Changes in the motility patterns of spermatozoa from the rabbit epididymis as assessed by computer-aided sperm motion analysis

Sperm maturation in the epididymis includes changes in their potential for motility that enables spermatozoa to reach the egg and penetrate its investments. The motility characteristics of spermatozoa from the testis, the epididymis, and vas deferens of the rabbit were investigated by computer-assisted sperm analysis (CASA). Various forms of motility were displayed by sperm from different regions of the epididymis released into incubation medium Testicular sperm were motile, although nonprogressive. The maximum percentage motility was expressed by sperm in the proximal cauda epididymidis, and forward progression was developed by spermatozoa from the distal caput. Once forward progression was established, the curvilinear velocity was about the same for sperm from all regions of the tract, whereas straight-line velocity increased between the mid-corpus and cauda and paralleled the decline in lateral displacement of the head. The maintenance of motility in vitro was best maintained by sperm from the distal regions of the tract although sperm from the distal caput maintained motility better than sperm from the proximal and midcorpus regions. Analysis of the motile sperm cells revealed several types of trajectories (“irregular,” “small circular,” “large circular and arcs,” “jagged” and “straight-line”) that were analyzed by discriminant analysis using the variables generated by CASA. Accuracy of classification varied from 70% to 96%, depending on the type of track. The classification function was then applied to the changes that occurred during incubation and showed that irregular trajectories gave way to small and then large circular tracks and progressive forms as sperm matured. © 1996 Wiley-Liss, Inc.     

Dying like rabbits: general determinants of spatio-temporal variability in survival

1. Identifying general patterns of how and why survival rates vary across space and time is necessary to truly understand population dynamics of a species. However, this is not an easy task given the complexity and interactions of processes involved, and the interpopulation differences in main survival determinants. 2. Here, using European rabbits (Oryctolagus cuniculus) as a model and information from local studies, we investigated whether we could make inferences about trends and drivers of survival of a species that are generalizable to large spatio-temporal scales. To do this, we first focused on overall survival and then examined cause-specific mortalities, mainly predation and diseases, which may lead to those patterns. 3. Our results show that within the large-scale variability in rabbit survival, there exist general patterns that are explained by the integration of factors previously known to be important at the local level (i.e. age, climate, diseases, predation or density dependence). We found that both inter- and intrastudy survival rates increased in magnitude and decreased in variability as rabbits grow old, although this tendency was less pronounced in populations with epidemic diseases. Some causes leading to these higher mortalities in young rabbits could be the stronger effect of rainfall at those ages, as well as, other death sources like malnutrition or infanticide. 4. Predation is also greater for newborns and juveniles, especially in population without diseases. Apart from the effect of diseases, predation patterns also depended on factors, such as, density, season, and type and density of predators. Finally, we observed that infectious diseases also showed general relationships with climate, breeding (i.e. new susceptible rabbits) and age, although the association type varied between myxomatosis and rabbit haemorrhagic disease. 5. In conclusion, large-scale patterns of spatio-temporal variability in rabbit survival emerge from the combination of different factors that interrelate both directly and through density dependence. This highlights the importance of performing more comprehensive studies to reveal combined effects and complex relationships that help us to better understand the mechanisms underlying population dynamics.     

Temporal and spatial patterns of annelid populations in intertidal sediments of the Quequén Grande estuary (Argentina)

Temporal and spatial patterns of polychaete and oligochaete populations inhabiting intertidal sediments of the Quequén Grande estuary (Buenos Aires Province, Argentina) were analysed monthly during a yearly period. Local sediments are poorly selected, very fine sands, with a high percentage of mud. Two sites, located at both banks of the estuary were studied: (1) Site N, with a comparatively steep slope and percentage of mud increasing with sediment depth; (2) Site Q, with a gentle slope and percentage of mud increasing towards the sediment surface. The assemblage of annelids was characterised by a very low specific richness, being composed just by 4 species: the polychaetes Laeonereis acuta, Boccardiella ligerica and Capitella sp., and the tubificid oligochaete Ilyodrilus cf. frantzi. Density of the nereid L. acuta reached a peak in late summer and a minimum in spring. The population of Capitella sp. also showed maximum densities in summer, but collapsed during early fall, disappearing completely from the study area. Densities of I. cf. frantzi were highly variable in time and space. Three of the 4 species showed maximum densities at site Q, where mud content was highest at the sediment surface. At this sampling site, most of the L. acuta population occurred within the upper 8 cm of the substrate. On the contrary, at site N, where mud and organic matter content increased with depth, this species was more abundant at subsurface layers (8–16 cm) than at the sediment surface.     

Sperm morphological abnormalities appearing in the male rabbit reproductive tract

The role of the excurrent duct system in producing and/or eliminating morphologically abnormal spermatozoa may modify the semen parameters and interfere with sperm fertilizing capacity. To study this process, changes in the morphology of spermatozoa during their transit through the reproductive tract in sexually mature rabbits were investigated. The incidence of head, midpiece and tail abnormalities as well as of multiple defects in a single spermatozoon, and the position of the cytoplasmic droplet along the sperm midpiece were evaluated in samples from the testis, 6 regions of the epididymis and the vas deferens. Spermatozoa were characterized by rapid migration of the cytoplasmic droplet when passing from the proximal to the distal caput of the epididymis, and spermatozoa with no droplet predominated in the distal epididymis and vas deferens. In passing from the testis to the proximal caput of the epididymis, the incidence of spermatozoa with an abnormal midpiece and those with multiple defects decreased significantly. The proportion of spermatozoa with abnormal heads was also lower in the testis, but no statistically significant differences were found, whereas there was no change in the proportion of those with abnormal tails. These results indicate that there must be a mechanism for the disposal of defective spermatozoa. No evidence of spermiophagy by luminal macrophages was observed in the extracts, although a few spermatozoa exhibited signs of degeneration, suggesting, that although intraepithelial phagocytosis has not been clearly demonstrated in the nonexperimental rabbit, sperm cells may undergo a form of autolysis within the lumen of the duct.     

Happy to breed in the city? Urban food resources limit reproductive output in Western Jackdaws

Urban areas expand worldwide, transforming landscapes and creating new challenging habitats. Some bird species, mainly omnivorous feeding on human waste and cavity nesters, commonly breed in these habitats and are, therefore, regarded as urban‐adapted. Although urban areas may provide new nesting sites and abundant human waste, the low breeding success found in some of these species suggests that the poor protein content in human waste might limit breeding parameters. We investigated whether the breeding success of a cavity nester and omnivorous species commonly breeding in urban areas, the Western Jackdaw (Corvus monedula), depended on the availability of good‐quality non‐urban food. We approached the objective by combining a literature review and experiments in the field. With the literature review, we compared jackdaw populations in different habitats across Europe and found that clutch size and number of fledglings per pair decreased with distance to non‐urban foraging grounds, even after controlling for the effect of colony size, latitude, and climate. In two experiments, we tested whether the breeding success of urban pairs could be increased by supplementing high‐quality food, first only during egg formation and second also until chick fledging. Food supplementation during egg formation led to larger eggs and higher hatching success than in urban control nests, but this did not result in higher chick survival. However, when food supplementation was prolonged until fledging in the second experiment, we observed a significant increase of nestling survival. These findings highlight that research and management actions should not only focus on species displaced by urbanization, but also on “urban‐adapted” species, as they might be suffering from a mismatch between availability of nesting sites in buildings and adequate non‐urban food resources. In these cases, nest sites should be provided in or close to adequate food resources.     

Testing the threat-sensitive predator avoidance hypothesis: physiological responses and predator pressure in wild rabbits

Predation is a strong selective force with both direct and indirect effects on an animal’s fitness. In order to increase the chances of survival, animals have developed different antipredator strategies. However, these strategies have associated costs, so animals should assess their actual risk of predation and shape their antipredator effort accordingly. Under a stressful situation, such as the presence of predators, animals display a physiological stress response that might be proportional to the risk perceived. We tested this hypothesis in wild European rabbits (Oryctolagus cuniculus), subjected to different predator pressures, in Doñana National Park (Spain). We measured the concentrations of fecal corticosterone metabolites (FCM) in 20 rabbit populations. By means of track censuses we obtained indexes of mammalian predator presence for each rabbit population. Other factors that could modify the physiological stress response, such as breeding status, food availability and rabbit density, were also considered. Model selection based on information theory showed that predator pressure was the main factor triggering the glucocorticoid release and that the physiological stress response was positively correlated with the indexes of the presence of mammalian carnivore predators. Other factors, such as food availability and density of rabbits, were considerably less important. We conclude that rabbits are able to assess their actual risk of predation and show a threat-sensitive physiological response.     

Computer assisted morphometric analysis of ram sperm heads: evaluation of different fixative techniques

The recent development of automated systems for morphometric sperm head analysis has provided a series of objective parameters which have facilitated the standardization of morphological semen evaluation. This current work attempts to establish the optimum fixing conditions for the morphometric characterization of ram spermatozoa. Ejaculates were obtained from 5 Merino rams used for periodic collection of semen and were diluted at 1:50 with TEST medium. Air-dried smears were fixed either in ethanol-ether (1:1), 50% methanol, 2% glutaraldehyde or SUZA fixative, in which case the smear was pretreated with chloramine. The samples were then stained with commercial kit Hemacolor. Once the preparations had been mounted, they were analyzed with the Sperm Class Analyzer automatic sperm morphometry analysis system (ASMA). The minimum number of sperm cells analyzed per sample was 100. The parameters evaluated were the area, perimeter, length, width, shape factor and mass. The results showed significant differences in sperm head dimensions between the 4 fixation techniques, with the lowest values for all parameters corresponding to the SUZA fixative, followed by glutaraldehyde, methanol, and finally ethanol-ether. In addition, there were significant variations between animals. It can, therefore, be concluded that the working protocol must be defined when performing morphometric analysis of ram semen and that the results obtained under different conditions of fixation cannot be entirely extrapolated. Equally, the high variability among individuals suggests that, in a species like the ram with a low index of teratozoospermia, there is a need for a revision of the classic definition of normality, which should include morphometric data.     

Quantitative changes in sperm head morphology during passage through the male excurrent duct system of the rabbit

A fine adjustment of sperm head size and shape occurs during maturation and storage within the male excurrent duct of the rabbit. This remodelling, as judged by morphometric values of area, perimeter, length, width, and shape factors, takes place mostly in passage from the seminiferous tubules of the testis to the distal caput of the epididymis. The dimensions of sperm heads from the distal corpus of the epididymis break the general tendency toward a reduction in size and more elliptical shapes. A period of transport and storage within the epididymal cauda and vas deferens follows in which there are no further changes in sperm head morphometry. It can be concluded that the period immediately following sperm release from the testis is crucial to the final morphological maturation of spermatozoa. Moreover, the fact that changes are detected in the appearance of sperm heads at successive stages of sperm maturation suggests that the dimensions of a particular epididymal spermatozoon may be taken as an approximate indication of its relative maturity. Mol. Reprod. Dev. 51:203–209, 1998. © 1998 Wiley-Liss, Inc.     

Development of mouse testis and epididymis following intrauterine exposure to a static magnetic field

In order to test if the in utero exposure to static magnetic fields affects testis and epididymis development in mice, females were exposed to 0.5-0.7 T, generated by a permanent magnet, from day 7 of gestation to the day of birth. No significant differences were found between exposed and sham-exposed animals with respect to body weight gain of dam during the gestational period, litter size, body weight of male pups at the day of birth, and body or testis-epididymis weight gain of pups from birth to day 35. Histopathologic evaluation of testis and epididymis of pups of 1, 5, 15, and 35 days of age showed no detectable alterations due to in utero exposure to static magnetic fields.     

Spatial pattern in a low-density population of the barnacle Balanus amphitrite Darwin

The spatial distribution of an intertidal population of the barnacleBalanus amphitrite was studied close to a sewage outfall nearQuequén, Argentina (38° 34S,58° 38 30 W). All individuals within an areaof 0.8 m² were mapped during 12 censuses, from September 1990to May 1993. Population density within the study area varied between 401 and99 ind m^-2. Spatial pattern was analysed using mean distancesto the nearest neighbour (NND), goodness of fit tests between observed andexpected frequency distributions of NND, and analysis of crowding. Thespatial pattern of the population was clumped during most of the studyperiod. This trend persisted, although not reaching statisticalsignificance, when the population density decreased as a consequence ofmortality and failure of successive annual recruitments. The cohortrecruited in summer 1992 (49 individuals) was randomly distributed relativeto adult barnacles already present within the study area. No consistentrelationship was observed between mortality and NND.