Distribution of sexes within the left and right uterine horns of cattle

In cattle, limited data are available regarding the sex ratio of the offspring in relation to the horn of gestation. Therefore, the objective of this study was to evaluate the sex ratio of fetuses gestated in the left and right uterine horns of cattle (Bos taurus, Bos indicus and crosses). The distribution of male and female fetuses in the left and right uterine horn was analyzed on gravid, abattoir-derived reproductive tracts and artificially inseminated crossbred cows. The total number of fetuses/calves and the sex of the fetuses/calves gestated in each uterine horn were used as the end point for side comparisons using the Glimmix Procedure. Of 64 gravid reproductive tracts evaluated, 29 (45.3%) pregnancies occurred in the left uterine horn, whereas 35 (54.7%) occurred in the right. The sex ratio (% males) of fetuses in the left uterine horn (37.9%) was significantly lower than the sex ratio detected in the right uterine horn (65.7%). Of 113 pregnancies evaluated in artificially inseminated heifers, 53 (46.9%) occurred in the left uterine horn, whereas 60 (53.1%) occurred in the right uterine horn. The sex ratio of calves gestated in the left uterine horn (35.8%) was significantly lower than the sex ratio of calves gestated in the right uterine horn (63.3%). In conclusion, in these experiments, a significantly greater proportion of males were gestated in the right uterine horn of cattle and a greater proportion of females in the left uterine horn. Further investigation is needed to determine the mechanisms underlying the observed disparity of the expected sex ratio within the uterine horns of cattle.     

The role of doublesex in the evolution of exaggerated horns in the Japanese rhinoceros beetle

Male‐specific exaggerated horns are an evolutionary novelty and have diverged rapidly via intrasexual selection. Here, we investigated the function of the conserved sex‐determination gene doublesex (dsx) in the Japanese rhinoceros beetle (Trypoxylus dichotomus) using RNA interference (RNAi). Our results show that the sex‐specific T. dichotomus dsx isoforms have an antagonistic function for head horn formation and only the male isoform has a role for thoracic horn formation. These results indicate that the novel sex‐specific regulation of dsx during horn morphogenesis might have been the key evolutionary developmental event at the transition from sexually monomorphic to sexually dimorphic horns.     

Genome-wide association mapping identifies the genetic basis of discrete and quantitative variation in sexual weaponry in a wild sheep population

Understanding the genetic architecture of phenotypic variation in natural populations is a fundamental goal of evolutionary genetics. Wild Soay sheep (Ovis aries) have an inherited polymorphism for horn morphology in both sexes, controlled by a single autosomal locus, Horns. The majority of males have large normal horns, but a small number have vestigial, deformed horns, known as scurs; females have either normal horns, scurs or no horns (polled). Given that scurred males and polled females have reduced fitness within each sex, it is counterintuitive that the polymorphism persists within the population. Therefore, identifying the genetic basis of horn type will provide a vital foundation for understanding why the different morphs are maintained in the face of natural selection. We conducted a genome-wide association study using ～36000 single nucleotide polymorphisms (SNPs) and determined the main candidate for Horns as RXFP2, an autosomal gene with a known involvement in determining primary sex characters in humans and mice. Evidence from additional SNPs in and around RXFP2 supports a new model of horn-type inheritance in Soay sheep, and for the first time, sheep with the same horn phenotype but different underlying genotypes can be identified. In addition, RXFP2 was shown to be an additive quantitative trait locus (QTL) for horn size in normal-horned males, accounting for up to 76% of additive genetic variation in this trait. This finding contrasts markedly from genome-wide association studies of quantitative traits in humans and some model species, where it is often observed that mapped loci only explain a modest proportion of the overall genetic variation.     

蝇蛹呼吸角的研究

本文首次研究了我国13种蝇蛹的呼吸角形态(8种有角,5种无),运用统计学方法论证了角参数的分类学价值,描述了光学显微镜和扫描电子显微镜下的显微结构。发现呼吸角呈管腔结构,它借呼吸角内导管将蛹内虫体的前气门与外界沟通。     

Structure of white rhinoceros (Ceratotherium simum) horn investigated by X-ray computed tomography and histology with implications for growth and external form

The nasal and frontal horns of two individuals of Ceratotherium simum were examined by x-ray computed tomography (CT scanning), gross observation of sectioned horn, and light microscopy of histological sections of the horn tissue. CT scans of both sets of horns reveal a periodic banding pattern that is evident upon gross observation of sections as darker bands of tissue. The overlap of these bands in both histological and CT slices suggests the presence of both a photoabsorbent component (melanin) and a radiodense component (calcium phosphate salts, most likely hydroxyapatite or octocalcium phosphate). The distribution of these two components in the horns is hypothesized to contribute to the differential wear patterns that produce the characteristic sweeping conical shape of rhinoceros horn from what otherwise (in the absence of wear and UV exposure) would be cylindrical blocks of constantly growing cornified papillary epidermis. Although extant rhinocerotids are unique in possessing a massive entirely keratinous horn that approximates the functions of keratin-and-bone horns such as those of bovid artiodactyls, the tissue structures that make up the horn are strikingly convergent with other examples of papillary cornified epidermis found in horses, artiodactyls, cetaceans, and birds.     

The intensity of sexual selection predicts weapon size in male bovids

As a classical example of a sexually selected trait, the horns of male bovids offer a prime opportunity to identify predictors of the intensity of sexual selection. Here I use the comparative method to quantify sexual and natural selection pressures behind interspecific variation in horn length. I show that male horn length depends on factors proposed to affect the mean mate number per mating male, correlating positively with group size and negatively with male territoriality. This suggests that whereas group size increases the opportunity for sexual selection, territoriality reduces it because territorial males are unable to follow and monopolize female groups as effectively as males in nonterritorial species. Sexual body size dimorphism also correlates positively with group size and negatively with territoriality, corroborating these factors as predictors of the intensity of sexual selection on males. Female horn length was unaffected by the factors related to mating system, suggesting that this trait is mainly under natural selection. Using female horn length as a proxy for forces of natural selection revealed a negative effect on male horn length. Thus where natural selection favors female horns, possibly as effective weapons against predators, a similar selection pressure on males might prevent them from evolving too elaborate horns through sexual selection. There was no correlation found between horn length and latitude, thus providing no support for the hypothesis that horns have a thermoregulatory function.     

Horn Length Is the Determining Factor in the Outcomes of Escalated Fights Among Male Japanese Horned Beetles, <Emphasis Type="Italic">Allomyrina dichotoma</Emphasis> L. (Coleoptera: Scarabaeidae)

Male horn length in some horned beetles shows a sigmoidal relationship with body size. This has often been considered as the reflection of alternative reproductive tactics of males based on body size. Large males should possess long horns to acquire females through fights with other males using their horns, whereas small males do not require long horns because they usually avoid intermale fights and adopt alternative tactics such as sneaking. This may lead to a prediction that horn length is a reliable indicator of the fighting ability of the male. We examined the effects of both male horn length and body size of Allomyrina dichotoma on the outcomes of escalated fights. Results indicate that male horn length was more important than body size in predicting the outcomes of fight, and this may support the hypothesis that the evolution of the horn dimorphism in male horned beetles is the result of different reproductive tactics.     

Distribution by sex of mouse fetuses in the intrauterine position

We examined whether or not the sex of the fetuses of polytocous animals distributes randomly in the position along the uterine horn in 255 mouse litters. The fetal sex ratio did not differ significantly among the three intrauterine segments (ovarian, middle, and cervical). Based on the number of fetuses examined in this study, it can be stated that even if sex ratio differences exist among the segments, the ratio in individual segments would fall mostly inside the ±0.1 range, when the overall sex ratio (M/(M+F)) is around 0.5.     

牛、绵羊角的遗传定位及遗传机制研究进展

角属于动物颅骨附属物,为反刍动物所特有。牛(Bos taurus)、绵羊(Ovis aries)角的表型包括野生型两角表型、人工驯化的无角表型、畸形角等多种。牛和绵羊是阐明角的质量性状和数量性状之间的关系以及质量性状的多基因调控机制等方面的理想动物模型。近年来,对角性状研究不断深入,在阐明新器官起源进化、自然选择、性别选择和人工选择对角表型的影响等方面取得了一系列进展。本文详细介绍了角的研究概况、多角表型遗传定位、无角位点基因遗传定位和畸形角等,并对目前牛和绵羊角的遗传机制及存在的问题进行了分析,以期为反刍动物角性状和其他特异性性状遗传机制研究提供参考。     

Sex ratio bias in postpartum-conceived Norway rat litters is produced by embryonic loss in midpregnancy

In rats, dams that conceive in their postpartum oestrus and then lose their firstborn litter bias the sex ratio of the litter toward females in utero. The present study identifies the source of litter sex ratio bias in these postpartum pregnant non-lactating dams. The female bias arises first through the postconception loss of embryos, and second, the loss occurs in midpregnancy between the attachment of the blastocyst to the uterine wall on day 5 and full metrial gland development on day 14. Some pregnancies were restricted to one uterine horn to see if this loss (and thus the opportunity for litter sex ratio biasing) was influenced by local factors operating within the uterine horn. Embryonic loss was more closely associated with the number of embryos implanting in a single horn than with the number implanting in the litter, demonstrating that local crowding within a horn is sufficient for the preferential loss of male embryos. This loss did not cause an obvious decrease in the size of the live-born litter because only those horns with a surfeit of embryos lost them. This process was the same in the right and left horns; both carried and lost the same numbers of embryos. A dam that conceives in her postpartum oestrus and then loses her suckling litter forgoes the implantation delay and uterine healing caused by lactation. Male embryos are less successful at implanting in a uterus only recently vacated by a previous litter.     

Contrasting patterns of sexually selected traits in Mediterranean and continental populations of European mouflon

The expression of sexually selected traits in highly dimorphic ungulates may be influenced by environmental quality. Variations in habitat conditions can impose different constraints on the allocation of energy resources to male life‐history traits, and possibly alter the female preferences for specific features. Here, we compared the horn growth patterns in male European mouflon Ovis aries musimon living in different habitats (Mediterranean vs. continental) but sharing a common genetic origin. We hypothesized that the expression of sexually selected traits such as horn development should be promoted in more favorable habitat conditions (i.e., Mediterranean). Using linear mixed models on data retrieved from individuals harvested under the same hunting regime, we found longer horns and greater individual variance in horn segment length in the Mediterranean population than in the continental one. Furthermore, Mediterranean rams showed no evidence of compensatory horn growth, as opposed to the continental rams. Unexpectedly, horn base circumference was greater in the continental habitat than in the Mediterranean one. The overall results suggest different patterns of investment in horns in the two populations, with seemingly stronger pressure and consequences of sexual selection on mouflon rams living in more favorable environments. Although the role of hunters' selectivity cannot be excluded a priori, our data suggest that the differences in the expression of sexually selected traits in our study populations may be influenced by environmental conditions. Because sexual selection can impose substantial fitness costs on individuals, further investigations on the trade‐offs between reproduction and survival would improve our understanding of the dynamics of mouflon populations living in different environmental conditions.     

Genome‐wide association reveals the locus responsible for four‐horned ruminant

Phenotypic variability in horn characteristics, such as their size, number and shape, offers the opportunity to elucidate the molecular basis of horn development. The objective of this study was to map the genetic determinant controlling the production of four horns in two breeds, Jacob sheep and Navajo‐Churro, and examine whether an eyelid abnormality occurring in the same populations is related. Genome‐wide association mapping was performed using 125 animals from the two breeds that contain two‐ and four‐horned individuals. A case–control design analysis of 570 712 SNPs genotyped with the ovine HD SNP Beadchip revealed a strong association signal on sheep chromosome 2. The 10 most strongly associated SNPs were all located in a region spanning Mb positions 131.9–132.6, indicating the genetic architecture underpinning the production of four horns is likely to involve a single gene. The closest genes to the most strongly associated marker (OAR2_132568092) were MTX2 and the HOXD cluster, located approximately 93 Kb and 251 Kb upstream respectively. The occurrence of an eyelid malformation across both breeds was restricted to polled animals and those carrying more than two horns. This suggests the eyelid abnormality may be associated with departures from the normal developmental production of two‐horned animals and that the two conditions are developmentally linked. This study demonstrated the presence of separate loci responsible for the polled and four‐horned phenotypes in sheep and advanced our understanding of the complexity that underpins horn morphology in ruminants.     

A 3.7 Mb Deletion Encompassing ZEB2 Causes a Novel Polled and Multisystemic Syndrome in the Progeny of a Somatic Mosaic Bull

Polled and Multisystemic Syndrome (PMS) is a novel developmental disorder occurring in the progeny of a single bull. Its clinical spectrum includes polledness (complete agenesis of horns), facial dysmorphism, growth delay, chronic diarrhea, premature ovarian failure, and variable neurological and cardiac anomalies. PMS is also characterized by a deviation of the sex-ratio, suggesting male lethality during pregnancy. Using Mendelian error mapping and whole-genome sequencing, we identified a 3.7 Mb deletion on the paternal bovine chromosome 2 encompassing ARHGAP15, GTDC1 and ZEB2 genes. We then produced control and affected 90-day old fetuses to characterize this syndrome by histological and expression analyses. Compared to wild type individuals, affected animals showed a decreased expression of the three deleted genes. Based on a comparison with human Mowat-Wilson syndrome, we suggest that deletion of ZEB2, is responsible for most of the effects of the mutation. Finally sperm-FISH, embryo genotyping and analysis of reproduction records confirmed somatic mosaicism in the founder bull and male-specific lethality during the first third of gestation. In conclusion, we identified a novel locus involved in bovid horn ontogenesis and suggest that epithelial-to-mesenchymal transition plays a critical role in horn bud differentiation. We also provide new insights into the pathogenicity of ZEB2 loss of heterozygosity in bovine and humans and describe the first case of male-specific lethality associated with an autosomal locus in a non-murine mammalian species. This result sets PMS as a unique model to study sex-specific gene expression/regulation.     

Disease and secondary sexual traits: effects of pneumonia on horn size of bighorn sheep

Secondary sexual traits (e.g., horns and antlers) have ecological and evolutionary importance and are of management interest for game species. Yet, how these traits respond to emerging threats like infectious disease remains underexplored. Infectious pneumonia threatens bighorn sheep (Ovis canadensis) populations across North America and we hypothesized it may also reduce horn growth in male sheep. We assess the effect of pneumonia on horn size in male bighorn sheep using 12 herd datasets from across the western United States that had horn growth and disease data. Disease resulted in 12–35% reduction in increment (yearly) length and 3–13% reduction in total horn length in exposed individuals. The disease effect was prolonged when pathogens continued to circulate in sheep populations. Further, disease likely delays the age at which horns reach ¾-curl and prevents achievement of full-curl. This is further evidenced with 6 of the 12 herds experiencing an increase in average age at harvest following die-off events.     

Teratogenic effects of dosage levels and time of administration of carbamazepine, sodium valproate, and diphenylhydantoin on craniofacial development in the CD-1 mouse fetus

The objective of this investigation was to study the teratogenic effects of dosage levels and time of administration of three anticonvulsant drugs (carbamazepine [CMZ], sodium valproate [NaV], and diphenylhydantoin [DPH]) on craniofacial development in the CD-1 mouse fetus. Pregnant females were intubated on each of days 8-10, 11-13, 14-16, and 8-16 of gestation with the following dose levels for each drug: 375, 563, 938 mg/kg CMZ; 225, 338, 563 mg/kg NaV; 50, 75, 125 mg/kg DPH. Appropriate control groups were maintained for each drug. On gestation day 17, pregnant females were killed and implantation sites were recorded as live, dead, or resorbed. All live fetuses were examined for craniofacial defects. Results of examination of 1,398 fetuses indicated that CMZ, NaV, and DPH were teratogenic and embryotoxic at all dose levels. This study indicated that the observed decrease in mean fetal weight was drug-, dose-, and time-dependent. There was a drug-, dose-, and time-dependent increase observed in the number of dead fetuses, whereas the number of resorbed fetuses was observed to be only time-dependent. The observed frequencies of hydrocephalies, secondary palatal clefts, and submucous palatal clefts were significant for all three factors (drug, dose, and time) whereas the observed frequencies of hematomas and exencephalies were significant only for drug and time. Cleft lips were observed only in the highest dose level of DPH. Uterine horn distribution of defects indicated that fetuses located at the proximal end of the horns were less subject to major defects than those fetuses located at the distal end of the uterine horns. Fetuses with craniofacial hematomas were found in the proximal one-third of the uterine horn, resorbed fetuses, and fetuses with submucous palatal clefts in the middle one-third of the uterine horns and dead fetuses and fetuses with exencephalies, cleft lips, and secondary palatal clefts were localized in the distal one-third of the uterine horns. In comparing the effect of drug, dosage, and time on the development of craniofacial malformations in the CD-1 mouse fetus, CMZ was the least teratogenic and embryotoxic of the three anticonvulsant drugs employed in this study.     

Juvenile hormone mediates sexual dimorphism in horned beetles

The causes and consequences of sexual dimorphism are major themes in biology. Here we explore the endocrine regulation of sexual dimorphism in horned beetles. Specifically, we explore the role of juvenile hormone (JH) in regulating horn expression in females of two species with regular sexual dimorphism for pronotal horns (females have much shorter horns than males) and a third species with a rare reversed sexual dimorphism for both pronotal and head horns (females have much larger horns in both body regions compared with males). Applications of the JH analog methoprene caused females of the two more typical species to grow significantly shorter pronotal horns than control females, whereas no consistent effect on pronotal horn development was detected in the third, sex-reversed species. Instead, females in this species showed an unexpected and significant increase in head horn expression in response to methoprene treatment. Lastly, horn shape was also affected in females of one of the regularly sexually dimorphic species, but in the opposite direction than horn length. Although methoprene exerted a feminizing effect on female horn length in this species, it significantly masculinized horn shape by inducing a peculiar shape change observed naturally only in males. Our results suggest that JH influences both overall size and shape of female horns, but does so flexibly and as a function of species, sex and horn location. We use our results to review current models on the role of endocrine mechanisms in development and evolution of horned beetle diversity.     

Compensatory Growth Limits Opportunities for Artificial Selection in Alpine Chamois

ABSTRACT In ungulates, big males with large weapons typically outcompete other males over access to estrous females. In many species, rapid early growth leads to large adult mass and weapon size. We compared males in one hunted and one protected population of Alpine chamois (Rupicapra rupicapra) to examine the relationship between horn length and body mass. We assessed whether early development and hunter selectivity affected age-specific patterns of body and horn size and whether sport hunting could be an artificial selection pressure favoring smaller horns. Adult horn length was mostly independent of body mass. For adult males, the coefficient of variation of horn length (0.06) was <50% of that for body mass (0.16), suggesting that horn length presents a lower potential for selection and may be less important for male mating success than is body mass. Surprisingly, early development did not affect adult mass because of apparent compensatory growth. We found few differences in body and horn size between hunted and protected populations, suggesting the absence of strong effects of hunting on male phenotype. If horn length has a limited role in male reproductive success, hunter selectivity for males with longer horns is unlikely to lead to an artificial selective pressure on horn size. These results imply that the potential evolutionary effects of selective hunting depend on how the characteristics selected by hunters affect individual reproductive success.     

Mechanical limits to maximum weapon size in a giant rhinoceros beetle

The horns of giant rhinoceros beetles are a classic example of the elaborate morphologies that can result from sexual selection. Theory predicts that sexual traits will evolve to be increasingly exaggerated until survival costs balance the reproductive benefits of further trait elaboration. In Trypoxylus dichotomus, long horns confer a competitive advantage to males, yet previous studies have found that they do not incur survival costs. It is therefore unlikely that horn size is limited by the theoretical cost–benefit equilibrium. However, males sometimes fight vigorously enough to break their horns, so mechanical limits may set an upper bound on horn size. Here, I tested this mechanical limit hypothesis by measuring safety factors across the full range of horn sizes. Safety factors were calculated as the ratio between the force required to break a horn and the maximum force exerted on a horn during a typical fight. I found that safety factors decrease with increasing horn length, indicating that the risk of breakage is indeed highest for the longest horns. Structural failure of oversized horns may therefore oppose the continued exaggeration of horn length driven by male–male competition and set a mechanical limit on the maximum size of rhinoceros beetle horns.     

Allometric plasticity in a polyphenic beetle

Abstract 1. Environmental conditions, such as variation in nutrition, commonly contribute to morphological variation among individuals by affecting body size and the expression of certain morphological traits; however the scaling relationship between a morphological trait and body size over a range of body sizes is generally assumed not to change in response to environmental fluctuation (allometric plasticity), but instead to be constant and diagnostic for a particular trait and species or population. The work reported here examined diet‐induced allometric plasticity in the polyphenic beetle Onthophagus taurus Schreber (1759) (Coleoptera: Scarabaeidae). 2. Male O. taurus vary in body size depending on larval nutrition. Only males above a critical body size threshold express fully developed horns; males smaller than this threshold develop only rudimentary horns or no horns at all. 3. Field populations that naturally utilise two different resources for feeding larvae (horse dung vs. cow manure) exhibited significant differences in the average scaling relationship between body size and male horn length over the same range of body sizes. Males collected from cow manure populations expressed consistently longer horns for a given body size than males collected from horse dung populations. 4. Males reared in the laboratory on horse dung or cow manure also exhibited significant differences in the average scaling relationship between body size and horn length. Differences between laboratory populations reared on horse dung or cow manure were of the same kind and magnitude as differences between field populations that utilise these different resources naturally. 5. These findings suggest that between‐population differences in scaling relationships between horn length and body size can be the product of differences in the quality of resources available to developing larvae. Results are discussed in the context of onthophagine mating systems and recent insights in the developmental and endocrine control of horn polyphenisms.     

Shape disparity of bovid (Mammalia,Artiodactyla) horn sheaths and horn cores allows discrimination by species in 3D geometric morphometric analyses

The bony cranial structures of even‐toed hoofed mammals are important for understanding ecology and behavior of ruminants. Horns, the cranial appendages of the family Bovidae, are covered in a layer of keratin that is often not preserved in the fossil record; however, this keratin sheath is intimately involved in the processes that influence horn shape evolution. To understand the relationship between these two components of horns, we quantified both core and sheath shape for four extant species using three‐dimensional geometric morphometric analyses in separate, core‐ and sheath‐specific morphospaces as well as a combined morphospace. We assessed correlations between the horn and sheath morphospaces using two‐block partial least squares regression, a Mantel test of pairwise distances between species, and Procrustes ANOVA. We measured disparity in the combined morphospace as Procrustes distances between mean shapes of cores and sheaths within and between species and as Procrustes variance. We also tested whether core and sheath shapes could be discriminated by taxon with a canonical variate analysis. Results show that horn core and sheath morphospaces are strongly correlated. The differences in shape between a species' core and sheath were statistically significant, but not as great as those between the cores and sheaths of different species when close relatives were not considered, and core and sheath Procrustes variances are not significantly different within species. Cores and sheath shapes were highly identifiable and were assigned to the correct clade 93% of the time in the canonical variate analysis. Based on these tests, horn cores are distinguishable in geometric morphometric analyses, extending the possibility of using geometric morphometrics to study the ecology and evolution of bovid horns to the fossil record.