Electra vs Callopora: life histories of two bryozoans with contrasting reproductive strategies in the White Sea

ABSTRACT

The life histories of two common boreal-Arctic bryozoans – Electra pilosa and Callopora craticula – living on kelps in the White Sea are described for the first time using colony mapping. Colony functional dynamics (sexual, feeding, budding and rejuvenation) was traced seasonally via recording zooidal states. During the ice-free season the population of the zygote spawner E. pilosa was represented by three generations – overwintered (maternal) and two young ones (daughter and granddaughter). The overwintered colonies exhibited two-phased reproduction and the ‘early’ daughter colonies reproduced just once. ‘Late’ colonies, together with the granddaughter generation, remained sterile. Four generations are described for the brooder C. craticula, three of which continuously produced larvae. While the two species co-exist on the same substratum, reproduction in E. pilosa started almost 1 month later (in late June), which could be explained by the insufficient abundance of phytoplankton in early summer to support the start of oogenesis and feeding cyphonautes larvae. The estimated maximal colony lifespan is 13 months in E. pilosa and 15 months in C. craticula. The broad comparison of bryozoan reproductive ecology in the White Sea showed that their life histories are much more diverse, complex and evolutionarily flexible than previously acknowledged.

KEYWORDS:

• Aquatic colonial invertebrates
• sexual reproduction
• Bryozoa

Acknowledgments

This study was performed using the laboratories and equipment of the Educational and Research Station “Belomorskaia” and the Centre for Molecular and Cell Technologies, Saint Petersburg State University. Mr A.A. Miroliubov, Zoological Institute, Russian Academy of Sciences, Saint Petersburg, kindly collected material under ice. We thank Dr M. Stachowitsch, University of Vienna, who revised an early draft of the manuscript and improved its English. We are also deeply indebted to two anonymous reviewers, whose constructive criticism and advice helped to improve the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The data described in this article are openly available in the Open Science Framework at DOI:10.17605/OSF.IO/TPA6U.

Supplementary material

Supplemental data for this article can be accessed here.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the Russian Science Foundation [grant 18-14-00086 (microscopy and statistical analysis)]; Saint Petersburg State University [grant 1.38.233.2015 and 1.42.1493.2015 (field collecting and material processing)]; and the Russian Foundation for Basic Research [grant 16-04-00243-a (histological work)].