Testing the navigational abilities of ocean migrants: displacement experiments on green sea turtles (Chelonia mydas)

Like many animals migrating through the oceans, sea turtles face difficult navigational tasks when they have to reach distant, specific sites. The paradigmatic case of Brazilian green turtles (Chelonia mydas), which nest on the tiny Ascension Island in the middle of the Atlantic Ocean, has often been the subject of hypotheses concerning their navigational mechanisms. To investigate their nature, we displaced 18 females from Ascension and tracked them by satellite after release from eight different points in the ocean, 60-450 km away from the island. Four turtles moved to Brazil soon after the release, 4 moved in various directions before heading to Brazil, and 10 reached the island. All the successful trips, bar 1, were winding but ended with a final straight segment of variable length, as if the turtles were searching for a sensory contact with the island which they obtained at various distances. The approach to Ascension mostly occurred from the direction opposite to the trade wind, suggesting a navigational role of wind-borne information originating from the island.     

Intrinsic worker mortality depends on behavioral caste and the queens’ presence in a social insect

According to the classic life history theory, selection for longevity depends on age-dependant extrinsic mortality and fecundity. In social insects, the common life history trade-off between fecundity and longevity appears to be reversed, as the most fecund individual, the queen, often exceeds workers in lifespan several fold. But does fecundity directly affect intrinsic mortality also in social insect workers? And what is the effect of task on worker mortality? Here, we studied how social environment and behavioral caste affect intrinsic mortality of ant workers. We compared worker survival between queenless and queenright Temnothorax longispinosus nests and demonstrate that workers survive longer under the queens’ absence. Temnothorax ant workers fight over reproduction when the queen is absent and dominant workers lay eggs. Worker fertility might therefore increase lifespan, possibly due to a positive physiological link between fecundity and longevity, or better care for fertile workers. In social insects, division of labor among workers is age-dependant with young workers caring for the brood and old ones going out to forage. We therefore expected nurses to survive longer than foragers, which is what we found. Surprisingly, inactive inside workers showed a lower survival than nurses but comparable to that of foragers. The reduced longevity of inactive workers could be due to them being older than the nurses, or due to a positive effect of activity on lifespan. Overall, our study points to behavioral caste-dependent intrinsic mortality rates and a positive association between fertility and longevity not only in queens but also in ant workers.     

Gehalte an polycyclischen aromatischen Kohlenwasserstoffen (PAK) in Oberböden Hamburgs

The contents of 19 polycyclic aromatic hydrocarbons (PAH) in topsoil samples from 108 sites within the territory of the federal state of Hamburg were analyzed. The investigation was performed to provide a view on background values in the metropolitan area and the influence of land use on PAH in soils. Known contaminated sites were not included in the investigation. Values in the area ranged from 0.1 to 44.3 mg/kg d.m. with a median of 3.6. 80% of the measurements were below 10 mg/kg d.m. Contents decreased strongly with a growing distance from the city’s center. The median is 4.4 mg/kg d.m. in the center, 1.3 in the rural periphery (marsh) and 0.4 mg/kg d.m. in preweichselian uplands (“geest”). PAH contaminations originate from diffuse atmospheric emissions caused by car traffic and room heating, but also by war damages which lead to widespread burnings and consequently to the widespread dispersion of remains. The contents measured are in the range of published values from other densely populated areas, although a comparatively comprehensive investigation from another region does not exist.     

Invertebrates control metal/metalloid sequestration and the quality of DOC/DON released during litter decay in slightly acidic environments

Plant litter and organic sediments are a main sink for metals and metalloids in aquatic ecosystems. The effect of invertebrate shredder (a key species in litter decay) on metal/metalloid fixation by organic matter is described only under alkaline water conditions whereas for slightly acidic waters nothing can be found. Furthermore, less is known about the effect of invertebrate shredders on the quality of dissolved organic carbon (DOC) and nitrogen (DON) released during litter decay. We conducted an experiment to investigate the impact of invertebrate shredder (Gammarus pulex) on metal/metalloid fixation/remobilization and on the quality of DOC/DON released under slightly acidic water conditions. During decomposition of leaf litter, invertebrate shredder facilitated significantly the emergence of smaller particle sizes of organic matter. The capacity of metal fixation was significantly higher in smaller particles (POM 2,000?C63???m) compared to original leaf litter and litter residues. Thus, G. pulex enhanced metal fixation by organic partition of sediments by increasing the amount of smaller particle of organic matter in aquatic ecosystems. In contrast, the capacity of metal/metalloid fixation in the smallest fraction of POM (<63???m) was lower compared with leaf residues in treatment without invertebrates. Remobilization of metals and metalloids was very low for all measured elements. A significant effect of invertebrates on quantitative formation of DOC/DON was confirmed. The quality of released DOC/DON, which may affect metal/metalloid remobilization, was also significantly affected by invertebrate shredders (e.g., more carboxylates). Hence, invertebrate shredder enhanced significantly the fixation of metals/metalloids into POM in slightly acidic environments.     

Unique and species-specific microbial communities in Oscarella lobularis and other Mediterranean Oscarella species (Porifera: Homoscleromorpha)

Homoscleromorph sponges such as Oscarella spp. are characterized by unique morphological features, and Homoscleromorpha were therefore recently proposed as the fourth class of sponges. The microbiology of these sponges was mainly studied by electron microscopy while molecular studies are scarce. The aim of this study was to characterize the bacteria in Oscarella sponges using molecular tools. Denaturing gradient gel electrophoresis revealed distinct bacterial profiles in five Oscarella species and several color morphs of Oscarella lobularis. These profiles are characteristic of low microbial abundance (LMA) sponges. This was further confirmed by analysis of a 16S rRNA clone library from O. lobularis that yielded a low phylum-level diversity with dominance of Alphaproteobacteria. Bacterial communities in O. lobularis were very similar among different individuals (collected at the same site and time), five different color morphs, and specimens from different depths and locations, indicating a species-specific association. These results allow novel insights into the microbiology of the first known LMA sponge genus within the new class Homoscleromorpha.     

A time-saving method for higher plant tests in hydroculture

For higher plant tests in hydroculture we developed a method to unify the usually separately performed germination and growth testing. This method renders unnecessary the time-consuming and laborious installation of the germinated plants into the growth system.