Exploring the regulatory role of nitric oxide (NO) and the NO-p38MAPK/cGMP pathway in larval settlement of the bryozoan Bugula neritina

The bryozoan Bugula neritina is a cosmopolitan marine fouling species that causes major fouling problems in sub-tropical waters. Settlement of B. neritina larvae can be triggered without an obvious external cue. Here, the negative regulatory role of nitric oxide (NO) during larval settlement of B. neritina was demonstrated to be mediated by cyclic guanosine monophosphate (cGMP). Although the regulatory role of the NO-p38 MAPK signaling axis in larval settlement was not evident, inhibition of nitric oxide synthase (NOS) led to the deactivation of p38 MAPK. Exclusive localization of NO and NO signaling components in sensory-related organs of the larvae is consistent with its signal transduction function in metamorphosis. Overall, this study provides new insights into the regulatory roles of the NO-p38MAPK/cGMP pathway in B. neritina settlement.     

Uncinaria stenocephala: assessment of antigens for the immunodiagnosis of canine uncinariosis

Although Uncinaria stenocephala is the most frequent hookworm in the intestine of dogs from Northern, Central and Southern Europe, little is known about its host-parasite relationship. Three groups of sera from dogs (Group 1: dogs naturally infected only by U. stenocephala; Group 2: helminth-free dogs at necropsy, and Group 3: dogs parasitized by other helminths) were analyzed by ELISA using U. stenocephala antigens from adult worms (somatic and excretory-secretory antigens) and from L3 larvae (somatic antigens). All three sources of antigens were found to be suitable for immunodiagnosis of canine uncinariosis with up to 90% efficacy. However, an analysis to assess the diagnostic value of the different antigens demonstrated that the adult excretory-secretory antigens had a higher diagnostic efficacy (96.7%), indicating that this is the best antigen source for the diagnosis of Uncinaria infection.     

Effects of prehatching salinity and initial larval biomass on survival and duration of development in the zoea 1 of the estuarine crab, Chasmagnathus granulata, under nutritional stress

The effects of individual larval biomass, and salinity experienced during embryogenesis (i.e., prehatching salinity) on starvation tolerance and growth of zoea 1 of the estuarine crab (Chasmagnathus granulata) were evaluated in laboratory experiments. Freshly hatched zoeae 1 were obtained from broods maintained at three salinities (15‰, 20‰ and 32‰), and cultured at 20‰ under different initial feeding periods and subsequent food deprivation (“point of reserve saturation” experiment: PRS) or under initial periods of food deprivation and subsequent feeding (point of no return experiment: PNR). Another group of larvae were used for determination of biomass (dry weight, carbon, and nitrogen) of zoea 1.Larval survival and duration of development depended on the length of feeding period: no larvae reached the second instar under complete starvation; survival was higher and duration of development shorter as the feeding period lengthened. After different initial feeding periods (PRS experiment), zoeae 1 that hatched from eggs incubated at the prehatching salinities of 15‰ and 20‰ showed higher survival and shorter duration of development than those at 32‰. Prehatching salinity also affected the amount of reserves accumulated during the first 2 days after hatching, with larvae from 15‰ and 20‰ showing the highest percentage of total accumulation of carbon and nitrogen. Initial larval biomass did not affect survival, but it had a slight effect on duration of development, with larger larvae (in terms of biomass) developing faster. After different initial starvation periods (PNR experiment), prehatching salinity did not affect survival, but it affected duration of development: larvae from 15‰ and 20‰ reached the second instar earlier. Variability in survival and duration of development was explained in part by among-brood variability in initial larval biomass: larvae with higher biomass showed higher survival and shorter duration of development. Thus, C. granulata, survival and duration of development under food stress depend on the interaction between environmental conditions experienced before and after hatching (pre- and posthatching factors, respectively).     

Developmental patterns of larval growth in the edible spider crab, Maja brachydactyla (Decapoda: Majidae)

The large edible spider crab Maja brachydactyla Balss, 1922, an overexploited coastal fishery resource in Galicia (NW Spain), is considered as a potential aquaculture candidate. Patterns of its larval growth were studied under controlled laboratory conditions (constant 18 ± 1 °C; 36‰ salinity; photoperiod ca. 12:12 h; lipid-enriched Artemia metanauplii provided as food). From hatching through complete larval development and metamorphosis to the first juvenile crab instar, changes in carapace size, dry weight (DW), ash content, elemental composition (carbon, hydrogen, nitrogen; CHN), and proximate biochemical composition (total proteins, lipids, carbohydrates; Pr, L, Ch) were measured in successive stages (zoea I, II, megalopa, crab I). Body size may be described as a linear function of the number of molting cycles, whereas the amounts of DW, CHN, Pr, L, and Ch per individual increased exponentially (3 to 9 fold). The highest growth rates were observed in L, C and H, the lowest in DW, Pr and N. As a consequence of these patterns, the C:N mass ratio as well as the fractions of L, C and H (in % of DW) increased significantly, while those of Pr and N decreased from 26% to 16% of DW. Throughout development, however, Pr remained the principal biochemical component of total DW. Positive correlations between biochemical and CHN data allow for estimates of Pr from N and of L from C values per individual. The patterns of larval growth observed in M. brachydactyla are, in general, similar to those previously described for other brachyuran crabs with a planktotrophic mode of larval development.     

On the systematic position of the family Gyrinidae (Coleoptera: Adephaga)

Various characters of adult and larval members of Adephaga and Cupedidae were analyzed, and suggest that Gyrinidae are the sister-group of the remaining Adephaga, and are not closely related to the remaining aquatic Adephaga. The aquatic families Noteridae, Amphizoidae, Hygrobiidae and Dytiscidae seem to form a well founded monophyletic unit. The following characters are considered as synapomorphies of Adephaga excluding Gyrinidae: bifurcate condition of the muscle (= M.) tentoriopraementalis inferior, reduction of hypopharynx, strongly developed prosternal process, reduction in size and specialized modification of the ventral sclerite of the mesothorax, strongly developed mesofurcal arms, a high mesopleural ridge, globular mesocoxae restricted to rotatory movements, invaginated sternum VIII (coxostemum), the strongly curved base of the median lobe of the aedeagus, which articulates with the parameres, the rotated position of the aedeagus in repose, fusion of the larval clypeolabrum with the frons and reduction of the larval lacinia. Mesal shifting of M. episterno-coxalis prothoracis, and the fusion of the apical portions of the malpighian tubules of either side are considered as synapomorphies of Adephaga excluding Rhysodidae and Gyrinidae. Lateral reduction of the meta “sternal” transverse ridge and the presence of the subcubital setal binding patch of the hind wing are considered as synapomorphic characters of Trachypachidae, Noteridae, Amphizoidae, Hygrobiidae and Dytiscidae. We postulate that the metacoxal fusion occurred independently in gyrmids and the common ancestor of Trachypachidae, Noteridae, Amphizoidae, Hygrobiidae and Dytiscidae. Consequently we consider this character state as another synapomorphy of Trachypachidae and Hydradephaga excluding Haliplidae and Gyrinidae. The following characters are considered as synapomorphies of Noteridae, Amphizoidae, Hygrobiidae and Dytiscidae: Loss of tactile setae on the head capsule, metafurcal origin on the intercoxal wall, expansion of the intercoxal wall, elongation of the subcubital setal binding patch, loss of Mm. furca-coxale anterior and posterior, reduction of the larval abdominal segments IX and X, and the shifting of the uropmphi onto the ventral side of segment VIII. Presence of M. tentorio-mandibularis and M. stipitopalpalis intemus are certainly primitive features of adult gyrinids but the distribution of these character states among most members of Adephaga is yet unclear. Chemical defence gland constituents point towards a very isolated position of Gyrinidae. The old age of the group, documented by a larva found in upper Permian deposits, may support the hypothesis of a sister-group relation-ship between Gyrinidae and the remainder of Adephaga.     

Bacillus thuringiensis Cry4Aa insecticidal protein: Functional importance of the intrinsic stability of the unique α4–α5 loop comprising the Pro-rich sequence

The long loop connecting transmembrane α4 and α5 of the Bacillus thuringiensis Cry4Aa toxin possesses a unique feature with Pro-rich sequence (Pro¹⁹³Pro¹⁹⁴_Pro¹⁹⁶) which was shown to be crucial for toxicity. Here, the structural role in the intrinsic stability of the Pro-rich sequence toward toxin activity was investigated. Three Val-substituted mutants (P193V, P194V and P196V) and one Phe-substituted mutant (P193F) were generated and over-expressed in Escherichia coli as inclusions at levels equal to the wild-type. Bioassays demonstrated that all mutants, particularly P193V and P193F whose inclusions were hardly soluble in carbonate buffer (pH 9.0), exhibited reduced toxicity, suggesting an essential role in toxin function by the specific cyclic structure of individual Pro residues. Analysis of the 65-kDa Cry4Aa structure from 10-ns molecular dynamics (MD) simulations revealed that the α4–α5 loop is substantially stable as it showed low structural fluctuation with a 1.2-Å RMSF value. When the flexibility of the α4–α5 loop was increased through P193G, P194G and P196G substitutions, decreased toxicity was also observed for all mutants, mostly for the P193G mutant with low alkali-solubility, suggesting a functional importance of loop-rigidity attributed by individual Pro-cyclic side-chains, particularly Pro¹⁹³. Further MD simulations revealed that the most critical residue−Pro¹⁹³ for which mutations vastly affect toxin solubility and larval toxicity is in close contact with several surrounding residues, thus playing an additional role in the structural arrangement of the Cry4Aa toxin molecule. Altogether, our data signify that the intrinsic stability of the unique Cry4Aa α4–α5 loop structure comprising the Pro-rich sequence plays an important role in toxin activity.     

Potentially handicapped but otherwise functional: Malformations in prey capture tools show no impacts on octopus life

Larval mortality is a keystone ecological factor for many benthic octopus since it mostly occurs before their settlement in the sea bottom as benthic juveniles. The literature had revealed that records of adult animals with morphological abnormalities (teratologies) are fewer in species with complex life cycle than in those with direct development. This is a direct consequence of the morphological, physiological, and development challenges that the transition from the larval to the adult morphology represents. During a routine fishing sample, we found an immature female horned octopus with additional buccal structures in two suckers of its ventral arms, likely rendering these suckers as inefficient. Based on the literature about the natural history of octopus, we provide evidence that these abnormalities were present at the moment of hatch. We evaluated the impact of the teratologies by comparing the shape of the buccal beaks and the trophic niche of the individual with five normal conspecifics. Although the beaks showed a different shape than normal individuals, the trophic niche was similar. Surprisingly, the teratological condition of the individual likely had no severe impacts on its life, even though it likely represents a handicap for its survival during its planktonic life. We also comment on other previous records from the literature of teratological adult octopus to highlight the amazing adaptive capacity of octopus to deal with challenging morphologies.     

Tidal and diurnal variations in larval fish abundance in an estuarine inlet in Ariake Bay,Japan: implication for selective tidal stream transport

We have conducted a preliminary study of tidal and diurnal variations in the distribution of dominant larval and juvenile fishes in the Chikugo River inlet (Ariake Bay, Kyushu, Japan) to determine whether selective tidal stream transport (STST) occurs. Larval and juvenile fish were collected from the mesohaline zone of the Chikugo River inlet during spring 2002. Temperature, salinity, depth, and current velocity were measured. Larval and juvenile abundance were compared among four tidal conditions, flooding tide, high tide, ebbing tide, and low tide, and between day and night. A total of 12 families, 15 species, and 5,577 individuals were collected. Temperature did not vary significantly with tidal conditions whereas salinity, depth, and current velocity varied significantly. Salinity also was correlated significantly and positively with depth. The abundance of most of the fishes was correlated positively and significantly with salinity and depth. Lateolabrax japonicus, Trachidermus fasciatus, Acanthogobius hasta, and other gobiid larvae (Gobiidae spp.) were significantly more abundant during high tide; in contrast, Coilia nasus and Neosalanx reganius were most abundant during low tide. The abundance of most of the fishes was higher during high tides at night than during the day, indicating the existence of STST, which may be strategically associated with ascending progress to upstream nursery areas.