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Journal of Zhejiang University SCIENCE B 2012 Vol.13 No.10 P.797-810


Absence of postzygotic isolating mechanisms: evidence from experimental hybridization between two species of tropical sea urchins

Author(s):  M. Aminur Rahman, Tsuyoshi Uehara, Aziz Arshad, Fatimah Md. Yusoff, Mariana Nor Shamsudin

Affiliation(s):  Laboratory of Marine Biotechnology, Institute of Bioscience, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia; more

Corresponding email(s):   aminur1963@gmail.com

Key Words:  Sea urchins, Echinometra, Hybridization, Gamete compatibility, Reproductive isolation, Speciation

M. Aminur Rahman, Tsuyoshi Uehara, Aziz Arshad, Fatimah Md. Yusoff, Mariana Nor Shamsudin. Absence of postzygotic isolating mechanisms: evidence from experimental hybridization between two species of tropical sea urchins[J]. Journal of Zhejiang University Science B, 2012, 13(10): 797-810.

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author="M. Aminur Rahman, Tsuyoshi Uehara, Aziz Arshad, Fatimah Md. Yusoff, Mariana Nor Shamsudin",
journal="Journal of Zhejiang University Science B",
publisher="Zhejiang University Press & Springer",

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%T Absence of postzygotic isolating mechanisms: evidence from experimental hybridization between two species of tropical sea urchins
%A M. Aminur Rahman
%A Tsuyoshi Uehara
%A Aziz Arshad
%A Fatimah Md. Yusoff
%A Mariana Nor Shamsudin
%J Journal of Zhejiang University SCIENCE B
%V 13
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%P 797-810
%@ 1673-1581
%D 2012
%I Zhejiang University Press & Springer
%DOI 10.1631/jzus.B1100152

T1 - Absence of postzygotic isolating mechanisms: evidence from experimental hybridization between two species of tropical sea urchins
A1 - M. Aminur Rahman
A1 - Tsuyoshi Uehara
A1 - Aziz Arshad
A1 - Fatimah Md. Yusoff
A1 - Mariana Nor Shamsudin
J0 - Journal of Zhejiang University Science B
VL - 13
IS - 10
SP - 797
EP - 810
%@ 1673-1581
Y1 - 2012
PB - Zhejiang University Press & Springer
ER -
DOI - 10.1631/jzus.B1100152

Two reef margin species of tropical sea urchins, Echinometra sp. C (Ec) and Echinometra oblonga (Eo), occur sympatrically on Okinawa intertidal reefs in southern Japan. hybridization between these species was examined through a series of cross-fertilization experiments. At limited sperm concentrations, where conspecific crosses reached near 100% fertilization, both heterospecific crosses showed high fertilization rates (81%–85%). The compatibility of the gametes demonstrated that if gamete recognition molecules are involved in fertilization of these species, they are not strongly species-specific. We found that conspecific crosses reached peak fertilization levels much faster than did heterospecific crosses, indicating the presence of a prezygotic barrier to hybridization in the gametes. Larval survival, metamorphosis, and juvenile and adult survival of hybrid groups were nearly identical to those of their parent species. Hybrids from crosses in both directions developed normally through larval stages to sexually mature adults, indicating that neither gametic incompatibility nor hybrid inviability appeared to maintain reproductive isolation between these species. In adults, Ec×Ec crosses gave the highest live weight, followed by Eo (ova)×Ec (sperm), Ec (ova)×Eo (sperm), and Eo×Eo. Other growth performance measures (viz., test size, Aristotle’s lantern length, and gonad index) of hybrid groups and their parental siblings showed the same trends. The phenotypic color patterns of the hybrids were closer to the maternal coloration, whereas spine length, tube-foot and gonad spicule characteristics, pedicellaria valve length, and gamete sizes showed intermediate features. Adult F1 hybrids were completely fertile and displayed high fertilization success in F1 backcrosses, eliminating the likelihood that hybrid sterility is a postzygotic mechanism of reproductive isolation. Conversely, intensive surveys failed to find hybrid individuals in the field, suggesting the lack or rarity of natural hybridization. This strongly suggests that reproductive isolation is achieved by prezygotic isolating mechanism(s). Of these mechanisms, habitat segregation, gamete competition, differences in spawning times, gametic incompatibility or other genetic and non-genetic factors appear to be important in maintaining the integrity of these species.

Darkslateblue:Affiliate; Royal Blue:Author; Turquoise:Article


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