Karyotypic analysis of the hermaphroditic viviparous polychaete, Hediste limnicola (Polychaeta: Nereididae): possibility of sex chromosome degeneration

Abstract

Karyotypes of the hermaphroditic polychaete Hediste limnicola were examined using an air-drying method and genetic material prepared from regenerating tail and newborn juveniles. Materials were obtained from a lineage of cultured worms originating from Watsonville Slough (California, USA) and maintained for six years in the laboratory. Giemsa-stained preparations were analysed by a computer-assisted image-analysing system for the identification of each chromosome pair. A diploid chromosome number of 26 was obtained from well-spread metaphase chromosomes of mitotic cells, consisting of metacentric (N ¼ 11), submetacentric (N ¼ 1) and telocentric (N ¼ 1) chromosomes. It is possible that hermaphroditism in this species evolved through loss of a pair of sex chromosomes, which are present in closely related congeneric species.

Cytogenetics of Hediste diversicolor (Annelida: Polychaeta) and comparative karyological analysis within Nereididae

“…Sato & Ikeda (1992) and Tosuji et al (2004) also suggested the presence of an XX-XY (male heterogametic) sex chromosome system for these species. In contrast, the closely related congener H. limnicola (Johnson 1903) presented a diploid number of 2n = 26 and absence of sex chromosomes (Tosuji et al 2010). In Nereis oligohalina (Rioja 1946) a 2n = 28 diploid number was observed with a karyotype composed of 7 metacentric, 1 submetacentric, 3 subtelocentric and 3 telocentric chromosome pairs (Ipucha et al 2007).…”