Hybridisation in the Brown Alga Carpophyllum: Investigating Morphology, Distribution and Wave Exposure
Hybridisation can result in new hybrid lineages, parental species extinctions, the transfer of adaptations, or the merging of parental lineages. Subsequently hybridisation has important implications for the species involved. Hybridisation has recently been confirmed between the Fucalean brown algae Carpophyllum angustifolium and Carpophyllum maschalocarpum using the ITS2 marker. This study conducted a detailed morphometric analysis combined with molecular data to investigate morphology distribution and exposure at two sites on the East Cape. Hybridisation was also morphologically investigated at Leigh, where the previous work had been unable to resolve hybrids using the ITS2 marker. Carpophyllum angustifolium, C. maschalocarpum and their hybrids had distinct and intermediate morphologies, and could be identified by stipe width alone. Individuals with hybrid genotypes with distinctive C. angustifolium morphotypes were also found, which suggests asymmetrical introgression is occurring. Some aspects of C. angustifolium and C. maschalocarpum morphology were found to be correlated with wave exposure. In the more exposed zones C. angustifolium individuals were longer, while C. maschalocarpum individuals were shorter, had thinner stipes and less frequent vesicle presence. There were also nonsignificant trends of C. maschalocarpum individuals having thinner lamina, and lower branch presence in higher wave exposures. The distributions of C. angustifolium, C. maschalocarpum and their hybrids were found to be correlated with exposure. Carpophyllum angustifolium was distributed only in the relatively exposed zones, while C. maschalocarpum was distributed mainly in the more sheltered zones. Hybrids were distributed in intermediate exposure zones where both parental species were present. The hybrid distributions could be a reflection of environmental selection or of the parental contact zone. Morphological evidence was found for hybridisation at Leigh, although there were differences between the morphologies of East Cape and Leigh clusters of C. angustifolium and hybrids. These differences could be due to environmental differences, genetic differentiation or different levels of introgression between the two locations. The general findings in this study support the existing literature on hybridisation, which mainly comes from terrestrial plant and animal species complexes.