title: Reproductive ecology and isolation ofPsittacanthus calyculatusandP. auriculatusmistletoes (Loranthaceae).
abstract: BACKGROUND
  Relationships between floral biology and pollinator behavior are important to understanding species diversity of hemiparasiticPsittacanthusmistletoes (c. 120 species). We aimed to investigate trait divergence linked to pollinator attraction and reproductive isolation (RI) in two hummingbird-pollinated and bird-dispersedPsittacanthusspecies with range overlap.
  
  
  METHODS
  We investigated the phylogenetic relationships, floral biology, pollinator assemblages, seed dispersers and host usage, and the breeding system and female reproductive success of two sympatric populations ofP. calyculatusandP. auriculatus, and one allopatric population ofP. calyculatus. Flowers in sympatry were also reciprocally pollinated to assess a post-mating component ofRI.
  
  
  RESULTS
  Hummingbird assemblages differed betweencalyculatuspopulations, while allopatric plants ofcalyculatusopened more but smaller flowers with longer lifespans and produced less nectar than those in sympatry. Bayesian-based phylogenetic analysis indicated monophyly forcalyculatuspopulations (i.e. both populations belong to the same species). In sympatry,calyculatusplants opened more and larger flowers with longer lifespans and produced same nectar volume than those ofauriculatus; populations shared pollinators but seed dispersers and host usage differed between species. Nectar standing crops differed between sympatric populations, with lower visitation incalyculatus. Hand pollination experiments indicated a predominant outcrossing breeding system, with fruit set after interspecific pollination two times higher fromcalyculatustoauriculatusthan in the opposite direction.
  
  
  CONCLUSIONS
  Given the low genetic differentiation betweencalyculatuspopulations, observed trait divergence could have resulted from changes regarding the local communities of pollinators and, therefore, expected divergence for peripheral, allopatric populations. UsingRIestimates, there were fewer heterospecific matings than expected by chance inP. calyculatus(RI4A= 0.629) as compared toP. auriculatus(RI4A= 0.20). When considering other factors of ecological isolation that affect co-occurrence, theRI4Cvalues indicate that isolation by hummingbird pollinators was less effective (0.20) than isolation by host tree species and seed dispersers (0.80 and 0.60, respectively), suggesting that host usage is the most important ecological isolation factor between the two species. Accordingly, the absolute and relative cumulative strength values indicated that the host tree species' barrier is currently contributing the most to maintaining these species in sympatry.
authors.affiliation: Laboratorio de Ecología, UBIPRO, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México , Tlalnepantla de Baz, Estado de México , Mexico.
authors.forename: Sergio
authors.initials: S
authors.lastname: Díaz Infante
authors.affiliation: Centro de Investigación en Ciencias Biológicas, Universidad Autónoma de Tlaxcala , Tlaxcala , Mexico.
authors.forename: Carlos
authors.initials: C
authors.lastname: Lara
authors.affiliation: Laboratorio de Ecología, UBIPRO, Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México , Tlalnepantla de Baz, Estado de México , Mexico.
authors.forename: María Del Coro
authors.initials: MD
authors.lastname: Arizmendi
authors.affiliation: Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México , Ciudad de México, Distrito Federal , Mexico.
authors.forename: Luis E
authors.initials: LE
authors.lastname: Eguiarte
authors.affiliation: Departamento de Biología Evolutiva, Instituto de Ecología, A.C. , Xalapa, Veracruz , Mexico.
authors.forename: Juan Francisco
authors.initials: JF
authors.lastname: Ornelas
keywords: Allopatry; Bird pollination; Character displacement; Hemiparasites; Hummingbird; Loranthaceae; Mexico