Clinal variation in a brown lemur (Eulemur spp.) hybrid zone: combining morphological, genetic and climatic data to examine stability.

Studies of hybrid zones can inform our understanding of reproductive isolation and speciation. Two species of brown lemur (Eulemur rufifrons and E. cinereiceps) form an apparently stable hybrid zone in the Andringitra region of southeastern Madagascar. The aim of this study was to identify factors that contribute to this stability. We sampled animals at 11 sites along a 90-km transect through the hybrid zone and examined variation in 26 microsatellites, the D-loop region of mitochondrial DNA, six pelage and nine morphological traits; we also included samples collected in more distant allopatric sites. Clines in these traits were noncoincident, and there was no increase in either inbreeding coefficients or linkage disequilibrium at the centre of the zone. These results could suggest that the hybrid zone is maintained by weak selection against hybrids, conforming to either the tension zone or geographical selection-gradient model. However, a closer examination of clines in pelage and microsatellites indicates that these clines are not sigmoid or stepped in shape but instead plateau at their centre. Sites within the hybrid zone also occur in a distinct habitat, characterized by greater seasonality in precipitation and lower seasonality in temperature. Together, these findings suggest that the hybrid zone may follow the bounded superiority model, with exogenous selection favouring hybrids within the transitional zone. These findings are noteworthy, as examples supporting the bounded superiority model are rare and may indicate a process of ecologically driven speciation without geographical isolation.

Genetic diversity among Angus, American Brahman, Senepol and Romosinuano cattle breeds.

The objective of this study was to quantify the genetic diversity among breeds under evaluation for tropical adaptability traits that affect the performance of beef cattle at the USDA/ARS SubTropical Agricultural Research Station (STARS) near Brooksville, FL, USA. Twenty-six microsatellite loci were used to estimate parameters of genetic diversity among the breeds American Brahman, Angus, Senepol and Romosinuano; the latter was comprised of two distinct bloodlines (Costa Rican and Venezuelan). Genotypes of 47 animals from each of these STARS herds were analysed for genetic diversity and genetic distance. Using two methods, the greatest genetic distance was detected between the Costa Rican line of Romosinuano and the Senepol. Gene diversity ranged between 0.64 (Costa Rican line of Romosinuano) and 0.75 (American Brahman). The breed relationship inferences, which are based on genetic distance, provide additional tools for consideration in future crossbreeding studies and for testing the relationship between quantified breed diversity and observed heterosis.

The slick hair coat locus maps to chromosome 20 in Senepol-derived cattle.

The ability to maintain normal temperatures during heat stress is an important attribute for cattle in the subtropics and tropics. Previous studies have shown that Senepol cattle and their crosses with Holstein, Charolais and Angus animals are as heat tolerant as Brahman cattle. This has been attributed to the slick hair coat of Senepol cattle, which is thought to be controlled by a single dominant gene. In this study, a genome scan using a DNA-pooling strategy indicated that the slick locus is most likely on bovine chromosome 20 (BTA20). Interval mapping confirmed the BTA20 assignment and refined the location of the locus. In total, 14 microsatellite markers were individually genotyped in two pedigrees consisting of slick and normal-haired cattle (n = 36), representing both dairy and beef breeds. The maximum LOD score was 9.4 for a 4.4-cM support interval between markers DIK2416 and BM4107. By using additional microsatellite markers in this region, and genotyping in six more pedigrees (n = 86), the slick locus was further localized to the DIK4835 - DIK2930 interval.

Remnants of ancient genetic diversity preserved within captive groups of scimitar-horned oryx (Oryx dammah).

Scimitar-horned oryx, now considered extinct in the wild, persists in large numbers in captivity. In this first molecular genetic study on this species, we explore the patterns of genetic diversity across European, North American, and a few other captive groups using microsatellite markers and mitochondrial control region sequencing. Strong population structure was not evident from microsatellite data but we discovered deep divergence within the mitochondrial DNA haplotypes from a network analysis where three disconnected networks were obtained, with estimated divergence times of c. 2.1-2.7 million years. Mismatch distribution analyses suggest population expansions c. 1.2 and 0.5 million years ago. We discuss our findings in the context of historical climatic changes in North Africa and use information obtained on current patterns of genetic diversity within captive groups to make recommendations for future captive management and reintroduction strategies.

Assessment of single nucleotide polymorphisms in genes residing on chromosomes 14 and 29 for association with carcass composition traits in Bos indicus cattle.

Objective of this study was to assess the association of SNP in the diacylglycerol O-acyltransferase 1 (DGAT1), thyroglobulin (TG), and micromolar calcium-activated neutral protease (CAPN1) genes with carcass composition and meat quality traits in Bos indicus cattle. A population of Brahman calves (n = 479) was developed in central Florida from 1996 to 2000. Traits analyzed were ADG, hip height, slaughter weight, fat thickness, HCW, marbling score, LM area, estimated KPH fat, yield grade, retail yield, sensory panel tenderness score, carcass hump height, and cooked meat tenderness measured as Warner-Bratzler shear force at 7, 14, and 21 d postmortem. Single nucleotide polymorphisms previously reported in the TG and DGAT1 genes were used as markers on chromosome 14. Two previously reported and two new SNP in the CAPN1 gene were used as markers on chromosome 29. One SNP in CAPN1 was uninformative, and another one was associated with tenderness score (P < 0.05), suggesting the presence of variation affecting meat tenderness. All three informative SNP at the CAPN1 gene were associated with hump height (P < 0.02). The TG marker was associated with fat thickness and LMA (P < 0.05), but not with marbling score. No significant associations of the SNP in the DGAT1 gene were observed for any trait. Allele frequencies of the SNP in TG and CAPN1 were different in this Brahman population than in reported allele frequencies in Bos taurus populations. The results suggest that the use of molecular marker information developed in Bos taurus populations to Bos indicus populations may require development of appropriate additional markers.

The polled locus maps to BTA1 in a Bos indicus x Bos taurus cross.

Two hundred and nine reciprocal backcross and F2 progeny produced by embryo transfer from Angus (Bos taurus) and Brahman (Bos indicus) parents and their 60 parents and grandparents were utilized to localize the locus (POLL) responsible for the polled phenotype in a genetic map of bovine chromosome 1. Progeny were scored for polled, scurred, and horned phenotypes at 1 year of age and again following skull disection at slaughter at 20 months of age. Phenotype frequencies were independent of gender. One hundred and forty-two informative meioses for POLL and 13 microsatellite loci with an average of 267 informative meioses per locus contributed to a genetic map spanning 124.6 cM with an average interval of 9.6 cM. POLL mapped proximal to the centromere and 4.9 cM from TGLA49 supporting a previous study that employed two anonymous microsatellites. Difficulties in discriminating between scurred and horned phenotypes indicate that bracketing markers will be essential for refining the model for inheritance of the horned, scurred, and polled phenotypes and for effective marker assisted selection (MAS) for polled.

Candidate gene analysis of GH1 for effects on growth and carcass composition of cattle.

We present an approach to evaluate the support for candidate genes as quantitative trait loci (QTLs) within the context of genome-wide map-based cloning strategies. To establish candidacy, a bacterial artificial chromosome (BAC) clone containing a putative candidate gene is physically assigned to an anchored linkage map to localise the gene relative to an identified QTL effect. Microsatellite loci derived from BAC clones containing an established candidate gene are integrated into the linkage map facilitating the evaluation by interval analysis of the statistical support for QTL identity. Permutation analysis is employed to determine experiment-wise statistical support. The approach is illustrated for the growth hormone 1 (GH1) gene and growth and carcass phenotypes in cattle. Polymerase chain reaction (PCR) primers which amplify a 441 bp fragment of GH1 were used to systematically screen a bovine BAC library comprising 60,000 clones and with a 95% probability of containing a single copy sequence. The presence of GH1 in BAC-110R2C3 was confirmed by sequence analysis of the PCR product from this clone and by the physical assignment of BAC110R2C3 to bovine chromosome 19 (BTA19) band 22 by fluorescence in situ hybridisation (FISH). Microsatellite KHGH1 was isolated from BAC110R2C3 and scored in 529 reciprocal backcross and F2 fullsib progeny from 41 resource families derived from Angus (Bos taurus) and Brahman (Bos indicus). The microsatellite KHGH1 was incorporated into a framework genetic map of BTA19 comprising 12 microsatellite loci, the erythrocyte antigen T and a GH1-TaqI restriction fragment length polymorphism (RFLP). Interval analysis localised effects of taurus vs. indicus alleles on subcutaneous fat and the percentage of either extractable fat from the Iongissimus dorsi muscle to the region of BTA19 harbouring GH1.

Report of the first workshop on the genetic map of bovine chromosome 1.

A report of the first workshop on the genetic map of bovine chromosome 1 (BTA1) is presented. Five laboratories contributed 31,962 informative meioses from 70 loci. Thirty-two loci which had been typed by at least two laboratories were used to construct a framework genetic map with a likelihood ratio support of at least 1000:1 for locus order. The resulting sex-averaged framework map contained 26 loci and spanned 163.6 CM. The lengths of the female and male maps were 159.5 CM and 165.3 CM, respectively, and there was evidence for an expansion in the telomeric one-third of the male map. Of the four cases where order for closely linked loci differed among the maps produced for each of the contributing laboratories, a consensus order was obtained for three in the framework map. The average genetic distance between framework loci on the sex-averaged map was 6.3 CM.

A methodological approach for the construction of a radiation hybrid map of bovine chromosome 5

A bovine 5,000 rad WG-RH panel was used to construct an RH map of bovine chromosome 5 (BTA5). Twenty-one microsatellites and thirteen genes were scored in the panel using PAGE and radioactive labeling. Marker retention ranged from 8.9 percent-25.8 percent and averaged 17.8 percent. Pairwise locus analysis placed all markers in a single syntenic group with a LOD support of 4.0. At a LOD support of 8.0, a centromeric group of 23 syntenic markers was formed. Telomeric groups of 11 and 9 markers were assembled with a LOD support of 6.0 and 8.0, respectively. All markers were ordered by maximum likelihood methods using the program RHMAP. Only 13 markers were ordered with a LOD support of at least 3.0, while 25 and 29 markers were ordered with a support of at least 2.0 and 1.0, respectively. Total length of the comprehensive RH map was 435.9 cR5,000, with an average marker separation of 12.8 cR5,000. The largest gaps in the map were 55.0 and 30.4 cR5,000 in length. The locus orders of markers common to both the RH map and the USDA-MARC linkage map were identical. The relationship between the RH and linkage maps was calculated to be 3.74 cR5,000/cM.