Developmental neuroanatomy of the Rosy Bitterling Rhodeus ocellatus (Teleostei: Cypriniformes)—A microCT study

ABSTRACTBitterlings are a group of teleost fish (Cyprinifromes: Acheilanathidae) notable for their brood parasitic lifestyle. Bitterling embryos develop as parasites inside the gill chamber of their freshwater mussel hosts. However, little is known about brain development in this species. Here, we have imaged the development of the brain of the Rosy Bitterling (Rhodeus ocellatus) at four embryonic stages (165, 185, 210, 235 hours post-fertilization) using micro-computed tomography (microCT) with special emphasis on developmental regionalization and brain ventricular organization. We provide a detailed neuroanatomical account of the development of the brain divisions with reference to The Atlas of Early zebrafish Brain Development and the updated prosomeric model. Segmentation and three-dimensional visualization of the ventricular system were performed in order to clarify changes in the longitudinal brain axis as a result of cephalic flexure during development. During early embryonic and larval development, we find that histological differentiation, tissue boundaries, periventricular proliferation zones, and ventricular spaces are all recognizable using microCT. Importantly, our approach is validated by the fact that the profile of CT values displayed here in the bitterling brain are consistent with genoarchitecture identified in previous studies. We also find developmental heterochrony of the inferior lobe in the Rosy Bitterling compared to the zebrafish. Our study provides a foundation for future studies of the brain development in the Rosy Bitterling, a valuable model species for studying the evolutionary adaptations associated with brood parasitism.

Anuran Heart Metamorphosis: Anatomical Support for Pulmonary Blood Separation in the Early Aquatic Phase

Background: In both larval and adult anurans, blood separation and respiratory physiology have remained an enigma. While various blood separation mechanisms have been proposed, the same structure is seen as playing a key role: the conus arteriosus. However, previous findings on its internal structure are contradictory, depending on the specifics of the 2D imaging methods used by different authors. To resolve this problem, we used high-resolution X-ray microtomography of whole Bufo bufo specimens to acquire the first detailed 3D descriptions of this complex structure through metamorphosis. Results: In early tadpoles two small valvular openings develop at the ventricular-conal junction, providing two paths separated by the septum coni and continuing into the aortic arches. Thus, structures to support segregated pulmonary circulation are fully developed well before the lungs appear. The external gills undergo partial resorption and retreat asymmetrically into a gill chamber formed by a hyoidal cover, leaving only a single opening on the left side, the opercular spout. Conclusions: The timing of events in Bufo circulatory development does not track the changing modes of respiration used by the developing tadpole. In particular, a system capable of double circulation carries only oxygen-depleted blood for a significant portion of the tadpole stage.

Evolution of vertebrate gill covers via shifts in an ancient Pou3f3 enhancer

Whereas the gill chambers of jawless vertebrates open directly into the environment, jawed vertebrates evolved skeletal appendages that drive oxygenated water unidirectionally over the gills. A major anatomical difference between the two jawed vertebrate lineages is the presence of a single large gill cover in bony fishes versus separate covers for each gill chamber in cartilaginous fishes. Here, we find that these divergent patterns correlate with the pharyngeal arch expression of Pou3f3 orthologs. We identify a deeply conserved Pou3f3 arch enhancer present in humans through sharks but undetectable in jawless fish. Minor differences between the bony and cartilaginous fish enhancers account for their restricted versus pan-arch expression patterns. In zebrafish, mutation of Pou3f3 or the conserved enhancer disrupts gill cover formation, whereas ectopic pan-arch Pou3f3b expression generates ectopic skeletal elements resembling the multimeric covers of cartilaginous fishes. Emergence of this Pou3f3 arch enhancer >430 Mya and subsequent modifications may thus have contributed to the acquisition and diversification of gill covers and respiratory strategies during gnathostome evolution.

Evolution of vertebrate gill covers via shifts in an ancient Pou3f3 enhancer

SummaryWhereas the gill chambers of extant jawless vertebrates (lampreys and hagfish) open directly into the environment, jawed vertebrates evolved skeletal appendages that promote the unidirectional flow of oxygenated water over the gills. A major anatomical difference between the two jawed vertebrate lineages is the presence of a single large gill cover in bony fishes versus separate covers for each gill chamber in cartilaginous fishes. Here we find that these divergent gill cover patterns correlate with the pharyngeal arch expression of Pou3f3 orthologs. We identify a Pou3f3 arch enhancer that is deeply conserved from cartilaginous fish through humans but undetectable in lampreys, with minor sequence differences in the bony versus cartilaginous fish enhancers driving the corresponding single versus multiple gill arch expression patterns. In zebrafish, loss of Pou3f3 gene function disrupts gill cover formation, and forced expression of Pou3f3b in the gill arches generates ectopic skeletal elements resembling the multiple gill cover pattern of cartilaginous fishes. Emergence of this Pou3f3 enhancer >430 mya and subsequent modifications may thus have contributed to the acquisition and diversification of gill covers and respiratory strategies during gnathostome evolution.

Identification and Characterization of Carboxyl Esterases of Gill Chamber-Associated Microbiota in the Deep-Sea Shrimp Rimicaris exoculata by Using Functional Metagenomics

ABSTRACTThe shrimpRimicaris exoculatadominates the fauna in deep-sea hydrothermal vent sites along the Mid-Atlantic Ridge (depth, 2,320 m). Here, we identified and biochemically characterized three carboxyl esterases from microbial communities inhabiting theR. exoculatagill that were isolated by naive screens of a gill chamber metagenomic library. These proteins exhibit low to moderate identity to known esterase sequences (≤52%) and to each other (11.9 to 63.7%) and appear to have originated from unknown species or from genera ofProteobacteriarelated toThiothrix/Leucothrix(MGS-RG1/RG2) and to theRhodobacteraceaegroup (MGS-RG3). A library of 131 esters and 31 additional esterase/lipase preparations was used to evaluate the activity profiles of these enzymes. All 3 of these enzymes had greater esterase than lipase activity and exhibited specific activities with ester substrates (≤356 U mg−1) in the range of similar enzymes. MGS-RG3 was inhibited by salts and pressure and had a low optimal temperature (30°C), and its substrate profile clustered within a group of low-activity and substrate-restricted marine enzymes. In contrast, MGS-RG1 and MGS-RG2 were most active at 45 to 50°C and were salt activated and barotolerant. They also exhibited wider substrate profiles that were close to those of highly active promiscuous enzymes from a marine hydrothermal vent (MGS-RG2) and from a cold brackish lake (MGS-RG1). The data presented are discussed in the context of promoting the examination of enzyme activities of taxa found in habitats that have been neglected for enzyme prospecting; the enzymes found in these taxa may reflect distinct habitat-specific adaptations and may constitute new sources of rare reaction specificities.

Probopyrus Buitendijki (Isopoda, Bopyridae), a Parasitic Isopod on Macrobrachium Rosenbergii in Timun River, Negeri Sembilan, Malaysia

A bopyrid isopod was found attached in the gill chamber of a wild giant freshwater prawn, Macrobrachium rosenbergii (De Man, 1879) from the Timun River, Negeri Sembilan (Malaysia) (2°28′N 102°02′E), with a prevalence of 0.27% (2/743). The specimens measured 18.25±0.35 mm in length and 15.25±0.35 mm in width. The body of the isopod was subcordate and slightly distorted. It has five oostegites, with black pigment. The first oostegites are large, the 2nd and 3rd are suboval and smaller, while the 4th and 5th are long and ending in sharp points. Both specimens were identified as adult female Probopyrus buitendijki (Horst, 1910). The isopod was found only in January of 2009 and 2010, which months recorded a relatively low rainfall. A histopathological study of the infected gill showed impairment of the gill filaments, necrosis, and hyperplasia. Such effects may reduce the respiration efficiency of the gills.

Growth and reproduction of Munida rutllanti (Decapoda: Anomura: Galatheidae) and impact of parasitism by Pleurocrypta sp. (Isopoda: Bopyridae) in the Adriatic Sea

Relative growth and reproductive biology of Munida rutllanti were investigated for the first time in the Adriatic Sea. A total of 938 individuals were analysed. Sex-ratio differed statistically from the expected 1:1. Six individuals exhibited secondary sex characteristics of both males and females. Carapace length of males ranged from 10.5 to 21.5 mm, while in females it ranged from 11.2 to 19.4 mm. Sexual dimorphism was observed in seven morphometric characters. Ovigerous females were first observed in summer and later in autumn with higher frequency. Realized fecundity showed wide variation (273–3250 eggs) and positive correlation between the brood and female size. An epicaridean isopod Pleurocrypta sp., parasitizing the gill chamber of both sexes was isolated and its effect on the oogenesis was studied by histological examination of host reproductive system. Growth inhibition, modification of secondary sex characteristics, as well as retardation of oogenesis and failure of oviposition, are repercussions of bopyrid infestation. Given the small prevalence (7.85%) of the bopyrid in the M. rutllanti Adriatic population, we assume that for the moment there is no severe effect on the host population dynamic.