Does Polymorphism Predict Physiological Connectedness? A Test Using Two Encrusting Bryozoans

Abstract

A colonial lifestyle necessitates communication between colony members to coordinate functions and enable resource sharing through physiological integration. Colonial integration is predicted to increase with both the size of the colony and the level of specialization (polymorphism). In modular colonies, although integration might be reflected in structural characteristics such as module spacing or branching patterns, physiological integration is fundamentally dependent on the level of connectedness between modules. In cheilostome bryozoans, funicular tissue links adjacent zooids through pores within zooid walls and is the most likely means of nutrient transport within colonies. We sought to determine whether the relative numbers of pores (septulae) and pore plates (septal chambers) per zooid differed across colony regions in a monomorphic species, Watersipora subtorquata, and one showing some polymorphism, Mucropetraliella ellerii. Within each species, the morphology of pore plates corresponded to functional predictions based on their position within the zooid, and connection numbers per zooid increased with colony size. Contrary to expectations, however, the more complex species, M. ellerii, had significantly fewer porous connections per zooid than W. subtorquata. Physiological connectedness was therefore not predicted by simple assessment of polymorphism in these species and may not be sufficient to infer colonial integration in related taxa.

Modularity is the mother of invention: a review of polymorphism in bryozoans

“…It appears that module dissociation is tied to polymorphism in bryozoans. However, a close examination of polymorphism in different genera and quantitative variation in interzooidal communication is warranted [see Bone & Keough, and Miles et al, ].…”

Intra-colonial diversity in the scleractinian coral,Acropora millepora: identifying the nutritional gradients underlying physiological integration and compartmentalised functioning

“…Inner colony regions generally acquire an energy surplus, since photosynthesis greatly exceeds respiration and competitive interactions are reduced ( Gladfelter, Michel & Sanfelici, 1989 ; Lirman, 2000a ). As such, energy accumulated by the inner regions can be mobilised via the coral’s gastrovascular system and concentrated in zones of maximal energetic demand, such as the growing edge ( Oren, Brickner & Loya, 1998 ; Bone & Keough, 2010 ; Marfenin, 2015 ).…”

“…Scleractinian corals are colonial organisms comprising multiple asexually produced and physiologically integrated polyps ( Oren et al, 2001 ; Bone & Keough, 2010 ). The colonial nature of scleractinian corals is highly beneficial, with modular coral colonies being able to attain large increases in size and volume isometrically, allowing the component units to remain small ( Vollmer & Edmunds, 2000 ; Hughes, 2005 ).…”

“…The colonial nature of scleractinian corals is highly beneficial, with modular coral colonies being able to attain large increases in size and volume isometrically, allowing the component units to remain small ( Vollmer & Edmunds, 2000 ; Hughes, 2005 ). This reduces the chance of whole colony mortality and increases colony exposure to exploitable environmental factors, such as sunlight and nutrition sources ( Nakamura & Yamasaki, 2006 ; Bone & Keough, 2010 ).…”

“…This is made possible through interconnecting tissues and a shared gastrovascular system ( Hemond, Kaluziak & Vollmer, 2014 ). Individual polyps can thus act as cooperative systems, buffering negative microhabitat effects, colonising hostile areas, and permitting resource sharing should some polyps fail to capture food or light ( Murdock, 1978 ; Gateno et al, 1998 ; Bone & Keough, 2010 ).…”