TY - JOUR

T1 - Comparative anatomy of internal incubational sacs in cupuladriid bryozoans and the evolution of brooding in free-living cheilostomes

AU - Ostrovsky, Andrew N.

AU - O'Dea, Aaron

AU - Rodríguez, Felix

PY - 2009/12

Y1 - 2009/12

N2 - Numerous gross morphological attributes are shared among unrelated freeliving bryozoans revealing convergent evolution associated with functional demands of living on soft sediments. Here, we show that the reproductive structures across free-living groups evolved convergently. The most prominent convergent traits are the collective reduction of external brood chambers (ovicells) and the acquisition of internal brooding. Anatomical studies of four species from the cheilostome genera Cupuladria and Discoporella (Cupuladriidae) show that these species incubate their embryos in internal brooding sacs located in the coelom of the maternal nonpolymorphic autozooids. This sac consists of a main chamber and a narrow neck communicating to the vestibulum. The distal wall of the vestibulum pos-sesses a cuticular thickening, which may further isolate the brood cavity. The presence of this character in all four species strongly supports grouping Cupuladria and Discoporella in one taxon. Further evidence suggests that the Cupuladriidae may be nested within the Calloporidae. Based on the structure of brooding organs, two scenarios are proposed to explain the evolution of the internal brood-ing in cupuladriids. The evolution of brood chambers and their origin in other free-living cheilostomes is discussed. Unlike the vast majority of Neocheilostomina, almost all freeliving cheilostomes possess nonprominent chambers for embryonic incubation, either endozooidal and im-mersed ovicells or internal brooding sacs, supporting the idea that internal embryonic incubation is derived. We speculate that prominent skeletal brood chambers are disadvantageous to a free-living mode of life that demands easy movement through sediment in instable sea-floor settings.

AB - Numerous gross morphological attributes are shared among unrelated freeliving bryozoans revealing convergent evolution associated with functional demands of living on soft sediments. Here, we show that the reproductive structures across free-living groups evolved convergently. The most prominent convergent traits are the collective reduction of external brood chambers (ovicells) and the acquisition of internal brooding. Anatomical studies of four species from the cheilostome genera Cupuladria and Discoporella (Cupuladriidae) show that these species incubate their embryos in internal brooding sacs located in the coelom of the maternal nonpolymorphic autozooids. This sac consists of a main chamber and a narrow neck communicating to the vestibulum. The distal wall of the vestibulum pos-sesses a cuticular thickening, which may further isolate the brood cavity. The presence of this character in all four species strongly supports grouping Cupuladria and Discoporella in one taxon. Further evidence suggests that the Cupuladriidae may be nested within the Calloporidae. Based on the structure of brooding organs, two scenarios are proposed to explain the evolution of the internal brood-ing in cupuladriids. The evolution of brood chambers and their origin in other free-living cheilostomes is discussed. Unlike the vast majority of Neocheilostomina, almost all freeliving cheilostomes possess nonprominent chambers for embryonic incubation, either endozooidal and im-mersed ovicells or internal brooding sacs, supporting the idea that internal embryonic incubation is derived. We speculate that prominent skeletal brood chambers are disadvantageous to a free-living mode of life that demands easy movement through sediment in instable sea-floor settings.

KW - Cupuladriidae

KW - Embryonic incubation

KW - Sexual reproduction

UR - http://www.scopus.com/inward/record.url?scp=70449377410&partnerID=8YFLogxK

U2 - 10.1002/jmor.10767

DO - 10.1002/jmor.10767

M3 - Article

C2 - 19572311

VL - 270

SP - 1413

EP - 1430

JO - Journal of Morphology

JF - Journal of Morphology

SN - 0362-2525

IS - 12

ER -