Most naked mole-rats Heterocephalus glaber are countershaded, with purple-grey dorsal but pale pink ventral skin. The exceptions to this coloration pattern are uniformly pink, and include newborn pups, most queens and breeding males, and very old animals. Countershading begins to appear at 2±3 weeks of age and begins to disappear at c. 7 years of age. Countershading may provide camou¯age when young naked mole-rats are above ground attempting to disperse. Therefore, reproductives and older workers may lose this coloration once they are unlikely to leave the burrow. Alternative hypotheses for pigmentation that we considered include: thermoregulation, and protection from abrasion or from damaging ultraviolet radiation. These hypotheses are not necessarily mutually exclusive, but do lead to different predictions regarding the development of pigmentation and which colony members should be countershaded.

This study examined the relationships between male agonistic, affiliative, and sexual behaviors and female estrus condition in captive adolescent and young-adult chimpanzees (Pan troglodytes). Data on agonistic, affiliative, and sexual behaviors of 11 males living in three social groups were collected during daily 45 minute observations over a 5 month period. Female estrus condition was assessed daily using the relative size of the female's ano-genital swelling. It was hypothesized that the presence of maximally tumescent females would generate conflicts between males, so an increase in inter-male agonism was predicted. Males exhibited higher rates of agonism toward other males when at least one female in the group was maximally tumescent. Male affiliative behavior directed toward other males and social play with males were affected by the presence and number of maximally tumescent females. Male sexual behaviors increased when maximally tumescent females were present.