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Marine Ecology Progress Series

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MEPS 642:103-116 (2020)  -  DOI: https://doi.org/10.3354/meps13332

Phenological shifts and genetic differentiation between sympatric populations of Sargassum horneri (Fucales, Phaeophyceae) in Japan

Yuri Homma1, Shujiro Okuda2, Masahiro Kasahara3, Fumio Takahashi3, Shinya Yoshikawa4, Shinya Uwai5,6,*

1Graduate School of Science and Technology, Niigata University, Ikarashi 2, Nishiku, Niigata, Niigata 950-2181, Japan
2Niigata University Graduate School of Medical and Dental Science, 1-757 Asahimachi, Chuoku, Niigata, Niigata 951-8501, Japan
3Graduate School of Life Sciences, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan
4Faculty of Marine Science and Technology, Fukui Prefectural University, 1-1 Gakuencho, Obama, Fukui 917-0003, Japan
5Faculty of Science, Niigata University, Ikarashi 2, Nishiku, Niigata, Niigata 950-2181, Japan
6Present address: Kobe University Research Center for Inland Seas, 1-1 Rokkodai, Nadaku, Kobe, Hyogo 657-8501, Japan
*Corresponding author:

ABSTRACT: Marked seasonality, especially in sexual reproduction, is common among seaweed species along temperate coasts and increases the possibility of successful fertilization in outcrossing species. A phenological shift in reproductive seasons, therefore, could be an effective isolation barrier between conspecific seasonal populations, although its power has not been verified in algae. Sargassum horneri, a major component of seaweed beds along the temperate coast of Japan, is known for variability in its reproductive phenology. To understand the significance of phenological shift as an isolation barrier in seaweed species, phenological investigations of S. horneri seasonal populations on the Sea of Japan coast of central Honshu, Japan, were combined with Bayesian cluster analysis based on a nuclear simple sequence repeat genotype. Results from these analyses concordantly suggest a genetic differentiation between the seasonal populations, although almost 20% of field-collected plants were estimated to be hybrids or have a hybrid origin based on results of Bayesian cluster analyses using experimental hybrids. A collapse of seasonal isolation was also detected at the site of the field investigation, and a high percentage of putative hybrids in the following generation at the site (41%) suggested significant seasonal isolation in the differentiation observed in this study.


KEY WORDS: Seasonality · Isolation barrier · Brown algae · Reproductive phenology · Seasonal isolation · Simple sequence repeat · Sea of Japan coast


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Cite this article as: Homma Y, Okuda S, Kasahara M, Takahashi F, Yoshikawa S, Uwai S (2020) Phenological shifts and genetic differentiation between sympatric populations of Sargassum horneri (Fucales, Phaeophyceae) in Japan. Mar Ecol Prog Ser 642:103-116. https://doi.org/10.3354/meps13332

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