Developmental Arrest during Embryonic Development of the Common Chameleon (Chamaeleo chamaeleon) in Spain

Abstract

Embryonic development of the common chameleon, Chamaeleo chamaeleon, was monitored from oviposition to hatching at a field site in southwestern Spain and in the laboratory under five experimental temperature regimes. Embryos were diapausing gastrulae at the time of oviposition; developmental arrest in the field continued as cold torpor during winter. Postarrest development in the field commenced in April, and hatching occurred in August, for a total incubation period of 10.5 mo. In the laboratory, one group of eggs was incubated at a constant warm (26 degrees C) temperature. The remaining treatments simulated field conditions and consisted of initial periods of warm temperature of 0, 27, 46, and 71 d, a subsequent 4-mo period of cold winter (16 degrees C) temperature, and a final period of warm (26 degrees C) temperature. Embryos in the constant warm temperature treatment were in diapause an average of 3 mo, with clutch means ranging from 2 to 4 mo. Hatching among clutches occurred over 2 mo. In contrast, for field and experimental eggs that experienced cold winter conditions, hatching within treatments occurred over 2-14 d; "winter" conditions synchronized development. The length of time between the end of cold conditions and hatching did not differ among treatments; development thus resumed as soon as temperature was suitable regardless of the initial period of warm temperature. Diapause in nature thus insures that embryos remain gastrulae after oviposition despite nest temperatures that may be warm enough to support development.

Determinants of incubation period: do reptilian embryos hatch after a fixed total number of heart beats?

“…By contrast, most squamates (including the two lizard species that we studied) delay oviposition until the embryo is partway (typically around 25%) through the total period of embryonic development (Shine, 1983;Andrews, 2004); and, thus, the number of heart beats estimated for lizards over the period from oviposition to hatching is substantially less than the total number over the entire course of embryogenesis. It would be of great interest to study lizards that lay their eggs at much earlier stages of embryonic development, as in some chameleons (Andrews et al, 2008) and to determine whether the inclusion of this 'missing' fraction (pre-laying) brings the sum heart beat count for lizards up to the same level as in birds and turtles.…”

“…Although many additional phenomena [e.g. embryonic diapause, precocial vs altricial hatching (Ar and Tazawa, 1999;Andrews et al, 2008)] can also affect the duration of the egg stage, much of the variation in total incubation periods appears to be driven by variation in rates of embryogenesis. Consistently, embryos developing at high temperatures have shorter development times than those kept at low temperatures (Deeming and Ferguson, 1991;Hoegh-Guldberg and Pearse, 1995).…”

Effects of incubation temperature on growth and performance of the veiled chameleon (Chamaeleo calyptratus)

“…These temperatures fall within the range of nest temperatures in nature for Chamaeleo chamaeleon, a close relative of C. calyptratus. The mean nest temperature for C. chamaeleon during spring and summer is about 251C and in August, just before hatching, the mean nest temperature is about 301C (Díaz-Paniagua, 2007;Andrews et al, 2008). Incubation at a constant temperature is appropriate for Chamaeleo species because females place their nests well below the soil surface where diel variation in temperature is substantially lower than seasonal variation.…”

A proposed mechanism for enhanced water-conservation in egg clutches of the Mexican Kingsnake, Lampropeltis mexicana (Serpentes: Colubridae)

“…Part of our model relies on the concept of uniform water gain over the entire egg surface, and water gain occurring at the same rate reported by Andrews (2008) and Díaz-Paniagua (1996) for lizards and tortoises, owing to the similarity in size and shape of the eggs of all three taxa. There is less increase in water-vapor pressure in small aggregations of eggs; thus, water-loss by gain is diminished or absent in intermediatesized aggregations.…”