Differential reproductive responses to contrasting host species and localities in Psittacanthus calyculatus(Loranthaceae) mistletoes

Abstract

Host trees are immediate environments for multi‐host mistletoes, so parasitizing different hosts implies exposure to varying environmental conditions between mistletoe generations. Therefore, to maximize reproductive fitness in heterogeneous environments (host species) mistletoes should adjust its reproductive responses in relation to circumstances. Here, we ask how reproductive traits of Psittacanthus calyculatus mistletoes vary on two host tree species (Crataegus mexicana, Prunus serotina) at three different localities. We followed individual mistletoes on each host species and at three localities through the flowering season to quantify traits related to reproductive effort and success, e.g. total number of buds, flowers and fruits produced. In buds about to open, we measured two anthers and quantified the number of pollen grains and their viability. Individual flowers were marked to obtain flower longevity data and were followed until fruit formation. At which time we measured and weighed the fruits and the seeds. Mistletoes from one locality produced more buds, flowers and fruits, and the flowers lasted longer, had larger anthers and produced more pollen as compared to the other two localities. However, mistletoes on Prunus serotina produced fewer floral buds, but their fruits were heaviest, longest and widest and ripened fastest across localities. The probability of fruit formation, percentage of fruits formed, and pollen viability were similar among the mistletoes, regardless of host species or locality. We propose that the observed differences in reproductive effort and success associated with host species or locality are plastic or adaptive in this mistletoe in response to varying conditions.

Efectos mediados por hospedero en la variación del tamaño de frutos del muérdago hemiparásito Psittacanthus schiedeanus (Loranthaceae)

“…In Psittacanthus calyculatus G. Don., fruit and seed size variation and probability of formation and ripening of the fruit are associated with host species growing in different geographical locations (Rodríguez-Mendieta et al, 2018;Lara et al, 2021). Based on these previous studies, both host species and study site, and its interaction, would significantly affect fitness measures, indicating that mistletoes' fruit size traits would be affected differently depending on the host species and their site of occurrence.…”

“…We found mistletoes growing on naturally distributed hosts (Liquidambar styraciflua, Quercus germana, Ostrya virginiana, Acacia pennatula) produced larger fruits than those on cultivated host species (Crataegus mexicana, Psidium guajava). These results suggest that reproductive responses of mistletoes (fruit size traits) are affected by host species, and these host-associated differences can promote differences in display associated with the attraction of their mutualistic seed dispersers and the consumption and gut processing of the fruits Ornelas, 2009, 2012;Rodríguez-Mendieta et al, 2018;Lara et al, 2021). Variation in fruit size of Psittacanthus mistletoes has been reported among geographically isolated populations (e.g., Díaz Infante et al, 2016) and among mistletoes growing on different host tree species (Lara et al, 2009;Ramírez and Ornelas, 2009;Rodríguez-Mendieta et al, 2018;Lara et al, 2021).…”

“…These results suggest that reproductive responses of mistletoes (fruit size traits) are affected by host species, and these host-associated differences can promote differences in display associated with the attraction of their mutualistic seed dispersers and the consumption and gut processing of the fruits Ornelas, 2009, 2012;Rodríguez-Mendieta et al, 2018;Lara et al, 2021). Variation in fruit size of Psittacanthus mistletoes has been reported among geographically isolated populations (e.g., Díaz Infante et al, 2016) and among mistletoes growing on different host tree species (Lara et al, 2009;Ramírez and Ornelas, 2009;Rodríguez-Mendieta et al, 2018;Lara et al, 2021). Fruits (and cupular pedicels) of P. schiedeanus are larger than those of P. calyculatus (Lara et al, 2009;Ramírez and Ornelas, 2009;Rodríguez-Mendieta et al, 2018;Lara et al, 2021) and P. auriculatus Eichler (Díaz Infante et al, 2016;Pérez-Crespo et al, 2016b).…”

“…Phenotypic differences between host tree species entail different intrinsic conditions for the development and growth of mistletoes and eventually affect characteristics of mistletoes' reproductive structures. Thus, traits that affect mistletoe dispersal (mediated by seed dispersers) and its successful establishment, such as fruit and seed size, would differ among mistletoes growing on different host tree species (Rodríguez- Mendieta et al, 2018;Lara et al, 2021).…”

“…Conditions in which mistletoes grow can promote differences in display of reproductive traits associated with the attraction of their seed dispersers and the gut processing of the fruits (Ramírez and Ornelas, 2012;Rodríguez-Mendieta et al, 2018;Lara et al, 2021). For instance, regurgitated fruits of Psittacanthus schiedeanus (Cham.…”