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Alopecia syndrome was identified in ring-tailed lemurs in the Berenty Reserve, southern Madagascar, in the late 1990s and spread extensively in 2001–2003. A ring-tailed lemur population inhabiting a 14.2-ha area has been studied with individual identifications since 1989. To understand the alopecia syndrome, we recorded the fur condition of all individuals (around 100 lemurs) in 2001, 2004, and 2005. The number and ratio of alopecic lemurs decreased over time from 19 lemurs (22%) in 2001 to 6 (6%) in 2004, to only 3 (3%) in 2005. Of the 19 alopecic lemurs in 2001, 15 were females and only 4 were males. They ranged in age from 2 to 15 years, with by far the highest occurrence of alopecia among young lemurs (2 years old: 55%; 3 years old: 50%; and 4 years old: 40%). Nine of the 19 animals (47%) recovered their fur condition over 3 years. The mortality rate of the alopecic females over the same period was 43%, similar to that of nonalopecic females (40%) as was their birth rate. Infant mortality was higher for alopecic mothers (57%) than for nonalopecic females (19%), although the difference was not significant.

Eviction of subordinate females is well known in female-dominated ring-tailed lemur society. In almost all cases, evictions result from a dominant matriline targeting aggression towards subordinate matrilines. Here, we report an eviction in a large, single matrilineal troop after the death of the troop’s “Grandmother.” Although the troop contained ≥18 individuals and 8 females over several years, no evictions occurred while the Grandmother was alive. After her death, a newly dominant female and her younger sisters evicted their nieces whose higher-ranking mother had already died. The younger relatives of the evicted females did not follow their mother and sisters but stayed in the natal troop. We suggest (1) the presence of certain females like Grandmother may function as a deterrent to eviction among descendants; (2) if eviction occurs within a single matriline, aggressors evict the most distant kin; (3) a newly dominant female may form a subgroup with her younger and subordinate sisters rather than older and higher-ranking ones to circumvent intragroup competition; and (4) the juveniles of evicted female kin do not always follow the nomadic evictees but may choose the safer strategy of remaining within their natal troop.

Alopecia (i.e. hair loss) in ring-tailed lemurs, or “bald lemur syndrome”, appeared in Berenty Reserve in the 1990s. The consumption of the leaves of Leucaena leucocephala, an introduced tree rich in toxic mimosine, has been linked to hair loss. Here, we show that individuals respond differently to the toxin, and bad fur condition is also influenced by other factors, particularly dietary diversity and social stress.

One pair of the submetacentric autosomes is especially large. Several pairs of the acrocentric autosomes are very small elements. Two pairs of small acrocentric autosomes bear secondary constriction near the centromere.