Reproductive Isolation in the Polydora Ligni Complex and the Streblospio Benedicti Complex (Polychaeta: Spionidae)
Results of experimental crosses between individuals from geographically separated populations indicate that Tampa Bay Polydora ligni are reproductively isolated from their North Carolina and Los Angeles morphological counterparts. The North Carolina and Los Angeles populations of P. ligni are interfertile. The Tampa Bay population of Streblospio benedicti is likewise reproductively isolated from the planktotrophic North Carolina population. In both genera, experimental crosses were conducted in the laboratory using individual worms that had been raised in isolation prior to the experimental cross. Female worms from unsuccessful interpopulation crosses were back-crossed to intrapopulation males to ensure female fertility. Inter- and intra population crosses in P. ligni were accomplished via artificial transfer of spermatophores from an isolated male to an isolated female. In Streblospio crosses, males and females from appropriate populations were placed together and monitored daily for reproductive activity. The presence of spermatophores with active sperm in Streblospio cultures was taken to indicate male fertility. In the P. ligni complex, reproductive breakdown appears to occur at the sperm transfer stage. In interpopulation crosses, females accept spermatophores from exotic males but the sperm fail to accumulate in the sperm storage organs of the female. In the S. benedicti complex, the breakdown is also at the sperm transfer stage. Males produce spermatophores in the presence (or absence) of exotic females but no viable larvae are produced from these crosses. Intrapopulational crosses in both genera are routinely successful. Morphological differences between the reproductively isolated P. ligni populations are inconsistent and variable making description of distinct species difficult. Morphological differences are present, at least in females, from the divergent S. benedicti populations.
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Document Type: Research Article
Publication date: 01 March 1991
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