No abstract

No abstract

The demographic and reproductive characteristics of dispersers in the fossorial rodent Ctenomys talarum, the tuco-tuco, were studied by removing animals from two experimental plots. Data on dispersers' attributes were compared with those of resident and transient individuals from previous capture–mark–release and removal studies performed in the same localities. Average weekly dispersal by tuco-tucos was 2.38% (range 0–5.75%) at Necochea and 5.75% (range 0–15.75%) at Mar de Cobo. The low proportion of dispersers reflects their fossorial habit. At Mar de Cobo, the sex ratios of dispersers and transients showed a 1:1 relationship, whereas residents showed an excess of females. All groups did not differ from a sex ratio of 1:1 at Necochea. At both localities, dispersers did not differ qualitatively from residents in age composition, litter size, or body mass. Transients and dispersers of both populations were characterized by a higher proportion of immature individuals than residents. We conclude that dispersal may be an important factor regulating the C. talarum population and may counteract the restrictions imposed by its subterranean habitat.

Patterns of infection among hosts in a population are often driven by intrinsic host features such as age or sex, as well as by positive or negative interactions between parasite species. We investigated helminth parasitism in 2 South American rodent species, Ctenomys australis and C. talarum (Octodontidae), to determine whether the unusual solitary and subterranean nature of these hosts would impact their patterns of infection. We applied generalized linear models to infection data on a total of 7 helminth species (1 in C. australis and 6 in C. talarum). Host age and season of capture influenced infection levels in some of the helminth species, but none were influenced by host body condition. In C. talarum, 4 pairs of helminth species showed significant associations, either asymmetrical or symmetrical, and with 3 of the 4 being positive; strong inter-specific facilitation appears likely in 1 case. Also, we found that female hosts, especially non-pregnant ones, harboured heavier infections of 2 nematode species than male hosts. This is in sharp contrast to the general male-bias reported for most studies of nematodes in wild mammals, and we develop explanations for these results based on the unusual ecology of these subterranean rodents.

The helminth parasite fauna of a natural population of the octodontid, Ctenomys talarum, was studied. Parasites that were found included the nematodes Heligmostrongylus sp. and Trichuris sp. Total prevalence of parasitism was 92.3%, mean intensity of infection was 22.7 worms, and mean abundance was 21 worms. Prevalence and mean abundance of infection with Heligmostrongylus sp. were higher in C. talarum males relative to females. Ecological and physiological causes, as well as the mating system of the host species, influence the likelihood of sex differences in parasite infection. The low parasite burden and diversity of C. talarum are associated with restrictions imposed by the subterranean habitat and with life-history traits of these rodents. Whether these findings apply to other Ctenomys spp. is unknown.

. 1991. Population and habitat characteristics of two sympatric species of Ctenomys (Rodentia: Octodontidae). Acta theriol. 36: 87 -94.Demography, spatial distribution, body size and habitat characteristics of two sympatric species of Ctenomys have been studied seasonally at Necochea (Buenos Aires Province, Argentina). Densities were 11.3 individuals/ha for Ctenomys talarum and 5.2 indiv./ha for Ctenomys australis. Breeding was seasonal for both species. Sex ratios were unbalanced in favour of females in C. australis while there were not significant differences between sexes in C. talarum. The spatial distribution for both populations was clumped and related to habitat characteristics. C. talarum was found in areas with higher plant biomass and harder soils, while C. australis was restricted to the areas with lower plant biomass and less compact soils. Spatial separation of these two species may be caused by different commitment to life underground resulting from differences in body size and energetics. Two possible explanations for the spatial distribution of C. australis and C. talarum are given.

Several factors capable of affecting the amount of resources available to an individual parasite, such as the number of other parasites in the host or host quality, may cause variability in reproductive success among parasites. Variation in egg output and mean egg volume was investigated among adult females of the nematode Graphidioides subterraneus, parasitic in the herbivorous subterranean rodent Ctenomys talarum (Octodontidae). Female nematode body size correlated strongly with the number of eggs produced. However, neither host body mass nor the number of other nematodes per host had any influence on the number or volume of eggs produced by the parasites. There was also no evidence for a trade-off between the number of eggs produced and mean egg volume among female nematodes. All these results suggest that resource supply to individual worms is not limited by host size or by the number of conspecific parasites vying for the same resources, despite the 30-fold variation in intensity of infection and the twofold variation in host body mass observed in the present study. Instead, resource availability does not appear to constrain reproduction in G. subterraneus, with its host providing a stable, predictable environment.

Trichuris pampeana Suriano and Navone, 1994 (Nematoda: Trichuridae) is redescribed from voucher specimens from the type host Ctenomys azarae Thomas, 1903 (Rodentia: Octodontidae) and from parasites collected from 2 populations of the subterranean rodent C. talarum Thomas, 1898 from Mar de Cobo and Necochea, Buenos Aires Province, Argentina. After a revision of these nematodes, it was confirmed that the following characters were not considered in the original description: bacillary band, cells from the esophagointestinal junction, ejaculatory duct, vas deferens, adanal papillae, vagina, oviduct, and rectum. Additional information about the spicular sheath, vulva, uteri, and ovary is provided. The morphological features given in this redescription allow to confirm the identity of T. pampeana as a valid species and also to distinguish it more clearly from other species of the genus.