Structural features of the epididymis in a dasyurid marsupial (Antechinus stuartii)

Summary The ductus epididymidis of the marsupial mouse Antechinus stuartii was divided into caput, corpus, and caudal regions using several constant morphological landmarks. Tubule diameter and epithelial height increased gradually from caput to cauda. In contrast, the surface area of the lumen of the ductus epididymidis increased to a maximum in the distal caput region, but decreased markedly in the distal cauda in association with characteristic changes in lumen shape (from circular to slit-shaped) and epithelial height. Epithelial cells of the ductus epididymidis were generally similar in structure to those described in other mammalian species. Principal and basal cells were common throughout the epithelium. Clear and mitochondria-rich cells were also identified, but occurred less frequently. Regional variations in cell ultrastructure were observed only in principal cells. Numerous vesicular inclusions occurred in the apical cytoplasm of cells in caput segments, membrane-bounded, electron-dense bodies were common in distal corpus regions, and a brush border of microvilli characterized the luminal surface of principal cells in caudal segments. Sperm index increased in the proximal caput, declined to basal levels in the distal caput and proximal corpus, and then increased to a maximum in segment 9 of the distal corpus and remained at about this level throughout the cauda epididymidis. Nuclear rotation, loss of cytoplasmic droplets, and other sperm maturational changes were observed along the epididymis. Discarded cytoplasmic droplets collected in large masses interspersed between aggregates of spermatozoa throughout the distal regions of the duct. There was no evidence of phagocytosis by principal cells of cytoplasmic droplets. The epididymis of A. stuartii differs from that of other mammals. The unusual caudal region, which has little storage capacity for sperm, is an unusual adaptation in a species in which the male is known to be polygamous.     

X chromosome inactivation in female embryos of a marsupial mouse (Antechinus stuartii)

Blastocysts and late gestation stages of the marsupial mouse, Antechinus stuartii, were examined cytologically and electrophoretically to investigate X chromosome activity during embryogenesis. A late replicating X chromosome was identified in the protoderm cells of female unilaminar blastocysts and in the cells of embryonic and extra-embryonic regions of older blastocysts. Sex chromatin bodies were also observed in female bilaminar and trilaminar blastocysts. The X linked enzyme -galactosidase showed no evidence of paternal allele expression in the extra-embryonic region of bilaminar blastocysts or in the yolk sac and embryonic tissue of known heterozygotes. It is concluded that the late replicating X chromosome is paternal in origin and that unlike the laboratory mouse, X inactivation is not correlated with cell differentiation in Antechinus.     

The role of photoperiod in the timing of reproduction in the Dasyurid Marsupial Antechinus stuartii

Summary Antechinus stuartii has one highly synchronized mating period which occurs at the same time each year. An analysis of the time of reproduction in 162 populations of A. stuartii shows that the onset of the mating period is correlated with the rate of change of photoperiod, rather than with critical photoperiodic length. The rate of change of photoperiod is different for two designated forms of this species and can be used as a predictor of these animals' reproductive timing. A rate of change model further explains the rigid and highly sunchronized nature of the mating period and, by providing a mechanism for reproductive isolation, offers an explanation for the evolution of the two forms of this species.     

Phase delay of the natural photoperiod alters reproductive timing in the marsupial Antechinus stuartii

The dasyurid marsupial Antechinus stuartii (20–40 g) has a brief, highly synchronized mating period in spring followed by complete male mortality. Analysis of breeding times in nature suggests that the rate of change of photoperiod is the main Zeitgeber for reproductive timing in this species. To test this hypothesis the natural photoperiod was phase delayed by two months, one experiment beginning in late summer, and the other in the autumn, before the spring breeding period.
The reproductive cycle of males and females exposed to the delay in summer was synchronously delayed by two months, coincident with the exact duration of the delay. Animals exposed to the two month phase delay in autumn also exhibited a delay in reproductive timing, but it was less synchronized than either the control or the other experimental group. Reproduction in control animals exposed to natural photoperiod was synchronous with that of a wild population monitored simultaneously. It is therefore likely that the rate of change of photoperiod is the dominant Zeitgeber for the reproductive cycle in this species.     

Relationship between longevity of spermatozoa after insemination and the percentage of normal embryos in brown marsupial mice (Antechinus stuartii)

Twenty-six female brown marsupial mice in a laboratory colony were mated at intervals ranging from 1 to 20 days between coitus and ovulation. The numbers of corpora lutea and normal embryos were counted. A multiple regression model examined the parabolic relationship between the proportion of normal embryos and the time from coitus to ovulation. The proportion of normal embryos increased until a mean of 9.5 days and decreased thereafter. This relationship was independent of the year of breeding and the number of corpora lutea. After survival of spermatozoa for up to 13 days in the female reproductive tract, the fertility levels of females was 88-92%. Low fertility levels after 13 days appeared to be due to a decrease in the number of spermatozoa. Reproductive tracts from 7 females killed after insemination and examined histologically showed many spermatozoa in the isthmus of the oviduct and the uterus at 5 days post coitum; spermatozoa confined to the isthmus between 6 and 13 days; and few spermatozoa in the isthmus at 14 days after copulation. A comparison between the fertility levels in the females which had been inseminated once and a further 17 females which had been inseminated 2 or 3 times suggested that spermatozoa from 2nd and 3rd inseminations can contribute spermatozoa for fertilization. In these females fertility levels did not decline with time after the first mating.     

Demographic responses of Antechinus stuartii (Marsupialia) to supplementary food

This study investigates the effects of supplementary feeding on populations of Antechinus stuartii, an insectivorous, semi-arboreal species of dasyurid marsupial. Animals were live-trapped, marked and released in three study areas in forest near Canberra, from September 1980 to November 1981. Supplementary food was supplied above ground in trees in one study area from January to November 1981, and in the second study area from January to May 1981, while the third study area was left unmanipulated as a control. The supplemented populations increased in numbers, mean body weights and survival, and showed decreased movements between traps and smaller overlaps in home ranges. Discontinuation of food in the second study area in May 1981 produced reciprocal shifts in these parameters. Reproduction, home-range area, mean head-body length, use of the terrestrial and arboreal parts of the habitat were largely unaffected by provision of supplementary food. In contrast to rodents, where fed populations usually increase rapidly due to immigration or increased reproduction, the supplemented populations of A. stuartii responded relatively slowly via increased survival of young. Population responses were probably retarded at the beginning of the experiments in summer due to the abundance of natural invertebrate prey, but became more obvious in winter when natural food was scarce. The added food probably contributed directly to increased numbers, survival and body weights, but may also have enhanced these parameters indirectly by allowing foraging animals to space out and avoid intraspecific intolerant contacts. These responses in A. stuartii suggest strongly that populations are limited by the food supply.     

Size breeds success: multiple paternity, multivariate selection and male semelparity in a small marsupial, Antechinus stuartii

Mating in the marsupial genus Antechinus is a synchronous annual event that is characterized by monoestry in females and abrupt postmating mortality in males. Male semelparity (multiple copulations during a single breeding season per lifetime) is often assumed to occur as a consequence of the intense mating effort expended by males in the rut, but the forces selecting for this remain elusive. Here, we investigate selection in male brown antechinus, Antechinus stuartii, and test two hypotheses for the evolution of semelparity: intermale competition and sperm competition. If intermale competition drives semelparity, we predicted that males would be under strong selection for large body size. If sperm competition is important, we predicted that selection would be strongest on scrotal size, a surrogate for testes volume. Using microsatellite markers, we found that 92% of females in free-living conditions mated with multiple males, producing litters of eight that had up to four fathers. These observations confirm the potential for sperm competition. Using selection analysis, we then found paternity success in 119 males to be related most strongly to body mass and scrotal size, thus providing support for both hypotheses. Large males presumably experience increased paternity success by gaining more matings or prolonged copulations via mate guarding, while large testes may allow increased sperm investment per copulation. Increased levels of free corticosteroid hormones in males facilitate the extreme mating effort during the short period of rut, but lead to immune suppression and consequently to the phenomenon of postmating mortality.     

Social and foraging components of the home range in Antechinus stuartii (Dasyuridae: Marsupialia)

The home range of Antechinus stuartii has two components. A small area (0.94 ha for males, 0.38 ha for females) is used for foraging, while a much greater social range (mean for males in a given year may exeed 5 ha; the mean for females never exceeded 3 ha) encompasses communal nests, which are used by both males and females. The foraging range of females is stable throughout the year. The foraging range may not coincide at all, or only partially coincide with her social range. By contrast, male foraging ranges drift through the year, and generally lie within their social range. Intersexual differences reflect the different selection pressures on the sexes. Females require access to resources to sustain a costly lactation, while males require a knowledge of many possible sites for mating and early resolution of agonistic interactions with other males with which they cohabit during mating.     

Seasonal changes in glomerular filtration rate in Antechinus stuartii (Marsupialia: Dasyuridae)

The small marsupial Antechinus stuartii experiences a synchronised life cycle that culminates in complete male mortality (within 3 weeks) following the 1 week mating period in mid-August (late winter). There are pronounced physiological changes in male A. stuartii over the life cycle and renal function was assessed for correlation with these changes. Glomerular filtration rate and urine and plasma electrolytes were determined in male and female A. stuartii in February, May, July and August. Females showed little change in glomerular filtration rate, except for pre-mating values in August which decreased. In contrast, glomerular filtration rate of males decreased significantly in July and August. Plasma sodium and chloride levels were higher in males than females and were higher in animals in July and August than in February and May. Plasma potassium levels dropped in both males and females in July and August. Plasma osmolality was higher in animals in February compared to animals from May and August. However, there were no significant sex or seasonal differences in urine electrolytes, although urea concentration was higher in females than males. Urine osmolality was higher in both sexes in July and August. There were no significant differences in total excretory rates of sodium, potassium or chloride between sexes or between seasons. Many of the alterations in renal function are correlated with known physiological and hormonal profiles in A. stuartii. This is the first observation of seasonal changes in glomerular filtration rate that are unrelated to dietary and water stresses. Accepted: 8 September 1997     

Seasonal changes in the reproductive anatomy of male Antechinus stuartii (Marsupialia: Dasyuridae)

Male Antechinus stuartii (Marsupialia: Dasyuridae) undergo significant endocrinological changes during their life history. The endocrine changes are associated with complete male mortality. The accessory reproductive tract of males is important for seminal plasma production, and changes associated with the reproductive cycle were not described in detail by earlier studies. The present study sought to describe some of the seasonal changes in structure of the male accessory reproductive tract in relation to the known hormonal changes. The epididymis, prostate, and bulbourethral glands are relatively undifferentiated in February and May, a time when plasma concentrations of testosterone are known to be low. By July, considerable hypertrophy and differentiation of the accessory reproductive tract are observed. This is most obvious in the bulbourethral glands, which change from being indistinguishable from one another in February and May to being three large morphologically and histologically distinct glands in July. The hypertrophy and secretory activity continue into August, the breeding season. These findings correlate with the hormonal profiles found in other studies of A. stuartii. J Morphol 231:261–275, 1997. © 1997 Wiley-Liss, Inc.     

Phenotype and gene flow in a marsupial (Antechinus flavipes) in contrasting habitats

Ecological factors are important drivers of phenotypic divergence, which may lead to incipient speciation. A variety of habitats should be preserved to maintain evolutionary potential. We used the marsupial, the yellow-footed antechinus ( Antechinus flavipes ) as a model species for investigating phenotypic differentiation between animals inhabiting two habitat types in south-eastern Australia: flood-plain river red gum and box–ironbark forests. All tested phenotypic characteristics varied between years at the same sites and therefore were not useful for investigating morphological specialization that may lead to speciation. Males generally were significantly heavier when antechinus densities were lower, but exceptions were found, possibly related to food availability. Teat-number variation recently has been shown to be associated with habitat specialization and incipient speciation within Antechinus agilis . We investigated genetic differentiation associated with this trait in A. flavipes . Population genetic analyses of microsatellite genotypes and mitochondrial DNA haplotypes revealed that sympatric 12-, 13- and 14-teat females in Chiltern forest were part of one freely interbreeding population. Our parentage analyses found two cases where 13-teat mothers produced 12-teat daughters. This suggests either plasticity or paternal genetic influence on the offspring's teat-number phenotype. Laboratory matings may be required to resolve the extent to which teat number is heritable in A. flavipes .  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 303–314.     

The effects of cortisol and testosterone on renal function in male Antechinus stuartii (Marsupialia)

Seasonal changes in the physiology of Antechinus stuartii result in complete male mortality after mating. The most important endocrine changes in males are large rises in plasma testosterone and cortisol concentrations. Glomerular filtration rate (GFR) in males declines coincident with high plasma testosterone and cortisol. In the present study GFRs were measured in males captured in May (when endogenous plasma testosterone and cortisol levels are low) and given depot injections of either saline, testosterone-only, cortisol-only or testosterone plus cortisol at doses designed to mimic plasma levels during the mating period. GFR decreased significantly with testosterone injection, independent of cortisol treatment. Urinary concentrations of sodium and chloride, and osmolality decreased significantly with cortisol treatment, although the addition of testosterone reversed the effect. Total urinary excretion of electrolytes was similar between groups. Plasma potassium levels significantly increased in testosterone plus cortisol treated males. Plasma sodium levels significantly increased and plasma chloride significantly decreased in all groups treated with cortisol. Water consumption significantly increased in all cortisol-treated males and food consumption significantly increased in all testosterone-treated males. The seasonal renal functional changes observed in A. stuartii were mimicked by testosterone administration. Accepted: 23 January 1998     

Acuariid, capillariid and hymenolepidid parasites of the dasyurid marsupial Antechinus stuartii Macleay, 1841, from southeastern Australia.

Stammerinema suffodiax sp. n. is described from the dasyurid marsupial Antechinus stuartii. It differs from S. soricis, the only other member of the genus, in lacking lateral body spines, as well as in the spicules and characters of the anterior extremity. As well as redescribing Synhimantus australiensis (Johnston and Mawson, 1952) now collected from the stomach of A. stuartii, a new capillariid, Capillaria rickardi from the stomach and two cestodes Hymenolepis aklei sp. n. and H. bradleyi sp. n. are described from the same host.     

Effects of breeding season and mating on total number and distribution of spermatozoa in the epididymis of the brown marsupial mouse, Antechinus stuartii

Changes in the number and distribution of spermatozoa in the epididymis of the adult brown marsupial mouse were examined during July/August in mated and unmated males. The effects of mating on epididymal sperm populations were studied in 2 groups of males each mated 3 times and compared with the number and distribution of spermatozoa in the epididymides of 4 unmated control groups. One testis and epididymis were removed from each animal (hemicastration) either before or early in the mating season to provide information on initial sperm content and distribution. The contralateral side was removed later in the mating season to examine the effects of mating or sexual abstinence on epididymal sperm distribution. Epididymal sperm number peaked in both the distal caput and distal corpus/proximal cauda epididymidis in late July. The total number of spermatozoa, including those remaining in the testis, available to each male at the beginning of the mating season in early August was approximately 4.4 x 10(6)/side. Although recruitment of spermatozoa into the epididymis from the testis continued until mid-August, sperm content of the epididymis reached a peak of about 3.5 x 10(6)/epididymis in early August. At this time approximately 0.9 x 10(6) spermatozoa remained in the testis which had ceased spermatogenic activity. Throughout the mating season, epididymal spermatozoa were concentrated in the distal corpus/proximal cauda regions of the epididymis and were replenished by spermatozoa from upper regions of the duct. Relatively few spermatozoa were found in the distal cauda epididymidis, confirming a low sperm storage capacity in this region. A constant loss of spermatozoa from the epididymis, probably via spermatorrhoea, occurred throughout the mating season and very few spermatozoa remained in unmated males in late August before the annual male die-off. Mating studies showed that an average of 0.23 x 10(6) spermatozoa/epididymis were delivered per mating in this species, but the number of spermatozoa released at each ejaculation may be as few as 0.04 x 10(6)/epididymis when sperm loss via spermatorrhoea is taken into account. We suggest that the unusual structure of the cauda epididymidis, which has a very restricted sperm storage capacity, may function to limit the numbers of spermatozoa available at each ejaculation and thus conserve the dwindling epididymal sperm reserves in order to maximize the number of successful matings which are possible during the mating season.