Search

Incubation temperature determines sex in the mugger crocodile, Crocodylus palustris . Exclusively females are produced at constant temperatures of 28.0°C through 31°C. At 32.5°C, only males are produced. Both sexes are produced in varying proportions at 31.5, 32.0, and 33.0°C. Embryo survival is not affected within this range, but developmental rate and total incubation time are strongly temperature dependent. In natural nests laid in breeding enclosures, cool incubation temperatures produced only females whereas males were produced only in warm nests. Clutch sex ratios were female or male biased. Yearly sex ratios (=percent male) varied from 0.05 to 0.58; overall sex ratio during six nesting seasons was 0.24 (1 male: 3 females). Sex ratio and incubation time vary with nest location and temperature in a manner consistent with the constant temperature results. Incubation time decreases with increasing incubation temperature, and is an accurate predictor of sex ratio in the field and laboratory. To date, temperature-dependent sex determination (TSD) has been reported in five species of Crocodylus and in three species of Alligatorinae; but the TSD patterns in these groups differ. The TSD pattern of C. palustris is similar to that of C. porosus . Nesting in C. palustris is synchronized with the seasonal availability of thermal regimes suitable for incubation. Resultant sex ratios are a consequence of when and where eggs are laid. Early nests are located in warm, sunny sites; in contrast, late season nests are located in the shade. An egg transplant experiment demonstrated that sex ratios could be altered by simple manipulations of nest temperatures in the field. The adaptive significance of TSD in crocodilians may relate to the influence of incubation temperature on various hatchling attributes, particularly growth.

We compare and contrast the signalling systems and social behaviors of Alligator mississippiensis, Crocodylus aculus, and Crocodylus mloticus . Our qualitative analysis focuses primarily on the behaviors of adults during three phases of reproduction: I. Defense of Territory and Courtship, II. Nesting and Incubation, and III. Hatching and Post Hatching. Signals and signal elements are very similar among the three species. For example, all have vocal, non-vocal acoustic, and visual signals, some transmitted through air or water and others through both media. In addition, each species' repertoire is composed of discrete, graded and complex signals. A few signals are unique to each species. However, their signalling systems differ in the temporal organization of the behaviors, and in the relative frequency in which certain functional groups of signals occuror in which signals occur in a particular sensory mode. Apparently, the signalling systems of C. acutus and C. niloticus are more similar to each other than either is to the signalling system of A. mississippiensis . The signalling systems of the crocodile species appear to be adapted to open water habitats in which visual signals are advantageous and to high density breeding groups and post-copulatory intersexual contact. In contrast, the Alligatorsignalling system appears adapted to a marsh habitat in which vocal signals are likely favored and to low density breeding groups.