A comparative study of libido in drakes: from phenotypes to molecules

Transcriptome analysis of testis and epididymis identifies key genes and pathways regulating gander sperm motility

Sperm motility is a critical indicator of semen quality and determines the reproduction performance in male poultry. However, compared to chickens and ducks, very little is known about the physiological basis of varying levels of sperm motility as well the underlying regulatory mechanisms in geese. To address this, in the present study, a systematic comparison of semen quality parameters and histomorphological characteristics and genome-wide transcriptomic profiles of testes and epididymis were performed in ganders with high and low sperm motility. Our results showed that the size, weight, and organ index of bilateral testes and epididymis of ganders from high sperm motility (HSM) group tended to be higher (P > 0.05) than those of ganders from low sperm motility (LSM) group, implying better reproductive organ development in HSM. The ejaculate volume, sperm density, sperm viability, and semen quality factor of the ganders were observed to be significantly higher in HSM than in LSM (P < 0.01), and the opposite was seen in sperm deformity rate (P < 0.01). Moreover, the ganders in HSM showed significantly higher testicular seminiferous epithelial thickness and seminiferous tubule diameter (P < 0.05), higher number of Sertoli cells (SC), spermatids (Sd), and spermatozoa (Sa, P < 0.05), as well as greater diameter and area of epididymal proximal efferent ductule (PED, P < 0.05) than those in LSM. Comparative transcriptomic analysis identified 1,828 and 483 differentially expressed genes (DEGs) in the testis and epididymis of ganders between HSM and LSM, respectively. Functional enrichment analysis revealed that these DEGs were significantly enriched in the Wnt signaling, Apelin signaling, melanogenesis, and GnRH signaling pathways. The protein-protein interaction network analysis further highlighted the hub genes. The testicular DEGs including PLCB1, PLCB2, WNT11, WNT4, and LRP6 were identified to regulate sperm motility through the Wnt signaling pathway, while the epididymal DEGs including WNT3A, WNT9B, SOX2, and SOX10 could affect sperm motility by regulating epididymal cellular proliferation and differentiation. These data provided new insights into the regulatory mechanisms of male poultry reproductive organ development and sperm quality and would be helpful for developing molecular approaches in the genetic improvement of goose fertility.

Molecular mechanisms of libido influencing semen quality in geese through the hypothalamic-pituitary-testicular-external genitalia axis

Libido plays a crucial role in influencing semen quality, yet the underlying regulatory mechanisms remain unclear. As a central axis in male goose reproduction, the hypothalamic-pituitary-testicular-external genitalia (HPTE) axis may contribute to the regulation of this process. In this study, we established a rating scale for goose libido based on average number of massages to erection (ANM) and the erection type, and evaluated semen quality across the entire flock. Correlation analyses showed that ANM was negatively correlated with sperm concentration (SC), acrosome integrity (AI), and semen quality factor (SQF), while positively correlated with morphological abnormal sperm (MAS) (P < 0.01). A comparison of semen quality and testicular histology between high libido (HG) and low libido (LG) groups showed that SC and SQF were significantly higher and MAS was lower in HG (P < 0.05). The lumen diameter of seminiferous tubules (LD) (P < 0.01) and the number of Sertoli cells (Sc) (P < 0.05) were also significantly greater in HG. Further, the number of spermatogonia (Sg) was significantly (P < 0.01) lower, and spermatocyte (Sp) and elongated spermatid (Se) were significantly higher in HG (P < 0.05). Through transcriptome sequencing (RNA-seq), we identified 98, 163, 2,474 and 400 differentially expressed genes (DEGs) in the hypothalamus, pituitary, testis and external genitalia, respectively. Gene Ontology (GO) analysis indicated that the term "male gonad development" was significantly enriched in the hypothalamus. Here, the expression of LHX9 was positively correlated with ANM, and negatively correlated with SC and SQF (P < 0.05). Additionally, WNT4 was positively correlated with ANM and MAS (P < 0.01), and negatively correlated with SC (P < 0.05), suggesting that LHX9 and WNT4 might serve as key upstream regulatory genes. Further analysis through Weighted Gene Co-Expression Network Analysis (WGCNA) showed that the yellow module (R = 0.89, P = 7e-09) was strongly associated with testicular development, with genes predominantly involved in male reproductive process. Based on these findings, we screened genes significantly correlated with LHX9 and WNT4 from the yellow module (|Cor |≥0.6, P < 0.05). These genes were significantly enriched in 8 pathways, primarily associated with metabolic processes, including drug metabolism - other enzymes, metabolism of xenobiotics by cytochrome P450, metabolic pathways, pyrimidine metabolism, glycerolipid metabolism, and riboflavin metabolism. Using the Maximal Clique Centrality (MCC) algorithm in the CytoHubba plug-in, SYCP3, DDX4, STRA8, AMH, MEIOB, CDT1, BCL2, PRIM1, and DLGAP5 were identified as hub genes. In conclusion, within the HPTE axis, libido might influence metabolism-related signaling pathways (mainly involving genes such as SYCP3, DDX4, STRA8, AMH, MEIOB, CDT1, BCL2, PRIM1, and DLGAP5) through LHX9 and WNT4 to regulate the development of the seminiferous tubules and germ cell number, ultimately affecting SC and MAS in geese. These findings offer practical insights into libido rating and shed light on the mechanisms by which libido regulates semen quality, potentially aiding in the improvement of goose breeding capacity.

Developmental variations of the reproductive organs of ganders from different goose breeds and the underlying mechanisms

A deep understanding of the dynamics and mechanisms of male reproductive tract development is necessary for adoption of either genetic techniques or environmental management practices for improving fertility and hatchability in poultry. However, compared with other poultry such as chickens and ducks, less is known about the age- and breed-related changes in the reproductive tract development of domestic goose ganders exhibiting relatively poor reproductive performance as well as the regulatory mechanisms. In the present study, by taking 2 Chinese domestic goose breeds (Sichuan White goose, SW and Gang goose, GE; Anser cygnoides) and one European goose breed (Landes goose, LD; Anser anser) as the experimental objects, we comprehensive analyzed the morphological, histological, and genome-wide transcriptomic variations in their testicular and external genital development during the period from hatching to sexual maturity. Results from histomorphological analysis demonstrated that the reproductive tract of all goose breeds developed in both age- and breed-dependent manners, and the left and right testis developed asymmetrically throughout posthatch development. The tenth week posthatch was a critical developmental stage for all goose ganders, because both the testicular and external genital histomorphological parameters significantly changed before and after this period. During the first 10 wk posthatch, the weight, organ index, or size of male reproductive organs developed more rapidly in SW than in LD, and so were the testicular parenchymal-to-interstitial ratio and the external genital lymphatic lumen diameter. However, the testicular seminiferous epithelium thickness, seminiferous tubule diameter, and Leydig cell number, as well as the external genital keratinized epithelium thickness were significantly higher in LD than in SW at 10 wk of age. Through comparative transcriptomics analysis and RT-qPCR validation, several pathways related to germ and somatic cell function, organ remodeling, and energy metabolism were thought to be responsible for the developmental variations in the early testicular development between Chinese and European domestic ganders, where 10 hub genes involved in the cell cycle, RNA polymerase II-dependent transcription, and mitotic cell division pathways might play essential roles. These data shed new light on the interbreed differences in the male goose reproductive tract development and the molecular mechanisms regulating male goose testicular functions and fertility.

Genome sequencing of drake semen micobiome with correlation with their compositions, sources and potential mechanisms affecting semen quality

Artificial insemination (AI) technology has greatly promoted the development of the chicken industry. Recently, AI technology has also begun to be used in the duck industry, but there are some problems. Numerous researchers have shown that microbes colonizing in semen can degrade semen quality, and AI can increase the harmful microbial load in hen's reproductive tract. Different from the degraded external genitalia of roosters, drakes have well-developed external genitalia, which may cause drake semen to be more susceptible to microbial contamination. However, information on the compositions, sources, and effects of semen microbes on semen quality remains unknown in drakes. In the current study, high-throughput sequencing technology was used to detect microbial communities in drake semen, environmental swabs, cloacal swabs, and the spermaduct after quantifying the semen quality of drakes to investigate the effects of microbes in the environment, cloaca, and spermaduct on semen microbiota and the relationships between semen microbes and semen quality. Taxonomic analysis showed that the microbes in the semen, environment, cloaca, and spermaduct samples were all classified into 4 phyla and 25 genera. Firmicutes and Proteobacteria were the dominant phyla. Phyllobacterium only existed in the environment, while Marinococcus did not exist in the cloaca. Of the 24 genera present in semen: Brachybacterium, Brochothrix, Chryseobacterium, Kocuria, Marinococcus, Micrococcus, Rothia, Salinicoccus, and Staphylococcus originated from the environment; Achromobacter, Aerococcus, Corynebacterium, Desemzia, Enterococcus, Jeotgalicoccus, Pseudomonas, Psychrobacter, and Turicibacter originated from the cloaca; and Agrobacterium, Carnobacterium, Chelativorans, Devosia, Halomonas, and Oceanicaulis originated from the spermaduct. In addition, K-means clustering analysis showed that semen samples could be divided into 2 clusters based on microbial compositions, and compared with cluster 1, the counts of Chelativorans (P < 0.05), Devosia (P < 0.01), Halomonas (P < 0.05), and Oceanicaulis (P < 0.05) were higher in cluster 2, while the sperm viability (P < 0.05), total sperm number (P < 0.01), and semen quality factor (SQF) (P < 0.01) were lower in cluster 2. Furthermore, functional prediction analysis of microbes showed that the activities of starch and sucrose metabolism, phosphotransferase system, ABC transporters, microbial metabolism in diverse environments, and quorum sensing pathways between cluster 1 and cluster 2 were significantly different (P < 0.05). Overall, environmental/cloacal microbes resulted in semen contamination, and microbes from the Chelativorans, Devosia, Halomonas, and Oceanicaulis genera may have negative effects on semen quality in drakes by affecting the activities of starch and sucrose metabolism, phosphotransferase system, ABC transporters, and quorum sensing pathways that are associated with carbohydrate metabolism. These data will provide a basis for developing strategies to prevent microbial contamination of drake semen.

Comparative transcriptome analysis identified crucial genes and pathways affecting sperm motility in the reproductive tract of drakes with different libido

Libido can affect the semen quality of male, and the sperm motility in semen quality parameters is a reliable index to evaluate the fertility of male. In drakes, the sperm motility is gradually acquired in testis, epididymis, and spermaduct. However, the relationship between libido and sperm motility in drakes has not been reported and the mechanisms of testis, epididymis, and spermaduct regulating the sperm motility of drakes are unclear. Therefore, the purpose of the present study was to compare the semen quality of drakes with libido level 4 (LL4) and libido level 5 (LL5), and tried to identify the mechanisms regulating the sperm motility in drakes by performing RNA-seq in testis, epididymis, and spermaduct. Phenotypically, the sperm motility of drakes (P < 0.01), weight of testis (P < 0.05), and organ index of epididymis (P < 0.05) in the LL5 group were significantly better than those in LL4 group. Moreover, compared with the LL4 group, the ductal square of seminiferous tubule (ST) in testis was significantly bigger in the LL5 group (P < 0.05), and the seminiferous epithelial thickness (P < 0.01) of ST in testis and lumenal diameter (P < 0.05) of ductuli conjugentes/dutus epididymidis in epididymis were significantly longer in the LL5 group. In transcriptional regulation, in addition to KEGG pathways related to metabolism and oxidative phosphorylation, lots of KEGG pathways associated with immunity, proliferation, and signaling were also significantly enriched in testis, epididymis, and spermaduct, respectively. Furthermore, through the integrated analysis of coexpression network and protein-protein interaction network, 3 genes (including COL11A1, COL14A1, and C3AR1) involved in protein digestion and absorption pathway and Staphylococcus aureus infection pathway were identified in testis, 2 genes (including BUB1B and ESPL1) involved in cell cycle pathway were identified in epididymis, and 13 genes (including DNAH1, DNAH3, DNAH7, DNAH10, DNAH12, DNAI1, DNAI2, DNALI1, NTF3, ITGA1, TLR2, RELN, and PAK1) involved in Huntington disease pathway and PI3K-Akt signaling pathway were identified in spermaduct. These genes could play crucial roles in the sperm motility of drakes with different libido, and all data the present study obtained will provide new insights into the molecular mechanisms regulating sperm motility of drakes.

Comparative Transcriptome Analysis Provided a New Insight into the Molecular Mechanisms of Epididymis Regulating Semen Volume in Drakes

Semen volume is an important factor in artificial insemination (AI) of ducks. In drakes, seminal plasma that is produced by the epididymis determines the semen volume. However, the mechanism of epididymis regulating semen volume of drakes remains unclear. Therefore, the aim of the present study was to preliminarily reveal the mechanism regulating the semen volume through comparing the epididymal histomorphology and mRNA expression profiles between drakes with high-volume semen (HVS) and low-volume semen (LVS). Phenotypically, drakes in the HVS group produced more sperm than drakes in the LVS group. In addition, compared with the HVS group, the ductal square of ductuli conjugentes (DC) and dutus epididymidis (DE) in epididymis was significantly smaller in the LVS group, and the lumenal diameter and epithelial thickness of DC/DE were significantly shorter in the LVS group. In transcriptional regulation, 72 different expression genes (DEGs) were identified from the epididymis between HVS and LVS groups. Gene Ontology (GO) analysis indicated that the DEGs were mainly related to hormone secretion, neurotransmitter synthesis/transport, transmembrane signal transduction, transmembrane transporter activity, and nervous system development (p < 0.05). Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analysis showed that the DEGs were significantly enriched in pathways associated with hormone and neurotransmitter transmission (p < 0.05). In addition, further analysis of the top five pathways enriched by KEGG, nine key candidate genes (including SLC18A2, SNAP25, CACNA1B, GABRG2, DRD3, CAMK2A, NR5A1, and STAR) were identified, which could play a crucial role in the formation of semen. These data provide new insights into the molecular mechanism regulating semen volume of drakes and make feasible the breeding of drakes by semen volume.

The Impacts of Female Access during Rearing on the Reproductive Behavior and Physiology of Pekin Drakes, and Flock Fertility

Simple Summary

Male and female ducklings are typically reared in same-sex groups. With the goal of improving the males’ reproductive performance, and overall flock fertility, some flock owners place several female ducklings into the otherwise all-male pens during rearing. However, the relationships between rearing, drake reproductive success, and flock fertility have not been confirmed. To fill these knowledge gaps, we compared the frequencies of correctly oriented mounts and circulating testosterone levels of drakes reared with and without physical access to females, and the impacts of these rearing treatments on flock fertility. Rearing treatment did not impact any of the measured variables; however, all were affected by age. Individual variation in behavior and testosterone measures were noted in both treatment groups. We conclude that rearing male ducklings with auditory and visual, but without physical access to female ducklings is sufficient for promoting reproductive behavior and physiology, and securing high fertility within this Pekin duck breed.

Abstract

Commercially housed Pekin ducks (Anas platyrhynchos) are typically reared in same sex groups to facilitate separate diet provisioning. Several female ducklings are sometimes mixed into the otherwise all-male pens. This practice is thought to increase flock reproductive success. To evaluate this hypothesis, we reared ducklings in alternating same-sex groups (150 hens or 30 drakes/pen; 8 groups/sex) and evaluated the impacts of rearing on drake mounting behavior, testosterone levels, and flock fertility. At 12 days, three females were placed into four of the male duckling pens. At 20–22 weeks of age, adjacent male and female pens were moved into pens within a breeder barn, and combined to form mixed-sex pens. The number of correctly aligned mounts performed by 10 focal drakes per pen was evaluated over 3 days (12 h/day) at 26, 32, and 45 weeks of age. Circulating testosterone concentrations were analyzed from blood plasma samples collected from the focal drakes at 15 (baseline), 22, 28, 34 and 45 weeks of age. Pen-level fertility was determined at 33–34 and 45–46 weeks of age. Mount and testosterone data were analyzed using a Generalized Linear Mixed Model and a Linear Mixed Model in R 4.0.5, with duck in pen as a random effect. A Linear Mixed Model was used to analyze fertility data, with pen as a random effect. None of the measured variables were impacted by rearing treatment, but all varied with flock age. Physical access to female ducklings during rearing did not enhance flock reproductive success.