The Limonium binervosum aggregate (Plumbaginaceae) in the British Isles

A taxometric analysis of 153 colonies of the agamospermous Limonium binervosum aggregate in the British Isles has revealed an ordered hierarchy of variation. A taxonomic treatment of the group describes five new species, redefines four others and describes other infraspecific variants as subspecies or varieties. Each species is morphologically distinct and has a defined geographic range. There are four widespread and morphologically variable species and five geographically restricted species (four monotypic). Limonium recurvum , previously described as a microspecies endemic to a small area of the Dorset Coast, has been widened to include all triploid (2 n = 27) L. binervosum agg. variants found also in W and N Ireland, SW Scotland and Cumbria. All other taxa are tetraploid, usually with 2 n = 35.     

A new Chinese species of Psathyrostachys (Poaceae) with notes on its karyotype

The new species Psathyrostachys stoloniformis native to China is described. The karyotype was investigated by C-, N-, and Ag-banding. The new species has 2n = 2x = 14, including 8 metacentric and 6 SAT-chromosomes with minute satellites, distributed either on 3 or on 4 chromosome pairs. The C-banding pattern comprises from one to six conspicuous and from zero to three very small bands per chromosome. Often two bands placed close together appear as one large band. The karyotype suggests that P. stoloniformis is closely related to P. juncea. N-banding produced very weak or no bands. Meiotic analyses of interspecific hybrids revealed a high chiasma frequency indicating that P. stoloniformis has the same basic genome (N) as P. huashanica , and P. fragilis.     

Detection of Rsp and Modifier Variation in the Meiotic Drive System SEGREGATION DISTORTER (SD) of DROSOPHILA MELANOGASTER

Identification of allelic variability at the two major loci (Sd and Rsp) that interact to cause sperm dysfunction in Segregation distorter (SD) males of D. melanogaster has been hampered by the difficulty in separating the elements recombinationally. In addition, small differences in the strength of Sd alleles or sensitivities of Rsp alleles to Sd are difficult to measure against background genetic or environmental variation. Viability effects of the markers used to score progeny classes may also introduce a bias. Removal of Sd and E(SD) from their second chromosome location to create a Dp(2;Y)Sd E(SD) chromosome eliminates these problems, since any combination of Rsp alleles can be easily tested without resorting to recombinational techniques. Further, since these pairs of Rsp alleles are compared in their response to Dp Sd E(SD) in the same individual males, background variation and viability effects can be easily removed to allow fine-scale resolution of Rsp differences. Tests of all possible pairwise combination of six laboratory chromosomes in this way revealed at least three and possibly four different Rsp allelic classes. In addition, the hierarchical nature of the tests further allowed for determination of the presence of linked suppressors or enhancers of Sd activity. A sample of 11 second chromosomes selected from a group recently isolated from a natural population was also unambiguously ordered as to Rsp allelic status using this approach. The resultant pattern was similar to that obtained for the laboratory chromosomes, except for the not unexpected observation that the natural population apparently harbored more drive suppressors. The pattern of results obtained from these pairwise combinations of Rsp alleles supports the notion that there are no dominance interactions within the group, but that each responds more or less independently to Sd in giving sperm dysfunction.     

Mitochondrial DNA polymorphisms in subterranean mole-rats of the Spalax ehrenbergi superspecies in Israel, and its peripheral isolates

Patterns of mitochondrial DNA (mtDNA) variation were examined in 133 mole-rats constituting all four chromosomal species (2n = 52, 2n = 54, 2n = 58, and 2n = 60) of the Spalax ehrenbergi superspecies in Israel, as well as the peripheral isolates of 2n = 60. In the main range of the complex, a total of 28 mtDNA haplotypes were found in 64 mole-rats, with most haplotypes being unique to either a single chromosomal species or population. mtDNA divergence increased from low to high diploid number in a north-to-south direction in Israel. Overall levels of mtDNA diversity were unexpectedly the highest in the 2n = 60, the youngest species of the complex. The mtDNA haplotypes can be separated into two major groups, 2n = 52-54 and 2n = 58-60, and a phylogenetic analysis for each group revealed evidence of a few haplotypes not sorted by diploid number. The overall patterns of mtDNA divergence seen within and among the four chromosomal species are consistent with the parapatric mode of speciation as suggested from previous studies of allozyme and DNA hybridization. In a separate data set the patterns of mtDNA variation were examined across the main geographic range and across peripheral semi-isolates and isolates of the 2n = 60 chromosomal species. Fifteen haplotypes were found in 69 mole-rats. High levels of mtDNA diversity characterized the main range, semi-isolated, and even some desert isolated populations. The peripheral isolates contain much mtDNA diversity, including novel haplotypes.      

Genetic and genomic relationships in Leymus Hochst

Genetic and genomic relationships among three taxonomically related species of Leymus, northern European L. arenarius (octoploid, 2n = 56), northern American/Pacific L. mollis (tetraploid, 2n = 28) and central Eurasian L. racemosus (tetraploid, 2n = 28), were examined using molecular and cytogenetic methods. The amplified fragment length polymorphism (AFLP) analysis clearly differentiated Icelandic populations of L. arenarius from Alaskan populations of L. mollis. The former group is more genetically homogeneous than the latter. Leymus arenarius in Iceland has a common gene pool and a relatively recent origin. The Alaskan L. mollis, on the other hand, is probably a glacial survival that has accumulated high level of genetic variation and has differentiated into subspecies. Analysis of the 18S-26S ribosomal genes, by restriction fragment length polymorphism (RFLP) and fluorescence in situ hybridization (FISH), revealed a very close relationship between the octoploid northern European L. arenarius and the tetraploid Eurasian L. racemosus, such that the former could have originated from the latter, probably via interspecific hybridization. Leymus-specific DNA sequences were isolated and used for analyzing genetic relatedness among five Leymus species and four Psathyrostachys species. The RFLP analysis of retrotransposon sequence pLm44 and ribosomal clone pTa71 clearly revealed a close relationship between these two genera, i.e. higher variation was found within genera than between them. The results support the previous notion that Leymus is autopolyploid having all genomes being designated Ns as in Psathyrostachys, but a major taxonomic revision of this group would require analysis of more species.     

Association analysis of gene polymorphism in alcohol metabolizing enzymes with risk for coronary atherosclerosis

The allele and genotype distribution of two alcohol dehydrogenase genes ADH1B (exon 3 polymorphism A/G (47His)), ADH7 (intron 5 polymorphism G/C) and cytochrome P450 2E1 gene (CYP2E1; 5'-flanking region G/C and intron 6 T/A polymorphisms) were examined in Russian (Tomsk, n = 125) healthy population and in coronary atherosclerosis patients (CA, n = 92). The genotype frequencies followed the Hardy-Weinberg equilibrium and the alleles were in linkage equilibrium or gametic equilibrium in the control sample. Only two CYP2E1 gene polymorphisms were in linkage disequilibrium. The frequencies of the derived alleles at ADH1B (*G (+MslI) allele), CYP2E1 (**C2 (+PstI) allele) and CYP2E1 (*C (-Dra I)2 allele) were 8.48 +/- 1.86%; 1.20 +/- 0.69% and 10.00 +/- 1.90%, respectively. The 2ADH7 gene polymorphism showed a high level of heterozygosity; the frequency of the ADH7*C (-Sty I) allele was 44.58 +/- 3.21%. A significantly higher frequency of CYP2E1 (*C2 (+Pst I)) allele has been revealed in the CA group (P = 0.043; OR = 4.23; 95% CI 1.03-20.01). The tendency to significant effect of A1A2 genotype in ADH1B Msl 1 polymorphism was observed for systolic blood pressure in the control group (P = 0.068). The statistically significant two-way interaction effects of ADH7 StyI and CYP2E1 DraI on diastolic blood pressure (P = 0.029) and on the serum high density lipoprotein level (P = 0,042) were also revealed. Association of A1A2 genotype in ADHIB Msl I polymorphism with reduced amount in a serum of a very low density lipoprotein level (P = 0.045) have also been shown. This may result from multifunctional activity of alcohol metabolizing enzymes and their involvement in many metabolic and free radical reactions in the body.     

Non-invasive monitoring of male and female numbat (Myrmecobius fasciatus: Myrmecobiidae) reproductive activity

The reproductive endocrinology of the highly endangered numbat (Myrmecobius fasciatus) is described for the first time. Patterns of faecal steroid secretion (progesterone [PM], oestradiol-17β [E2] and testosterone [TM] metabolites) were examined within a captive numbat population over 1 year and revealed a highly synchronized seasonal pattern of reproduction. TM secretion increased progressively from September to November, peaked in December and then decreased in February. All females displayed luteal phases (1-3), between late-November to late-March, in association with pregnant (Pr, n=4), non-productive mated oestrous cycles (NMEC, n=8) and non-mated oestrous cycles (NEC, n=6). The mean oestrous cycle length was 30.2±1.1d (n=11) and was comprised of a mean follicular (n=11) and luteal (n=18) phase length of 16.2±1.6d and 14.0±0.8d, respectively. No variation in mean luteal phase length or PM concentration according to cycle type (Pr, NMEC, NEC) or cycle number (1st, 2nd or 3rd cycle) was detected. Longitudinal profiling of PM secretion confirmed that the female numbat is seasonally polyoestrous and that the luteal phase occurs spontaneously. Changes in the secretion of E2 provided little instructive information on oestrous cycle activity. Mating success was 31%, with age and subject having no effect on mating success. Timing of introduction, of male to female, appeared to impact mating success, with paired animals introduced for a shorter time frame (≤14d) prior to the first observed mating successfully producing young. Collectively, results of the present study confirm that PM and TM can be reliably used to index numbat reproductive activity.     

Influence of estradiol on cortisol secretion in ovariectomized cynomolgus macaques (Macaca fascicularis)

In an investigation of cortisol secretion in fully mature, ovariectomized cynomolgus monkeys (Macaca fascicularis), we compared monkeys that were given either placebo (OVX, n = 26) or 17beta estradiol (E(2 )) (EST, n = 26) in a daily oral dose. Serum cortisol concentrations were measured prior to the experimental manipulation and 3, 6, 9, and 12 months following initiation of treatment. Pretreatment cortisol values did not differ between groups. Assessment of the treatment period values revealed that cortisol concentrations were significantly higher ( approximately 10%) in the EST than in the OVX monkeys. Cortisol also varied significantly across periods of sampling. This time-dependent variation was attributable to elevations in months 6 and 9 (when daylight was generally long), relative to months 3 and 12 (when daylight was relatively short). The modest stimulatory effect of estrogen on corticosteroid production observed in this study is consistent with what has been seen in women, and contrasts with the more robust effects observed in New World monkeys. The possible relationship between season and cortisol secretion observed here has not been previously described in monkeys.     

Plasticity in body composition in breeding birds: what drives the metabolic costs of egg production?

Body composition in vertebrates is known to show phenotypic plasticity, and changes in organ masses are usually rapid and reversible. One of the most rapid and reversible changes is the transformation of the female avian reproductive organs before breeding. This provides an excellent system to investigate the effects of plasticity in organ size on basal metabolic rate (BMR) through relationships between organ masses and BMR. We compared body composition of female European starlings (Sturnus vulgaris) during various reproductive stages over 3 yr and investigated the pattern of changes in reproductive and nonreproductive organ mass during follicular development and ovulation. Furthermore, we analyzed the relationship between organ mass and resting metabolic rate (RMR) in nonbreeding, laying, and chick-rearing females. Our analysis revealed marked variation in organ masses between breeding stages but no consistent pattern among years except for kidney and pectoralis muscle. Furthermore, changes in nonreproductive organs did not parallel the cycle of growth and regression of the reproductive organs. The oviduct gained 62% of its 22-fold increase in mass in only 3 d, and oviduct regression was just as rapid and began even before the final egg of the clutch was laid, with 42% of the oviduct mass lost before laying of the final egg. In laying females, 18% of variation in mass-corrected RMR was explained by the mass of the oviduct (r2=0.18, n=80, P<0.0005), while pectoralis muscle mass in nonbreeding individuals and liver and gizzard mass in chick-rearing females were the only organs significantly related to RMR (r2=0.31-0.44). We suggest that the nonreproductive organs are affected more by changes in local ecological conditions than the reproductive state itself and that the activity and maintenance cost of the oviduct is high enough that selection has led to a very tight size-function relationship for this organ.     

Hormonal regulation of apoptosis in the endometrium of common marmosets (Callithrix jacchus)

Phase-dependent apoptotic changes in the human endometrium during an ovarian cycle imply a potential role of steroids in the regulation of apoptosis. The present study was undertaken to determine the direct role of hormones in endometrial apoptosis in marmosets (Callithrix jacchus), a primate species which shows similarity to humans in terms of the cycle length and pattern. Endometrial apoptosis was detected by 3'-end labeling (TUNEL) in various phases of ovarian cycle in naturally cycling healthy marmosets (n=14) and also in ovariectomized marmosets (n=13) treated with either estradiol alone (E) or progesterone alone (P) or estradiol followed by progesterone (E+P). Expressions of apoptosis associated genes such as Bcl-2 family members (Bax and Bcl-2), proliferating cell nuclear antigen (PCNA)--a proliferation marker and steroid receptors, ERalpha and PR A were analysed by immunohistochemical methods. Apoptosis was intense in the glandular epithelial cells of endometrium during the mid-luteal phase as compared to other phases in naturally cycling animals; in the E+P group as compared to other groups of ovariectomized animals (P<0.05). Pronounced apoptosis in the mid-luteal phase was accompanied by the increased expression of Bax in glandular epithelial cells; while Bcl-2 immunoreactivity remained unchanged. PCNA expression was higher in the naturally cycling animals in the follicular phase and in the E group of the ovariectomized animals as compared those in the other groups. Immunoreactive ERalpha and PR A in glandular epithelial cells were most abundant during early follicular phase in naturally cycling animals and in both E and E+P groups among the ovariectomized animals. The present study highlights the importance of apoptosis in endometrial remodeling during the ovarian cycle and secondly, the role of both estradiol and progesterone in the regulation of apoptosis.     

Genetic variation of Eryngium campestre L. (Apiaceae) in Central Europe

In Germany, Eryngium campestre is restricted to dry habitats along the rivers Rhine and Elbe and to a few areas in Central Germany. This distribution pattern is usually regarded as a typical pattern of postglacial immigration. In the present study, we investigated whether these two geographically distinct distribution areas are genetically differentiated and whether conclusions can be drawn regarding colonization history. To analyse the phylogeographic structure of E. campestre in Central Europe, 278 individuals from 29 populations within Germany and from further reference populations within Europe were analysed. We applied amplified fragment length polymorphisms to examine their genetic relatedness. Our analyses revealed three groups: a Mediterranean group additionally including two Rhine populations; a Rhine–Main group which further includes the westernmost population from the central German dry area; and one group which includes all eastern populations. Our results show that the two geographically distinct areas are genetically differentiated. As genetic diversity within the Elbe populations is very low, we conclude that this area, which was strongly affected through the late glacial maximum, was colonized relatively recently. High genetic diversity in the Rhine populations indicates a contact zone where lineages of different origin met. This would imply that today's patterns of genetic variation were caused through glacial range contractions and expansions. The present study is one of the first studies that deal with the postglacial distribution pattern of a dry grassland plant species in Central Europe and the results suggest that a survival of E. campestre at least during the Dryas cold stage might be possible.     

Long-term data on basic reproductive parameters and evaluation of endocrine,morphological, and behavioral measures for monitoring reproductive status in a group of semifree-ranging Tonkean macaques (Macaca tonkeana)

Cycle and gestation lengths, menstruation patterns, female genital swelling characteristics, and male-female consortship durations are reported in a semifree-ranging group of Tonkean macaques (Macaca tonkeana) studied over a 12 year period. In addition, profiles of urinary estrone conjugates (E1C) and immunoreactive pregnanediol glucuronide (PdG) throughout four complete menstrual cycles in two females and three full-term pregnancies are presented. Based on intermenstrual intervals, a mean cycle length of 37–41 days (n = 55 cycles in 10 females) was found. Gestation length averaged 173 days (n = 27 pregnancies in eight females). Measurement of PdG immunoreactivity in urine revealed a cyclic pattern with a 5–15-fold increase between follicular and luteal phase concentrations, suggesting that PdG is a reliable indicator of ovarian cyclicity and luteal function. In contrast to PdG, E1C excretion showed no clear pattern throughout the cycle; however, highest values of E1C were usually found shortly before the onset of the luteal phase PdG rise at the presumed time of ovulation. Levels of both hormones were elevated during the first half of gestation and showed a marked increase throughout the second half, with maximum E1C concentrations being up to 100-fold higher than nonpregnant levels. Consortships by the male and occurrence of female genital swelling were long lasting (on average 5–10 days and 13 days, respectively) and were restricted to the follicular phase of the cycle. The day of maximal swelling and day of detumescence as well as the end of male consortship were closely associated with the periovulatory period. Swellings and consortships were longer following lactational ammenorhea than for subsequent cycles. The evolutionary significance of the cyclical changes undergone by females upon their relations with males is discussed. © 1996 Wiley-Liss, Inc.     

A karyological analysis of the artificial hybridization between Clarias gariepinus (Burchell, 1822) and Heterobranchus longifilis Valenciennes, 1840 (Pisces; Clariidae)

A karyological analysis of an artificial hybridization (reciprocal crosses) between two African clariid catfish, Clarias gariepinus (Burchell, 1822) and Heterobranchus longifilis Valenciennes, 1840, was performed. C. gariepinus has a standard karyotype of 2 n = 56, while H. longifilis has 2 n = 52. The hybrids revealed an intermediate karyotype (2 n = 54), and it appears as if they have totalized the haploid chromosome number of both parental species, excluding gynogenesis or androgenesis. The hybrid karyotype is considered as aneuploid, although the hybrids proved to be fertile. No variation was found in the hybrids karyotypes.     

The cytotaxonomy ofEmilia spp. (Asteraceae: Senecioneae) occurring in Brazil

Analysis of several populations in a large part of the distribution area of the genusEmilia in Brazil has revealed only two species: the diploidE. sonchifolia and the tetraploidE. fosbergii. The more widely reportedE. coccinea was not found. They show a karyotype constancy in morphology and chromosome number (2n = 10 and 2n = 20, respectively), C-banding pattern and number of secondary constrictions. Some indications were found thatE. fosbergii may be an allopolyploid and that its ancestors had different genome sizes.     

C-heterochromatin and extra (B) chromosome distribution in six species of the Nabis (Heteroptera, Nabidae) with the modal male karyotype 2n = 16 + XY

The basic male karyotype of the six Nabis species (Heteroptera, Nabidae) is confirmed as being 2n=16+XY. The chromosomes are holokinetic while male meiosis is achiasmatic. The sex chromosomes undergo postreduction and in second metaphase show distance pairing, registered in all nabid species examined so far. Using C-banding technique for the first time in the family Nabidae, the heterochromatin was revealed on chromosomes of six species. The species showed different amount and distribution of C-heterochromatin. Only in Nabis (Dolichonabis) limbatus did the C-bands distribution make possible the identification of every chromosome pair in the karyotype. In other species, C-bands were found in some of the autosomes and the X, localized either interstitially or at telomeres. Only the Y usually showed relative stability ofthe C-banding pattern. In four of six species, extra (B) chromosomes were observed and their behaviour in meiosis described.     

Fecal dehydroepiandrosterone (DHEA) immunoreactivity as a noninvasive index of circulating DHEA activity in young male laboratory rats

Evidence suggests that dehydroepiandrosterone (DHEA) plays a key role in stress and coping responses. Fecal sampling permits assessment of hormone-behavior interactions reliably and effectively, but no previous study has compared circadian- or stress-dependent alterations between serum DHEA and its fecal metabolites. In the current study, young (28 d of age) male rats were assigned to either an experimental (n = 6) or control (n = 6) group. Rats in the experimental group were exposed to a forced swim test to assess their behavioral and physiologic response to an environmental stressor; blood samples were drawn before the test (baseline), immediately after the test, and at 2 later time points. Only fecal samples were collected from control animals. Fecal DHEA and corticosterone metabolites were monitored in all animals for 24 h. DHEA metabolites in control rats exhibited significant diurnal variation, showing a similar temporal pattern as that of corticosterone metabolites. In addition, fecal and serum DHEA levels were highly correlated. Significant peaks in both DHEA and corticosterone metabolite levels were detected. These data suggest that measures of fecal DHEA can provide a complementary, noninvasive method of assessing adrenal gland function in rats.     

Genistein and daidzein modulate in vitro rat uterine contractile activity

The present study investigated the effect of genistein, daidzein and estradiol on in vitro rat uterine responsiveness to oxytocin (OT) and PGF(2)alpha or luprostiol (L). In a first experiment, animals were either sham-operated (SH; n=5), or ovariectomized (OVX; n=20) and orally treated for three months with either genistein (G; n=5; 10 microg/g BW/d) or daidzein (D; n=5; 10 microg/g BW/d) or 17 alpha-ethinylestradiol (E; n=5; 23 microg/kg BW/d) or untreated (OVX; n=5). At necropsy, the basal uterine tension was lower in OVX, G and D than in SH, the highest value being measured in E. Oxytocin (10(-12); 10(-11) M) or PGF(2)alpha (10(-12); 10(-9) M) induced an increase in SH, but not in OVX, E and G. In D, only the highest doses were efficient. In a second experiment, 20 intact animals were s.c. injected with either genistein (G; n=5; 10 microg/g BW) or daidzein (D; n=5; 10 microg/g BW) or estradiol benzoate (E; n=5; 23 microg/kg BW) or vehicle (C: controls; n=5), and killed 24 h later. In C and E, OT (10(-15) to 10(-10) M) or L (10(-12) to 10(-7) M) stimulated uterine contractile activity in a dose-dependent manner until a maximal level. On the opposite, in G and D, contractile agents (except the highest luprostiol doses) did not stimulate myometrium contractions. Moreover, radioligand binding assays showed that genistein or daidzein inhibited the specific binding of [(3)H] estradiol to the calf uterus estrogen receptor (ER). Therefore, it could be postulated that both genistein and daidzein might bind to the rat uterus ER, inducing either anti-estrogenic or very weak estrogenic effects (depending on the experimental conditions) on in vitro uterine responsiveness to OT and PGF(2)alpha or luprostiol.     

In vitro biofilm formation of commensal and pathogenic Escherichia coli strains: impact of environmental and genetic factors

Our understanding of Escherichia coli biofilm formation in vitro is based on studies of laboratory K-12 strains grown in standard media. However, pathogenic E. coli isolates differ substantially in their genetic repertoire from E. coli K-12 and are subject to heterogeneous environmental conditions. In this study, in vitro biofilm formation of 331 nondomesticated E. coli strains isolated from healthy (n = 105) and diarrhea-afflicted children (n = 68), bacteremia patients (n = 90), and male patients with urinary tract infections (n = 68) was monitored using a variety of growth conditions and compared to in vitro biofilm formation of prototypic pathogenic and laboratory strains. Our results revealed remarkable variation among the capacities of diverse E. coli isolates to form biofilms in vitro. Notably, we could not identify an association of increased biofilm formation in vitro with a specific strain collection that represented pathogenic E. coli strains. Instead, analysis of biofilm data revealed a significant dependence on growth medium composition (P < 0.05). Poor correlation between biofilm formation in the various media suggests that diverse E. coli isolates respond very differently to changing environmental conditions. The data demonstrate that prevalence and expression of three factors known to strongly promote biofilm formation in E. coli K-12 (F-like conjugative pili, aggregative adherence fimbriae, and curli) cannot adequately account for the increased biofilm formation of nondomesticated E. coli isolates in vitro. This study highlights the complexity of genetic and environmental effectors of the biofilm phenotype within the species E. coli.     

Genetic diversity of Annona crassiflora (Annonaceae) in northern Minas Gerais State

Genetic diversity analyses of tropical tree species are relevant to landscape management, plant genetic resource inventory, and biological conservation of threatened species. Annona crassiflora is an endangered fruit tree native to the Cerrado biome that is threatened by reduction of natural populations and fruit extraction. We examined the intra- and interpopulational genetic diversity of this species in the northern region of Minas Gerais State. Seventy-two individuals from four natural populations were genotyped using RAPD markers. We found moderate genetic diversity among populations, with Shannon's I index varying between 0.31 and 0.44, and Nei's genetic diversity (H(E)) for the population set equal to 0.31. AMOVA indicated a greater genetic variation within (77.38%) rather than among populations (22.62%), tending towards isolation by distance (Mantel's r = 0.914; P = 0.089). Nei's genetic identity estimates among populations revealed a hierarchical pattern of genetic similarity of form [(CA1, CA2), MC], [(GM)], corroborating the high genetic differentiation between spatially isolated populations.     

Response of anestrous ewes to the ram effect after follicular wave synchronization with a single dose of estradiol-17beta

Anestrous ewes respond to the introduction of rams with either an ovulation within 2-3 days that may be followed by luteal phases of normal or short length, with delayed ovulations (5-6 days later), or with the luteinization of follicles. The aim of this work was to study the relationship between the growth status of the largest follicle present when rams are introduced and the type of ovarian response in non-treated ewes and in ewes treated with estradiol-17beta before ram introduction. Thirteen anestrous Corriedale ewes were divided into 2 groups: E2 (n = 7) and C (n = 6). The E2 ewes received a single dose of 50 microg estradiol-17beta 5 days before the introduction of the rams to synchronize the onset of their follicle waves, while C ewes remained untreated. When the rams were introduced, all E2 ewes had the largest follicle in a growing stage in contrast with the C ewes (3 out of 6; P < 0.05). Five C and 4 E2 ewes ovulated after the introduction of the rams (Day 3.4 +/- 0.4 for C vs. 4.8 +/- 0.3 for E2 ewes, respectively, P < 0.05). Only one ewe from each group developed a normal luteal phase: 4 C and 3 E2 ewes had short luteal phases. One C ewe and 2 E2 ewes had short luteal phases originating from follicles that did not ovulate. After the first luteal phase, all ewes returned to anesirus without a second ovulation or luteal phase. The remaining E2 ewe did not ovulate or show any changes in progesterone serum concentrations. We conclude that the growth status of the largest follicle alone does not determine the ovarian responding pattern of anestrous ewes to the ram effect.