The evolution of breeding systems and niches in Meconopsis Viguier (Papaveraceae) species from the eastern Tibetan region

Abstract

Concerns have been raised about the viability of populations of Tibetan alpine forb species due to increased grazing, harvesting and climate change. This requires knowledge of the ecological niches and breeding systems of the species. I selected Meconopsis Viguier (Papaveraceae) as a representative iconic genus. To understand the evolution of divergent traits amongst species requires a phylogenetic tree. I generated trees using (i) DNA sequences of its and trnl genes and (ii) morphological and life history traits. The trees place Tibetan Meconopsis and Meconella (Arctic poppies) as sister clades, and these as sister clade with Papaver. The trees suggest polyploidy had a major role in the evolution of Meconopsis. Pollination trials in the field showed that species with 2n=56 chromosomes were self-incompatible (GSI) but some 2n=84 and 2n=76 species were partially or strongly self-compatible (SC). I suggest polyploidy disrupts the GSI mechanism but diploidisation can enable it to re-establish before mutation has degraded it too far. Thus, the evolution of different ploidy levels can lead to changes in breeding systems. Further, I distinguished two pollination syndromes in Meconopsis that also relate to ploidy: (i) GSI or SC flowers with open blue, violet or yellow petals that have a long style and are pollinated by Bombus and/or Dipteran. (ii) SC Flowers in which red or yellow petals enclose the stamens and stigma, and the style is short, that are pollinated by Diptera (2n=84 M. punicea and 2n=76 M. integrifolia var. integrifolia). Bombus were effective and frequent out-cross buzz-pollinators at lower altitudes but were scarce at high altitude. Diptera were frequent everywhere but caused much self-pollen transfer. I suggest that a polyploidy driven transition to SC allowed high altitude Meconopsis species or varieties to become dependent on Dipteran vectors and they co-evolved to attract and shelter certain Diptera. I also quantified the visual discrimination of petal colours by Bombus and Diptera, and found that red flowers are better discriminated by Diptera. I characterise ecological niches of 11 Meconopsis species. I recorded species abundance or absence and habitat factors at 6828 sites across the eastern Tibetan region. Suites of climate (degree-days and precipitation), substrate, vegetation, grazing (by livestock, pikas or marmots) and disturbance factors were significant predictors of abundance. Again, clades with different ploidy levels and breeding systems also showed ecological differentiation. The blue Aculeatae clade was most abundant in cold, well-drained stony sites with little competition. The violet Aculeatae clade was most abundant in wetter, grazing protected sites. The high-ploidy clades (2n=76, 84) were more common, more competitive - occurring amongst taller vegetation and on deeper soils, more tolerant of ungulate trampling, and occurred at sites with lower precipitation. I also assessed the impact of harvesting Meconopsis species for use in traditional medicine, which suggested that some species are experiencing local declines but others are not. By combining these results I suggest how different Meconopsis species respond to changes in grazing, harvesting and climate. The high ploidy SC species appear to have a greater ability to persist when rare. -- provided by Candidate.