THE FUNCTIONAL ORGANIZATION OF FILTRATION NEPHRIDIA

(1) Based on the classical studies of Goodrich, protonephridia are believed to be phylogenetic antecedents of metanephridia. It is argued here that the primary factor determining the type of nephridium expressed is body size rather than phylogenetic status. (2) The proposed model defines a nephridium functionally and predicts two general configurations for filtration nephridia in animals. (3) Application of the model to metanephridial and protonephridial systems indicates differences in the sites of ultrafiltration and mechanisms of pressure generation. (4) Metanephridial systems function by muscle-mediated filtration of vascular fluid into a coelomic space before modification by an excretory duct. (5) Protonephridial systems function by cilia-mediated filtration of extracellular fluid into the lumen of a protonephridial terminal cell before modification in an adjoining duct. (6) The model predicts a correlation between animals with blood vessels and metanephridia, and animals without blood vessels and protonephridia. The correlation is shown to be nearly perfect. (7) Exceptions to the model are discussed. (8) Original experimental evidence is given for the permeability of the protonephridial terminal cell to iron dextran and its reabsorption by the protonephridial duct in the polychaete, Glycera dibranchiata. (9) Experimental data for proto- and metanephridial systems are summarized and shown to support the proposed model. (10) The ultrastructure of the exceptional amphioxus ‘protonephridium’ is reviewed and original data are presented. Its organization is structurally and perhaps functionally intermediate between proto- and metanephridial systems. (11) An original ultrastructural comparison is made of monociliated nitration cells in a size range of larval invertebrates from five phyla. Filtration cells that are structurally intermediate between protonephridial solenocytes and metanephridial podocytes are noted in larvae intermediate in body size between the two extremes. The comparative data suggest that (i) podocytes and solenocytes are homologous cells and (ii) that body size is correlated with which of the two designs is expressed. (12) The fates of larval podocytes are followed through metamorphosis in three species. The results confirm the equivalence of podocytes and solenocytes as suggested by the comparative analysis. They further indicate that which morph is expressed is a function of body design factors discussed in the model. (13) Protonephridia are believed to be primitive to metanephridia because they occur in presumably primitive animals and in ontogenetic stages of many animals with metanephridia as adults. It is suggested here that the distribution of protonephridia is related to small body size and the lack of blood vessels, regardless of phylogenetic status. The occurrence of protonephridia in the larvae of species with metanephridia as adults is explained similarly as a function of the small larval size and lack of blood vessels.     

Predation creates haloes of bare space among prey on rocky seashores in New South Wales

Field observations on rocky shores in New South Wales suggested a link between pools or wet crevices, predatory whelks foraging from them, and areas around the crevices that were mostly bare of prey (‘haloes’). Whelks were most common in and around crevices but ventured out to feed. Previous work had shown that foraging excursions were cyclical over time. The community of prey also changed with distance from crevices, most types of prey being more abundant further away. A field experiment showed this pattern to be at least partly due to the crevice-bound foraging of the whelks. Experimental removal of whelks over 2 years at several sites caused the gradients in the abundance of prey with distance from crevices to disappear, whilst these patterns persisted and even grew more intense in adjacent control areas. This combination of biotic and physical processes (predation, desiccation, foraging behaviour) is discussed as an important influence on spatial patterning in this and other communities.     

CALCIUM BALANCE AND MOULTING IN THE CRUSTACEA

1. Crustaceans have a high content of calcium, which is chiefly located in the skeleton as calcium carbonate. Calcium is generally the most abundant cation in the body. 2. During intermoult, the exoskeleton is usually fully calcified and the animal is in calcium equilibrium with its environment. 3. In the premoult stages calcium is resorbed from the skeleton and may be lost to the environment or stored within the body. Typically, losses are high and storage is small in aquatic species, whilst most terrestrial forms store much larger amounts of calcium and losses are reduced. Loss of calcium in soluble form by aquatic species must be by outward transport across the gills. 4. Calcium is stored in a variety of different ways, usually with a common taxonomic theme. The main forms are as calcium phosphate granules in cells of the midgut gland (Brachyura), gastroliths (Astacidea and some Brachyura), the haemocoel (some Brachyura) the posterior midgut caeca (Amphipoda) and the ventral portion of the body generally in the Isopoda. 5. At ecdysis, the skeleton is shed and the calcium remaining in it is lost from the body. 6. Recalcification begins immediately, or shortly after, ecdysis using calcium mobilized from the stores. Simultaneously, or when the stores are exhausted, other sources of calcium are utilized. These are calcium in the water (aquatic species), the food (aquatic and terrestrial species) and the exuviae (chiefly terrestrial species). 7. Marine species store little calcium and must obtain the bulk of their requirement (ca. 95%) from the water. Fresh-water species also store little calcium but have, seemingly, adapted to the lower availability of calcium by increasing the affinity of the calcium-absorbing mechanism. The rates of uptake of calcium are consequently similar in marine and fresh-water species. 8. A high degree of storage is essential for terrestrial crustaceans as they do not have access to a large aquatic reservoir of calcium. These large reserves enable the animals to reach an advanced stage of calcification, allowing the resumption of foraging and feeding necessary for completion of calcification. 9. The control of calcium metabolism during the intermoult cycle is poorly under stood. β Ecdysone appears to control the resorption of calcium and the formation of calcium stores during premoult, but the mechanism of control of calcium metabolism during postmoult and intermoult is unknown. 10. The concentration of calcium in the haemolymph of most species is high, but a large proportion of this is in non-ionized form. In premoult, total calcium levels rise as a result of calcium resorption but little change occurs in the concentration of ionized calcium. Postmoult generally sees a fall in blood calcium, sometimes below the intermoult value.     

RARE MALE MATING ADVANTAGE: A REVIEW

1. The phenomenon of frequency-dependent selection with an advantage for the rare type over the common type is intriguing because it implies balancing selection. Thus the high level of genetic variability as found in natural populations can be explained without the necessity of considerable genetic load. Rare male mating advantage is here defined as frequency-dependent male sexual fitness with the rare type of male favoured. Such a rare male effect has been found to be very widespread in insects, at least under laboratory conditions, but there are several problems associated with this phenomenon which will be discussed in this review. 2. To determine whether male mating success is frequency-dependent, the quantity to be considered, most appropriately, is male sexual fitness of the one type relative to the other type (K_M). Other approaches are discussed and it is shown that they confound differential mating success with frequency dependence of mating success. Moreover, it is shown that Levene's indices, previously designed as a measure of differential mating success, confound mating success with assortment, making these indices less useful. 3. The theoretical relationship between frequency dependence of male mating success and total sexual fitness is more complicated than would be expected beforehand. Some examples are given to clarify this issue. 4. Statistical tests to determine frequency dependence of male mating success have often been carried out in the past by determining the significance of deviations from random mating for each male type frequency separately. This procedure must be considered incorrect, because a change in male mating success over frequencies has to be tested. A correct way to do this is by testing all frequencies together in one single statistic, with only a moderate assumption about the type of frequency dependence. When mating success depends on frequency in a more irregular way, alternative tests are available, in which mating success at one frequency can be tested against any other frequency. 5. The rare male effect has been studied most thoroughly in Drosophila, and has been demonstrated for many Drosophila species. The effect has been demonstrated for some other insects as well, and also for vertebrates. The rare male effect has been found for types of males differing in specific genotype (visible mutants, karyotypes), genetic background and geographic origin. A rare male effect has also been demonstrated for non-genetic properties such as temperature of rearing. Though much less common than rare male mating advantage, there are some examples of rare female mating advantage. The expression of the rare male effect may be affected by several factors, such as age of the females, temperature or experimental approach. 6. Only a few studies on rare type mating advantage in Nature have been carried out, but some positive evidence is available. 7. It is pointed out that mating success will be frequency-dependent if both types of males differ pronouncedly in mating behaviour, but the nature of this frequency dependence may vary. If one type of male is more vigorous than the other type, a one-sided rare male effect can be explained on the basis of male–male competition. Quite often, though, a two-sided rare male effect has been found for males not greatly differing in mating behaviour or mating success. Three types of explanations are considered: (a) The females prefer to choose the rare type of male; (b) The rare type of male compensates for its rarity by becoming more sexually active; (c) No individual behaviour is altered. 8. As to the question whether the rare male effect could be an artefact of the experimental setup, the following points are relevant; (a) Biases as a result of alternate marking resulting in rare male mating advantage are theoretically possible, but are shown to be unimportant in explaining the rare male effect for Drosophila. (b) An effect analogous to the effect of alternate marking due to finite sample size is conceivable, but probably less important than suggested by Bryant et al. (1980). (c) When males are not sampled randomly with respect to place in the vial, bias may be introduced, resulting in a spurious rare male effect. (d) We feel that the standpoint of Bryant et al. (1980) that there is not yet any good evidence for the existence of a rare male effect is not sustained. Positive proof in favour of the existence of the rare male effect is that the effect can be modified by changing only one factor, such as odour. The artifacts just mentioned cannot explain why a rare male effect should be present in the one but absent in the other situation.     

Human mesenchymal stromal cells do not promote recurrence of soft tissue sarcomas in mouse xenografts after radiation and surgery

Background. Mesenchymal stromal cells (MSCs) promote wound healing, including after radiotherapy (RT) and surgery. The use of MSCs in regenerative medicine in the context of malignancy, such as to enhance wound healing post-RT/surgery in patients with soft tissue sarcomas (STSs), requires safety validation. The aim of this study was to determine the effects of human MSCs on STS growth in vitro and local recurrence and metastasis in vivo. Methods. Human primary STS and HT-1080 fibrosarcoma lines were transduced to express luciferase/eGFP (enhanced green fluorescent protein). Sarcoma cells were co-cultured or co-injected with bone marrow–derived MSCs for growth studies. Xenograft tumor models were established with STS lines in NOD/SCID/γ_c^null mice. To emulate a clinical scenario, subcutaneous tumors were treated with RT/surgery prior to MSC injection into the tumor bed. Local and distant tumor recurrence was studied using histology and bioluminescence imaging. Results. MSCs did not promote STS proliferation upon co-culture in vitro, which was consistent among MSCs from different donors. Co-injection of MSCs with sarcoma cells in mice exhibited no significant tumor-stimulating effect, compared with control mice injected with sarcoma cells alone. MSC administration after RT/surgery had no effect on local recurrence or metastasis of STS. Discussion. These studies are important for the establishment of a safety profile for MSC administration in patients with STS. Our data suggest that MSCs are safe in STS management after standard of care RT/surgery, which can be further investigated in early-phase clinical trials to also determine the efficacy of MSCs in reducing morbidity and to mitigate wound complications in these patients.     

Soft anatomy and the affinities of conodonts

Recent claims that conodonts are members of the Craniata or Vertebrata are based in part upon soft tissue features that have been preserved in a small number of specimens. These features include what appear to be radials in the caudal fin and paired structures that have been identified as eye remnants. The evidence for radials is limited, but credible. However, the anatomy of extant cyclostomes suggests that the paired structures are more reasonably interpreted as otic capsules than the remnants of sclerotic eye capsules. Moreover, even if these structures are the remnants of eyes, conodonts might equally well be a sister group to the craniates as a member of that group. Aside from these paired structures, conodont fossils exhibit no features that are suggestive of a cartilaginous skeleton. Given that cyclostome fossils sometimes show evidence of the cartilages of the head, the apparent absence of a similar skeleton in conodont animals calls into question the claim that they are craniates. The simple single chevron shape of conodont myomeres also suggests that they lie outside of the Craniata. All living craniates have double-chevron myomeres as adults, whereas simple myomeres of the conodont type are found in the non-craniate cephalochordates. Thus the available soft tissue evidence suggests that conodonts are best regarded as the sister group of the craniates.     

Geographic variation of the Greater white-toothed shrew (Crocidura russula Hermann, 1780 Mammalia, Soricidae)

A multivariate morphometric study of the Greater white-toothed shrew ( C. russula ) throughout its Palearctic range was carried out to search for patterns of geographic variation within the species boundary. Burnaby's and multiple group principal component analysis allowed the adjustment of raw data with respect to within-sample allometric variation. Multivariate 'size-free'results show a stepped cline with the phenotypical trait reduction and shape change from the eastern to the western Maghreb. Pleistocene fossil mandibles proved to have low phenetic distances with eastern populations (Tunisia, east Algeria) and it is argued that their character set is the primitive condition. The ancestral Mid-Pleistocene shrews lived in a relatively more humid climate. Geo-climatic changes in the north African range during the Quaternary provoked phenetic variation of C. russula and, it can be argued, evolution of the modern western C.r. yebalensis. A historical process can thus be assumed as the main cause of this categorical variation, by segmentation of the species range due to geo-climatic events. Morphometric discontinuity within the C. russula Maghreb range is shown to be congruent with karyological and biochemical studies. Moroccan and Tunisian shrews differ, for example, in NFa chromosomes and electrophoretical traits. A stasipatric process should be invoked to explain categorical variation in the Maghreb range. Colonization and divergence of insular populations results in more or less differentiated geographic races. The populations of Ibiza and Pantelleria are close to the species threshold (Nei's D ≥ 0.1). The process of speciation undergone by the Greater white-toothed shrew results in a complex pattern of geographic variation, including both allopatric and non-allopatric modes.     

Variable egg development of Dinocras spp. (Plecoptera, Perlidae) and the stonefly seed bank theory

1. Temperature dependence of egg development of Dinocras cephalotes (Curtis) (three German and one Norwegian population) and Slovenian D. megacephala (Klapálek) was studied under a constant 14 : 10 light : dark photoperiod and constant temperature ranges of 4–24 °C and 4–18 °C, respectively. D. cephalotes was also incubated under seasonal field conditions; natural daylength and fluctuating temperatures had no modifying effect. 2. Both species have very similar lower threshold temperatures (4 and 3.5 °C, respectively), thermal demand for development (c. 600 degree days) and high dependence of mean incubation period on temperature (exponents of regressions near 1.5). Present data on D. cephalotes agree with the literature on British and Norwegian material of the same species. 3. Development occurs only at cue temperatures above the lower threshold. Cue temperatures range from 6 °C (some D. megacephala) to 14 °C (some D. cephalotes) and vary strongly within and between egg masses of D. cephalotes. Variation is not random, but seems to be genetically determined. 4. The variable temperature response renders study of effects of particular experimental regimes, and comparisons between local populations, difficult. 5. A latitudinal gradient in cue temperatures for development from 6 °C at c. 46 °N to 12 or even 14 °C at c. 61 °N seems to reflect reduced diversity at high latitudes. 6. Average success of spontaneous hatching exceeded 90% between 12 and 20 °C, but declined towards higher and lower temperatures. 7. Unhatched eggs were not dead but in parapause; development at other, higher or lower, temperatures was induced. Spontaneous plus induced hatching success approached 90%. Developing eggs rarely died; most dead eggs were apparently unfertilized. 8. Dormant plecopteran eggs are proposed to form a seed bank in stream bed sediments. Highly successful development after up to 220 days of dormancy was ascertained in Dinocras, and survival for up to 3 years is reported for other Perloidea. 9. Only systellognathan egg morphology provides options for long dormancy; the other plecopteran superfamilies, notably Nemouroidea, follow different strategies.     

Seasonal dynamics of the planktonic community in Lake Druzhby, Princess Elizabeth Land, Eastern Antarctica

1. The temporal abundance and composition of the plankton of a continental Antarctic lake (Lake Druzhby) situated in the Vestfold Hills, Eastern Antarctica was investigated from December 1992 to December 1993. The system was dominated by microbial plankton (cyanobacteria, heterotrophic bacteria and protozoans) with few metazoans. 2. Chlorophyll a concentrations ranged between 0.15 and 1.1 μg l^–1 and showed highest levels from late winter to spring. 3. Heterotrophic bacteria ranged between 75 and 250 × 10⁶ l^–1 with highest abundances in late winter/spring. Mean bacterial biovolumes showed considerable seasonal variation (0.05–0.31 μm³). Largest biovolumes occurred in summer and this was the time of highest community biomass. 4. Heterotrophic nanoflagellates reached highest abundances in late summer (maximum 14 × 10⁵ l^–1). Their mean biovolume also exhibited considerable seasonal variation, ranging between 1.77 and 27.0 μm³, with largest size resulting in community biomass peaking in early summer. Ciliated protozoa were poorly represented and sparse. Phototrophic nanoflagellates were sparse in this lake; instead the phototrophic plankton was dominated by a small rod-shaped cyanobacterium which constituted the largest carbon pool in the system. It was common throughout the year, its biomass peaking in autumn. Its presence is discussed in relation to lake morphometry and light climate. 5. Heterotrophic flagellate grazing rates ranged from 6.78 bacteria cell^–1 day^–1 at 2 °C to 11.8 bacteria cell^–1 day^–1 at 4 °C. They remove around 2% of the bacterial carbon pool per day during summer and winter. 6. Nutrient levels were low and recorded in pulses. Dissolved and particulate organic carbon were also low, usually less than 3 mg l^–1 and 600 μg l^–1, respectively. The carbon pools were derived from autochthonous sources. This lake system is driven by bottom-up forces and lacks top-down control, which fits into the picture currently seen for continental Antarctic lakes.