In its 1990 recommendations, the ICRP considered the radiation risks after exposure during prenatal development. This report is a critical review of new experimental animal data on biological effects and evaluations of human studies after prenatal radiation published since the 1990 recommendations. Thus, the report discusses the effects after radiation exposure during pre-implantation, organogenesis, and fetogenesis. The aetiology of long-term effects on brain development is discussed, as well as evidence from studies in man on the effects of in-utero radiation exposure on neurological and mental processes. Animal studies of carcinogenic risk from in-utero radiation and the epidemiology of childhood cancer are discussed, and the carcinogenic risk to man from in-utero radiation is assessed. Open questions and needs for future research are elaborated. The report reiterates that the mammalian embryo and fetus are highly radiosensitive. The nature and sensitivity of induced biological effects depend upon dose and developmental stage at irradiation. The various effects, as studied in experimental systems and in man, are discussed in detail. It is concluded that the findings in the report strengthen and supplement the 1990 recommendations of the ICRP.

https://journals.sagepub.com/doi/pdf/10.1016/S0146-6453%2803%2900021-6

Biological effects after prenatal irradiation (embryo and fetus): ICRP Publication 90 Approved by the Commission in October 2002

The vigilance behaviors and association patterns of adult female squirrel monkeys (Saimiri oerstedi) in Parque Nacional Corcovado, Costa Rica were studied over the annual reproductive cycle to identify a possible adaptive function associated with the unusually close within-group birth synchrony prevalent in Saimiri populations. Raptor association with the troops, predation attempts, and monthly changes in food abundance were also documented. Seasonal fluctuations in food abundance probably constrained the timing of births among three contiguous troops to a two month period. The close within-troop birth synchrony (majority of births occurring within a week) is suggested to be advantageous because of intense predation pressure on neonate squirrel monkeys. Adult females with neonates cooperate in anti-predator vigilance and defense of neonates. Participation in these maternal associations may increase the probability of neonate survivorship. Variable gestation length in squirrel monkeys may reflect a lability in the duration of gestation to allow coordination of the timing of births among females in a troop.

Birth synchrony in squirrel monkeys (Saimiri oerstedi): a strategy to reduce neonatal predation

The mating system of squirrel monkeys (Saimiri oerstedi) in Parque Nacional Corcovado, Costa Rica was studied and used to develop a model to interpret the evolution of seasonal sexual dimorphism in squirrel monkeys (Saimiri spp.). Adult male body weights in captivity and the wild may increase more than 20%, beginning approximately two months prior to and continuing through the annual two month, breeding season. Female inter-troop transfer was common in the study population, but male troop residence was stable. Instances of agression among adult males in the troop, even in sexual contexts, were rare. Reproductively mature males enlarged to varying degrees by the start of the breeding season and cooperated in mobbing females to olfactorily evaluate female, estrous condition. Female mate preference corresponded to a ranking based on relative male enlargement. The largest male obtained 70% of the copulations observed in the 1984 breeding season. Little evidence exists that females typically mate with more than one male during the period of peak receptivity. Seasonal enlargement in males is suggested to be the result, of both male intrasexual competition and female choice.

Mating patterns in squirrel monkeys (Saimiri oerstedi)

The ontogeny of foraging in squirrel monkeys, Saimiri oerstedi

We compared the interactions between vigilance, risk from avian predators, and typical group size for three species of squirrel monkey (Saimiri oerstedii, S. boliviensis, and S. sciureus). Field studies of each species in relatively undisturbed habitats provided data including behavioral interactions between avian predators and squirrel monkeys and the latter's vigilance response, habitat use, group size, population density and within-group food competition. Three hypotheses were examined. The first two identified aspects of the habitat structure exploited by squirrel monkeys and their avian predators as key parameters. (1) The overall success of avian attacks is a function of the density of understory vegetation present to hinder these birds from closely approaching individual troop members. (2) The extent of continuous canopy forest cover within habitats underlies which of two vigilance strategies are exhibited. Preemptive vigilance occurs when monkeys allocate time to visual scrutiny in a manner consistent with the intent of obtaining advance warning on the approach of an avian predator. During reactive vigilance, in contrast, monkeys are not overtly vigilant against an aerial attack until an attack or other stimulus strongly indicative of immediate risk occurs. Preemptive vigilance occurs in open habitats with little canopy, while reactive vigilance predominates when birds can make effective ambush attacks from forest canopy cover. Both hypotheses were supported. Group sizes vary significantly across the three squirrel monkey species with S. boliviensis having the largest and S. sciureus the smallest mean group size. Our third hypothesis examined the premise that group size in social animals reflects a tradeoff between predation risk (whether based on long-term observations or extrapolated from habitat structure) and within-group food competition. The power of this tradeoff mechanism to explain group-size variation was contrasted with a simpler, one parameter model, within-group food competition under an ideal free distribution. The ideal free distribution approach was consistent with the observed ranking of group sizes, whereas the tradeoff model provided mixed results. In retrospect, the weakness of the tradeoff model is not surprising. Changes in the risk incurred by individual members of a squirrel monkey troop as a consequence of variation in group size are likely of much smaller magnitude than the risk exposure resulting from local habitat structure.

Are Vigilance, Risk From Avian Predators and Group Size Consequences of Habitat Structure? A Comparison of Three Species of Squirrel Monkey (Saimiri oerstedii, S. boliviensis, and S. sciureus)

Squirrel monkeys of 2 subspecies, Bolivian and Colombian, were removed from their mothers on the day of birth and nursery reared for up to 2 years of age. Infants were tested weekly for 12 weeks, then monthly for 1 year, and at 2 years of age. Tests included morphology (body weight, crown-rump length, and head measurements), behavior (reflexes, activity, reaction to the surrogate), and physiology (heart rate, respiratory rate, temperature and optokinetic nystagmus). Data show some likenesses and some differences between the 2 subspecies.

The growth and development of the squirrel monkey (Saimiri Sciureus).

Normative values were obtained for triiodothyronine and thyroxine from four species of Old World primate (chimpanzees, rhesus monkeys, African green monkeys and talopoin monkeys) and a single species of New World primate (squirrel monkeys) represented by two subspecies, Colombian and Bolivian. The Bolivian squirrel monkeys exhibited the lowest values for both triiodothyronine and thyroxine. Male talapoins had the highest levels of thyroxine. Significant differences were found in levels of triiodothyronine and thyroxine between males and females of the same species and between the two subspecies of squirrel monkeys. Triiodothyronine:thryroxine ratios were consistently lower in the males of all species examined.

Comparative normal levels of serum triiodothyronine and thyroxine in nonhuman primates.

The serum of male squirrel monkeys was analyzed for levels of thyroxine (T4) and triiodothyronine (T3) at intervals corresponding to (1) preparation 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.

Seasonal changes in the thyroid hormones of the male squirrel monkey.

I t has long been known that high-intensity irradiation can cause morphological birth defects and mental impairment in humans (Dekaban, 1968; Rugh, 1973). A few studies on the effects of prenatal irradiation on postnatal development of the nonhuman primate have been published, showing graded effects proportional to the dose and the time of irradiation (Rugh et al., 1966; Rugh, 1973; Brizzee et a]., 1978). Studies on the effect of irradiation on the chemistry of the brain have been largely limited to rodent experiments. The response of the cholinergic enzyme system of the rat brain to irradiation has been found to be dose-dependent (Adlard and Dobbing, 1972; Valcana and Timiras, 1974); to vary with the source or type of the irradiation (Catravas and McHale, 1975): and also to be influenced not only by the stage of development of the animal at the time of irradiation (Maletta and Timiras, 1966: Maletta et al., 1967; Valcana and Timiras, 1974: Valcana et al., 1974), but also by the elapsed time between irradiation and death (Valcana and Timiras, 1974). The data reported here are part of a comprehensive study on the effect of prenatal gamma irradiation on the postnatal development of the squirrel monkey, which was undertaken to obtain comparative data from a nonhuman primate and to demonstrate the potential value of the squirrel monkey as a model for human studies. This paper is concerned with the cholinergic enzymes of the 30-dayold monkey prenatally exposed to 10 rad or 100 rad of cobalt-60 (\"Co) gamma rays.

B. Kaack

Papers

The growth and development of the squirrel monkey (Saimiri Sciureus).

Comparative normal levels of serum triiodothyronine and thyroxine in nonhuman primates.

Seasonal changes in the thyroid hormones of the male squirrel monkey.

The effect of prenatal gamma irradiation on the cholinergic enzymes of the brain in the 30-day-old squirrel monkey.