Many mistletoe species produce 'bird'-pollinated flowers; however, the reproductive biology of the majority of these species has not been studied. Psittacanthus auriculatus is a Mexican endemic mistletoe, most common in open, dry mesquite grassland. Knowledge of the reproductive biology of P. auriculatus is essential for understanding species formation and diversification of Psittacanthus mistletoes, but it is currently poorly understood. Thus, we studied floral biology and phenology, nectar production and breeding system and pollination of this species. The hermaphroditic red-pink flowers open from the middle to the tip and petals are curly, but remain partially fused forming a floral tube of ca. 20-mm long. Flowers are partially protandrous, produce large amounts of nectar, last 2 days, and stigma receptivity is highest during the second day. We recorded hummingbirds (Cynanthus latirostris, Hylocharis leucotis, Amazilia beryllina, A. violiceps, Calothorax lucifer, Archilochus colubris) and less commonly butterflies (Agraulis vanillae, Anteos clorinde, Papilio multicaudatus, Phocides urania, Phoebis sennae) as floral visitors. P. auriculatus flowers are self-compatible. However, this mistletoe is an obligate animal-pollinated species, as the sensitive stigma avoids self-pollination. Under natural conditions, reproductive success was higher than in manually selfed or cross-pollinated flowers, likely due to the traplining foraging behaviour of hummingbirds. We suggest that the apparent efficient foraging behaviour of hummingbirds maintains gene flow among P. auriculatus, promoting outcrossing.
Aim: The formation of the Trans-Mexican Volcanic Belt (TMVB) played an important role in driving inter-and intraspecific diversification at high elevations. However, Pleistocene climate changes and ecological factors might also contribute to plant genetic structuring along the volcanic belt. Here, we analysed phylogeographical patterns of the parrot-mistletoe Psittacanthus calyculatus to determine the relative contribution of these different factors. Location: Trans-Mexican Volcanic Belt. Methods: Using nuclear and chloroplast DNA sequence data for 370 individuals, we investigate the genetic differentiation of 35 populations across the species range.We conducted phylogenetic, population and spatial genetic analyses of P. calyculatus sequences along with ecological niche modelling and Bayesian inference methods to gain insight into the structuring of genetic variation of these populations.Results: Our analyses revealed population structure with three genetic groups corresponding to individuals from Oaxaca and those from the central-eastern and western TMVB regions. A significant genetic signal of demographic expansion, an eastto-west expansion predicted by species distribution modelling, and approximate Bayesian computation analyses strongly supported a scenario of habitat isolation and invasion of TMVB by P. calyculatus during the late-Pleistocene.Main conclusions: The genetic differentiation of P. calyculatus may be explained by the combined effects of (1) geographical isolation linked to the effects of the glacial/interglacial cycles and environmental factors, driving genetic differentiation from congeners into more xeric vegetation and (2) the invasion of TMVB from east to west, suggesting a role for both colonization and glacial/interglacial cycles models.
Background: It was suggested that ecological patterns can be used to infer the nature of ecological processes (i.e., competition) that structure communities. Analysis of patterns of resource partitioning under the classical niche paradigm (competitive niche differentiation in exploiting limited resources) has traditionally been used to understand the structure of communities. On the contrary, neutral theory states that patterns result from neutral processes such as stochasticity and dispersal abilities. Thus, if any ecological process gives rise to a characteristic ecological pattern, the comparative study of patterns with appropriate neutral models may reveal the magnitude of that process. In this study, we analyzed patterns of resource utilization of a waterbird community in Lake Acuitlapilco, an epicontinental lake in central Mexico. In February 2011 to January 2012, we recorded foraging behaviors of waterbird species in two niche dimensions or axes: feeding technique and foraging habitat. The pattern of resource utilization was characterized by niche breath and niche overlap. Results: Results showed that waterbird species in Lake Acuitlapilco were specialists in resource utilization patterns and therefore were vulnerable to fluctuations in resources, particularly feeding habitat. Niche overlaps were generally largest among species belonging to the same guild. To test competition as an ecological process that plays a role in the community structure, observed niche overlaps were compared with niche overlaps generated with null models of communities in the absence of competition using the RA4 randomization algorithm. Habitat and observed bidimensional overlaps were higher than those of randomly generated communities. Conclusions: Our study suggested that other processes can be used to predict resource utilization patterns instead of competition alone, as suggested by neutral theory. Future studies analyzing the mechanisms that structure waterbird communities should include the use of null models to support their conclusions.
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