Evolutionary origins and life-history correlates of coloniality in the epiphytic fern genus Platycerium (Polypodiaceae).

Many animals live in cooperative groups comprised of morphologically differentiated individuals that subdivide labour to help the group persist in harsh, unpredictable environments. Recently it has been shown that a colonial fern from Australasia, Platycerium bifurcatum (Polypodiaceae), sub-divides labour similarly, with individuals producing morphologically different fronds depending on their vertical position within the colony. The genus contains approximately 18 taxa, which range from solitary to colonial. Whether other Platycerium species exhibit similar morphological differentiation remains poorly understood, and the evolutionary origins of coloniality along with its life-history correlates across the genus remain unknown. Here, we use ancestral state reconstruction to explore the evolution of coloniality and morphologically differentiated division of labour in the genus Platycerium. We found coloniality to be likely ancestral in Platycerium, with the condition being lost twice across the phylogeny. Eight Platycerium species exhibited colonies with morphologically differentiated individuals. This condition is derived and likely evolved twice within the genus. Coloniality was also negatively correlated with nest frond length and width but was unrelated to strap frond length. Overall, results reveal the evolutionary origins and life-history correlates of coloniality across the genus Platycerium, and support a scenario in which a colonial species with morphologically variable colony members evolved gradually from a solitary species.