The Reproductive Biology and Behaviour of Captive Female Matschie's Tree Kangaroos Dendrolagus matschiei.
PhD Thesis, University of Washington, Seattle, Washington.
All species of tree kangaroos (Dendrolagus spp.) are considered vulnerable or threatened in the wild. Their numbers have been reported to be adversely affected by hunting and habitat destruction in Australia and New Guinea (Martin 1992, Hutchins & Smith 1990, Kennedy 1986, Pernetta & Hill 1986). In captivity, breeding has not sustained viable populations for most species and the reproductive rates of all species are below their potential (Steenberg & Smith 1990). One reason for problems in captive management is a lack of knowledge about Dendrolagus reproductive biology. This genus differs morphologically and behaviorally from the more well known terrestrial kangaroo species.The present study documented both the physiological and behavioral aspects of estrous cycles of captive Dendrolagus matschiei females. The estrous cycle-length data based on steroid hormones were obtained from radioimmunoassay measurements of estrogen and progestin concentrations from fecal samples. This was the first quantitative fecal steroid analysis study on a marsupial species. Behavioral correlates of estrus were measured through focal animal observations. From both of these data sets, hypotheses were tested addressing how this genus fits into the general pattern of marsupial reproduction.The mean ($\pm$ one standard deviation) length of the estrous cycles for captive D. matschiei was 56.83 $\pm$ 3.12 days (n = 6) based on fecal estrogen profiles and 54.17 $\pm$ 5.74 (n = 6) based on fecal progestin profiles. For two of the females, reproductive behaviors occurred at approximately the calculated time of estrus, giving further support to the duration of estrous cycles. Several behavioral indicators of estrus were documented. Two other general patterns emerged from the hormone profiles of the female D. matschiei: (1) A spike of estrogen around the time of ovulation and (2) a rise in progestin after the estrogen peak. D. matschiei seems to have a similar reproductive cycle with several notable differences to those of other known macropodids. The D. matschiei estrous cycle is longer than all other known macropod cycles by at least 10 days. The gestation length of 44.2 days for D. matschiei (Heath et al. 1990) is also longer than any other known macropodid species by at least 6 days. Life history data obtained from captive tree kangaroo historical records showed that D. matschiei has an extended age of female sexual maturity which is later than other macropodids, and that D. matschiei has a reduced fecundity rate. The reason for these differences could be based on D. matschiei's ecological niche. It is an arboreal folivore with a relatively low metabolic rate (McNab 1978) which could result in an overall slower reproductive output.
Biotechnologische Möglichkeiten zur Beeinflussung des Nachkommengeschlechts bei Nashorn und Elefant.
The biotechnological potential for manipulating offspring sex in the rhinoceros and the elephant.
Dr. med. ved. Dissertation
Leibniz-Institut für Zoo- und Wildtierforschung (IZW) im Forschungsverbund Berlin e.V.
Leitung: Dr. Robert Hermes
Zoo Hannover und Taronga Zoo (Australien)
All extant rhinoceros and elephant species are endangered in the wild; yet urgently needed captive breeding to stabilise world populations of some species turns out to be a substantial challenge. One key issue in captive breeding is the unwanted high proportion of male offspring, a serious problem particularly in very small populations. If manipulating offspring sex was a feasible, successful and safe option, a higher number of females could be produced. This would accelerate population growth, thereby significantly improving the viability of populations and thus the conservation of these impressive animals. The ability to select sex would be especially useful in species close to extinction such as the northern white rhinoceros (Ceratotherium simum cottoni) with only two remaining female breeding candidates, worldwide. To date, the only reliable method to select offspring sex is the Beltsville sperm-sorting technology in combination with artificial insemination (AI) or in vitro fertilisation (IVF). This technique is based on flow cytometric separation of X and Ychromosome bearing spermatozoa in relation to their DNA content.
The aim of this study was to determine the feasibility of spermatozoa from elephants and rhinoceroses for flow cytometrical sex-sorting and to conduct basic investigations on sperm sex-sorting in these megaherbivores by exploring and establishing species-specific sorting conditions. First, the theoretical sortability of the spermatozoa was established through determination of the sperm sorting index (SSI). This index is calculated by multiplying the difference in relative DNA content between X and Y- chromosome bearing spermatozoa (as calculated by the flow cytometer) with the profile area of the sperm head. The resulting SSI values indicated that spermatozoa from the African savannah elephant (Loxodonta africana) deliver best preconditions for successful sex-sorting in the flow cytometer, followed by those of the Asian elephant (Elephas maximus). The general sortability of spermatozoa from the examined rhinoceros species [black (Diceros bicornis), white (Ceratotherium simum) and Indian rhino (Rhinoceros unicornis] was shown to be very similar among each other and lower when compared to the elephant species or to livestock.
Second, basic parameters for flow cytometric sex-sorting of spermatozoa from the black and the white rhinoceros and the Asian elephant were determined. Species-specific semen extenders, suitable for sex-sorting, and an appropriate DNA staining protocol (suitable amount of stain, incubation time and temperature) were developed. Sperm sex-sorting of rhinoceros spermatozoa thereby turned out to be challenging. Using the methods developed here, successful sex-sorting spermatozoa into specific X and Y- chromosome bearing populations produced high purity (94 %) but the sperm quality after sorting (sperm integrity: 42.0 ± 5.4 %; sperm motility: 11.5 ± 6.1 %) and the sorting efficiency (300 – 700 sperm/s) are still low. The high viscosity of rhinoceros ejaculates strongly interferes with DNA staining and sorting. The main component of the viscous fraction, a glycosilated protein with a molecular weight of 250 kDa molecular weight (most likely originating from the bulbourethral gland), was characterised via gel electophoresis and mass spectrometry. Investigating the liquefaction of the seminal plasma, the addition of the enzymes α-amylase and collagenase was shown to significantly decrease the viscosity without affecting sperm motility or integrity. In initial trials of enzyme addition to rhinoceros sperm samples that were too viscous for a processing by the flow cytometer, viscosity was reduced sufficiently enough to sort, indicating that enzyme treatment might allow better use of rhino ejaculates for sex-sorting.
The sex-sorting protocol developed for the Asian elephant provided very good results for post-sorting sperm quality (sperm integrity: 64.8 ± 3.2 %; motility: 70.8 ± 4.4 %) and purity (94.5 ± 0.7 %) and a reasonable sorting efficiency (1,945.5 ± 187.5 sperm/s). A successful protocol for cryopreservation of Asian elephant spermatozoa was also developed (post-thaw sperm integrity: 52.0 ± 5.8 %) by optimising the cryopreservation protocol (sperm handling pre- and post-cryopreservation, composition of cryomedium) and employing the directional freezing technology. Best post-thaw sperm quality was achieved using a two-step dilution of freshly collected and centrifuged spermatozoa in Blottner’s Cryomedia (285 mOsmol/kg) containing 16 % of egg yolk and a final glycerol concentration of 7 % before freezing. Spermatozoa were slowly cooled to 4 – 5°C and cryop reserved in large volumes of 2.5 or 8 ml at a concentration of 150 x 106 sperm/ml.
In the Asian elephant, the results of these studies have already permitted the use of sexsorted spermatozoa for AI. The sorting protocol appears to be technically reliable. However, AI using sex-sorted Asian elephant sperm has not yet produced any gestation. Regarding all the rhinoceros species, the poor post-sort sperm motility and integrity as well as the sorting efficiency have not yet enabled the application of sex-sorted spermatozoa to be used for AI at present, but their use in IVF may still be feasible.
This is the first study to explore the potential of flow cytometric sex-sorting of spermatozoa from several species of rhinoceroses and elephants. In terms of its practical value, the developed protocols are ready to be applied in elephants, whereas in the rhinoceros species further research is likely to be required. The results demonstrate the potential of the developed techniques and provide a promising base for the future use of the technology in the conservation management of the endangered megaherbivores.
Parthenogenesis in Komodo dragons.
Nature 444, 1021-1022 (21 December 2006) | doi:10.1038/4441021a; Received 4 October 2006; Accepted 16 November 2006; Published online 21 December 2006.
Should males and females be kept together to avoid triggering virgin birth in these endangered reptiles?
Parthenogenesis, the production of offspring without fertilization by a male, is rare in vertebrate species, which usually reproduce after fusion of male and female gametes. Here we use genetic fingerprinting to identify parthenogenetic offspring produced by two female Komodo dragons (Varanus komodoensis) that had been kept at separate institutions and isolated from males; one of these females subsequently produced additional offspring sexually. This reproductive plasticity indicates that female Komodo dragons may switch between asexual and sexual reproduction, depending on the availability of a mate — a finding that has implications for the breeding of this threatened species in captivity. Most zoos keep only females, with males being moved between zoos for mating, but perhaps they should be kept together to avoid triggering parthenogenesis and thereby decreasing genetic diversity.
Daten zur Fortpflanzungsphysiologie des asiatischen Elefanten (Elephas maximus) im Zoologischen Garten Zürich.
Dr. med. vet. Disseration
Klinik für Andrologie und Gynäkologie, Veterinär-medizinische Fakultät der Universität Zürich
Referent: Prof. Dr. K. Zerobin, Korreferent: PD Dr. E. Isenbügel
Zusammenfassung: siehe hier
Summary: see here