Data from: Reproductive ecology and isolation of Psittacanthus calyculatus and P. auriculatus mistletoes (Loranthaceae)

Background: Relationships between floral biology and pollinator behavior
are important to understanding species diversity of hemiparasitic
Psittacanthus mistletoes (c. 120 species). We aimed to investigate trait
divergence linked to pollinator attraction and reproductive isolation (RI)
in two hummingbird-pollinated and bird-dispersed Psittacanthus species
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 of P. calyculatus and P. auriculatus, and one
allopatric population of P. calyculatus. Flowers in sympatry were also
reciprocally pollinated to assess a post-mating component of RI. Results:
Hummingbird assemblages differed between calyculatus populations, while
allopatric plants of calyculatus opened more but smaller flowers with
longer lifespans and produced less nectar than those in sympatry.
Bayesian-based phylogenetic analysis indicated monophyly for calyculatus
populations (i.e. both populations belong to the same species). In
sympatry, calyculatus plants opened more and larger flowers with longer
lifespans and produced same nectar volume than those of auriculatus;
populations shared pollinators but seed dispersers and host usage differed
between species. Nectar standing crops differed between sympatric
populations, with lower visitation in calyculatus. Hand pollination
experiments indicated a predominant outcrossing breeding system, with
fruit set after interspecific pollination two times higher from
calyculatus to auriculatus than in the opposite direction. Conclusions:
Given the low genetic differentiation between calyculatus populations,
observed trait divergence could have resulted from changes regarding the
local communities of pollinators and, therefore, expected divergence for
peripheral, allopatric populations. Using RI estimates, there were fewer
heterospecific matings than expected by chance in P. calyculatus (RI4A =
0.629) as compared to P. auriculatus (RI4A = 0.20). When considering other
factors of ecological isolation that affect co-occurrence, the RI4C values
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.