This project investigates pollination, reproduction and gene flow in the Colorado Springs evening primrose (Oenothera harringtonii, Onagraceae), a species endemic to southeastern Colorado.
The flowers of Oenothera harringtonii open soon after sunset and are pollinated primarily by two hawkmoth species, Manduca quinquemaculata and Hyles lineata. Hawkmoths have been documented to travel up to 20 miles in just one night, and may therefore contribute significantly to long-distance gene flow among populations. These moths feed on the nectar of Oenothera flowers, which they locate by the strong fragrance produced by the flowers.
A combination of field, greenhouse, and molecular tools are being used to understand which pollinators visit flowers, to what they are attracted (floral scent, size, nectar sugar concentration, etc.), whether plants are successfully reproducing (demographic data, hand pollinations), and to examine patterns of gene flow (microsatellite markers). In addition, we also collect community level data to assess habitat preferences and local floral resources for pollinators.
Long-Distance Gene Flow
The importance of animal pollination has been highlighted in recent years due to its role in commercial agriculture and emerging patterns of widespread pollinator decline. Importantly, pollinators do not merely facilitate the fertilization of ovules. Through their movement patterns they directly influence the paternity, quality and future competitive ability of the resulting seeds. Long-distance pollination has widespread implications ranging from limiting population divergence, accelerating the spread of adaptive traits, disrupting gene complexes and maintaining species cohesion. This is particularly the case for floral traits where long distance pollinators act as agents of selection while also constraining divergence. Once considered rare, direct measures of pollen movement (paternity analysis) have revealed that long distance gene flow is more frequent than expected and has been documented over surprising large distances. However, most of these studies have focused on wind-pollinated trees, and few have investigated long-distance movement in short-lived forbs or moth movement over landscape scales. Although many studies show correlation between geographic variation in floral traits and pollinator communities, few provide evidence of phenotypic selection.
Here, a synthetic approach is taken to investigate how geographic variation in floral morphology and scent is maintained despite high levels of among-population gene flow. This project focuses on Oenothera harringtonii, an endemic annual species with gravity-dispersed seeds, allowing for direct measures of lifetime fitness, inclusion of range-wide populations and gene flow via pollen dispersal. Unlike other systems, O. harringtonii is pollinated primarily by one group of pollinators, hawkmoths, rather than equally by two or more groups (e.g. bees and hawkmoths). The autecology of O. harringtonii and its pollinators should allow for a comprehensive evaluation of range-wide geographic divergence in floral traits, evidence of pollinator-mediated selection through measurements of lifetime fitness, and an understanding of the role of gene flow in constraining divergence.
Habitat Fragmentation
Oenothera harringtonii is found in an increasingly fragmented landscape; however, little is known of the impacts that fragmentation may have on this species and on the community of pollinators upon which it relies for reproduction and long-term population persistence. Studying populations in both fragmented/developed and unfragmented areas will allow us to determine the extent to which habitat fragmentation may negatively impacting both hawkmoth populations as well as populations of O. harringtonii.
The results of this project will help identify the consequences of habitat fragmentation for this endemic species and may provide a better understanding of the potential impacts on similarly threatened species. Results of this work will also have direct relevance to management of O. harringtonii populations, which are state-imperiled.
Conservation Implications
Oenothera harringtonii is endemic to the shortgrass prairie of the middle Arkansas River Valley of southeastern Colorado. This area is known for the Niobrara Formation, a unique geologic feature, and high levels of rarity and endemism, supporting 12 endemic, 30 state-, and 20 globally-imperiled plant species. The combination of rare, imperiled and endemic plants and the intense development pressures (residential, commercial, military, mining and recreational) have made the region a primary focus of conservation efforts in Colorado. However, little is known of the biology of these threatened plants, particularly with regard to their pollination ecology, limiting the ability of land managers to determine appropriate conservation and management practices. Due to the threats imposed, O. harringtonii is considered vulnerable to extinction both globally (G3) and in the state (S3) and is a target species for The Nature Conservancy’s Central Short grass Prairie Ecoregional Assessment.
Because Oenothera harringtonii is an annual, it is likely to respond rapidly to changes in habitat quality and can serve as an indicator species for other endangered plants in this region. Therefore, the results of this project may influence land use decisions in the middle Arkansas River Valley of Colorado and may provide a model for efforts to mitigate the effects of land use change on pollinators and the plants on which they depend. Lastly, because Oenothera harringtonii depends on hawkmoths for reproduction, this work will determine the extent to which nocturnal pollinators face a unique set of threats.
email: kskogen@chicagobotanic.org phone: (847) 835-6919
the Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL 60022.
all content © Krissa Skogen 2010
the Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL 60022.
all content © Krissa Skogen 2010
