Rzhavsky A.V.†, Kupriyanova E.K. 2019. Evolution of spirorbin brooding: a phylogenetic analysis and a test of an oxygen limitation hypothesis // Invertebrate Zoology. Vol.16. No.4: 409–430 [in English].

Australian Museum Research Institute, Australian Museum, 1 William Street, Sydney NSW 2010 Australia. E-mail: elena.kupriyanova@austmus.gov.au

doi: 10.15298/invertzool.16.4.09

ABSTRACT: Spirorbinae is a group of small calcareous tubeworms (family Serpulidae) living in flat coiled tubes and incubating their embryos either in tubes or in opercular chambers. The controversy whether tube or opercular incubation is ancestral is unresolved and the costs and benefits of the two incubation types are not understood. The oxygen limitation hypothesis (Harris, 1972) suggests that as opercular incubators predominantly live in tropical waters and opercular incubation evolved as an adaptation to lower oxygen content experienced by embryos of tube incubators. The hypothesis implies that tube incubation is ancestral and opercular incubation evolved as spirorbins penetrated into lower latitudes. The aim of this study was to examine the evolution of brooding in spirorbins. The phylogenetic analysis of morphological characters was used to determine whether the opercular incubation is derived and whether types of opercular incubation evolved independently. We also tested for a relationship between the type of brooding and the geographical distribution in relation to the dissolved oxygen content. The results confirmed that opercular brooding is derived and that two types of opercular brooding originated independently. Tube brooders inhabit waters with higher oxygen content that opercular brooders do. We re-formulated the oxygen limitation hypothesis suggesting that the constraints imposed on tube incubation in warmer waters are related to the increased energetic costs of parental brood ventilation.

KEY WORDS: Serpulidae, Polychaeta, tube brooding, opercular brooding, oxygen consumption.

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