11th ICRS Abstract book - Nova Southeastern University

Poster Mini-Symposium 26: Biodiversity and Diversification of Reef Organisms
26.1230
Gamete Competition Is A Prezygotic Barrier in Broadcast Spawning Sea Urchins: Evidence From
Mixing Gametes Of Two Species And Rearing The Offspring
M. Aminur RAHMAN* 1 , Tsuyoshi UEHARA 2
1 Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Panama, Balboa, Panama,
2 Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus,
1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan, Okinawa, Japan
Two tropical sea urchins belonging to the genus Echinometra, Echinometra sp. A (Ea) and Echinometra
sp. C (Ec) occur nearly sympatrically and abundantly on Okinawan intertidal reefs. Earlier studies have
confirmed that the two species are reproductively isolated and introgression is either very low or nonexistence
between them. To understand which mechanism(s) maintain their genetic integrity, a series of
cross-fertilization and gamete competition experiments was conducted in the laboratory. Similar to
previous studies, fertilization rates in heterospecific crosses were high when eggs of Ec and sperm of Ea
were involved, whereas they were significantly lower with eggs of Ea and sperm of Ec, even at a very
high sperm concentration. Gamete incompatibility probably prevents hybridization between eggs of Ea
and sperm of Ec. However, because eggs of Ec are readily fertilized by sperm of Ea, gamate
incompatibilty itself is probably not responsible for the absence of Ec x Ea hybrids in the field. We
found that different exposure times of eggs and sperm at various sperm concentrations showed that
conspecific crosses reached asymptotic fertilization level much sooner than heterospeciific crosses,
indicating that conspecific sperm have higher affinity to their eggs than heterospecific sperm. In gamete
competition experiments, eggs from either species or both in equal proportions were mixed with the
sperm from either species or both in equal proportions at various sperm concentrations and the resulting
larvae were reared through metamorphosis to 4-5 month old juveniles. Tubefoot spicules in Ea x Ea
were always bihamate (100%), whereas those in Ec x Ec were always triradiate (100%). The spicule
morphologies of the hybrids were intermediate mixes and tended toward maternal affinities; these
differences were used to identity hybrids and their parental genotypes in each gamete competition
experiment. We found that at lower sperm concentration (1.05 x 105/ml) where conspecifics reached
only 60-70% fertilization, very few Ec x Ea (1.3-3.3%) hybrids were produced. At the sperm
concentration (1.05 x 106/ml) where conspecific crosses showed near 100% fertilization, more Ec x Ea
hybrids were found (8.7-12.7%) but no Ea x Ec hybrids. At higher sperm concentrations, 1.05 x 107/ml,
1.05 x 108/ml, and 1.05 x 109/ml, the percentages of Ec x Ea and Ea x Ec hybrids produced from the
various competitive fertilizations were 13.3-18.0 and 0, 18.7-21.3 and 0.7-2.0, and 22.7-26.7 and 2.7-
4.5, respectively. Moreover, in each gamete mixing experiments, the proportion of Ec x Ec conspecifics
was significantly higher than that of Ea x Ea, suggesting that larger eggs of Ec may present a larger
target for sperm than those of Ea, thereby producing higher numbers of Ec juveniles than Ea. Overall,
the production of only a few hybrids in each competition experiment is likely due to conspecific sperm
outcompeting heterospecific sperm for fertilization. Ea occurs mainly on the reef flat while Ec occurs on
the reef’s seaward margin, so most individuals are not found near each other. Their spawning seasons
overlap extensively, and if they spawn simulataneoulsly, incoming waves would mix and then sweep
gametes of Ec over the reef flat to mix with gametes of Ea.. Most of the eggs of Ec would likely be
fertilized by sperm of Ec before they mixed with gametes of Ea on the reef flat, and excess sperm of Ec
would have a competitive advantage to fertilized the remaining unfertilized eggs of Ec. Conversely, the
incompatibility of eggs of Ea with sperm of Ec, decreases the chances of Ea x Ec hybrids. Consequently,
habitat partitioning and asymmetric gamete compatibility both have significant roles in maintaining
species boundaries between these broadcast spawning urchins.
26.1231
Diversity And Abundance Of Reef Macro Invertebrates (Mollusca, Echinodermata)
in The Southern Gulf Of California, México
Maria Dinorah HERRERO-PEREZRUL*1
1 Pesquerias y Biologia Marina, CICIMAR-IPN, La Paz, Mexico
There are three important islands in the southern Gulf of California, included in a Marine
Protected Area, San José (SJI), Espíritu Santo (ESI) and Cerralvo (CRI). The islands
support coral communities with associated invertebrates, especially mollusks and
echinoderms. Some species of both groups are currently under protection or subjected to
fishery. Even though the islands are protected, little is known about the diversity and
abundance of these macro invertebrates. The objective of this work was to estimate the
diversity and abundance of macro mollusks and echinoderms at these three islands. The
study was done from February 2005 to February 2007, each island was visited twice,
considering two seasons, warm (Jun-Nov) and cold (Dec-May). A total of 165 belt
transects (25 x 2 m) were done to estimate species richness, diversity and abundance on
each island and season. A total of 20 species of echinoderms (5310 individuals) and 19 of
macro mollusks (2020 individuals) were identified. Species richness and abundance was
statistically different among the islands for both Phyla; however, diversity showed no
differences. Species assemblage was different on each island. ESI had more echinoderms
and SJI had more mollusks. The most abundant echinoderms were asteroids, followed by
echinoids and holothurians. The dominant species were the sea star Phataria unifascialis,
followed by the sea urchin Tripneustes depressus and the holothurian Holothuria
fuscoscinerea. Regarding mollusks, the gastropods were the most abundant with 12
species, whilst bivalves had only 7. SJI and CRI had more gastropods species than ESI.
The dominant gastropod and bivalve were Serpulorbis margaritaceus and the mother of
pearl Pinctada mazatlanica, which is currently under special protection. Commercial
species were not so abundant, like Isostichopus fuscus and Muricanthus princeps.
26.1232
A Quantitative Assessment Of The Cryptobenthic Fish Assemblage On Isolated Coral
Colonies in The Tropical Eastern Pacific.
Adriana ALZATE VALLEJO 1 , Fernando A. ZAPATA* 1 , Alan GIRALDO 1
1 Biology, Universidad del Valle, Cali, Colombia
The cryptobenthic fish assemblage associated to small, isolated massive and branching coral
colonies at Gorgona Island, Colombia, was examined using two sampling methods. We
compared samples obtained by direct capture using a 1m 3 net-box and application of clove oil
against samples obtained by visual censuses. A total of 38 species belonging to 16 families were
recorded through both methods combined. More species were recorded by direct capture (33
species) than by visual censuses (23 species). Mean species richness was significantly greater in
samples obtained by direct capture (4.2 species) than in samples obtained by visual census (2.4
species; p