Body mass for brown lemur species is in the middle range for extant lemurs, with populations ranging between 1.8 and 2.4 kg in mean body mass (Kappeler, 1990, 1991; Glander et al., 1992; Gerson, 2000; Johnson et al., 2005; Johnson, unpublished data). Notably, variation is greater within subspecies than among them. Populations in drier western habitats are considerably smaller than those found in humid eastern forests (Albrecht et al., 1990; Godfrey et al., 1990). For example, in E. f. rufus, mean body mass in western populations from Anjamba is 1.8 kg (Gerson, 1999, 2000), while mean weight at Ranomafana in the east is 2.2 kg (Glander et al., 1992; Johnson et al., 2005). These ecogeographic size differences have been observed across lemur taxa and may be related in complex ways to variation in climate, seasonality, and forest productivity (Albrecht et al., 1990).
As in nearly all strepsirhines, male and female brown lemurs are typically similar in body size and other morphological traits (e.g., Kappeler, 1990). However, some divergent patterns of sexual dimorphism have been detected in brown lemur populations, again with considerable variation within taxa. Johnson et al. (2005) examined sex differences in three populations of brown lemurs in the southeast: E. f. rufus at Ranomafana, E. albocollaris at Vevembe, and hybrids of these taxa at Andringitra. They found sex differences in canine size in E. albocollaris and the hybrids (with larger canines in males) in conjunction with body-size monomor-phism. E. f. albifrons (Kappeler, 1996) and western E. f. rufus at Anjamena (Gerson, 1999, 2000) also demonstrate this pattern. However, E. f. rufus at Ranomafana exhibited significant female-biased size dimorphism and canine monomorphism (Johnson et al., 2005). These differences are suggestive of divergent patterns of intrasexual competition, perhaps linked to local ecological conditions, but further behavioral studies are required to test these associations. Another variable potentially linked to male-male competition in brown lemurs is testis size. All populations examined thus far have demonstrated relatively high testis volume, indicative of high levels of sperm competition and consistent with their multimale/ multifemale mating systems (Kappeler, 1997; Johnson et al., 2005).
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