The B chromosomes of Claytoniacaroliniana (Portulacaceae) and maple forest dieback

Abstract

Claytoniacaroliniana (Michx.) is a perennial early-flowering species regularly occurring in northeastern American maple forests and frequently possessing accessory (B) chromosomes. A cytological study of Claytonia populations growing in eight maple stands diversely affected by dieback has shown important variations in their B chromosome levels. The severity of dieback was negatively correlated with the presence of the B chromosomes, the observed data being adequately adjusted (R = 0.957 and 0.947) to the values estimated from the explicative variables. Different hypotheses are considered to explain the phenomenon: coincidence with a preexisting situation related to marginal habitats; ecological changes in dieback-damaged zones; or the present influence of stresses affecting both B chromosomes of Claytonia and maple trees by divergent or anologous processes.

Étapes initiales du développement in situ de Claytonia caroliniana var. caroliniana

“…On peut aussi imaginer que des facteurs de l'environnement puissent activer certains bourgeons pJut6t que d'autres et creer des %derives chromosomiques~~ (Lewis 1970) dans certaines circonstances. Ceci n'explique pas l'origine des chromosomes 13 de la claytonie et n'exclut pas que leur disparition puisse &re causee par d'autres mkcanismes (Gervais et al 1989). …”