Alfredo Castro-Vázquez

Reproductive biology of the corn mouse, Calomys musculinus, a Neotropical Sigmodontine

In this paper we are summarizing almost twenty years of studies on the reproductive structures and processes of the corn mouse, Calomys musculinus. A comprehensive view of the reproductive anatomy, physiology and behavior in the laboratory is presented and complemented with observations in the field. The position of the corn mouse in a comparative view of mammalian reproductive cycles is discussed. Also, the reproductive peculiarities of the corn mouse are considered from the perspective of the evolutionary relationships with other Neotropical and Nearctic sigmodontines and, more generally, in the context of the family Muridae. Our results support the view of an early divergence of Neotropical and Nearctic lineages of the Sigmodontinae, and thus Osvaldo Reig’s hypothesis.

Biología reproductiva del ratón maicero, Calomys musculinus, un sigmodontino neotropical. En este trabajo se resumen casi veinte años de estudios de las estructuras y los procesos reproductivos del ratón maicero, Calomys musculinus. Una visión abarcativa de la anatomía, la fisiología y el comportamiento reproductivos estudiados en el laboratorio es complementada con observaciones en el campo. Se discute la posición del ratón maicero en una visión comparativa de los ciclos reproductivos de los mamíferos. Asimismo, las peculiaridades reproductivas de este ratón son evaluadas desde la perspectiva de sus relaciones evolutivas con otros sigmodontinos neárticos y neotropicales, y más ampliamente, en el contexto de la familia Muridae. Los resultados apoyan la opinión de una divergencia temprana entre los linajes sigmodontinos neárticos y neotropicales, y por tanto, la hipótesis de Osvaldo Reig.

Precopulatory fighting and other aggressive interactions during mating encounters in the corn mouse, Calomys musculinus (Muridae, Sigmodontinae)

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.