Precopulatory sexual cannibalism in fishing spiders (Dolomedes triton): a role for behavioral syndromes

Precopulatory sexual cannibalism (predation of a potential mate prior to copulation) offers an extreme example of intersexual conflict, a current focus in behavioral ecology. The aggressive-spillover hypothesis, posits that precopulatory sexual cannibalism may be a nonadaptive by-product of a general syndrome of voracity (aggression towards prey) that is expressed in multiple behavioral contexts. In this view, selection favoring high levels of voracity throughout ontogeny spills over to cause sexual cannibalism in adult females even when it is not necessarily beneficial. Using the North American fishing spider, Dolomedes triton, we present the first in depth test of this hypothesis. We found support for three aspects of the spillover hypothesis. First, voracity towards hetero-specific prey results in high feeding rates, large adult size, and increased fecundity. Second, juvenile and adult voracity are positively correlated (i.e., voracity is a consistent trait over ontogeny). Third, voracity towards hetero-specific prey is indeed positively correlated with precopulatory sexual cannibalism. Assays of antipredator behavior further revealed positive correlations between boldness towards predators, voracity and precopulatory sexual cannibalism. Overall, our results support the notion that precopulatory sexual cannibalism in D. triton is part of a behavioral syndrome spanning at least three major contexts: foraging, predator avoidance, and mating.     

Interaction and impacts of two introduced species on a soft-sediment marine assemblage in SE Tasmania

Introduced species are having major impacts in terrestrial, freshwater and marine ecosystems world-wide. It is increasingly recognised that effects of multiple species often cannot be predicted from the effect of each species alone, due to complex interactions, but most investigations of invasion impacts have examined only one non-native species at a time and have not addressed the interactive effects of multiple species. We conducted a field experiment to compare the individual and combined effects of two introduced marine predators, the northern Pacific seastar Asterias amurensis and the European green crab Carcinus maenas, on a soft-sediment invertebrate assemblage in Tasmania. Spatial overlap in the distribution of these invaders is just beginning in Tasmania, and appears imminent as their respective ranges expand, suggesting a strong overlap in food resources will result from the shared proclivity for bivalve prey. A. amurensis and C. maenas provide good models to test the interaction between multiple introduced predators, because they leave clear predator-specific traces of their predatory activity for a number of common prey taxa (bivalves and gastropods). Our experiments demonstrate that both predators had a major effect on the abundance of bivalves, reducing populations of the commercial bivalves Fulvia tenuicostata and Katelysia rhytiphora. The interaction between C. maenas and A. amurensis appears to be one of resource competition, resulting in partitioning of bivalves according to size between predators, with A. amurensis consuming the large and C. maenas the small bivalves. At a large spatial scale, we predict that the combined effect on bivalves may be greater than that due to each predator alone simply because their combined distribution is likely to cover a broader range of habitats. At a smaller scale, in the shallow subtidal, where spatial overlap is expected to be most extensive, our results indicate the individual effects of each predator are likely to be modified in the presence of the other as densities increase. These results further highlight the need to consider the interactive effects of introduced species, especially with continued increases in the number of established invasions.Communicated by M.S. Johnson, Crawley     

Model estimation of land-use effects on water levels of northern prairie wetlands.

Wetlands of the Prairie Pothole Region exist in a matrix of grassland dominated by intensive pastoral and cultivation agriculture. Recent conservation management has emphasized the conversion of cultivated farmland and degraded pastures to intact grassland to improve upland nesting habitat. The consequences of changes in land-use cover that alter watershed processes have not been evaluated relative to their effect on the water budgets and vegetation dynamics of associated wetlands. We simulated the effect of upland agricultural practices on the water budget and vegetation of a semipermanent prairie wetland by modifying a previously published mathematical model (WETSIM). Watershed cover/land-use practices were categorized as unmanaged grassland (native grass, smooth brome), managed grassland (moderately heavily grazed, prescribed burned), cultivated crops (row crop, small grain), and alfalfa hayland. Model simulations showed that differing rates of evapotranspiration and runoff associated with different upland plant-cover categories in the surrounding catchment produced differences in wetland water budgets and linked ecological dynamics. Wetland water levels were highest and vegetation the most dynamic under the managed-grassland simulations, while water levels were the lowest and vegetation the least dynamic under the unmanaged-grassland simulations. The modeling results suggest that unmanaged grassland, often planted for waterfowl nesting, may produce the least favorable wetland conditions for birds, especially in drier regions of the Prairie Pothole Region. These results stand as hypotheses that urgently need to be verified with empirical data.     

High levels of genetic subdivision of marine and estuarine populations of the estuarine catfishCnidoglanis macrocephalus (Plotosidae) in southwestern Australia

The cobblerCnidoglanis macrocephalus (Valenciennes) is an endemic marine and estuarine catfish from southern Australia. Conflicting views on the degree of isolation of the estuarine populations underscore general questions about genetic divergence in coastal species. Although estuaries are widely recognized as ecologically important, little work has been done on their role in favouring genetic divergence. In order to estimate the extent of genetic subdivision among nearshore marine and estuarine populations, electrophoretic variation of enzymes was examined in seven marine and six estuarine populations of cobbler from sites spanning 1500 km along the southwest Australian coastline. Among all populations, the mean standardized variance in allelic frequencies (F _ST) for six polymorphic loci was 0.277, a high value comparable to those of other shallow-water teleosts whose life-history characteristics and habitat preferences restrict their dispersal capability. The pattern of genetic identities between populations showed divergence between west and south coast sites. Within these regional groups, however, there was substantial heterogeneity, much of which was associated with estuaries. Among all six estuarine sites, the averageF _ST was 0.333, 40% higher than the value of 0.237 for the marine sites. Low estimates of the genetically effective number of migrants suggest population subdivision between marine and estuarine environments and between similar habitat types. This study indicates the importance of habitat in affecting the connectedness of populations, even in apparently open marine systems.     

Male choice

Summary Male preference for large females as mates was demonstrated in the wood-boring weevil, Brentus anchorago (Coleoptera: Brentidae) by observation and by mate choice experiments in which the complicating factor of male rivalry was eliminated. Adult weight varied at least 23-fold in a large breeding aggregation in Panama. Drilling females guarded by males were larger than unguarded drilling females, and the number of males attending a drilling female increased with length of the female. Thus despite a sex ratio of about 1:1, males were unevenly distributed among the females. A male attending a female had on average about 1 rival male in his vicinity (Lloyd's Index of Mean Crowding). Male preference for large females in the absence of rival males was directly tested in choice arenas on the surface of the host tree. When a large and a small female were simultaneously presented, large and small males alike mated first with the large female. Male choice of large females is probably adaptive in Brentus anchorago because larger females lay larger eggs, which produce larger offspring in a competitive larval environment. Male choice in this species is associated with high male mating investment and time commitment per female, and not with high male parental investment.     

Purification of triolein for use in semipermeable membrane devices (SPMDs)

Analyses of triolein-containing semipermeable membrane devices (SPMDs) have sometimes been impeded by interferences caused by impurities endemic to triolein that codialyze with the analytes. Oleic acid and methyl oleate have been the most troublesome of these impurities because of their relatively high concentrations in triolein and because significant residues of both can persist even after size exclusion chromatographic (SEC) fractionation. These residues have also been blamed for false-positive signals during bioindicator testing of SPMD dialysates. To prevent these problems, a simple, cost-effective procedure was developed for purifying triolein destined for use in SPMDs: the bulk triolein is repeatedly (6x) partitioned against methanol. Tests of the procedure show that 14C-oleic acid is completely removed from the triolein. After SEC fractionation, dialysates of standard-size SPMDs made with the purified triolein contain less than 5 microg of methyl oleate as compared to sometimes more than 500 microg for dialysates (also after SEC) of SPMDs made with unpurified triolein. Gas chromatographic analyses with flame ionization and electron capture detection show that the purification treatment also greatly reduces the number and size of peaks caused by unidentified contaminants in the triolein. Microtox basic assay of dialysates of SPMDs shows that those made with the purified triolein have lower acute toxicities than dialysates of SPMDs made with unpurified triolein. Yeast estrogen screen (YES) testing of SPMDs fabricated with unpurified and purified triolein demonstrates that the purification process removes all background estrogenic activity.     

Ammonia removal from facultative pond effluents in a constructed wetland and an aerated rock filter: performance comparison in winter and summer.

The effluent from a facultative pond loaded at 80 kg BOD ha(-1) day(-1) was treated in a subsurface horizontal-flow aerated rock filter (RF) and a subsurface horizontal-flow constructed wetland (CW) planted with Typha latifolia. Over a 12-month monitoring period BOD and TSS removals were higher, and effluent ammonia concentrations lower, in the RF than in the CW (> 75% vs. 25-75%, and 3.6 mg N L(-1) vs. 6 mg N L(-1), respectively). However, the ammonia concentration was lower in the CW effluent than in the aerated RF effluent during mid-July to mid-September (1.1 mg N L(-1) vs. 2.2 mg N L(-1)), but in winter it was higher than the influent concentration. Overall the performance of the aerated RF was better and more consistent than that of the CW.     

Dissipation of oxytetracycline, chlortetracycline, tetracycline and doxycycline using HPLC-UV and LC/MS/MS under aquatic semi-field microcosm conditions

A mixture of four tetracyclines; oxytetracycline (OTC), chlortetracycline (CTC), tetracycline (TC), and doxycycline (DC) was applied in fifteen 12000l outdoor microcosms at four treatment levels plus controls each with three replicates (n = 3). The dissipation times of parent compounds were monitored and half-lives (DT50) of 1-4 days, depending on treatment level were recorded. This is in accordance with half-lives from previous findings in bench-top experiments. Parent compound DT50, were determined using HPLC-UV. Furthermore, the samples were analyzed for ten different tetracycline products using LC/MS/MS. Two products were found for chlortetracycline; 4-epi-anh-chlortetracyline and the iso-chlortetracycline. Iso-forms were only found for CTC and only at the highest treatment (300 microg l(-1)). The half-lives, trajectories, and relative amounts of the products were analogous for all four tetracyclines. DT50 for products were less than 1.2 days. Formation of 4-epi-anh-tetracyclines, occurred at neutral to weak alkaline conditions.