experiments to determine the degree of reproductive isolation both between the
sympatric E. lucunter and E. viridis, in the Caribbean, and with the allopatric
E. vanbrunti from the eastern Pacific. They reported that, contrary to the predictions of the ‘speciation by reinforcement hypothesis’, the degree of incompatibility
between the allopatric E. lucunter and E. vanbrunti is higher than between the
sympatric E. lucunter and E. viridis. Crosses between E. viridis and E. vanbrunti
produced rates of fertilization almost equal to those of homogamic crosses, while
sperm of E. lucunter were found to be able to fertilize eggs of the other two
species. However, few E. lucunter eggs are fertilized by heterospecific sperm
(Lessios and Cunningham 1993). In the wild E. lucunter and E. viridis maintain
their genetic integrities despite having this unidirectional gamete isolation.
Allozyme data placed the speciation event of the sympatric species after the rise of
the isthmus. Thus there is no correlation between genetic divergence and strength
of reproductive isolation (Lessios and Cunningham 1993).
Later work by McCartney and Lessios (2002) confirmed these findings and
demonstrated a much stronger block to cross-species fertilization of E. lucunter
eggs than was previously shown. They reported that gamete incompatibility in
these species is weaker in sympatry than in allopatry, and based on the mtDNA
data in McCartney et al. (2000), such gamete incompatibility in these species arose
in the last 1.5 million years.
Zigler et al. (2008) looked at egg energetics, fertilization kinetics, and population structure in echinoids with facultatively feeding larvae. This work included
C. rosaceus, one of only two echinoid species known to have facultatively
planktotrophic larvae. The eggs of C. rosaceus resemble those of echinoid species
with obligately feeding larvae in egg energetic density, egg buoyancy and fertilization kinetics, but resemble non feeding larvae in time to metamorphosis, the
early formation of the coelom and the reduced allocation to larval feeding structures (Zigler et al. 2008).
Cross-fertilization experiments between C. rosaceus and C. subdepressus by
Zigler et al. (2008) revealed that bidirectional gametic incompatibility has evolved
between the two species. These species are commonly found together or within close
proximity to one another in the shallow waters of the Caribbean in Panama (both
species live in the sand, but C. rosaceus is typically more common in turtle grass
beds). These species have no temporal reproductive isolation, as both have ripe
gonads for much of the year, but with peaks from July to October (Lessios 1984).
The results of Zigler et al. (2008) indicate that the small eggs of C. subdepressus
are particularly resistant to fertilization by C. rosaceus sperm, while the larger
C. rosaceus eggs are slightly more vulnerable to fertilization by C. subdepressus
sperm, but at levels that are unlikely to results in conspecific fertilizations in nature.
Research on the sea urchin sperm protein bindin in sea urchin species found off
the coasts of Panama has been conducted by Zigler and Lessios (2003a, b, 2004),
McCartney and Lessios (2004), Zigler et al. (2005), and Geyer and Lessios (2009).
Bindin is a sea urchin sperm protein that mediates sperm-egg attachment and
membrane fusion. Across echinoid genera, its divergence has been shown to be
correlated with heterospecific incompatibility in fertilization (Zigler et al. 2005).
4 Echinoderm Diversity in Panama
123
sympatric E. lucunter and E. viridis, in the Caribbean, and with the allopatric
E. vanbrunti from the eastern Pacific. They reported that, contrary to the predictions of the ‘speciation by reinforcement hypothesis’, the degree of incompatibility
between the allopatric E. lucunter and E. vanbrunti is higher than between the
sympatric E. lucunter and E. viridis. Crosses between E. viridis and E. vanbrunti
produced rates of fertilization almost equal to those of homogamic crosses, while
sperm of E. lucunter were found to be able to fertilize eggs of the other two
species. However, few E. lucunter eggs are fertilized by heterospecific sperm
(Lessios and Cunningham 1993). In the wild E. lucunter and E. viridis maintain
their genetic integrities despite having this unidirectional gamete isolation.
Allozyme data placed the speciation event of the sympatric species after the rise of
the isthmus. Thus there is no correlation between genetic divergence and strength
of reproductive isolation (Lessios and Cunningham 1993).
Later work by McCartney and Lessios (2002) confirmed these findings and
demonstrated a much stronger block to cross-species fertilization of E. lucunter
eggs than was previously shown. They reported that gamete incompatibility in
these species is weaker in sympatry than in allopatry, and based on the mtDNA
data in McCartney et al. (2000), such gamete incompatibility in these species arose
in the last 1.5 million years.
Zigler et al. (2008) looked at egg energetics, fertilization kinetics, and population structure in echinoids with facultatively feeding larvae. This work included
C. rosaceus, one of only two echinoid species known to have facultatively
planktotrophic larvae. The eggs of C. rosaceus resemble those of echinoid species
with obligately feeding larvae in egg energetic density, egg buoyancy and fertilization kinetics, but resemble non feeding larvae in time to metamorphosis, the
early formation of the coelom and the reduced allocation to larval feeding structures (Zigler et al. 2008).
Cross-fertilization experiments between C. rosaceus and C. subdepressus by
Zigler et al. (2008) revealed that bidirectional gametic incompatibility has evolved
between the two species. These species are commonly found together or within close
proximity to one another in the shallow waters of the Caribbean in Panama (both
species live in the sand, but C. rosaceus is typically more common in turtle grass
beds). These species have no temporal reproductive isolation, as both have ripe
gonads for much of the year, but with peaks from July to October (Lessios 1984).
The results of Zigler et al. (2008) indicate that the small eggs of C. subdepressus
are particularly resistant to fertilization by C. rosaceus sperm, while the larger
C. rosaceus eggs are slightly more vulnerable to fertilization by C. subdepressus
sperm, but at levels that are unlikely to results in conspecific fertilizations in nature.
Research on the sea urchin sperm protein bindin in sea urchin species found off
the coasts of Panama has been conducted by Zigler and Lessios (2003a, b, 2004),
McCartney and Lessios (2004), Zigler et al. (2005), and Geyer and Lessios (2009).
Bindin is a sea urchin sperm protein that mediates sperm-egg attachment and
membrane fusion. Across echinoid genera, its divergence has been shown to be
correlated with heterospecific incompatibility in fertilization (Zigler et al. 2005).
4 Echinoderm Diversity in Panama
123