Asexuality and the coexistence of cytotypes


  • Present address: Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523-1177, USA.

Author for correspondence: Rebecca Hufft Kao Tel: +1 970 491 5179 Fax: +1 970 491 3862 Email:


  • • Reproductive isolation via apomixis is one way for newly created cytotypes to persist and coexist with other cytotypes. Arnica cordifolia (Asteraceae) has both triploid and tetraploid cytotypes co-occurring in many locations. The rate of apomixis in each cytotype was explored as a mechanism for the maintenance of sympatric cytotypes.
  • • Flow cytometry was used on both adults and seeds from mixed cytotype populations to estimate reproductive mode and to evaluate the relationship between cytotype frequency and reproductive success. Flowering time was surveyed to look for temporal reproductive isolation between cytotypes.
  • • Both triploids and tetraploids can be asexual. Apomixis in A. cordifolia is usually autonomous, not pseudogamous as previously thought. Sexual reproduction appears to be uncommon. The minority cytotype in each population does not produce fewer seeds, confirming that minority cytotype exclusion is unlikely to occur via reproductive disadvantage. Triploids flowered earlier than tetraploids, but with much overlap.
  • • Asexual reproduction is an important factor promoting the coexistence of cytotypes in this system. Other mechanisms maintaining populations of sympatric cytotypes are not well studied or understood and warrant further investigation.