Bacterial community dynamics during embryonic development of the little skate (Leucoraja erinacea)

Background Microbial transmission from parent to offspring is hypothesized to be widespread in vertebrates. However, evidence for this is limited as many evolutionarily important clades remain unexamined. There is currently no data on the microbiota associated with any Chondrichthyan species during embryonic development, despite the global distribution, ecological importance, and phylogenetic position of this clade. In this study, we take the first steps towards filling this gap by investigating the microbiota associated with embryonic development in the little skate, Leucoraja erinacea, a common North Atlantic species and popular system for chondrichthyan biology. Methods To assess the potential for bacterial transmission in an oviparous chondrichthyan, we used 16S rRNA amplicon sequencing to characterize the microbial communities associated with the skin, gill, and egg capsule of the little skate, at six points during ontogeny. Community composition was analyzed using the QIIME2 pipeline and microbial continuity between stages was tracked using FEAST. Results We identify site-specific and stage-specific microbiota dominated by the bacterial phyla Proteobacteria and Bacteroidetes. This composition is similar to, but distinct from, that of previously published data on the adult microbiota of other chondrichthyan species. Our data reveal that the skate egg capsule harbors a highly diverse bacterial community–particularly on the internal surface of the capsule–and facilitates intergenerational microbial transfer to the offspring. Embryonic skin and external gill tissues host similar bacterial communities; the skin and gill communities later diverge as the internal gills and skin denticles develop. Conclusions Our study is the first exploration of the chondrichthyan microbiota throughout ontogeny and provides the first evidence of vertical transmission in this group.

Field Monitoring of Tritia mutabilis (Linnaeus, 1758) Egg Capsule Deposition and Intracapsular Embryonic Patterns Using Artificial Substrates and Machine Learning-Based Approaches

Tritia mutabilis (Linnaeus, 1758) represents a marine gastropod species of ecological and economical importance especially in coastal areas of the central Adriatic Sea (Italy). T. mutabilis encloses its fertilized eggs within capsules which play a protective role in the embryo defense against adverse environmental factors. Egg capsules are attached to any hard substrates and the availability of adequate substrates for oviposition represents therefore a major determinant of reproductive output of this species. The aim of the present study was to provide the first comprehensive monitoring of T. mutabilis egg capsule deposition and intracapsular embryonic patterns using specific artificial substrates and innovative analytical approaches. Square-based pyramid structures were placed within an area subjected to small-scale fishing activity along the Italian coastal waters of the central Adriatic Sea and monitored from March to June 2019. In addition, a machine learning-based approach was developed in order to speed up and automate time-consuming counting procedures of egg capsules attached on each pyramid. Overall, egg capsules were deposited on the almost totality of the artificial substrates reaching values of the surface coverage per site ranging from 31 to 97%. These findings lead to a quantitative estimation of egg number per site included between 27,060 and 62,940 capsules. Our results demonstrate that using these artificial substrates together with monitoring of both egg capsule deposition patterns and intracapsular developmental stages may be useful to improve the T. mutabilis stock management.

Embryonic and Larval Development of Thai Pangas Pangasianodon Hypopthalmus (Sauvage, 1878) Under Hatchery Condition

The embryonic and larval development of Pangasianodon hypophthalmus was investigated during peak spawning periods (May-July 2019). The fertilized eggs were adhesive and spherical with a greenish‐brown egg capsule. The yolk sac was yellowish‐brown in color and 1.00–1.70 mm in diameter. The first cleavage stage, embryonic shield, head, tail region, neural grooves and somites were apparent after fourteen hours post‐fertilization. The ranges of incubation period were from 18.00-20.00 hrs at a temperature of 26-30°C. The newly hatched larvae were transparent and light yellowish in color with a body length of 2.98–3.10 mm. Eye pigment appeared and the heart started to work within 12-16 hrs of hatching. The mouth became well developed at the age of 24 hrs; barbules were prominent, elongated and look like threads. The yolk sac was fully absorbed and the palatine teeth were fully increased during the 3 days pro‐larval stage. The stomach became functional and aerial respiration started after 3 days of larval development. After 72 hrs, the young fry was well‐developed, and appeared an adult, and length was measured up to 7.20±0.02 mm. When daily ration of pangas larvae is insufficient cannibalism was recorded. This study must be supportive for researcher and nursery owner on the biology and ecology of the fish, which might be helpful for appropriate measure of sustainable nursery, rearing and management technology of pangas. Bangladesh J. Zool. 49(1): 147-159, 2021

Intergenerational microbial transmission in the little skate (Leucoraja erinacea)

Microbial transmission from parent to offspring is hypothesized to be universal in vertebrates. However, evidence for this is limited as many clades remain unexamined. Chondrichthyes, as one of the earliest–branching vertebrate lineages, provide an opportunity to investigate the phylogenetic breadth of this hypothesis. To assess the potential for bacterial transmission in an oviparous chondrichthyan, we used 16S rRNA amplicon sequencing to characterize the microbial communities associated with the skin, gill, and egg capsule of the little skate, Leucoraja erinacea, at six points during ontogeny. We identify site-specific microbiomes dominated by the bacterial phyla Proteobacteria and Bacteroidetes, a composition similar to, but distinct from, that of other chondrichthyans. Our data reveal that the skate egg capsule harbors a highly diverse bacterial community–particularly on the internal surface of the capsule–and facilitates intergenerational microbial transfer to the offspring. Embryonic skin and external gill tissues host similar bacterial communities; the skin and gill communities later diverge as the internal gills and skin denticles develop. Our study is the first exploration of the chondrichthyan microbiome throughout ontogeny and provides the first evidence of vertical transmission in this group, which may be the primary mechanism for the signature of phylosymbiosis previously observed in elasmobranchs.

Studies on neotropical Phasmatodea XXI: Sigaruphasma, a new genus of Hesperophasmatini Bradley & Galil, 1977, from Hispaniola with the descriptions of two new species (Phasmatodea: Cladomorphinae)

The new Hesperophasmatini–genus Sigaruphasma gen. nov. from Hispaniola is described and illustrated. It is remarkable for violating several of the previously stated diagnostic features of the tribe Hesperophasmatini Bradley and Galil, 1977. It is well characterized by the cylindrical, cigar–like body of females, proportionally very short legs, strongly broadened profemora of females, lacking sensory–areas on the probasisternum and profurcasternum as well as the smooth egg–capsule. Two new species are described from the Dominican Republic, both from the males, females and eggs. S. bouladoui sp. nov. occurs in the eastern portion of Hispaniola (Monseñor Nouel, San Cristóbal, San José de Ocoa and Samaná provinces) and has fully winged males. S. armatum sp. nov. occurs in the southern and southeastern Dominican Republic (Barahona, La Vega, San José de Ocoa, Elías Piña, Santiago provinces) and has apterous males with a strong body spination. Both species show a remarkable range of intraspecific variability and polymorphism, which is described and illustrated.

Heterotrophic Carbon Fixation in a Salamander-Alga Symbiosis

The unique symbiosis between a vertebrate salamander, Ambystoma maculatum, and unicellular green alga, Oophila amblystomatis, involves multiple modes of interaction. These include an ectosymbiotic interaction where the alga colonizes the egg capsule, and an intracellular interaction where the alga enters tissues and cells of the salamander. One common interaction in mutualist photosymbioses is the transfer of photosynthate from the algal symbiont to the host animal. In the A. maculatum-O. amblystomatis interaction, there is conflicting evidence regarding whether the algae in the egg capsule transfer chemical energy captured during photosynthesis to the developing salamander embryo. In experiments where we took care to separate the carbon fixation contributions of the salamander embryo and algal symbionts, we show that inorganic carbon fixed by A. maculatum embryos reaches 2% of the inorganic carbon fixed by O. amblystomatis algae within an egg capsule after 2 hours in the light. After 2 hours in the dark, inorganic carbon fixed by A. maculatum embryos is 800% of the carbon fixed by O. amblystomatis algae within an egg capsule. Using photosynthesis inhibitors we show that A. maculatum embryos and O. amblystomatis algae compete for available inorganic carbon within the egg capsule environment. Our results confirm earlier studies suggesting a role of heterotrophic carbon fixation during vertebrate embryonic development. Our results also show that the considerable capacity of developing A. maculatum embryos for inorganic carbon fixation precludes our ability to distinguish any minor role of photosynthetically transferred carbon from algal symbionts to host salamanders using bicarbonate introduced to the egg system as a marker.

A new species of the genus Parapachymorpha Brunner von Wattenwyl, 1893 (Phasmida, Phasmatidae, Clitumninae) from Laos

Parapachymorpha is one of eight genera within the tribe Medaurini of subfamily Clitumninae (Phasmatidae). It was established by Brunner von Wattenwyl (1893), with the type species Parapachymorpha nigra by subsequent designation of Kirby (1904), from Myanmar. Species of this genus are widely distributed in oriental tropics (Laos, China, Thailand, Myanmar, Vietnam and Cambodia), with only 11 known species in the world (Brock et al. 2018, Ho 2017). Species of the genus Parapachymorpha can be recognized by following characters (Brunner von Wattenwyl 1893;1907, Henmemann & Conle 2008, Ho 2017): 1) body robust in female and slender in male with long leg in relation to the length; 2) body surface of female granulose or spinose; 3) mesonotum of female more and less expanded posteriorly; 4) abdominal tergites lacking expanded prostero–lateral angles in both sexes; 5) laminal supraanalis undeveloped in female; 6) semi–tergite of male irregularly rectangular, with an additional finger­–like ventro–apical appendix on the lower margin and reduced or absent; 7) egg capsule oval to oblong and covered with a raised net–like structure in lateral view; 8) micropylar plate oval; 9) operculum concave or convex. In the present study, we describe additional species, Parapachymorpha minuta sp. nov. from Laos, with photographs of both sexes of adults and egg.