No abstract

At present, it is well known that populations of human bone marrow stromal cells (HBMSCs) can differentiate into osteoblasts and produce bone. However, the amount of cells with osteogenic potential that is ultimately obtained will still be dependent on both patient physiological status and culture system. In addition, to use a cell therapy approach in orthopedics, large cell numbers will be required and, as a result, knowledge of the factors affecting the growth kinetics of these cells is needed. In the present study we investigated the effect of dexamethasone stimulation on the in vivo osteogenic potential of HBMSCs. After a proliferation step, the cells were seeded and cultured on porous calcium phosphate scaffolds for 1 week, and then subcutaneously implanted in nude mice for 6 weeks, in order to evaluate their in vivo bone-forming ability. Furthermore, the effect of donor age on the proliferation rate of the cultures and their ability to induce in vivo bone formation was studied. In 67% of the assayed patients (8 of 12), the presence of dexamethasone in culture was not required to obtain in vivo bone tissue formation. However, in cultures without bone-forming ability or with a low degree of osteogenesis, dexamethasone increased the bone-forming capacity of the cells. During cellular proliferation, a significant age-related decrease was observed in the growth rate of cells from donors older than 50 years as compared with younger donors. With regard to the effect of donor age on in vivo bone formation, HBMSCs from several donors in all age groups proved to possess in vivo osteogenic potential, indicating that the use of cell therapy in the repair of bone defects can be applicable irrespective of patient age. However, the increase in donor age significantly decreased the frequency of cases in which bone formation was observed.

Host discrimination, i.e. the ability to distinguish unparasitized hosts from parasitized ones, and to reject the latter for egg laying is present in many parasitic wasp species. This property is classically considered as an example of contest competition, and is supposed to have a number of functions. However, different species do not react to each other's marks and lay eggs in hosts parasitized by the other species. Apparently the marks used for recognition are specific.Multiparasitization is the best strategy when hosts are scarce and the egg supplies of the parasitoids are not limited. Interspecific host discrimination is not an ESS.Superparasitization within one species would have selective advantage if the number of unparasitized hosts is small and the wasp has a reasonable chance to lay her egg in a host that is not parasitized by herself, and if the chance for her offspring to survive the competitive battle with the first parasitoid larva is not too small. This is shown to be the case.However, marks are not individual and wasps cannot distinguish hosts parasitized by themselves from those parasitized by others. The hypothesis is tested that the egg laying strategy (i.e. the decision to superparasitize) of wasps is dependent on the number of conspecifics that is searching simultaneously for hosts, since this determines the chance that a parasitized host encountered by a wasp is parasitized by herself.It is shown that host discrimination cannot be regarded as a case of contest competition. Other aspects of superparasitization, related to interference and population regulation, sex allocation and encapsulation are briefly discussed.

Food uptake of Drosophila melanogaster larvae was limited by removing larvae from the food after different periods. Some of these larvae were transferred to culture jars ‐without food to study further development. The minimal feeding period necessary to complete development was 48 hours at 25°C; the larvae must have reached the third instar. Mortality of larvae with feeding periods of 40 hours or more was low. Pupa***rium formation was retarded only in larvae with a feeding period of 48 hours. Sex ratio of emerging adults was not influenced by underfeeding. Weight of adults was taken twice: alive and dried. Females were always somewhat heavier than males. Underfeeding may produce adults with weights only 1/4 to 1/5 of the normal weight. The larvae removed from the food at different intervals were weighed alive and dried, and a growth curve was thus constructed. Increase in live weight was observed until 72 hours after hatching, whereas dry weight reached its maximum after 84 hours. The difference is due to water loss preceding puparium formation. During the pupal stage a slight decrease in dry weight is noted, presumably caused by metabolism. During the starvation period between removal from the food and puparium formation, a loss of weight is found which depends on the duration of the starvation period. Zusammenfassung FRAßDAUER, WACHSTUM UND VERPUPPUNG BEI LARVEN VON DROSOPHILA MELANOGASTER. 1. Ein Experiment wird beschrieben, bei dem die Nahrungsaufnahme von Drosophila‐Larven nach verschiedenen Zeiträumen unterbrochen wurde. Die Larven winden teils auf einen Agarboden ohne Nahrung überführt und teils gewogen, getrocknet und wieder gewogen. 2. Die Dauer der verschiedenen Entwicklungsstadien war bei ungestörten Larven ungefähr dieselbe, wie sie Demerec (1950) angibt. Nur der Beginn der Puparienbildung lag etwas früher. Wenn die Larven nach der zweiten Häutung auf den Agarboden ohne Nahrung überführt wurden, gingen Larven, welche nur 48 Stunden gefressen hatten, etwas später zur Puparienbildung über. Die Entwicklung war nicht verzögert bei Larven, welche länger gefressen hatten. 3. Nur Larven, welche mindestens 48 Stunden gefressen hatten, verpuppten sich. Sie müssen also die zweite Häutung vollzogen haben. Es wurde, keine größere prozentuelle Zunahme von Verpuppungen gefunden, wenn die Larven länger gefressen hatten. Die Mortalität der Puppen war etwas größer, wenn die Tiere nur 48 oder 54 Stunden fressen konnten. 4. Das Geschlechterverhältnis der schlüpfenden Imagines wurde von der Dauer des Aufenthalts auf dem Nährboden nicht beeinflußt. 5. Der Gewichtszunahmckoeffizient der Larven, c = 1/gt · dg/dt, blieb bis 54 Stunden derselbe. Danach nahm er ab und wurde ach 84 Stunden null. 6. Das Lebendgewicht der Larven war nach 72 Stunden am höchsten, während das Trockengewicht noch bis zu 84 Stunden zunahm. Dieser Unterschied wurde durch den Wasserverlust der Larven verursacht, welcher der Puparienbildung vorausgeht. Während der Puparienbildung und der ersten 12 Stunden des Puppenstadiums findet weiterer Wasserverlust...

Ovipositing females of the cynipid waspPseudeucoila bochei discriminate between parasitized and unparasitized hosts, which results in a far more uniform distribution of eggs over the hosts than would be obtained if oviposition were random (Fig. 1,a -f).For the description of the distributions a few models were worked out, which rest on the assumption that the hosts are probed at random. The total number of effective probes made in a larva during the experiment is a random variable with a Poisson distribution and an expectation λ. The chance that at a certain probe an egg will be laid (δ) is dependent on the number of eggs present (j); 1=δ<δ≧δ≧δ.... In model I it was assumed that the female had only the ability to distinguish parasitized from unparasitized hosts. The chance that an egg will be laid in an unparasitized host when it is probed, δ, is considered to be equal to 1, while δ=δ=...=δ <1 (Fig. 2, 1,a -f). When the mean number of eggs present in a host was larger than about 1.1, this model did not describe the distribution of eggs satisfactorily (Fig. 3).It seemed that the ovipositing female is not only able to distinguish parasitized from unparasitized hosts, but also to distinguish thenumber of eggs present in a host. In model II it was assumed that the wasp could distinguish between hosts with 0, 1, and 2 or more eggs: the chance that an egg would be laid in a host containing 2, 3, 4, ... eggs was, hence, the same in this model δ<δ=δ=...=δ (Fig. 2, 1,c,e ,f). This model described the distributions of eggs much better (Figs. 4 and 5), but at mean numbers of eggs per host above 2 it was apparently inadequate.Two other models were then tried, in which the chance δ that an egg would be laid in a host decreased with the number of eggs already present (j). In model III (Fig. 2) the chance decreased according to the function δ =δ/j (δ=1, δ<1). Fig. 1,d ,e,f , gives some examples. In model IV the chance δ =δ (δ=1, δ<1) (see Fig. 1,d ,e,f ).From the comparison of Figs. 6 and 7 it is clear that model IV gives the best description of the distributions of eggs found.The value of these models is discussed, and plans for both an approach through experimental analysis and simulation models are given. In an Appendix the mathematical derivation of the models is presented.