Quantifying the influence of small omnivorous fishes on seagrass epiphyte load

The influence of two cryptic, seagrass‐inhabiting omnivorous fishes, the fan‐bellied leatherjacket Monacanthus chinensis and the variable sabretoothed blenny Petroscirtes variabilis, on seagrass epiphyte biomass are described. Overall, M. chinensis significantly reduced epiphyte biomass by 35·1% after 18 h in experimental aquaria, whilst P. variabilis showed a non‐significant 15·7% reduction. It is concluded that some cryptic omnivorous species play an important role in epiphyte removal in seagrass beds.     

Mediolateral cell intercalation in the dorsal, axial mesoderm of Xenopus laevis

The pattern of mediolateral cell intercalation in mesodermal tissues during gastrulation and neurulation of Xenopus laevis was determined by tracing cells labeled with fluorescein dextran amine (FDA). Patches of the involuting marginal zone (IMZ) of early gastrula stage embryos, labeled by injection of FDA at the one-cell stage, were grafted to the corresponding regions of unlabeled host embryos. The host embryos were fixed at several stages, serially sectioned, and examined with fluorescence microscopy and three-dimensional reconstruction. Patterns of mixing of labeled and unlabeled cells show that mediolateral cell intercalation occurs in the posterior, dorsal mesoderm as this region undergoes convergent extension and differentiates into somites and notochord. In contrast, it does not occur in any dorsoventral sector of the anterior, leading edge of the mesodermal mantle. These results, taken with other evidence, suggest that the mesoderm of Xenopus consists of two subpopulations, each with a characteristic morphogenetic movement, cell behavior, and tissue fate. The migrating mesoderm (1) does not show convergent extension; (2) migrates and spreads on the blastocoel roof; (3) is dependent on this substratum for its morphogenesis; (4) shows little mediolateral intercalation; (5) consists of the anterior, early-involuting region of the mesodermal mantle; and (6) differentiates into head, heart, blood island, and lateral body wall mesoderm. The extending mesoderm (1) shows convergent extension; (2) is independent of the blastocoel roof in its morphogenesis; (3) shows extensive mediolateral intercalation; (4) consists of the posterior, late-involuting parts of the mesodermal mantle; and (5) differentiates into somite and notochord.     

Complementary strand-specific sequences from unique fragments of adenovirus type 2 DNA for hybridization-mapping experiments

Separation of the complementary strands of adenovirus type 2 DNA by poly(U,G)-CsCl density gradient centrifugation permitted studies of Ad2³ DNA renaturation with independently variable concentrations of each complementary strand. Single-stranded DNA was isolated by hydroxylapatite chromatography following exhaustive incubation under such conditions, and was found to selectively represent sequences of the complement present in excess during the incubation. This result was exploited in a general method for isolation of complementary strand-specific sequences of radioactively labeled Ad2 DNA or restriction enzyme fragments of Ad2 DNA. Liquid phase saturation-hybridization experiments were carried out with labeled DNA representing each complementary strand of the six endo R.EcoRI cleavage fragments of Ad2 DNA and unlabeled messenger RNA prepared from HeLa cells late after productive infections with Ad2. The results were combined with the known endo R.EcoRI cleavage map of Ad2 DNA to construct a low-resolution map showing physically separated regions, on both complementary strands of Ad2 DNA, represented in mRNA late after infection.     

Relationship of mRNA from Productively Infected Cells to the Complementary Strands of Adenovirus Type 2 DNA

The complementary strands of adenovirus type 2 (Ad2) DNA were separated by buoyant density gradient centrifugation with poly (U, G). The complementary strand DNA was shown to remain intact through the course of strand separation. The l-strand of Ad2 DNA, appearing in the less dense complex with poly (U, G) in neutral CsCl density gradients, was shown to have a buoyant density in alkaline (pH 12.5) CsCl density gradients which is 2 to 3 mg per ml greater than that of its complement (h-strand). Renaturation of purified complementary strand DNA was observed only in mixtures of h- and l-strand DNA, and then with the second-order reaction rate expected for Ad2 DNA. Hybridization of the complementary strands of Ad2 DNA with cytoplasmic mRNA isolated from infected HeLa cells was performed in liquid phase and analyzed by hydroxylapatite chromatography. Before viral DNA synthesis (6 h after infection), 13 to 18% of the h-strand and 30 to 35% of the l-strand were represented in viral mRNA. Late (18 h) after infection the mRNA represented 20 to 25% and 63 to 68% of the h- and l-strands, respectively. Most, if not all sequences present in viral mRNA before viral DNA synthesis were also present in the cytoplasm late in infection.     

Hydroxyapatite Chromatography and Formamide Denaturation of Adenovirus DNA

Denatured adenovirus DNA was retained by hydroxyapatite columns under conditions generally used for selective retention of double-stranded DNA, probably due to several partially complementary sequences within single-stranded DNA. It was found that addition of formamide reduced the fraction of sonically treated, denatured adenovirus DNA bound to hydroxyapatite from about 30% to less than 1%. This led to a study of the effect of formamide on the melting temperature (T(m)) of double-stranded DNA in solution or bound to hydroxyapatite. The T(m) of DNA decreases 0.56 C/1% formamide, a value determined in buffered solutions with purified formamide.     

Autoradiographic confirmation of mucus-mediated absorption in the halfbeak Hyporhamphus regularis ardelio (Whitley, 1931)

In an investigation of the relationship between acidic glycoproteins released in the pharynx and oesophagus of Hyporhamphus regularis ardelio and 'juice' released from Zostera capricorni by pharyngeal milling, autoradiographs of thin sections of guts of fish fed C¹⁴ labelled seagrass leaves revealed high emission densities in the acidic glycoprotein sheath surrounding the ingesta. This indicates that 'juice' liberated from seagrass is taken up by the mucus.     

Chemical Deterrence of a Marine Cyanobacterium against Sympatric and Non-sympatric Consumers

This study investigates the influence of mesograzer prior exposure to toxic metabolites on palatability of the marine cyanobacterium, Lyngbya majuscula. We examined the palatability of L. majuscula crude extract obtained from a bloom in Moreton Bay, South East Queensland, Australia, containing lyngbyatoxin-a (LTA) and debromoaplysiatoxin (DAT), to two groups: (1) mesograzers of L. majuscula from Guam where LTA and DAT production is rare; and (2) macro- and mesograzers found feeding on L. majuscula blooms in Moreton Bay where LTA and DAT are often prevalent secondary metabolites. Pair-wise feeding assays using artificial diets consisting of Ulva clathrata suspended in agar (control) or coated with Moreton Bay L. majuscula crude extracts (treatment) were used to determine palatability to a variety of consumers. In Guam, the amphipods, Parhyale hawaiensis and Cymadusa imbroglio; the majid crab Menaethius monoceros; and the urchin Echinometra mathaei were significantly deterred by the Moreton Bay crude extract. The sea hares, Stylocheilus striatus, from Guam were stimulated to feed by treatment food whereas S. striatus collected from Moreton Bay showed no discrimination between food types. In Moreton Bay, the cephalaspidean Diniatys dentifer and wild caught rabbitfish Siganus fuscescens were significantly deterred by the crude extract. However, captive-bred S. fuscescens with no known experience with L. majuscula did not clearly discriminate between food choices. Lyngbya majuscula crude extract deters feeding by most mesograzers regardless of prior contact or association with blooms.     

EVOLUTION OF IDENTITY SIGNALS: FREQUENCY‐DEPENDENT BENEFITS OF DISTINCTIVE PHENOTYPES USED FOR INDIVIDUAL RECOGNITION

Identifying broad‐scale evolutionary processes that maintain phenotypic polymorphisms has been a major goal of modern evolutionary biology. There are numerous mechanisms, such as negative frequency‐dependent selection, that may maintain polymorphisms, although it is unknown which mechanisms are prominent in nature. Traits used for individual recognition are strikingly variable and have evolved independently in numerous lineages, providing an excellent model to investigate which factors maintain ecologically relevant phenotypic polymorphisms. Theoretical models suggest that individuals may benefit by advertising their identities with distinctive, recognizable phenotypes. Here, we test the benefits of advertising one's identity with a distinctive phenotype. We manipulated the appearance of Polistes fuscatus paper wasp groups so that three individuals had the same appearance and one individual had a unique, easily recognizable appearance. We found that individuals with distinctive appearances received less aggression than individuals with nondistinctive appearances. Therefore, individuals benefit by advertising their identity with a unique phenotype. Our results provide a potential mechanism through which negative frequency‐dependent selection may maintain the polymorphic identity signals in P. fuscatus. Given that recognition is important for many social interactions, selection for distinctive identity signals may be an underappreciated and widespread mechanism underlying the evolution of phenotypic polymorphisms in social taxa.