Selective mortality of a coral reef damselfish: role of predator–competitor synergisms

Phenotypic variability within cohorts of juvenile organisms can serve as the basis for selective mortality. Previous studies have demonstrated the important role that predators play in this process but not the impact of competitors on selective predation. We use a combination of lab and field studies to evaluate the effect of the presence of adult competitor damselfish (Dascyllus aruanus and Pomacentrus moluccensis; family Pomacentridae) on the selective mortality of newly-arrived (settled) lemon damselfish (P. moluccensis) by resident predator fishes (Pseudochromis fuscus Pseudochromidae and Cheilodipterus quinquelineatus Apogonidae). Lab trials consisted of mesocosm experiments in which the behaviour, mortality, and physiological condition (measured as lipid content) of surviving P. moluccensis settlers from each of three treatments: (1) predators absent, (2) predators present, and (3) predators and competitors present, were compared. The field study involved stocking newly settled P. moluccensis on natural bommies (patch reefs) which had either been subject to a partial removal of resident fish (predators and competitors) or left alone. Results indicated there was very strong condition-based selective mortality in both the lab and field trials. In both cases there was a strong positive relationship between mortality and the lipid content of surviving fish; implying low-condition fish were selectively removed. The mesocosm trials indicated that the strength of mortality as well as condition selectivity was higher when competitors were present than when they were absent. Behavioural observations in the mesocosm study suggest that attention by juvenile P. moluccensis to the movements and occasional chases of the competitors (especially D. aruanus) reduced their vigilance to the predators. These results suggest the important and interactive roles which condition of newly settled reef fish and interspecific competition can play in the outcomes of post-settlement predation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

p-loci: a computer program for choosing the most efficient set of loci for parentage assignment

Determining how many and which codominant marker loci are required for accurate parentage assignment is not straightforward because levels of marker polymorphism, linkage, allelic distributions among potential parents and other factors produce differences in the discriminatory power of individual markers and sets of markers. p-loci software identifies the most efficient set of codominant markers for assigning parentage at a user-defined level of success, using either simulated or actual offspring genotypes of known parentage. Simulations can incorporate linkage among markers, mating design and frequencies of null alleles and/or genotyping errors. p-loci is available for windows systems at http://marineresearch.oregonstate.edu/genetics/ploci.htm.     

Development of a competitive immunoassay for the determination of N-(2-hydroxyethyl)valine adducts in human haemoglobin and its application in biological monitoring

Ethylene oxide (EO) is an important industrial compound and a directly acting mutagen. Human exposure to it can be monitored by the determination of haemoglobin (Hb) adducts. An immunoassay that quantifies the N-terminal adduct N-(2-hydroxyethyl)valine in whole blood was developed and its potential usefulness as a tool for biologically monitoring occupational exposure demonstrated. Analytical reliability was confirmed in a comparative study with gas chromatography-mass spectrometry (range 0.040-589 nmol g^-1 Hb, correlation coefficient 0.98, n=10). The assay was configured as a competitive enzyme-linked immunosorbent assay to facilitate the rapid throughput of samples. The assay uses a whole blood matrix and has a working range of 10-10 000 pmol N-(2-hydroxethyl)valine g^-1 Hb. The assay does not appear to be affected by structurally similar metabolites and has been used to determine adducts in human blood samples. The first results from potentially exposed workers indicate the assay might be a powerful tool for the routine occupational biomonitoring of EO exposure.     

Two theories of origin of the land-plant sporophyte: Which is left standing?

Questions concerning the two competing theories of the development of alternating generations in land plants, the homologous theory and the antithetic theory, have never been fully resolved. In the majority of recent accounts there appears to have been increasing de facto support (if one considers the ontogenetic processes and phylogenetic consequences discussed) for the antithetic theory. However, this preference is usually not plainly stated (as such) in these discussions, and some support has also continued for the homologous theory. The crux of both theories (homologous and antithetic) centers upon how the sporophyte may have originated in the life cycle. One problem with the homologous theory is that it is not made explicit how the development of a dependent sporophyte could have occurred in the life cycle (when the precedent organisms are considered to have had free-living, putatively similar, gametophytes and sporophytes). The antithetic theory, by contrast, offers a definite ontogenetic mechanism or process (retention of the zygote on the gametophyte, delay of zygotic meiosis, with zygotic mitoses occurring first) by which a dependent sporophyte might have originated and persisted, in the context of a life cycle formerly lacking a sporophyte generation. Also, a review of a variety of evidence (morphological, cytological, biochemical, etc.) would appear to lend more support to the antithetic theory than to the homologous theory. In discussing types of algae now known to be most clearly related to land plants (i.e., charophytes, particularly advanced forms), the type of life cycle exhibited by these particular algae (haplontic, with zygotic meiosis; no sporophyte present) suggests that only an antithetic origin of the sporophyte in land plants is actually feasible.