Total Internal Reflection Accounts for the Bright Color of the Saharan Silver Ant

The Saharan silver ant Cataglyphis bombycina is one of the terrestrial living organisms best adapted to tolerate high temperatures. It has recently been shown that the hairs covering the ant’s dorsal body part are responsible for its silvery appearance. The hairs have a triangular cross-section with two corrugated surfaces allowing a high optical reflection in the visible and near-infrared (NIR) range of the spectrum while maximizing heat emissivity in the mid-infrared (MIR). Those two effects account for remarkable thermoregulatory properties, enabling the ant to maintain a lower thermal steady state and to cope with the high temperature of its natural habitat. In this paper, we further investigate how geometrical optical and high reflection properties account for the bright silver color of C. bombycina. Using optical ray-tracing models and attenuated total reflection (ATR) experiments, we show that, for a large range of incidence angles, total internal reflection (TIR) conditions are satisfied on the basal face of each hair for light entering and exiting through its upper faces. The reflection properties of the hairs are further enhanced by the presence of the corrugated surface, giving them an almost total specular reflectance for most incidence angles. We also show that hairs provide an almost 10-fold increase in light reflection, and we confirm experimentally that they are responsible for a lower internal body temperature under incident sunlight. Overall, this study improves our understanding of the optical mechanisms responsible for the silver color of C. bombycina and the remarkable thermoregulatory properties of the hair coat covering the ant’s body.     

Directional fixation of mutations in vertebrate evolution

Summary We have made pairwise comparisons between the coding sequences of 21 genes from coldblooded vertebrates and 41 homologous sequences from warm-blooded vertebrates. In the case of 12 genes, GC levels were higher, especially in third codon positions, in warm-blooded vertebrates compared to cold-blooded vertebrates. Six genes showed no remarkable difference in GC level and three showed a lower level. In the first case, higher GC levels appear to be due to a directional fixation of mutations, presumably under the influence of body temperature (see Bernardi and Bernardi 1986b). These GC-richer genes of warm-blooded vertebrates were located, in all cases studied, in isochores higher in GC than those comprising the homologous genes of cold-blooded vertebrates. In the third case, increases appear to be due to a limited formation of GC-rich isochores which took place in some cold-blooded vertebrates after the divergence of warm-blooded vertebrates. The directional changes in the GC content of coding sequences and the evolutionary conservation of both increased and unchanged GC levels are in keeping with the existence of compositional constraints on the genome.     

The SV40 TC-II(kappa B) enhanson binds ubiquitous and cell type specifically inducible nuclear proteins from lymphoid and non-lymphoid cell lines.

We have characterized the complexes resulting from the specific binding in vitro of proteins present in nuclear extracts of several lymphoid and non-lymphoid cell lines to the TC-I and TC-II sequences of the simian virus 40 (SV40) enhancer. No proteins could be detected, binding selectively to the TC-I sequence, but two proteins TC-IIA and TC-IIB were identified interacting specifically with both the TC-II/kappa B enhanson, 5'-GGAAAGTCCCC-3' (important for the activity of the SV40 enhancer in vivo), and with the related H-2Kb enhanson, 5'-TGGGGATTCCCCA-3'. The binding of these two proteins to mutated TC-II enhansons correlates with the effect of these mutations in vivo, suggesting that both proteins may be important for SV40 enhancer activity. The TC-IIA binding activity was present in nuclear extracts of mature lymphoid B cells and was increased in pre-B cell nuclear extracts by lipopolysaccharide (LPS) and cycloheximide treatment. Furthermore, complex formation between the TC-IIA protein and the TC-II enhanson was efficiently competed by the kappa B motif from the kappa chain enhancer, indicating that TC-IIA is the NF-kappa B factor or a closely related protein. However, in contrast to previous reports, a TC-IIA/NF-kappa B-like protein whose properties could not be distinguished from those of the TC-IIA protein present in lymphoid B cells, was found in nuclear extracts of several untreated non-lymphoid cell lines, notably of HeLa cells, but not of undifferentiated F9 embryonal carcinoma (EC) cells [F9(ND)]. The TC-IIA binding activity which was moderately increased in HeLa cell nuclear extracts by 12-O-tetradecanoylphorbol-13-acetate (TPA) and/or cycloheximide treatment could be induced in nuclear extracts of F9(ND) cells by cycloheximide, but not by TPA. Moreover, the TC-IIA binding activity could be induced in cytosolic fractions from F9(ND) cells by treatment with deoxycholate, indicating that these cells contain an inhibitor protein similar to the previously described NF-kappa B inhibitor, I kappa B. The second TC-II enhanson binding protein, TC-IIB, which could be clearly distinguished from the TC-IIA/NF-kappa B-like protein, by a number of differential properties, resembles the previously described KBF1/H2TF1 protein as it binds with a higher affinity to the H-2Kb enhanson than to the TC-II/kappa B enhanson, and its pattern of methylation interference on the H-2Kb and TC-II/kappa B enhansons is identical to that reported for the KBF1/H2TF1 protein.(ABSTRACT TRUNCATED AT 400 WORDS)