Effect of elevation on sexual reproduction in alpine populations of Saxifraga oppositifolia (Saxifragaceae)

Abstract

Self-compatibility in high arctic and alpine areas is regarded as an adaptation to low pollinator abundance. However, high genetic variability as a consequence of outcrossing is, with regard to population persistence, favorable in highly stochastic environments such as tundra habitats. To evaluate these contradictory scenarios, I performed in situ pollination experiments to examine the breeding system of the predominant outcrosser Saxifraga oppositifolia in ten populations at two different elevations in the Swiss Alps. Pollinator limitation was detected at both elevations, but fruit set in naturally pollinated flowers was only slightly less at the higher elevation. Increased pollinator limitation at high compared with low elevation thus could not be demonstrated in this experiment. Hand-crossings yielded equal mean proportion seed set at both elevations, and so did hand-selfings. This constant pattern of the breeding system in S. oppositifolia indicates selective factors that lead to the maintenance of a high level of outcrossing even in high-elevation populations. Based on sex allocation models, it was expected that a high ovule number should be selectively advantageous in a plant-pollinator system where chance visitation or selfing play important roles. However, female reproductive offer in terms of ovule number per flower did not change from low to high elevation. Since neither increased pollinator limitation nor increased seed set in selfed flowers was found at high compared with low elevation, the prerequisites for testing the hypothesis were not given. This study contradicts the hypothesis that inimical environmental factors in alpine or arctic habitats necessarily select for increased selfing rates in a preferentially outcrossing species like S. oppositifolia.

Negative impacts of a vertebrate predator on insect pollinator visitation and seed output in Chuquiraga oppositifolia, a high Andean shrub

“…Totland 2001), and outbreeding is the dominant breeding system in long-lived species (e.g. Arroyo and Squeo 1990;Gugerli 1998). It thus would be of great interest to learn whether lizard effects are found in other high mountain areas in the world, and study its repercussions at the level of community structure.…”

Causes of the genetic architecture of south-west European high mountain disjuncts

“…In the central to southern European high mountains, S. oppositifolia is diploid (2n = 26), at least within its Alpine distribution (Küpfer and Rais 1983;Kaplan 1995), and reproduces mainly by cross-pollination through dayflying butterflies and flies (Stenström and Molau 1992;Heß 2001), although selfing is possible (Gugerli 1997(Gugerli , 1998. The species has a wide ecological tolerance, especially in relation to altitude (temperature), soil type and water availability.…”

Demographic consequences of age-structure in extreme environments: population models for arctic and alpine ptarmigan

“…Arctic and alpine organisms cope with extreme environments with specialized life history strategies, and a suite of other biochemical, morphological, and behavioral adaptations (Martin 2001;Martin and Wiebe 2004). Studies along environmental gradients have shown that offspring number, offspring size, and adult survival often covary with latitude or altitude in plants (Eriksen et al 1993;Gugerli 1998), invertebrates (Mani 1968;Blanckenhorn 1997;Baur and Baur 1998), and terrestrial vertebrates (Berven 1982;Dobson 1992;Krementz and Handford 1984). Arctic and alpine organisms are often long-lived and may be some of the most effective sentinel species for detecting biological responses to environmental change (Morris and Doak 1998;Inouye et al 2000; Barbraud and Weimerskirch 2001;Cooch et al 2001;Derocher et al 2004).…”