Squirrel monkey reproduction: the "fatted" male phenomenon and seasonal spermatogenesis

Lack of seasonal changes in biochemical constituents of bonnet monkey semen

The seasonal changes in the production of semen were investigated in four proven-fertile bonnet males (Macaca radiata), maintained under ordinary laboratory conditions. The various physical and biochemical characteristics of 190 ejaculates collected at different seasons of the year were analyzed. There were no significant changes in the responses to penile stimulation, in semen volume, sperm density, and in the concentrations of fructose, citric acid, sialic acid, maltase, amylase, and protein of seminal plasma, attributable to season.

Seasonal changes in the thyroid hormones of the male squirrel monkey

The serum of male squirrel monkeys was analyzed for levels of thyroxine (T4) and triiodothyronine (T3) at intervals corresponding to (1) preparations for breeding, (2) termination of breeding, and (3) well after the breeding season. Highest concentrations of hormones were found prior to breeding when body weight was also highest. Significant differences in hormone levels were found across sampling period. The interaction between gonadotropins and thyroid hormones is discussed.

Effects of lesions of globus pallidus on species-typical display behavior of squirrel monkeys

In a study of brain mechanisms underlying species-typical communication, systematic testing has been conducted on the effects of cerebral lesions on the mirror display of squirrel monkeys. The mirror display is a highly predictable variation of a naturally occurring display used by male squirrel monkeys in a show of aggression, in courtship and in greeting. Of the 5 features of the display, vocalization, thigh-spreading and forward thrusts of the erect phallus are the major and most regularly occurring manifestations, constituting the so-called trump display. Testing has been performed on more than 100 animals with lesions in various structures of the brain. The present report describes the positive effects of electro-coagulation of certain parts of the globus pallidus. Lesions of the medial segment have resulted in an enduring elimination or fragmentation of the trump display. Recovery of the display may occur with lesions predominantly involving the external segment, while destruction of the caudalmost pallidum is without effect. A variety of evidence indicates that the behavioral changes are not due to a deterioration of health, motor disabilities, seasonal factors or motivation. When weighed against the negative or transitory effects of lesions of numerous other structures of the brain, the present findings support the hypothesis that the striatal complex plays a basic role in the organized expression of species-typical behavior.

Contrasting effects of living in heterosexual pairs and mixed groups on the structure of social attraction in squirrel monkeys (Saimiri)

The structure of social attraction was assessed in pair- and group-living squirrel monkeys (Saimiri) using paired-comparison and single-stimulus preference tests. Effects of the social environment were most prominent in females. Females housed with a single male showed sharply increased attraction to like-sex strangers and less pronounced increase in attraction to opposite-sex strangers, as compared to group-living females. Differences between pair- and group-living males were in the same direction found with females, but less extreme. Most group-living monkeys strongly preferred familiar animals to strangers regardless of sex, and like-sex to opposite-sex familiars. Change in the structure of social attractions in response to variations in the composition of the social environment appears to be an important factor in the maintenance of the species-typical grouping pattern in the squirrel monkey.