Zoology - Research Publications
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ItemHost shift capability of a specialist seed predator of an invasive plant: Roles of competition, population genetics and plant chemistry(Springer Science and Business Media LLC, 2014-02-01)
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ItemNew Bone Formation and Microstructure Assessed by Combination of Confocal Laser Scanning Microscopy and Differential Interference Contrast Microscopy(SPRINGER, 2014-03-01)Bone is a mineralized connective tissue that is continuously and microstructurally remodeled. Altered bone formation and microstructure arise in pathological bone conditions such as osteoporosis, osteonecrosis, fracture repair, and Paget disease of bone. A proper and objective assessment of bone formation and microstructure will provide insight into the understanding of bone pathogenesis and remodeling. Here, new bone formation ex vitro and its microstructure were evaluated in in vivo multiple sequential polychrome-labeled samples using confocal laser scanning microscopy (CLSM), which generated clearer and more reliable images of thick bone sections than conventional fluorescence microscopy (CFM). Intriguingly, fine details of the bone microstructural features, including the mineralization fronts, quiescent versus active osteons, and Volkmann's channel, were elucidated using CLSM, which defines the relationship between morphological changes and function, when combined with differential interference contrast microscopy. Furthermore, CLSM provided objective evaluations of bone formation, such as the ratio of labeled areas of new bone formation in a rabbit model when compared with CFM. Altogether, new bone formation and its microstructure can be evaluated more adequately using a combination of CLSM and DIC microscopies.
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ItemSingle locus complementary sex determination in Hymenoptera: an "unintelligent" design?(Springer Science and Business Media LLC, 2006-01-05)The haplodiploid sex determining mechanism in Hymenoptera (males are haploid, females are diploid) has played an important role in the evolution of this insect order. In Hymenoptera sex is usually determined by a single locus, heterozygotes are female and hemizygotes are male. Under inbreeding, homozygous diploid and sterile males occur which form a genetic burden for a population. We review life history and genetical traits that may overcome the disadvantages of single locus complementary sex determination (sl-CSD). Behavioural adaptations to avoid matings between relatives include active dispersal from natal patches and mating preferences for non-relatives. In non-social species, temporal and spatial segregation of male and female offspring reduces the burden of sl-CSD. In social species, diploid males are produced at the expense of workers and female reproductives. In some social species, diploid males and diploid male producing queens are killed by workers. Diploid male production may have played a role in the evolution or maintenance of polygyny (multiple queens) and polyandry (multiple mating). Some forms of thelytoky (parthenogenetic female production) increase homozygosity and are therefore incompatible with sl-CSD. We discuss a number of hypothetical adaptations to sl-CSD which should be considered in future studies of this insect order.
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ItemNo Preview AvailableSteroid-independent regulation of uterine oxytocin receptors(WILEY, 2004-04-01)The oxytocin receptor is an important contractile-associated protein, up-regulated at term in the myometrium in many mammalian species. We conducted studies in a novel animal model to challenge the general view that gonadal steroids are a major regulatory factor of uterine oxytocin receptors. Female marsupials have separate uteri and, in monovular species such as the tammar wallaby, the conceptus is present in one uterus whereas the contralateral uterus is empty. A marked increase in myometrial oxytocin receptors occurs only in the gravid uterus. Fetectomy experiments demonstrated that local embryo-derived factors stimulate this gravid uterus-specific increase in oxytocin receptors, and that uterine distension is probably not a key component in this regulatory pathway. Unilateral ovariectomy has no significant effect on uterine oxytocin receptors, emphasizing the impact of the conceptus on oxytocin receptor regulation and the minimal influence of gonadal steroids on parturition in this species. Our data highlight that regulation of uterine oxytocin receptor expression is multifactorial, and does not necessarily rely on gonadal steroids.
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ItemNo Preview AvailableMechanisms of relaxin action in the reproductive tract - Studies in the relaxin-deficient (Rlx(-/-)) mouse(NEW YORK ACAD SCIENCES, 2005-01-01)The major functions of relaxin (RLX) are associated with female reproductive tract physiology, namely, the regulation of biochemical processes involved in remodeling of extracellular matrix components in the cervix and vagina at term. Studies in RLX-deficient mice (Rlx-/-) demonstrate that although females give birth to live young without apparent dystocia, the pubic symphysis is not elongated, and they have abnormal cervical and vaginal morphology. The current study examined phenotypic differences in collagen, matrix metalloproteinases (MMP), and estrogen receptors (ERs) in the cervix and vagina of pregnant Rlx+/+ and Rlx-/- mice. Neither collagen nor TGFbeta1 mRNA levels in the cervix and vagina differed significantly between Rlx+/+ and Rlx-/- at any stage of gestation, except on gestation day 18.5, with an increase in alpha(1)-I collagen and TGFbeta1 expression in Rlx-/- mice. MMP gene expression was also increased in Rlx-/- mice, especially at term. Administration of recombinant H2 RLX (0.05 microg/microL/h) to Rlx-/- mice for 6 d from gestation day 12.5 caused a significant decrease in alpha1-I collagen and MMP-13 gene expression in the cervix and vagina, but it had no effect on TGFbeta1. There was also a significant reduction in ERbeta expression in RLX-treated Rlx-/- mice. Interestingly, RLX treatment caused a significant decrease in LGR7 expression in these reproductive tissues. In summary, these data show increases in MMP gene expression in Rlx-/- mice that are not correlated with changes in collagen expression. Furthermore, we report a novel ER phenotype in the cervix and vagina of Rlx-/- mice.
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ItemNo Preview AvailableOxytocin and estrogen receptor expression in the myometrium of pregnant relaxin-deficient (Rlx(-/-)) mice(NEW YORK ACAD SCIENCES, 2005-01-01)Relaxin decreases oxytocin-stimulated rat myometrial contractions in vitro. This study used pregnant relaxin-deficient (Rlx-/-) mice to investigate the interaction between relaxin, oxytocin receptor (OTR), and estrogen receptor (ER) expression in the myometrium. Myometrial OTRs were significantly decreased on gestation day 18.5 in Rlx-/- mice than in Rlx+/+ mice. An increase in ERalpha in Rlx+/+ mice at term was correlated with a decrease in ERbeta, which was not observed in Rlx-/- mice. Treatment of Rlx-/- mice with relaxin had no effect on OTR, LGR7, or ERalpha expression, but it caused a significant decrease in ERbetas.
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ItemAn Introduced Competitor Elevates Corticosterone Responses of a Native Lizard (Varanus varius)(UNIV CHICAGO PRESS, 2015-05-01)Glucocorticoid hormone profiles are increasingly used as physiological markers to infer the strength of species interactions that can influence fitness and ensuing population dynamics of animals. Here we investigated two aims. First, we measured the effect of a 90-min capture stress protocol on the plasma corticosterone responses of a large native Australian lizard, the lace monitor (Varanus varius). Second, we compared the basal and postcapture stress corticosterone responses of lace monitors in habitats where they were exposed to high or low densities of the European red fox (Vulpes vulpes), an introduced competitor. Lace monitors responded to the capture stress protocol by significantly increasing plasma levels of corticosterone above basal at 45- and 90-min-postcapture blood-sampling intervals. In habitats with high fox densities, lace monitors produced a significantly greater basal and capture-stress-induced corticosterone response compared to individuals in low-fox density habitat. A significant interaction among fox density, time postcapture, and body condition was also found to influence plasma corticosterone values. These results suggest competition with red fox, perhaps via nutritional stress and increased hypersensitivity of the adrenocortical axis in lizards. At present, without further research, we do not understand whether such responses mediate lizard fitness or whether they have adaptive or maladaptive consequences for lizard populations in response to red fox competition. Nevertheless, our results help broaden understanding of the physiological implications arising from species interactions and specifically how introduced competitors could mediate diverse impacts on native biodiversity.
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ItemA Framework for Identifying Selective Chemical Applications for IPM in Dryland Agriculture(MDPI, 2015-12-01)Shifts to Integrated Pest Management (IPM) in agriculture are assisted by the identification of chemical applications that provide effective control of pests relative to broad-spectrum pesticides but have fewer negative effects on natural enemy (beneficial) groups that assist in pest control. Here, we outline a framework for identifying such applications and apply this framework to field trials involving the crop establishment phase of Australian dryland cropping systems. Several chemicals, which are not presently available to farmers in Australia, were identified as providing moderate levels of pest control and seedling protection, with the potential to be less harmful to beneficial groups including predatory mites, predatory beetles and ants. This framework highlights the challenges involved in chemically controlling pests while maintaining non-target populations when pest species are present at damaging levels.
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ItemLow female birth weight and advanced maternal age programme alterations in next-generation blastocyst development(BIOSCIENTIFICA LTD, 2015-05-01)Low birth weight is associated with an increased risk for adult disease development with recent studies highlighting transmission to subsequent generations. However, the mechanisms and timing of programming of disease transmission to the next generation remain unknown. The aim of this study was to examine the effects of low birth weight and advanced maternal age on second-generation preimplantation blastocysts. Uteroplacental insufficiency or sham surgery was performed in late-gestation WKY pregnant rats, giving rise to first-generation (F1) restricted (born small) and control offspring respectively. F1 control and restricted females, at 4 or 12 months of age, were naturally mated with normal males. Second-generation (F2) blastocysts from restricted females displayed reduced expression of genes related to growth compared with F2 control (P<0.05). Following 24 h culture, F2 restricted blastocysts had accelerated development, with increased total cell number, a result of increased trophectoderm cells compared with control (P<0.05). There were alterations in carbohydrate and serine utilisation in F2 restricted blastocysts and F2 restricted outgrowths from 4-month-old females respectively (P<0.05). F2 blastocysts from aged restricted females were developmentally delayed at retrieval, with reduced total cell number attributable to reduced trophectoderm number with changes in carbohydrate utilisation (P<0.05). Advanced maternal age resulted in alterations in a number of amino acids in media obtained from F2 blastocyst outgrowths (P<0.05). These findings demonstrate that growth restriction and advanced maternal age can alter F2 preimplantation embryo physiology and the subsequent offspring growth.
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ItemUrban habitat complexity affects species richness but not environmental filtering of morphologically-diverse ants(PEERJ INC, 2015-10-22)Habitat complexity is a major determinant of structure and diversity of ant assemblages. Following the size-grain hypothesis, smaller ant species are likely to be advantaged in more complex habitats compared to larger species. Habitat complexity can act as an environmental filter based on species size and morphological traits, therefore affecting the overall structure and diversity of ant assemblages. In natural and semi-natural ecosystems, habitat complexity is principally regulated by ecological successions or disturbance such as fire and grazing. Urban ecosystems provide an opportunity to test relationships between habitat, ant assemblage structure and ant traits using novel combinations of habitat complexity generated and sustained by human management. We sampled ant assemblages in low-complexity and high-complexity parks, and high-complexity woodland remnants, hypothesizing that (i) ant abundance and species richness would be higher in high-complexity urban habitats, (ii) ant assemblages would differ between low- and high-complexity habitats and (iii) ants living in high-complexity habitats would be smaller than those living in low-complexity habitats. Contrary to our hypothesis, ant species richness was higher in low-complexity habitats compared to high-complexity habitats. Overall, ant assemblages were significantly different among the habitat complexity types investigated, although ant size and morphology remained the same. Habitat complexity appears to affect the structure of ant assemblages in urban ecosystems as previously observed in natural and semi-natural ecosystems. However, the habitat complexity filter does not seem to be linked to ant morphological traits related to body size.