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

作　　者：M.Aminur RAHMAN Tsuyoshi UEHARA Aziz ARSHAD Fatimah Md.YUSOFF Mariana Nor SHAMSUDIN 

机构地区：[1]Laboratory of Marine Biotechnology,Institute of Bioscience,Universiti Putra Malaysia,43400 UPM Serdang,Selangor,Malaysia [2]Department of Chemistry,Biology and Marine Science,Faculty of Science,University of the Ryukyus,1 Senbaru,Nishihara-cho,Okinawa 903-0213,Japan [3]Department of Aquaculture,Faculty of Agriculture,Universiti Putra Malaysia,43400 UPM Serdang,Selangor,Malaysia

出　　处：《Journal of Zhejiang University-Science B(Biomedicine & Biotechnology)》2012年第10期797-810,共14页浙江大学学报（英文版）B辑（生物医学与生物技术）

基　　金：Project supported by the Japan Society for the Promotion of Science (JSPS);the Research University Grant Scheme (RUGS) of Universiti Putra Malaysia (UPM) Vide Project (No. 05-03-10-1034RU)

摘　　要：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 F 1 hybrids were completely fertile and displayed high fertilization success in F 1 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 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 F 1 hybrids were completely fertile and displayed high fertilization success in F 1 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 sugges

关 键 词：Sea urchins Echinometra HYBRIDIZATION Gamete compatibility Reproductive isolation SPECIATION 

分 类 号：Q953[生物学—动物学]