PHENOTYPIC SELECTION IN HAWKMOTH-POLLINATEDPLATANTHERA BIFOLIA:TARGETS AND FITNESS SURFACES

Abstract

Abstract. The present study explored phenotypic selection on phenological and morphological reproductive traits in hawkmoth-pollinated Platanthera bifolia (Orchidaceae), a Eurasian perennial herb displaying bisexual, long-spurred flowers. The work was carried out during three flowering seasons (1993)(1994)(1995) in a Swedish population. Fitness was estimated as the number of pollinia removed (male fitness) and fruits produced (female fitness). Targets and patterns of selection were compared between years and sex functions by the use of multiple linear regression (including correlational selection estimates, i.e., of combination of traits), analysis of covariance, and projection pursuit regression (PPR). Results from the nonparametric surface-fitting-method PPR showed that selection was mostly linear, thus justifying the use of the parametric methods. In all study years, male and female fitness were highest in plants with many flowers. This reflects that flower number sets an upper limit to fitness and that a large inflorescence attracts more pollinators. In 1994, the summer was dry and the average spur length of P. bifolia was shorter than in the other years. In this year, male and female fitness were positively related to spur length, apparently because the spur of short-spurred plants was somewhat too short relative to the tongue length of the local pollinator for optimal pollen export and import. Additionally, the dry weather in 1994 caused a tendency for correlational selection, which was not found in the other years of study. Among small individuals (apparently more sensitive to drought than large ones), early-flowering plants had higher male and female fitness. The results show that patterns of selection may vary both between years and between sex functions in perennial hermaphroditic plants. The present study is one of the first to consider correlational selection in plants, which probably is of common occurrence and deserves to be investigated more.Key words. Correlational selection, curvature selection, female fitness, hawkmoths, male fitness, orchids, phenotypic selection, plant reproduction, pollination, projection, selection surfaces.Received August 3, 1998. Accepted July 16, 1999. Since the foundation of evolutionary biology, natural selection mediated by pollinators has been considered to have shaped the great diversity in floral variation among angiosperms (Darwin 1862). Indeed, pollinator-mediated selection has been documented in a number of recent studies (e.g.,

Nectar composition in moth-pollinated Platanthera bifolia and P. chlorantha and its importance for reproductive success

“…In long-spurred plants, such as Platantherans, one of the most important flower characters that influence pollinator activity and RS is spur length. Despite the fact that we did not measure this trait, its importance was documented for many plants, including Platanthera species (Maad 2000;Boberg and Ägren 2009;Nilsson 1988;Alexandersson and Johnson 2002;Little et al 2005;Moré et al 2012;Boberg et al 2014). Moreover, the size of the spur is often linked to nectar production.…”

“…The wide varieties of flower types that have evolved in plants are adapted in different ways to their pollinators. The structure of the flower and other traits that include colour or scent are often subjected to pollinator-mediated selection (Maad 2000;Leiss and Klinkhamer 2005;Nepi et al 2018;Parachnowitsch et al 2019). One of these traits being the evolutionary answer for pollinators' preferences is nectar.…”

Armament Imbalances: Match and Mismatch in Plant-Pollinator Traits of Highly Specialized Long-Spurred Orchids

“…Flowers were covered for a period of 48 hours in order to prevent pollinator access and to allow nectar to accumulate in the spur. We also recorded the total number of flowers produced by each plant during the flowering season as well as plant height, as these variables may affect pollinator attraction and reproductive success [17], [22], [34]. However, since both variables were significantly correlated, subsequent analyses were performed using only the number of flowers.…”

“…These traits are expected to be subject to directional [15], [18]-[22] or (once the optimum is achieved) stabilizing selection [23], [24]. These expectations presume that pollinator mouthparts are equal or longer than the floral tube length.…”

El Rol De Los Compuestos Orgánicos Volátiles Florales en Las Interacciones Planta-Insecto

“…Aun así, existe una brecha de conocimiento sobre cómo la diversidad de los COVs y sus funciones han evolucionado en la naturaleza. Por otra parte, los estudios relativos a la selección de señales visuales, incluyendo el color, han sido bien documentados (Maad 2000, Sletvold et al 2010, Schiestl et al 2011, Renoult et al 2013.…”