School of Biological Sciences, Institute for Conservation Biology and Environmental Management, University of Wollongong, Wollongong, NSW 2522, Australia.
Mol Ecol. 2010 Feb;19(3):508-20. doi: 10.1111/j.1365-294X.2009.04501.x. Epub 2010 Jan 11.
Populations of obligately estuarine taxa are potentially small and isolated and may lack genetic variation and display regional differentiation as a result of drift and inbreeding. Hybridization with a wide-ranging marine congener should introduce genetic variation and reduce the effects of inbreeding depression and genetic drift. However, high levels of hybridization can cause demographic and genetic swamping. In southeastern Australia hybridization occurs between obligately estuarine Black bream (Acanthopagrus butcheri) and migratory marine Yellowfin bream (Acanthopagrus australis). Here, we surveyed genetic variation at eight microsatellite loci and the mitochondrial control region of juvenile fish from five coastal lagoons (including temporal replication in two lagoons) (total n = 970) to determine the frequency and persistence of hybridization, and its likely consequence for the estuarine restricted A. butcheri. Of 688 juvenile fish genotyped 95% were either A. australis (347) or hybrids (309); only 5% (32) were A. butcheri. Most hybrids were later generation hybrids or A. butcheri backcrosses, which are likely multi-generational residents within lagoons. Far greater proportions of hybrid juveniles were found within two lagoons that are generally closed to the ocean (>90% hybrid fish within generally closed lagoons vs. 12-27% in permanently or intermittently open lagoons). In both lagoons, this was consistent across multiple cohorts of fish [79-97% hybrid fish (n = 282)]. Hybridization and introgression represent a major threat to the persistence of A. butcheri and have yet to be investigated for large numbers of estuarine taxa.
半洄游性鱼类的种群数量可能较小且较为孤立，由于遗传漂变和近亲繁殖，它们可能缺乏遗传变异性，并表现出区域分化。与广布的海洋近缘种杂交应引入遗传变异性，并减少近亲繁殖衰退和遗传漂变的影响。然而，高水平的杂交可能导致种群和遗传的淹没。在澳大利亚东南部，半洄游性黑鲈（Acanthopagrus butcheri）和洄游性海洋黄鲈（Acanthopagrus australis）之间发生杂交。在这里，我们调查了五个沿海泻湖（包括两个泻湖的时间复制）（总 n = 970）中幼鱼的 8 个微卫星基因座和线粒体控制区的遗传变异，以确定杂交的频率和持久性，以及其对限制在河口的 A. butcheri 的可能后果。在 688 条被基因分型的幼鱼中，有 95%是 A. australis（347 条）或杂交种（309 条）；只有 5%（32 条）是 A. butcheri。大多数杂交种是后来的杂交种或 A. butcheri 的回交种，它们很可能是泻湖内的多代居民。在两个通常与海洋隔绝的泻湖中发现了更多的杂交幼鱼（在通常封闭的泻湖中，杂交鱼类的比例超过 90%，而在永久性或间歇性开放的泻湖中，杂交鱼类的比例为 12-27%）。在两个泻湖中，这种情况在多批鱼类中都是一致的[79-97%的杂交鱼类（n = 282）]。杂交和基因渗入对 A. butcheri 的生存构成了重大威胁，但尚未对大量的河口物种进行调查。
