title: Variation in style morph frequencies in tristylous Lythrum salicaria in the Iberian Peninsula: the role of geographical and demographic factors.
abstract: OBJECTIVE
  The balance between stochastic forces and negative frequency-dependent selection largely determines style morph frequencies in heterostylous populations. Investigation of morph frequencies at geographical range limits can provide insights into the forces maintaining the floral polymorphism, and the factors causing biased morph ratios. Here, we investigate style morph frequencies in populations at the south-western European range limit of tristylous Lythrum salicaria, to explore the role of demographic and geographical factors influencing morph ratios in its native range.
  
  
  METHODS
  We measured morph composition and evenness, and the size of 96 populations, along a north to south latitudinal transect from Galicia to Andalucia, Iberian Peninsula, traversing a steep climatic gradient. To examine the potential influence of morph-specific fitness components on morph ratios, we examined reproductive traits in 19 populations.
  
  
  RESULTS
  Most populations of L. salicaria were trimorphic (94·79 %), the majority exhibiting 1 : 1 : 1 morph ratios (68·75 %). Populations with biased morph ratios had a deficiency of the short-styled morph. Population size and morph evenness were positively associated with latitude, with smaller populations and those with less even morph ratios occurring towards the south. Greater variance in morph evenness was evident at the southern range margin. There were no consistent differences in components of reproductive fitness among style morphs, but southern populations produced less fruit and seed than more northerly populations.
  
  
  CONCLUSIONS
  Our results demonstrate the influence of finite population size on morph frequencies in L. salicaria. However, they also illustrate the resilience of Iberian populations to the factors causing deviations from isoplethy and morph loss, especially at the southern range limit where populations are smaller. The maintenance of tristyly in small populations of L. salicaria may be aided by the genetic connectivity of populations in agricultural landscapes resulting from gene flow through pollen and seed dispersal.
authors.affiliation: Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal and joana.costa@uc.pt.
authors.forename: Joana
authors.initials: J
authors.lastname: Costa
authors.affiliation: Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal and.
authors.forename: Sílvia
authors.initials: S
authors.lastname: Castro
authors.affiliation: Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal and.
authors.forename: João
authors.initials: J
authors.lastname: Loureiro
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2.
authors.forename: Spencer C H
authors.initials: SC
authors.lastname: Barrett
mesh_terms: D005828:Genetics, Population; D031561:Lythrum / Q000235:genetics / Q000502:physiology*; D011156:Population Density; D012639:Seeds; D013030:Spain; D053833:Wetlands
keywords: Frequency-dependent selection; Iberian Peninsula; Lythrum salicaria; genetic drift; isoplethy; population size; range limits; stochastic forces; tristyly