was maintained at 1 individualr1 l of seawater. The algal stones were changed at an interval of 15 days with new ones to supplement them with adequate algal foods. The
culture was continued up to 1 year by which time both the parental species and their reciprocal hybrids contained mature gametes. Growth performance and health conditions
of the cultured urchins were monitored through monthly samplings.
2.7. Data analysis Statistical analysis in this experiment was performed by one way analysis of variance.
Ž .
Comparison between treatment means was carried out by analysis of variance ANOVA Ž
. followed by Duncan’s Multiple Range Test Duncan, 1955 and the significance of
variation between the means was tested using the computerized Stat View version 4.0 program.
3. Results
Cross-fertilization between the two sympatric Echinometra sp. A and Echinometra sp. C was conducted using all possible combinations. During each cross-fertilization
experiment, eggs from the same female and sperm from the same male were used and gametes from different individuals of the same species were not mixed together. In
crosses with the eggs of 13 female Echinometra sp. A, the percent fertilization of the
Ž .
conspecific controls Ea = Ea averaged 99.78 and was higher than that obtained from Ž
. Ž
. the corresponding Ec = Ea crosses 92.82 , but was not significantly so P 0.05 .
Ž .
Ž The mean percentage of fertilization of Ea = Ea 99.78 differed significantly P -
. Ž
. Ž .
0.05 from that of the Ea = Ec crosses 42.38 Table 1 . In crosses with the eggs of
13 females of Echinometra sp. C, the percent fertilization of the conspecific controls
Table 1 Performance of hybrid groups and their conspecific controls from fertilization to 3-month-old juvenile urchins
All values represent meanS.D. with ranges in parentheses. Mean values for groups within each experiment Ž
. with common superscripts in the same column are not significantly different P 0.05 .
1 2
Ž . Ž .
Ž . Ž .
Treatment groups Fertilization
Survival Metamorphosis
Recovery
a a
a a
Ea=Ea 99.780.45
73.002.64 88.893.85
69.453.23 Ž
. Ž
. Ž
. Ž
. 99.00–100.00
70.00–75.00 86.67–93.33
69.05–72.86
a a
a a
Ec=Ea 92.823.31
68.002.00 84.443.85
64.771.14 Ž
. Ž
. Ž
Ž .
86.00–95.00 66.00–70.00
80.00–86.67 63.74–66.00
b b
b b
Ea=Ec 42.388.00
50.331.52 68.893.85
56.681.54 Ž
. Ž
. Ž
. Ž
. 29.00–50.00
49.00–52.00 66.67–73.33
55.20–58.28
a a
a a
Ec=Ec 99.310.85
72.331.63 86.676.67
65.231.55 Ž
. Ž
. Ž
. Ž
. 98.00–100.00
71.00–74.00 80.00–93.33
63.89–66.92
1
Matured larvae that were deemed competent for metamorphosis after a 20- to 24-day culture period in laboratory condition.
2
Three-month-old juvenile urchins that were transferred to flow-through sea water system for advanced culture.
Ž .
Ž .
Ec = Ec averaged 99.31 and was significantly different P - 0.05 from that ob-
tained from the corresponding Ea = Ec crosses, but it did not differ significantly Ž
. Ž
. P 0.05 from that of Ec = Ea crosses Table 1 . Therefore, cross fertilization was
highly asymmetrical. Ec ova are easily fertilized by either Ec or Ea sperm, but even a Ž
y1
. very high concentration of Ec sperm above 10
dilution of ‘dry’ sperm produced a Ž
. very low percent of fertilization 42.38 of Ea ova. This reduction, at least, may be due
to the presence of gamete recognition protein binding system as reported by Metz and Ž
. Ž
. Palumbi 1996 and Metz et al. 1994 . These results followed the same trends as
Ž .
reported by Uehara et al. 1990 . Survival of mature larvae for the hybrid produced using the eggs of Ec was not
Ž .
significantly different P 0.05 from the pure parental matings. On the other hand, the Ž
. Ž
. survival rate for the reciprocal hybrid Ea = Ec was significantly
P - 0.05 lower Ž
. Table 1 . In this case mortality usually occurred during various stages of larval
development. The laboratory-raised larvae of the parental species and the hybrids reached a state of
metamorphosis at about 20–24 days of age as evidenced by having large rudiment. Complete metamorphosis from feeding larvae to feeding adult took place in about 1 day
after settlement on red algal substratum. This included the complete development of adult internal organs as well as the formation of the adult mouth, anus, tubefeet, and
spines. Completion of metamorphosis was the same and the rate of development was
Ž .
equivalent among all treatments Table 1 . Moreover, the time required to complete development from the eight armed stage to metamorphosed juvenile was similar among
all treatments. The majority of the larvae were metamorphosed to young juveniles on Ž
. CRAS collected from the shallow sea within 1 day and there were no particular
deformitiesrdefects observed in the metamorphosed juvenile hybrids, Ec = Ea and Ž
. Ea = Ec. The Ea = Ec hybrids showed significantly
P - 0.05 lower metamorphosis rate compared with other groups, but Ec = Ea hybrids did not differ significantly
Ž .
P 0.05 from their pure parental species. After 3 months of rearing, the juvenile urchins were transferred to a grow out system
with flow-through sea water. It was found that the recovery of Ea = Ec hybrids was Ž
. significantly
P - 0.05 lower compared to parental species controls, but the hybrids Ž
. .
Ec = Ea did not differ significantly P 0.05 from these. The detailed growth and survival of the hybrids and their parental species at the end
of the experimental period are summarized in Table 2 while the growth trend is depicted in Fig. 1. It was observed that though the hybrids were intermediate to their parental
species, the growth of hybrids was much faster than the slow-growing conspecific Ec = Ec. and slightly less than the fast-growing Ea = Ea cross under identical rearing
Ž .
conditions Table 2 and Fig. 1 . The mean total weight gained by Ea = Ea, Ec = Ec, Ec = Ea, and Ea = Ec was 14.5 0.12, 9.1 0.01, 13.8 0.09, and 13.5 0.03 g
respectively during the culture period of 1 yr. Between the two hybrids, Ec = Ea values were consistently higher than Ec = Ec and reciprocal cross Ea = Ec although, slightly
Ž .
Ž .
but statistically significantly P - 0.05 less than Ea = Ea Table 2 . The mean weight Ž
. gained by the hybrids and parental species differed significantly P - 0.05 . Among the
four groups, the weight gain between Ec = Ea and Ea = Ec was not significantly Ž
. Ž
. different P 0.05 , while they differed significantly P - 0.05 from other groups but
Table 2 Ž
. Ž
. Echinometra sp. A Ea and Echinometra sp. C Ec
Details of growth and survival of the conspecific controls and hybrids produced experimentally at the end of Ž
. the study period. Standard error S.E. and ranges are in parentheses. A total of 30 specimens were measured
for weight and volume with 10 per replicate for each treatment. Parametersrtreatments
Ea=Ea Ec=Ea
Ea=Ec Ec=Ec
U a
ab bc
c
Ž . Ž
. Ž
. Ž
. Ž
. Mean initial weight g
0.16 0.003 0.15 0.002
0.14 0.003 0.13 0.002
Ž .
Ž .
Ž .
Ž .
0.15–0.16 0.14–0.15
0.13–0.14 0.12–0.13
a b
b c
Ž . Ž
. Ž
. Ž
. Ž
. Mean final weight g
14.7 0.12 13.9 0.09
13.6 0.03 9.2 0.10
Ž .
Ž .
Ž .
Ž .
14.6–14.8 13.8–14.0
13.6–13.7 9.1–9.3
a b
b c
Ž . Ž
. Ž
. Ž
. Ž
. Weight gain g
14.5 0.12 13.8 0.09
13.5 0.03 9.1 0.01
Ž .
Ž Ž
. Ž
. 14.4–14.6
13.7–13.90 13.4–13.5
9.0–9.2
a b
b c
Ž . Ž
. Ž
. Ž
. Ž
. Wet gonad weight g
2.39 0.030 2.27 0.027
2.22 0.025 1.30 0.017
Ž .
Ž .
Ž .
Ž 2.25–2.53
2.18–2.40 2.10–2.35
1.21–1.40
3 a
b b
c
Ž .
Ž .
Ž .
Ž .
Ž .
Test volume cm 11.4 0.17
10.4 0.12 10.1 0.01
6.4 0.04 Ž
. Ž
. Ž
. Ž
. 11.2–11.6
10.2–10.5 10.0–10.2
6.4–6.5
a a
b a
Ž . Ž
. Ž
. Ž
. Ž
. Survival
84.44 1.92 77.78 1.11
70.00 1.92 82.22 2.94
Ž .
Ž .
Ž .
Ž .
83.33–86.67 76.67–80.0
66.67–73.33 76.67–86.67
U
Ž .
Mean values in each row having same superscript were not significantly different P 0.05 .
the values were comparatively much closer to their fast growing parental Ea species. Ž
. Test volumes length = width = height also followed the same trends as those of weight
Ž .
Ž .
gain Table 2 . The fresh weight of edible gonad was significantly P - 0.05 lowest in Ec = Ec. The hybrids contained a large amount of gonad, but slightly less than Ea = Ea,
Ž . Fig. 1. Mean live weights g attained by the parental species controls and hybrids produced experimentally
Ž .
Ž .
using Echinometra sp. A Ea and Echinometra sp. C Ec during the culture period of 1 year when they contained mature gametes; maternal species are named first. A total of 30 specimens were measured every
month with 10 per replicate for each treatment. ANOVA analysis showed that growth of the hybrids, both of Ž
. the reciprocal crosses were not statistically significant P 0.05 but that they both differed significantly from
Ž .
the controls P - 0.05 . Hybrids always showed a different but closer relations, in terms of live weight, to their parental Echinometra sp. A.
Ž .
although the values were significantly different P - 0.05 . The reciprocal hybrids did not differ significantly. The gonad production showed an increment of 21.6 in F
1
Ž .
hybrids over mid-parents mean of both parental species . While it showed an increase of 74.6 in F hybrid of Ec = Ea and 70.8 in F hybrid of Ea = Ec over the inferior
1 1
parents Ec. Survival was highest in Ea = Ea followed by Ec = Ec, and Ec = Ea in that
Ž .
Ž .
Fig. 2. Echinometra sp. A Ea
and Echinometra sp. C Ec
and their reciprocal hybrids, produced Ž .
Ž . Ž .
experimentally, 1 year after metamorphosis; maternal species named first. A Ea=Ea; B Ea=Ec; C Ž .
Ec=Ea and D Ec=Ec. Bar indicates 2.0 cm.
Ž .
order, which were not significantly different P 0.05 but the hybrid, Ea = Ec differed Ž
. Ž
. significantly P - 0.05 from other groups Table 2 . Therefore, the results of growth
Ž .
and survival indicated that the hybrids Fig. 2 in both directions were viable in
lab-reared conditions. The 1-year-old mature hybrids exhibited color patterns similar to those of their maternal colorations, although the reciprocal hybrids were closer to Ea in
Ž .
size Fig. 2 .
4. Discussion
