Differences in spawning time drive cryptic speciation in the coral Acropora divaricata
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ORIGINAL PAPER
Differences in spawning time drive cryptic speciation in the coral Acropora divaricata Mao Furukawa1 · Shun Ohki1 · Seiya Kitanobo1 · Hironobu Fukami2 · Masaya Morita1 Received: 26 April 2020 / Accepted: 29 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Most of the reef-building Acropora corals around Okinawa Island spawn in May and/or June. We found that two morphotypes of Acropora divaricata spawned in August and/or September. The “robust” and “slender” morphotypes differed in branch width and in the diameter of axial corallites. Histological analyses showed that the onset of gamete production/maturation occurred from June onwards. Most of the other Acropora species spawned from late May to early June. A. florida, which spawned in May/June, initiated gamete production in early April. We assumed that the two morphotypes of A. divaricata were reproductively isolated from most of the other Acropora species because of differences in the spawning seasons. We found that the spawning seasons of the two morphotypes slightly overlapped in 2015 but not in 2019, and inter-morphotype gamete compatibility was high. However, population genetics analyses and a phylogeny of the mitochondrial d-loop region showed that they were genetically distinct and rarely hybridized. Thus, the broadcast-spawning coral A. divaricata might have speciated when there might have been only a low possibility of interspecific gamete interaction.
Introduction Morphology is tremendously important for taxonomic description and species identification in the field. However, cryptic speciation is suggested in many taxa and morphological differences in cryptic species are often subtle (e.g., Bickford et al. 2007; Suzuki et al. 2016). Cryptic species complexes are reported for many taxa (e.g., Grundt et al. 2006; Caputi et al. 2007; Pfenninger and Schwenk 2007), and may be distributed sympatrically (Boissin et al. 2008; Ladner and Palumbi 2012; Suzuki et al. 2016) and allopatrically (Caputi et al. 2007; Ross et al. 2010). Species descriptions for the marine invertebrates are crucial for understanding diversity
Responsible Editor: C. Voolstra. Reviewed by undisclosed experts. * Masaya Morita [email protected]‑ryukyu.ac.jp 1
Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Sesoko, Motobu, Okinawa 905‑0227, Japan
Faculty of Agriculture, Department of Marine Biology and Environmental Science, University of Miyazaki, Miyazaki, Japan
2
and increasing the conservation of these animals, especially in the reef-building corals. The coral Acropora is a broadcast-spawning marine invertebrate. Speciation in the genus Acropora may be driven in part by hybridization between species (Veron 1995; Mao 2019). Gamete interaction and recognition may be determinants of reproductive isolation in this broadcast spawner (e.g., Willis et al. 2006). Genomic information of several Acropora species has shown that hybridization has occurred during speciation (Mao et al. 2018), but relevant data o
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