José Coda

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.

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.

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.

Demographic dynamics of Akodon azarae (Cricetidae: Sigmodontinae) in linear habitats of agricultural landscapes of central Argentina

ABSTRACT Linear habitats are capable of providing essential resources for small mammals within agroecosystems. We analyzed demographic parameters of Akodon azarae in a linear habitat of central Argentina. We used capture-mark-recapture models to determine temporal variations in survival, recruitment and population growth rate. The effects of temperature, rainfall and vegetation cover as well as of population abundances on the mentioned parameters were assessed in a 10-year study. Survival and growth rate showed seasonal variation, which was greater than the interannual variability observed. Temperature affected only recruitment. Linear habitats would provide resources for long term survival and reproduction of A. azarae.