Seasonality In Reproductive Activity Research Articles

Some reproductive characteristics in common donkey male (Equus asinus)-A mini review

In contrary to most domestic livestock species, the common donkey (Equus asinus) is widely known as an animal with a marked seasonality in reproductive activity .The annual cycle of daily photoperiod has been identified as the determining factor in the sexual activity. A synthesis of the particularities of donkey reproduction is important and constitutes a basis of scientific reflection for managing asine livestock farms and to establish a well conservation plan for the different breeds around the world. It is necessary to have a perfect knowledge of the seasonal physiological changes in order to optimize the reproductive characteristics in donkeys.The objective of this paper is to review the current state of knowledge on the reproductionseasonality in common donkey. We start with a remainder of some anatomical of the genital apparatus and sexual behavior aspects. Moreover, the investigations undertaken by many authors reveal the influence of the season on testicular biometry, histology, seminal and hormonal parameters in male donkeys’ populations. In conclusion, despite scientific controversy on reproductive seasonal character in donkeys, it could likely be influenced by several factors mainly the photoperiod.

Growth dynamics and mortality of the intertidal encrusting sponge Halichondria okadai (Demospongiae, Halichondrida)

A periodical survey of the growth of an intertidal encrusting sponge Halichondriaokadai was conducted on a rocky intertidal shore on the Izu Peninsula, southern Japan. The area covered by each of 16 marked sponges was monitored, and the fusion and fission of specimens were recorded from June 1995 to June 1998. During the investigation, 15 of the original specimens managed to survive accompanying fusions or fissions and only one colony completely disappeared. Ten fusions and 23 fissions were observed in total. The maximum death rate during a semilunar period was 16.7% and cumulative mortality throughout the study period was 46.1%, indicating that the mortality of H. okadai is lower than that of other species previously reported. There was no particular seasonal pattern in the occurrences of fusion, fission and death of sponges. However, fissions were frequently observed in the latter half of the study period and were sometimes followed by fusions or death of specimens. Positive growth rates were often observed during warmer months, and specimens showed little growth or regression in winter. Seasonal patterns in surface area were thought to be related to seasonality in reproductive activity.

Reproduction in four populations of brooding periwinkle (Littorina) at Ravenscar, North Yorkshire: adaptation to the local environment?

The current study examines the reproductive patterns found within four ovoviviparous, brooding periwinkle populations on one shore in the north-east coast of England; the boulder dwelling populations Littorina saxatilis H (upper-shore form with thin shell and large aperture) and L. saxatilis M (mid-shore form with thick shell and small aperture), and the barnacle-dwelling L. saxatilis B (small form similar in morphology to L. saxatilis M) and L. neglecta. Littorina saxatilis H showed distinct seasonality in reproductive activity, unlike L. saxatilis M, and produced significantly larger eggs and embryos than the latter population. Littorina saxatilis M maintained a significantly higher weight-specific fecundity and reproductive activity throughout the year than L. saxatilis H and produced a larger number of small embryos.The two barnacle-dwelling populations also showed distinct seasonality in reproductive activity and neither of the populations contained reproductively active females during the winter months. There was no significant difference in egg size between the two populations, but L. saxatilis B produced larger crawlaways than did L. neglecta. Even though L. saxatilis B was significantly larger in body and shell size, L. neglecta had a higher weight-specific fecundity than the former population. The possibility that the observed differences in egg and juvenile size, fecundity and seasonality between the four populations can be attributed to microscale adaptation to the local environment is discussed.

Reproduction of the Fiddler Crabs Uca longisignalis and Uca spinicarpa in a Gulf of Mexico Salt Marsh

Monthly field sampling of active animals in a Louisiana coastal salt marsh monitored changes in size class frequency distributions, ovarian development of females, and rates of egg extrusion for two species ofUca endemic to the Gulf of Mexico. Ovigerous females occurred no earlier than February forUca spinicarpa and April forUca longisignalis. Peak percentages of ovigerous females were observed in June 1992 forUca longisignalis (67%) and in March 1993 forUca spinicarpa (85%). Peaks in ash-free dry weight (AFDW, in g) of females coincide with peak periods of ovarian development and subsequent ovigery. Mean biomass as AFDW of males and females combined forUca longisignalis was 0.26 g individual−1 and forUca spinicarpa was 0.17 g individual−1. A significant correlation existed between AFDW and carapace width in both species, males and females.U. longisignalis appears to be of warm-temperate lineage, and its reproductive activity is the more seasonally restricted, with later ovarian development, earliest egg laying delayed to late spring, and peak ovigery in summer. In keeping with putative tropical affinities ofUca spinicarpa, ovarian development is episodic over a longer-period from late winter to summer, and eggs are produced earlier in the year. The more striking seasonality in reproductive activity and biomass peaks forUca longisignalis may also reflect some nutritional dependency on temperate, annual marsh plants that characterize its preferred habitats.

Seasonal sexually dimorphic distribution of neuropeptide Y-like immunoreactive neurons in the forebrain of the lizard Podarcis hispanica

Since neuropeptide Y (NPY) is involved in several sex-specific physiological and behavioral processes, a sexual dimorphic distribution is expected in forebrain areas that take part in the control of reproduction physiology and sexual behavior. This question has been studied in the lizard Podarcis hispanica by comparing the distribution of NPY-like immunoreactive cells in several forebrain areas of males and females during the season of active (spring/summer) and inactive (fall/winter) reproductive activity. Both qualitative observations and statistical analysis (analysis of variance) indicate that the number of reactive cells within two forebrain areas, the lateral septum and the periventricular preoptic nucleus, depends on the sex ( P = 0.02) and season ( P = 0.03) and that, in fact, intersexual differences depend on the season of the reproductive annual cycle ( P = 0.046). Other areas, such as the amygdaloid nucleus sphericus, show neither sexual dimorphism ( P = 0.67), nor seasonal variation in the number of reactive cells ( P = 0.18), nor seasonal variation of the intersexual differences ( P = 0.75). When analyzed independently, the lateral septum shows a clear sexual dimorphism in favour of females ( P = 0.003) whereas the number of reactive cells in the periventricular preoptic nucleus is significantly higher ( P = 0.006) in males than in females. In the case of the preoptic nucleus, this sexual dimorphism is clearly accentuated during the season of reproductive activity ( P = 0.007), but this dependence is not so clear for the lateral septum ( P = 0.059). In the light of these findings the possible roles of NPY on the regulatory mechanisms of sexual behavior and other aspects of the physiology of reproduction are discussed.

A comparison of breeding and moult cycles and life histories in two tropical starling species: the Blue‐eared Glossy Starling Lamprotornis chalybaeus and Rüppell's Long‐tailed Glossy Starling L. purpuropterus

The Blue‐eared Glossy Starling Lamprotornis chalybaeus and Rüppell's Long‐tailed Glossy Starling Lamprotornis purpuropterus were investigated in the field and in aviaries at Lake Nakuru National Park, Kenya for seasonality in reproductive activity and moult. The former species was found to be a seasonal breeder which nests after the onset of the heavy rains in April. Although some birds had large gonads prior to the rains in the dry season no nesting occurred. The rains were contemporary with increases in gonadal size and the plasma titres of LH, testosterone (T) in males and estradiol (E2) in females. These hormones are associated with the initiation of breeding activity. As breeding ceased in July and the moult began, the plasma titres again decreased. There was a bimodal breeding pattern which paralleled a change in biotope preference for nesting. Early nests, in the heavy rains, were on the open savanna and later nests were in the acacia forest. Late nesting birds also had delayed peaks in gonadal size, plasma titres of LH, T and E2 and a delayed moult onset. Data on individual captive birds demonstrate that these annual cycles have a distinctly individual character superimposed on the seasonal trends.In Rüppell's Long‐tailed Glossy Starlings no seasonality in breeding was found although the flight feather moult commenced and was completed in all individuals at about the same time. The moult extended over about ten months, so a great deal of breeding‐moult overlap was present. The absence of seasonality in field birds was reflected in the aviary birds, which had no pronounced cycles in the reproductive parameters measured (gonadal size, LH, T and E2 plasma titres). Breeding in field birds was regulated on a pair basis and correlated with increases in duetting. The striking differences in the seasonal organization between this species and Blue‐eared Glossy Starlings were presumably due to the different biotope preferences and social behaviour of the two species.

PROGRESS AND PROBLEMS IN LOBSTER BROODSTOCK DEVELOPMENT

AbstractA major impediment to commercial farming of the lobster Homarus is lack of control over reproduction. Without it, a steady supply of seed cannot be insured, nor can selective breeding be applied. The major block in the reproduction of either laboratory‐mated or wild‐caught inseminated females has been low frequency of egg extrusion. Prior to 1976, 5 extrusions were documented at the Bodega Marine Laboratory. Only one of these hatched successfully. Since late 1976, however, 10 females mated in the laboratory and 8 females inseminated in nature have successfully extruded. Of these ovigerous females, 5 hatched viable progenies and the remainder subsequently lost their eggs.Most of these reproductive events occurred during a 22‐week experiment in which laboratory‐mated and field‐inseminated females were held in large tanks (37 cm × 74 cm × 49 cm deep) in a 3 temperature × 2 photoperiod design. Mortality was highest (5/18 or 28%) in the highest temperature schedule (18–22°C), lower (3/36 or 8%) in the middle temperature schedule (14–18°C) and zero (0/18) at lower temperatures (10–15°C). Molting followed a similar ordering, 67% at high temperatures, 64% at medium temperatures and 50% at low temperatures. The rate of extrusion showed an inverse pattern with only 6% in the high, 14% in the medium and 22% in the low temperature schedules. Photoperiod had an apparent effect only in the low temperature schedule with 2 molts in the short day and 7 in the long day cycle. Ovarian maturation was monitored during the experiment by a candling technique. Candling scores are correlated with actual ovary appearance and weight for 35 females sacrificed at the study's conclusion.Progress in broodstock development has come chiefly through better husbandry (larger tanks, varied diet, as well as improved sampling techniques and record keeping practices), and in part through the success of H. gammarus females in crosses to H. americanus males. Two overall results of significance to lobster broodstock development are the evidence of shorter than 2‐year cycles in some females, and the lack of marked seasonality in reproductive activity. Two problems, in addition to understanding the complex interplay of molting and ovarian development, are shell disease and loss of eggs following extrusion.

Environmental physiology of reptilian breeding cycles: Role of temperature

Phenological data indicate that most reptiles, even in tropical regions, exhibit some seasonality in reproductive activity; in most temperate species, a single, relatively brief breeding period alternates with a period of sexual quiescence. In lizards, the most studied of the Reptilia, it appears that exogenous, climatic factors act to synchronize these cycles, although some species may also exhibit endogenous ( circannual) rhythmicity. Rainfall may influence egg laying in some tropical lizards. Photoperiodism probably also affects certain aspects of the gonadal cycle in a few species, but many reports of photoperiodism have been questioned on the basis of inadequate experimental design. Of all the environmental factors, temperature appears to be the single most important and widespread of the timing cues for saurian reproduction. Available data on the basic reproductive endocrinology in reptiles are reviewed and it is suggested that reptiles may possess only a single (FSH-like) gonadotropin (GTH). Studies on the mechanisms by which changes in temperature generate seasonal reproductive cycles indicate that several loci may be involved. They may act at the level of the central nervous system in relation to GTH-releasing factors and, likewise, may modify the response of the CNS to photoperiodic changes. The physiological responsiveness of the pituitary gonadotropes per se may be altered by temperature but this hypothesis is untested. The possibility that the peripheral metabolism (e.g., half-life) of GTH may also vary with temperature has also not been tested. In both sexes, the peripheral target tissues (gonads) are highly temperature sensitive. More importantly, gametogenesis and steroidogenesis may be differentially affected by changes in temperature; their relative temperature sensitivities vary among species. These two processes also show different sensitivities to the level of circulating GTH.

Ecological adaptation and mammalian reproduction.

Some of the major variations in mammalian reproductive cycles are discussed from the viewpoint of their broad adaptive values. In natural populations a nonpregnant cycle is an exception in long-lived animals and a disaster in short-lived prey species. Acceptable alternatives are either to safeguard agaisnt the occurrence of a nonpregnant cycle or to recover and recycle as quickly as possible. Mammalian female cycles are categorized as Type I Type II and Type III. In Type I both ovulation and pseudopregnancy are spontaneous. Subtype A includes medium length cycles and Subtype B long cycles. In Type II ovulation is induced and pseudopregnancy is spontaneous with the similar subtypes. In Type III both ovulation and corpus luteum formation are spontaneous but pseudopregnancy is induced via the release of luteotropin following copulation. Induced and spontaneous ovulation delayed implantation seasonal breeding and postpartum estrus serve different functions in animals in natural population. It appears that induced ovulation is the more widespread phenomenon and that spontaneous ovulation occurs in a more restricted number of species. Delayed implanatation occurs in widely scattered species and groups within many orders but also the physiological controls vary. At least some degree of seasonality in reproductive activity is almost universal in natural.a Postpartum estrus seems to have developed independently many times and its distribution is sporadic throughout many mammalian speices. The necessity of trying to understand the significance of variations seen in reproductive cycles is stressed. After some basic patterns are established appropriate species can be selected to test some of the hypothesis rather than haphazardly studying forms just because they are available.