In sympatric species, a region of the bindin molecule reportedly evolves at high
rates under strong positive selection (Metz and Palumbi 1996), whereas in allopatric species (e.g. T. ventricosus in the Caribbean and T. depressus in the eastern
Pacific), bindin variation was reported to be low, with no evidence of positive
selection. However, this does not appear to be the case for all sea urchin species.
Lytechinus williamsi and L. variegatus, which have overlapping distributions in
the Caribbean, show no clear evidence of selection (Zigler and Lessios 2004).
While in spatially overlapping E. lucunter and E. viridis, positive selection was
only found to have accumulated along the bindin lineage of E. lucunter
(McCartney and Lessios 2004). Further, Geyer and Lessios (2009) found no evidence to suggest that the source of selection on bindin in E. lucunter is
reinforcement, as bindin showed no evidence of stronger selection in areas of
sympatry relative to areas of allopatry. Geyer and Lessios (2009) propose that the
evolution of this molecule is a result of the processes acting within species, such as
sexual selection and sperm competition.
The reproductive cycle of the starfish O. reticulatus in Isla Solarte, Bocas del
Toro Archipelago, was studied from February 2000 to February 2001 by Guzman
and Guevara (2002a). Males and females with ripe gonads were observed almost
every month, however, the gonad index revealed peaks in reproductive activity,
during July, November, and January. Gonad maturation was not triggered by
changes in water temperature (these ranged from 27 °C to 30 °C), but may have
responded to chemical cues in the water (e.g. nutrients, salinity) (Guzman and
Guevara 2002a).
Guzman et al. (2003) assessed the reproductive status of two commercial
species of sea cucumber, I. badionotus and H. (H.) mexicana in the Caribbean of
Panama. They reported that for both species the minimum reproductive length was
13–20 cm with a weight of 150 g. Both species were gonochoric with a 1:1 sex
ratio. Gametogenesis and spawning occurred throughout the year; however there
were periods of peak reproductive activity, between July and November for
I. badionotus and from February to July for H. (H.) mexicana (Guzman et al.
2003).
4.3.3 Evolution
Molecular work on echinoids in Panama started with Lessios (1979), who used
geminate species of Panama (E. tribuloides and E. thouarsii, D. antillarum and D.
mexicanum, E. viridis, E. lucunter and E. vanbrunti) to test the molecular clock
hypothesis. This hypothesis predicts that each protein changes at a constant rate, so
that the degree of divergence between two species is linearly related to the time for
which their lineages have remained separate (Wilson et al. 1977). Lessios (1979)
found that this does not hold for Panamanian echinoids, as very different rates of
divergence were found in the enzymatic proteins between geminates in the
different genera. Eucidaris and Echinometra exhibited transisthmian distances
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S. E. Coppard and J. J. Alvarado
rates under strong positive selection (Metz and Palumbi 1996), whereas in allopatric species (e.g. T. ventricosus in the Caribbean and T. depressus in the eastern
Pacific), bindin variation was reported to be low, with no evidence of positive
selection. However, this does not appear to be the case for all sea urchin species.
Lytechinus williamsi and L. variegatus, which have overlapping distributions in
the Caribbean, show no clear evidence of selection (Zigler and Lessios 2004).
While in spatially overlapping E. lucunter and E. viridis, positive selection was
only found to have accumulated along the bindin lineage of E. lucunter
(McCartney and Lessios 2004). Further, Geyer and Lessios (2009) found no evidence to suggest that the source of selection on bindin in E. lucunter is
reinforcement, as bindin showed no evidence of stronger selection in areas of
sympatry relative to areas of allopatry. Geyer and Lessios (2009) propose that the
evolution of this molecule is a result of the processes acting within species, such as
sexual selection and sperm competition.
The reproductive cycle of the starfish O. reticulatus in Isla Solarte, Bocas del
Toro Archipelago, was studied from February 2000 to February 2001 by Guzman
and Guevara (2002a). Males and females with ripe gonads were observed almost
every month, however, the gonad index revealed peaks in reproductive activity,
during July, November, and January. Gonad maturation was not triggered by
changes in water temperature (these ranged from 27 °C to 30 °C), but may have
responded to chemical cues in the water (e.g. nutrients, salinity) (Guzman and
Guevara 2002a).
Guzman et al. (2003) assessed the reproductive status of two commercial
species of sea cucumber, I. badionotus and H. (H.) mexicana in the Caribbean of
Panama. They reported that for both species the minimum reproductive length was
13–20 cm with a weight of 150 g. Both species were gonochoric with a 1:1 sex
ratio. Gametogenesis and spawning occurred throughout the year; however there
were periods of peak reproductive activity, between July and November for
I. badionotus and from February to July for H. (H.) mexicana (Guzman et al.
2003).
4.3.3 Evolution
Molecular work on echinoids in Panama started with Lessios (1979), who used
geminate species of Panama (E. tribuloides and E. thouarsii, D. antillarum and D.
mexicanum, E. viridis, E. lucunter and E. vanbrunti) to test the molecular clock
hypothesis. This hypothesis predicts that each protein changes at a constant rate, so
that the degree of divergence between two species is linearly related to the time for
which their lineages have remained separate (Wilson et al. 1977). Lessios (1979)
found that this does not hold for Panamanian echinoids, as very different rates of
divergence were found in the enzymatic proteins between geminates in the
different genera. Eucidaris and Echinometra exhibited transisthmian distances
124
S. E. Coppard and J. J. Alvarado