Growth and senescence in colonies of Botryllus schlosseri (Pallas) (Ascidiacea)

Abstract

Colonial growth by blastogenetic budding in colonies of Botryllus schlosseri has been studied in field and laboratory. It can be expressed either by the number of individuals making up the colony at the various blastogenetic generations or through growth rates defined as rn-1 = xn/xn-1 = growth rate at generation (n — 1)th, where xn is the number of adult zooids of the n—th generation and xn-1 that of generation (n — 1)th. This second method seems to be better. Maximum growth is seen between the 2th and 4th blastogenetic generation; then the rate falls until it stabilizes around a constant value. In the laboratory it oscillate around 1. After the phase of sexual reproduction, that lasts for 3-4 blastogenetic generations, the colonies show areas of suffering in both lots and an increasing mortality. The senescence of the colonies seems to consist essentially of a reduction of the renewing capacity of the tunic. © Taylor & Francis Group, LLC.