Gametogenesis and reproductive behavior in the echinoid Lytechinus variegatus

Abstract

Gametogenesis and behavior facilitating reproduction were studied in the echinoid Lytechinus variegatus (Lamark 1816), found off Key Biscayne, Florida, during 1993. Oocyte diameters and qualitative staging of gonad sections indicated a sustained peak in reproductive state from April to June followed by a decrease in reproductive state by August and a shorter reproductive peak by November. Ripe females censused during both reproductive seasons showed substantial variation in oocyte size suggesting that sporadic, small scale spawning events commonly occur in this population. Counts of urchins in nested quadrats showed that L. variegatus aggregates at no fewer than 4 different spatial scales (0.0625, 0.25, 1.0 , and 2.0 m 2 ) with aggregations at larger scales being most common, especially prior to reproductive seasons. A noticeably higher amount of food in guts at these times suggests that these aggregations may be formed during random encounters during periods of increased feeding activity, which may also build up energy reserves for reproduction. Marked urchins were arranged in artificial aggregations of various sizes to investigate potential reproductive interactions. Most urchins moved 1 to 3 m d -1 throughout the year. Most encounters among urchins were of short duration and occurred randomly. Urchins placed in the largest aggregations dispersed most slowly during April and June, the periods with the highest mean oocyte diameters. The incidence of heterosexual pairing among naturally occurring pairs of urchins was random, suggesting that L. variegatus may not be able to distinguish gender. Sex ratio of the population was skewed in favor of males. The data suggest that numerous small scale spawning events take place during an extended reproductive season and that intraspecific encounters occur during this season entirely by chance. This method of spawning may enhance outcrossing.

Influence of Sperm and Phytoplankton on Spawning in the Echinoid Lytechinus variegatus

“…A complete list of individuals, test date, treatment, and response is provided in the supplemental material online at http://www.biolbull.org/supplemental/. These patterns match published data for this species (Beddingfield and Mc-Clintock, 2000;McCarthy and Young, 2002). Sea urchin diameters ranged from 2.9 to 7.5 cm (average 4 cm).…”

“…Previous research indicated that the spawning season extended from late spring to early fall (Beddingfield and McClintock, 2000;McCarthy and Young, 2002), and that guided our seasonal sampling scheme. Individuals were collected on one of 12 dates in the 2008 and 2009 spawning seasons from March to November, with most sampling concentrated in the summer, when preliminary data suggested it was a more predictable season for collecting ripe animals (DRL, pers.…”

Effects of water-borne gametes on the aggregation behavior of Lytechinus variegatus

“…This suggests that ripe individuals (1) might not be able to find each other easily, (2) randomly find each other and stay together either seasonally or for a short time, (3) are waiting to respond to a localized cue to temporarily aggregate or (4) do not aggregate for reproduction. It appears that L. variegatus does not seasonally aggregate as previously investigated (McCarthy & Young 2002). Therefore, if small-scale reproductive aggregations occur, they must be short term and result from either random encounters or a very localized cue.…”

“…Further, it is likely that such cues will only induce spawning and behavioral responses in small groups within a population. Asynchronous oocyte distributions among ripe females (Beddingfield & McClintock 1998, McCarthy & Young 2002 …”

“…Populations of the echinoid Lytechinus variegatus reproduce from February through June and again from October through November off SE Florida (McCarthy & Young 2002 (Sokal & Rohlf 1995). A Kruskal-Wallis test was used to determine where the number of urchins in each category varied between 1994 and 2002 (Sokal & Rohlf 1995) Spawning responses of natural and artificial aggregations.…”