Importance of intraspecific variation in the pollination and seed dispersal functions of a double mutualist animal species

Although most plants depend on different animals for pollination and seed
dispersal, sometimes the same animal species provides both functions,
being thus involved in what has been termed a ‘double mutualism’. Very
little is known on the effectiveness of such species as both pollinators
and seed dispersers, and even less on the intraspecific level differences
at the contribution of an animal mutualist to plant fitness. In this
study, we focused on the interaction between a Mediterranean shrub Cneorum
tricoccon L. (Rutaceae) and the Balearic lizard Podarcis lilfordi L.
(Lacertidae) in order to assess: (1) the role of this lizard as a
legitimate pollinator of the plant (previously thought to be exclusively
insect-pollinated), and (2) the intraspecific variation in the use of
flowers and fruits by lizard individuals, comparing males, females and
juveniles. We further evaluated whether lizards show different fruit size
selection depending on sex and age, with potential consequences for seed
germination. Lizards visited more flowers and selected more hermaphrodite
flowers than insects did, leading to relative increases in both fruit and
seed set. Interestingly, female and juvenile lizards were the main flower
visitors, whereas males were the main fruit consumers. Males selected the
largest fruits (bearing the largest seeds) though this did not increase
seed germination, which was only ca. 15%. We concluded that P. lilfordi
acts as a legitimate pollinator of C. tricoccon and, thus, confirm that
this system constitutes a new case of double mutualism, especially common
in island compared to mainland systems. Moreover, our findings show a
large variation among conspecific individuals in their role as either
pollinators or seed dispersers, with potential implications for plant
reproductive success. Our study, therefore, highlights the importance of
evaluating plant-animal interactions at the intraspecific level, and calls
for more in-depth studies on the consequences of such intraspecific
variation.