Reproductive ecology and isolation ofPsittacanthus calyculatusandP. auriculatusmistletoes (Loranthaceae)

Abstract

BackgroundRelationships 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.MethodsWe 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.ResultsHummingbird 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.ConclusionsGiven 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.

The influence of climatic niche preferences on the population genetic structure of a mistletoe species complex

“…These studies have shown that P. schiedeanus and P. calyculatus share the most frequent hummingbird pollinators and seed dispersers. Thus, a strong effect of pollinators and seed dispersers on population differentiation, although possible, appears to be unlikely (D ıaz Infante et al, 2016). Nevertheless, the mobility of bird dispersal agents might lead to increased gene flow and the presence of admixed individuals in regions in which different genetic clusters come into contact, such as Oaxaca (M. J. P erez-Crespo, J. F. Ornelas, A. Gonz alez-Rodríguez, E. Ruiz-Sanchez, A.…”

“…Total genomic DNA was extracted from 601 sampled individuals using a modified cetyl trimethyl ammonium bromide (CTAB) protocol (Doyle & Doyle, ) and a DNeasy Plant Mini kit (Qiagen) employing the manufacturer's protocol. DNA sequences for the chloroplast trn L‐ trn F IGS (295 bp) were obtained for 530 individuals across the sampled populations (Table S1) from previously published works (Díaz Infante et al ., ; Ornelas et al ., ; M. J. Pérez‐Crespo J. F. Ornelas, A. González‐Rodríguez, E. Ruiz‐Sanchez, A. A. Vásquez‐Aguilar & S. Ramírez‐Barahona, unpublished; GenBank accession numbers: –, –, –).…”

Phylogeography and population differentiation in the Psittacanthus calyculatus (Loranthaceae) mistletoe: a complex scenario of climate–volcanism interaction along the Trans‐Mexican Volcanic Belt

“…Psittacanthus calyculatus is a morphologically variable species that possibly intergrades with P. schiedeanus (Kuijt, ; Ornelas et al., ). Its orange‐to‐red, hummingbird‐pollinated flowers are self‐compatible (Azpeitia & Lara, ; Díaz Infante, Lara, Arizmendi, Eguiarte, & Ornelas, ), and its purplish‐black, fleshy (one‐seed) fruits are consumed by several bird species (Díaz Infante et al., ; Lara, Pérez, & Ornelas, ). According to Kuijt (), it commonly parasitizes Quercus along the TMVB, but it has a broad range of hosts ( c .…”

“…50 host tree species of diverse angiosperm families), including non‐native tree species in agricultural landscapes or near cities (Pérez‐Crespo, Lara, & Ornelas, and references therein). Although cross‐seed inoculation experiments have shown local adaptation to their hosts (Lara et al., ), the broad host range of P. calyculatus suggests low host specificity and, consequently, the distribution of genetic variation in this species is unlikely influenced by the distribution of potential host species at a larger geographical scale (Díaz Infante et al., ; Ornelas et al., ).…”

Genetic Differentiation and Fragmentation in Response to Climate Change of the Narrow Endemic Psittacanthus auriculatus

“…For instance, the extinction risk of P. auriculatus is low parasitizing widely distributed host species with low vulnerability to extinction like A. schaffneri (86% prevalence; Dı´az Infante et al, 2016). Also, our future projections suggest that the distribution of suitable habitat for P. auriculatus would remain similar to current conditions and might even expand its range in which given the key resources provided to pollinators and seed dispersers and its role as soil facilitator, even in a situation of extreme drought.…”