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

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.