Fertilization success of the New Zealand geoduck,Panopea zelandica: Effects of sperm concentration, gamete age and contact time

Abstract

Valuable aquaculture and fisheries industries for the North American geoduck, Panopea generosa, have driven interest in developing similar ventures for other geoduck species including P. zelandica from New Zealand. However, little is known about the fertilization kinetics of this species, or the conditions under which the amount and quality of larvae can be maximized. We determined the effects of sperm concentration, gamete age and contact time on the fertilization success of P. zelandica using an extended-Vogel-Czihak-Chang-Wolf (EVCCW) model. The model provided a good fit to laboratory data when applied to individual contact times. For a contact time of 10 s, optimal fertilization was achieved at concentrations of approximately 10 4 sperm lL À1 , but this decreased to as little as 10 2 sperm lL À1 for contact times of several minutes. Optimal fertilization was always <100% (max. observed 70%) and the proportion of fertilized eggs decreased rapidly at sperm concentrations above the optimal. According to the model this was due to a slow block to polyspermy. If commercial hatchery facilities ensure that broodstock are in ripe condition, and use sperm <30-min old, then optimal fertilization can be expected at sperm densities of 10 2 -10 3 sperm lL À1 at contact times of 5-10 min.

Growth, Survival, and Feeding Rates for the GeoduckPanopea globosaDuring Larval Development

“…Taken together, results for survival and growth obtained suggest that P. globosa has significant aquaculture potential. This potential may be increased with the adaptation of new fertilization strategies developed for the New Zealand geoduck Panopea zelandica (see Gribben et al [2014]). …”

Practical fertilization procedure and embryonic development of the New Zealand geoduck clam (Panopea zelandica)

“…The yield of embryos can be substantially affected by the ratio of sperm:egg during fertilization (Dong et al , 2012). For example, low sperm:egg ratios can reduce the probability of gamete contact, while high ratios can increase the risk of polyspermy (Gribben et al , 2014). Polyspermy can then cause dissolution of egg membranes and abnormal embryo development (Stephano & Gould, 1988; Clotteau & Dubé, 1993; Encena et al , 1998).…”

“…In a study to investigate the production of triploid P. generosa , Vadopalas & Davis (2004) successfully used a sperm:egg ratio of 40:1. More recently, in New Zealand, Gribben et al (2014) conducted a comprehensive study to investigate the fertilization kinetics of P. zelandica , and recommended a broad sperm:egg ratio of 5,000–50,000:1 for hatchery production with fresh gametes (<30 min old), a starting egg density of 20 eggs ml −1 , and a sperm-egg contact time of 5–10 min. Under these conditions, greater sperm densities resulted in high percentages of polyspermy and poor fertilization success.…”

Mathematical Models of Fertilization—An Eco-Evolutionary Perspective

“…To our knowledge, there is currently no direct empirical evidence for these fertilization functions under isogamous or near-isogamous conditions (although they coincide with other, previously derived fertilization functions as the ratio of gamete numbers increases; Fig Whereas anisogamous fertilization functions have been applied to explicit empirical fertilization data for both internal fertilization (Schwartz et al 1981;Fearon and Wegener 2000) and external fertilization (Warner et al 1995;Styan and Butler 2000;Gribben et al 2014;Okamoto 2016), the same has not yet been done for isogamous functions, and it remains unconfirmed whether these functions capture the key biological processes that influence fertilization in isogamous organisms. For example, it is not clear how polyspermy (see below) would function along the continuum from isogamy to anisogamy and oogamy, and currently no model accounts for isogamy and polyspermy at the same time.…”

“…Derived by Millar and Anderson (2003). Applied in a study of fertilization success in New Zealand geoducks (Gribben et al 2014).…”