Alisa CHALMERS (Department of Zoology, Graduate School of Science, Kyoto University）
Keiko SHIMIZU(Primate Research Institute, Kyoto University)
Life histories and hormones: variations by habitat in three populations of Macaca fuscata
Environment and nutrition have been shown to alter the timing and occurrence of life history traits in short-lived organisms. This study aims to investigate whether environment and nutrition may also have an effect on the life history traits of long-lived organisms by examining changes in both life history traits and steroid hormones in Japanese macaques. The possibility of developing an extended period of adolescence, menopause, and increased longevity in artificial conditions was also explored. Life history traits, including age at first birth, age at last birth, total number of offspring, interbirth interval, and age at death were collected for females living in wild (N<=34), provisioned (N<=201), and captive (N<=69) conditions in Japan for the past 30-50 years. Fecal samples were also gathered from each of the populations and analyzed for cortisol. The results show that all life history traits (except for age at first birth) differed significantly (P<0.01) between the wild vs. provisioned/captive conditions, indicating a strong nutritional influence. Cortisol was two times higher on average (P<0.01) in provisioned (Avg.=0.43ng/ul, N=68) and wild (Avg.=0.40ng/ul, N=41) populations compared to captive (Avg.=0.23ng/ul, N=32). These results provide no evidence for the development of extended adolescence or menopause with improved nutrition, although lifespan in captive (Avg.=17.52years) and provisioned groups (Avg.= 18.45years) are nearly double that of the wild population (Avg.=10.83years). Furthermore, these results suggest that cortisol levels are significantly affected by environmental factors, but not nutrition since only the wild and provisioned populations show significant differences in cortisol relative to the captive population.
Rizaldi（Primate Research Institute, Kyoto University）
Dominance relations among young Japanese macaques in a captive group
I studied development of dominance relations among young Japanese macaques (Macaca fuscata) born in 2002, 2003, 2005 and 2008 in a captive group. This study aimed to analyze the process of: 1) early establishment of dyadic dominance relationships, 2) accomplishment of linear hierarchies, 3) inheritance of mothers rank, and 4) rank changes following a mother’s rank reversal. I examined the ability of young monkeys to make behavioral adjustments when changes in the group’s social hierarchy have occurred.
Dominance rank order among infant peers has been recognized from the onset of aggressive behaviors. More than 60 percent of dyadic relationships between peers are unidirectional and about 90% was correlated with their mothers’ ranks. The rank order was linear and circular triads were rarely found. The dyadic relationships were stable in most cases even from the earliest period of their development. Variation on the degree of stability, linearity and inheritability could be influence of some factors, such as ongoing learning process that prerequisite for young individual, sexual difference, group size and rearing conditions. When dominance reversal occurred among mothers, young offspring could outrank particular target individuals soon after their mothers have previously outranked the target. Young monkeys obviously change their behavior performance, such head flagging, aggressive intervention and successive aggression after their mothers’ rank elevated.
These results indicate that infants may realize the dominance rank of their mothers relative to peer’s mother before the onset of aggressive behavior and adjust their behavior by perceiving social status of their peers. It is most likely that infants might not need to experience “trials and errors” in the process of determining their own statuses among peers. They could play active roles to integrate with a complex social network in their groups The results strongly suggest the importance of spontaneous behavioral adjustments of juvenile monkeys when they came into the situation that they could get higher status in the group, and actively pursue the rank reversal. These findings could give important insights into the mechanism of matrilineal rank inheritance and how young monkeys integrate with complex social networks in their group.
散布パターン特定のため、2005年にサル糞から採集した散布種子の内果皮遺伝子型をヤマモモのマイクロサテライトーカー(Terakawa et al. 2006)を用いて解析したところ、散布距離は平均270.1m、最大634mであった。また、いずれの糞にも複数の結実木由来の種子が混在しており、それらの結実木間の距離は平均161.5m、最大573mであることが示された(Terakawa et al. 2008)。本結果は、サルは遊動域内の様々な場所にある結実木の種子を混在させて長距離運ぶことを示し、サルによる散布はヤマモモの集団内間の遺伝子流動の促進に寄与する生態系機能であることと、サル不在の種子島における長距離散布や遺伝子流動の機会の低下を示唆するものであった。
動物が生きていくためには、摂取した食物から栄養分やカロリーを吸収しなくてはならず、どれだけの食物を必要とするのかは、その動物がどれだけ効率的に食物を消化・吸収できるか(消化率)によって決まる。一般的に、食物が消化管内に留まる時間は平均滞留時間(mean retention time: MRT)という指標で表され、有蹄類においては体重とMRTは比例し、MRTが長くなると消化率が高くなることが知られている(Illius and Gordon 1992; Clauss et al. 2007)。しかし、霊長類において消化率との関連性を同時に検証した研究はほとんどなく、体重による影響についてもほとんどわかっていない。そこで本研究では、飼育下のニホンザルを対象に、消化管マーカーを用いた実験ならびに消化試験を行ない、食物の質や量およびサルの体重がMRTと消化率に及ぼす影響を検証した。