Cyclic variation of chiasma frequency and distribution in Podarcis sicula (Reptilia: Lacertidae)

The seasonal variations of chiasma frequency and distribution have been studied in the lizard: Podareis sicula. In this species, as in Phyllodactylus (King & Hayman, Chromosoma 69: 131–154, 1978), chiasma frequencies vary following a definite annual cycle, and clearly different trends are shown by interstitial and terminal chiasmata. A comparison between these seasonal chiasma frequency variations and those of environmental temperature shows the existence of a clear correlation between these two parameters. However, this correlation is different in the two types of chiasmata, and may be different within the same type of chiasma depending on the period of the year. A more significant correlation is observed between chiasma cycles and annual variations of the haematic levels of sexual steroid hormones. In particular we observe a highly significant correlation between interstitial chiasma frequencies and testosterone concentration. A less precise correlation between terminal chiasma frequencies and estradiol concentration is also observed. In Podarcis, as in Phyllodactylus, the sperm that will be used for fertilization derive from the spermatocytes showing the highest rate of interstitial chiasmata. This supports the hypothesis that the cyclic variations in interstitial chiasma frequencies represent a mechanism to ensure an adequate level of variability in a given population. The above mentioned correlation between chiasma frequencies and steroia hormone concentrations suggests that the seasonal chiasma cycles are controlled by the same environmental and hormonal factors regulating the spermatogenetic cycle.