Abstract
Simple SummaryMammalian hybrids frequently form in nature between closely related species, and the majority are sterile due to the production of chromosomally unbalanced gametes. In Italy, the widespread wild boar has had negative consequences for free-range pig farming, which is considered the best practice for pig welfare and is a common method of farming most autochthonous pig breeds. This study aimed to analyze the sperm DNA integrity, sperm meiotic segregation and nuclear spatial organization in a boar–pig hybrid, for the first time, to evaluate its fertilizing capacity. The results show that the hybrid presented a high frequency (64%) of motile spermatozoa with a regular chromosome composition and a specific spatial distribution. This study underlines how fertile boar–pig hybrids represent a growing problem for conserving autochthonous pig breeds.A wide range of mammalian hybrids has recently been found by chance or through population-screening programs, but studies about their fertilizing capacity remain scarce and incomplete. Most of them are assumed to be sterile due to meiotic arrest caused by the failure of chromosome pairings. In this study, we evaluated both sperm meiotic segregation, by 2D fluorescent in situ hybridization (FISH) analysis, and sperm quality (Sperm Chromatin Structure Assay) by flow cytometer in a fertile boar–pig hybrid (2n = 37,XY) originating from a Nero Siciliano pig breed (Sus scrofa domesticus) and a wild boar (Sus scrofa ferus). Spermatozoa were also separated by a dual-layer (75–60%) discontinuous Percoll gradient, resulting in two fractions with a significantly better overall quality in the motile sperm fraction. These data were confirmed by FISH analysis also, where the frequencies of spermatozoa with a regular chromosome composition were 27% in total sperm fraction and 64% in motile sperm fraction. We also evaluated the nuclear architecture in all counted spermatozoa, showing a chromatin distribution changing when chromosome abnormalities occur. Our results demonstrate that the chromosome pairing has a minimal effect on the sperm segregation and semen quality of a boar–pig hybrid, making it fertile and harmful for the conservation of autochthonous pig breeds.
Highlights
Over the last decade, several studies have reported a rising number of mammalian hybrids, originating by accident or design [1,2,3] and considered sterile with some exceptions [4].Recent studies showed crosses between domestic pig (DP) and wild boar (WB), belonging to the same Sus scrofa (Ssc) species [5]
There are very few studies about boar–pig hybrid fertility, and the existing studies are mainly related to the fertility of sows, which is considered the primary source of economic loss for pork producers [7]
We evaluated the nuclear architecture of these chromosomes in all counted spermatozoa in specific regions: the green (Ssc 15) detached signal was detected in the apical part of the sperm head (85%), the red (Ssc 17) detached signal was detected in the medial part of the sperm head (85%) and the green and red or yellow signals were detected in the basal part of the sperm head (88%)
Summary
Several studies have reported a rising number of mammalian hybrids, originating by accident or design [1,2,3] and considered sterile with some exceptions [4].Recent studies showed crosses between domestic pig (DP) and wild boar (WB), belonging to the same Sus scrofa (Ssc) species [5].
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