Testate Amoebae as Indicators of the Magnitude of Seasonal Moisture Variability in Sphagnum Peatlands
Numerous proxies have been developed over the past few decades to reconstruct the paleohydrology of peatland systems, including testate amoebae, a group of moisture-sensitive protozoa. Testate amoebae have been successfully used to infer patterns of multi-decadal moisture variability; however, variability at shorter timescales may also influence community composition. The objectives of this study were to determine if the composition of testate amoeba communities is influenced by seasonal moisture variability and, if so, develop models to infer the magnitude of seasonal moisture variability from fossil assemblages.
Testate amoebae and surface moisture conditions, including hourly measurements of relative humidity within the upper few centimeters of Sphagnum, were examined throughout the growing season at 78 sites within eleven peatlands of Pennsylvania and Wisconsin. Cluster analysis and non-metric multidimensional scaling (NMS) were used to describe patterns in community composition, and these patterns were compared to environmental variables to assess controls on testate amoebae. Results suggest that testate amoebae can not only be used as indicators of mean water-table depth, as in previous studies, but also seasonal variability, with particular species and communities characteristic of highly variable environments. The calibration data from this study was used to identify time periods of exceptionally high moisture variability in late Holocene testate amoeba records from the Great Lakes region, using a series of modern analogue based models. These reconstructions suggest that this new tool, when used in tandem with mean water-table depth reconstructions, can provide insights into the fine-scale structure of late Holocene moisture changes.
Bone Morphogenetic Protein-2 expression is sexually dimorphic in the adult zebra finch forebrain: an immunocytological study.
Songbirds are excellent models towards understanding the estrogenic modulation of constitutive and induced neurogenesis, synaptic plasticity and learning. Bone morphogenetic proteins (BMPs), which are critical for the establishment of the vertebrate CNS, also affect neurogenesis and synaptic plasticity later in development and adulthood. Several BMPs are expressed in the adult zebra finch brain, and telencephalic BMP2 transcription is increased following brain injury and aromatization. However, whether (or not) BMP2 is translated constitutively or in association with injury is unclear. Adult finches (4 per sex) received unilateral, penetrating brain injuries and were perfused 3 or 7 days later. The brains were stained using an antibody specific to a recombinant BMP2 peptide. BMP2 expression was prominent in cells clustered around the damaged meso- and nidopallia. Immunopositive cells were also seen in many other areas including the neurogenic subventricular zone (SVZ), and song nuclei Area X and RA. A comparison of cell densities across these areas and the entopallium (an undamaged nucleus ventral to the needle tract) revealed significant differences due to sex, brain area and the interaction of these variables. All these effects appear to be driven by immunoreactive cells that define Area X in males but fail to distinguish it from the surrounding medial striatum in females. Thus, BMP2 is expressed in a sexually dimorphic manner in areas involved in song learning and immediately surrounding areas of brain damage in the zebra finch. Future studies will focus on the role(s) of BMP2 in synaptic plasticity, learning and injury-induced neurogenesis.
Supported by NS042767.
The MPNmag of Syrian Hamsters is Sexually Dimorphic in Neuronal Subtype
The medial preoptic area (MPOA) plays a critical role in male sex behavior. A subdivision of the MPOA, the magnocellular division of the medial preoptic nucleus (MPNmag), regulates male mating behavior in the Syrian hamster. Lesions of the MPNmag eliminate male mating behavior. Several lines of evidence suggest that the MPNmag integrates pheromonal and hormonal signals to regulate behavior. For example, the MPNmag is stimulated in males exposed to female pheromones with circulating testosterone; the MPNmag of the female is not stimulated even if testosterone is present. These results suggest that there are fundamental sex differences in MPN mag. Previous studies in our lab show that males have significantly more neurons in the MPNmag, in cresyl violet stained tissue. In this study neurons were identified as large round cells with single nucleoli. More recently we found that immunolabeling with NeuN, a neuronal marker, uncovered an additional set of neurons with multiple nucleoli that were not assessed in the previous study. The goal of this study is to determine if there are sexual dimorphisms in the number of single versus multiple nucleoli neurons within the MPNmag.
Neurons with single and multiple nucleoli were counted in tissue immunolabeled for NeuN and counterstained with cresyl violet. Our results indicate that adult males have more neurons with a single nucleolus, yet females have more neurons with multiple nucleoli making total neuron number the same between the sexes. As neurons with multiple nucleoli have been shown to be more active our results support the hypothesis that the MPN mag of male is fundamentally different from that of females.
Mutlidecadal Hydroclimatic Fluctuations Trigger the Initiation and Episodic Expansion of a Floating Kettlehole Peatland
Floating Sphagnum-dominated kettle-hole peatlands are common features of glaciated landscapes. Ecologists have long been interested in these systems as archives of post-glacial environmental change and have sought to understand the processes governing floating peatland initiation and expansion. The widely accepted, though seldom tested, developmental model invokes climate-independent succession of pond-marginal plant communities and lateral expansion of floating vegetation over open water. In contrast, we hypothesize that floating mat expansion is episodic and driven by multidecadal hydroclimatic fluctuations. Under this model, drought exposes organic sediments to colonization by sedges and/or wetland shrubs, subsequent increases in water level cause floatation of peat, and the resulting hydrologic stability is conducive to Sphagnum colonization. We have conducted a preliminary test of this hypothesis by reconstructing the developmental history of a floating kettle-hole peatland in Erie County, Pennsylvania (Titus Bog) using multi-core, multi-proxy paleoecological analyses and comparing spatiotemporal patterns of peatland initiation and expansion to independent records of past hydroclimate. Results indicate that Titus Bog transitioned from a pond to a floating peatland at the western margin around 870 50 yr BP, coincident with a period of major hydroclimatic fluctuations during the Medieval Climate Anomaly. The floating peatland rapidly expanded throughout the rest of the basin several hundred years later (390 75 yr BP) during another interval of prolonged drought recorded in tree ring records from much of North America, including western Pennsylvania. Our results suggest that transient high-magnitude droughts may force kettle-hole ecosystems over critical thresholds, permanently transforming their structure and function.
Caribbean damselfish with varying territory quality: correlated behaviors but not a syndrome
The behavioral syndrome hypothesis suggests that individuals within a population behave differently due to specific behavioral types and these should be consistent in a variety of contexts. In contrast, for territorial animals that live in stochastic environments, natural selection should favor animals that show behavioral flexibility and can modulate behavior in relation to current territory quality. We examined the territorial behavior of a natural population of male beaugregory damselfish by enhancing territory quality using artificial breeding sites and comparing their behavior to males on lower quality natural sites. When male fish were defending high quality artificial territories, they had higher levels of aggression toward male conspecifics and courtship toward females than when on low quality natural territories. We also found that aggression and courtship behaviors were correlated on natural sites, but not artificial. Behaviors were not correlated when males switched from natural to artificial territories or from artificial to natural territories. These results indicate that males assess their current territories and adjust behaviors accordingly and that courtship and aggression behaviors are not linked within a permanent behavioral syndrome.