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Attacks on a wild infant ring-tailed lemur (Lemur catta) by immigrant males at Berenty Madagascar interpreting infanticide by males.

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American Journal of Primatology 67:267–272 (2005)
BRIEF REPORT
Attacks on a Wild Infant Ring-Tailed Lemur (Lemur catta)
by Immigrant Males at Berenty, Madagascar: Interpreting
Infanticide by Males
SHINICHIRO ICHINOn
Graduate School of Asian and African Area Studies, Kyoto University, Kyoto, Japan
An orphaned infant ring-tailed lemur (Lemur catta) was attacked
persistently by immigrant males and disappeared with severe wounds
at Berenty Reserve, Madagascar. Prior to the attacks, two troop members
disappeared. On 20 November 1998, the only resident male in Troop C2B
disappeared suddenly. After the disappearance, nine males from three
neighboring troops approached, but only six males continued to shadow
the troop. Of the females, the one lactating female attacked the males the
most frequently. On 21 January 1999, the lactating female disappeared
and her infant was orphaned. Subsequently, five attacks on the infant by
immigrant males were observed for five consecutive days from January
23 to 27. The aggression was persistent and specifically targeted the
infant, suggesting that the attacks were purposeful aggression, rather
than redirected or accidental aggression. The primary attacker was the
most dominant of the immigrant males, and mated with females in the
next mating season. Am. J. Primatol. 67:267–272, 2005.
r 2005 WileyLiss, Inc.
Key words: infanticide; reproductive tactics; orphan; ring-tailed lemur;
Madagascar
INTRODUCTION
Infanticide by males is a relatively common phenomenon in primates [van
Schaik & Janson, 2000]. The adaptive significance of this phenomenon has been
highly controversial [Hrdy, 1979; Haufater & Hrdy, 1984; Sussman et al., 1995;
van Schaik & Janson, 2000]. The most commonly accepted theory in recent years
considers infanticide by males to be a male reproductive strategy [van Schaik &
Janson, 2000]. According to the classic sexual-selection hypothesis on which the
male reproductive strategy theory is based, the female that loses an infant to
Contract grant sponsor: Ministry of Education, Science and Culture of Japan.
n
Correspondence to: Shinichiro Ichino, Graduate School of Asian and African Area Studies,
Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan. E-mail: ichino@jambo.africa.kyoto-u.ac.jp
Received 4 August 2003; revised 22 February 2005; revision accepted 3 March 2005
DOI 10.1002/ajp.20183
Published online in Wiley InterScience (www.interscience.wiley.com).
r
2005 Wiley-Liss, Inc.
268 / Ichino
infanticide returns rapidly to ovarian cycling, comes into estrus more quickly
then she would have otherwise, and copulates with an infanticidal male [Haufater
& Hrdy, 1984; Sugiyama, 1965].
Ring-tailed lemurs form multimale–multifemale, female resident troops
[Jolly, 1966] and exhibit strict reproductive seasonality [Koyama et al., 2001;
Sauther, 1991]. Attacks on infants by male ring-tailed lemurs may also be
regarded as a male reproductive tactic [Hood, 1994; Pereira & Weiss, 1991]. At
least nine cases of infant attacks were observed in a semifree-ranging population
at the Duke University Primate Center [Jolly et al., 2000]. Pereira and Weiss
[1991] proposed a model of the ring-tailed lemur mating system that included the
hypothetical co-evolution of female and male reproductive tactics. According
to their model, immigrant males kill unrelated infants that are vulnerable.
However, only two cases of infant attack by males have been reported in wild
ring-tailed lemur populations [Hood, 1994; Jolly et al., 2000], both of which were
observed at Berenty Reserve. In the first case, a nontroop male killed an
abandoned infant that had fallen to the ground [Hood, 1994]. The killer male did
not immigrate into the infant’s troop after the incident. Thus, Hood’s [1994]
observation was not a typical case as described in the model of Pereira and Weiss
[1991]. In the second case, an immigrant male bit an infant while he was being
chased by resident males during an attempt to join a troop [Jolly et al., 2000].
It is not possible to exclude the possibility that the attack was redirected or
accidental aggression.
Thus, more information is required to help test the model of Pereira and
Weiss [1991]. In this paper, I present a case of attacks on a wild infant ring-tailed
lemur by immigrant males.
MATERIALS AND METHODS
This study was conducted at Berenty Reserve, southern Madagascar. Jolly
and her colleagues [2002] have studied ring-tailed lemurs there since the 1960s.
Koyama and his colleagues [2001, 2002] have conducted continuous long-term
research since 1989 in a 14.2-ha area that partly overlaps Jolly’s study area. I
observed attacks on an infant in Troop C2B, one of the troops in Koyama’s study
area. Troop C2B consisted of six individuals, including three adult females and
one adult male, in November 1998.
The attacks were observed during my 14-month study that lasted from
August 1998 to September 1999. In this paper I use the notes that I recorded as ad
libitum sampling [Altmann, 1974] from 20 November 1998 to 28 January 1999.
The emission of a ‘‘spat call,’’ the typical submissive call [Jolly, 1966; Pereira &
Kappeler, 1997], was used as an operational indicator of dominance.
RESULTS
Immigration of New Males
On 20 November 1998, the lone adult male (NT) in Troop C2B disappeared
suddenly. It is possible that he died. Subsequently, nine males from three
different troops approached Troop C2B. Six males continued to shadow the troop
until January 1999. By 20 January, I had observed a total of 45 attacks on the
immigrating males by troop females. The only lactating female (MI-91~) attacked
the males the most frequently (80.0%, 36 cases).
Attacks on Infants by Immigrant Males / 269
Attacks on an Infant by Immigrant Males
On 21 January 1999 the lactating female (MI-91~) disappeared from Troop
C2B and probably died. Her 4-month-old daughter (MI-9198~) was orphaned.
After the female disappeared, a total of five attacks on the infant by immigrant
males were observed over the next 7 days (Table I). The two attackers were the
most dominant male (TJ) and the second-most dominant male (SH-93#) of the
immigrant males (Table I).
The first attack (case 1) was observed at 0706 hr on 23 January. When
the troop females moved away from the infant, an immigrant male (TJ)
approached and attacked the infant. A female (RH) came back immediately
and chased away the male. At 1558 hr on 24 January, another male (SH-93#)
also attempted to attack the infant. However, the infant’s grandmother (MI)
chased him.
The second attack (case 2) was observed at 1524 hr on 25 January. TJ, the
dominant immigrant male, responded to the infant’s distress call by turning back
and searching for the infant, which he then attacked. Two adult females (RH and
MI) chased the male immediately.
Around 0600 hr on January 26, the infant was found near the tourist
cafeteria with deep (5 cm) slashes on each hind leg (Fig. 1). At 0748 hr, the third
attack (case 3) was observed. When the infant exchanged calls with a juvenile
female, TJ noticed the call, approached, and attacked the infant. No females
supported the infant at that time. After the attack, the infant remained sitting
alone in a bush until the evening.
The fourth attack (case 4) was also observed on 26 January. At 1757 hr, when
the troop females came back near the infant, the infant began to follow the
traveling troop. At 1801 hr, TJ passed under the tree where the infant was
feeding with troop females. He seemed to notice the infant, but remained sitting
under the tree for around 30 min, looking up into the tree. At 1834 hr, TJ
suddenly climbed the tree and attacked her. The infant dropped to the ground,
and the other male (SH-93#) on the ground attacked her. The infant’s
grandmother (MI) chased SH-93# immediately. At 1851 hr, TJ attempted to
approach the infant again. However, her grandmother (MI) chased him away
again.
The fifth attack (case 5) was observed at 1746 hr on 27 January. The infant
was resting with troop females at 1736 hr. At 1742 hr, when the females moved
away from the infant, TJ attacked the infant. The infant’s grandmother (MI)
came back and chased TJ immediately.
On 29 January, the infant disappeared from the study area and probably
died. At 0900 hr she was sitting in a bush and seemed to be unhealthy. That was
the last time I observed her, and her carcass was never found.
TABLE I. Observed Cases of Attacks on Infant (MI-9198~)
Case
1
2
3
4
5
Date
Jan.
Jan.
Jan.
Jan.
Jan.
23
25
26
26
27
Time
Attackers
7:06
15:24
7:48
18:34
17:46
TJ
TJ
TJ
TJ, SH-93#
TJ
270 / Ichino
Fig. 1. Wounds on the hind legs of an infant (MI-9198~).
After the Attacks on the Infant
After the infant disappeared, only three males, including the most dominant
male (TJ), successfully completed immigration into Troop C2B. They mated with
troop females in the next mating season (Ichino, unpublished data). The other
three males disappeared from Troop C2B by April 1999.
DISCUSSION
An orphaned infant ring-tailed lemur was attacked and presumably killed by
immigrant males. The attacks were persistent and specifically targeted the infant.
An immigrant male (TJ) responded to the distress calls from the infant and
attacked her (cases 2 and 3). Multiple sneak approaches by males toward infants
have been observed at the Duke University Primate Center (DUPC) [Pereira &
Weiss, 1991] (Pereira, personal communication). These observations suggest that
attacks on infants by males are purposeful aggressions, rather than accidental or
redirected aggressions.
After the lone troop male disappeared, the newly immigrant males attacked
the infant. This case is similar to what has been reported for gorillas [Watts,
1989]. However, ring-tailed lemur troops usually contain several males. Troop
males may play a role in defending infants against lethal aggression by immigrant
males. Troop males have attacked and tried to drive nontroop males off
[Nakamichi & Koyama, 1997; Pereira & Weiss, 1991], and have often responded
to infant distress calls by running toward the infant (Pereira, unpublished data;
Ichino, unpublished data).
Attacks on Infants by Immigrant Males / 271
The primary attacker (TJ) was the most dominant of the immigrant males
(Table I), and mated with the troop females in the next mating season. These
results are consistent with the prediction from the model of Pereira and Weiss
[1991], which is based on the sexual-selection hypothesis. However, it remains
obscure how males gain a reproductive benefit from infanticide in these strictly
seasonal breeders [Sussman et al., 1995]. Jolly et al. [2000] argued that
reproductive effort during lactation may affect the mother’s physical condition,
which is related to the birth rate and infant survival rate in the following
year, and this hypothesis is partly supported by observations at the DUPC
(Pereira, unpublished data).
Of the troop females, the lactating female attacked the immigrant males the
most frequently. Aggression by the lactating female has been observed at the
DUPC and is considered a female counterstrategy for infanticide [Pereira &
Weiss, 1991]. Ring-tailed lemur females can attack and disperse males effectively
because they are dominant over males [Jolly, 1966; Kappeler, 1990]. In contrast,
nonlactating females (including the infant’s grandmother) rarely attacked the
males even after the infant was orphaned, although they supported the infant
when she was attacked by the males. This observation suggests that ring-tailed
lemur females rarely defend infants cooperatively against lethal attack by
immigrant males.
ACKNOWLEDGMENTS
I thank Jean de Heaulme and his family for their kind hospitality and
permission to carry out this study at Berenty Reserve; A. Randrianjafy, director of
the Botanical and Zoological Park of Tsimbazaza, and the Government of the
Malagasy Republic for their kind permission to perform this research in
Madagascar; G. Yamakoshi for his useful comments; N. Koyama for his invaluable
advice; and M.E. Pereira for his useful comments and kind permission to refer to
his unpublished data. This work was supported by Grants-in-Aid for Scientific
Research from the Ministry of Education, Science and Culture of Japan to
N. Koyama (no. 06610072).
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