Assessing between-colony oxygen isotope variability in the coral Porites lobata at Clipperton Atoll

The eastern Pacific warm tongue is a region of stable and elevated sea surface temperature (SST) located just north of the equator in the eastern Pacific. This warm water mass is thought to influence the position of the Intertropical Convergence Zone (ITCZ) in the eastern Pacific and to directly influence climate in Central America. To assess the use of corals in the development of paleoclimatic reconstructions in this region, we have developed oxygen isotope (δ¹⁸O) time-series from multiple specimens of the massive coral Porites lobata collected at Clipperton Atoll (10°18′N, 109°13′ W). Six near-monthly δ¹⁸O records from different sized (age) colonies where produced for the interval 1986–1994, and three of these were extended back to 1969. All corals sampled were found to contain numerous fish-grazing skeletal scars (～0.5?mm deep scallop shaped hiatuses). Samples collected at 1?mm intervals showed anomalous ¹⁸O/¹⁶O in the area of a bite scar, with 2 to 2.5?mm sampling intervals (10–12/year) minimizing these effects. Our results show that the average δ¹⁸O disequilibrium offset (vital effect) from equilibrium seawater composition for individual corals can vary by up to 0.4‰. However all δ¹⁸O results suggest that the vital effect offset is constant over time. Similar “offsets” are observed in the tops of old (age=～100?y) and young (age=～10?y) colonies, further suggesting that the biologically mediated vital effect offset does not change as a Porites colony ages. A 6-coral average composite δ¹⁸O record was constructed from 1985–1994 and a 3-coral average δ¹⁸O_anomaly record was constructed from 1969–1994. Regression analysis between monthly SST and the 6 coral average δ¹⁸O records yields an r ² correlation of 0.54 (individual r ²-values ranged from 0.27–0.55). The 3 coral δ¹⁸O_anomaly average record has an even lower correlation to SST, with an r ² of 0.40. Potential causes of the only moderate correlation to SST are explored and we find that inferred salinity effects, fish grazing scars, and slight chronology imperfections have all contributed to a reduced correlation to SST. Nevertheless, all El Niño events in this time period appear to be recorded by coral skeletal δ¹⁸O.     

Histidine residue modification inhibits binding of murine β nerve growth factor to its receptor

The reaction of the β subunit of murine nerve growth factor (NGF) with diethylpyrocarbonate (DEP) results in the quantitative modification of histidine residues and the loss of binding to rabbit superior cervical ganglia microsomes. No conformational changes accompanied the conversion as judged by fluorescence spectra. Hydroxylamine converted the carbethoxy derivatives back to the unmodified imidazoles and simultaneously restored the capacity of NGF to bind to its receptor. Modification of des (1–9) NGF, from which His-4 and His-8 have been quantitatively removed, results in the same loss in binding activity, suggesting that His-75 and/or His-84 may play an important role in hormone-receptor interactions.     

Social complexity and the fractal structure of group size in primate social evolution

Compared to most other mammals and birds, anthropoid primates have unusually complex societies characterised by bonded social groups. Among primates, this effect is encapsulated in the social brain hypothesis: the robust correlation between various indices of social complexity (social group size, grooming clique size, tactical behaviour, coalition formation) and brain size. Hitherto, this has always been interpreted as a simple, unitary relationship. Using data for five different indices of brain volume from four independent brain databases, we show that the distribution of group size plotted against brain size is best described as a set of four distinct, very narrowly defined grades which are unrelated to phylogeny. The allocation of genera to these grades is highly consistent across the different data sets and brain indices. We show that these grades correspond to the progressive evolution of bonded social groups. In addition, we show, for those species that live in multilevel social systems, that the typical sizes of the different grouping levels in each case coincide with different grades. This suggests that the grades correspond to demographic attractors that are especially stable. Using five different cognitive indices, we show that the grades correlate with increasing social cognitive skills, suggesting that the cognitive demands of managing group cohesion increase progressively across grades. We argue that the grades themselves represent glass ceilings on animals' capacity to maintain social and spatial coherence during foraging and that, in order to evolve more highly bonded groups, species have to be able to invest in costly forms of cognition.     

Stay or stray? Evidence for alternative mating strategy phenotypes in both men and women

In all comparative analyses, humans always fall on the borderline between obligate monogamy and polygamy. Here, we use behavioural indices (sociosexuality) and anatomical indices (prenatal testosterone exposure indexed by 2D : 4D digit ratio) from three human populations to show that this may be because there are two distinct phenotypes in both sexes. While males are more promiscuous and display higher prenatal testosterone exposure than females overall, our analyses also suggest that the within-sex variation of these variables is best described by two underlying mixture models, suggesting the presence of two phenotypes with a monogamous/promiscuous ratio that slightly favours monogamy in females and promiscuity in males. The presence of two phenotypes implies that mating strategy might be under complex frequency-dependent selection.     

Secretion of glucagon and insulin in hypophysectomized rats: effect of tolbutamide.

Normal and hypophysectomized (hypox) rats, fed ad libitum, received intraperitoneal injections of tolbutamide (75 mg/kg/day) or of saline for 6 weeks. 24 h after the last injection, blood samples were taken for glucose, insulin and glucagon determinations. In normal rats, tolbutamide treatment did not alter serum glucose, insulin and glucagon, although it suppressed the secretion of insulin and glucagon by the pancreatic islets. In hypox rats, tolbutamide decreased serum glucose and insulin, elevated serum glucagon and stimulated the secretion of glucagon, but not that of insulin by the pancreatic islets. In addition, tolbutamide treatment increased the glucagon response to arginine in normal, but not in hypox rats. The serum glucose response to arginine was decreased by tolbutamide treatment and by hypophysectomy and, thus, appeared independent of the glucagon rise or preexisting glucagon level. We conclude that tolbutamide treatment decreased the secretion of glucagon and insulin in normal rats and stimulated that of glucagon in hypox rats, perhaps because of the low levels of insulin in the serum and in the pancreas of the latter. Our results are compatible with the hypothesis that the pancreatic action of tolbutamide is influenced by the pituitary.     

Size and structure of freely forming conversational groups

Data from various settings suggest that there is an upper limit of about four on the number of individuals who can interact in spontaneous conversation. This limit appears to be a consequence of the mechanisms of speech production and detection. There appear to be no differences between men and women in this respect, other than those introduced by women’s lighter voices. Robin Dunbar, formerly Professor of BiologicalAnthropology at University College London, is currently Professor of Psychology at the University of Liverpool, where he carries out research on the behavior and ecology of human and nonhuman primates. Neil Duncan M.D. has recently qualified as a medical practitioner. Dan Nettle is carrying out doctoral research on the evolution of language.     

The site of active uptake of atmospheric water in larvae of Tenebrio molitor

Larvae starved and desiccated for 8 days will then take up water from 93% r.h., the gain ceasing by 7 days. The rate and amount of uptake were the same in those starved at 0% r.h. as in those starved at 53% r.h. Tying off the last abdominal segment prevents uptake while tying off the first abdominal segment allowed one-third as much gain as controls. This supports the theory that active uptake of atmospheric water is by way of the rectum and not the body cuticle. Because of the time taken to reach equilibrium, of the same uptake after exposure at 53% as after 0% r.h., and of a large overshoot in uptake, it is suggested that the phenomenon in this species is a by-product of drying the faeces and not a vital aspect of the physiology of water balance.