Surface-bound Immunoglobulin as a Marker of B Lymphocytes in Man

IMMUNOLOGICAL reactions in many species depend on two functionally different types of small lymphocytes, thymus-derived T lymphocytes and bone marrow-derived B lymphocytes¹. In the mouse, the θ antigen is a marker for T lymphocytes, while membrane-bound Ig is found on θ-negative lymphocytes². This has raised the question whether the presence of surface-bound Ig³ may be regarded as a marker for B lymphocytes. We have obtained data indicating that this is the case with human lymphocytes.     

What factors contribute to an ownership advantage?

In most taxa, owners win fights when defending a territory against intruders. We calculated effect sizes for four factors that potentially contribute to an 'owner advantage'. We studied male fiddler crabs Uca mjoebergi, where owners won 92% of natural fights. Owners were not more successful because they were inherently better fighters (r=0.02). There was a small effect (r=0.18) of the owner's knowledge of territory quality (food availability) and a medium effect (r=0.29) of his having established relations with neighbours (duration of active tenure), but neither was statistically significant. There was, however, a significant effect due to the mechanical advantage the owner gained through access to the burrow during fights (r=0.48, p<0.005).     

New Australopithecus robustus fossils and associated U-Pb dates from Cooper's Cave (Gauteng, South Africa)

Australopithecus robustus is one of the best represented hominin taxa in Africa, with hundreds of specimens recovered from six fossil localities in the Bloubank Valley area of Gauteng Province, South Africa. However, precise geochronological ages are presently lacking for these fossil cave infills. In this paper, we provide a detailed geological background to a series of hominin fossils retrieved from the newly investigated deposit of Cooper's D (located partway between Sterkfontein and Kromdraai in the Bloubank Valley), including uranium-lead (U-Pb) ages for speleothem material associated with A. robustus. U-Pb dating of a basal speleothem underlying the entire deposit results in a maximum age of 1.526 (±0.088) Ma for Cooper's D. A second U-Pb date of ca. 1.4 Ma is produced from a flowstone layer above this basal speleothem; since this upper flowstone is not a capping flowstone, and fossiliferous sediments are preserved above this layer, some of the hominins might be slightly younger than the calculated age. As a result, we can broadly constrain the age of the hominins from Cooper's D to between 1.5 and approximately 1.4 Ma. Extinct fauna recorded in this comparatively young deposit raise the possibility that the Bloubank Valley region of South Africa represented a more stable environmental refugium for taxa relative to tectonically more active East Africa. The sediments of the deposit likely infilled rapidly during periods when arid conditions prevailed in the paleoenvironment, although it is unclear whether sediment deposition and bone deposition were necessarily contemporaneous occurrences. We reconstruct the paleoenvironment of Cooper's D as predominantly grassland, with nearby woodlands and a permanent water source. The hominin teeth recovered from Cooper's D are all from juveniles and can be confidently assigned to A. robustus. In addition, two juvenile mandibular fragments and an adult thoracic vertebra are tentatively attributed to A. robustus.     

Delayed setting of the photoperiodic response in recombinant clones of the aphid species Sitobion avenae

1. To explore the possible causes of apparent changes in reproductive mode from obligate to cyclical parthenogenesis over time in recombinant clones of the aphid Sitobion avenae Fabricius, all F1 progenies from various crosses were tested for several consecutive years for sexual morph production, after several weeks' exposure to a short photoperiod. 2. Variable proportions of the F1 progenies from selfing and outcrossing holocyclic clones did not produce mating females when induction was attempted in the year of hatching, but only after further induction, the following year or after. This ‘delayed setting of the photoperiodic response’ (DSPR) was much stronger in recombinants from crosses involving only clones from oceanic regions than in those involving one clone from a region with a continental climate. 3. F1 progenies resulting from crosses between one holocyclic and one intermediate clone did not show DSPR. It appeared again in the F2. 4. DSPR preferentially affected the latest hatched clones in a given progeny. 5. This phenomenon is neither an experimental artefact nor as a result of clone contamination. It appears to be because of a genetically controlled quantitative trait affecting the length of the ‘interval timer’, and may represent an adaptation of holocyclic aphid clones from oceanic regions to unpredictable winter climates.     

Interspecific assistance: fiddler crabs help heterospecific neighbours in territory defence

Theory predicts that territory owners will help established neighbours to repel intruders, when doing so is less costly than renegotiating boundaries with successful usurpers of neighbouring territories. Here, we show for the first time, to our knowledge, cooperative territory defence between heterospecific male neighbours in the fiddler crabs Uca elegans and Uca mjoebergi. We show experimentally that resident U. elegans were equally likely to help a smaller U. mjoebergi or U. elegans neighbour during simulated intrusions by intermediate sized U. elegans males (50% of cases for both). Helping was, however, significantly less likely to occur when the intruder was a U. mjoebergi male (only 15% of cases).     

Keeping up appearances: male fiddler crabs wave faster in a crowd

Courtship displays are often energetically and temporally costly as well as highly conspicuous to predators. Selection should therefore favour signalling tactics that minimize courtship costs while maintaining or increasing signal attractiveness. In fiddler crabs, males court females by waving their one greatly enlarged claw in a highly conspicuous and costly display. Here, we investigate whether courting males adjust their wave rate, and therefore the cost of courtship, to the current level of competition. We show that display rate increases as competition increases and that when competition is removed, males reduce their display rate by 30 per cent. These results suggest that male fiddler crabs actively reduce the cost of courtship by adjusting their wave rate in response to the immediate level of competition.     

Why do ovigerous females approach courting males? Female preferences and sensory biases in a fiddler crab

Perceptual biases explain the origin and evolution of female preference in many species. Some responses that mediate mate choice, however, may have never been used in nonmating contexts. In the fiddler crab, Uca mjoebergi, mate‐searching females prefer faster wave rates and leading wave; however, it remains unclear whether such responses evolved in a mating context (i.e., the preference has effect on the fitness of the female and her offspring that arise from mating with a particular male) or a nonmating contexts (i.e., a female obtains direct benefits through selecting the male with a more detectable trait). Here, we compared the preferences of mate‐searching with those of ovigerous females that are searching for a burrow and do not concern about male “quality.” Results showed that as both mate‐searching and ovigerous females preferentially approached robotic males with faster wave rates. This suggests that wave rate increases detectability/locatability of males, but the mating preference for this trait is unlikely to evolve in the mating context (although it may currently function in mate choice), as it does not provide fitness‐related benefit to females or her offspring. Wave leadership, in contract, was attractive to mate‐searching females, but not ovigerous females, suggesting that female preference for leadership evolves because wave leadership conveys information about male quality. We provide not only an empirical evidence of sensory biases (in terms of the preference for faster wave), but the first experimental evidence that mating context can be the only selection force that mediates the evolution of male sexual traits and female preference (in terms of the preference for leading wave).