Instance of Melanosis in the Gonads of Male Indian Robin, Saxicoloides fulicata (Lin.)

Abstract

In excess of 300 Indian Robin (S. fulicata Lin.) males were examined during different phases of the reproductive cycle (180 during the breeding phase and 140 during the remaining phases) for the presence of melanin pigment in the testes. Melanosis (melanin localization) was evident during the regression (31%), preparatory (40%), and progressive (31%) phases in one or both testes of a specimen but was never observed in the breeding phase. Further, melanin was localized only in the intertubular area and was never found in the tubular elements or the tunic. Histomorphological studies of pigmented and nonpigmented testes and of the adrenals taken from these specimens suggest that spermatogenesis in the nonpigmented testes is slightly more advanced than in the pigmented testes and that the melanosis might have developed due to a malfunction of the adrenals.

Testicular melanization has evolved in birds with high mtDNA mutation rates

“…Some authors have suggested that testicular melanogenesis in birds does not take place during the period of spermatogenesis (Anthony & Buss, 1974; Lake, 1981; Agrawal & Bansal, 1983; Hore et al. , 1994; and see references in Anthony & Buss, 1974 for exceptions).…”

“…), we considered that they contained melanin when their colour was black or grey (see Appendix S1). Previous authors have determined that the presence of these colours in the testes of birds is because of melanin granules (Anthony & Buss, 1974; Aire, 1979; López & Paramio, 1980; Lake, 1981; Agrawal & Bansal, 1983; Hore et al. , 1994).…”

“…As some authors have suggested that testicular melanization is associated with the gonadal cycle of birds (Anthony & Buss, 1974; Lake, 1981; Agrawal & Bansal, 1983; Hore et al. , 1994; see however references in Anthony & Buss, 1974 for exceptions), we determined whether prevalence of testicular melanization was correlated between breeding and nonbreeding seasons in 20 species for which two or more adult males (range: 2–38 specimens) were examined in both periods.…”

“…In birds, testicular melanin has been found in the interstitium, wall of seminiferous tubules, tunica albuginea and epididymis (Anthony & Buss, 1974; Aire, 1979; López & Paramio, 1980; Agrawal & Bansal, 1983). The occurrence of bird testicular melanin has been suggested to be associated with the gonadal cycle, melanogenesis being absent during the period of spermatogenic activity and appearing during the regression period (Anthony & Buss, 1974; Lake, 1981; Agrawal & Bansal, 1983; Hore et al. , 1994).…”