The digital pads of the tree frog, Hyla cinerea. I. The epidermis

As the digital pad cells grow from the germinal epithelium, the desmosomes on the distal surface oF tile cells become aligned and form pegs filled with tonofilaments on the surface of the outer row of cells. The outer pad cells are separated from each other distally, thus the cell and the pegs form two sizes of protrusions in series on the pad surface which can fit into substratum/irregularities. A dense material, apparently derived from transforming bodies in the cells, coats the plasma membrane of the surface cells, presumably to strengthen them.     

The digital pads of the tree frog, Hyla cinerea. II. The mucous glands

The mucous glands consist of a single row of cells surrounded by smooth muscle. The cells are attached at their apical and basal regions and only cytoplasmic projections loosely link the lateral aspects of adjacent cells. Material accumulates in the cisternae of the rough endoplasmic reticulum, appears to form into dense granules in the Golgi apparatus, and then before being secreted, undergoes chemical and morphological alterations. Since some glands secrete onto the dorsal epidermis of the digits, the mucous is believed to function as a wetting agent for the skin as well as an aid to climbing.     

Fish larvae assemblages in the Gulf of California

The distributional diversity and assemblages of fish larvae in the Gulf of California indicated two main seasonal stages and two transitional periods: in winter, the tropical water mass is confined to the south‐east portion of the mouth of the Gulf and larval fish assemblages are dominated by subtropical and temperate‐subarctic species; in summer; tropical water invades the Gulf and assemblages are dominated by tropical species. Both seasonal stages are separated by transitional periods coinciding with strong latitudinal temperature gradients. During the autumn and spring transitional periods, the Gulf of California splits into three regions: a northern region where temperate and subarctic species spawn from autumn to spring, a southern region dominated by tropical and subtropical species year round and a central region where tropical and temperate assemblages merge. Seasonal changes in the location of the regions, as well as the borders between them, show expansion and contraction of the northern and southern faunas related to the general oceanic circulation patterns during the year.     

Gonadal development and spawning of female ocean whitefish, Caulolatilus princeps (Pisces: Branchiostegidae) in the Bay of La Paz, B.C.S., Mexico

The developmental stages of the gonads and the spawning season of the ocean whitefish, Caulolatilus princeps , were determined. Gonad maturation is annual, and the spawning season is prolonged, from late autumn to early spring. From November to March, around 80% of the females were in an advanced mode of gonadal development, and in April most gonads were spent. From May to October the gonads were at rest and preparing for the next spawning season.
The gonadosomatic index describes the reproductive activity of the species adequately.     

Developmental interdeterminacy in embryos of the leech Helobdella triserialis

In embryonic development of the leech Helobdella triserialis, each of the four paired positionally identifiable, ectodermal teloblasts (N, O, P, and Q) generates a bandlet of blast cell progeny that merges with ipsilateral bandlets into a germinal band. Left and right germinal bands coalesce into the germinal plate which gives rise to the segmental tissues of the leech and wherein the progeny of each teloblast generate a characteristic pattern of epidermal and neuronal cells. Experiments reported here show that the positionally identified O teloblast sometimes generates the P pattern and vice versa. The reversal of these teloblasts' generative identities was shown to correspond to the formation of chiasmata by their blast cell bandlets, so that the positions of their bandlets in the germinal band are reversed as well. Thus it is the position of the bandlet in the germinal band, rather than the position of the parent teloblast, which correlates with the fate of o and p blast cells. Moreover, two types of ablation experiments have shown that, in the absence of generative P teloblast progeny, those cells which would normally generate the O pattern take on a new fate and give rise to the P pattern in the nervous system, both at the gross pattern level in the segmental ganglia, and at the level of identified neurons in the peripheral nervous system. If related, these phenomena suggest that the O and P teloblasts, which derive from the symmetric cleavage of the OP proteloblasts, have a common developmental pluripotency. And in that case, the fates of their progeny are determined hierarchically on the basis of relative position in the nascent germinal band, with P-type fate being preferred.     

Cell interactions in the developing epidermis of the leech Helobdella triserialis

In embryonic development of the leech Helobdella triserialis, each of the four paired ectodermal teloblasts contributes some progeny to a characteristic dorsal or ventral territory of the epidermis. To ascertain the relative roles of cell lineage and cell interactions in generating the highly regular epidermal distribution pattern of the various ectodermal cell lines, a series of experiments was carried out in which the ablation of particular teloblasts was combined with the intracellular injection of cell lineage tracers. The results showed that, after the ablation of an OP proteloblast, or of an O, P, or Q teloblast, the epidermal progeny of the remaining ipsilateral and contralateral teloblasts spread into the territory normally occupied by the epidermal progeny of the ablated teloblast. In this spreading process, cells may cross the ventral midline but not the dorsal midline. The spread of epidermal progeny of one teloblast in response to ablation of another teloblast is contrasted with the failure of the neuronal progeny of one teloblast to replace any missing neural tissue. It appears, therefore, that all epidermal cell lines are of equal developmental potential, regardless of their teloblast of origin, with the eventual location of any epidermal cell in the body wall being governed by interactions between cells within the developing epidermis.     

Characteristics of an SV40-plasmid recombinant and its movement into and out of the genome of a murine cell

A bacterial plasmid carrying the early region of SV40 (pOT) has been stably established in high molecular weight (hmw) DNA of mouse L cells by selection for the herpes virus thymidine kinase (tk) gene. DNA blotting has demonstrated that most cell lines contain multiple discrete copies of pOT, generally with an intact SV40 early region. No free copies of pOT have been detected. Both pOT and tk sequences may be amplified up to 20–200 copies of the SV40 early region. In contrast to the uniform staining pattern normally observed in SV40-transformed lines, indirect immunofluorescence using antiserum to the SV40 T antigen has demonstrated that the expression of the early region is heterogeneous in these cell lines. This fraction expressing T is characteristic of a given cell line, and varies from 0 to 99% positive. Several pOT cell lines have been fused to simian cells, and replicating low molecular weight DNAs were isolated from the heterokaryons. Transformation of E. coli with this DNA demonstrates that pOT can be rescued from hmw DNA in L cells and reestablished as a plasmid in E. coli. Excision is generally precise when pOT is introduced to the murine cells as a supercoiled molecule, and imprecise when pOT is introduced in linear form.     

Horizontal dynamics of zooplankton in subtropical Lake Blanca (Uruguay) hosting multiple zooplankton predators and aquatic plant refuges

The Gulf of California, Mexico, consists of unique environmental conditions resulting in a rich array of biological diversity. Nematodes are present in most marine sediments and are probably the most abundant metazoans. This research analyses and compares nematode biodiversity in two shallow, littoral locations of the Gulf and compares the results with other Pacific and Atlantic faunae. Samples collected in Punta Estrella and Santa Clara were processed for nematode extraction by standard methods. A total of eighty genera were identified, sixty-seven occurring in coarser sediments at Punta Estrella and fifty-five in more silty sediments at Santa Clara. Nematode abundance was higher at the latter location, on average. The region was not especially high or low in diversity compared to other littoral sites, and was most similar to locations in Europe with a corresponding ecology but at temperate latitudes. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Trophic level and overlap of sea lions (Zalophus californianus) in the Gulf of California, Mexico

Stable isotope and scat analyses were used in concert to determine trophic level and dietary overlap among California sea lions from different rookeries in the Gulf of California. Isotopic analysis of the fur of sea lion pups revealed differences in δ¹⁵N and δ¹³C values among rookeries during the breeding season. Mean δ¹⁵N and δ¹³C values varied from 20.2‰ to 22.4‰ and from −15.4‰ to −14.0‰, respectively. The pattern of differences among rookeries was similar between years in most cases. Isotopic variations among rookeries were associated with differences in prey consumption. There was a significant correlation between δ¹⁵N value and trophic level, as determined by scat analysis. Joint application of isotopic and scat analyses allowed us to identify how the feeding habits of sea lions vary with location. Our results suggest the presence of spatial structure in available prey as well as the localized use of prey by sea lions across the Gulf of California.     

Linking fish consumption patterns and health risk assessment of mercury exposure in a coastal community of NW Mexico

We aimed at characterizing the methylmercury (MeHg) exposure through fish consumption in two populations (common general and fishing-related population (FRP)) using a probabilistic health risk assessment in children, women of childbearing age, and adults in Mazatlán. The hazard quotients (HQs) were obtained from fish consumption, defined through a survey, and the levels of mercury in fishery products, obtained from published information. The average fish ingestion rate (IR_food) was higher in the FRP (167.85 g d^?1) than in the general population (GP) (140.9 g d^?1). However, HQs were significantly (p < 0.05) higher in the GP (ranging from 0.18 to 10.91) compared to the FRP (0.20 to 2.48); significant differences were also found among groups of both populations. Remarkably, children in both populations exhibited the highest proportions of risk, reaching up to 97% in GP. For all populations, fish consumption was the most important variable influencing MeHg exposure. Overall, for MeHg exposure, there is no safe level of fish consumption without risk, and actions should be taken to mitigate possible risk; further research with current data is needed to assess potential health risks associated with MeHg exposure, particularly in children.     

MHC gene configuration variation in geographically disparate populations of California sea lions (Zalophus californianus)

Major histocompatibility complex (MHC) class II DRB genotypes were examined in two geographically isolated populations of California sea lions (Zalophus californianus) (Gulf of California and California coastal Pacific Ocean). Genomic DNA from 227 California sea lions was examined using eight sequence-specific primer (SSP) pairs flanking the putative peptide-binding site. A total of 40 different Zaca-DRB genotype configurations were identified among the 227 individuals. Using SSP-PCR, significant differences were found between coastal California and Gulf of California Zalophus populations in numbers of DRB sequences per individual and configuration of sequences within individuals. Additionally, unique local patterns of MHC diversity were identified among the Midriff Island animals. These population differences are consistent with either ecologically distinct patterns of selection pressures and/or geographical isolation. The consequences of these partitioned MHC configurations at the population level are as yet unknown; however, the worldwide increase in emerging marine diseases lends urgency to their examination.     

Tidal influence on the evolution of egg size in the grunions (Leuresthes,Atherinidae)

Synopsis The duration of natural in-beach-sand incubation of Gulf of California and California grunion embryos is dictated by the tidally-driven wave activity in their respective habitats. Analyses of these tidal regimes reveal that the incubation period can be three times longer on beaches of the California coast than on those of the northern Gulf.In response to the more irregular tides of California, Leuresthes tenuis, the less primitive of the two species, has evolved an egg volume 310% larger than the Gulf grunion, L. sardina. The. larger egg not only supplies greater yolk reserves for differentiation, growth and maintenance, but also produces a larger embryo. The more abundant yolk stores and greater embryo size helps California grunion embryos to remain viable in the sand longer than those of the Gulf grunion.     

REACTION OF FIN WHALES BALAENOPTERA PHYSALUS TO AN EARTHQUAKE

ABSTRACT

Whales living within seismically active regions are subject to intense disturbances from strong sounds produced by earthquakes that can kill or injure individuals. Nishimura & Clark (1993) relate the possible effects of underwater earthquake noise levels in marine mammals, adducing that T-phase source signal level (10- to 30- Hz range) can exceed 200 dB re: 1 μPa at 1 m, for a magnitude 4–5 earthquake, sounds audible to fin whales which produce low frequency sounds of 16–20/25–44 Hz over 0.5–1s, typically of 183 dB re: 1 μPa at 1 m. Here we present the response of a fin whale to a 5.5 Richter scale earthquake that took place on 22 February 2005, in the Gulf of California. The whale covered 13 km in 26 min (mean speed = 30.2 km/h). We deduce that the sound heard by this whale might have triggered the costly energy expenditure of high speed swimming as a seismic-escape response. These observations support the hypothesis of Richardson et al. (1995) that cetaceans may flee from loud sounds before they are injured, when exposed to noise in excess of 140 dB re: 1 μPa 1 m.     

Thermal elution chromatography and the resolution of nucleic acids on hydroxylapatite

Thermal elution chromatography of nucleic acids on hydroxylapatite was studied from a technical standpoint. It is shown that current methods for selecting elution buffers are inadequate. The construction of window diagrams for the purpose of determining suitable conditions is demonstrated. The resolving ability of various buffer-hydroxylapatite systems was studied in some detail. The best system for resolving single- from double-stranded nucleic acids was found to be the use of potassium phosphate together with Bio-Rad HTP (non-DNA grade) which has been preheated in phosphate buffer. Sodium phosphate gives the best resolution among various species of double-stranded nucleic acid.     

Different sensitivities of acetylcholine-induced “after-hyperpolarization” compared to dopamine-induced hyperpolarization,to ouabain or to lithium-replacement of sodium,in rabbit sympathetic ganglia

The ganglionic potentials elicited by a test dose of acetylcholine (ACh) acting nicotinically consist of an initial depolarization followed by a longer “after-hyperpolarization” (after-HP). The after-HP is abolished selectively and relatively rapidly after treatment with ouabain or with Li-replacement of 90% of Na in Ringer. The hyperpolarizing response to a test dose of dopamine (DA), however, is as or more resistant than the ACh-depolarization to either treatment. These findings provide further strong evidence that the slow inhibitory postsynaptic potential (s-IPSP), for which DA is the transmitter in these ganglia, is $\text{not}$ mediated by an activation of an electrogenic NaK pump.     

Activation of the contractile system in crustacean muscle: Ultrastructural evidence for the role of the T system

Freeze-fracture and thin sections of lobster abdominal fast flexor muscle were used to study the morphology of the sarcoplasmic reticulum (SR) and T system of crustacean muscle. Tannic acid mordanting, which can result in a dense black deposit in the T system lumen, was used to distinguish T system from SR membranes. Ferritin was also used as an extracellular tracer to confirm the tannic acid method. The T system consists of an extensive network of flattened sacs which fills most of the space between the mycfibrils and is in close contact with them. The SR also appears as flattened sacs, sometimes with fenestrations. There is extensive junctional contact between the SR and T system. Quantitative estimates of the volume and surface area of the membranes show that the T system has about 50 % more surface area than the SR. The intramembrane particle (IMP) density of the PF face of the T system is about 1100/ μm² membrane, while the IMP density of the PF face of the SR is about 4800/ μm² membrane. In morphology, extent, and IMP density, the T system of lobster abdominal fast flexor muscle appears (AFF) adapted to provide at least part of the Ca²⁺ for muscle activation and the transport system for relaxation.     

Levels of diurnal predation on a school of flat-iron herring,Harengula thrissina

Synopsis The incidence of diurnal predation (0800–1600h) on schools of several hundred thousand adult flat-iron herring,Harengula thrissina, was quantified. Nine species of piscine predators perpetrated 653 attacks and 158 captures during 42.5 h of observation. Four predators: cabrilla,Mycteroperca rosacea, cornetfish,Fistularia commersonii, green jack,Caranx caballus, and black skipjack,Euthynnus lineatus, were responsible for 92% of the attacks and 96% of the successes. Among these predators attack rates (attacks × time^–1) and success rates (successes × attacks^–1) varied with respect to time of day, although all predators were active throughout the day. As a consequence, the herring school experienced fairly homogeneous attack and success rates. These rates were estimated as roughly half the crepuscular attack rates but they were sustained over a much longer period. Piscivorous predators, particularly those species frequently found in association with schooling prey, may be focusing their attacks on opportunities, not specific times of day and/or light levels. More direct information needs to be gathered on diurnal as well as crepuscular attack and success rates in order to assess the impact that piscine predators have on schooling prey.     

Vicariance and dispersal across Baja California in disjunct marine fish populations

Abstract.— Population disjunctions, as a first step toward complete allopatry, present an interesting situation to study incipient speciation. The geological formation of the Baja California Peninsula currently divides 19 species of fish into disjunct populations that are found on its Pacific Coast and in the northern part of the Gulf of California (also called the Sea of Cortez), but are absent from the Cape (Cabo San Lucas) region. We studied the genetic makeup of disjunct populations for 12 of these 19 fish species. Phylogeographic patterns for the 12 species can be separated into two major classes: a first group (eight species) showed reciprocal monophyly and high genetic divergence between disjunct populations. A second group (four species) displayed what appeared to be panmictic populations. Population structure between Pacific Coast populations, across the Punta Eugenia biogeographic boundary, was also evaluated. While dispersal potential (inferred by pelagic larval duration) was a poor predictor of population structure between Gulf of California and Pacific populations, we found that population genetic subdivision along the Pacific Coast at Punta Eugenia was always positively correlated with differentiation between Pacific and Gulf of California populations. Vicariant events, ongoing gene flow, and ecological characteristics played essential roles in shaping the population structures observed in this study.     

Equilibrium ligand binding assays using labeled substrates: nature of the errors introduced by radiochemical impurities

The effects of radiochemical impurities in a labeled substrate on the characteristics of the experimental equilibrium binding plots were examined. The protein (receptor) was assumed to be a monomer or an oligomer composed of identical, noninteracting subunits. The substrate was assumed to be chemically and radiochemically impure (Case I) or just radiochemically impure (Case II). In both cases, the apparent free substrate concentration required for half-saturation of the protein, [S]_0.5,app, increases linearly with increasing total protein concentration. Reciprocal plots and Scatchard plots are nonlinear. The curvature of both plots is opposite to that observed for the heterogeneity of binding sites. Hill plots are curved with average slopes >1 in the region of half-saturation. If the radiochemical impurity goes undetected, the experimental data might lead an investigator to suggest a number of unnecessarily complicated binding models. The plots obtained in the presence of a radiochemical impurity are very similar to those seen when the receptor protein is a dissociable dimer and K_s (monomer) <K_s (dimer). However, in the dimer model the variation of [S]_0.5 with total protein concentration is nonlinear. The most direct way of assessing the radiochemical purity of a labeled substrate is to vary the binding protein concentration at a fixed concentration of S¹. If all of the radioactivity resides in S¹, the concentration of the PS¹ complex will approach [S¹]_t as [P]_t increases, while the free unbound radioactivity will be driven toward zero. If the labeled substrate is radiochemically impure, “saturating” protein will not bind all of the label. This procedure will detect some types of major impurities missed by paper chromatography (e.g., ³H₂O and nonreactive isomers of S¹).