Levels of apomictic and amphimictic seed formation in a natural population ofCoprosma robusta(Rubiaceae) in Riccarton Bush, Christchurch, New Zealand

Abstract

Facultative autonomous apomictic seed formation has been identified in Coprosma robusta by flow cytometry. Twenty-one (84%) of the plants sampled produced some seeds with an embryo-toendosperm ploidy ratio (2:4) consistent with autonomous embryo development from a single unreduced egg nucleus, and autonomous endosperm development from two unreduced polar nuclei. The average number of apomictic seeds produced in the population was about 15%. Remaining seeds have an embryo-to-endosperm ploidy ratio of 2:3, consistent with sexual reproduction. Dissections of individual apomictic seeds confirmed that the 4C peak occurs in the endosperm, the 2C peak in the embryo. In sexually derived seeds the embryo has a 2C peak and the endosperm is multiploid with 3C and 6C. In both apomictic and sexual seeds the woody endocarp has 2C and 4C peaks.

Determination of apomixis by flow cytometry in two species of Lachemilla (Rosaceae) in Ecuador

“…These values suggest that an unreduced female gamete was solely involved in the formation of the embryo (2n) while two unreduced central embryo sac nuclei merged (2n+ 2n = 4n) during formation of the endosperm. No male cell intervention was required in the formation of these apomictic seeds [16,19,23,54]. A similar autonomous apomictic mechanism has also been registered in the sister genus, Alchemilla [4,16], to our knowledge our result is the first case of such reproductive system in the New World genus Lachemilla.…”

“…Furthermore, Diptera is the main group of visitors and pollinators at high altitudes and latitudes due to its greater plasticity for adaptation to harsh weather conditions (e.g. low temperature, heavy rainfall and strong winds), less dependence on floral rewards, and longer foraging time as they do not feed progeny unlike Hymenoptera [15,23,48,51,52]. Because, they do not pollinate Lachemilla hirta and L. hispidula, their importance lies in that they are the main source of food for many predators and parasitoids present in these plant species [33,34,48].…”

“…Apomixis has allowed plants to colonize sites that have been disturbed or covered by glaciers and increase their distribution at an altitudinal and latitudinal level, even more than related taxa that reproduced sexually. It has been seen that in these regions the autonomous apomixis is more prevalent than the pseudogamy due to the weather conditions [23][24][25].…”

Apomixis in indigenous New Zealand woody seed plants and its ecological and wider significance: a working hypothesis

“…Four plants of Hedycarya arborea, sourced from Queen Charlotte Sound, were planted in the Botanic Gardens in 1957, and since then spread widely throughout this planted forest, which also supports a resident breeding population of the New Zealand pigeon that regularly visit nearby Riccarton Bush in search of food. We have confirmed levels of apomictic and amphimictic seed formation in a female-biased population of the indigenous dioecious shrub Coprosma robusta in Riccarton Bush using flow cytometry (Heenan et al 2003).…”

“…Knowledge about apomixis status may be of potential benefit for the management of existing forest remnants and the design and management of restoration projects. As pointed out by Heenan et al (2003), the extent of apomixis and sexual reproduction in individual plants and populations is also likely to have important implications for species conservation, in particular for those species with sparse, small, or fragmented populations.…”