Assessing non-reproductive labour in Platycerium bifurcatum

In complex animal societies, group members often sub-divide labor by
focusing on different tasks such as reproduction and defense. While
division of labor is well documented in animals, little is known about
whether colonial plants exhibit similar patterns in task differentiation.
To help bridge this gap in our understanding of sociality, we investigated
non-reproductive division of labor in the staghorn fern (Platycerium
bifurcatum, Polypodiaceae), an epiphyte that forms colonies of many
individual plants, which coalesce into a communal water and nutrient
store. We conducted a series of field observations and glasshouse
experiments to answer three questions: 1) Are individuals in the upper
regions of colonies shaped in ways that facilitate the capture of airborne
particulate matter (e.g., leaf-litter)? 2) Do individuals at the apex of
colonies decay in ways that inhibit the invasion of colonies by other
plant species? 3) Does the anatomy of fronds at the bottom of colonies
facilitate water storage? Results show that individuals at the top of
colonies were larger and more lobed, which fostered the retention of leaf
litter within communal nests. Plants located at the top of colonies also
repetitively collapsed over the upper surface of nests as they decayed,
inhibiting the germination and growth of foreign plant species. Lastly,
individuals at the bottom of colonies produced thicker fronds with larger
intra-cellular spaces, which facilitated the storage of rainwater captured
above. Overall results demonstrate clear patterns in non-reproductive
division of labor within staghorn fern colonies that are similar to highly
social animals.