Fig 2. Monthly average (± SE) body weights (kg) of captive (circles, N = 11) and wild (green triangles; adapted from Smuts et al., 1980; N = 26) male lions through 30 mo (2.5 yr) [10].

Red circles denote months when captive males were actively gaining weight and grey circles represent months where the rate of weight gain slowed. Trend lines are solid for captive lions and dashed for wild lions. The black arrow indicates the earliest age, 14 mo (1.2 yr), and body weight, 105 kg, at which spermatozoa were present in captive male urine (n = 2). The grey arrow denotes when spermatogenesis should be occurring in wild lions based on the age, 24 mo (2.0 yr), at which they reach ~105 kg and the open arrow is the age (26 mo, 2.2 yr) and body weight (113 kg) when males reach puberty in the wild based on behavioral observations [10] and the earliest age spermatozoa were found in seminiferous tubules in wild males [16]. (Modified data on wild lions by Smut et al., used with permission from John Wiley and Sons) [10].