Growth and development of staghorn fern colonies ( Platycerium bifurcatum , Polypodiaceae)

Abstract The staghorn fern (Platycerium bifurcatum, Polypodiaceae) is an epiphyte from Australasia that has evolved a colonial life history from solitary ancestors. Recent research has documented how patterns in frond morphology of colony members lead to the development of a shared water and nutrient nest. However, within-colony spatial patterns in individual growth and recruitment remain poorly resolved. Here, we bridge this gap in our understanding of staghorn fern colonies by developing a simple graphical model that predicts within-colony gradients in the size and age of individuals, which we then tested by dissecting several mature colonies. Next, we conducted two glasshouse experiments that documented in situ growth and recruitment behaviour of young sporophytes. Consistent with our model, results showed that individuals at the top of colonies were consistently larger and older than those below. Experimental results showed that individuals grew upwards within colonies through time, while new colony members recruited in a downwards direction, thus accounting for patterns in the size and age of individuals along the vertical profile of colonies. Overall results illustrate that staghorn fern colonies grow and develop in predictable ways that have important implications for colony-level patterns in reproductive skew and division of labour.