Biological and ecological traits of Anthemis chrysantha J. Gay (Asteraceae), a critically endangered species

Resumo

Anthemis chrysantha (Asteraceae) is a winter annual plant with erect habit which reaches a height of 30 cm. Its emergence period begins in autumn, flowering occurs from early March to late May, and fruits mature mostly in June, after that the plant dies. This species is endemic to North Africa and Cartagena (Murcia, southeast of Spain) and it is classified as Critically Endangered according to the International Union for Conservation of Nature (IUCN) categories, and as En Peligro de Extinción in the Catálogo Regional de Flora Silvestre Protegida de la Región de Murcia. Due to this fact and the little prior knowledge about the species, the aim of this thesis is to study biological ad ecological traits of A. chrysantha in order to establish appropriate measures for its conservation. Thus, this work includes the study of: (1) morphology, anatomy and germination behavior of the heteromorphic achenes of A. chrysantha; (2) the spatial and temporal dispersal traits of the achenes and the implication of their dispersal strategy for the species; (3) the ability of the species to form a soil seed bank and the role that it can play in the maintenance of the population in an arid and unpredictable environment; (4) the level of genetic diversity, including the genetic variation within and between natural populations of the species, using ISSR markers; and (5) two different introduction methods, transplant of plants grown in a greenhouse and direct achene sowing, for testing them regarding to the survival and the establishment of the populations. According to the obtained results from the conducted tests, A. chrysantha produces two morphs of achenes: white and dark achenes which differ in size, weight, anatomy, and germination behavior. White achenes germinate in high percentages at different conditions, but dark achenes do not germinate. Dark achenes have dormancy due to the thickness of their pericarp, which makes difficult the entry of water and also prevents germination by mechanical restriction. This work also demonstrates the two achenes type remain on the dead mother plant from the fruiting period (early summer) to late spring forming a seasonal aerial seed bank, and rain is necessary to release the achenes from the capitula (ombrohydrochory), which are mainly dispersed at short distances (atelechory). The aerial seed bank is an effective trait to ensure the maintenance of this species in its unpredictable habitat, but A. chrysantha has also the ability to form a persistent soil seed bank (PSB), with fluctuations of achene density due to the variability in annual rainfall and where dark dormant achenes are largely responsible for the permanent fraction. A PSB plays a crucial role in the maintenance of the annual population of this endangered plant and the study, carried out during five consecutive years, highlights its importance in dry years. In addition, the genetic diversity study of the Spanish populations shows that both at the species and population level the genetic variation of A. chrysantha is high, with a high within-population variability and a low, differentiation between populations. The ISSR markers have detected genetic variation among Spanish and Algerian A. chrysantha populations, which could support the proposal of Sánchez et al. (2002) for recognizing the rank of subspecies, at least, for the Spanish populations. Finally, the two introduction methods seem to be valid for the establishment of A. chrysantha, in spite of the reproductive failure after two years due to the dry spring in 2012. However, if the next years are conducive, the formation of a possible PSB could provide dramatic populations recovery and this fact could be of great interest for the species conservation. In conclusion, this work goes into the biology of this threatened species and we hope that it will become a very useful tool for establishing appropriate measures for the species conservation when the Regional Administration carry out its recovery plan.