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Variability in female estrus expression has been identified as a barrier to captive panda reproduction [Lindburg and Millard, 1995]. In China, researchers have reported that 80% of female giant pandas in captivity exhibit “weak estrus,” or “the absence of overt estrous behavior” [Shuling et al., 1997]. Previous research on the reproductive endocrinology and behavior of female giant pandas has been limited to one to three animals, limiting understanding of the causal factors related to variable estrous expression in captive animals. In 1997 a study was initiated to evaluate the reproductive biology and behavior of one of the largest captive populations of female giant pandas in China. A checksheet was developed to track the presence or absence of 13 behavioral and physiological indices of estrus in six captive females. Daily urine samples were analyzed for estrogens and progestins by enzyme‐immunoassay to determine whether ovulation took place. The behavioral and physiological indicators were aligned to the estrogen peak to examine the relationship between behavior of and ovarian hormones. Analyses of urinary ovarian hormones indicated that all females ovulated during the study. The data revealed that behavioral and physiological indices differed in their temporal relationship to ovarian hormones. Scent‐marking was present 6 days before the estrogen peak, but not afterwards. Bleat and chirp vocalizations were closely associated with the estrogen peak; however, receptive behaviors, such as lordosis and “tail up when touched,” were most closely associated with falling estrogens. Although all females displayed some type of estrous behavior during the study, individual females varied in the presence or absence of attractive, proceptive, and receptive behaviors. Despite the variation in the behavior of individual females, the hormonal data suggest that the variability in estrous expression in this population was not hormonally based. Zoo Biol 21:449–466, 2002. © 2002 Wiley‐Liss, Inc.

The hormones of the endocrine pancreas are believed to play an important role in early development. The development of the pancreas and the appearance of hormone-producing cells during embryogenesis have been extensively studied in mammals and birds. Relatively little work has been done in other vertebrates, and there are no published studies regarding the order Crocodilia. Given the pivotal phylogenetic position of crocodilians, Alligator mississippiensis provides an interesting species in which to study the embryonic development of the endocrine pancreas. The aims of the present study were (1) to investigate the morphological development of the pancreas and (2) to determine the initial appearance and regional distribution of the pancreatic endocrine cells in the embryonic alligator. At each stage of development serial sections of pancreatic tissue were stained with hematoxylin and eosin to aid in morphological description. Using immunocytochemistry sections were stained to detect the presence of insulin, glucagon, somatostatin, and pancreatic polypeptide. The dorsal pancreatic bud was first observed at stage 8, coincident with the appearance of insulin-containing and glucagon-containing cells. Somatostatin-containing cells were first detected at stage 10. At stage 13 the ventral pancreatic bud was first observed. At stage 14 the dorsal and ventral pancreatic buds fused and insulin, glucagon, and somatostatin were found throughout the pancreas. Not until stage 17 was pancreatic polypeptide first detected. Unlike the other hormones, pancreatic polypeptide was rare or absent in the dorsal region of the pancreas. In later stages of development, somatostatin-containing cells were the most abundant and constituted 35-40% of all hormone-containing cells. The sequence of appearance of insulin and glucagon found in the alligator is the same as that found in mammals and birds. Copyright 1994, 1999 Academic Press