Growth and water relations in a central North Carolina population of <Emphasis Type="Italic">Microstegium vimineum</Emphasis> (Trin.) A. Camus

The ability of an invasive plant to occupy new areas is often attributed to both morphological and physiological plasticities that allow them to remain viable over a wide range of environmental conditions. Studies addressing the ecological requirements of Microstegium vimineum often consider soil moisture or soil moisture along with other factors as important explanatory components for the establishment and persistence of this invasive monocot. However, controlled studies specifically targeting water relations in M. vimineum are needed. Therefore, the purpose of this study was to determine how different water availabilities influence the growth and physiological performance of M. vimineum. This study utilized experimental microcosms to achieve different water availabilities including low soil moisture (<15% water), moderate soil moisture (ca. 20–30%), and flooded conditions. While both flooded and low soil moisture resulted in diminished growth, M. vimineum still survived under these conditions. Physiological processes including C₄ metabolism, minimum stress under low water conditions, and the ability to increase tissue rigidity may confer some advantages to M. vimineum during periods of limiting water conditions. Similarly, the proportionally low root biomass, shallow root structure, and its ability to maintain stable water relations during flooding and/or soil waterlogging may facilitate M. vimineum’s ability to invade mesic habitats. It is likely, therefore, that the capacity to tolerate both low soil moistures and flooded conditions has enhanced the ability of M. vimineum to populate disturbed systems in central North Carolina.     

Severe and rapid population declines in exotic birds

A particularly vexing phenomenon within invasion ecology is the occurrence of spontaneous collapses within seemingly well-established exotic populations. Here, we assess the frequency of collapses among 68 exotic bird populations established in Hawaii, Puerto Rico, Los Angeles and Miami. Following other published definitions, we define a ‘collapse’ as a decline in abundance of ≥90 % within ≤10 years that lasts for at least 3 years. We show that 44 of the 68 exotic bird populations have exhibited declines at some point within their time series. Sixteen of the populations declined sufficiently to be defined as collapsed. It took on average 3.8 ± 1.8 years for populations to decline into a collapsed state, and this state persisted on average for 7.1 ± 6.3 years across (collapsed) populations. We compared the severity and duration of declines across all 44 declining populations according to taxonomic Order and geographic region. Neither variable explained substantial variation in the metrics of collapse. Our results indicate that severe, rapid, and persistent population declines may be common among exotic populations. We suggest that incorporating the probability and persistence of collapses into management decisions can inform efforts to enact control or eradication measures. We also suggest that applying our approach to other taxa and locations is crucial for improving our understanding of when and where collapses are likely to occur.     

Intra- and inter-specific effects of mast seeding on seed fates of two sympatric <Emphasis Type="Italic">Corylus</Emphasis> species

We released seeds of two sympatric tree species, Corylus mandshurica (seed with thinner seed hull, higher nutrition) and C. heterophylla (seeds with thicker seed hull, lower nutrition) in the masting year of C. mandshurica in 2008, and C. heterophylla in 2009, respectively, to investigate how seed masting of the two sympatric Corylus species affects seed removal and dispersal fitness of the two species differently at both intra- and inter-specific levels. At intra-specific level, the authors found mast seeding of both C. mandshurica and C. heterophylla significantly reduced seed removal, seed consumption, but increased seed dispersal distance and seed dispersal fitness of the released seeds. Mast seeding of C. mandshurica increased seed caching of C. mandshurica. At inter-specific level, the authors found mast seeding of C. mandshurica reduced seed removal of C. heterophylla, but mast seeding of C. heterophylla did not significantly reduce seed removal of C. mandshurica. Mast seeding of C. mandshurica reduced seed consumption of C. heterophylla, while mast seeding of C. heterophylla reduced seed consumption of C. mandshurica. We found mast seeding of C. mandshurica significantly reduced seed dispersal distance of C. heterophylla, while mast seeding of C. heterophylla significantly increased seed dispersal distance of C. mandshurica. We found that mast seeding of C. mandshurica significantly increased seed dispersal fitness of C. heterophylla, while mast seeding of C. heterophylla did not significantly increase seed dispersal fitness of C. mandshurica. More studies are needed to reveal the ecological consequences of mast seeding at inter-specific or community-level. Seed traits may attribute the differences of mast seeding at inter-specific level. Because seeds with thinner seed hull and higher nutrition were more harvested and eaten by rodents, mast seeding of C. mandshurica might have reduced seed removal and seed consumption, but increased dispersal fitness of C. heterophylla (seeds with thicker seed hull, lower nutrition). Therefore, synchrony among species is, or is not, selectively beneficial to the focus species depends on seed traits which determine gains from mast seeding at inter-specific level.     

A climate for contemporary evolution

A new study of divergence in freshwater fish provides strong evidence of rapid, temperature-mediated adaptation. This study is particularly important in the ongoing debate over the extent and significance of evolutionary response to climate change because divergence has occurred in relatively few generations in spite of ongoing gene flow and in the aftermath of a significant genetic bottleneck, factors that have previously been considered obstacles to evolution. Climate change may thus be more likely to foster contemporary evolutionary responses than has been anticipated, and I argue here for the importance of investigating their possible occurrence.     

Deadly liaisons: fatal attraction between CCN matricellular proteins and the tumor necrosis factor family of cytokines

Recent studies have revealed an unexpected synergism between two seemingly unrelated protein families: CCN matricellular proteins and the tumor necrosis factor (TNF) family of cytokines. CCN proteins are dynamically expressed at sites of injury repair and inflammation, where TNF cytokines are also expressed. Although TNFα is an apoptotic inducer in some cancer cells, it activates NFκB to promote survival and proliferation in normal cells, and its cytotoxicity requires inhibition of de novo protein synthesis or NFκB signaling. The presence of CCN1, CCN2, or CCN3 overrides this requirement and unmasks the apoptotic potential of TNFα, thus converting TNFα from a proliferation-promoting protein into an apoptotic inducer. These CCN proteins also enhance the cytotoxicity of other TNF cytokines, including LTα, FasL, and TRAIL. Mechanistically, CCNs function through integrin α₆β₁ and the heparan sulfate proteoglycan (HSPG) syndecan-4 to induce reactive oxygen species (ROS) accumulation, which is essential for apoptotic synergism. Mutant CCN1 proteins defective for binding α₆β₁-HSPGs are unable to induce ROS or apoptotic synergism with TNF cytokines. Further, knockin mice that express an α₆β₁-HSPG-binding defective CCN1 are blunted in TNFα- and Fas-mediated apoptosis, indicating that CCN1 is a physiologic regulator of these processes. These findings implicate CCN proteins as contextual regulators of the inflammatory response by dictating or enhancing the cytotoxicity of TNFα and related cytokines.     

Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders

Background  

Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability among these early-generation hybrid crosses to determine the strength of the initial barrier to gene exchange. We also created contemporary-generation hybrids in the lab and evaluated the extent to which selection has affected fitness over approximately 20 generations of admixture. Additionally, we examined the inheritance of quantitative phenotypic variation to better understand how evolution has progressed since secondary contact.