title: Plasticity and regeneration of gonads in the annelidPristina leidyi.
abstract: BACKGROUND
  Gonads are specialized gamete-producing structures that, despite their functional importance, are generated by diverse mechanisms across groups of animals and can be among the most plastic organs of the body. Annelids, the segmented worms, are a group in which gonads have been documented to be plastic and to be able to regenerate, but little is known about what factors influence gonad development or how these structures regenerate. In this study, we aimed to identify factors that influence the presence and size of gonads and to investigate gonad regeneration in the small asexually reproducing annelid,Pristina leidyi.
  
  
  RESULTS
  We found that gonad presence and size in asexual adultP. leidyiare highly variable across individuals and identified several factors that influence these structures. An extrinsic factor, food availability, and two intrinsic factors, individual age and parental age, strongly influence the presence and size of gonads inP. leidyi. We also found that following head amputation in this species, gonads can develop by morphallactic regeneration in previously non-gonadal segments. We also identified a sexually mature individual from our laboratory culture that demonstrates that, although our laboratory strain reproduces only asexually, it retains the potential to become fully sexual.
  
  
  CONCLUSIONS
  Our findings demonstrate that gonads inP. leidyidisplay high phenotypic plasticity and flexibility with respect to their presence, their size, and the segments in which they can form. Considering our findings along with relevant data from other species, we find that, as a group, clitellate annelids can form gonads in at least four different contexts: post-starvation refeeding, fission, morphallactic regeneration, and epimorphic regeneration. This group is thus particularly useful for investigating the mechanisms involved in gonad formation and the evolution of post-embryonic phenotypic plasticity.
authors.affiliation: Department of Biology, University of Maryland, College Park, MD 20742 USA ; Institut Jacques Monod, Paris, France.
authors.forename: B Duygu
authors.identifier: 0000-0002-1900-965X
authors.initials: BD
authors.lastname: Özpolat
authors.affiliation: Department of Biology, University of Maryland, College Park, MD 20742 USA.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Sloane
authors.affiliation: Department of Biology, University of Maryland, College Park, MD 20742 USA ; Department of Biology, Indiana University, Bloomington, IN USA.
authors.forename: Eduardo E
authors.initials: EE
authors.lastname: Zattara
authors.affiliation: Department of Biology, University of Maryland, College Park, MD 20742 USA.
authors.forename: Alexandra E
authors.initials: AE
authors.lastname: Bely
keywords: Annelida; Asexual reproduction; Germline; Gonad regeneration; Nanos; Parental effect; Phenotypic plasticity; Piwi; Starvation; Vasa