The dominance of seismic signaling and selection for signal complexity in Schizocosa multimodal courtship displays

Schizocosa wolf spiders show tremendous diversity in courtship complexity, with different species employing varying numbers of components within and across sensory modalities. Using a comparative approach, we investigate the importance of each signaling modality in the courtship display of five Schizocosa species (three stridulating and two drumming) by assessing mating success under manipulated signaling environments. Irrespective of the degree of male ornamentation, the three stridulating species exhibit a dependence on the seismic, but not visual, signaling environment for mating success. Mating was independent of signaling environment for the two drumming species. We next ask whether the degree to which each species depends upon a signaling modality for mating (i.e., modality importance) is correlated with the estimated modality-specific signal complexity. We first calculate effect sizes for the influence of seismic versus visual signaling environments on the likelihood to mate for ten Schizocosa species and then use an element-counting approach to calculate seismic and visual signal complexity scores. We use a phylogenetic regression analysis to test two predictions: (1) the importance of seismic signaling is correlated with seismic signal complexity and (2) the importance of visual signaling is correlated with visual signal complexity. We find a significant relationship between visual signal importance and visual signal complexity, but no relationship between seismic signal importance and seismic signal complexity. Finally, we test the hypothesis that selection acts on complexity per se by determining whether seismic and visual signal complexity is correlated across species. We find support for this hypothesis in a significant relationship between seismic and visual signal complexity.     

Factors affecting the evacuation decisions of coastal households during Cyclone Aila in Bangladesh

Despite sincere efforts by concerned agencies and recent improvements in hazard warnings, thousands of at-risk people did not evacuate during Aila, a category-I tropical cyclone that struck southwestern coastal Bangladesh in 2009. This study investigated the responses of the people affected by Aila to cyclone warnings and associated evacuation orders, and unveiled behavioural aspects that explain why they did or did not comply with the evacuation orders. Utilising the primary data collected from 420 households living in the severely affected coastal sub-district Koyra, located in Khulna District, this study found that although more than 97% of the households had received cyclone warnings and evacuation orders before Aila's landfall, only around 26% had evacuated. We also examined this study's empirical findings for factors that had dissuaded people from complying with the evacuation orders. Relevant test statistics along with results from principal component analysis suggested that the significant and systematic absenteeism of households from disaster preparedness training appears to be one of the key determinants that affected their evacuation decisions, along with factors related to warning messages, the attributes of cyclone shelters, risk perception, and socioeconomic aspects. A number of recommendations are also presented in this study for people at risk to improve their evacuation rates in future emergencies, not only to save their own lives but also to save their livestock.     

The origin of speciation: trace metal kinetics over natural water/sediment interfaces and the consequences for bioaccumulation

The speciation of heavy metals was measured over a variety of natural and undisturbed water/sediment interfaces. Simultaneously, two benthic species (oligochaete Limnodrilus spp. and the midge Chironomus riparius) were exposed to these sediments. Under occurring redox conditions, free ion activities of trace metals Cd, Cu, Ni, Pb, and Zn were measured with a chelating exchange technique, while geochemical conditions (i.e., redox) remained in tact. Free ion activities were compared with total dissolved concentrations in pore waters and surface waters in order to relate speciation to bioaccumulation. Limnodrilus spp. and C. riparius have accumulation patterns that could be linked to time-dependent exposure concentrations, expressed as chemical speciation, in the surface water and the sediment's pore water. Concentrations of free metal ions in the overlying surface water, rather than in sediment pore water, proved to be the best predictor for uptake. For the first time, measurements are obtained from sediments without disturbing physical-chemical conditions and thus bioavailability, a major restriction of other studies so far.