Time- and dose-related effects of a gonadotropin-releasing hormone agonist and dopamine antagonist on reproduction in the Northern leopard frog (Lithobates pipiens).

Gonadotropin-releasing hormone (GnRH) stimulates luteinizing hormone release to control ovulation and spermiation in vertebrates. Dopamine (DA) has a clear inhibitory role in the control of reproduction in numerous teleosts, and emerging evidence suggests that similar mechanisms may exist in amphibians. The interactions between GnRH and DA on spawning success and pituitary gene expression in the Northern leopard frog (Lithobates pipiens) were therefore investigated. Frogs were injected during the natural breeding season with a GnRH agonist [GnRH-A; (Des-Gly10, D-Ala6, Pro-NHEt9)-LHRH; 0.1µg/g and 0.4µg/g] alone and in combination with the dopamine receptor D2 antagonist metoclopramide (MET; 5µg/g and 10µg/g). Injected animals were allowed to breed in outdoor mesocosms. Time to amplexus and oviposition were assessed, and egg mass release, incidences of amplexus, egg mass weight, total egg numbers and fertilization rates were measured. To examine gene expression, female pituitaries were sampled at 12, 24 and 36h following injection of GnRH-A (0.4µg/g) alone and in combination with MET (10µg/g). The mRNA levels of the genes lhb, fshb, gpha, drd2 and gnrhr1 were measured using quantitative real-time PCR. Data were analyzed by a two-way ANOVA. Both GnRH-A doses increased amplexus, oviposition and fertilization alone. Co-injection of MET with GnRH-A did not further enhance spawning success. Injection of GnRH-A alone time-dependently increased expression of lhb, fshb, gpha and gnrhr1. The major effect of MET alone was to decrease expression of drd2. Importantly, the stimulatory effects of GnRH-A on lhb, gpha and gnrhr1 were potentiated by the co-injection of MET at 36h. At this time, expression of fshb was increased only in animals injected with both GnRH-A and MET. Spawning success was primarily driven by the actions of GnRH-A. The hypothesized inhibitory action of DA was supported by pituitary gene expression analysis. The results from this study provide a fundamental framework for future time- and dose-response investigations to improve current spawning methods in amphibians.

Understanding the individual to implement the ecosystem approach to fisheries management.

Ecosystem-based approaches to fisheries management (EAFMs) have emerged as requisite for sustainable use of fisheries resources. At the same time, however, there is a growing recognition of the degree of variation among individuals within a population, as well as the ecological consequences of this variation. Managing resources at an ecosystem level calls on practitioners to consider evolutionary processes, and ample evidence from the realm of fisheries science indicates that anthropogenic disturbance can drive changes in predominant character traits (e.g. size at maturity). Eco-evolutionary theory suggests that human-induced trait change and the modification of selective regimens might contribute to ecosystem dynamics at a similar magnitude to species extirpation, extinction and ecological dysfunction. Given the dynamic interaction between fisheries and target species via harvest and subsequent ecosystem consequences, we argue that individual diversity in genetic, physiological and behavioural traits are important considerations under EAFMs. Here, we examine the role of individual variation in a number of contexts relevant to fisheries management, including the potential ecological effects of rapid trait change. Using select examples, we highlight the extent of phenotypic diversity of individuals, as well as the ecological constraints on such diversity. We conclude that individual phenotypic diversity is a complex phenomenon that needs to be considered in EAFMs, with the ultimate realization that maintaining or increasing individual trait diversity may afford not only species, but also entire ecosystems, with enhanced resilience to environmental perturbations. Put simply, individuals are the foundation from which population- and ecosystem-level traits emerge and are therefore of central importance for the ecosystem-based approaches to fisheries management.

Neuroendocrine control of spawning in amphibians and its practical applications.

Across vertebrates, ovulation and sperm release are primarily triggered by the timed surge of luteinizing hormone (LH). These key reproductive events are governed by the action of several brain neuropeptides, pituitary hormones and gonadal steroids which operate to synchronize physiology with behaviour. In amphibians, it has long been recognized that the neuropeptide gonadotropin-releasing hormone (GnRH) has stimulatory effects to induce spawning. Extensive work in teleosts reveals an inhibitory role of dopamine in the GnRH-regulated release of LH. Preliminary evidence suggests that this may be a conserved function in amphibians. Emerging studies are proposing a growing list of modulators beyond GnRH that are involved in the control of spawning including prolactin, kisspeptins, pituitary adenylate cyclase-activating polypeptide, gonadotropin-inhibitory hormone and endocannabinoids. Based on these physiological data, spawning induction methods have been developed to test on selective amphibian species. However, several limitations remain to be investigated to strengthen the evidence for future applications. The current state of knowledge regarding the neuroendocrine control of spawning in amphibians will be reviewed in detail, the elements of which will have wide implications towards the captive breeding of endangered amphibian species for conservation.

Development of an in vitro Ovary Culture System to Evaluate Endocrine Disruption in Wood Frog Tadpoles.

Gonad-mesonephros complexes from wood frog (Lithobates sylvaticus) tadpoles were incubated in vitro for 1 wk to examine direct effects of naphthenic acids (NA) and 17α-ethinylestradiol (EE2) on ovarian differentiation. Histological images reveal successful preservation of gonadal integrity where cultured oocytes exhibited no significant differences in diameters and areas compared to uncultured conditions. Ovaries exposed to 10 µg/L 17α-EE2 contained oocytes with significantly advanced atresia and diminished areas and diameters, indicating a degree of ovarian regression. A significant reduction in oocyte area was observed in ovaries exposed to 3 mg/L of a commercial extract of petroleum-derived NA. This novel approach has applications for screening direct effects of endocrine-disrupting chemicals on gonadal function in tadpoles.

Computational and serologic analysis of novel and known viruses in species human adenovirus D in which serology and genomics do not correlate.

In November of 2007 a human adenovirus (HAdV) was isolated from a bronchoalveolar lavage (BAL) sample recovered from a biopsy of an AIDS patient who presented with fever, cough, tachycardia, and expiratory wheezes. To better understand the isolated virus, the genome was sequenced and analyzed using bioinformatic and phylogenomic analysis. The results suggest that this novel virus, which is provisionally named HAdV-D59, may have been created from multiple recombination events. Specifically, the penton, hexon, and fiber genes have high nucleotide identity to HAdV-D19C, HAdV-D25, and HAdV-D56, respectively. Serological results demonstrated that HAdV-D59 has a neutralization profile that is similar yet not identical to that of HAdV-D25. Furthermore, we observed a two-fold difference between the ability of HAdV-D15 and HAdV-D25 to be neutralized by reciprocal antiserum indicating that the two hexon proteins may be more similar in epitopic conformation than previously assumed. In contrast, hexon loops 1 and 2 of HAdV-D15 and HAdV-D25 share 79.13 and 92.56 percent nucleotide identity, respectively. These data suggest that serology and genomics do not always correlate.