Gametogenesis in placental and non‐placental ovicellate cheilostome Bryozoa

Abstract

Oogenesis is compared in two cheilostome bryozoans with contrasting reproductive strategies. from southern Britain: Chartella papyracea (Ellis & Solander) is a non–placental ovicellate brooder, whereas Bugula flabellata (Thompson in Gray) is a placental brooder. The ovarian cycles are similar, and each oocyte develops in tandem with a single nurse cell. Eggs of both species are telolecithal, However, those of B. flabellata are less than 20% the volume of those of the other species, and there are considerable differences in the ultra‐structure of oogenesis. In both cases, spermatogenesis has the typical bryozoan pattern. Precocious insemination of the oocyte occurs in both species.

Independent evolution of matrotrophy in the major classes of Bryozoa: transitions among reproductive patterns and their ecological background

“…In Gymnolaemata, the largest bryozoan class with >1000 genera, matrotrophy was, until recently, known only in relatively few taxa -in the viviparous family Epistomiidae (genera Epistomia, Synnotum) and in the families Bugulidae (Bicellariella, Bugula), Candidae (Scrupocellaria), and Hippothoidae (Celleporella). These taxa are among the majority of gymnolaemates that brood their embryos in extrazooidal incubation chambers (ovicells) (Marcus 1938, 1941, Woollacott & Zimmer 1972, 1975, Dyrynda 1981, Dyrynda & King 1982, 1983, Dyrynda & Ryland 1982, Hughes 1987, Santagata & Banta 1996, Ostrovsky 1998.We report here the results of an extensive lightmicroscopic anatomical study, revealing that EEN is far more common in gymnolaemates than previously realized. The results point out seemingly independent appearances of matrotrophy.…”

From Incipient to Substantial: Evolution of Placentotrophy in a Phylum of Aquatic Colonial Invertebrates

“…Noteworthy, among bryozoans various degrees of matrotrophy are reported in the cheilostome genus Bugula alone, in which the embryonic enlargement ranges from 6.3‐ to 500‐fold in different species (Woollacott and Zimmer ; Dyrynda and King ; see also Table ). This closely reminds a continuum of variation in matrotrophic provisioning recorded in such fish genera as Poeciliopsis , Nomorhamphus , and Dermogenys (see Reznick et al , 2007a).…”

“…The same is true of species from the family Epistomiidae (pattern V) in which uninterrupted EEN is supported by intracolonial transport of nutrients via funicular cords (Marcus ; Dyrynda ; Dyrynda and King ). Thus, similarly to oogenesis, matrotrophic nutrition occurs independently of the presence or absence of a functioning polypide in the zooid (see Dyrynda and Ryland ; Dyrynda and King ; Ostrovsky , 2009). This suggests a high degree of colonial integration enabling an inter‐zooidal distribution of nutrients to nonfeeding (including, incubating) zooids.…”

“…Of more importance is that the first larvae will be released earlier in matrotrophs because their oogenesis is shorter. For instance, it takes about 6 weeks from the beginning of the egg formation in the ovary until the larval release in nonmatrotrophic cheilostome Chartella papyracea , and just 3 weeks in matrotrophic Bugula flabellata (Dyrynda and Ryland ; Dyrynda and King ). Such a strategy (simultaneous embryonic growth and development) would benefit the species with ephemeral colonies that live in seasonal waters, allowing them to occupy free biotopes/niches because of the more rapid production of the first generation of larvae.…”

Some Bryozoa species recently introduced into the Azores: reproductive strategies as a proxy for further spread

“…These wide-ranging research results encompass different aspects of larval, post-settlement and colonial performance. Bugula neritina embryos grow about 500 times larger, favoured by a placenta-like mechanism [90], while the increase factor in other Bryozoa [25] varies between 7 and 30; in general, the larger the egg, the lesser the nutrient input during the embryonic stage.…”