A note on the accessory glands of the reproductive system of the scolopendromorph centipede, Cormocephalus anceps anceps Porat

The function of the reproductive accessory glands has not before been investigated. Their prominence arouses interest in their possible function. A preliminary histological, histochemical, and biochemical analysis has been undertaken in order to start to answer this question. No definite conclusions can, however, be made from the results obtained. From evidence accumulated on the behaviour of the sexes and the peaks of secretion production it seems likely that the product of the female glands would be used to coat the eggs with a colleterial substance. The male Geophilomorpha, Scolopendromorpha, and Lithobiomorpha all spin webs on which they place a spermatophore during courtship, and all three groups possess two well developed pairs of accessory glands which may be responsible for the production of web material. The Scutigeromorpha, on the other hand, only possess a single vestigeal pair of glands and do not spin a web. It is suggested that the accessory glands of the male produce web material although this still remains unproven.     

The evolution of sperm transfer mechanisms in the Diptera

The known occurrence of spermatophores in the Diptera and some possible modes of transition to other mechanisms of sperm transfer are outlined. The closed systems of transfer, and the significance of modifications of gonopore shape in some species, are discussed.     

The variation of the centipede Scolopendra amazonica in Africa

African centipedes labelled Scolopendra amazonica (Buecherl) and S. morsitans L. in the collection of the British Museum (Natural History) have been examined. All are regarded, at present, as S. amazonica but in many respects S. amazonica in Africa shows greater variation than do S. amazonica and S. morsitans in India. North African populations are very distinct.     

Age-related sperm transfer and sperm competitive ability in the male hide beetle

The influence of male age on reproductive success after a singlemating has been explored widely; however, few studies have investigatedwhether quantitative or qualitative differences in male spermare responsible for the observed patterns. Moreover, the roleof male age on sperm competitive ability has been largely ignored.We examined the importance of male age on the probability andamount of sperm transferred during a single mating and exploredwhether sperm competitive ability varies with male age in thehide beetle Dermestes maculatus, a species where sperm viabilitydoes not vary with male age. We also investigated whether spermtransfer rates varied with female age. We found that the probabilityof sperm transfer and the amount of sperm transferred variedwith male, but not female, age. All males performed behaviorallysuccessful copulations, but intermediate-age and old males weremore likely to transfer sperm successfully and also transferreda greater quantity of sperm than young males. Old males wereless likely to transfer sperm than intermediate-age males, butif they did transfer sperm successfully, they transferred comparableamounts. Sperm competitive ability varied with male age andreflected the quantity of sperm transferred. On average, intermediate-agemales achieved greater fertilization success when competingagainst young or old males than when competing against otherintermediate-age males. Old males were poor competitors againstintermediate-age males, but they achieved significantly higherrates of fertilization when competing against young males. Ourfindings suggest that quantitative differences in the amountof sperm transferred determine male success in sperm competitionin the hide beetle.     

Pattern of sperm transfer in redback spiders: implications for sperm competition and male sacrifice

Many sperm competition studies have identified copulation durationas an important predictor of paternity. This result is ofteninterpreted as a sperm transfer effect—it is assumed thatsperm transfer is limited by copulation duration. Here we testthe assumption of duration-dependent sperm transfer in the Australianredback spider, Latrodectus hasselti, in which a correlationbetween copulation duration and paternity has been implicatedin the evolution of a rare male self-sacrifice behavior. Maleredbacks facilitate sexual cannibalism by females during copulation.Sexual cannibalism is apparently adaptive for redback males,in part because it results in longer copulations (25 versus11 min.), and copulation duration is positively correlated withpaternity. We assessed sperm transfer in normal copulationsand in copulations that we terminated at 5, 10, or 20 min. Ourresults show that the paternity advantage of sexual cannibalismis not owing to time-dependent sperm transfer, as redback malestransfer the majority of their sperm within the first 5 minof copulation. This suggests that the link between copulationduration and paternity may instead be owing to cryptic femalechoice or the transfer of nongametic ejaculatory substances.Results further indicate that the act of cannibalism itselfmight play a role in mediating sperm transfer. This study highlightsthe importance of understanding mechanisms of sperm transferwhen attempting to interpret the outcome of sperm competitionstudies.     

The impact of ovulation mode on sperm quantity and quality in mammals

Ovulation generally takes two forms: spontaneous and induced. These two ovulatory modes are predicted to cause different levels of male–male competition due to differences in males’ ability to predict the timing of ovulation of females that use each mode. Ovulation mode has been shown to be correlated with differences in testis size, but it is not known whether ovulation type influences ejaculate traits, specifically sperm quantity (sperm concentration, ejaculate volume, total motile sperm per ejaculate) and/or sperm quality (% sperm motility, % normal sperm). Using a cross-species comparative analysis of 130 mammals, we found that sperm concentration and total motile sperm per ejaculate were significantly greater in spontaneous ovulators. In contrast, ejaculate volume, % sperm motility and % normal sperm were unrelated to ovulation type. These data show that ovulation alters sperm quantity by increasing sperm concentration but not ejaculate volume, and that sperm quality does not vary with ovulation mode.     

The component community structure of larval trematodes in the pulmonate snail Helisoma anceps

Factors that affected the component community structure of larval trematodes in the pulmonate snail Helisoma anceps in Charlie's Pond, North Carolina, were studied over a 15-mo period using a multiple mark-recapture protocol. Patent infections of 8 species were observed in 1,485 of 4,899 snails examined. Reproductive activity, population size, and survival rate of the snail population were estimated to evaluate the extent of resource availability for the parasites. Antagonistic interactions between trematode species that occurred at the infracommunity level had a neglible effect on the composition and structure of the component community. The patterns observed at this level were related to temporal heterogeneity in the abundance of infective stages (mostly miracidia), differential responses of trematode species to the diverse and constantly changing distribution of snail size and abundance, differential mortality of snails infected with certain trematode species, constant recruitment of 1 trematode species over time, and the existence of predictable disturbances such as the complete mortality of the host population and recruitment of a replacement population during a 6-8 wk period. The last factor operated as a reset mechanism for this snail-trematode system once each year. A model of patch dynamics, with snails as patch resources, best explains the organization and dynamics of this system.     

The taxonomy and biology of the centipede Scolopendra amazonicain the Sudan

The life history, reproduction, food and parasites of a population of Scolopendra amazonica Bücherl from the south bank of the Blue Nile at Khartoum, Sudan are described and discussed and Sudanese specimens are compared with Indian S. amazonica and Scolopendra morsitans.     

Mechanisms of sperm removal and sperm transfer in Orthetrum coerulescens (Fabricius) (Odonata: Libellulidae)

ABSTRACT An account of the structure of the secondary genitalia of male Orthetrum coerulescens (Fabricius) is given together with an outline of the internal genitalia of the female. Observations on the experimental inflation of the penis are described. No sperm was released during fast inflations and deflations of the penis, but sustained inflation of the penis led to the release of a clear fluid followed by the slow discharge of sperm. Examination of natural copulations in the field has shown that rapid rhythmic movements at up to 5 Hz take place in the male's third abdominal segment throughout most of copulation, but towards the end they cease though inflation is maintained. It is suggested that the rapid movements coincide with the removal of rival sperm from the female and that sperm is transferred to the female only during the maintained inflation. Possible mechanisms of sperm translocation, sperm removal and sperm transfer are discussed with reference to male and female genital structures and the action of relevant muscles.     

The evolution of segmentation of centipede trunk and appendages

The segmentation of centipedes is interpreted in the light of a biphasic model of segmentation (holomeric plus meromeric). The mid-body anomaly (e.g. in the alternating short and long terga, or in the sequence of segments with and without spiracles) is regarded as due to an early patterning of the embryo, occurring before the onset of meromeric segmentation and affecting a level within the fourth eosegment of the trunk. Comparisons with the Diplopoda suggest that genital structures such as millipede gonopods did probably develop originally at this spot, whose position remained marked even after the transition from a putatively progoneate to the current opisthogoneate condition of centipedes, perhaps following gene duplication and divergence of expression patterns of the paralogues. A new lower limit for the number of leg-bearing segments [27, in a male specimen of Schendylops oligopus (Pereira, Minelli & Barbieri,1995)] is established for Geophilomorpha. Coevolutionary trends involving the segmentation of the trunk, the segmentation of the appendages (especially the antennae), the postembryonic developmental schedule and the presence or absence of regeneration ability supports a recent view of the appendages as evolutionarily divergent duplicates of the main body axis.     

Decomposition in situ of the sublittoral Antarctic macroalgaDesmarestia anceps Montagne

 Large amounts of detached Antarctic macroalgae accumulate in hollows of the seabed, where decomposition rates of the detached macroalgae are expected to be low, caused by lack of contact of the major part of the macroalgae with the sediment. To determine decomposition rates in Antarctic waters, untreated and pre-killed Desmarestia anceps fronds contained in nylon net bags were studied for 10 months under natural conditions in Factory Cove, Signy Island. Physical decomposition was shown to be more important than microbial decomposition. A weight loss of 40% occurred in untreated material within 313 days, while pre-killed material almost all disappeared within 90 days. Despite the weight loss, changes in chlorophyll a content were negligible during the experiment. Changes in the C:N ratio and tissue N indicated low rates of microbial decomposition. Therefore, it was concluded that weight loss was mainly caused by fragmentation, and particles disappearing from the nets accounted for most of the loss of original tissue. It remains unknown as to how long nutrients stay in Antarctic macroalgal litter before they become available to the system. Received: 16 March 1995/Accepted: 18 June 1995     

The segmentation cascade in the centipede Strigamia maritima: involvement of the Notch pathway and pair-rule gene homologues

The centipede Strigamia maritima forms all of its segments during embryogenesis. Trunk segments form sequentially from an apparently undifferentiated disk of cells at the posterior of the germ band. We have previously described periodic patterns of gene expression in this posterior disc that precede overt differentiation of segments, and suggested that a segmentation oscillator may be operating in the posterior disc. We now show that genes of the Notch signalling pathway, including the ligand Delta, and homologues of the Drosophila pair-rule genes even-skipped and hairy, show periodic expression in the posterior disc, consistent with their involvement in, or regulation by, such an oscillator. These genes are expressed in a pattern of apparently expanding concentric rings around the proctodeum, which become stripes at the base of the germ band where segments are emerging. In this transition zone, these primary stripes define a double segment periodicity: segmental stripes of engrailed expression, which mark the posterior of each segment, arise at two different phases of the primary pattern. Delta and even-skipped are also activated in secondary stripes that intercalate between primary stripes in this region, further defining the single segment repeat. These data, together with observations that Notch mediated signalling is required for segment pattern formation in other arthropods, suggest that the ancestral arthropod segmentation cascade may have involved a segmentation oscillator that utilised Notch signalling.     

The male reproductive system and mechanism of sperm transfer in Argulus japonicus (Crustacea: Branchiura)

The histomorphology of the male reproductive system and surface morphology of the “peg-and-socket” in Argulus japonicus are described from serial sagittal and transverse sections and scanning electron micrographs. The prostate complex consists of a glandular part, a reservoir for storing the secretion, and an efferent duct opening into the ejaculatory duct. The openings of both the vas deferens and the prostate duct into the ejaculatory duct are guarded by sphincters. The ejaculatory ducts, which are lined by tall columnar epithelial cells, do not open into the cuticle-lined genital atrium but are blind-ending tubes. This observation and results obtained from observing live specimens, as well as the fact that no spermatophores are formed, suggest that semen could leave the ejaculatory duct only after puncturing of its walls. It is suggested that sperm transfer is accomplished in the following manner: during copulation contraction of the muscular walls of the vas deferens and prostate duct causes semen to be pumped into the ejaculatory duct, which is then closed off by sphincters and a high internal pressure is developed. When a spermathecal spine penetrates the walls of the ejaculatory duct, semen flows from the ejaculatory duct into the spermathecal vesicle due to the higher pressure in the ejaculatory duct. This mechanism is analogous to the sucking up of fluid with a hypodermic syringe. © 1993 Wiley-Liss, Inc.