Andrea R. Steinmann

Factors affecting home range size and overlap in Calomys venustus (Muridae: Sigmodontinae) in Argentine agroecosystems

Summary In this study, information concerning home range size and overlap of Calomys venustus (Thomas, 1894), in relation to sex, population size, and breeding periods is provided. The present study was carried out on a railway bank in southern Cordoba Province (Argentina), between October 1994 and September 1997, using the capture-mark-recapture method. Home range size in C. venustus depended on breeding period and population size, and was independent of sex. The degree of home range overlap was dependent on breeding and non-breeding periods and overlap type (intra- or intersexual), but was independent of population density. During the breeding period, females showed a small degree of intrasexual home range overlap. In general, male home ranges largely overlapped with females. The conclusion is that differences in home range size of C. venustus could be determined by season and population size. Moreover, the degree of inter- and intrasexual home range overlap during the breeding period suggested that males and females of C. venustus use space differently. Females did not share their home range with other females, while males fully shared it with both sexes, and male spacing is influenced by female distribution.

Commensal and wild rodents in an urban area of Argentina

The aim of this study was to determine the rodent species, distribution, and abundance in an urban area, in relation to epidemiology risk or damage, so as to elaborate a control program. The first sampling was done between May and July of 1998 on 31 vacant lots, 5 rubbish dumps, 15 stream banks, 18 railway banks and 28 vacant areas. Between August 1999 and June 2000 seasonal samples were taken in the same habitats. At each capture site 20 snap traps and 10 live traps were installed. Of 1253 animals captured, 74% were commensal rodents (Mus domesticus, Rattus rattus and Rattus norvergicus) and 26% were wild rodents (Calomys musculinus, Akodon dolores, A. azarae and C. venustus). M. domesticus was the population that numerically predominated in every sampled habitat. C. musculinus was the second most abundant species and its distribution was related to open space (vacant areas, railway banks, stream banks and rubbish dumps). The basic information found by this work will allow us to consider and measure the risk of a possible human infection in a specific area. Thus, human diseases can be prevented by controlling rodent reservoirs and/or by avoiding contact between rodents and humans.

Size and overlap of home range inCalomys musculinus (Muridae: Sigmodontinae)

Home range size and overlap ofCalomys musculinus (Thomas, 1913) was examined in relation to sex and breeding periods. The study was carried out in four 0.25 ha enclosures, in a natural pasture, between October 2002 and July 2003. The four enclosures functioned as independent populations and each was considered a replicate. The capture, mark and recapture method was used. Home range size and overlap inC. musculinus depended on sex and period. Home range size of males was always larger than that of females. Females showed a small degree of intra-sexual home range overlap during the breeding period. In general, male home ranges overlapped with females. We conclude that differences in home range size inC. musculinus is determined by sex and breeding period. Moreover, the degree of inter- and intra-sexual home range overlap during the breeding period suggests that both males and females ofC. musculinus use space differently. Females did not share their home range with other females, while males fully shared it with both sexes, and male spacing is influenced by the distribution of females. A promiscuous-polygynous mating system is suggested forC. musculinus.

Territorial behaviour in corn mice, Calomys musculinus (Muridae: Sigmodontinae), with regard to mating system

We studied territorial behaviour of Calomys musculinus, a promiscuous-polygynous species, in order to test the predictions that during the breeding period, home-range-owner females are more aggressive than home-range intruders and that males do not display territorial behaviour. At the core of the breeding season, we conducted 136 intrasexual and 66 intersexual encounters. The study was carried out in four 0.25-ha enclosures, each containing one independent population. We studied territorial behaviour utilising focal animal sampling to record behaviour. Encounters were conducted in a circular opaque arena (COA) near the home-range’s activity mathematical centre (AMC). Amicable behaviour was not observed in any of the 78 trials among females. The rates of aggressive and submissive behaviour per female–female encounters varied in relation to whether they were home-range owners or intruders, the former being aggressive, the latter submissive. So we could link these drives to the territorial behaviour of C. musculinus. This result fits well with the already known territoriality of C. musculinus during the breeding season. In contrast, the 58 intrasexual male encounters did not show direct aggressive interactions between them. The rates of the different behaviours between males did not vary in relation to whether they were home-range owners or intruders. In our study, which took place during the breeding period, C. musculinus males were nonterritorial, and they never exhibited aggressiveness towards females.

Corn mice (Calomys musculinus) movement in linear habitats of agricultural ecosystems

Abstract Movement patterns of Calomys musculinus in linear habitats were studied in relation to sex, season, year, abundance, and width of border. Movement distances (MDs) were measured by seasonal capture, mark, and recapture samples during 2 years in wide and narrow borders in agroecosystems. The smallest MDs were registered in autumn and the highest in spring. In the breeding period MDs of males were larger than those of females. In the nonbreeding period MDs were similar between sexes. Effects of sex on MD were consistent with the promiscuous mating system of C. musculinus. MDs were greater in narrow than in wide borders. The narrowness of suitable habitats would force the mice to extend foraging trips in narrow borders. Opportunistic behavior of C. musculinus allows it to use linear habitats in a similar way to the 2-dimensional natural habitats.

Inter-male aggression with regard to polygynous mating system in Pampean grassland mouse, Akodon azarae (Cricetidae: Sigmodontinae)

Based on the hypothesis that, in Akodon azarae, polygyny operates through female defence, we studied inter-male aggression in order to test the following predictions: during the breeding period (1) resident males are more aggressive than intruder males in the presence of females (FP), and (2) aggressive behaviour is independent of male condition (resident or intruder) in the absence of females (FA). To test our predictions, we used the resident male behavioural response towards an intruder male in relation to FP or FA. We conducted 30 encounters in FP and 27 in FA in 0.79-m2 round enclosures placed in the Espinal Reservation. Our results support the prediction that, in FP, the intensity of aggressive behaviour exhibited by males varied in relation to resident or intruder condition. Resident males showed high levels of aggression towards intruders, and intruders exhibited the greatest values of submissive behaviours with residents. In FA, the intensity of aggressive behaviour did not vary in relation to resident or intruder condition. Both resident and intruder males exhibited low aggressive behaviour and inter-male encounters resulted mainly in non interactive behaviours. Our results support the hypothesis that, in A. azarae, the polygynous mating system operates through female defence.

Mating strategies of Pampean mouse males

Patterns of space use and sexual dimorphism are frequently used to infer mating systems. We examined body size and home range size and intra- and intersexual overlap degree in order to elucidate mating strategy of Akodon azarae males. We studied spacing patterns using 113 and 129 home ranges established by males and females, respectively, in four 0.25 ha enclosures during the breeding season. Significant differences between sexes in home range size and overlap degree were found. Male home ranges were always larger than those of females. We observed exclusive space use among males and among females. Considering only those males that shared their home ranges with females, average intersexual overlap value was about 50%. Males mainly overlap their home ranges with home ranges of two or three females. Significant differences in body size were found between males and females, with males being larger. We concluded that space use and sexual dimorphism in this species is consistent with patterns characteristic of polygynous rodents, and we propose a polygynous system in A. azarae.

Agricultural land-use intensity and its effects on small mammals in the central region of Argentina

Agriculture intensification is one of the main threats to biodiversity in agricultural systems. The effectiveness of conservation strategies in these systems depends mainly on the compromise between biodiversity conservation and agricultural land use. The aim of this study was to assess the effect of land-use intensity, characteristics of linear habitats (field borders) and their surrounding fields (landscape) on small mammal richness and abundance in agricultural systems of Argentina. In autumn 2009, we performed a removal sampling in 60 traplines located in the field borders of high or low land-use intensity regions. In traplines under high land-use intensity we found seven species while under low land-use intensity we found ten. Characteristic species of grasslands and woodlands such as Monodelphis dimidiata, Thylamys pallidior, Necromys lasiurus and Graomys griseoflavus were only captured in traplines under low land-use intensity. Higher numbers of Calomys musculinus species (habitat generalist) were observed under high land-use intensity while Akodon azarae and Oxymycterus rufus species, known as habitat specialists, were more frequently found in the low land-use intensity region. Border width and height, as well as land use of both sides of the border, were major variables for explaining small mammal abundances. Our results suggest that conservation of wide field borders with characteristics similar to those of natural habitats would be crucial for sustainable management of Pampean agricultural systems which hold high richness and abundance of small mammal species.

Do polygynous males of Akodon azarae (Rodentia: Sigmodontinae) vary their mating tactics at low availability of females?

Abstract We examined in Akodon azarae if at low availability of females (sex ratio biased toward males, 3:1), the mating tactics of males are determined by the number of receptive females to which they have access, or by the number of male competitors with which they interact. To test these hypotheses, we measured the home range size and overlap degree. At the beginning of the reproductive season, we studied spacing patterns using 57 and 30 home ranges established by reproductive males and females in three enclosure populations. We statistically compared our results with those previously obtained in enclosure populations with a sex ratio of 1:1. Male home range sizes were larger than those recorded in populations with a sex ratio of 1:1. The degree of male intra-sexual overlap increased about 3.5 times with respect to that observed under a sex ratio of 1:1. The increase in home range sizes and intra-sexual overlap degree of reproductive males reflects that A. azarae males may adjust their spacing strategy to increase their mating opportunities at low density of females. Our results suggest that at low breeding female availability, male mating tactics could be determined by the number of receptive females to which they have access.

Multiple Paternity in a Wild Population of the Corn Mouse: Its Potential Adaptive Significance for Females

Mating with multiple males within a single reproductive event is a common female mating strategy in mice and voles, but its adaptive function is often unclear. In this study, we used 7 microsatellite loci to investigate if multiple paternity occurs in wild populations of the socially promiscuous Calomys musculinus. We also analyzed if multiple paternity increases litter size and/or genetic variability among offspring. In addition, we examined if multiple paternity occurs more frequently in litters conceived at high population density than those conceived at low population density. By genotyping 23 females and their 135 embryos (5.9 ± 1.6 SE pups per female), we found that 56.5% of the litters were sired by 2 or 3 males. We found no association between multiple paternity, litter size, and genetic variability. In addition, multiple paternity did not vary in relation to population density. Our results provide clear evidence of multiple paternity and offer the first genetic documentation of mating systems in mice in Argentina. We discuss the extent of multiple paternity in relation to potential adaptive strategies in female corn mouse. El apareamiento con múltiples machos durante un solo evento reproductivo es una estrategia común de acoplamiento en hembras de ratones y ratas de campo, sin embargo su función adaptativa a menudo es poco clara. En este estudio, hemos utilizado 7 loci de microsatélites para investigar si existe paternidad múltiple en poblaciones silvestres del ratón maicero (Calomys musculinus) especie socialmente promiscua. También analizamos si la paternidad múltiple aumentaó el tamaño de la camada y/o su variabilidad genética. Además, se analizó si la paternidad múltiple ocurre con más frecuencia en camadas concebidas a alta densidad poblacional, que las concebidas a baja densidad poblacional. El genotipado de 23 hembras y sus 135 embriones (5.9 ± 1.6 ES crías por hembra) demostró que, al menos el 56.5% de las camadas son engendradas por dos o tres machos. No se encontró asociación entre la paternidad múltiple, tamaño de la camada y la variabilidad genética. Además, la paternidad múltiple no varió en relación con la densidad de la población. Nuestros resultados proveen clara evidencia de paternidad múltiple y ofrecen la primera documentación genética de sistemas de apareamiento en ratones en Argentina. Discutimos el alcance de la paternidad múltiple con relación a potenciales estrategias adaptativas en hembras del ratón maicero.