Occurrence of imposex and seasonal patterns of gametogenesis in the invading veined rapa whelk Rapana venosa from Chesapeake Bay, USA

Abstract

The prevalence and intensity of imposex and observations on the seasonal gametogenic cycle are reported for the Asian veined rapa whelk Rapana venosa (Valenciennes, 1846), an invader of the Chesapeake Bay on the North American Atlantic coast. Adult whelks from opportunistic collections by commercial fishermen demonstrated inactivity from mid-November through early March, copulation from February through mid-November, and egg-laying activity from late May through August. All imposex females examined did not have a functional vas deferens (below Stage 3 on the vas deferens scale of Gibbs et al. 1987; J Mar Biol Assoc UK 67:507-523) and were expected to function normally in reproduction. Although a preponderance of imposex females over 'normal' females by a ratio exceeding 2:1 was observed in 4 out of 5 regions examined in lower Chesapeake Bay, there was no significant difference in the numbers of functional females (imposex females and normal females) observed in any region. Shell lengths and wet tissue weights (g) of both imposex females and males were approximately the same and sexual dimorphism was not apparent at the population level. However, true female rapa whelks had lower wet tissue weights than either imposex females or males. Individual rapa whelks did not appear to be food-limited in the Chesapeake Bay, and the described reproductive activity suggests continued invasion within Chesapeake Bay habitats.

Sexual differentiation and variations sexual characteristics <i>Rapana venosa</i> (Valenciennes, 1846)

“…Our present studies found wider spectrum of color gonads of both males and females, than is available in previously published material (Chuhchin, 1961a, 1984, Mann et al, 2006, Micu et al, 2009, Lanfrankoni et al, 2009, Saglam and Duzgunes, 2014. Moreover it is shown that the diversity of these colors is not (necessarily) associated with intersex status of individuals.…”

“…In the western part of the Black Sea off the coast of Romania (Agigea littoral) the females (with no penis) had yellow gonads (Micu et al, 2009). Rapa whelk female gonads in Chesapeake Bay were completely yellow in color with special indication for "no penis" females (Mann et al, 2006). That qualification "no penis" is because of besides true females in Chesapeake Bay and in the Romanian Black Sea Agigea littoral area as well there were imposex females registered.…”

“…venosa imposex females in Chesapeake Bay had penis lengths ranging from 1.9mm to 25mm and gonads that were either completely yellow or a mix of yellow and pale orange (Mann et al, 2006). In the Black Sea Agigea littoral area imposex females had penis (1.14mm-6.94mm) and yellow-orange gonads (Micu et al, 2009).…”

“…Thus the color of the gonads of imposex females individuals approaching the color of the gonads of young males by (Chuhchin, 1961a) and it can be assumed that this is a consequence of masculinization. Number of imposex females (IF) in the western part of the Black Sea is approximately 30% the number of females (F: IF = 3.26:1) after (Micu et al, 2009), whereas in 4 out of 5 Chesapeake Bay geographic regions examined the preponderance of imposex females over 'normal' females (penis length = 0) by at least a 2:1 ratio (Mann et al, 2006).…”

“…High ecological plasticity of the species and a favorable complex of environmental factors allowed R. venosa to colonize the Black Sea coastal waters fast enough and continue resettlement through the Mediterranean basin in the various areas of the eastern and western Atlantic (Chuhchin, 1984, Mann et al, 2004, 2006, Lanfrankoni et al, 2009, Bondarev, 2010, Bondarev, 2014. The need for adaptation to different environmental conditions, as well as significant changes in the ecosystem of the Black Sea have occurred since the time of invasion (Bondarev, 2014) led to a diverse morphogenesis (Bondarev, 2010, Bondarev, 2013.…”