Reproductive and Mating Success in the Small-Mouthed Salamander (Ambystoma texanum) Estimated via Microsatellite Parentage Analysis

Bateman’s principles of sexual selection predict that the sex with “cheaper” gametes may maximize reproductive efforts by mating multiply and so display greater positive covariance between reproductive and mating success. We conducted a semi-controlled breeding experiment to genetically quantify sexual selection in adult Ambystoma texanum, a sexually monomorphic salamander with simple courtship behaviors. We used four polymorphic microsatellite loci to genotype 57 adults enclosed in a breeding wetland and compared their multilocus profiles to that of 862 embryos collected from the enclosure. The molecular data were used to assign parentage, investigate the mating system, and measure sexual selection intensity. Parentage analyses indicated 36% of dams and 93% of sires were genetically sampled via their gametes but physically unsampled, suggesting that a large number of breeders over-wintered within the enclosure and/or some females released into the enclosure were already inseminated. We used the genetic data to generate estimates of individual reproductive and mating success and we interpret these in light of salamander behavior and sexual selection theory. The incidence of multiple mating in females (86%) was considerably higher than in males (32%) and the standardized variance in mating success was significantly greater in females. The correlations between reproductive and mating success were significant and of similar magnitude between the sexes, indicating that both sexes increased reproductive success through increased mating success. This pattern may be a function of differential opportunities for mating success between the sexes. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Impacts of the invasive fungus Austropuccinia psidii (myrtle rust) on three Australian Myrtaceae species of coastal swamp woodland

Exotic fungal pathogens can substantially affect individuals and populations of susceptible native plant species, potentially resulting in changes in community structure and composition. Austropuccinia psidii (myrtle rust) is a pathogenic fungus native to South America that affects species in the plant family Myrtaceae. The pathogen was introduced accidentally to Australia and first detected in NSW in April 2010. Ecological impacts have been poorly studied in the native range of A. psidii and even less in its Australian introduced range. In order to assess the potential impact of A. psidii on coastal swamp woodland, two glasshouse experiments were conducted using three co‐occurring species: Melaleuca quinquenervia, Leptospermum laevigatum and Baeckea linifolia. Plants of each species were grown individually (Experiment 1) and in mixed species assemblages (Experiment 2), with half inoculated with A. psidii and the other half remaining as controls. Infection level was assessed and impact on seedling survival and growth recorded. In both experiments L. laevigatum and M. quinquenervia seedlings were heavily infected and showed high degrees of susceptibility with negative effects on growth (height, biomass and number of leaves). In contrast, no B. linifolia seedling presented visible symptoms of disease, although seedlings showed reduced growth. Melaleuca quinquenervia seedlings had greater infection levels and suffered greater growth reductions than L. laevigatum in both experiments. However, there was no significant difference in the relative abundance of the three species in the mixed‐species experiment. This study provides a better understanding of the potential impacts of A. psidii in this vegetation community and has significant implications for the conservation and management of Australian Myrtaceae‐dominated plant communities generally.     

Deciduousness in a seasonal tropical forest in western Thailand: interannual and intraspecific variation in timing, duration and environmental cues

Seasonal tropical forests exhibit a great diversity of leaf exchange patterns. Within these forests variation in the timing and intensity of leaf exchange may occur within and among individual trees and species, as well as from year to year. Understanding what generates this diversity of phenological behaviour requires a mechanistic model that incorporates rate-limiting physiological conditions, environmental cues, and their interactions. In this study we examined long-term patterns of leaf flushing for a large proportion of the hundreds of tree species that co-occur in a seasonal tropical forest community in western Thailand. We used the data to examine community-wide variation in deciduousness and tested competing hypotheses regarding the timing and triggers of leaf flushing in seasonal tropical forests. We developed metrics to quantify the nature of deciduousness (its magnitude, timing and duration) and its variability among survey years and across a range of taxonomic levels. Tree species varied widely in the magnitude, duration, and variability of leaf loss within species and across years. The magnitude of deciduousness ranged from complete crown loss to no crown loss. Among species that lost most of their crown, the duration of deciduousness ranged from 2 to 21 weeks. The duration of deciduousness in the majority of species was considerably shorter than in neotropical forests with similar rainfall periodicity. While the timing of leaf flushing varied among species, most (∼70%) flushed during the dry season. Leaf flushing was associated with changes in photoperiod in some species and the timing of rainfall in other species. However, more than a third of species showed no clear association with either photoperiod or rainfall, despite the considerable length and depth of the dataset. Further progress in resolving the underlying internal and external mechanisms controlling leaf exchange will require targeting these species for detailed physiological and microclimatic studies.     

Tn916 insertion mutagenesis in Escherichia coli and Haemophilus influenzae type b following conjugative transfer.

Transposon Tn916 was shown to be capable of direct conjugative transfer in broth and membrane matings between strains of Escherichia coli K12 and between E. coli K12 and Haemophilus influenzae type b. Only Tn916 was transferred, but Tn916 donor ability was not itself inheritable by the recipients and seemed to be associated with the presence of Tn916 on a non-conjugative pBR322-derived vector in the original donor strain. Transfer of Tn916 by conjugation was found to be an efficient method for producing insertion mutations in the chromosome of recipient cells. Although such insertions were unstable when the cells were grown under non-selective conditions, it was possible to show that over 40% of the isolated Tn916 insertions in the chromosome of E. coli K12 were in gene(s) concerned with histidine biosynthesis, implying that there is a partial hot-spot for Tn916 insertion on the E. coli K12 chromosome. When a strain of H. influenzae type b was used as a recipient, out of approximately 1500 transconjugants tested, two mutants were isolated with insertions in genes controlling the expression of iron-regulated transferrin-binding proteins. These mutants constitutively produced major 76 kDa and minor 90 kDa proteins which bound transferrin, even when grown under iron-sufficient conditions. Tn916 insertion mutagenesis, following transfer by conjugation, is a convenient method for isolating mutations in genes concerned with iron acquisition by this important human pathogen.     

Cyclothiazide Unmasks an AMPA-Evoked Release of Arachidonic Acid from Cultured Striatal Neurones

Abstract: The joint, but not independent, activation of α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and metabotropic glutamate receptors induces liberation of arachidonic acid from cultured mouse striatal neurones. We examined whether blocking AMPA receptor desensitisation with cyclothiazide would modify this response. Cyclothiazide strongly potentiated the combined AMPA/(1 S ,3 R )-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD)-evoked release of arachidonic acid (EC₅₀ of ∼7 µ M ) but did not modulate the basal, ACPD, or NMDA response. The enhanced liberation of arachidonic acid, observed in the presence of cyclothiazide, was due to the appearance of a genuine AMPA response that was independent of an associative activation of metabotropic receptors. The potentiated and nonpotentiated AMPA responses were inhibited by both competitive [2,3-dihydroxy-6-nitro-7-sulphamoylbenzo( f )quinoxaline] and 2,3-benzodiazepine noncompetitive (GYKI 53655 and GYKI 52466) receptor antagonists. Cyclothiazide was equally effective at potentiating the AMPA response in either the presence or absence of glucose, suggesting that the increased glutamate-evoked arachidonic acid release observed in these cells under conditions of glucose deprivation is not due to reduced AMPA receptor desensitisation. The enhanced liberation of arachidonic acid measured in the presence of cyclothiazide appeared to result from a large (fourfold) elevation of the AMPA-induced increase in intracellular calcium level. Therefore, an AMPA-evoked mobilisation of arachidonic acid could potentially contribute to non-NMDA receptor-mediated neurotoxicity, which has been observed in neuronal cells in the presence of cyclothiazide.     

Caveolin-1 null (-/-) mice show dramatic reductions in life span

Caveolae are 50-100 nm flask-shaped invaginations of the plasma membrane found in most cell types. Caveolin-1 is the principal protein component of caveolae membranes in nonmuscle cells. The recent development of Cav-1-deficient mice has allowed investigators to study the in vivo functional role of caveolae in the context of a whole animal model, as these mice lack morphologically detectable caveolae membrane domains. Surprisingly, Cav-1 null mice are both viable and fertile. However, it remains unknown whether loss of caveolin-1 significantly affects the overall life span of these animals. To quantitatively determine whether loss of Cav-1 gene expression confers any survival disadvantages with increasing age, we generated a large cohort of mice (n = 180), consisting of Cav-1 wild-type (+/+) (n = 53), Cav-1 heterozygous (+/-) (n = 70), and Cav-1 knockout (-/-) (n = 57) animals, and monitored their long-term survival over a 2 year period. Here, we show that Cav-1 null (-/-) mice exhibit an approximately 50% reduction in life span, with major declines in viability occurring between 27 and 65 weeks of age. However, Cav-1 heterozygous (+/-) mice did not show any changes in long-term survival, indicating that loss of both Cav-1 alleles is required to mediate a reduction in life span. Mechanistically, these dramatic reductions in life span appear to be secondary to a combination of pulmonary fibrosis, pulmonary hypertension, and cardiac hypertrophy in Cav-1 null mice. Taken together, our results provide the first demonstration that loss of Cav-1 gene expression and caveolae organelles dramatically affects the long-term survival of an organism. In addition, aged Cav-1 null mice may provide a new animal model to study the pathogenesis and treatment of progressive hypertrophic cardiomyopathy and sudden cardiac death syndrome.     

Characterization of synaptically connected nuclei in a potential sensorimotor feedback pathway in the zebra finch song system

Birdsong is a learned behavior that is controlled by a group of identified nuclei, known collectively as the song system. The cortical nucleus HVC (used as a proper name) is a focal point of many investigations as it is necessary for song production, song learning, and receives selective auditory information. HVC receives input from several sources including the cortical area MMAN (medial magnocellular nucleus of the nidopallium). The MMAN to HVC connection is particularly interesting as it provides potential sensorimotor feedback to HVC. To begin to understand the role of this connection, we investigated the physiological relation between MMAN and HVC activity with simultaneous multiunit extracellular recordings from these two nuclei in urethane anesthetized zebra finches. As previously reported, we found similar timing in spontaneous bursts of activity in MMAN and HVC. Like HVC, MMAN responds to auditory playback of the bird's own song (BOS), but had little response to reversed BOS or conspecific song. Stimulation of MMAN resulted in evoked activity in HVC, indicating functional excitation from MMAN to HVC. However, inactivation of MMAN resulted in no consistent change in auditory responses in HVC. Taken together, these results indicate that MMAN provides functional excitatory input to HVC but does not provide significant auditory input to HVC in anesthetized animals. We hypothesize that MMAN may play a role in motor reinforcement or coordination, or may provide modulatory input to the song system about the internal state of the animal as it receives input from the hypothalamus.     

Genetic variation in the bovine myostatin gene in UK beef cattle: allele frequencies and haplotype analysis in the South Devon

Work on Belgian Blue cattle revealed that an 11 base pair (bp) deletion within the bovine myostatin gene (GDF8) is associated with the double-muscled phenotype seen in this breed. Investigations focusing on other European breeds known to show double-muscling identified several mutations within the coding region of the gene associated with the double-muscled phenotype in different breeds. The number of mutations found suggest that myostatin is highly variable within beef cattle. Variations that alter the structure of the gene product such that the protein is inactivated are associated with the most pronounced form of double-muscling as seen in the Belgian Blue. However, other mutations may have a less extreme affect on muscle development. While overt double-muscling gives rise to a high incidence of dystocia (calving difficulty), it is possible that some variants may give enhanced muscling, but with limited calving problems. We describe sequence analysis of the myostatin gene in ten beef breeds commonly used in the UK and show that the 11-bp deletion responsible for double-muscling in the Belgian Blue is also present in the South Devon cattle population. Allele frequencies and haplotypes in the South Devon and a polymerase chain reaction (PCR) based test for the deletion are described. PCR amplification across the deleted region provides a quick and effective test with clear identification of heterozygous individuals. We discuss our results with regard to the effect of genotype on phenotype and differences observed between the Belgian Blue and the South Devon.