Numerosos estudios experimentales realizados en varias especies de mamíferos, pero principalmente en ratones y ratas de laboratorio, demostraron que el aislamiento social afecta profundamente los comportamientos individuales. Este estudio fue diseñado para comprender cómo los comportamientos agresivos y exploratorios de machos de Calomys musculinus, sexualmente maduros, podrían verse afectados por las condiciones de alojamiento. El estudio se realizó en bioterio durante marzo y mayo de 2018. Durante una semana, 35 machos fueron alojados en condición solitaria y 30 en condición agrupada (3 individuos por caja). Para estudiar el comportamiento de exploración se utilizó una cámara de desplazamiento. Para el estudio de agresividad, en una arena circular se realizaron enfrentamientos diádicos de 5 minutos de duración cada uno de ellos, entre individuos provenientes del mismo tratamiento. Los resultados obtenidos en este estudio experimental apoyaron la hipótesis planteada: los machos de C. musculinus alojados individualmente fueron más exploradores y menos agresivos que los provenientes de la condición agrupada. La mayor agresividad de los machos de C. musculinus alojados en grupo se vio reflejada por la intensidad de las aproximaciones ofensivas, ataques o persecuciones exhibidos durante los enfrentamientos intrasexuales. Nuestros resultados constituyen un aporte importante para la interpretación de futuros estudios en C. musculinus que requieran tanto del alojamiento transitorio de individuos, como del establecimiento de colonias fundadoras de breve permanencia en bioterio, de la conformación de una colonia bioterio o de la constitución de grupos experimentales.
Effect of the social status of housing in captivity on individual behaviors: Calomys musculinus as species ecological model. Several experimental studies conducted in various mammalian species, but mainly in laboratory mice and rats, demonstrated that social isolation deeply affects individual behaviors. This study was designed to understand how aggressive and exploratory behaviors of sexually mature Calomys musculinus males could be affected by housing conditions. The study was conducted in laboratory during March and May 2018. During one week, 35 males were housed in solitary condition and 30 in grouped condition (3 individuals per box). A displacement camera was used to study the scanning behavior. For the study of aggressiveness, dyadic confrontations of 5 minutes each were carried out in a circular arena, between individuals from the same treatment. The results obtained in this experimental study supported our hypothesis: C. musculinus males housed alone were more exploratory and less aggressive than those from the grouped condition. The greater aggressiveness of the C. musculinus males housed in a group was reflected by the intensity of the offensive approaches, attacks or persecutions exhibited during intra-sexual trials. Our results constitute an important contribution for the interpretation of future studies in C. musculinus that require both the transitory accommodation of individuals, the establishment of founder colonies of short stay in the bioterium, the formation of a bioterium colony, or the constitution of experimental groups.
Agonistic interactions and receptivity of females during mating encounters in the corn mouse (Calomys musculinus) were studied. Twenty-nine couples were observed for copulatory behavior during postpartum estrus; 14 of them were composed of males and females that had bred together at least once (familiar male group), and 15 were composed of a male and a female each with reproductive experience, but were unknown to each other (strange male group). No significant differences between the familiar male and the strange male group were found in either the mount latency or the intromission latency. The strange male group showed a trend to have higher mount and intromission frequencies, both at the first and the second ejaculatory series, although some of these differences did not reach statistical significance. Also, males in the strange male group showed significantly higher ejaculatory thrust frequencies, both at the first and the second ejaculatory series, than males in the familiar male group. The post-ejaculatory interval was significantly longer in the strange male group. The incidence of all agonistic behaviors other than a stereotyped kind of fighting that precedes copulation (“precopulatory fighting”) was higher in strange male group than in the familiar male group. In both groups, aggressive postures were more frequently seen in females than in males, and conversely, submissive postures were significantly more frequent in males than in females. Also, females in the strange male group made significantly more approaches than those in the familiar male group. Taken together, these findings suggest that C. musculinus is a non-monogamous species.