Hybridisations between Mytilus edulis and Mytilus galloprovincialis and performance of pure species and hybrid veliger larvae at different temperatures

Abstract

The mussels Mytilus edulis L. and Mytilus galloprovincialis Lamark hybridise naturally in the wild along the Atlantic coast of Europe producing a patchwork of mixed pure species and hybrid populations. Individuals of both species were spawned in the laboratory and were hybridised in a series of reciprocal crosses. After 72 h, the proportion of eggs which developed into larvae (%yield) and the proportion of those larvae which had a normal veliger morphology (%normality) were estimated and compared between pure species and hybrid families. There were no significant differences in %yield or %normality between pure species and hybrids, but significant differences were evident between the offspring from different parents irrespective of whether they were hybrids or pure species. Therefore confirmation of hybrid heterosis in laboratory studies should not be based on a single, or a few reciprocal crosses. Hybrid and pure species veliger larvae were grown for approximately 4 weeks at 10, 14 or 20 °C. In all trials, pure M. galloprovincialis larvae grew significantly faster at 20 °C than either reciprocal hybrid or pure M. edulis larvae. Irrespective of temperature, in general, hybrid larvae grew slower than larvae of either pure species. Increased exposure to planktonic predation due to slow growth can be interpreted as selection against hybrids and this may play a role in the structure and distribution of mixed pure species and hybrid populations.