Effect of different husbandry systems on the reproductive development of post-weaning ram lambs under tropical conditions

Two groups of three-to four-month-old weaning ram lambs were studied for 20 months, beginning with weaning at between three and four months. Group 1 was comprised of nine ram lambs which were reared under an intensive husbandry system, and given standard nutrition and mineral supplements throughout the study. Group 2 was comprised of nine rams which were reared under the traditional nomadic/extensive management system, in which the only source of feed was the available pasture. The reproductive traits studied include: age, weight and scrotal circumference at puberty and at all corresponding ages up to 23 months, libido and sexual dexterity and semen characteristics at puberty and all corresponding ages. In the intensively managed rams, the average age at puberty was 6.4+/-0.5 mos. The averages of the other parameters at puberty were: body weight (BW), 21.7+/-2.5kg; scrotal circumference (SC), 18.5+/-1.3cm; libido score, 1.7+/-0.7 and sexual dexterity, 1.7:0.8. In the extensively managed rams, the average age at puberty was 7.8+/-0.3 mos. The average values of the various parameters at puberty were: BW, 17.3+/-1.2kg; SC, 15.2+/-1.4cm; libido score, 3.2+/-0.6 and sexual dexterity, 3.2:1.8. The inter- and intra-group variations in all the parameters at puberty and at all corresponding ages were significant. The average morphological sperm cell abnormalities at puberty were: 25.2+/-3.4% and 31.6+/-8.3% for rams reached puberty and at all corresponding ages than the extensively reared flock. Certain factors that influence post-weaning reproductive development and performance are discussed.     

A model for the evolution and control of generative apomixis

A model is presented for the evolution and control of generative apomixis—a collective term for apomixis in animals and diplosporous apomixis in flowering plants. Its development takes into account data obtained from studies of apomictic-like processes in sexual organisms and in non-apomictic parthenogens, as well as data obtained from studies of generative apomicts. This approach provides insights into the evolution and control of generative apomixis that cannot be obtained from studies of generative apomicts alone. It is argued that the control of the avoidance of meiotic reduction during egg production in generative apomicts resides at a single locus, the identity of which can vary between lineages. This variation accounts for the observed variation between taxa in the pattern of avoidance of meiotic reduction. The affected locus contains a wild-type allele that codes for meiotic reduction and excess copies of a mutant allele that codes for its avoidance. The dominance relationship between these is determined by their ratio and by the environment. Environmental differences between female generative cells and somatic cells are such that the phenotypic expression of the mutant allele is favoured in the former, while that of the wild-type allele is favoured in the latter. This is important, for the locus is also involved in the control of mitosis which would be disrupted by the expression of the mutant allele in somatic cells. The requirement to maintain a viable pattern of growth and development explains why the wild-type allele is retained by generative apomicts, and this in turn explains why the ability to produce meiotically reduced eggs is retained by facultative forms and why it appears to be suppressed in, rather than absent from, obligate forms. The requirement for excess copies of the mutant allele in generative cells explains why generative apomicts are typically polyploid, as this condition provides a simple and effective means of generating the correct balance of mutant and wild-type alleles. Environmental effects can also lead to the dominance relationship between wild-type and mutant alleles varying between generative cells. In plants, this can lead to the apomixis gene being expressed, and thus to meiotic reduction being avoided, in only some ovules. Meiotically reduced, as well as meiotically unreduced, eggs are produced when this occurs. If compatible and viable pollen is available the meiotically reduced eggs may be fertilized, resulting in these organisms reproducing as facultative apomicts. It is argued that the control and evolution of parthenogenesis in generative apomicts varies between taxa. In some, the parthenogenetic initiation of embryos may result from the acquisition of a parthenogenesis gene or genes; but there is no reason to believe that this is either a general or a common requirement. Indeed, in some it may be an ancestral trait, these apomicts differing from their sexual ancestors in the ability to mature, rather than in the ability to initiate, embryos from unfertilized eggs; or it may result from physiological or developmental changes induced, for example, by polyploidization, hybridization, or the avoidance of meiotic reduction. In some plants it may be induced by pollination (without fertilization) or by the activity of a developing endosperm. Although it is argued that most generatively apomictic lineages may have acquired this form of reproduction relatively easily, by the acquisition of a mutation at a single locus, it is argued that newly initiated lineages may often be reproductively inefficient. These will begin to accumulate mutations that improve the efficiency of apomictic reproduction. Thus several loci may be involved in the control of generative apomixis in established lineages, even though only a single locus was involved in its initiation in these lineages. Care must be taken to distinguish between these initiator and modifier genes when considering the evolution of generative apomixis. Finally, it is argued that although generatively apomictic lineages have easily acquired this form of reproduction, its evolution in some taxa may be so difficult, requiring the acquisition of mutations simultaneously at two or more loci, that these may never acquire it. Thus, evidence obtained from taxa that have successfully made the transition from sexual reproduction to generative apomixis that its evolution was straightforward should not be used as evidence that its evolution will always be relatively easily achieved. Its uneven taxonomic distribution indicates that it is much more easily evolved by some taxonomic groups than by others.     

Life history of captive gray-cheeked mangabeys: Physical and sexual development

Ontogeny refers to every aspect of the development of an individual. In this respect growth and sexual maturation are useful life-history parameters that can be correlated with developmental features of social behavior. In this paper, I analyze body-weight growth and sexual maturation in captive gray-cheeked mangabeys (Cercocebus albigena). I also describe the development of external morphological characteristics, used as “physical markers.” Body-weight growth is analyzed in 15 males and 7 females. Individual weight velocity curves for animals of both sexes showed an, early peak around 2 years of age. Males had a later growth spurt, peaking between 4 and 6 years of age. Females showed no clear second growth acceleration (spurt), but they experienced an interruption of their weight growth deceleration between 3 and 5 years of age, which is generally coincident with puberty. In females there is a close relationship between weight and the occurrence of the first swelling of their sexual skin. These developmental parameters are compared to those described in baboons and macaques.     

Embryogenic protoplast cultures of orange jessamine (Murraya paniculata) and their regeneration into plants flowering in vitro

Embryogenic callus was induced from the hypocotyl region of seedlings germinated from immature embryos of orange jessamine (Murraya paniculata (L.) Jack) on Murashige & Tucker (1969) medium containing 50 g l^-1 sucrose, 5.0 mg l^-1 benzyladenine, 2.5 mg l^-1 2,4-dichlorophenoxyacetic acid and 600 mg l^-1 malt extract. Isolated protoplasts divided to produce callus on Murashige & Tucker (1969) medium containing 50 g l^-1 sucrose, 0.01 mg l^-1 gibberellin A₄₊₇ and 600 mg l^-1 malt extract. Callus developed to plantlets via somatic embryogenesis on Murashige & Tucker (1969) medium with 50 g l^-1 lactose but no plant growth regulators. These plantlets flowered in vitro on half strength Murashige & Tucker (1969) medium containing 50 g l^-1 sucrose after 2 months culture.Abbreviations BA benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - FDA fluorescein diacetate - FM full strength MT medium - FMG full strength MT medium +1 mg l^-1 GA₃ - GA₃ gibberellin A₃ - GA₄₊₇ gibberellin A₄₊₇ - HM half strength MT medium - HMG half strength MT medium +1 mg l^-1 GA₃ - MT Murashige & Tucker (1969)     

Changes in circulating levels of immunoreactive follicle stimulating hormone, luteinizing hormone, and testosterone during sexual development in the rhesus monkey, Macaca mulatta

Basal serum levels of follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T) and the responsiveness of these hormones to a challenge dose of luteinizing hormone releasing hormone (LHRH), were determined in juvenile, pubertal, and adult rhesus monkeys. The monkey gonadotrophins were analyzed using RIA reagents supplied by the World Health Organization (WHO) Special Programme of Human Reproduction. The FSH levels which were near the assay sensitivity in immature monkeys (2.4 +/- 0.8 ng/ml) showed a discernible increase in pubertal animals (6.4 +/- 1.8 ng/ml). Compared to other two age groups, the serum FSH concentration was markedly higher (16.1 +/- 1.8 ng/ml) in adults. Serum LH levels were below the detectable limits of the assay in juvenile monkeys but rose to 16.2 +/- 3.1 ng/ml in pubertal animals. When compared to pubertal animals, a two-fold increase in LH levels paralleled changes in serum LH during the three developmental stages. Response of serum gonadotrophins and T levels to a challenge dose of LHRH (2.5 micrograms; i.v.) was variable in the different age groups. The present data suggest: an asynchronous rise of FSH and LH during the pubertal period and a temporal correlation between the testicular size and FSH concentrations; the challenge dose of LHRH, which induces a significant rise in serum LH and T levels, fails to elicit an FSH response in all the three age groups; and the pubertal as compared to adult monkeys release significantly larger quantities of LH in response to exogenous LHRH.     

Photoperiodic induction of diapause in normal and allatectomized precocious pupae of Papilio machaon

Diapause in the swallowtail, Papilio machaon occurs at the pupal stage in response to short days during larval development. The precocious pupae obtained by allatectomy also entered diapause in response to short days. The photoperiodic induction of diapause in precocious pupae was very similar to that in normal pupae in spite of the abbreviation of the last-larval instar. The critical photoperiod for diapause in the precocious pupae was 14.5 h, being about the same as that in normal pupae. Occurrence of diapause in the swallowtail is closely associated with the pupal stage and the induction process may be triggered by the cessation of juvenile hormone secretion.     

Precocious reprogramming of eupyrene-apyrene spermatogenesis commitment induced by allatectomy of the penultimate larval instar of the moth Actias selene

A possible causal relationship between the switch-over from eupyrene to apyrene spermatogenesis and pupation in Lepidoptera was examined in Actias selene. Precocious pupation, 11 days earlier than in the controls, was induced by allatectomy on the first day of the penultimate larval instar. The course of the eupyrene spermatogenesis, until nuclear elongation in the spermatid, is not related to pupation. In both allatectomized and control individuals, eupyrene metaphases appear 8 days after ecdysis of the fourth larval instar. Nuclear elongation, however, is triggered in the allatectomized individuals earlier than in the controls, probably by the premature decline of the juvenile hormone titre following allatectomy. Apyrene commitment, on the other hand, is directly related to pupation, as apyrene spermatogenesis begins 2 days after pupation in both control and allatectomized individuals.     

Maturation and germination of Phaseolus vulgaris embryonic axes in culture

In this study of embryo development in Phaseolus vulgaris L., we found that immature embryonic axes placed in culture show a growth lag before germinating. The length of this lag phase varies according to axis age at excision, but is not affected by transfer to fresh medium, alteration of sucrose concentration between 0.5 and 2%, or whether the culture medium is liquid or agar-solidified. The lag phase was shortened by both actinomycin D and cordycepin treatment, and by treatment with 10^-5 to 10^-6 M benzyladenine. The effect of abscisic acid (ABA) varied with concentration: below a certain level, it had no effect on the lag phase, but above that level it inhibited, germination. This threshold concentration was 10^-7 M for 20-d-old axes but increased to 10^-5 M by the time the axes were 32 to 34 d old. To determine whether the axes were continuing their embryonic development during the lag phase, we tested them for desiccation-tolerance and for synthesis of phaseolin, a seed storage protein which is specific for embryos of P. vulgaris. The ability to germinate after rapid desiccation was acquired by axes at 26 d past anthesis; when axes younger than this were placed in culture, they developed desiccation-tolerance during the lag phase of growth, indicating that they were continuing embryonic maturation. Phaseolin was present in isolated axes, although at lower levels than in cotyledons. It accumulated during axis development in parallel with total protein, staying at about 1% of total protein content. When isolated immature axes were pulsed with ³H-or ¹⁴C-amino acids, they incorporated label into phaseolin, shown by precipitation with anti-phaseolin antibody. Isolated axes from mature seeds, however, did not synthesize detectable amounts of phaseolin. Immature axes cultured in vitro for a period of one to several days continued synthesizing phaseolin until the day prior to visible germination. Treatment of cultured axes with ABA increased the amount of precursor amino acids incorporated into protein, but had a small or no effect on the relative proportion of phaseolin synthesized. We conclude that P. vulgaris axes in culture continue to develop embryonically for a period of time which seems to be under intrinisc control by the axis. This contrasts with precocious germanation, a pattern of embryo behavior seen in many other species. When such embryos are excised from seeds while immature and placed in culture, they switch promptly from embryo development into germination. If ABA or water stress is responsible for preventing precocious germination, it may be that a high level of ABA is maintained or synthesized internally by embryonic axes of Phaseolus, while in other embryos the maternal environment supplies ABA and/or causes water stress.Abbreviations ABA Abscisic acid - BA benzyladenine     

Patterns of puberal development in Sahiwal and Brahman cross bulls in tropical Australia. I. Growth and semen characteristics

Reproductive development was monitored in 13 1 2 Brahman (BX), 20 3 4 BX, 8 1 2 Sahiwal (SX) and 11 3 4 SX crossbred bulls between one and two years of age. Liveweight increased during wet season (0.7 kg/day) and decreased during dry season conditions (-0.25 kg/day). Scrotal circumference (SC) increased from 18.6 to 25.0 cm, but decreased slightly during the later stages of the dry season. First ejaculates containing 50 x 10(6) spermatozoa were obtained from 25% of the bulls at 15.3 months of age and from 84% by two years of age. Sperm motility and morphology showed no consistent pattern, but number of sperm per ejaculate increased and seminal fructose concentrations decreased with advancing age. Significant genotype differences were noted for SC and seminal characteristics. Estimated age and liveweight at puberty were 570, 563, 578 and 542 days, and 251, 265, 247 and 256 kg for 1 2 BX, 3 4 BX, 1 2 SX and 3 4 SX bulls, respectively.