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Reproduction biology of the roe deer (Capreolus capreolus) and newer domestic data about the offspring and losses
Abstract
Obligate embryonic diapause is one of the features within reproduction biology of the roe deer. In the period of the diapausa independently from the pregnancy the corpus luteum (CL) is active, but the hormone production is stabilised at a low level. The quantity of oestradiol and prolactin increases only before and during the implantation. The reactivation of the blastocyst is not a consequence of the change in maternal hormone production (progesterone, oestradiol, prolactin); there is a uterus-specific hormone which is supposed to be responsible for starting the embryo development. In roe deer the well-known luteolysis mechanism does not work, the CL remains from December till January, despite the fact that the doe is pregnant or not, and so the possibility of another rutting season is excluded (strictly mono-oestrous species). In the examined populations the fertility rate occurred high (88-100%), the pregnancy rate is 88-100%. The average number of foetuses (primary natality) 1.67-2.16, average number of born fawns 1.54-2.06 (secondary natality), the reared litter size 0.94-1.55 (tercier natality). The distribution of foetus number: 1 foetus 13.46%, 2 foetuses 73.72,3 and 4 foetuses 5.77%. The distribution of reproductive losses: intrauterinal 2.83-18.0% (primary mortality) and rearing losses 6.01-42.45% (secondary mortality). However, it can be expressed, that the main part of reproductive losses occurs in the rearing period (May-September). The preventive game management and hunting efforts should be concentrated on this period.
In the agricultural landscape, thousands of animals are killed yearly as a result of agricultural machinery innovation, mostly because of a higher harvesting speed and wider cutting bars. Harvesting machines besides predation by red fox ( Vulpes vulpes L.) on roe deer ( Capreolus capreolus L.) in the intensively managed cultural landscape are the most crucial factor in fawn mortality. This article offers an evaluation of the mostly used preventive methods, which aim to drive roe deer does along with their fawns out of fodder meadows prepared for harvest in the Czech Republic. Evaluation of efficiency and effectiveness of the different methods was made based on the questionnaire survey published in a professional hunting journal. The assessment of responses from a survey was followed by a field-based investigation conducted before fodder harvesting. The devices studied for efficiency were acoustic, optical and scent deterrents in comparison to the traditional search method combined with volunteers and hunting dogs. The results show differences in the number of fawns saved per hectare. A significant difference was found only between the optical deterrent method (0.4 fawns saved per hectare) and traditional search method (0.09 fawns saved per hectare). This study found no substantial difference among various deterring devices in terms of their effectiveness in reducing the mortality of roe deer fawns. Thus, it is important to explore the innovative methods in the future that can work most effectively for saving not only deer fawns, but also other game animals in the cultural landscape.
Knowledge about the mechanisms of embryonic diapause in European roe deer Capreolus capreolus (Linnaeus, 1758), although first described 140 years ago, is not extensive. In contrast to post mortem publications, this is an in-vivo study which monitored individual ovarian and uterine dynamics during diapause by transrectal ultrasonography. Ten roe deer were examined at 4 to 6-week intervals starting from the end of the breeding season (August) until after implantation (January). Sonographic appearance of corpora lutea and their average number observed per animal did not differ between pregnant (3.6) and non-pregnant (3.2) does prior to implantation. However, in pregnant animals (n = 5) endometrial changes associated with embryonic diapause were identified. The endometrium in pregnant does were low in echogenicity compared to the non-pregnant. Changes in echogenicity of the endometrium were first detected three months before implantation. Observed endometrial changes were quantified by computer-assisted grey scale analysis. Mean medians of grey scale histograms were lower in pregnant compared to non-pregnant animals beginning as from October. In late December and January, embryonic structures were detected in animals in which a low echogenic endometrium had been observed earlier. Ultrasonography and grey scale analysis characterised efficiently the dynamic processes in the uterus and ovary during embryonic diapause in pregnant and non-pregnant roe deer.
This paper investigates variation in female fecundity in relation to effects of age and body weight within and between 15 populations of roe deer Capreolus capreolus (Linnaeus, 1758) in Britain. Analyses were based on carcass material and fecundity was assessed from the presence/absence and number of fertilised ovulations (corpora lutea) and implanted foetuses. A significant proportion (> 10%) of does ovulated in their first year in some populations, but such precocious reproductive activity rarely resulted in successful implantation of a foetus. Generally, the majority of yearling does (in their second year) conceived successfully, but average potential litter size was lower than among older animals. There was no consistent age- related variation in fecundity among does older than 2 years. Differences in fecundity between age and body weight classes suggest weight thresholds may exist for the onset of puberty and for successful conception as an adult. Fecundity of adults and yearlings was highly variable between populations and in some populations was considerably lower than previously reported for this species. Although differences between populations were correlated with differences in body weight, this relationship was insufficient to explain the wide variation in fecundity across Britain, suggesting fecundity body weight thresholds will be defined independently in separate populations.
The ultrastructure of 4 roe deer blastocysts at different stages of embryonic development were studied. During delayed implantation, the outer surface of the trophoblast possessed numerous microvilli and periodic invaginations or caveolae. There was a marked lack of organelles such as mitochondria or endoplasmic reticulum in the cytoplasm of the trophoblast cells, though many lipid droplets, granular inclusions and a lamina of fine fibrillae were present. Elongation of the blastocyst was associated with a decrease in the size and number of the microvilli, the disappearance of lipid droplets and granular inclusions, a reduction in the amount of fibrillar material and a dramatic increase in the development of mitochondria, granular endoplasmic reticulum, ribosomes and Golgi apparatus. The histology of the ovaries and uterus was studied in 31 roe deer. No prominent changes occurred in the ovaries at any stage of development; all ovaries possessed active CL and showed signs of follicular growth and atresia. Changes in the degree of mitotic activity, epithelial cell height, endometrial vascularity and stromal edema were observed in the uterus throughout the period of delayed implantation and during the phase of rapid embryonic growth. Elongation of the embryo was associated with a marked decline in the height of the glandular epithelium and an increase in endometrial vascularity. The most important ultrastructural changes in the uteri of 6 roe deer were observed in the endometrial glands. Delayed implantation was associated with the accumulation of numerous supranuclear vesicles derived from the Golgi apparatus, while the resumption of embryonic growth was correlated with their sudden disappearance. When elongation was completed, there was a sudden decrease in the cellular activity of these endometrial glands.
The roe deer blastocyst is in diapause between August and December, after which time it expands and elongates rapidly before implantation. Blood samples were taken from 30 animals to define temporal changes in reproductively important hormones to investigate the physiological cues present at embryo reactivation. In 15 of these animals, changes in uterine and conceptus protein synthesis and secretion, and luteal progesterone release during diapause and reactivation, were assessed after culture of these tissues in vitro. Oestradiol concentrations remained low during diapause (1.07 +/- 0.4 pg ml(-1)) and expansion (1.2 +/- 0.4 pg ml(-1)) but increased by 30 times at trophoblast elongation (49.17 +/- 0.37 pg ml(-1)). Prolactin remained at basal concentrations (4.69 +/- 0.86 ng ml(-1)) and increased after implantation (12.34 +/- 2.71 ng ml(-1)). Peripheral progesterone concentrations and luteal progesterone release remained constant throughout diapause, reactivation and implantation (peripheral progesterone: 3.82 +/- 1.97 ng ml(-1); luteal progesterone: 6.72 +/- 0.81 ng mg(-1) protein). Incorporation of a radiolabel into conceptus secretory proteins increased by four times at expansion compared with diapause, whereas incorporation into endometrial secretions remained constant. At elongation, incorporation into endometrial secretions increased two times and conceptus secretions increased 32 times. Two-dimensional electrophoresis and fluorography showed that the profile of endometrial secretory proteins was constant until implantation when qualitative changes were evident. Although a role for an endocrine maternal trigger of reactivation from diapause cannot be dismissed, these data provide no supporting evidence and indicate that the conceptus itself may drive reactivation.
Progesterone (P) and estrogens (E) were determined in the pheripheral plasma of pregnant and nonpregnant roe deer with the beginning of the breeding season, (July) until time of expected parturition in May/June of the following year. (Exp. A). In nonpregnant animals, P (mean ng/ml ± SEM) increased from 0.12 ± 0.02 in July to 1.69 ± 0.36 in August. From August through March, mean values ranged between 1.93 ± 0.61 and 3.00 ± 0.65, followed by a decrease in April (1.09 ± 0.39) with basal levels reached in May (0.1 ± 0.04). In the pregnant animals, P similarly started to rise in July to a first peak (3.55 ± 0.48) in August; values thereafter were between 2.08 ± 0.19 and 2.80 ± 0.27 until December. A second increase up to 4.81 ± 0.68 in January was observed in pregnant animals, which was of different magnitude from the nonpregnant animals. A gradual decrease from 4.45 ± 0.57 to 1.01 ± 0.44 occurred from March to May. Concentrations of E (mean pg/ml ± SEM) varied between 57 ± 7 and 107 ± 27 in the nonpregnant animals and were higher in the pregnant animals during the last 6 months of gestation. In a more intensive study of 2 nonpregnant animals (Exp. B), P exhibited a short elevation at the end of July and the beginning of August, followed by a continuous increase throughout the period examined (October). It is concluded that the corpus luteum remains active once it has formed, even in the nonpregnant animal, during the greater portion of the reproductive period. The data obtained also suggest that in the pregnant animal, placental P and E production commences at the time of placental attachment in January.
W latach 1966-1980 w środowisku krajobrazu rolniczego o pow. 15 tys. ha przeprowadzono badania nad funkcjonowaniem populacji sarn. Celem badan bylo uzyskanie danych dotyczących dynamiki liczebności, rozrodu, śmiertelności, przezywalności oraz struktury wieku i plci. Na podstawie zebranych danych sporządzono bilans ilościowy populacji
Summary1. Females should adjust their reproductive effort prior to substantial investment. For roe deer, due to delayed implantation, this adjustment may occur at ovulation/fertilization during the summer rut, or at implantation in mid-winter. We investigated the effects of climate and maternal phenotype (mass, condition, age) on potential litter size (number of fertilized ovulations) and implantation failure (number of fertilized ovulations less number of fetuses) of 818 individual roe does from nine populations across Britain.2.Potential litter size varied from 1 to 4, with 0–100% of does per population polyovulating. Among prime-aged does, 16.7–54.5% subsequently failed to implant at least one blastocyst.3.Individual fecundity was determined by the combined effects of maternal phenotypic quality and age, but acting at different stages of the reproductive process: potential litter size increased with increasing maternal body mass; implantation failure was independent of phenotypic quality, but varied in relation to maternal age, being lowest for prime-aged does, somewhat higher for yearlings, but higher still for senescent females.4.Implantation failure increased with increasing initial potential litter size, perhaps related to physiological malfunction. Implantation was often an all-or-nothing process, with females either implanting all or failing to implant any of their fertilized blastocysts.5.Climatic factors were not consistently correlated with individual female fecundity within populations, but between populations implantation failure increased with climatic severity.6.For species such as roe deer, where females rely on food intake rather than fat reserves for reproduction, we suggest that a two-step process shapes patterns of reproductive output: body mass first sets an upper limit to potential litter size at conception, then reproductive output is limited mainly by senescence and climatic severity through implantation failure.
Time- and sex-specific summer survival of roe deer fawns was estimated using capture-mark-recapture methods in two enclosed
populations living in contrasting conditions. The population of Trois Fontaines (eastern France) was roughly constant in size
throughout the study period, while in Chizé (western France), the population experienced frequent summer droughts and numbers
decreased continuously during the study. Early survival of fawns was low and highly variable over the years at both Chizé
and Trois Fontaines, and demonstrated marked variations between cohorts that need to be taken into account when modelling
roe deer population dynamics. In Trois Fontaines, fawn survival was positively correlated with early body growth and total
rainfall in May and June. In Chizé, fawn survival decreased with increasing density and tended to increase with increasing
rainfall in May and June and adult female body mass. These factors explained more than 75% of the variability in early survival
observed in both populations. Variation between cohorts had different consequences for the two populations. At Trois Fontaines,
cohort variation was limited to a numerical effect on early survival. However at Chizé, cohort variation was long-lasting
and affected the phenotypic quality of survivors at later ages, and thereby future survival and breeding abilities (both numerical
and quality effects). Male and female fawns had similar survival over their first summer in both populations. This result
contrasts with the lower survival of young males often observed in ungulates. Two ultimate causes can be proposed to account
for the low and variable survival of roe deer fawns over the first summer: the high energy expenditures incurred by does during
each breeding attempt and/or the low absolute body size of newborn roe deer fawns.
This study was conducted during 5 consecutive years with a total of 555 wild female roe deer (Capreolus capreolus L.) caught in the National Reserve of Chizé Forest (France). To study the relationships between embryo development and progesterone concentrations, 78 wild females caught in 1987/88 and four captive does were analysed. Pregnancy diagnosis was evaluated using an ultrasonographic technique and progesterone concentrations were measured by radioimmunoassay.In December (period of delayed implantation) mean plasma progesterone concentrations were around 3.37 ± 0.15 ng/ml. An increase to 4.34 ± 0.09 ng/ml was observed in February. These levels were achieved in synchrony with an increase of the vesicle diameter of the embryo in the uterus of pregnant females. The first embryos were detected with ultrasonography before the end of January. The mean number of embryos per pregnant female ranged between 1.47 and 1.51. The correlation between the number of embryos per female and progesterone concentrations was significant (P < 0.001). It is concluded that in the pregnant female, plasma progesterone rises at the time of embryo development in January. The data obtained also confirm a high reproductive rate, in which 98% of adult females in a wild population were reproductively active.
Progesterone (P) and estrogens (E) were determined in the peripheral plasma of pregnant and nonpregnant roe deer with the beginning of the breeding season (July) until time of expected parturition in May/June of the following year (Exp. A). In nonpregnant animals, P (mean ng/ml ± SEM) increased from 0.12 ± 0.02 in July to 1.69 ± 0.36 in August. From August through March, mean values ranged between 1.93 ± 0.61 and 3.00 ± 0.65, followed by a decrease in April (1.09 ± 0.39) with basal levels reached in May (0.1 ± 0.04). In the pregnant animals, P similarly started to rise in July to a first peak (3.55 ± 0.48) in August; values thereafter were between 2.08 ± 0.19 and 2.80 ± 0.27 until December. A second increase up to 4.81 ± 0.68 in January was observed in pregnant animals, which was of different magnitude from the nonpregnant animals. A gradual decrease from 4.45 ± 0.57 to 1.01 ± 0.44 occurred from March to May. Concentrations of E (mean pg/ml ± SEM) varied between 57 ± 7 and 107 ± 27 in the nonpregnant animals and were higher in the pregnant animals during the last 6 months of gestation. In a more intensive study of 2 nonpregnant animals (Exp. B), P exhibited a short elevation at the end of July and the beginning of August, followed by a continuous increase throughout the period examined (October). It is concluded that the corpus luteum remains active once it has formed, even in the nonpregnant animal, during the greater portion of the reproductive period. The data obtained also suggest that in the pregnant animal, placental P and E production commences at the time of placental attachment in January.
Excerpt
The roe deer, Capreolus capreolus, is the only artiodactyle known to exhibit delayed implantation (Short & Hay, 1966). In Great Britain, mating normally occurs between late July and mid-August and after fertilization development proceeds to the blastocyst stage before growth is arrested (Prell, 1938). Blastocysts remain free in the uterine lumen for about 5 months from August until early January before growth is resumed, implantation occurs and development proceeds normally. The majority of kids are born between mid-May and mid-June, and twins are common.
In the roe, the long period of delayed implantation ends in early January very soon after the winter solstice (22nd December) when the days are just beginning to lengthen (Short & Hay, 1966). The change in photoperiod may, therefore, act as an environmental cue, causing changes in the reproductive system of the doe and resulting in the resumption of embryonic development. This seems probable
The results presented in this paper indicate that delayed implantation in the roe deer is due to a lack of certain factors which are needed to induce and support the process of embryonic growth. These factors are eventually supplied, in the first weeks of January, as a secretion emanating from the endometrial glands. This secretion contains uterine specific and serum proteins, about 20 free amino acids, protein bound glucose and galactose and, rather surprisingly, a free ketose which appears to be fructose. Elongation of the roe deer blastocyst is also correlated with a rise in the concentration of plasma estrogens, an endocrine change that may stimulate the endometrial glands into secretory activity. However, since simultaneous changes were not observed in the ovaries, the elevated estrogen levels may be a consequence rather than a cause of embryonic growth.
The relationship between the corpus luteum and the uterus in terms of the secretion of oxytocin and PGF2 alpha was investigated in free-living and captive roe deer Capreolus capreolus. During the breeding season the corpus luteum contained oxytocin and oxytocin-neurophysin mRNA, and secreted oxytocin in response to administration of the PGF2 alpha analogue cloprostenol. The oxytocin receptor was present in the uterus during the bleeding season and during delayed implantation; however, in contrast to the situation observed in other ruminants in which it has been studied, administered oxytocin did not stimulate uterine secretion of PGF2 alpha. Trophoblast interferon was undetectable at any stage of conceptus development. The absence of the mechanism underlying episodic uterine secretion of PGF2 alpha during luteolysis, which may account for the monoestry of roe deer, is consistent with the previously observed luteolytic effect of the PGF2 alpha analogue.
Embryonic diapause, or delayed implantation as it is sometimes known, is said to occur when the conceptus enters a state of suspended animation at the blastocyst stage of development. Blastocysts may either cease cell division so that their size and cell numbers remain constant, or undergo a period of very slow growth with minimal cell division and expansion. Diapause has independently evolved on many occasions. There are almost 100 mammals in seven different mammalian orders that undergo diapause. In some groups, such as rodents, kangaroos, and mustelids, it is widespread, whereas others such as the Artiodactyla have only a single representative (the roe deer). In each family the characteristics of diapause differ, and the specific controls vary widely from lactational to seasonal, from estrogen to progesterone, or from photoperiod to nutritional. Prolactin is a key hormone controlling the endocrine milieu of diapause in many species, but paradoxically it may act either to stimulate or inhibit growth and activity of the corpus luteum. Whatever the species-specific mechanisms, the ecological result of diapause is one of synchronization: It effectively lengthens the active gestation period, which allows mating to occur and young to be born at times of the year optimal for that species.