The ecology of helminths in populations of small mammals

A review of field data indicates the ubiquitous occurrence of parasites in small mammal communities, with the heligmosome nematodes in many cases dominant members of the helminth fauna. The population dynamics of the heligmosomes are discussed in relation to the interpretation of patterns of infection observed in the field. Laboratory data are then used to indicate ways in which the parasites might reflect or influence the population biology of their hosts. The aim of the paper is to suggest the potential significance of parasitism for the ecology of small mammal populations.     

Effect of short-term removal of infant rats from the female on lactation.

Removal of the young for a single period of at least 12 hours at the age of 15 days led to a marked increase in 85Sr retention in the maternal organisms and to a decrease in its transfer to the young in the milk. Study of 85Sr transfer in the milk showed that, if the litter was completely changed on the 16th day after birth, the female immediately accepted foster young. Repeated removal of the young on the 14th day and 15th day of life for a length of time which had no effect in a single removal likewise led to a decrease in 85Sr transfer in the milk and to raise 85Sr retention in the female. The gradual decrease which occurs in lactation during the weaning period is probably caused by diminution of the suckling stimulus on the part of the young, as they lose their physical dependence on the female.     

Sympatric wolf and coyote populations of the western Great Lakes region are reproductively isolated

Interpretation of the genetic composition and taxonomic history of wolves in the western Great Lakes region (WGLR) of the United States has long been debated and has become more important to their conservation given the recent changes in their status under the Endangered Species Act. Currently, the two competing hypotheses on WGLR wolves are that they resulted from hybridization between (i) grey wolves (Canis lupus) and western coyotes (C. latrans) or (ii) between grey wolves and eastern wolves (C. lycaon). We performed a genetic analysis of sympatric wolves and coyotes from the region to assess the degree of reproductive isolation between them and to clarify the taxonomic status of WGLR wolves. Based on data from maternal, paternal and bi‐parental genetic markers, we demonstrate a clear genetic distinction between sympatric wolves and coyotes and conclude that they are reproductively isolated and that wolf–coyote hybridization in the WGLR is uncommon. The data reject the hypothesis that wolves in the WGLR derive from hybridization between grey wolves and western coyotes, and we conclude that the extant WGLR wolf population is derived from hybridization between grey wolves and eastern wolves. Grey‐eastern wolf hybrids (C. lupus × lycaon) comprise a substantial population that extends across Michigan, Wisconsin, Minnesota and western Ontario. These findings have important implications for the conservation and management of wolves in North America, specifically concerning the overestimation of grey wolf numbers in the United States and the need to address policies for hybrids.     

Gastrointestinal helminths and protozoa from two raccoon populations in Kansas

A survey in Kansas compared the prevalence of gastrointestinal helminths and protozoa in 2 raccoon (Procyon lotor) populations; a population in a typical rural setting and a relatively undisturbed population on a military reservation. Gastrointestinal tracts of 128 raccoons were examined. Freeze storage of alimentary tracts prevented collection of data on trematode prevalence. Helminth infections other than trematodes included 1 acanthocephalan, 2 cestodes, and 3 nematodes. Helminths were found in all raccoons from the population on the military installation and 96% of those from the rural population. Prevalence of helminths was generally greater in raccoons from the population living in the rural setting. Eimeria spp. and Sarcocystis sp. were also found, whereas Giardia spp. and Cryptosporidium parvum were not.     

The impact of short-term predator removal on vole dynamics in an arctic-alpine landscape

During 1991–95, mammalian predators (weasel, Mustela nivalis , stoat, M. erminea , mink, M. vison , and red fox, Vulpes vulpes ) were excluded in late summers from a 2 ha piece of a north Norwegian mountain slope. The exclosure extended from an outpost of luxuriant sub-arctic birch forest to a typical arctic–alpine habitat complex, including productive willow scrublands, tundra heaths, dry ridges and snow-beds. The exclosure thus encompassed the entire range of habitat conditions encountered in a typical north Fennoscandian mountain and tundra landscapes. During 1991–95, the exclosure was predator-proof from late July to late September. In wintertime and in early summer, the exclosure was accessible to mammalian predators. Vole dynamics in the short-term exclosure were compared to dynamics in five reference areas with similar habitat conditions.
In 1991, when vole densities were rising in the area, neither collective vole densities nor densities of individual vole species differed significantly between the exclosure and the replicated controls. Spring densities of voles were never significantly different between the exclosure and the controls. With respect to autumnal densities of voles, however, the exclosure was a statistical outlier in the peak year 1992 and throughout the gradual decline phase of 1993–95. In the peak year, the difference in collective vole densities was modest (30%), but increased to two-fold during the first two decline years and was almost four-fold in the crash year of 1995. The strongest response was displayed by field voles ( Microtus agrestis ), hypothesized to be the pivotal prey species of weasels, especially by females and young individuals, i.e. by the functional categories especially sensitive to mammalian predation. These results are consistent with the hypothesis that predation plays a pivotal role for the regulation of herbivorous mammals in relatively productive arctic–alpine habitats.     

Differential vulnerability of lambs to coyote predation

Coyote-lamb interactions in 65-ha pastures were observed during a study of Komondor dogs guarding sheep. Vulnerability of lambs to coyote predation was related to total time lambs were exposed to coyotes in the enclosures and total time present in the flock. Lambs were most vulnerable during the first two weeks of exposure (P < 0.001, X² = 49.3), and were somewhat less vulnerable in the next 4 weeks of exposure. If the lambs survived 6 weeks of exposure, their chances of succumbing to predation were small. Lambs were most vulnerable if they were added to an established flock. Orphan lambs were more vulnerable than ewe-reared lambs. Even though the coyotes in this study were persistent in attacking lambs, their success was limited for at least 3 reasons. First, the lambs sometimes refused to run from the coyotes. In addition, they occasionally actively defended themselves by foot-stomping, butting and approaching the coyote. Finally, no lambs were killed while in close proximity to a guardian dog. Based on this study, predation might best be reduced by minimizing introductions of new lambs, and especially orphan lambs, to established flocks, and by using a guardian dog, if possible.     

Evolutionarily stable strategies and short-term selection in Mendelian populations re-visited

This note concerns a one locus, two allele, random mating diploid population, subject to frequency-dependent viability selection. It is already known that in such a population, any evolutionarily stable strategies (ESS), if only accessible by the genotype-to-phenotype mapping, is the phenotypic image of a stable genetic equilibrium (Eshel, I. 1982. Evolutionarily stable strategies and viability selection in Mendelian populations. Theor. Popul. Biol. 22(2), 204-217; Cressman et al. 1996. Evolutionary stability in strategic models of single-locus frequency-dependent viability selection. J. Math. Biol. 34, 707-733). The opposite is not true. We find necessary and sufficient parametric conditions for global convergence to the ESS, but we also demonstrate conditions under which, although a unique, genetically accessible ESS exists, there is another, "non-phenotypic" genetically stable equilibrium.     

Effect of short-term cyclophosphamide administration on rabbit sperm]

Daily injection in the rabbit of 60 mg cyclophosphamide, during four days, product during 8 to 9 weeks one importance decrease of the number and the mobility of the ejaculated spermatozoa. This interval correspond with the spermatogenesis and epididymal transit period. Low doses injections product only one mobility decrease.     

Effect of short-term hypothyroidism on reproduction in the bitch

Hypothyroidism in bitches has been reported to cause a variable interestrus interval, infertility, abortion, and stillbirth. The objective of this study was to evaluate the effect of experimentally induced hypothyroidism in bitches on fertility, pregnancy, parturition, and neonatal health. Eighteen healthy multiparous bitches were used; hypothyroidism was induced (by radioiodine administration) in nine bitches and the remaining nine served as untreated controls. After breeding, bitches were evaluated for pregnancy, fetal resorption, gestation length, litter size, duration and strength of uterine contractions (during parturition), interval between delivery of pups, viability of pups at birth, periparturient survival, and weight of pups at birth through 4 weeks of age. Bitches were bred a median of 19 weeks after induction of hypothyroidism. All bitches became pregnant and delivered term litters. There was no difference in the interestrus interval, litter size, or gestation length between hypothyroid and control bitches. Duration of uterine contractions was longer, but contraction strength was weaker in hypothyroid than control bitches; however, the interval between delivery of pups was not affected. Periparturient puppy mortality was significantly higher in litters from hypothyroid bitches. Viability scores and weight at birth were significantly lower in pups from hypothyroid bitches than controls. There was no difference between groups in pup weight gain during the first 4 weeks, in the interval from birth to the eyes opened, or to the onset of walking. Although hypothyroidism of relatively short duration did not affect fertility, it prolonged parturition and reduced pup survival in the periparturient period.     

Biological control of helminths

As a potential component in future integrated parasite-control strategies, biological control by means of predacious fungi seems to be moving from a promising possibility toward becoming a reality, and the netforming nematode-destroying fungus Duddingtonia flagrans appears to be the candidate of choice. Not only has this fungus been found in, and isolated from, fresh sheep, cattle and horse faeces, but it also appears to be the only fungus that is able to consistently and significantly reduce the number of infective trichostrongyle larvae in faeces from animals fed fungal spores. Results from the last few years have shown that D. flagrans is able to trap and destroy free-living stages of the most important and common trichostrongylid larvae with very similar external life-cycles, as well as larvae of parasites with a slightly different transmission biology (Nematodirus spp., Dictyocaulus viviparus). The introduction of microfungi for biological control could be as part of a feed supplement or incorporated in feed-blocks presented to animals which are raised under relatively intensive conditions and constant surveillance. Apart from the special niche for organic farmers, such a product would be suited for horses, small ruminants (as either milking herds or housed daily for other reasons), cattle in special situations and free-roaming pigs. The most important constraint, still, for a major breakthrough in biological control in the latter is the lack of good antagonists against the long-lived and rather resistant infective stages of parasites, being transmitted as larvae inside the egg. Since the first Conference on Novel Approaches to the Control of Helminth Parasites of Livestock in Armidale, Australia, 1995, there has been a steady evolution within the area of biological control of parasitic nematodes. Today this principle is being exploited and tested out in almost all parts of the world, under various climatic conditions and production systems. Where, in the past, a large part of the work focused on cattle and to a lesser degree horse and sheep parasites, the focus of the research in many of the newly involved countries is on small ruminants, because of their importance to primarily small-scale farmers in local communities. Today research and trials are either on-going or being planned in many developing countries, as well as in countries in transition. The involvement of multinational agencies in addition to national and industrial interests is very welcome and should increase the chances and keep up the momentum for development and implementation of biological control in future animal production around the world.     

Evaluating short-term effects of omnivorous fish removal on water quality and zooplankton at a subtropical lake

We evaluated a biomanipulation program to test for short-term changes in water quality (chlorophyll a, Secchi depth, total phosphorus) and macrozooplankton biomass following partial removal of omnivorous gizzard shad Dorosoma cepedianum. The removal occurred at a eutrophic subtropical lake, and responses were compared to an unmanipulated control lake using a before-after-control-impact paired series analysis. The removal reduced the biomass of large (>300 mm) gizzard shad by 75% over 2 years via a subsidized commercial gill net fishery. However, the total population biomass of gizzard shad was reduced by approximately 32% from an average pre-manipulation biomass of 224 kg ha⁻¹ due to the size selectivity of the gear, which did not effectively capture small fish (<300 mm). No significant short-term changes in chlorophyll a concentration, Secchi depth, total phosphorus concentration or macrozooplankton biomass were detected following biomanipulation. The partial removal may have fallen short of the biomass reduction required to cause ecosystem responses. Our results suggest that moderate omnivore removals (i.e., <40% biomass reduction) will have little short-term benefits to these lakes, and future manipulations should use a less size-selective gear to achieve a larger total biomass reduction.