Reproductive Season Research Articles

Using micro-CT to explore bone density variations in the skulls of the vulnerable Opsariichthys uncirostris uncirostris (Three-lips fish) during reproductive migration to a Lake Biwa tributary.

Not much is known about the changes in bone density due to fish reproductive migration. We used micro-CT and inferential statistics to determine whether the relative bone density in the skulls of adult Three-lips fish, that seasonally upstream migrated to a Lake Biwa tributary, changed across their known reproductive season. The relative bone density significantly decreased as standard length and condition factor (K) increased in both sexes. This negative relationship is likely due to age and hormonal effects in the fish. Results from the bone density analysis also revealed that male Three-lips fish had potentially lower relative bone density (although not significantly different) than females during peak reproductive migration, i.e., July to August. On average, male Three-lips fish are larger in length and weight than females, and in many species, females prefer larger males to smaller males, viewing their size as an indicator of genetic fitness and their ability to provide protection. Resources in the skulls of Three-lips males may be distributed in such a way that increases reproductive success, i.e., size at the expense of quality. In addition, individuals with slightly less dense bones, particularly males, appeared later than those with denser bones during the peak of the reproductive season. The high energy demands involved with aggression in males, often requires resource mobilization from various tissue compartments and could explain the slightly lower density in the latter half of the peak migration. Furthermore, Three-lips individuals that migrated earlier and later during the reproductive season may have more energy reserves than those that had been in the river for some time, hence the variable bone density between individuals. This study serves as a foundation for future studies on the effects of migration, changes in physiology and age on bone density analysis of Three-lips fish and other species in various ecosystems.

Meta-analysis of experimental studies of the effect of melatonin monotherapy on the levels of thyroid hormones and glucocorticoids in rats kept under standard condition

Melatonin is known to modulate circadian and seasonal rhythms in metabolism, reproduction, and behavior. However, the effect of exogenous melatonin supplementation on the functioning of the thyroid and adrenal glands in species without a clear seasonality in reproduction is still unclear. Using a meta-analysis of publications, to investigate the effect of melatonin monotherapy on the concentrations of pituitary thyroid-stimulating hormone, thyroid hormones (TG), pituitary adrenocorticotropic hormone and corticosterone (CS) in rats kept under standard laboratory conditions. In our work, using the Review Manager 5.3 program, we conducted a meta-analysis of publications examining the effect of melatonin monotherapy on the functioning of the thyroid gland (22 papers) and adrenal glands (20 papers) in rats kept under standard conditions. According to the results of our meta-analysis, the effects of melatonin on the levels of TG and CS depend on the dose and duration of therapy. A decrease in TG and CS was associated with therapy lasting no more than 4-5 weeks and with high doses of melatonin. An increase in CS and a trend toward increased TG levels were observed with longer therapy. However, a few studies have observed a decrease in TG with very long-term melatonin therapy (≥32 weeks). Among all TGs, total thyroxine (T4) showed maximum sensitivity to exogenous melatonin, which indicates the influence of melatonin on the secretory function of the thyroid gland. In addition, melatonin increased the relative weight of the adrenal glands. There was no convincing evidence that the effects of melatonin were influenced by the route and timing of administration, or the timing of blood sampling. As a result, exogenous melatonin can modulate TG and CS levels, even in species without a clear seasonality in reproductive function.

Comparación de características testiculares mediante ultrasonografía B mode y Doppler en alpacas (<i>Vicugna pacos</i>) tui y adultos

The aim of this study was to compare testicular characteristics using B mode and Doppler ultrasonography in tui and adult alpacas. The study was carried out at the Chuquibambilla Experimental Center of the National University of the Altiplano, Puno, Peru, during the reproductive season (March). In total, 15 male tuis (G1) from 12 to 14 months of age and 14 adults (G2) from 24 to 36 months of age were used. B mode ultrasonographic characteristics (length [mm], width [mm], area [cm2] and testicular volume [cm3]) and Doppler (resistance index [RI], pulsatility index [PI] and testicular vascular area [ AVT]) were registered with a Draminski 4Vet® device and a a micro convex and linear transducer with a frequency of 9 MHz. The data were analysed using a 2x2 factorial design. The length, width, volume and testicular area within each age group did not present significant differences between the right and left testicle, however, the measurements of the adult alpacas were significantly greater than those of the tuis (p<0.05). The IR was similar in both age groups, but AVT was higher in tuis compared to adults.

Larval Transport Pathways for Lutjanus peru and Lutjanus argentiventris in the Northwestern Mexico and Tropical Eastern Pacific

Understanding how ocean currents influence larval dispersal and measuring its magnitude is critical for conservation and sustainable exploitation, especially in the Tropical Eastern Pacific (TEP), where the larval transport of rocky reef fish remains untested. For this reason, a lagrangian simulation model was implemented to estimate larval transport pathways in Northwestern Mexico and TEP. Particle trajectories were simulated with data from the Hybrid Ocean Coordinate Model, focusing on three simulation scenarios: (1) using the occurrence records of Lutjanus peru and L. argentiventris as release sites; (2) considering a continuous distribution along the study area, and (3) taking the reproduction seasonality into account in both species. It was found that the continuous distribution scenario largely explained the genetic structure previously found in both species (genetic brakes between central and southern Mexico and Central America), confirming that the ocean currents play a significant role as predictors of genetic differentiation and gene flow in Northwestern Mexico and the TEP. Due to the oceanography of the area, the southern localities supply larvae from the northern localities; therefore, disturbances in any southern localities could affect the surrounding areas and have impacts that spread beyond their political boundaries.

Cba-miR-222-3p involved in photoperiod-induced apoptosis in testes of striped hamsters by targeting TRAF7.

The role of miRNAs in the regulation of seasonal reproduction in rodents, particularly in relation to photoperiod changes, is still poorly understood. Previous studies on miRNA transcriptomes of striped hamster (Cricetulus barabensis) testes have indicated that the photoperiodism of testes, especially apoptosis, may be influenced by miRNAs. As a functional miRNA, cba-miR-222-3p in striped hamster testes exhibits suppression under a short photoperiod. To elucidate the potential role of testicular cba-miR-222-3p in the seasonal reproduction of striped hamsters, we exposed male striped hamsters to different photoperiods or injected miRNA agomir into the testes and observed the effects of these treatments, particularly some indicators related to apoptosis. The results showed that the levels of apoptosis in the testes increased in short daylength, accompanied by a significant decrease in cba-miR-222-3p expression and an increase in TRAF7 expression. Dual luciferase reporter assays verified the targeting relationship between cba-miR-222-3p and TRAF7 predicted by bioinformatics. In addition, the expression of TRAF7 decreased in the testes, which injected miRNA agomir, leading to inhibition of apoptosis, and the expression of key genes (MEKK3, p38, p53) in the downstream MAPK signaling pathway of TRAF7 was suppressed. These results suggest that short daylength induces testicular apoptosis in striped hamsters, and one possible mechanism is that the decreased expression of miR-222-3p in testes reduces the repression of TRAF7 translation, thereby activating the MAPK pathway and affecting the level of testicular apoptosis. These findings reveal the potential role of miR-222-3p in animal reproduction and provide new insights into the regulation of rodent populations.

Ovarian and testicular ripening process, reproductive season and size at maturity in Octopus hubbsorum (Cephalopoda: Octopodidae)

ABSTRACT This paper contributes to the knowledge of the reproductive biology of Octopus hubbsorum Berry 1953. Its reproductive season in Bahía Magdalena, Baja California Sur ranges from May to October. The increase of gonadosomatic index in females coupled with the decline in Guerra’s index and the increase in oocyte diameter in May and September were indicative of spawning. The total sex ratio was 1:1; males were larger than females. Females reach sexual maturity at 119.7 mm of dorsal mantle length and 628.6 g of total weight. This paper also addressed different aspects on reproductive studies, allowing the identification of the type of gonadal development as a group-synchronous type and the transition from physiological to functional maturity, in both qualitative and quantitative terms (proportion of oocyte stages). Detailed descriptions of the oogenesis/folliculogenesis stages of O. hubbsorum are presented with detailed photographs (in Supplemental online material).

Adaptive divergence in reproductive seasonality and underlying physiological features fit Rattus norvegicus to live as opportunistic breeders.

How organisms respond to complex environments is one of the unsolved problems in ecology. Life history patterns of a species provide essential information on how different populations may respond and adapt to environmental changes. Compared to typical seasonal breeders, which have limited distributions, the worldwide distribution of brown rats (Rattus norvegicus) across highly complex and divergent habitats suggests they exhibit exceptional adaptiveness. However, the difference in physiological mechanisms by which brown rats respond and adapt to markedly different environments is seldom investigated. Here, we reveal a significant divergence in reproductive seasonality and environmental responses between two brown rat subspecies: one subspecies, R. n. caraco, lives in the temperate zone, and another subspecies, R. n. norvegicus, lives in the subtropical region. Although R. n. caraco displayed a significantly higher reproductive seasonality than R. n. norvegicus, both subspecies adapted to sub-optimal breeding conditions mainly by regulating the seminal vesicle rather than testis development. Especially in responding to severe winter conditions in high-latitude regions, bodyweight-dependent recovery of testicular development in adults enables R. n. caraco to initiate reproduction more rapidly when conditions are suited. These findings elucidate a regulatory process of how brown rats live as opportunistic breeders by benefiting from enhanced semen production.

Factors determining semen sample collection and semen quality parameters in African penguins Spheniscus demersus

Our research focuses on semen collection from 42 African penguin males, grouped by age, habituation levels, and reproductive season timing. We assess behavioral and physiological responses to dorso-abdominal massage, evaluating species-specific seminal traits using conventional and advanced methods. Positive behavioral responses corresponded with successful semen collection. Young and human-reared males exhibited more favorable behaviors, and samples containing spermatozoa were more likely collected during the reproductive season. Age did not influence sample collectability or spermatozoa presence, though mature males produced higher semen volumes. Young males exhibited more sperm morphological abnormalities, especially outside the breeding season. Sperm concentration and number per ejaculate showed no significant differences across age or seasonal groups. Young males had higher motile and progressive sperm percentages, while mature males had more static sperm. Additionally, percentages of live sperm and intact acrosomes were higher in mature males. Young males and samples from non-reproductive season presented more dead sperm with damaged acrosomes. Plasma membrane integrity positively correlated with age for live sperm and negatively for dying sperm. This research demonstrates the feasibility of semen collection from African penguins regardless of habituation level, fills the knowledge gap by describing sperm morphological abnormalities, and provides insights into using flow cytometry in Sphenisciformes.

Spatiotemporal changes in the community and demography of mesozooplankton in the eastern Indian sector of the Southern Ocean during austral summer 2018/2019

The Southern Ocean is facing rapid environmental changes. However, few studies have been conducted on the spatiotemporal variability of mesozooplankton communities under recent climatic conditions, particularly in the eastern Indian sector. This study describes the spatiotemporal variability of the mesozooplankton community and the demographics of large copepods and krill in this sector, sampled through a Rectangular Mid-Water Trawl with 1 m2 mouth area (RMT1) during the austral summer of 2018/2019 as part of the KY1804 survey. Cluster analysis indicated that the mesozooplankton community was divided into five groups that showed only small longitudinal differences, as they were affected by oceanic fronts. Part of the variability was explained by physical (local upwelling) and biological features (e.g., the occurrence of species showing a specific spatial distribution, such as Euphausia crystallorophias). Horizontal changes in the zooplankton community structure were not attributed to temporal changes during the 2-month sampling period. The demographics of the dominant species, Calanoides acutus, Calanus propinquus, Metridia gerlacheri, and Thysanoessa macrura, exhibited significant temporal differences in abundance or mean stage index (MSI) between the early and late seasons. These differences matched the growth rates estimated in previous studies, suggesting that their growth during the study period was constant without regional differences. There were no evident changes in the abundance or demographics of Rhinalanus gigas, suggesting that they were in their reproductive season. These species-specific demographics could be explained by the species life cycles: growth in C. acutus and C. propinquus and reproduction in R. gigas during the austral summer. Abundances and MSIs confirmed the growth of dominant copepods and krill during the sampling period; however, no evident seasonal changes were observed in the zooplankton community structure. The findings of this study contribute to the understanding of lower trophic levels in marine ecosystems and the present carbon cycle in the eastern Indian sector of the Southern Ocean.

Clutch attendance and call parameters are linked to mating success in a glassfrog with paternal care.

Females of some species improve their reproductive success not only by being choosy and selecting males with certain traits, but also by sequentially mating with multiple males within one reproductive season. However, it is relatively unknown whether females also evaluate parental care during mate choice and, if they do, whether males actively communicate their care status to approaching females. We monitored a natural population of the glassfrog Hyalinobatrachium valerioi, a species with sequential polyandry and paternal care, to assess the role of parental care and advertisement calling on male mating success. Using field observations and acoustic analysis, we found that even in this species which has single-note calls, variations in call parameters allow for individual discrimination. Calling was strongly associated with mating success in H. valerioi males. Males with longer calls achieved the highest total mating success over the entire study period, indicating that females might have a preference for longer calls. Moreover, active calling and the presence of clutches were both linked to male mating success on a given night, although we cannot fully exclude that the link between presence of clutches and mating success is due to attractive call features alone. Call parameters differed between males when they were calling on top of their clutches, compared to sitting on the leaf directly, which might provide reliable cues about parental state to approaching females. These findings demonstrate the prominent role of acoustic communication and female choice in a species with male parental care and sequential polyandry.

Impact of semen cryopreservation season on invitro embryo production of prepubertal goat oocytes.

Goat production is affected by reproductive seasonality. Invitro embryo production (IVEP) could overcome this effect. This study aimed to evaluate the impact of the season of semen collection/freezing on IVEP of prepubertal goat oocytes and on sperm quality and functionality concerning capacitation. Semen from six fertile bucks was collected, pooled and cryopreserved in spring and autumn and used for IVEP of oocytes recovered during the breeding season. Oocytes were IVM in TCM-199 with hormones, EGF and cysteamine; fertilized and cultured in BO-IVF and BO-IVC media (IVF Bioscience, UK). Semen samples were assessed at 0 and 3 h after culture in capacitating (BO-IVF, CAP) and non-capacitating conditions for sperm plasma membrane and acrosome integrity, mitochondrial membrane potential (MMP), intracellular calcium and plasma membrane lipid disorder. Blastocyst production was higher with spring sperm compared to autumn (12.0% vs. 2.1%, respectively; p < .05). After CAP, acrosome reaction and intracellular calcium were higher (p < .05) in spring than autumn sperm. No differences were found in other sperm parameters. In conclusion, seasonal variations in the IVEP of prepubertal goats could be linked to differences in sperm ability to undergo invitro capacitation.

Seasonal dimorphism as an expression of sexual dimorphism: Influence of gonad maturity on the body shape of a rocky intertidal polyplacophoran

Seasonal dimorphism in the body shape of marine invertebrates has been poorly explored compared to vertebrates. We aim to investigate through traditional (body length/width ratio, dorsal elevation ratio and angle of elevation) and geometric (centroid size and shape geometric configurations) morphometrics the effect of gonad maturity (via the gonadosomatic index [GSI] and gonad development stages [GDS]) on changes in body shape in males and females of two latitudinally different populations of the broadcast-spawning intertidal mollusc Chiton articulatus. We confirmed that C. articulatus does not present external sexual dimorphism since sex does not have a significant effect on body shape (1%); instead, dimorphism was seasonal and related to the reproductive season, and varied across populations, probably because in the subtropical zone additional energy is invested in shell (scleritome) bending at the same time as the gonad matures, which is opposite of what occurs in the tropical zone. C. articulatus shows a narrower body shape (i.e., diminished body width) during its gonad maturity compared to the rest of the GDS and is corroborated by a body length/width ratio that contributes the greatest variation in the geometric shape descriptors (18%), just below the centroid size (24%). The expression of centroid size differences shows a correspondence with the change in body dimensions expressed by the three morphometric ratios during gonad maturity. The use of traditional body ratios over time may be useful in polyplacophoran molluscs as a proxy tool to estimate gonad maturity and to provide a reliable indication of the reproductive season.

Elevated vitamin D levels in diurnally-active female fruit bats

Animal species have evolved to enhance their survival by focusing their temporal activity on specific parts of the diurnal-nocturnal cycle. Various factors, including inter-specific competition and anti-predator behavior, as well as anthropogenic effects like light pollution, have prompted some species to expand or shift their temporal niches. Our study focuses on the temporal niche shift of the Egyptian fruit bat (Rousettus aegyptiacus) to diurnal activity in Israel.Through an extensive citizen-science study, we assessed the distribution of these bats’ diurnal activity across Israel. We also documented the sex and age of bats from a colony known for its diurnal activity and collected blood samples from them for metabolic analysis.Our findings indicate that the shift toward daytime activity predominantly takes place in urban settings and is mostly exhibited by females. We found a significant physiological effect of this temporal shift, namely: diurnal bats’ vitamin D levels were significantly higher, and their parathyroid hormone (PTH) levels were significantly lower than those of nocturnal bats.We suggest that the reproductive metabolic demands of female bats might be a key factor driving this shift to diurnal activity. We hypothesize that the increase in vitamin D, derived from sunlight hours, might play a crucial role in regulating calcium homeostasis, thus contributing to the bats’ physiological needs during the reproduction season.

Increased Reproductive Output and Telomere Shortening Following Calcium Supplementation in a Wild Songbird.

Life history theory predicts increased parental investment comes with fitness costs, often expressed as negative effects on survival and future reproduction. To better understand the costs of reproduction and life history trade-offs, we evaluated calcium supplementation at a high-elevation site in Colorado as a novel approach to experimentally alter reproductive investment in nesting female Tachycineta bicolor (tree swallow). Calcium is a nutrient critical to avian reproduction as the intake of natural calcium is essential for egg production, embryo development, and nestling growth. Altering calcium availability exclusively during the breeding season allowed examination of individual biological responses to experimental modification of reproduction, as well as the reproductive costs associated with egg production and laying an entire clutch. As a functional endpoint and proxy for fitness and longevity, telomere length was measured at the beginning and end of each breeding season. Telomeres-protective "caps" at the ends of chromosomes-have been shown to shorten with aging and a variety of stressors, including higher reproductive output. Results demonstrate that tree swallow mothers supplemented with calcium during the breeding season experience higher reproductive output and produce offspring with longer telomeres, which came at the cost of relatively shorter telomeres during the reproductive season. These findings provide additional support for reproductive trade-offs, and also challenge previous calcium supplementation studies that suggest excess calcium reduces the cost of reproduction.

Retrotransposon involves in photoperiodic spermatogenesis in Brandt's voles (Lasiopodomys brandtii) by co-transcription with flagellar genes

Photoperiod is a pivotal factor in affecting spermatogenesis in seasonal-breeding animals. Transposable elements have regulatory functions during spermatogenesis. However, whether it also functions in photoperiodic spermatogenesis in seasonal breeding animals is unknown. To explore this, we first annotated 5,501,822 transposons in the whole genome of Brandt's voles (Lasiopodomys brandtii), and revealed that LINEs were the most abundant, comprising 16.61 % of the genome. Following closely, SINEs accounted for 10.13 %, LTRs for 7.54 %, and DNA transposons for 0.70 %. Subsequently, we exposed male Brandt's voles to long-photoperiod (LP, 16 h/day) and short-photoperiod (SP, 8 h/day) from their embryonic stages, and obtained testes transcriptome at 4 and 10 weeks after birth. Differential expression and Pearson analysis indicated strongly positive correlations between the expression of differentially expressed retrotransposons and the adjacent genes. KO, KEGG and GSEA results showed that sperm flagellar genes were most enriched nearby the retrotransposons such as Dnah1, Dnah2, Dnah17, Dnali1. RT-PCR results showed that SINE/Alu_1213291 co-transcripted with Dnali1 gene. Our findings first reveal the regulatory function of transposons in photoperiodic spermatogenesis, providing insights into the role of photoperiod in seasonal reproduction in wild animals.

GPS-telemetry as a method to assess nest attendance by a female broad-snouted caiman Caiman latirostris

Crocodylians exhibit parental care, guarding their eggs during incubation to ensure offspring survival. We present the first description of nest attendance of a wild broad-snouted caiman using GPS-telemetry. During the reproductive season of 2022, we tracked a 1.8-metre female in the Tapacurá reservoir, a water source bordered by Atlantic Forest remnants and human settlements in north-eastern Brazil. Telemetry data revealed that 75.8% of the female’s position records were near the nest, suggesting parental care and nest protection. However, the female periodically returned to water. We observed no differences in proximity to the nest between day and night-time, which could be possibly related to different egg predators in the area foraging at different times of the day. Furthermore, the period when the nest was unattended could be associated with either feeding activities or avoidance of human presence. This research brings light on an important part of the reproductive behaviour of broad-snouted caimans in their natural environment, highlighting the importance of GPS-telemetry as a tool for monitoring reproductive behaviour of crocodylians, while contributing to understanding their biology under human-influenced settings. Keywords: Atlantic Forest, crocodylian, movement, parental care, reproductive biology

Individual variation in breeding phenology and postnatal development in northern bats (Eptesicus nilssonii).

Bats inhabiting northern latitudes are faced with short reproductive seasons during which they must produce and rear pups before fattening up in time to survive the winter hibernation. Therefore, the timing of parturition has considerable impacts on future fitness prospects for the mother and pup. However, little is known about individual variation in breeding phenology and its consequences for postnatal development within bat populations. Here, we studied the phenology of breeding in Eptesicus nilssonii across 7 years using data collected by day-to-day monitoring of a breeding colony in Norway (60.1° N) for which the identity and age of each mother (N = 8) and pup (N = 28) were known. Using mixed-effect models, we found that arrival at the colony was influenced by temperature conditions from mid-April to mid-May across all females, but that there were strong and consistent individual differences in arrival- and parturition time across years. Females generally arrived ~32.1 days before giving birth, but the gestation duration was reduced if females arrived late and prolonged if females left the colony when faced with cold weather conditions. Pups born later in the season were born smaller but had higher growth rates during the most rapid growth period (<10 days old). The within-individual effects suggest that the higher growth rates could be due to mothers compensating (e.g. through increased food intake) for late parturition rather than by improved food availability. Date of parturition did not influence adult body size in pups. Pups became volant at the earliest only 13.1 days after birth and approached adult flight patterns during their first flight week. Our results suggest that E. nilssonii is highly adapted to a short breeding season by producing large, fast developing and early volant pups, despite the environmental pressures bats face at northern latitudes.

Features of the dynamics of the reproductive cycle of female reindeer in the taiga and tundra zones

Reindeer remains one of the least studied animals from the point of view of genetics and reproduction of all animals that are use by humans in economic activities. In Russia, reindeer is use as a farm animal to produce environmentally friendly meat with high nutritional value. Reindeer is also the basis of economic activity for the indigenous peoples of the Arctic. Depending on the climatic zone, there are two methods of breeding reindeer - tundra and taiga. For more effective breeding and planning of reproduction work of this species of animals, it is necessary to have clear knowledge about the features of their reproductive cycle. Reindeer are animals with a pronounced seasonal reproduction; in addition, the timing of calving and rutting season can shift significantly depending on changes in weather conditions. According to researchers, the gestation period of northern females has a very high variability. The aim of this work was to conduct research on the differences in the timing of the beginning and end of the calving and rutting periods, their dynamics, as well as the duration of pregnancy in female reindeer in reindeer herding farms in the taiga and tundra climatic zones. To compare the dynamics and timing of calving and rutting, data were collected on the recording of matings and calvings in reindeer herding farms in the tundra zone of the Arctic regions of the Russian Federation (Taimyr Peninsula and Yamal Peninsula) and in the taiga zone (Buryatia). Because of the research, it was found that not only the timing of the rut, but also the timing of calving have differences in time in the tundra and taiga habitat zones of reindeer, in addition, they can shift even within the same climatic zone depending on weather conditions. The pregnancy period under unfavorable weather conditions can be shorten or extend.

Form-assortative mating behaviors of individuals from parasitic and non-parasitic populations of Arctic lamprey (Lethenteron camtschaticum)

Abstract Evolutionary theory predicts that assortative mating is crucial for sympatric speciation by generating reproductive isolation between diverging populations. Here, we investigate the potential of form-assortative mating, an assumed mating pattern in lampreys, for sympatric speciation. By continuously recording mating activity between anadromous and freshwater-resident forms of L. camtschaticum that greatly differ in body size, we show that lampreys tend to mate with individuals of similar size in experimental conditions. However, we highlight that this pattern does not result from a choice of same-form partner but is the result of the simultaneous action of a preference of males – whatever their size – for large anadromous females, a higher competitive ability of aggressive males and physical constraints on heteroform pairs. Moreover, we do not advocate that sympatric speciation, as the sole consequence of form-assortative mating through sexual selection, is a plausible mechanism for the diversification of lampreys as a significant number of sneaking behaviors were observed in freshwater-resident males toward large anadromous females. Broader attention should be given to mechanisms other than sexual selection that may lead to form-assortative mating, such as variations in spatial or temporal distribution of alternative forms during reproductive season.

Elucidating maternal provisioning for bivalve larvae under ocean acidity extreme events

Ocean acidity extreme (OAX) events, triggered by climate change and anthropogenic activities, are projected to become more intense and frequent in coastal ecosystems, devastating marine bivalves and ecosystems they support. Maternal effects adaptively modulate offspring performance in response to climatic stressors, but whether and to what extent they can confer offspring resistance to OAX remain largely unknown. Here, we investigated impacts of OAX on the parental and larval lipidomes of Manila clams (Ruditapes philippinarum) to add further insights into the energetic nature of maternal effects. A total of 177 significantly down-regulated lipid components (categorized into glycerolipids mainly) were shown in OAX-stressed adults compared with those reared under ambient conditions, and following parental conditioning, larvae also exhibited a further decreasing down-regulation of the glycerolipid components. Triacylglycerols were identified as the predominant composition of glycerolipids and the primary sources of energy for gonadal maturation and larvae development. Yet, larvae spawn from adults exposed to OAX had significantly lower contents of triacylglycerols than those without a prior history of parental conditioning, with the carbon chain length and unsaturation degree of the triacylglycerol components being significantly affected. The latter was also in line with significant increases in the production of triacylglycerol byproducts (diacylglycerols). Overall, our findings suggest that when OAX prevailed during reproductive seasons of Manila clams, maternal effects could be maladaptive by depressing the energetic deposition of larvae, and may not be a potential adaptive modulator of marine bivalves to cope with unprecedented environmental change.