Cristina Busch

Spatial distribution and attributes of a population of Ctenomys talarum (Rodentia: Octodontidae)

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Genetic structure in a solitary rodent (Ctenomys talarum): implications for kinship and dispersal

The genetic structure of a population provides critical insights into patterns of kinship and dispersal. Although genetic evidence of kin structure has been obtained for multiple species of social vertebrates, this aspect of population biology has received considerably less attention among solitary taxa in which spatial and social relationships are unlikely to be influenced by kin selection. Nevertheless, significant kin structure may occur in solitary species, particularly if ecological or life history traits limit individual vagility. To explore relationships between genetic structure, kinship, and dispersal in a solitary vertebrate, we compared patterns of genetic variation in two demographically distinct populations of the talar tuco‐tuco (Ctenomys talarum), a solitary species of subterranean rodent from Buenos Aires Province, Argentina. Based on previous field studies of C. talarum at Mar de Cobo (MC) and Necochea (NC), we predicted that natal dispersal in these populations is male biased, with dispersal distances for males and females being greater at NC. Analyses of 12 microsatellite loci revealed that in both populations, kin structure was more apparent among females than among males. Between populations, kinship and genetic substructure were more pronounced at MC. Thus, our findings were consistent with predicted patterns of dispersal for these animals. Collectively, these results indicate that populations of this solitary species are characterized by significant kin structure, suggesting that, even in the absence of sociality and kin selection, the spatial distributions and movements of individuals may significantly impact patterns of genetic diversity among conspecifics.

DNA fingerprinting reveals polygyny in the subterranean rodent Ctenomys talarum

DNA fingerprinting was used to characterize patterns of paternity in two populations of Ctenomys talarum from Buenos Aires Province, Argentina. The multilocus probe PV47–2 was used to detect variation in genomic DNA extracted from 12 females, their 32 offspring, and 14 putative sires. For 11 out of 12 litters examined, a single male capable of providing all nonmaternal bands was identified. Within each study population, individual males sired more than one litter, suggesting that C. talarum is polygynous. No evidence of multiple paternity of litters was found. High band‐sharing values among females suggest that further research is needed to assess the population genetic structure of this species.

Comportamiento social y reproductivo del roedor subterráneo solitario Ctenomys talarum (Rodentia: Ctenomyidae) en condiciones de semicautiverio

The social and reproductive behavior of the subterranean rodent Ctenomys talarum (Thomas, 1898) was studied in a seminatural enclosure resembling both the complexity of the natural burrow system and the sex ratio observed in wild populations. Contrary to expectations based on their solitariness and their rather simple social system, the interactions among individuals of this species were diverse and complex. Auditory, tactile and chemical communication were of importance during territory guarding, courtship and copulatory behavior. Individuals from different populations differing in ecological attributes behaved in substantially different ways. Males from Mar de Cobo, a population characterized by a high density and a skewed sex ratio favouring females, behaved aggressively, which resulted in frequent wounding. Males from Mar de Cobo established a dominance hierarchy among them, which preceded courtship and, eventually, resulted in the dominant male monopolizing mating activity. On the contrary, males from Necochea, a population showing low density and an even sex ratio, behaved less aggressively; dominance relationships were absent, and males performed courtship behaviors in the presence of other males.

Owl Predation on Two Sympatric Species of Tuco-Tucos (Rodentia: Octodontidae)

Predation by owls upon two sympatric species of subterranean rodents of the genus Ctenomys was studied by comparing characteristics of individuals that were field-trapped and preyed upon. Predators took a greater proportion of the smaller C. talarum than of the larger C. australis in comparison to that estimated from their respective field densities. Only subadult individuals of C. australis were found among pellets. For C. talarum , a greater proportion of subadults than of adults was observed in pellets. We suggest that this pattern is determined both by constraints imposed by size of prey on the ability of a predator to handle large prey and by greater exposure of dispersing subadults to predation. Differential predation possibly maintains the habitat segregation observed between C. talarum and C. australis .

A method for studying social and reproductive behaviour of subterranean rodents in captivity

A methodology for studying the social and reproductive behaviour of solitary subterranean rodents under laboratory conditions is proposed. A first account ofCtenomys talarum (Thomas, 1898) behaviour is also provided with the aim of evaluating the proposed methodology and to advance presently unknown information on its social behaviour and mating system. The device is a seminatural enclosure, departing from traditional test cages with respect to increased: (1) size, (2) structural complexity, (3) social complexity, and (4) resemblance to natural conditions. It consists of artificial burrows each comprising 3.5 m of tunnel, a resource cage and a nest box, resembling the structural complexity described forC. talarum burrows. Burrows are connected to a common space, which allows social interaction among various individuals. Animals were observed in the seminatural enclosure — 3 females and 2 males, in accordance with sex ratios found in natural populations — for a period of 6 months. We obtained data related to reproductive and social behaviour: marking, aggression, vocalization, courtship and copulation, pregnancy, pup development, and parental care. The proposed system enables the collection of behavioural data as yet unavailable due to the secretive habits and aggressiveness that characterize this group of rodents, coupled with the difficulties associated with simulating subterranean conditions.

Acoustic signals of a solitary subterranean rodent Ctenomys talarum (Rodentia: Ctenomyidae): physical characteristics and behavioural correlates

Abstract. The purpose of this study was to analyse and describe vocalizations of a solitary subterranean rodent, Ctenomys talarum. In adult C. talarum five different sounds (four true vocalizations and one mechanical sound) were recorded during different behavioural contexts. Using data from the laboratory and literature, we classified these vocalizations as territorial, distress, and mating calls. We found that the vocalization range in C. talarum is shifted towards low frequencies, which transmit better in underground burrows and match well the hearing range described for other species of subterranean rodents. These low-frequency vocalizations, also found in other non-related subterranean rodents, may reflect an adaptation to the acoustic conditions of the habitat.

Ritmos de actividad locomotora y uso de las cuevas en condiciones seminaturales en Ctenomys talarum (Rodentia, Octodontidae)

Ctenomys es un genero de roedores subterraneos que vive en sistemas de galerias cerrados a la superficie del suelo y por lo tanto lleva a cabo la mayoria de sus actividades en ausencia de luz. Sin embargo a diferencia de otros roedores subterraneos sus salidas a la superficie son frecuentes. En este trabajo fueron evaluadas, en Ctenomys talarum (Thomas, 1898) la existencia y las caracteristicas de los ritmos locomotores de actividad para distintas condiciones experimentales. Ademas, fueron analizadas la permanencia y preferencia por distintos sectores del sistema de galerias. El 25 % de los individuos de C. talarum analizados, para las distintas condiciones de fotoperiodo y temperatura ambiente evaluadas, mostraron actividad ritmica. Por otra parte, los individuos no presentaron un patron generalizado de permanencia y preferencia por sectores definidos en el sistema de galerias

Use of chemical communication by the subterranean rodent Ctenomys talarum (tuco-tuco) during the breeding season.

Solitary subterranean rodents with a low frequency of direct contact between conspecifics are expected to use chemical communication to coordinate social and reproductive behavior. We examined whether reproductive tuco-tucos (Ctenomys talarum) were able to discriminate the reproductive condition, sex, and source population of conspecifics by means of chemical cues contained in urine, feces, soiled shavings, or anogenital secretions. During preference tests in which animals had direct contact with these chemical cues, tuco-tucos were able to determine the reproductive condition of opposite sex conspecifics independent of the source of odor. When only olfactory cues were available, both sexes discriminated reproductive condition of opposite sex individuals using urine. Females were also able to discriminate the reproductive condition of males using soiled shavings. Females spent more time investigating male odors than female odors; except in the case of feces, breeding males spent similar amounts of time investigating male and female odors. No preferences were detected for opposite sex urine from members of an animals own versus another population. The role of chemical cues in territory defense and breeding performance by this highly territorial subterranean rodent is discussed.

Intraspecific Variation in Effective Population Size in Talar Tuco-Tucos (Ctenomys talarum): The Role of Demography

Abstract Effective population size (Ne) is a fundamental concept that links population structure to the evolutionary processes that shape genetic variation. Demographic estimates of Ne may be influenced by a number of factors, including adult sex ratio and variance in individual reproductive success. Genetic estimates of Ne are influenced not only by these variables but also by neighborhood size, degree of population substructure, and historical changes in population size. Hence, comparisons of demographic and genetic estimates of Ne may yield important insights into the parameters that determine effective size. To explore interactions between demography and Ne, we compared estimates of effective population size/census size (Ne/N) for 2 demographically distinct populations of the talar tuco-tuco (Ctenomys talarum), a subterranean rodent from Buenos Aires Province, Argentina. Examination of data on adult sex ratios and reproductive success obtained from long-term field studies of C. talarum at Mar de Cobo and Necochea led us to predict that Ne/N should be smaller for Mar de Cobo. Demographic and genetic estimates of Ne/N were consistent with this prediction. However, interpopulation variation in Ne/N was greater for the genetic data set. Based on analyses of microsatellite variation, we suggest that this result is due primarily to differences in current demography, rather than historical reductions in population size. The observed differences in Ne/N imply that the strength of genetic drift differs between Mar de Cobo and Necochea, thereby potentially affecting patterns and rates of diversification among populations of C. talarum.