Juvenile Development Research Articles

Temperature-size responses during ontogeny are independent of progenitors' thermal environments.

Warming generally induces faster developmental and growth rates, resulting in smaller asymptotic sizes of adults in warmer environments (a pattern known as the temperature-size rule). However, whether temperature-size responses are affected across generations, especially when thermal environments differ from one generation to the next, is unclear. Here, we tested temperature-size responses at different ontogenetic stages and in two consecutive generations using two soil-living Collembola species from the family Isotomidae: Folsomia candida (asexual) and Proisotoma minuta (sexually reproducing). We used individuals (progenitors; F0) from cultures maintained during several generations at 15 °C or 20 °C, and exposed their offspring in cohorts (F1) to various thermal environments (15 °C, 20 °C, 25 °C and 30 °C) during their ontogenetic development (from egg laying to first reproduction; i.e., maturity). We measured development and size traits in the cohorts (egg diameter and body length at maturity), as well as the egg diameters of their progeny (F2). We predicted that temperature-size responses would be predominantly determined by within-generation plasticity, given the quick responsiveness of growth and developmental rates to changing thermal environments. However, we also expected that mismatches in thermal environments across generations would constrain temperature-size responses in offspring, possibly due to transgenerational plasticity. We found that temperature-size responses were generally weak in the two Collembola species, both for within- and transgenerational plasticity. However, egg and juvenile development were especially responsive at higher temperatures and were slightly affected by transgenerational plasticity. Interestingly, plastic responses among traits varied non-consistently in both Collembola species, with some traits showing plastic responses in one species but not in the other and vice versa. Therefore, our results do not support the view that the mode of reproduction can be used to explain the degree of phenotypic plasticity at the species level, at least between the two Collembola species used in our study. Our findings provide evidence for a general reset of temperature-size responses at the start of each generation and highlight the importance of measuring multiple traits across ontogenetic stages to fully understand species' thermal responses.

Characterization of adaptive expression regulation of yellowtail kingfish (Seriola lalandi) leptin, receptor, and receptor overlapping transcript genes in response to fasting and re-feeding strategies.

Leptins and other related genes have been proven to play vital roles in food intake, weight control, and other life activities. While the function of leptins in yellowtail kingfish (Seriola lalandi) has not yet been explored, in the present study, we investigated the structure and preliminary function of four leptin-related genes in S. lalandi. In detail, the sequence of two leptin genes (lepa and lepb), one leptin receptor gene (lepr), and one leptin receptor overlapping transcript (leprot) gene were obtained by homology cloning and RACE methods, in which lepa and lepb have similar structure. Moreover, homologous sequence alignment and evolutionary analysis of all four genes were clustered with Seriola dumerili. The tissue distribution of these four genes in thirteen tissues of yellowtail kingfish was detected by RT-qPCR. Both lepa and leprot were highly expressed in the brain and ovary, while lepb was highly expressed in the pituitary, gill, muscle, and ovary; lepr was highly expressed in the gill, kidney, and ovary. Additionally, these four genes also played roles in embryo development and early growth and development of larvae and juveniles of yellowtail kingfish. Finally, the function of leptin and leptin-related genes was investigated during fasting and re-feeding adaption of yellowtail kingfish. The results showed that these four genes have different regulation functions in five tissues; for example, the mRNA levels of lepa, lepr, and leprot in the brain decreased during fasting and immediately increased after re-feeding, while the mRNA level of lepb did not show significant fluctuation during starvation but significantly lowered after re-feeding. However, lepa and lepb mRNA levels were significantly elevated during fasting and returned to control levels after re-feeding, and there were no significant changes in the expression of lepr and leprot in the liver during fasting and after re-feeding. Moreover, the body mass of fish in the experimental group was measured, and compensatory growth was found after the resumption of feeding. These results suggested that leptin and receptor genes play different functions in different tissues to regulate the physiological state of fish in food deficiency and gain processes.

Law’s Silence on Cyberbullying to Children in Indonesia

With the advancement of the Internet, cyberbullying is fast emerging as a significant issue and a new form of violence in Indonesia. Additionally, whether the Internet has become a catalyst for conventional bullying is a critical question that must be addressed. In Indonesia, cyberbullying is now recognized as an imminent concern with regard to juvenile behaviour and development outcomes. The Indonesian legal system, however, has no direct legislation on cyberbullying. The existing laws on juvenile crimes and online offenses do not adequately address specific concerns raised by cyberbullying. This article explores the correlation between high exposure to violent content over the Internet and the recent increase in violence among children in Indonesia. The effect of cyberbullying victimization and its potential to create perpetrators of bullying has been explored within the context of the inadequacy of the current Indonesian legal system’s response to online harassment, particularly the lack of adequate laws against cyberbullying.

Timing-specific parental effects of ocean warming in a coral reef fish.

Population and species persistence in a rapidly warming world will be determined by an organism's ability to acclimate to warmer conditions, especially across generations. There is potential for transgenerational acclimation but the importance of ontogenetic timing in the transmission of environmentally induced parental effects remains mostly unknown. We aimed to disentangle the effects of two critical ontogenetic stages (juvenile development and reproduction) to the new-generation acclimation potential, by exposing the spiny chromis damselfish Acanthochromis polyacanthus to simulated ocean warming across two generations. By using hepatic transcriptomics, we discovered that the post-hatching developmental environment of the offspring themselves had little effect on their acclimation potential at 2.5 months of life. Instead, the developmental experience of parents increased regulatory RNA production and protein synthesis, which could improve the offspring's response to warming. Conversely, parental reproduction and offspring embryogenesis in warmer water elicited stress response mechanisms in the offspring, with suppression of translation and mitochondrial respiration. Mismatches between parental developmental and reproductive temperatures deeply affected offspring gene expression profiles, and detrimental effects were evident when warming occurred both during parents' development and reproduction. This study reveals that the previous generation's developmental temperature contributes substantially to thermal acclimation potential during early life; however, exposure at reproduction as well as prolonged heat stress will likely have adverse effects on the species' persistence.

Water Level Fluctuation Effect on Fish Reproduction Success

Alteration of water levels of the lake/reservoir due to changes in river discharges, upstream abstraction, and drawdown regulation due to hydropower generation has been reported as among the major challenges to fish physiology and ultimately reproduction. Variations in lake/reservoir water levels influence biodiversity and the abundance of lake/reservoir biota. Variations have the greatest impacts in the littoral zones hence, interfering with fish spawning, incubation, and hatching of eggs, as well as the development of larvae, postlarvae, and juveniles. This particular paper reviews the literature available on the effect of the reservoirs/lakes’ water level fluctuations on fish reproduction success using the documentary view method. The literature argues that water level fluctuations have both positive and negative impacts depending on frequency, magnitude, and duration and the species exposed. Extreme fluctuations tend to bring more adverse impacts. It further indicates that extreme and untimely water level fluctuation has direct impacts on the aquatic habitats and ultimately impacts fish assemblage and their populations. Few articles indicate the range of decrease or increase of water level, duration of such events, and effects they have on reservoir/lake ecosystem functions and fish physiology. Nevertheless, quantification of moderate and extreme water level fluctuation and associated effects is lacking. Although water level fluctuation is an important environmental cue for aquatic organisms, literature shows that the reduction of extreme water level variations especially multiannual variations is vital for fish reproduction. Therefore, upstream water use and reservoir operations should take into consideration the effects of water level fluctuations on reservoir structure, biological functions, and ultimate effects on fish reproduction.

Widespread Production of Polyunsaturated Aldehydes by Benthic Diatoms of the North Pacific Ocean's Salish Sea.

Diatoms are key primary producers across marine, freshwater, and terrestrial ecosystems. They are responsible for photosynthesis and secondary production that, in part, support complex food webs. Diatoms can produce phytochemicals that have transtrophic ecological effects which increase their competitive fitness. Polyunsaturated aldehydes (PUAs) are one class of diatom-derived phytochemicals that are known to have allelopathic and anti-herbivory properties. The anti-herbivory capability of PUAs results from their negative effect on grazer fecundity. Since their discovery, research has focused on their production by pelagic marine diatoms, and their effects on copepod egg production, hatching success, and juvenile survival and development. Few investigations have explored PUA production by the prolific suite of benthic marine diatoms, despite their importance to coastal trophic systems. In this study, we tested eight species of benthic diatoms for the production of the bioactive PUAs 2,4-heptadienal, 2,4-octadienal, and 2,4-decadienal. Benthic diatom species were isolated from the Salish Sea, an inland sea within the North Pacific ecosystem. All species were found to be producers of at least two PUAs in detectable concentrations, with five species producing all three PUAs in quantifiable concentrations. Our results indicate that production of PUAs from Salish Sea benthic diatoms may be widespread, and thus these compounds may contribute to benthic coastal food web dynamics through heretofore unrecognized pathways. Future studies should expand the geographic scope of investigations into benthic diatom PUA production and explore the effects of benthic diatoms on benthic consumer fecundity.

Comparison of Juvenile Development of Maize and Sorghum in Six Temperate Soil Types under Extreme Water Regimes

Climate change requires the introduction of alternative crops in certain temperate areas due to the warmer and drier growing seasons. Maize, one of the most important crops, is projected to become less tolerant of a drier climate. Therefore, it is necessary to find an alternative species that is less susceptible to environmental stressors. This study compared the germination, growth vigour, and stress tolerance of maize and sorghum grow in six types of soil under three water regimes. The results indicate that sorghum germination is faster and more uniform. The most significant differences in germination rates were found in chernozem (88.9% and 72.2% for sorghum and maize, respectively) and saline solonetz (74.4% and 63.3% for sorghum and maize, respectively). Maize exhibited higher growth vigour only in three cases, i.e., under solonetz–flooding, shifting sand–drought, and brown forest floor–flooding conditions. An ANOVA showed a significant difference between sorghum and maize stress conditions due to soil conditions and water availability (p < 0.0001). Sorghum can be a suitable alternative to maize, but only in areas with hot, dry periods and in areas where the soil is not too prone to waterlogging, regardless of its quality.

Stress conditions extend maternal care and delay juvenile development in crayfish

Abstract Maternal care in crayfish has been extensively studied, but little is known of its response to environmental factors. We studied the duration of maternal care and its association with the juvenile development of marbled crayfish Procambarus virginalis in adverse environmental conditions. We exposed females with developmental stage 3 juveniles to environments of low water volume (LW) with food provided, low water volume with no feed (starvation) (LWS), and low water volume without feeding plus an intruder (red swamp crayfish male) (LWSI). A control group with standard water level/feed conditions was included for comparison. Groups were monitored for up to 90 days. The LWS group showed significantly prolonged maternal care (~65 days) as indicated by an extended attachment phase, delayed moulting of mothers (~53 days), and retarded juvenile development. In the LWSI group, conflict precluded extended maternal care. Low use of shelter and feeding was evident under all stress conditions. The results showed that crayfish females modify maternal care in accordance with conditions, providing a longer period of safety for offspring under adverse circumstances. It is possible that the expression of maternal pheromones can manipulate the developmental rate in juveniles, a topic for future research.

Comb size, shape complexity and laterality of laying hens reared in environments varying in resource choice

The comb is an ornament involved in signalling condition in domestic fowl. We hypothesised that comb size, comb shape complexity (i.e., rugosity, the comb perimeter jaggedness), and comb laterality of laying hens would be influenced by the degree of environmental enrichment experienced during juvenile development in the form of resource choice. We conducted a 2 × 2 factorial crossover experiment with pullets reared in pens containing four perches of equal length and four litter areas of equal size. Pullets were exposed to a single choice vs multiple choices of perch and litter types (i.e., all the same vs all different) during Weeks 1–4 (Period 1) and/or Weeks 5–15 (Period 2) of rearing (n = 4 pens/treatment combination) prior to transfer to standard adult laying pens for Weeks 16–27 (Period 3). In Week 27, combs were photographed, and comb laterality (hanging on left or right side) was noted. Using a custom-made image analysis programme, we captured comb area (mm2), perimeter length (mm), and rugosity ((perimeter length – horizontal length) / horizontal length) from comb photographs of 6–7 randomly selected hens/pen. We predicted that hens reared in the multi-choice environment during Periods 1 and 2 would have larger, more complex, and left-side-biased combs than those in the other treatment groups, reflecting lower allostatic load. The predicted comb side bias was based on a possible bias in head posture/movements associated with greater right eye/ear use and left-brain hemispheric dominance. Contrary to our predictions, we detected an overall right-side bias in comb laterality, and no associations between resource choice treatment in Period 1 or Period 2 and comb area, perimeter length, rugosity, or laterality of the adult hens. Thus, variation in allostatic load resulting from the rearing treatments was insufficient to modify the trajectory of comb morphological development, possibly due to a ceiling effect when comparing environmental treatments on the positive end of the welfare spectrum. We found that left-lopping combs had shorter perimeters than right-lopping combs. However, among hens with left-lopping combs, those with larger combs were heavier and had less feather damage, while among hens with right-lopping combs, those with longer-perimeter combs were heavier and tended to have less comb damage. In conclusion, comb characteristics were related to physical condition at the individual level but did not serve as sensitive integrated indicators of hen welfare in response to basic vs enhanced resource choice during rearing.

Larval competition between three endemic fruit flies (Diptera: Tephritidae) of differing phylogenetic relatedness

AbstractWithin a fruit, fruit fly larvae can be subject to scramble competition, in which density‐dependent effects can influence the fitness of subsequent adults. While there is significant research on tephritid interspecific larval competition, it has been conducted in invasive situations where the species are evolutionarily novel to each other. There has been no published research investigating larval competitive interactions between naturally coexisting, endemic species. We ran laboratory‐based, intraspecific and interspecific larval competition trials involving three co‐occurring Bactrocera species of differing genetic relatedness and also measured aspects of juvenile development rate to test possible mechanisms of competitive difference. Larval density had an influence on intraspecific competition in Bactrocera tryoni, Bactrocera neohumeralis and Bactrocera jarvisi, with a decreasing percentage of pupation with increasing larval density. Interspecific competition between B. tryoni and B. neohumeralis, and between B. tryoni and B. jarvisi was influenced by the interaction between species and density. The intensity of competition between B. tryoni and B. neohumeralis was minimal but high between B. tryoni and B. jarvisi. B. jarvisi produced larger eggs and had faster initial larval growth rates than the other two species, but it took the longest time for pupation to occur. Our results conflict with theory, as the greatest competition was observed between the two more distantly related species (B. tryoni and B. jarvisi) rather than between the two most closely related species (B. tryoni and B. neohumeralis). Further, and contrary to other studies, egg size, hatch rate and larval growth rate did not provide B. jarvisi with a competitive advantage; thus, larval size does not appear to be a mechanism of larval competition between B. tryoni and B. jarvisi.

PP2B-Dependent Cerebellar Plasticity Sets the Amplitude of the Vestibulo-ocular Reflex during Juvenile Development.

Throughout life, the cerebellum plays a central role in the coordination and optimization of movements, using cellular plasticity to adapt a range of behaviors. Whether these plasticity processes establish a fixed setpoint during development, or continuously adjust behaviors throughout life, is currently unclear. Here, by spatiotemporally manipulating the activity of protein phosphatase 2B (PP2B), an enzyme critical for cerebellar plasticity in male and female mice, we examined the consequences of disrupted plasticity on the performance and adaptation of the vestibulo-ocular reflex (VOR). We find that, in contrast to Purkinje cell (PC)-specific deletion starting early postnatally, acute pharmacological as well as adult-onset genetic deletion of PP2B affects all forms of VOR adaptation but not the level of VOR itself. Next, we show that PC-specific genetic deletion of PP2B in juvenile mice leads to a progressive loss of the protein PP2B and a concurrent change in the VOR, in addition to the loss of adaptive abilities. Finally, re-expressing PP2B in adult mice that lack PP2B expression from early development rescues VOR adaptation but does not affect the performance of the reflex. Together, our results indicate that chronic or acute, genetic, or pharmacological block of PP2B disrupts the adaptation of the VOR. In contrast, only the absence of plasticity during cerebellar development affects the setpoint of VOR, an effect that cannot be corrected after maturation of the cerebellum. These findings suggest that PP2B-dependent cerebellar plasticity is required during a specific period to achieve the correct setpoint of the VOR.

Оценка потенциального риска хлоридов и их влияние на всхожесть семян и развитие проростков растений

The article discusses the negative effect of de-icing materials (DM) and salts in their composition on plant seedlings germination and development. The influence of sodium and potassium cations and chlorine anion on phytotoxicity index is considered. The dynamics of test-plants (Avena sativa L., Raphanus sativa L., Hordeum vulgare L.) response on a number of test-indicators depending on the concentration of basic salts in DM by a promising method of phytotesting was analyzed. The analyzed DMs in concentrations higher than 1% have an inhibitory effect. The DM at 14–16 g/L suppresses root length of test plants (more than 50%) relative to the control. The low content of heavy metals, such as Cd, Cu, Pb, in the analyzed DM samples indicates the toxicity of sodium chloride as an active de-icing agent. The results of statistical analysis convincingly prove the high phytotoxicity of sodium chloride (NaCl) in relation to such indicators of the juvenile test-plant development as germination, the primary root length and the coleoptile height. Increasing the NaCl concentration in the solution from 0.75 to 1% was strongly toxic to the test-plants (more than 50%). Potassium chloride (KCl) in the concentration range of 0.1–1.0% showed no phytotoxicity. The KCl presence in the NaCl-included de-icing reagent reduces its phytotoxicity and allows the toxicity level of the agent to be assessed as “moderately toxic”.

A matter of new life and cell death: programmed cell death in the mammalian ovary.

The mammalian ovary is a unique organ that displays a distinctive feature of cyclic changes throughout the entire reproductive period. The estrous/menstrual cycles are associated with drastic functional and morphological rearrangements of ovarian tissue, including follicular development and degeneration, and the formation and subsequent atrophy of the corpus luteum. The flawless execution of these reiterative processes is impossible without the involvement of programmed cell death (PCD). PCD is crucial for efficient and careful clearance of excessive, depleted, or obsolete ovarian structures for ovarian cycling. Moreover, PCD facilitates selection of high-quality oocytes and formation of the ovarian reserve during embryonic and juvenile development. Disruption of PCD regulation can heavily impact the ovarian functions and is associated with various pathologies, from a moderate decrease in fertility to severe hormonal disturbance, complete loss of reproductive function, and tumorigenesis. This comprehensive review aims to provide updated information on the role of PCD in various processes occurring in normal and pathologic ovaries. Three major events of PCD in the ovary-progenitor germ cell depletion, follicular atresia, and corpus luteum degradation-are described, alongside the detailed information on molecular regulation of these processes, highlighting the contribution of apoptosis, autophagy, necroptosis, and ferroptosis. Ultimately, the current knowledge of PCD aberrations associated with pathologies, such as polycystic ovarian syndrome, premature ovarian insufficiency, and tumors of ovarian origin, is outlined. PCD is an essential element in ovarian development, functions and pathologies. A thorough understanding of molecular mechanisms regulating PCD events is required for future advances in the diagnosis and management of various disorders of the ovary and the female reproductive system in general.

Frogs and flows: Using life‐history traits and a systematic review to establish water‐dependent functional groups for stream frogs in New South Wales, Australia

AbstractHydrological alteration has contributed to the global decline of stream frogs. Flows support stream frog reproduction, juvenile development, food resources, and maintain habitats for all life stages. At present, there is a lack of information regarding the specific water requirements necessary for the conservation of stream frogs. To address this gap, we developed a traits‐based approach that serves as a valuable tool for grouping and prioritising water‐dependent stream frog species to inform future research priorities and environmental flow design. In this study, we focussed on 53 Australian frog species and analysed eight species traits to develop water‐dependent functional groups for stream frogs. We classified frogs based on their level of water dependency using an agglomerative hierarchical clustering analysis and a systematic review of water requirements and water management threats. The distinguishing traits that determined functional groups were: tadpole body type, egg clutch type, stream breeding habitat type, and documented association with flowing water and water permanence. Our study identified two distinct water‐dependent groups: facultative stream spawners, capable of reproducing in both stream and non‐stream habitats, and obligate stream spawners, restricted solely to stream habitats. Importantly, we highlight that the obligate stream spawners are the most sensitive group to within‐channel flow alteration and should be prioritised for water management decisions in lotic environments. This study represents the first comprehensive overview of the importance of hydrology for stream frogs and identifies the critical need for additional research and validation to enhance our understanding of stream frog responses to flows regimes.

Early ontogenesis from embryo to juvenile in Senegalese sole Solea senegalensis under laboratory conditions.

Senegalese sole, Solea senegalensis, is a flatfish of high commercial value in the world. It has been identified as an interesting and promising species for marine commercial aquaculture diversification in Europe for at least four decades and was introduced to China in 2003. Early ontogenesis from embryo to juvenile stages in S. senegalensis was analysed under controlled laboratory conditions to provide morphological information for aquaculture. From 0 to 59 days post hatching (dph), 10-20 larvae were sampled and measured each day (0-17 dph) or every 2-6 days (17-59 dph). Morphological characteristics from the egg to the juvenile stage were described. The eggs were separate and spherical with multiple oil globules. After 3 dph, the yolk sac was completely absorbed, mouth and anus were open, a swim bladder appeared, and larvae began feeding on rotifers (Brachionus plicatilis). The larvae began metamorphosis as the notochord flexed upward and the left eye migrated upward after 10 dph. The left eye migrated to the dorsal midline at 15 dph. At 19 dph, the left eye was translocated to the right-ocular side, and the juveniles adopted a benthic lifestyle. The swim bladder degenerated, and the juveniles completed metamorphosis at 23 dph. The growth patterns of some parameters (TL, SL, BH, BW) during larval and juvenile development stages were identified. The inflection points, which are slopes of growth changes, were calculated in growth curves. Three inflection points occurring in the growth curves of larvae and juveniles were found to be associated with metamorphosis, weaning, and transitions in feeding habits. The basic information of embryo development and ontogenesis in this study represents a valuable contribution to the S. senegalensis industry, especially in artificial breeding and rearing techniques.

Evolutionary origins of Fibonacci phyllotaxis in land plants

Fibonacci phyllotaxis is commonly seen in all major groups of land plants. While a precise correlation is found between the internal pattern of the primary vascular system and the external pattern of appendages on the stem surface, it remains a big question how this regularity of Fibonacci phyllotaxis came into being in the course of evolution. Here I address this problem with a model describing phylogenetic and ontogenetic changes in vascular phyllotaxis based on two hypotheses. The first is that the Fibonacci pattern of vascular connection is uniquely determined by the primary arrangement of incipient primordia, the sources of the primary signal system in vascular tissue differentiation. The second is that the surface-area-to-volume ratio of primary vascular tissues serves as a measure of fitness in evolution. The model explains the empirical rule on the manner in which vascular connection is reconfigured during ontogeny, especially during juvenile development. Fossil and phylogenetic evidence suggests that Fibonacci phyllotaxis appeared shortly after the innovation of indefinite lateral organ initiation in a regular sequence.

The role of adaptive resistance in a widespread freshwater mussel species

Abstract Organism features, such as size, weight, sex and age, among others, can influence the success of parasitism. For species that depend on a host to complete their life cycle, such as freshwater mussels (Bivalvia, Unionida), understanding how these traits influence parasitism can help guide management actions aimed at improving their reproductive success, ultimately benefitting their conservation. In this study, the physiological compatibility between the duck mussel Anodonta anatina and its host fish was investigated in a simultaneous infestation experiment on four (three native and one non‐native) fish species using sympatric and allopatric host strains. The success of glochidia metamorphosis in juvenile mussels was evaluated as a function of host species, strain and fish length. Successful metamorphosis was achieved in almost all fish species tested and differences were detected between allopatric and sympatric strains, with higher values found in allopatric hosts. Allopatric strains of primary hosts produce more juveniles than marginal hosts and non‐native species. In addition, larger fish have lower rates of metamorphosis. The results confirm recent findings showing high variation in the metamorphosis success of A. anatina glochidia among different native and non‐native hosts, both in the natural environment and in artificial laboratory infestations. Allopatric hosts were more suitable for encystment, demonstrating potential adaptive immunity, not yet observed in A. anatina. Nevertheless, A. anatina may temporarily exploit the naivety of smaller fish regardless of strain. Overall, the results suggest that mussel propagation, reproduction and reintroduction efforts should consider the mechanisms that influence adaptive immunity in fish, including differences in compatibility within and between populations of sympatric and allopatric host strains. This situation should be taken into account, as successful metamorphosis is an important factor in the selection of hosts for juvenile development, especially in efforts to propagate endangered mussel species.

Juvenile octocorals acquire similar algal symbiont assemblages across depths

Establishment of the coral–algal symbiosis begins during early ontogeny when juveniles acquire a mix of algae from their environment that often differs from the adults’ algal assemblages. Despite the importance of the type of Symbiodiniaceae to this symbiosis, it is largely unknown how coral host identity and environment affect symbiosis establishment and is affected by the genetic composition of the symbionts. Here, we reciprocally transplanted planulae of the octocoral Rhytisma fulvum (Forskål, 1775) across depths and monitored the algal assemblages in the developing juveniles for 11 months. We then compared these to adult assemblages using ITS2 metabarcoding. Juveniles were consistently dominated by Symbiodinium, in addition to multiple Cladocopium species, which shifted in dominance with the juvenile age but maintained high similarity across depths. The type of Symbiodiniaceae environmentally available thus likely contributes to the algal symbionts that are initially acquired, while host identity may play a significant role in selecting for symbionts that are maintained during juvenile development.

The source of microbial transmission influences niche colonization and microbiome development.

Early life microbial colonizers shape and support the immature vertebrate immune system. Microbial colonization relies on the vertical route via parental provisioning and the horizontal route via environmental contribution. Vertical transmission is mostly a maternal trait making it hard to determine the source of microbial colonization in order to gain insight into the establishment of the microbial community during crucial development stages. The evolution of unique male pregnancy in pipefishes and seahorses enables the disentanglement of both horizontal and vertical transmission, but also facilitates the differentiation of maternal versus paternal provisioning ranging from egg development, to male pregnancy and early juvenile development. Using 16S rRNA amplicon sequencing and source-tracker analyses, we revealed how the distinct origins of transmission (maternal, paternal and horizontal) shaped the juvenile internal and external microbiome establishment in the broad-nosed pipefish Syngnathus typhle. Our data suggest that transovarial maternal microbial contribution influences the establishment of the juvenile gut microbiome whereas paternal provisioning mainly shapes the juvenile external microbiome. The identification of juvenile key microbes reveals crucial temporal shifts in microbial development and enhances our understanding of microbial transmission routes, colonization dynamics and their impact on lifestyle evolution.

Potential energetic and oxygenic benefits to unstable photosymbiosis in the cladobranch slug, Berghia stephanieae (Nudibranchia, Aeolidiidae)

ABSTRACT Some cladobranch sea slugs host algae (Symbiodiniaceae), forming stable or unstable photosymbiotic relationships. Although some benefits from retaining symbionts have been described in stable photosymbioses, unstable photosymbioses remain largely uninvestigated. We examined two potential benefits – nutrition and oxygen produced via photosynthesis – in the unstable cladobranch model species, Berghia stephanieae. To investigate potential nutritive benefits, we conducted transmission electron microscopy and observed both partially digested symbionts and lipid droplets, indicating that B. stephanieae benefits energetically from hosting zooxanthellae through digestion. Since increased temperatures can cause oxygen limitation, any oxygenic benefits B. stephanieae receives from photosynthesis could influence their thermal tolerance, allowing photosynthetic slugs to withstand higher temperatures than specimens where photosynthesis is limited or absent. To assess this, we measured the maximum temperature they can withstand before succumbing to heat-shock under three light intensities (0, 100 and 700 µmol m-2s-1). Oxygen uptake was measured before and after heat-shock to determine whether uptake was affected by thermal stress. Slugs exposed to high light displayed significantly lower thermal limits than those at zero or moderate light, indicating exposure to acute high light negatively impacts thermal tolerance. Lastly, we assessed if and how light affects juvenile development and survival. Juveniles exposed to moderate light survived longest, while both other light intensities reduced survival. These investigations demonstrate that unstable photosymbiosis provides B. stephanieae with nutritive benefits during different ontogenetic stages. Oxygenic benefits are less clear, as slugs exposed to thermal stress in dark and under moderate light did not display different thermal tolerances.