onwards, all adult males overlapped breeding and moult, whereas only 11% of the females did so. The start of moult varied from 6 June to 25 August, and was significantly earlier in males. Only 18% of the birds completed the moult, whereas the remaining individuals retained a variable number of inner primaries and/or secondaries. Interestingly, not only was the number of retained primaries positively associated with the date of moult, but so too was the primary number of birds in which the moult started. We view this as an adaptation allowing the replacement of the most important feathers for flight when the time available for moult is short. Body condition did not vary with the progress of moult when date was taken into account, but fat reserves still tended to decrease and then increase. The body condition was correlated positively with the wing raggedness, so Savi's Warblers do not compensate for an increasing wing load during moult.     

Seasonal changes in moult,body mass and reproductive condition in siskins Carduelis spinus exposed to daylength regimes simulating different latitudes

Birds use change in daylength during the year to time events during their annual cycles. Individual Eurasian siskins Carduelis spinus can breed and winter in widely separated areas in different years. Birds at different latitudes will experience different changes in photoperiod. So how does latitude affect photoperiodic control? Our aim in this study was to find whether Siskins caught from the wild in Britain and exposed to different photoperiodic regimes, typical of widely separated latitudes, would differ in the subsequent timing and duration of their moults and associated processes. Siskins were caught in late February and early March, and initially kept outside on natural photoperiods. From the spring equinox (21 March), they were divided into three groups kept under photoperiodic regimes that simulated latitudes 40°, 55° and 70°N respectively. All three groups showed highly significant subsequent changes in body mass, fat scores and cloacal protuberance size. Moult of the primary feathers started during June – August (mean 9 July), and lasted 61–99 days (mean 75 days). Birds that started to moult late in the season had shorter moult durations. All individuals showed lower mass and fat levels during moult than before or after moult. Crucially, there were no significant differences in the timing of these events between the three photoperiodic groups. Apparently these birds did not use prevailing absolute photoperiod or the prevailing rate of change in photoperiod to time moult‐related seasonal events, but used instead some other feature of the annual photoperiod cycle or some form of interval timer linked to photoperiod.     

Sexual differences in the absolute growth pattern of the Indo-Pacific sandy shore crab Matuta lunaris

The absolute growth pattern of Matuta lunaris (Forskål) is assessed, based on moult increment data and analyses of size frequency distributions. Both sexes show determinate growth with maturity occurring at the terminal puberty moult. However, Matuta lunaris is unusual as the sexes differ markedly in their growth patterns. Males mature at a larger size than females and grow to a larger maximum size. Male growth is characterized by relatively constant moult increments and an unknown and possibly variable number of immature instars with widely overlapping size ranges. In contrast, female growth is characterized by relatively large moult increments and a fixed number of instars, each with restricted size ranges.     

Book lung development in the embryo,postembryo and first instar of the cobweb spider,Parasteatoda tepidariorum C. L Koch, 1841 (Araneomorphae,Theridiidae)

Light and electron microscopy were used to compare spider book lung development with earlier studies of the development of horseshoe crab book gills and scorpion book lungs. Histological studies at the beginning of the 20th century provided evidence that spider and scorpion book lungs begin with outgrowth of a few primary lamellae (respiratory furrows, saccules) from the posterior surface of opisthosomal limb buds, reminiscent of the formation of book gills in the horseshoe crab. In spider embryos, light micrographs herein also show small primary lamellae formed at the posterior surface of opisthosomal limb buds. Later, more prominent primary lamellae extend into each book lung sinus from the inner wall of the book lung operculum formed from the limb bud. It appears most primary lamellae continue developing and become part of later book lungs, but there is variation in the rate and sequence of development. Electron micrographs show the process of air channel formation from parallel rows of precursor cells: mode I (cord hollowing), release of secretory vesicles into the extracellular space and mode II (cell hollowing), alignment and fusion of intracellular vesicles. Cell death (cavitation) is much less common but occurs in some places. Results herein support the early 20th century hypotheses that 1) book lungs are derived from book gills and 2) book lungs are an early step in the evolution of spider tracheae.     

THE PRIMARY MOULT OF WADERS ON THE ATLANTIC COAST OF MOROCCO

Data from 3659 waders of 23 species live-trapped in the years 1971-73 on the Atlantic coast of Morocco during the period of autumn moult and migration are analysed to estimate duration and timing of primary moult. Common Sandpiper was the only species to moult primaries in its first autumn (unless published ageing criteria are incorrect). Several species showed a low incidence of arrested primary moult and a higher incidence was observed in Ringed, Kentish and Grey Plovers. This is discussed in relation to breeding and migration. Similar rates of primary feather replacement relative to specific moult duration were observed in all species for which information was available. Comparisons between species and with published studies showed that variations in rate of moulting between species and between different geographical populations of the same species were largely due to differences in feather growth rate rather than in the numbers of primaries concurrently in growth. Variations in rate between individuals of the same population were achieved, at least in the first part of moult, by differences in feather dropping rate resulting in differences in the numbers of primaries growing concurrently. The timing and duration of moult in different populations and differences between breeding and non-breeding components were closely related to the requirements of other annual cycle activities, notably breeding and migration. Non-breeding birds summering in Morocco had started moult early. Locally breeding birds had an early start to a fairly slow moult which overlapped with breeding and which in some cases passed through an arrested stage. Birds breeding in cold temperate and arctic regions and wintering in Morocco moulted in a short time soon after arrival. In some cases, notably in Ringed Plovers, birds had commenced moulting on the breeding grounds and arrested moult during migration. Most Redshank and possibly Dunlin migrated in active wing moult. The fastest primary moult was achieved by high arctic breeding birds, Curlew Sandpiper and possibly Little Stint, which stopped to moult in Morocco before moving on to wintering areas further south. This situation is contrasted with that of populations of these two and other species wintering in the southern hemisphere where moult occurs over an extended period during the northern winter.