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.