Seasonal reproductive cycle of the Galapagos tortoise (Geochelone nigra) in captivity

The reproductive physiology of nine Galapagos tortoises (Geochelone nigra) was studied from February 1988 to May 1989. The study encompassed the annua l reproductive cycle to include complete mating and nesting sequences. Male (n = 4) and female (n = 5) seasonal reproductive changes were determined t hroughout the study with endocrine analysis and ultrasonographic examinatio ns. Males displayed a prenuptial rise in serum testosterone ((x) over bar /- SE = 6.62 +/- 0.92 ng/ml in August) during which gonadal maturation and spermatogenesis are thought to occur. The male reproductive cycle appears c onsistent with the prenuptial spermatogenic pattern exhibited by other trop ical turtles. In the females, testosterone rose during the mating period (( x) over bar +/- SE = 499.3 +/- 124.6 pg/ml in October) prior to ovulation a nd is probably related to receptivity in the females. Progesterone was more variable, brit also peaked during the mating period ((x) over bar +/- SE = 1,017.2 +/- 220.6 pg/ml in October) and appears related to ovulation. Estr adiol rose several months prior to mating ((x) over bar +/- SE = 75.5 +/- 1 1.9 pg/ml in July) and was correlated with increased serum calcium levels. This increase in estradiol is thought to stimulate vitellogenesis several m onths prior to mating. Nesting occurred from November 1988 to April 1989, d uring which six clutches were laid. Clutch size ranged from eight to 17 egg s. Both male and female Galapagos tortoises display seasonal physiological changes that function to regulate annual reproductive patterns. (C) 1998 Wi ley-Liss, Inc.