Can there be more predators than prey?

The theorem that there can be no more species in a habitat than the kinds of resources on which they depend is discussed. It is shown that two predators can be limited by different stages of the life cycle of the same prey species, and that two herbivores can be limited if they depend on different parts of the same plant. This leads to the question, in what circumstances can two measurable quantities, x₁ and x₂, be regarded as different resources for the purposes of the theorem, and it is shown that if x₁ is functionally dependent on x₂, so that a knowledge of one value at any time specifies the other, then they are the same resource, but that otherwise they can act as different resources, even if they are highly correlated. It is shown that variables such as climate and invading species, which are not themselves influenced by the densities of the species to be limited, are irrelevant in determining the number of resources or limiting factors present.     

Should the brain be regarded as a computer?

In recent years analogies between thinking processes and computer mechanisms have been pointed out. There exist, however, also considerable differences between higher cerebral activities and computers. It seems, therefore, hazardous to consider the human brain exclusively as a computer.     

Complex memories in honeybees: can there be more than two?

Foraging honeybees are likely to learn visual and chemical cues associated with many different food sources. Here, we explore how many such sources can be memorized and recalled. Marked bees were trained to visit two (or three) sugar feeders, each placed at a different outdoor location and carrying a different scent. We then tested the ability of the bees to recall these locations and fly to them, when the training scents were blown into the hive, and the scents and food at the feeders were removed. When trained on two feeder locations, each associated with a different scent, the bees could correctly recall the location associated with each scent. However, this ability broke down when the number of scents and feeder locations was increased to three. Performance was partially restored when each of the three training feeders was endowed with an additional cue, namely, a distinct colour. Our results suggest that bees can recall a maximum of two locations when each is associated with a different scent. However, this number can be increased if the scent cues are augmented by visual cues. These findings have implications for the ways in which associations are established and laid down in honeybee memory.     

The HIN-200 family: more than interferon-inducible genes?

The HIN-200 family was initially grouped together based on their hemopoietic expression, interferon-inducibility, nuclear localization, and characteristic 200 amino-acid domains. In this review, we performed a comprehensive search of genome databases and determined the location of previously characterized and predicted genes within the human, mouse, and rat HIN-200 loci. Several novel proteins were predicted in the mouse and rat. We also discuss recent advances in our understanding of this family of proteins and highlight the most important findings. In addition to a role in interferon biology, there is now good evidence supporting a role for these proteins as regulators of cell proliferation and differentiation. The activity of HIN-200 proteins is not restricted to the hemopoietic system as they are expressed and can function in a variety of other cells and tissues. The importance of HIN-200 proteins in disease now is beginning to be understood as they appear to be involved in autoimmunity and may act as tumor suppressor proteins.     

Should smears in a colposcopy clinic be taken after the application of acetic acid?

Conventionally, cervical smears obtained during a colposcopic examination are taken before the application of acetic acid. However, this occasionally precipitates bleeding and removes epithelium from the cervix, particularly in the presence of cervical pathology, making colposcopic evaluation difficult. This study examined the possibility of deferring the smear until the end of the colposcopic examination. In the first part of the study, the cytologic results on cervical samples taken from the same patient before and after the application of acetic acid were compared. In the second part of the study, only one smear was taken per patient (either before or after colposcopic assessment) to eliminate the possibility that the taking of the first smear affected the quality of the second. The results of both parts of the study showed that deferring the smear until after the application of acetic acid leads to an unacceptably high rate of unsatisfactory and falsely negative smears. Thus, deferring the taking of the cervical smear until after the colposcopic evaluation results in a poor cytologic evaluation, although it might facilitate the colposcopic examination in some patients.     

Dinophysis norvegica (Dinophyceae), more a predator than a producer?

Several studies have proved that some Dinophysis species are capable of ingesting particulate organic matter besides of being photosynthetic, a form of nutrition termed mixotrophy. Phagotrophy may be an important aspect of the life history of the genus Dinophysis and the key to understand its ecology. We used modern techniques coupling flow cytometry and acidotropic probes to detect and score food vacuolated Dinophysis norvegica cells in natural samples. In addition, feeding experiments were conduced under controlled conditions to observe if D. norvegica would grow feeding on the cryptophyte Teleaulax amphioxeia. The results of the field observations showed a frequency of phagotrophy between 25 and 71% in a natural D. norvegica population from the Baltic Sea, which is higher than previous reports (1–20%). Although molecular methods have proved that the kleptoplastids of the D. norvegica from the Baltic Sea are from T. amphioxeia, the laboratory experiments showed that the presence of T. amphioxeia in the cultures did not enhance the survival rate of D. norvegica neither in phototrophic nor in heterotrophic conditions. We suggest that the D. norvegica Kleptoplats are obtained through a heterotrophic or mixotrophic protist, which have been feeding on cryptophytes, as it has recently been shown for Dinophysis acuminata. Our main conclusion is that D. norvegica, and probably all other species from the genus Dinophysis, is mainly phagotrophic and feeds on a larger prey than T. amphioxeia. Autotrophy through kleptoplastidy would be a secondary feature used as a complementary or short-term survival strategy.