ALBERT

Description: Maternal provisioning can have profound effects on offspring phenotypes, or maternal effects, especially early in life. One ubiquitous form of provisioning is in the makeup of egg. However, only a few studies examine the role of specific egg constituents in maternal effects, especially as they relate to maternal selection (a standardized selection gradient reflecting the covariance between maternal traits and offspring fitness). Here, we report on the evolutionary consequences of differences in maternal acquisition and allocation of amino acids to eggs. We manipulated acquisition by varying maternal diet (milkweed or sunflower) in the large milkweed bug, Oncopeltus fasciatus . Variation in allocation was detected by examining two source populations with different evolutionary histories and life-history response to sunflower as food. We measured amino acids composition in eggs in this 2 × 2 design and found significant effects of source population and maternal diet on egg and nymph mass and of source population, maternal diet, and their interaction on amino acid composition of eggs. We measured significant linear and quadratic maternal selection on offspring mass associated with variation in amino acid allocation. Visualizing the performance surface along the major axes of nonlinear selection and plotting the mean amino acid profile of eggs from each treatment onto the surface revealed a saddle-shaped fitness surface. While maternal selection appears to have influenced how females allocate amino acids, this maternal effect did not evolve equally in the two populations. Furthermore, none of the population means coincided with peak performance. Thus, we found that the composition of free amino acids in eggs was due to variation in both acquisition and allocation, which had significant fitness effects and created selection. However, although there can be an evolutionary response to novel food resources, females may be constrained from reaching phenotypic optima with regard to allocation of free amino acids. An investigation of amino acids allocated to eggs as maternal effects in a milkweed bug.

Description: Mixing dissolution, a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals, is commonly considered to form cavernous macroporosity (e.g. flank margin caves and banana holes) in eogenetic karst aquifers. On small islands, macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface, suggesting that dissolution processes are decoupled from surface hydrology. Mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pCO 2 was assumed to be homogeneously distributed within the phreatic zone. Here, we report data from two abandoned well fields in an eogenetic karst aquifer on San Salvador Island, Bahamas, that demonstrate pCO 2 in the phreatic zone is distributed heterogeneously. The pCO 2 varied from less than log -2.0 to more than log -1.0 atm over distances of less than 30 m, generating dissolution in the subsurface where water flows from regions of low to high pCO 2 and cementation where water flows from regions of high to low pCO 2. Using simple geochemical models, we show dissolution caused by heterogeneously distributed pCO 2 can dissolve 2.5 to 10 times more calcite than the maximum amount possible by mixing of fresh water and seawater. Dissolution resulting from spatial variability in pCO 2 forms isolated, globular chambers lacking initial entrances to the surface, a morphology that is characteristic of flank margin caves and banana holes, both of which have entrances that form by erosion or collapse after cave formation. Our results indicate that heterogeneous pCO 2 , rather than mixing dissolution, may be the dominant mechanism for observed spatial distribution of dissolution, cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings. This article is protected by copyright. All rights reserved.

Description: During early development, many aposematic species have bright and conspicuous warning appearance, but have yet to acquire chemical defenses, a phenotypic state which presumably makes them vulnerable to predation. Body size and signal luminance in particular are known to be sensitive to variation in early nutrition. However, the relative importance of these traits as determinants of predation risk in juveniles is not known. To address this question, we utilized computer-assisted design (CAD) and information on putative predator visual sensitivities to produce artificial models of postmetamorphic froglets that varied in terms of body size and signal luminance. We then deployed the artificial models in the field and measured rates of attack by birds and unknown predators. Our results indicate that body size was a significant predictor of artificial prey survival. Rates of attack by bird predators were significantly higher on smaller models. However, predation by birds did not differ between artificial models of varying signal luminance. This suggests that at the completion of metamorphosis, smaller froglets may be at a selective disadvantage, potentially because predators can discern they have relatively low levels of chemical defense compared to larger froglets. There is likely to be a premium on efficient foraging, giving rise to rapid growth and the acquisition of toxins from dietary sources in juvenile poison frogs. During early development many aposematic species have bright and conspicuous warning appearance, but have yet to acquire chemical defenses, a phenotypic state which presumably makes them vulnerable to predation. We deployed artificial prey of green-and-black poison frogs in the field, and show that rates of attack by bird predators were significantly higher on smaller model prey. This suggests that at the completion of metamorphosis smaller froglets may be at a selective disadvantage. There is likely to be a premium on efficient foraging, giving rise to rapid growth and the acquisition of toxins from dietary sources in juvenile poison frogs.

Description: Accelerated sea-level rise and the potential for an increase in frequency of the most intense hurricanes due to climate change threaten the vitality and habitability of barrier islands by lowering their relative elevation and altering frequency of overwash. High-density development may further increase island vulnerability by restricting delivery of overwash to the subaerial island. We analyzed pre- and post-Hurricane Sandy (2012) LiDAR surveys of the New Jersey coast to assess human influence on barrier overwash, comparing natural environments to two developed environments (commercial and residential) using shore-perpendicular topographic profiles. The volume of overwash delivered to residential and commercial environments is reduced by 40% and 90%, respectively, of that delivered to natural environments. We use this analysis and an exploratory barrier island evolution model to assess long-term impacts of anthropogenic structures. Simulations suggest that natural barrier islands may persist under a range of likely future sea-level rise scenarios (7–13 mm/yr) whereas developed barrier islands will have a long-term tendency toward drowning.

Description: Sphagnum moss is an important genus of plants responsible for large stores of soil organic carbon associated with wet habitats such as northern peatlands. Northern peatlands, which contain globally significant quantities of legacy carbon, may be vulnerable to enhanced summer moisture deficits due to climate change. We adapted HYDRUS-1D and a semi-arid soil moisture model to investigate the role of microtopographic position and depth-dependence of peat hydraulic properties on Sphagnum moisture stress response to current and projected climate conditions in an idealized northern Michigan peatland. Water table (WT) level was shown to have a strong control on pore-water pressure ( ψ ), and thus on Sphagnum moisture stress. As a result of the close correspondence between surface peat hydraulic properties for hummocks and hollows used to parameterize our model, microtopographic position was shown to have a greater impact on Sphagnum moisture stress. Model behaviour suggests that, while ψ maintains equilibrium-profile values relative to the WT level for relatively shallow values, surface ψ becomes non-linearly related to WT level below a value of approximately -0.4 m, thus greatly increasing the likelihood of desiccation under future climate scenarios where growing season soil moisture deficits are projected to increase. The simulated range of instantaneous and cumulative moisture-stress for hollows under future climate conditions closely corresponds to the contemporary range exhibited by hummocks. Therefore, in order to assess the competitive advantage of various Sphagnum species to future climate conditions, we argue that more data are needed to better inform a physiological ψ -based moisture-stress threshold, the evolution of the stress response to increasing levels of desiccation, and its subsequent recovery dynamics. This article is protected by copyright. All rights reserved.