A case of nascent speciation: unique polymorphism of gonophores within hydrozoan Sarsia lovenii

Abstract

Revealing the mechanisms of life cycle changes is critical for understanding the processes driving hydrozoan evolution. Our analysis of mitochondrial (COI, 16S) and nuclear (ITS1 and ITS2) gene fragments resulted in the discovery of unique polymorphism in the life cycle of Sarsia lovenii from the White Sea. This polymorphic species exhibits two types of gonophores: hydroids produce both free-swimming medusae and attached medusoids (phenotypic polymorphism). Our phylogenetic analysis revealed the intrinsic genetic structure of S. lovenii (genetic polymorphism). Two haplogroups inhabiting the White Sea differ in their reproductive modes. Haplogroup 1 produces attached medusoids, and haplogroup 2 produces free-swimming medusae. Our experiments indicated the possibility of free interbreeding between haplogroups that likely is a rare event in the sea. We propose that inter-haplogroup crossing of S. lovenii in the White Sea may be limited by discordance in periods of spawning or by spatial differences in habitat of spawning specimens. Our finding can be interpreted as a case of nascent speciation that illustrates the patterns of repeated medusa loss in hydrozoan evolution. Life cycle traits of S. lovenii may be useful for elucidating the molecular mechanisms of medusa reduction in hydrozoans.

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“…Also has been reported the presence of the CubozoanTripedalia cystophora Conant, 1897; however, hydromedusae and S. lovenii (M. Sars, 1846) are very similar morphologically, however, the latter has not been recorded for the Gulf of Mexico yet. The features that allow to distinguish S. tubulosa from S. lovenii are: a smaller umbrella in adult specimens; rounded bulbs with greenish and orange colorations and gonads located in the distal part of the manubrium, covering 2/3 of it (Kramp, 1959;Jung, 2003;Prudkovsky et al, 2019). Most of the specimens in this study presented the umbrella everted inside out, however, the features previously mentioned were distinguished.…”

New data on the development of the brachiopod Hemithiris psittacea (Rhynchonelliformea: Rhynchonellida)

“…In the current study, H. psittacea collected at 9 m depth developed in the laboratory at 2-4 °C; this temperature corresponds to that of the shallow water layer (0-10 m depth) in Kandalakshskii Bay of the White Sea in June and in October-November (Prudkovsky et al, 2019). The development of H. psittacea from the San Juan Channel was studied by the method of artificial insemination by Freeman (2003) at 10-12 °C and by Long (1964) at 10 °C; H. psittacea in the San Juan Channel breeds in December and January (Long, 1964).…”

Odd family reunion: DNA barcoding reveals unexpected relationship between three hydrozoan species

“…Non-reproductive L. tenuis colonies with fully-developed nematothecae are nonetheless commonly encountered in the field ( Sars, 1874 ; Vervoort, 2006 ; Moura, 2015 ), suggesting no correlation between the presence of nematothecae and gonothecae. Environmental variability, on the other hand, impacts hydroid morphology and results in polymorphism within colonies ( e.g ., Dudgeon & Buss, 1996 ; Griffith & Newberry, 2008 ; Prudkovsky, Ekimova & Neretina, 2019 ). Some characters in the polyp may not be expressed when the colonies are grown in the laboratory ( Brinckmann-Voss, 1970 ; Migotto, 1996 ; Migotto & Cabral, 2005 ).…”