Predation Risk and Opportunity Cost of Fleeing While Foraging on Plants Influence Escape Decisions of an Insular Lizard

Cost‐benefit models of escape behaviour predict how close a prey allows a predator to approach [flight initiation distance (FID)] based on cost of not fleeing (predation risk) and cost of fleeing (loss of opportunities). Models for FID have been used with some success to predict distance fled (DF). We studied effects of foraging opportunity cost of fleeing and examined differences between age‐sex groups in the omnivorous Balearic Lizard, Podarcis lilfordi. Balearic lizards forage on the ground for invertebrate prey and climb the thistle Carlina corymbosa to forage on its inflorescences. We studied escape behaviour in three experimental groups, with human beings as simulated predators: lizard foraging above ground on C. corymbosa, foraging on the ground away from thistles and on the ground with cut inflorescences. Flight initiation distance was shorter for lizards with cut inflorescences than for (1) lizards above ground due to the greater risk above ground due to conspicuousness of black lizards on yellow flowers; and (2) lizards on ground away from flowers due to the cost of leaving while feeding. The only age‐sex difference was slightly greater FID for adult males than subadults, presumably because larger adult males are more likely to be attacked by predators. Other potential factors affecting this difference are discussed. Experimental group and age‐sex group did not interact for FID or DF. Because lizards foraging on inflorescences above ground fled to the base of the plants to refuge provided by spiny thistle leaves, their DF was shorter than in the other groups, which fled across the ground, usually without entering refuge. DF did not differ between groups on the ground or among age‐sex groups. The predicted shorter DF for lizards with cut inflorescences than on ground without inflorescences did not occur. We hypothesize that the opportunity cost was small due to the abundance of blooming thistles and that DF may be less sensitive to opportunity cost than FID.     

Electrophysiology of a chick neuronal nicotinic acetylcholine receptor expressed in Xenopus oocytes after cDNA injection

Brain nicotinic acetylcholine receptors (nAChRs) are made up of protein subunits that differ from those constituting muscle nAChRs. To characterize the physiological properties of one class of avian brain nicotinic receptor, we injected the nuclei of Xenopus oocytes with full-length cDNAs for the ligand binding (alpha 4) and structural (n alpha) subunits. Injected oocytes had large ACh-induced currents in the microampere range that were insensitive to alpha-bungarotoxin, as expected for neuronal nAChRs. We found that these brain nAChRs incorporate at least two alpha 4 subunits and that their functional properties differ from muscle nAChRs in at least two respects: the elementary conductance is considerably smaller (20 pS), and channels in outside out patches stop functioning within a few minutes.     

Conversion of testosterone to estradiol may not be necessary for the expression of mating behavior in male Syrian hamsters (Mesocricetus auratus)

Male sexual behavior is mediated in part by androgens, but in several species, mating is also influenced by estradiol formed locally in the brain by the aromatization of testosterone. The role of testosterone aromatization in the copulatory behavior of male Syrian hamsters is unclear because prior studies are equivocal. Therefore, the present study tested whether blocking the conversion of testosterone to estradiol would inhibit male hamster sexual behavior. Chronic systemic administration of the nonsteroidal aromatase inhibitor Fadrozole (2.0 mg/kg/day) for 5 or 8 weeks did not significantly increase mount latency or reduce mount frequency, intromission frequency, ejaculation frequency, or anogenital investigation relative to levels shown by surgical controls. However, Fadrozole effectively inhibited aromatase activity, as evidenced by the suppression of estrogen-dependent progesterone receptor immunoreactivity in the male hamster brain. The JZB39 anti-progesterone receptor antibody labeled significantly more neurons in brains of sham-treated hamsters than in brains of Fadrozole-treated hamsters. These data suggest that aromatization of testosterone to estradiol is not necessary for normal mating behavior in Syrian hamsters.     

Characterization of an avian (Gallus gallus domesticus) TCR alpha delta gene locus.

Mammalian TCR delta genes are located in the midst of the TCR alpha gene locus. In the chicken, one large V delta gene family, two D delta gene segments, two J delta gene segments, and one C delta gene have been identified. The TCR delta genes were deleted on both alleles in alpha beta T cell lines, thereby indicating conservation of the combined TCR alpha delta locus in birds. V alpha and V delta gene segments were found to rearrange with one, both or neither of the D delta segments and either of the two J delta segments. Exonuclease activity, P-addition, and N-addition during VDJ delta rearrangement contributed to TCR delta repertoire diversification in the first embryonic wave of T cells. An unbiased V delta 1 repertoire was observed at all ages, but an acquired J delta 1 usage bias occurred in the TCR delta repertoire. The unrestricted combinatorial diversity of relatively complex TCR gamma and delta loci may contribute to the remarkable abundance of gamma delta T cells in this avian representative.     

Cortactin interacts with WIP in regulating Arp2/3 activation and membrane protrusion

BACKGROUND: Modulation of actin cytoskeleton assembly is an integral step in many cellular events. A key regulator of actin polymerization is Arp2/3 complex. Cortactin, an F-actin binding protein that localizes to membrane ruffles, is an activator of Arp2/3 complex. RESULTS: A yeast two-hybrid screen revealed the interaction of the cortactin Src homology 3 (SH3) domain with a peptide fragment derived from a cDNA encoding a region of WASp-Interacting Protein (WIP). GST-cortactin interacted with WIP in an SH3-dependent manner. The subcellular localization of cortactin and WIP coincided at the cell periphery. WIP increased the efficiency of cortactin-mediated Arp2/3 complex activation of actin polymerization in a concentration-dependent manner. Lastly, coexpression of cortactin and WIP stimulated membrane protrusions. CONCLUSIONS: WIP, a protein involved in filopodia formation, binds to both actin monomers and cortactin. Thus, recruitment of actin monomers to a cortactin-activated Arp2/3 complex likely leads to the observed increase in cortactin activation of Arp2/3 complex by WIP. These data suggest that a cortactin-WIP complex functions in regulating actin-based structures at the cell periphery.     

Effects of landscape matrix on population connectivity of an arboreal mammal,Petaurus breviceps

Ongoing habitat loss and fragmentation is considered a threat to biodiversity as it can create small, isolated populations that are at increased risk of extinction. Tree‐dependent species are predicted to be highly sensitive to forest and woodland loss and fragmentation, but few studies have tested the influence of different types of landscape matrix on gene flow and population structure of arboreal species. Here, we examine the effects of landscape matrix on population structure of the sugar glider (Petaurus breviceps) in a fragmented landscape in southeastern South Australia. We collected 250 individuals across 12 native Eucalyptus forest remnants surrounded by cleared agricultural land or exotic Pinus radiata plantations and a large continuous eucalypt forest. Fifteen microsatellite loci were genotyped and analyzed to infer levels of population differentiation and dispersal. Genetic differentiation among most forest patches was evident. We found evidence for female philopatry and restricted dispersal distances for females relative to males, suggesting there is male‐biased dispersal. Among the environmental variables, spatial variables including geographic location, minimum distance to neighboring patch, and degree of isolation were the most important in explaining genetic variation. The permeability of a cleared agricultural matrix to dispersing gliders was significantly higher than that of a pine matrix, with the gliders dispersing shorter distances across the latter. Our results added to previous findings for other species of restricted dispersal and connectivity due to habitat fragmentation in the same region, providing valuable information for the development of strategies to improve the connectivity of populations in the future.     

Similar hypotensive responses to resistance exercise with and without blood flow restriction

Low intensity resistance exercise (RE) with blood flow restriction (BFR) has gained attention in the literature due to the beneficial effects on functional and morphological variables, similar to those observed during traditional RE without BFR, while the effects of BFR on post-exercise hypotension remain unclear. The aim of the present study was to compare the blood pressure (BP) response of trained normotensive individuals to RE with and without BFR. In this cross-over randomized trial, eight male subjects (23.8 ± 4 years, 74 ± 3 kg, 174 ± 4 cm) completed two exercise protocols: traditional RE (3 x 10 repetitions at 70% one-repetition maximum [1-RM]) and low intensity RE (3 x 15 repetitions at 20% 1-RM) with BFR. Blood pressure measurements were performed after 15 min of seated rest (0), immediately after and 10 min, 20 min, 30 min, 40 min, 50 min and 60 min after the experimental sessions. Similar hypotensive effects for systolic BP (SBP) were observed for both protocols (P < 0.05) after exercise, with no differences between groups (P > 0.05) and no statistically significant difference for diastolic BP (P > 0.05). These results suggest that in normotensive trained individuals, both traditional RE and RE with BFR induce hypotension for SBP, which is important to prevent cardiovascular disturbances.     

Intraspecific Concerted Evolution of the rDNA ITS1 in Anopheles farauti Sensu Stricto (Diptera: Culicidae) Reveals Recent Patterns of Population Structure

We examined the intraindividual variation present in the first ribosomal internal transcribed spacer (ITS1) of Anopheles farauti to determine the level of divergence among populations for this important malarial vector. We isolated 187 clones from 70 individuals and found regional variation among four internal tandem repeats. The data were partitioned prior to analysis given the presence of a paralogous ITS2 sequence, called the 5'-subrepeat, inserted in the ITS1 of most clones. A high level of homogenization and population differentiation was observed for this repeat, which indicates a higher rate of turnover relative to the adjacent 'core' region. Bayesian analysis was performed using several substitutional models on both a combined and a partitioned data set. On the whole, the ITS1 phylogeny and geographic origin of the samples appear to be congruent. Some interesting exceptions indicate the spread of variant repeats between populations and the retention of ancestral polymorphism. Our data clearly demonstrate concerted evolution at the intraspecific level despite intraindividual variation and a complex internal repeat structure from a species that occupies a continuous coastal distribution. A high rate of genomic turnover in combination with a high level of sequence divergence appears to be a major factor leading to its concerted evolution within these populations.     

Inhibition of NIH 3T3 cell proliferation by a mutant ras protein with preferential affinity for GDP.

Substitution of asparagine for serine at position 17 decreased the affinity of rasH p21 for GTP 20- to 40-fold without significantly affecting its affinity for GDP. Transfection of NIH 3T3 cells with a mammalian expression vector containing the Asn-17 rasH gene and a Neor gene under the control of the same promoter yielded only a small fraction of the expected number of G418-resistant colonies, indicating that expression of Asn-17 p21 inhibited cell proliferation. The inhibitory effect of Asn-17 p21 required its localization to the plasma membrane and was reversed by coexpression of an activated ras gene, indicating that the mutant p21 blocked the endogenous ras function required for NIH 3T3 cell proliferation. NIH 3T3 cells transformed by v-mos and v-raf, but not v-src, were resistant to inhibition by Asn-17 p21, indicating that the requirement for normal ras function can be bypassed by these cytoplasmic oncogenes. The Asn-17 mutant represents a novel reagent for the study of ras function by virtue of its ability to inhibit cellular ras activity in vivo. Since this phenotype is likely associated with the preferential affinity of the mutant protein for GDP, analogous mutations might also yield inhibitors of other proteins whose activities are regulated by guanine nucleotide binding.