Search Results (28)

Egg production in Gallus gallus domesticus represents a complex, economically critical trait shaped by multiple interrelated phenotypes, including age at first egg, total egg number, egg weight, and clutch characteristics. These traits are governed by polygenic inheritance and modulated by environmental factors, making the dissection of their genetic architecture essential for improving breeding efficiency, particularly under the emerging “long-life layers” production model. This systematic review aimed to integrate current knowledge on the genetic and molecular basis of egg production traits through analysis of genome-wide association studies and related genomic approaches. A structured literature search identified 27 eligible studies, which were evaluated following PRISMA guidelines. Data extraction and meta-analysis were conducted using standardized genome annotations and computational pipelines. The synthesis of available evidence demonstrates moderate to high heritability for key reproductive traits and highlights consistent genomic signals across multiple chromosomes. Importantly, the findings reveal a shift toward a systems-level understanding of egg production, involving conserved biological pathways related to neuroendocrine regulation, folliculogenesis, and energy metabolism. The integration of diverse genomic approaches enables the development of more precise, breed-specific selection strategies. Overall, these advances support a transition from traditional selection toward molecularly informed breeding frameworks, with significant implications for productivity, sustainability, and global food security. Full article

Clutch persistence, defined as the ability to sustain consecutive egg-laying cycles, is a pivotal determinant of profitability in the poultry industry, particularly for aging laying hens (≥65 weeks). However, the molecular mechanisms governing this trait remain elusive, largely due to the traditional “ovary-centric” paradigm that overlooks systemic regulation by the gut microbiota. To address this knowledge gap, the present study aimed to dissect the comprehensive regulatory network governing clutch persistence using integrated multi-omics analyses. A total of 20 sixty-five-week-old Rhode Island Red (RIR) laying hens with cumulative egg production exceeding 300 eggs but distinct clutch persistence were stratified into a high-clutch persistence group (HCP, ≥25 clutches, n = 10) and a low-clutch persistence group (LCPLCP, ≤15 clutches, n = 10). Multi-omics profiling, including ovarian transcriptomics, proteomics, and metabolomics; serum metabolomics; and cecal microbiota 16S rRNA sequencing was performed. Data integration and association mining were conducted via Spearman correlation analysis with stringent thresholds (r > 0.6, p < 0.01). Integrated analyses revealed a “gut–ovary axis” regulatory model mediated by a lipid mediator network, operating through a three-tiered mechanism: (1) Gut Initiation: The HCP group exhibited enriched cecal γ-Proteobacteria, which promoted biosynthesis of lipid precursors. (2) Serum Transport: Key serum lipid mediators, most notably LysoPC (22:6) (VIP = 4.5) and cholesterol ester CE (20:4), served as critical carriers transducing gut-derived signals to the ovary. (3) Ovarian Execution: These lipid signals activated a core ovarian metabolic pathway centered on the PLA2G6-ALOX15B-AGPAT3 axis, which coordinated follicular development and ovulation by supplying steroid hormone synthesis substrates, exerting anti-inflammatory effects, and stabilizing membrane structures. Collectively, this study demonstrates that gut microbiota modulates clutch persistence in aging laying hens via lipid mediators, orchestrating a systemic “gut–serum–ovary” regulatory cascade. These findings provide a novel molecular framework for extending the economic egg-laying cycle through the targeted manipulation of intestinal microbiota or serum lipid metabolism. Full article

Improving egg production under heat stress remains a major challenge in tropical poultry breeding. This study demonstrates that clutch length and hen-day egg production are robust indicators of genetic variation in heat tolerance and directly applicable to climate-resilient breeding programs in Thai native chickens. Records from 2400 Pradu Hang Dum hens across five generations were analyzed using a reaction-norm repeatability model with the temperature–humidity index (THI) as an environmental covariate. A THI threshold of 74 was identified, beyond which heat stress altered the genetic expression of both traits. Heritability estimates declined with an increasing THI, from 0.49 to 0.32 for clutch length and from 0.37 to 0.26 for hen-day egg production, indicating reduced additive genetic control under heat stress. Genetic correlations between baseline performance and heat-stress sensitivity were moderately to strongly negative (−0.46 to −0.54), revealing antagonism between productivity under thermoneutral conditions and heat tolerance. Reaction-norm breeding values showed substantial genotype-by-environment interactions, highlighting heterogeneity in heat-stress responses among genotypes. Despite thermal challenges, positive genetic trends were observed, with an average genetic trend of 1.34 eggs per generation for clutch length and 8.8 percent per generation for hen-day egg production. These results demonstrate that genetic improvement can be sustained under heat stress and support the integration of THI-based reaction-norm evaluations to identify genotypes combining reproductive efficiency with enhanced heat tolerance for climate-resilient breeding programs. Full article

Nest architecture and surrounding habitat features can strongly influence the reproductive success of cavity-nesting birds; however, quantitative data from natural environments remain limited. We examined how nest structure and surrounding habitat features correlate with reproduction in the small bee-eater (Merops orientalis). A total of 38 natural nests were monitored during the breeding season. The Conway–Maxwell–Poisson model showed that cavity depth was a significant positive predictor of clutch size (β = 0.46 ± 0.22 SE, p = 0.036), whereas entrance diameter and nest height were not significantly related. Principal component analysis (PCA) of standardized cavity dimensions (cavity depth, entrance diameter, and nest height) showed that nest height (captured by PC2) was strongly associated with higher breeding success (OR = 0.002, p = 0.021), whereas overall cavity size (PC1) had a weaker, marginally positive correlation (OR = 3.87, p = 0.09). Habitat distance variables showed only weak, non-significant trends after accounting for multicollinearity. Nest structural traits explained more variation in reproductive performance than landscape variables (pseudo-R² = 0.80 for clutch size; 0.59 for breeding success). Field monitoring of 38 nests showed a mean clutch size of 3.9 eggs, an overall hatching success of 77.5%, and a fledging success of 51.2%, yielding a 37.1% breeding success. Our results highlight the importance of conserving sandy streambanks and mitigating human disturbance in proximity to active nests to conserve breeding success in small bee-eaters. As these findings were based on one site and a single breeding season, broader generalizations will require replication across additional years and locations. Full article

The tomato hind grouper (Cephalopholis sonnerati) is an emerging aquaculture species, with significant commercial value and promising farming potential. To advance the theoretical framework for artificial breeding, this study systematically investigated the embryogenesis, early larval morphology, growth patterns, and heritable traits of the species. The results indicated fertilization and hatching rates of 88.67 ± 3.93% and 79.67 ± 7.55%, respectively, with an average egg diameter of 0.87 ± 0.02 mm. Hatching occurred 22:55 h after fertilization at 24.80 ± 0.70 °C, corresponding to 568.42 degree-hours, and the newly hatched larvae measured 2.09 ± 0.12 mm in total length. Interestingly, as the fish grows, the color of its head patches shifts from yellow to red, providing a visible trait that can be used for early growth screening. After 15 months of graded rearing, marked growth disparities were observed among individuals originating from the same clutch, with the fast-growing group weighing 457.12 ± 58.68 g, which was 2.9 times greater than that of the slow-growing group. These findings underscore the potential of C. sonnerati as a valuable aquaculture species. Future efforts should prioritize enhanced broodstock selection and the development of fast-growing germplasm to increase its cultivation potential. Full article

To accelerate breeding progress for egg production traits in Lindian chickens, the genetic parameters for egg production and clutch-related traits in Lindian chickens were evaluated in the present study. Data regarding the age at first egg (AFE), egg number (EN), average clutch length (ACL), and average pause length (APL) were collected from two generations of Lindian chickens based on individual egg production records at 32 weeks of age (32–wk), 43–wk, and 52–wk. The results showed that the AFE of Lindian chickens was 179.3 d of age, with a heritability of 0.35. The heritability was 0.26 for EN32, 0.28 for EN43, and 0.34 for EN52. ACL showed moderate-to-high heritability (h² = 0.3–0.54), but APL traits showed low heritability (h² = 0.09–0.14). There were high positive genetic and phenotypic correlations for EN in the three periods from the start of laying up to 32–wk, 43–wk, and 52–wk. EN had high negative genetic correlations with AFE (r_G = −0.47–−0.80) and high positive genetic correlations with ACL (r_G = 0.45–0.81). The correlation between EN and APL was positive for 32–wk and 43–wk, but negative for 52–wk. These results indicated that the egg production of Lindian chickens could be improved by the selection of AFE, early EN, and ACL. Full article

Limited research exists on the breeding ecology of the black francolin (Francolinus francolinus) in northern Pakistan. This study assessed egg dimensions, clutch size, hatching, fledging, and overall breeding success across different habitats and nests (n = 25) at Totali Game Reserve, Buner. Generalized linear models (GLMs) were used to analyze the effects of nest site characteristics and nest traits on breeding parameters. Egg dimensions were consistent across sites whereas bush nests had slightly wider eggs. The average clutch size was 5.9 ± 1.7 eggs, with an average of 4.8 ± 1.0 hatchlings per nest. A total of 111 chicks fledged, averaging 4.4 ± 1.0 per nest, yielding an overall breeding success rate of 75.5%. Nests containing six eggs had higher hatching success (76.6%). GLMs results showed a significant positive relationship between clutch size and hatchling, while nest site and traits had no significant effects. However, fledgling success was positively influenced by hatchling numbers, with nests in wetland habitats yielding significantly more fledglings (4.6 ± 0.9) than those from dryland habitats (4.0 ± 1.2). These findings suggest Black Francolins prefer nesting in wetland areas in bushes, likely due to better protection and favorable conditions. Full article

Thresholds can be an effective tool in conservation planning, as they can form a defensible target for habitat conservation or restoration. Generalized thresholds must be used with caution, however, as threshold responses may vary with species and spatial scale. The objectives of this study were to identify the scales at which forest-dwelling birds respond to both habitat availability and critical thresholds in forest cover associated with their occurrence, and to assess if life history traits relate to either scale of response or critical threshold. Using point count data from the Ontario Breeding Bird Atlas, I generated concentric buffers ranging from 100 m to 10 km radius around a random subset of point counts and described forest cover and species occurrence within each buffer. I assessed the likelihood of occurrence of each species at each scale of analysis using logistic regression and identified forest cover thresholds below which the occurrence of each species becomes unlikely using fitted regression curves and ROC plots. Species varied in their response to both landscape scale and forest cover, based on relative growth rate, clutch size, and site fidelity. The mean response to forest cover was 30.8%, with landscape scale ranging from 200 m to 9 km. Despite this range, pragmatic approaches to conservation planning are still possible. Full article

The Sardinian grass snake, Natrix helvetica cetti, is an island-endemic subspecies with a restricted and highly fragmented distribution confined to Sardinia, Italy. Information on its reproductive biology and wild offspring remain scarce in the scientific literature. This present study reports the first recorded data on a clutch of eggs laid by a wild melanistic female N. h. cetti that exhibited lethargy when observed basking, prompting a brief period of health monitoring and screening for the presence of the pathogenic fungus Ophidiomyces ophidiicola (Oo). The clutch yielded nine hatchlings, for which phenotypic data are provided and compared with existing information on the Natrix natrix complex. Both the adult female and its offspring tested negative in the Oo screening. The body size of the adult grass snake, specifically its snout-to-vent length of 48.3 cm, is the smallest ever recorded for a gravid female N. helvetica. This may indicate that maturity is reached at particularly small sizes, a distinctive trait of this intriguing island subspecies, suggesting the need for further investigation. Full article

More than 40 hypotheses predict associations between features of nest architecture and at least one measure of reproductive success. However, quantitative studies of reproductive consequences of nest characteristics remain scarce. In addition, most studies were conducted on model species of which nests can be easily monitored with artificial nest-boxes. Here, we review the replicability of research protocols and findings in model species, with many repeat studies focusing mainly on nest-size components, animal-derived nest material, or fresh greenery in model species of secondary hole-nesting birds: Blue Tits (Cyanistes caeruleus), Great Tits (Parus major), Tree Swallows (Tachycineta bicolor), and Starlings (Sturnus spp.). The studies looked for correlations between nest traits and aspects of breeding performance that can be easily quantified in the field, such as clutch size, brood size at hatching or fledging, the percentage of eggs that hatch or fledge, or nestling characteristics assumed to reflect qualities associated with survival probabilities (e.g., morphometry, body condition, blood profiles). We discuss the consequences of poor replicability of research methodologies and provide explanations for why many of these studies reported poor associations between nest design and breeding success at different spatiotemporal scales. We also make suggestions for future research. Full article

We designed a common garden design to collect data on female reproductive traits from three populations of the southern grass lizard Takydromus sexlineatus, testing the hypothesis that a species-specific pattern of seasonal shifts in reproductive allocation should be shared by geographically separated populations. Of the seven examined traits, six differed among populations, with four of the six also differing among successive clutches. Females grew longer during the breeding season and produced more eggs in the first clutch than in the subsequent clutches; egg size was unchanged throughout the breeding season. After removing the influence of female size or postpartum body mass we found the following. First, postpartum body mass, clutch mass, and relative clutch mass were greater in the Wuzhishan population than in the Shaoguan and Zhaoqing populations. Second, egg size was greatest in the Wuzhishan population and smallest in the Zhaoqing population. Third, clutch size was greatest in the Wuzhishan population and smallest in the Shaoguan population. Females did not trade-off egg size against number within each population × clutch combination. Our study validates the hypothesis tested, supports the conventional view that reproductive output is highly linked to maternal body size in lizards, and follows the classic prediction that females with different amounts of resources to invest in reproduction should give priority to adjusting the total number rather than size of their offspring. Full article

This study aimed to determine the impact of various pressures on the functional composition of OCH (Odonata, Coleoptera, and Heteroptera) in streams within the northwest Rif region of Morocco. We examined how OCH traits respond to human-induced pressures in selected stream sites in Morocco’s northwestern Rif region. OCH specimens were collected from 36 sites using a Surber sampler with dimension of 20 × 20 cm and mesh size of 500 µm over the course of two years, from 2021 to 2023. We measured physico-chemical and hydraulic parameters such as temperature, pH, DO, and NO-3. Sixty-seven trait attributes from 11 trait classes were assigned to the collected OCH taxa at the family level. Following the delineation of sites along the gradient of impacts in the study area, we categorized 7 sites as slightly impacted sites (SISs), 19 sites as moderately impacted sites (MISs), and 10 sites as heavily impacted sites (HISs). We successfully identified and categorized the traits as either vulnerable or tolerant based on RLQ models. Traits such as reproductive cycles per year and tegument respiration, which were positively correlated with SISs in the RLQ model and also positively correlated with depth and chlorine, were identified as vulnerable traits. Crawling locomotion and full water swimming were identified as tolerant traits. The distribution patterns of the OCH taxa revealed a robust correlation between the taxa and the sampling sites. Notably, taxa such as Nepidae, Naucoridae, and Corixidae exhibited widespread distribution and a strong association with the SISs. On the other hand, traits related to living macroinvertebrate food sources and reproduction in vegetation, specifically clutches, exhibited a negative correlation with total dissolved solids. Incorporating OCH functional traits into biomonitoring programs allows for a more comprehensive assessment of river ecosystems. This approach provides a nuanced understanding of how different stressors impact the community composition and overall ecological health. Full article

Improving the efficiency of hens and extending the egg-laying cycle require maintaining high egg production in the later stages. The ovarian follicles, as the primary functional units for ovarian development and oocyte maturation, play a crucial role in regulating the continuous ovulation of hens. The egg production rate of laying hens is mostly affected by proper follicle growth and ovulation in the ovaries. The objective of this study was to identify the key genes and signaling pathways involved in the development of ovarian follicles in Taihang hens through transcriptome screening. In this study, RNA sequencing was used to compare and analyze the transcriptomes of ovarian follicles at four developmental stages: small white follicles (SWF), small yellow follicles (SYF), F5 follicles, and F2 follicles, from two groups: the high continual production group (H-Group) and the low continual production group (L-Group). A total of 24 cDNA libraries were constructed, and significant differential expression of 96, 199, 591, and 314 mRNAs was detected in the SWF, SYF, F5, and F2 follicles of the H and L groups, respectively. Based on the results of GO and KEGG enrichment analyses, each stage of follicle growth possesses distinct molecular genetic features, which have important effects on follicle development and significantly promote the formation of continuous production traits through the biosynthesis of steroid hormones, cytokine–cytokine receptor interaction, and neuroactive ligand–receptor interaction. Additionally, through STEM analysis, we identified 59 DEGs, including ZP4, KCNH1, IGFs, HMGA2, and CDH1, potentially associated with follicular development within four significant modules. This study represents the first transcriptome investigation of follicles in hens with high and low egg-producing characteristics at four crucial developmental stages. These findings provide important molecular evidence for understanding the regulation of follicular development and its variations. Full article

The variation in egg and clutch mass in sympatric species at high altitudes is poorly understood, and the potential causes of variation are rarely investigated. This study aimed to describe the interspecific variation in avian egg and clutch mass among 22 sympatric bird species at an altitude of 3430 m. Our objective was to reduce potential confounding effects of biotic/abiotic factors and investigated hypotheses concerning allometry, clutch size, parental care, nest predation, and lifespan as possible correlates and explanations for the observed variation. Our findings indicated that both egg and clutch mass evolve with body mass across species. We found that egg mass variation was not explained by clutch size when controlling for allometric effects, which contrasts the “egg mass vs. clutch size trade-off” hypothesis. Additionally, we found that clutch mass was positively associated with parental care (reflected by development period) but negatively associated with predation rate. By substituting egg mass and clutch size into the models, we found that clutch size was significantly correlated with parental care, predation rate, and lifespan, while egg mass was only significantly associated with development period. Overall, these findings support life-history theories suggesting that reduced clutch size or mass is associated with a higher risk of predation, reduced parental care, but longer adult lifespan. Interestingly, our results indicate that clutch size has a greater influence on these factors compared to egg mass. This could be attributed to the fact that smaller clutch sizes result in a more notable decrease in energetic allocation, as they require a reduced effort in terms of offspring production, incubation, and feeding, as opposed to solely reducing egg size. These findings contribute to the growing evidence that life-history and ecological traits correlate with egg and clutch mass variation in sympatric species. However, further research is needed to explore the potential evolutionary causes underlying these patterns. Full article

The Montagu’s harrier Circus pygargus is considered a rare species at the Italian level, and vulnerable at the European level. The main threat for these farmland birds is represented by agricultural practices; in fact, it nests on the ground in agricultural environments; therefore, at harvest time nests are often destroyed (with the eggs and chicks) by farm machinery. We examined the reproductive traits (clutch size, laying date, hatching, and fledging date and success) of the Montagu’s harrier population in central Italy (about 10% of its population in Italy) where nest protection has been implemented through electric fences and metallic meshes. By using a Bayesian probabilistic network, we modeled the sequence of events that determine its reproductive success (percentages of eggs hatched and chicks fledged) and simulated the effects of different environmental and management scenarios. Our model explained the hatching and fledging success with 90.20% and 95.12% accuracies, respectively. We found that crop type and height, laying date, type and delay of nest protection have specific effects on the reproductive success of this population. Our findings demonstrate that it is possible to optimize the monitoring of this population and significantly increase its reproductive success by acting selectively upon the environmental and management attributes of the breeding area. Our decision tool allowed us to produce several rules for the optimized monitoring and conservation of the Montagu’s harrier population in central Italy. The methodological approach proposed here is suitable for application to any farmland bird population on a local scale. Full article