How an introduced seaweed can affect epibiota diversity in different coastal systems

Invasions by non-indigenous species have the potential to alter the biodiversity of recipient systems. The magnitude of this effect often depends on the nature of the invaded communities and the ecology of the invader. We investigated the impacts of the Japanese seaweed Sargassum muticum (Phaeophyceae, Fucales) on biodiversity in a rocky and sedimentary environment on two islands in the North Sea. In each case, we compared the epibiota of non-indigenous S. muticum with epibiota communities on taxonomically related and structurally similar native seaweed hosts. Total and average species richness on S. muticum were similar on the rocky shore (60 species and 22±6 species, respectively) and the sandy shore (64 species and 20±3 species, respectively). However, community structure and species composition differed significantly between the environments. On the rocky shore, another native fucoid seaweed, Halidrys siliquosa, supported an epibiota community very similar to that of the invader. On the sandy shore, the only other abundant native habitat-providing algal species was Fucus vesiculosus. This species supported a different and less diverse assemblage of associated taxa. We conclude that S. muticum enhances epibiota diversity in the sedimentary environment, probably by increasing the substratum availability and habitat heterogeneity. In contrast, it has negligible impacts on epibiota diversity in the rocky shore environment, where it does not represent a fundamentally new habitat component. We conclude that even within the same region, the consequences of non-indigenous species on biodiversity cannot be generalised but depend on the composition and structural complexity of the species in the recipient community. This paper is dedicated to Udo Schilling, Chief Diving Officer, Alfred Wegener Institute who trained all of the authors in the waters off Helgoland to be scientific divers. The work reported here and in previous publications has been made possible through Udo’s training and support. We remain grateful for his enthusiasm, effort and patience.     

Colonial recognition of fungus in the fungus-growing ant Acromyrmex subterraneus subterraneus (Hymenoptera: Formicidae)

Summary. Leaf cutting ants live in symbiosis with a basidiomycete fungus that is exploited as a source of nutrients for the ant larvae. Tests of fungus transport demonstrated that Acromyrmex subterraneus subterraneus workers discriminate concolonial fungus from alien fungus, and rejected the latter. Larvae and pupae of the ant were used as controls. Chemical analysis of the fungus revealed a great similarity between its hydrocarbon profile and that found on the ant brood. Experiments with lures showed that chemical extracts from the fungus are responsible for this discrimination process. Moreover, the presence of brood inside the fungus seemed to be important for discrimination of the fungus by workers. Resident workers accepted concolonial broodless fungus less than concolonial fungus inoculated with brood odor. Fungus seems to acquire colonial odor passively, simply by contact with the brood. The impact of fungus volume present in the nest on closure of the colony is discussed. We show here for the first time the importance of a symbiotic vegetal organism in colonial recognition in social insects. Received 14 April 2000; accepted 29 September 2000     

Fernmeßverfahren

The combination of remote sensing methods like Doppler lidar and FTIR allows remote determination of mass fluxes of gases. Doppler lidar measures the three-dimensional wind vector in the vicinity of diffuse sources, or the velocity of air in a chimney plume if an industrial complex is monitored. FTIR is a multicomponent remote sensing method for gas concentrations. The Fourier transformation of an interferogram of a Michelson interferometer within a FTIR system converts the recorded intensity (function of optical path length) to a spectral signal (function of wavenumber). Both information, velocity and concentration, give the mass fluxes of the tracer (gas). A first test was performed at Munich-Nord power station with FTIR and cw-Doppler lidar. Fluxes of CO₂, CO, NO, and HCl were determined. The results are in good agreement with the fluxes measured byin situ instruments of the power station. The method can be used to control industrial complexes from an outside observation site.     

Einsatz der Hasse-Diagrammtechnik zur vergleichenden Datenanalyse von Biomarkerantworten und ökotoxikologischen Tests

Ecotoxicological investigations focus on biological systems and their response to chemically induced stress. Experimental techniques are much more developed than deterministic dynamic modelling. In this methodological contribution a technique is presented, based on lattice theory. This technique, also calledHasse diagram technique, allows data analysis with respect to comparative evaluation. Hasse diagrams are used

? to suggest a possible measure of microbial diversity,

? to analyze dependencies between phospholipid fatty acids and simple geochemical parameters on an ordinal scale and

? to visualise complex results of interactions of humic substances with xenobiotics.

     

How many gamergates is an ant queen worth?

Ant reproductives exhibit different morphological adaptations linked to dispersal and fertility. By reviewing the literature on taxa where workers can reproduce sexually (i.e. become gamergates) we show that (1) species with a single gamergate generally have lost the winged queen caste, whereas only half of the species with several gamergates have, and (2) single-gamergate species have smaller colonies than multiple-gamergate species. Comparison with "classical" ants without gamergates, where having one vs having several winged queens are two distinct syndromes, suggests that having one vs having several gamergates are not. Gamergate number does not affect the success of colony fission, but retention of the queen caste permits the option of independent foundation.     

Changes in the cuticular hydrocarbons of incipient reproductives correlate with triggering of worker policing in the bulldog ant Myrmecia gulosa

In social insects, conflicts over male parentage can be resolved by worker policing. However, the evolution of policing behavior is constrained by the ability of individuals to identify reproductive nestmates, or their eggs. We investigated the occurrence of worker policing and its underlying chemical communication in the bulldog ant Myrmecia gulosa. Although workers have functional ovaries and can lay male-destined eggs, they do not reproduce in queenright colonies. To determine if their sterility is a consequence of worker policing, we experimentally induced worker reproduction in the presence of a queen. Some individuals were seized and immobilized by nestmates, and sometimes killed as a consequence. Although the ovarian development of immobilized individuals was variable, their cuticular hydrocarbon profiles were intermediate between reproductive and nonreproductive workers, indicating they were in the process of starting to reproduce. Approximately 29% of these incipient reproductive workers were successfully policed. To test for policing on eggs, we transferred viable worker eggs to queenright colonies and monitored their acceptance. Furthermore, we compared the surface hydrocarbons of the different types of eggs to determine whether these chemicals could be involved in egg recognition. We found that although there were differences in hydrocarbon profiles and discrimination between queen and worker-laid eggs, viable eggs were not destroyed. Our results strongly support the idea that cuticular hydrocarbons are involved in the policing of reproductive workers. A low level of worker policing appears sufficient to select for self-restraint in workers when few fitness benefits are gained by selfish reproduction. Policing of eggs may thus be unnecessary.     

Effects of starvation,season, and diet on the free amino acid and protein content of<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> females

Effects of food availability and season on the free amino acid (FAA) and total protein content of the copepod Calanus finmarchicus females were investigated in two mesocosm experiments on the Norwegian west coast in spring and autumn. Starved C. finmarchicus females showed no change in total FAA content, but the FAA pool composition changed drastically. During the first 10 days of starvation the protein content showed a moderate decline (<2 µg ind ^-1); however, during the following 21 days the total content was drastically reduced, from 63 to 9 µg ind ^-1. This supports the notion of a sequential catabolism of endogenous nutrients during starvation. In females at high food concentrations, the body protein content increased during spring, but decreased during autumn. The FAA pool composition of females differed between spring and autumn in 14 of the 18 FAA investigated. Reduced body protein content and increased proportion of essential free amino acid were observed during starvation. Similar changes were observed in females sampled at the end of the mesocosm experiments in the autumn. The results suggest that mature C. finmarchicus females are in a negative protein balance during autumn, despite high food concentrations, contributing to a lower fitness than in females maturing during the spring.