The effect of divergent selection for uterine capacity on fetal and placental development at term in rabbits: Maternal and embryonic genetic effects1

Litter size components traits in two Algerian rabbit lines

<p>The aim of this study was to estimate the limiting litter size components in rabbit females from a Synthetic line (n=32) and a Local population (n=34). Ovulation rate, number of implanted and live embryos were counted by laparoscopy at 12 d after mating. Prolificacy (total newborn, number born alive and mortality) and embryonic, foetal and prenatal survival at day of birth of the 3^rd gestation were measured. The analysed traits were body weight of the female at mating, ovulation rate, implanted, live and resorbed embryos, embryonic, foetal and prenatal survival, as well as total newborn, number born alive and mortality at birth. Synthetic line females had a higher ovulation rate compared to the Local population (11.03±0.23 vs. 8.41±0.23 corpora lutea; <em>P</em>&lt;0.0001). Synthetic line displayed a higher number of implanted embryos (10.00±0.25 vs. 7.85±0.25 embryos; <em>P</em>&lt;0.0001). No difference was found between groups for number of resorbed embryos. Similar embryonic, foetal and prenatal survival rates were reported between the Synthetic line and the Local population. Additionally, total newborn was higher in the Synthetic line than in the Local population (+1.46 kits; <em>P</em>&lt;0.05). A principal components analysis was performed. The first four principal components (PC) explained more than 90% of the total variation in both lines. Total newborn, number born alive and live embryos were the main variables defining the 1^st PC. Resorbed embryos and foetal survival were located in the 2^nd PC. Ovulation rate and embryonic survival were the predominant variables defining the 3^rd PC. The body weight of females was located in the 4^th PC. The phenotypic correlation between total newborn and its components were high and positive in both lines, except for ovulation rate and total newborn, where it was moderate in Synthetic line. In conclusion, the females from Synthetic line have a higher total newborn than those from Local population, as a consequence of a higher number of released oocytes and embryos that successfully reach implantation. However, a higher uterine crowding in Synthetic line seems to limit survival of foetuses that reach term of gestation, while ovulation rate is the principal limiting factor of total newborn in Local population.</p>

Investigation of the oviductal glycoprotein 1 (OVGP1) gene associated with embryo survival and development in the rabbit

An association study was performed in rabbits between early embryo survival and development, and the nonconservative SNP 12944C>G located in exon 11 and the triallellic microsatellite [(GT)(15)T(G)(5), (GT)(14)T(G)(5), and (GT)(11)T(G)(7))] located in the promoter region of the oviductal glycoprotein 1 (OVGP1) gene. We analyzed an F(2) cross of 2 lines of rabbits divergently selected for uterine capacity. A total of 172 and 159 females were slaughtered at 48 and 72 h of gestation, respectively, to determine whether OVGP1 influences ovulation rate, fertilization rate, early embryo survival, and embryonic stage of development. The results of the SNP indicated that all genotypes showed similar early embryo survival and a similar embryonic stage of development at 48 h of gestation. However, at 72 h of gestation, the GG genotype showed greater early embryo survival than the CC genotype (0.56 embryos) and their embryos presented less embryonic development. Analysis of the microsatellite was performed to ascertain the presence or absence of the allele (GT)(14)T(G)(5). At both stages of gestation, the (GT)(14)T(G)(5)/(GT)(14)T(G)(5) genotype showed greater early embryo survival (0.94 and 1.54 embryos at 48 and 72 h of gestation, respectively) and less embryonic development than the homozygous genotypes without the allele (GT)(14)T(G)(5).

Heritable variation in maternal yolk hormone transfer in a wild bird population

Differential reproductive investment by the mother can critically influence offspring development and phenotype, and strong selection is therefore expected to act on such maternal effects. Although a genetic basis is a prerequisite for phenotypic traits to respond to selection and thus to evolve, we still know very little about the extent of heritable variation in maternal effects in natural populations. Here, we present the first estimates of intrafemale repeatability across breeding seasons and estimates of heritability of hormone-mediated maternal effects in a wild population of collared flycatchers (Ficedula albicollis). We found that maternal yolk testosterone (T) concentrations, yolk mass, and egg mass were moderately to highly repeatable within females across years, whereas intrafemale consistency of maternal yolk androstenedione (A4) deposition was low yet statistically significant. Furthermore, maternal yolk T transfer, yolk mass, and egg mass were significantly heritable, whereas yolk A4 transfer was not. These results strongly suggest that two major maternal yolk androgens are differentially regulated by genes and the environment. Selection on heritable variation in maternal yolk T deposition has the potential to shape the rate and direction of phenotypic change in offspring traits and can thereby accelerate or impede the response to selection in natural populations.

Identification of single-nucleotide polymorphism in the progesterone receptor gene and its association with reproductive traits in rabbits

A total of 598 F2 does from a cross between the high and low lines selected divergently for uterine capacity during 10 generations were used in a candidate gene analysis. The presence of major genes affecting the number of implanted embryos and uterine capacity has been suggested in lines divergently selected for uterine capacity. Uterine capacity is a main component of litter size. The progesterone receptor gene was tested as a candidate gene to determine whether polymorphisms explain differences in litter size and its components. Fragments of the promoter region and exons 1-8 were amplified and sequenced. One SNP was found in the promoter region, 2464G>A, three SNPs in the 5'-UTR exon 1, and a silence SNP in exon 7. The first four SNPs were segregated in two haplotypes. The allele G found in the promoter region was found in 75% of the high-line parental animals and in 29% of the low-line parental animals. The GG genotype had 0.5 kits and 0.5 implanted embryos more than the AA genotype. At 48 hr of gestation, the difference in early embryo survival and embryonic stage of development was small. However, at 72 hr of gestation, the GG genotype had 0.36 embryos more than the AA genotype and also had a more advanced embryonic stage of development, showing a lower percentage of compacted morulae and a higher percentage of blastocysts. The difference in litter size between the GG and GA genotypes was similar to the difference found between homozygote genotypes; however, differences in implanted embryos, early embryo survival, and embryo development were not detected between the GG and GA genotypes.