Clarke Margaret R, Zucker Evan L, Ford Randall T, Harrison Richard M
Tulane National Primate Research Center, Covington, Louisiana, USA.
Am J Primatol. 2007 Apr;69(4):477-84. doi: 10.1002/ajp.20354.
Behavioral observations on juvenile mantled howlers are limited by visually undifferentiated genitalia; however, animals can be sexed when they are very young or if they are captured. Behavioral data and fecal samples from juveniles during month-long field studies from 1993 to 1995 were analyzed to determine whether there are developmental differences in behavior or hormone concentrations that can be used to differentiate males from females. The subjects were juveniles of known sex and age from five different social groups on Hacienda La Pacifica, Costa Rica. Based on 749.8 hr of focal-animal sampling, there were no sex differences in daily activity patterns. There were no sex differences in proximity to mothers and other group members, and age differences reflected howler life-history patterns. There were no differences in estradiol or testosterone concentration by age or sex. Juvenile monomorphy thus extends beyond morphology to behavioral and hormonal similarity as well. Most juveniles are forced out of their natal groups and remain solitary until they join new groups by supplanting all same-sex adult group members. Monomorphy may allow them to spend more time in natal groups, and thus both reduce the solitary period and allow the juveniles to improve social skills needed for later immigration. While this strategy may benefit juvenile howlers, it remains a problem for those who wish to study juvenile sex differences from a distance.
对幼年鬃毛吼猴的行为观察受到其外观上难以区分的生殖器的限制；不过，在动物非常年幼或被捕获时可以确定其性别。对1993年至1995年为期一个月的野外研究中幼年吼猴的行为数据和粪便样本进行了分析，以确定在行为或激素浓度方面是否存在可用于区分雄性和雌性的发育差异。研究对象是来自哥斯达黎加拉帕西菲卡庄园五个不同社会群体的已知性别和年龄的幼年吼猴。基于749.8小时的焦点动物取样，日常活动模式不存在性别差异。与母亲及其他群体成员的亲近程度不存在性别差异，年龄差异反映了吼猴的生活史模式。雌二醇或睾酮浓度在年龄或性别方面没有差异。因此，幼年吼猴的单态性不仅体现在形态上，在行为和激素方面也具有相似性。大多数幼年吼猴会被迫离开它们出生的群体，保持独居状态，直到通过取代所有同性成年群体成员加入新的群体。单态性可能使它们能够在出生群体中待更长时间，从而既缩短独居期，又能让幼年吼猴提高日后迁移所需的社交技能。虽然这种策略可能对幼年吼猴有益，但对于那些希望从远处研究幼年吼猴性别差异的人来说，这仍然是个问题。
