Flexible foraging movements of leatherback turtles across the North Atlantic Ocean

Some marine species have been shown to target foraging at particular hotspots of high prey abundance. However, we show here that in the year after a nesting season, female leatherback turtles (Dermochelys coriacea) in the Atlantic generally spend relatively little time in fixed hotspots, especially those with a surface signature revealed in satellite imagery, but rather tend to have a pattern of near continuous traveling. Associated with this traveling, distinct changes in dive behavior indicate that turtles constantly fine tune their foraging behavior and diel activity patterns in association with local conditions. Switches between nocturnal vs. diurnal activity are rare in the animal kingdom but may be essential for survival on a diet of gelatinous zooplankton where patches of high prey availability are rare. These results indicate that in their first year after nesting, leatherback turtles do not fit the general model of migration where responses to resources are suppressed during transit. However, their behavior may be different in their sabbatical years away from nesting beaches. Our results highlight the importance of whole-ocean fishing gear regulations to minimize turtle bycatch.     

Behavioral differences between Pogonomyrmex rugosus and dependent lineage (H1/H2) harvester ants

The discovery of genetic caste determination (GCD) in populations of Pogonomyrmex harvester ants raises many questions about the evolution and persistence of such populations. The genetic caste determination arises from the existence of two distinct, but mutually dependent, genetic lineages within a population. Workers always develop from a combination of the two lineages, but their sister queens develop from within-lineage matings. Maintaining genetic caste determination appears to be costly because many queen-destined eggs are wasted when a colony is not in the reproductive stage, yet these populations appear to be widespread. We investigated whether inter-lineage workers have novel traits that give GCD colonies a selective advantage in certain environments. In particular, we compared ecologically relevant behavioral characteristics of inter-lineage workers in H-lineage colonies with co-occurring normal colonies of P. rugosus. First, we measured colony defensive response toward a simulated vertebrate predator. Second, we set up direct competitive foraging and recruitment experiments between dependent lineage and P. rugosus colonies. Last, we measured individual aggressive response to foreign inter-lineage and P. rugosus workers. We found that H1/H2 inter-lineage workers explored objects on the nest more thoroughly and responded much more aggressively to simulated predator disturbance than the P. rugosus colonies. In individual encounters, H1/H2 inter-lineage and P. rugosus workers were equally aggressive toward foreign ants, but both worker types could discriminate P. rugosus from inter-lineage intruders and were more aggressive toward ants of the alternate type to themselves. When competing directly for resources, however, P. rugosus colonies consistently dominated seed piles. In summary, H1/H2 GCD colonies show distinct behavioral differences, but there is no clear ecological advantage from the traits we examined.     

Fundamental trade-offs generating the worldwide leaf economics spectrum

Recent work has identified a worldwide "economic" spectrum of correlated leaf traits that affects global patterns of nutrient cycling and primary productivity and that is used to calibrate vegetation-climate models. The correlation patterns are displayed by species from the arctic to the tropics and are largely independent of growth form or phylogeny. This generality suggests that unidentified fundamental constraints control the return of photosynthates on investments of nutrients and dry mass in leaves. Using novel graph theoretic methods and structural equation modeling, we show that the relationships among these variables can best be explained by assuming (1) a necessary trade-off between allocation to structural tissues versus liquid phase processes and (2) an evolutionary tradeoff between leaf photosynthetic rates, construction costs, and leaf longevity.     

Effects of cyanobacterium Fischerella ambigua isolates and cell free culture media on zebrafish (Danio rerio) embryo development

The toxic effects of several species of fresh water cyanobacteria, notably Microcystis species and associated toxins, the microcystins, Anabaena species (anatoxin), Nodularia sp. (nodularin), and Cylindrospermopsis raciborskii (cylindrospermopsin), are well known. Little, however, is known about the effects of secondary metabolites other than alkaloids. Early life stage tests with zebrafish (Danio rerio) were used to detect bioactive properties of compounds released by healthy cyanobacteria (Fischerella ambigua), particularly on the early developmental stages of fish. This approach, using F. ambigua is probably most valuable as it shows the toxicity of healthy growing cyanobacteria. The effects of cyanobacterial secondary metabolites on the embryonic stages of fish are of considerable interest as many aquatic creatures, particularly fish, are unable to avoid the potential toxins that may be released by undesirable algal blooms or as a result of allelopathic effects. In the current study, the zebrafish (D. rerio) was used as a model experimental system to investigate the effects of ambigols A and C, tjipanazole D and C, 2,4-dichlorobenzoic acid, cell free culture media, and media extracts of a terrestrial/fresh water strain of the cyanobacterium F. ambigua on embryo development. Fish embryo tests performed with the cell free culture medium showed that after 3h of exposure to undiluted culture medium all fish embryos died. At a tenfold dilution the process of epiboly (formation of the gastrula) was retarded in all embryos, lesions were observed, and their general development was significantly arrested, finally followed by death. The same tests performed with extracts (dichloromethane, n-butanol, and residual cell free culture medium) of the cell free culture medium, ambigol A, ambigol C, 2,4-dichlorobenzoic acid and tjipanazole D showed only ambigol A to have an influence on zebrafish development at concentrations>or=1 mg/l (2.06 microM). After 55 h all embryos showed pectoral oedema, irregularly shaped fin folds, bent tails, and unusual circular neoplasms in the dorsal tail fin fold. Due to the high concentration of ambigol A used in this assay these effects were considered to be of minor importance when compared to those of the culture medium.