Genetic Analysis of Putative Triploid Miscanthus Hybrids and Tetraploid M. sacchariflorus Collected from Sympatric Populations of Kushima, Japan

Miscanthus ?×giganteus, a triploid hybrid between tetraploid M. sacchariflorus and diploid M. sinensis, has considerable potential as a bioenergy crop. Currently only one genotype is widely cultivated, increasing its vulnerability to diseases during production. Finding new hybrids is important to broaden genetic resources of M. ×giganteus. Three putative triploid hybrids were discovered in a sympatric population of tetraploid M. sacchariflorus and diploid M. sinensis in Kushima, Japan. The hybrid nature of the triploids was determined by morphological analysis and sequencing the ribosomal DNA internal transcribed spacer (ITS) region. The triploids had awns on their florets, which is a common characteristic of diploid M. sinensis, and sheath hairs, which is typical of tetraploid M. sacchariflorus. All triploids showed heterozygosity in their ribosomal DNA ITS sequences. Based on these results, it is confirmed that the triploids are hybrids and novel genotypes of M. ×giganteus. Natural crossing between tetraploid M. sacchariflorus × diploid M. sinensis may also lead to the production of tetraploid hybrids. ITS analysis of tetraploid plants showed that one maternal parent of the triploid hybrids, K-Ogi-1, had heterozygous ITS, which was different than the other analyzed tetraploid, M. sacchariflorus. Thus, K-Ogi-1 was likely of hybrid origin. These tetraploid hybrids can also be utilized as parents in M. ×giganteus breeding. Since all hybrids identified in this study had tetraploid M. sacchariflorus as maternal parents, collecting and analyzing seeds from tetraploid M. sacchariflorus in sympatric areas could be an effective strategy to identify natural Miscanthus hybrids that can be used as bioenergy crops.     

An improved embryo-rescue protocol for hybrid progeny from seedless Vitis vinifera grapes × wild Chinese Vitis species

A highly efficient technique of embryo rescue is critical when using stenospermocarpic Vitis vinifera cultivars (female parents) to breed novel, disease-resistant, seedless grape cultivars by hybridizing with wild Chinese Vitis species (male parents) having many disease-resistance alleles. The effects of various factors on the improvement of embryo formation, germination, and plantlet development for seven hybrid combinations were studied. The results indicated that Beichun and Shuangyou were the best male parents. The best sampling time for ovule inoculation differed among the female parents. When hybrid ovules were cultured on a double-phase medium with five different solid medium types, percent embryo formation was highest (11.3–28.3%) on a modified MM3 medium. Percentages of embryo germination (15.4–55.4%) and plantlet development (11.15–44.6%) were all highest when embryos were cultured on Woody Plant Medium?+?5.7 μM indole-3-acetic acid?+?4.4 μM 6-benzylaminopurine?+?1.4 μM gibberellic acid?+?2% sucrose?+?0.05% casein hydrolysate?+?0.3% activated charcoal?+?0.7% agar. In the absence of other amino acids, the addition of proline significantly increased embryo formation (36.1%), embryo germination (64.6%), and plantlet development (90.5%). A highly efficient protocol has been developed for hybrid embryo rescue from seedless V. vinifera grapes?×?wild Chinese Vitis species that results in a significant improvement in breeding efficiency for new disease-resistant seedless grapes.     

Biochemical genetics of hybrid sunfish: Differential survival of heterozygotes

Allelic segregation in reciprocal backcrosses involving the largemouth bass (Micropterus salmoides) and the F₁ hybrid (largemouth bass × smallmouth bass, M. dolomieui) was investigated to determine the extent of euheterosis and luxuriance. The frequencies of allelic isozymes encoded in the lactate dehydrogenase E, malate dehydrogenase B, and isocitrate dehydrogenase loci were determined for reciprocal backcross progeny subjected to different selection pressures. The progeny of the backcross (male F₁ × female largemouth bass) underwent a rapid loss of heterozygous individuals in a natural pond environment. When the offspring of this same mating were placed in artificial pools, where cannibalism is the main source of mortality, heterozygosity was advantageous. There was a marked correlation of increased heterozygosity at these enzyme loci with an increased growth rate. None of the above responses to selection was observed when the F₁ hybrid served as the maternal parent in the reciprocal backcross. A maternal factor in the egg cytoplasm may influence the expression of heterosis.     

Miscanthus: Genetic Diversity and Genotype Identification Using ISSR and RAPD Markers

Due to the limited number of molecular studies focused on European gene pool investigation, it is necessary to perform plant material recognition. Eighteen accessions of three Miscanthus species, namely, M. × giganteus, M. sinensis, M. sacchariflorus were evaluated with the use of molecular marker systems such as: inter simple sequence repeats (ISSRs), random amplified polymorphic DNA (RAPD), and by estimation of ploidy level based on flow cytometry. As a result, only one ISSR primer (ISSR1) and three RAPD primers (RAPD1, RAPD2, RAPD4) were required to identify all genotypes. Moreover, the use of the above mentioned molecular markers enable the proper species recognition of the interspecific hybrid M. × giganteus “Floridulus,” which has been previously mislabeled as M. floridulus. The highest genetic similarity coefficient (0.94) was observed between M. × giganteus clones, which indicates that the genetic diversity within this species was very low. Whereas M. sinensis genotypes represented a relatively wide diversity with similarity coefficient of 0.58. Cluster analysis using UPGMA grouped the 18 accessions in three clusters according to species affiliation including relabeled M. × giganteus “Floridulus,” which proved to be closely related to M.  × giganteus. Similar groupings were evident in the PCoA analysis.     

Action of a juvenile hormone analogue on the activity of Periplaneta americana corpora allata in vitro and on juvenile hormone III levels in vivo

The effects of the juvenile hormone (JH) analogue fenoxycarb (ethyl[2-(4-phenoxyphenoxy)-ethyl]carbamate) on the activity of corpora allata (CA) from adult female Periplaneta americana have been investigated. The in vitro biosynthesis of JH III by isolated CA was inhibited by about 85% in the presence of a high concentration (1 × 10⁻⁴ M) of fenoxycarb. However, at lower concentrations (1 × 10⁻⁶ M and 1 × 10⁻⁸ M) no inhibition of JH biosynthesis was apparent. Topical treatment of adult female cockroaches with fenoxycarb (100 μg/insect) did not reduce the subsequent rate of JH III biosynthesis by CA in vitro. By contrast, the same treatment markedly reduced the titre of endogenous JH III in intact cockroaches. These results suggest that CA activity in adult female P. americana may be controlled by negative feedback, and that this system of control is dependent on the maintenance of contact between the CA and nervous or humoral factors in the intact insect. Alternatively, it is possible that treatment with fenoxycarb increases the rate at which endogenous JH is metabolized.     

Membrane receptors for Vicia graminea anti-N lectin and its binding to native and neuraminidase-treated human erythrocytes

Membrane receptors for Vicia graminea (Vg) lectin on human red cells were analyzed using deoxycholate lysates obtained from ¹²⁵I-erythrocyte membranes incubated with a purified lectin immobilized on Sepharose 4B. The glycoproteins (GP) specifically bound to the gel were eluted and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. Using native erythrocytes the results obtained demonstrate that N red cells have exposed Vg receptors located on GPα (synonym glycophorin A) and GPδ (synonym glycophorin B) whereas on M erythrocytes the Vg receptors are restricted to GPδ. The presence of Vg receptors was also found on the hybrid glycoprotein (made of the N-ter of GPδ and C-ter of GPα) carried by St(a+) erythrocytes. A similar amount of radioactivity was bound to Vg-Sepharose incubated with neuraminidase-treated N or M membranes. The material eluted was tentatively identified as asialo GPα and asialo GPδ, suggesting that numerous receptors have been uncovered mainly on asialo GPα species from M erythrocytes. No glycoprotein component could be identified from the material eluted from Vg Sepharose incubated with native or neuraminidase-treated membrane from a Tn(+) individual. Scatchard plot analysis obtained from binding experiments at equilibrium with M, N, and St(a+) cells revealed the existence of at least two classes of receptors both on native and neuraminidase-treated erythrocytes. Desialylation of the M, N, and St(a+) erythrocytes resulted in an increase in the number of low- and high-affinity binding sites but had no significant effect on the association constants. However, high-affinity binding constants were about six times higher with N (7.07 × 10⁷ and 6.61 × 10⁷m^?1 for native and neuraminidase-treated N cells, respectively) as compared to M erythrocytes (1.13 × 10⁷ and 1.17 × 10⁷m^?1 for native and neuraminidase-treated M cells, respectively) whereas the low-affinity binding constants were similar for all types of cells (in the range of 0.1 to 0.3 × 10⁷m^?1). The number of Vg binding sites increases from 0.085 × 10⁵ to 0.8 × 10⁵ (high affinity) and from 2.10 × 10⁵ to 6.25 × 10⁵ (low affinity) per native and neuraminidase-treated N cell, respectively. On native and neuraminidase-treated M cells the number of Vg receptors increases from 0.011 × 10⁵ to 0.51 × 10⁵ (high affinity) and 0.13 × 10⁵ (low affinity), respectively. The large increase in the number of Vg receptors on neuraminidase-treated M cells is correlated with a large increase in agglutinability. Under similar treatment St(a+) cells behave like N erythrocytes whereas only 0.16 × 10⁵ Vg receptors of low affinity could be detected on neuraminidase-treated Tn erythrocytes. The results demonstrate that sialic acid is not required for binding and favor the view that the binding site of V. graminea lectin accommodates with two types of erythrocyte membrane receptors, one including both a contribution of polypeptide and oligosaccharide chains and a second which involves a simple interaction with sugar sequence Galβ1–3GalNAc available only when sialic acids are removed. The latter disaccharide is recognized by the Arachis hypogea lectin which therefore inhibits further binding of the V. graminea to neuraminidase-treated erythrocytes.     

When interspecific prezygotic barriers break down: hybridization between two Potamogeton species (P. wrightii and P. perfoliatus) and comparison of the artificial and natural hybrids

Interspecific hybridization played an important role in speciation and evolution of angiosperms. Although the widespread occurrence of natural hybrids in the genus Potamogeton has been studied intensively, few successful experimental hybridization studies have been reported in this genus. In the present study, critical experimental hybridization was conducted using Potamogeton?×?intortusifolius, a natural hybrid widely distributed in China, and its parents (P. perfoliatus and P. wrightii). The absence of prezygotic barriers between P. wrightii and P. perfoliatus was observed, which contributes to the frequent hybridization of these species in nature. The pollen tube growth rates of P. perfoliatus were much faster than those of P. wrightii in the style of that species. However, the conspecific pollen tubes were competitively advantageous in P. perfoliatus styles. The interspecific hybridization could be applied bidirectionally, and 28 F1 hybrid individuals were successfully obtained from P. wrightii?×?P. perfoliatus, despite the low germination possibility of the hybrid seeds. Both the artificial and natural hybrids exhibited intermediate morphological characters but presented much lower fertility. The sterility of P.?×?intortusifolius is mainly due to its low female fitness. However, the offspring from P. wrightii?×?P.?×?intortusifolius indicated the potential for backcrossing in nature. This is the most successful attempt at artificial hybridization in this genus so far. The possible route for restoration of fertility and the fitness of the hybrids are also discussed in this paper.     

Improved Feedstock Option or Invasive Risk? Comparing Establishment and Productivity of Fertile <Emphasis Type="Italic">Miscanthus × giganteus</Emphasis> to <Emphasis Type="Italic">Miscanthus sinensis</Emphasis>

The perennial grass genus Miscanthus has great promise as biomass feedstock, but there are concerns about potential invasion outside production fields. While the sterile hybrid Miscanthus × giganteus is currently one of the leading feedstock options due to its low invasive potential, fertile varieties are being developed to reduce establishment costs, and their invasive risks need to be further assessed. We performed seed addition experiments in Ohio and Iowa, USA to examine the establishment, flowering, persistence, and shoot biomass per plot of a fertile M. × giganteus biotype (‘PowerCane’) and two Miscanthus sinensis biotypes, one feral, and one ornamental. Seeds were added to small, replicated plots in each of the 2 years under two seeding densities and two competition treatments, and plots were monitored for 2–3 years. The ‘PowerCane’ biotype established better, survived better, and produced greater amounts of biomass per plot than both M. sinensis biotypes. All three biotypes flowered by the second or third year after establishment, with inflorescences more numerous in ‘PowerCane’ and the Ornamental M. sinensis biotypes. Effects of seeding density and competition on these patterns were minor in most cases. Our research suggests that ‘PowerCane’ exhibits many traits shared by both biomass crops and invasive species: multi-year persistence, high biomass potential, and fertility. We suggest that the benefits of a seeded M. × giganteus should be carefully weighed against its increased invasive risk prior to deployment across the landscape.     

Reduced clonal reproduction indicates low potential for establishment of hybrids between wild and cultivated strawberries (Fragaria vesca × F. × ananassa)

The genus Fragaria (Rosaceae) contains 24 species, including hybrid species such as the garden strawberry (Fragaria × ananassa Duch.). Natural hybridization between Fragaria species has repeatedly been reported, and studies on the hybridization potential between F. × ananassa and its wild relatives have become increasingly important with the outlook for genetically modified garden strawberries. In Europe, a candidate species for hybridization with garden strawberries is the common woodland strawberry (Fragaria vesca L.). Although a previous field survey indicated that the potential for hybridization between F. vesca and F. × ananassa is low, it is not clear whether the lack of natural hybrids is caused by known pre- and postzygotic barriers, or whether hybrid plants lack the fitness to establish in natural F. vesca populations. We grew different F. vesca and F. vesca × F. × ananassa hybrid clones with and without competition in a greenhouse and assessed biomass production, clonal reproduction, and sexual reproduction of plants. While some hybrid clones exceeded F. vesca in biomass production, general clonal reproduction was much lower and delayed in hybrids. Furthermore, hybrids were sterile. These results demonstrate a mechanism by which the general lack of F. vesca × F. × ananassa hybrids in natural habitats can be explained, in addition to the known low hybridization potential between garden and woodland strawberries. We conclude that hybrids have a competitive disadvantage against co-occurring F. vesca plants due to inferior and delayed clonal reproduction, and that the potential for hybrid establishment under natural conditions is low.     

A second ×<Emphasis Type="Italic">Cyclobotrya</Emphasis> (Dryopteridaceae) from Brazil

× Cyclobotrya amalgamata , a new intergeneric hybrid between Cyclodium meniscioides var. meniscioides and Polybotrya osmundacea, is described and illustrated. It was found in the state of Ceará, northeastern Brazil, growing in a mixed population with both parents. It is morphologically intermediate between its parents and has misshapen sporangia and spores. It represents the second hybrid in ×Cyclobotrya.     

Fine structure of the sterile testis of hybrid threespine stickleback between marine and landlocked forms

The process and cause of male sterility of a hybrid between female marine (M) and male landlocked (L) forms (M ? × L ♂) of the threespine stickleback were studied by examining the testes of this hybrid and backcross offspring between M ? and F₁ (L ? × M ♂) (MOLM ♂). In the M form numerous spermatids were elaborated and contained in the apical processes of the Sertoli cells, whereas in the ML and MOLM forms there were a number of macrophages in the lobular cavity with numerous projected pseudopodia engulfing voraciously the spermatids. As a result of this heavy phagocytosis the seminiferous lobules were quite vacant. Curiously, the Sertoli cells also actively project its processes and pseudopodia to catch the spermatids. In addition to morphometrical, behavioral and biochemical-genetic differences, these findings of sterility seem to suggest that the M form and L form represent independent species.     

Cytogenetic implications of artificial hybrids between the hawaiian silversword alliance and North American tarweeds (Asteraceae: Heliantheae—Madiinae)

Two vigorous transoceanic, bigeneric hybrids, Dubautia laevigata (n = 14) × Raillardiopsis muirii (n = 8) and [Dubautia knudsenii × laxa] (n = 14) × Madia bolanderi (n = 6), and one vigorous transoceanic trigeneric hybrid, Dubautia scabra (n = 14) × [M. bolanderi × R. muirii], between mainland tarweeds and Hawaiian silversword allies were artificially produced and subjected to cytogenetic analysis. In addition to univalents, ≈46–80% of the microsporocytes scored from these hybrids exhibited from one to four bivalents. However, some of the bivalents scored in the second bigeneric hybrid represented infragenomic association of Dubautia chromosomes. Stainable pollen of these hybrids ranged from 4.4 to 49%, mostly comprising large, tetracolporate, apparently diploid grains. The functionality of such grains was demonstrated in the primary hybrid M. bolanderi × R. muirii that was used to produce the trigeneric hybrid, and suggests the possible mode of origin of the Hawaiian genome via allopolyploidy. Illustrations of parents and F₁s indicate that the hybrids produced in this study generally exhibit intermediate character states. However, the phenotypes of the “ray” flowers in hybrids between discoid and radiate species were noticeably unpredictable; in one case intermediacy appeared to be expressed largely in quantitative terms, while in two others intermediacy appeared to be expressed largely in qualitative terms.     

Application of in vitro pollination of opened ovaries to obtain Brassica oleracea L. × B. rapa L. hybrids

This study presents the results of experiments concerning: (1) interspecific hybridization of Brassica oleracea × Brassica rapa via application of in vitro placental pollination and (2) embryological analysis of the process of resynthesis of Brassica napus. In order to overcome certain stigma/style barriers, B. rapa pollen was placed in vitro on an opened B. oleracea ovary (with style removed). Pollinated ovaries were cultured on Murashige and Skoog (MS) medium. After 24-d culture, the developing embryos were isolated from immature seeds and transferred onto MS medium supplemented with 0.47 μM kinetin, 0.49 μM 1-naphthaleneacetic acid, and 10% (v/v) coconut water. When the embryos had turned green, they were immediately placed onto MS medium with 100 μM kinetin. After development of the seedling, plantlets were transferred to soil. Chromosome doubling was achieved after another week. Cytometric analysis of nuclear DNA confirmed the hybrid nature of the plants. Resynthesis of B. napus can be performed through interspecific hybridization of B. oleracea × B. rapa followed by embryo rescue and genome doubling.     

Molecular characterization of two natural hybrids from the Iberian Peninsula: <Emphasis Type="Italic">Ranunculus × luizetii</Emphasis> and <Emphasis Type="Italic">R. × peredae</Emphasis> (Ranunculaceae)

Two nothospecies, Ranunculus × luizetii and R. × peredae (Ranunculaceae), were analyzed and discussed. For this purpose, Amplified Fragment Length Polymorphism (AFLP) markers, nuclear rDNA sequences (ITS1, 5.8S and ITS2) and pollen viability were conducted. The profiles of these hybrid samples were compared to their putative progenitors. Several additive polymorphic sites detected in the ITS sequences of the hybrid samples (R. × luizetii and R. × peredae) also confirmed their derived origins from ribotypes of their parental taxa (R. parnassiifolius subsp. parnassiifolius × R. pyrenaeus; R. amplexicaulis × R. cabrerensis subsp. cabrerensis, respectively). Despite the lack of exclusive AFLP markers reported in both hybrids, presumably due to effects of introgression, the concerted evolution of many rDNA polymorphisms towards either of the parental ribotypes indicated their ancient origin. Pollen fertility estimation in R. × luizetii presented a mean value of 60.58%, which showed that hybrid samples are well established and fertile. However, a larger difference was observed in R. × peredae, where the mean value of pollen fertility was very low (18.91%).     

Are you more than the sum of your parents’ genes? Phenotypic plasticity in a clonal vertebrate and F1 hybrids of its parental species

All known vertebrate clones have originated from hybridization events and some have produced distinct evolutionary lineages via hybrid speciation. Amazon mollies (Poecilia formosa) present an excellent study system to investigate how clonal species have adapted to heterogeneous environments because they are the product of a single hybridization event between male sailfin mollies (Poecilia latipinna) and female Atlantic mollies (Poecilia mexicana). Here, we ask whether the hybrid species differs from the combination of its parental species’ genes in its plastic response to different environments. Using a three-way factorial design, we exposed neonates produced by Amazon mollies and reciprocal F1 hybrid crosses to different thermal (24°C and 29°C) and salinity (0/2, 12, and 20 ppt) regimes. We measured various ontogenetic and life history characteristics across the life span of females. Our major results were as follows: (1) Reaction norms of growth and maturation to temperature and salinity are quite similar between the two hybrid crosses; (2) Amazon molly reaction norms were qualitatively different than the P. latipinna male and P. mexicana female (L×M) hybrids for the ontogenetic variables; (3) Amazon molly reaction norms in reproductive traits were also quite different from L×M hybrids; and (4) The reaction norms of net fertility were very different between Amazon mollies and L×M hybrids. We conclude that best locale for Amazon mollies is not the best locale for hybrids, which suggests that Amazon mollies are not just an unmodified mix of parental genes but instead have adapted to the variable environments in which they are found. Hybridization resulting in asexuality may represent an underappreciated mechanism of speciation because the unlikely events required to produce such hybrids rarely occur and is dependent upon the genetic distance between parental species.     

Molecular distinction of C × R hybrid (Coffea congensis × Coffea canephora) from morphologically resembling male parent using rbcL and matK gene sequences

Interspecific C × R hybrid (Coffea congensis × Coffea canephora) in India is cultivated as mixed population with male parent C. canephora as this species is an efficient pollen donor for enhanced yield. But distinction of C × R hybrid from C. canephora in old plantation is difficult due to varying plant sizes of C × R hybrid and often resembles with C. canephora. C × R hybrid cultivated under different agroclimatic conditions show distinct vegetative growth pattern with varying yields. Thus development of DNA marker for identification of C × R hybrid is important for clonal propagation and seed preparation from selective individuals. In this study, two DNA bar coding loci of chloroplast genome (rbcL and matK) of parents, F1 hybrid and its back cross progeny were partially sequenced to identify SNPs as DNA marker for distinction of C × R hybrid from C. canephora. Seven SNPs in the matK gene sequence and three nucleotides in the rbcL gene sequence were identified as DNA markers for the genetic identity of C. congensis. These SNPs were found in F1 and advanced progenies of C × R hybrid due to maternal inheritance. Large number of samples of C × R hybrids with varying morphological features revealed no polymorphism among C × R hybrid and C. congensis. Thus, the SNPs in C. congensis can be used as DNA markers for precise identification of C × R hybrid for production of clones besides tagging the chloroplast inheritance in advanced progenies.     

Expression of human interferon β in mammary glands of transgenic rabbits

A biotechnological system for the production of human β-interferon was developed on the basis of a hybrid gene constructed from the coding sequence of the β interferon gene, inserted into the first exon of the sheep beta-lactoglobulin gene. It is intended for the expression of human β-interferon in mammary glands of transgenic animals. Two lines of transgenic rabbits were obtained using the hybrid gene. The tissue specificity of the expression of the transgene and the frequency of its inheritance in the first and second generations were studied. The activity of interferon was 2.2 × 10⁴ ? 7.2 × 10⁴ IU per milliliter of milk of transgenic female rabbits.     

Genetic distance as a predictor of heterosis and hybrid performance within and between heterotic groups in sunflower

Heterosis is significant for seed yield and is one of the driving forces behind the hybrid seed industry in cultivated sunflower (Helianthus annuus L). Heterotic groups in sunflower, if any other than the female and male inbred-line groups exist, have not been well studied or described. The primary aims of this study were to assess the utility and validity of a series of proposed heterotic groups and estimate correlations between genetic distance, heterosis, and hybrid performance for seed yield in sunflower. Fortytwo female by male heterotic group (A × R) and 81 female by female heterotic group (A × B) single-cross hybrids were grown in Corvallis, Ore., and Casselton, N.D., in 1996 and 1997. Heterosis was significant for seed yield and plant height but not for seed oil concentration and days to flowering. Genetic distances were significantly correlated with hybrid seed yield when estimated from AFLP fingerprints (G _D) (r = 0.63 for A × R and 0.79 for A × B hybrids), but not from coancestries (G _C) (r = -0.02 for A × R and 0.54 for A × B hybrids). G _D (R ² = 0.4) was a poor predictor of hybrid seed yield. The proposed heterotic groups in sunflower seem to have utility, but do not seem to be as strongly differentiated as those in corn (Zea mays L.). The highest-yielding hybrids were from the B_C× R_B heterotic pattern; however, several B_C× B_C hybrids (within-group hybrids) were among the top-yielding hybrids. The outstanding performance of certain B_C× B_C hybrids casts some doubt on the validity of the B_C group. Substantial genetic diversity seems to be present within and between heterotic groups in sunflower. Received: 1 September 1998 / Accepted: 14 September 1999     

Predicting primate responses to “Stochastic” demographic events

Comparative approaches in contemporary primate behavioral ecology have tended to emphasize the deterministic properties of stochastic ecological variables. Yet, primate responses to ecological fluctuations may be mediated by the interactions among demographic processes at the levels of individuals, groups, and populations. In this paper I examine long-term data collected from June 1982–July 1998 on one expanding group of muriquis (Brachyteles arachnoides) at the Estação Biologica de Caratinga, Minas Gerais, Brazil to explore the demographic and life history correlates of reproductive seasonality and skewed infant sex ratios. Variation in the size of annual birth cohorts (≥2 infants) was positively related to variation in the annual distribution of births (r _s=0.96,n=10,p<0.01), indicating the importance of considering the effects that the number of reproductive females may have on interpretations of reproductive seasonality. The female-biased infants sex ratio documented from 59 births was attributed exclusively to multiparous mothers. Primiparous mothers produced comparable numbers of sons (n=6) and daughters (n=7), and were increasingly likely to produce daughters with each subsequent reproductive event. Seven of the 11 females that have produced≥3 infants to date exhibited biases in favor of daughters whereas only 1 was biased in favor of sons. Variation in female sensitivity to local resource competition at different stages of their life histories may account for the female-biased infant sex ration in this population.