Interspecific Spawning between a Recent Immigrant and an Endemic Damselfish (Pisces: Pomacentridae) in the Hawaiian Islands

The Indo-Pacific damselfish Abudefduf vaigiensis (Quoy & Gaimard, 1825) was first observed in the Hawaiian Islands in the early 1990s and is now clearly established as a breeding population in the Islands. Sightings of fish with color patterns intermediate between those of A. vaigiensis and the very similar endemic Hawaiian sergeant, Abudefduf abdominalis (Quoy & Gaimard, 1825), suggest that hybridization of the two has occurred naturally. This study provides direct evidence of crossbreeding from observations and video footage of two separate spawnings in nearshore waters of O‘ahu and a third spawning in a public aquarium display tank. Reproductive behaviors were similar in intraand interspecific spawning. However, one important difference was the absence of courtship by the male A. abdominalis toward the female A. vaigiensis in the interspecific spawnings. Instead, the female A. vaigiensis initiated spawning and the male A. abdominalis remained to fertilize, guard, fan, and clean the hybrid clutch along with a previous clutch until the embryos hatched. Embryos collected from one hybrid clutch showed normal embryonic development and subsequently hatched to produce viable swimming larvae. These observations represent a rare example of interspecific spawning in the damselfish family (Pomacentridae) and an exceptional opportunity to study hybridization and introgression in a wild population of coral reef fishes. Natural interspecific hybridization is an important evolutionary process that is relatively well studied in plants, but more recently recognized to play an important role in animal evolution as well (Dowling and Secor 1997, Arnold et al. 1999). Natural hybridization can affect changes in genetic diversity and population dynamics and can lead to adaptive evolution and evolutionary diversification (Arnold et al. 1999). Studies on hybridization in the marine environment are important to address questions on the evolutionary mechanisms that lead to speciation in the sea (Rocha et al. 2005). Interspecific hybridization in fishes is commonly reported in freshwater species but relatively infrequent in marine species (Hubbs 1955). Although evidence of hybridization primarily based on body coloration patterns exists for several families of coral reef fishes (e.g., Pomacanthidae, Chaetodontidae) (Randall et al. 1977, 2001, Pyle and Randall 1994, Randall 1996), documented observations of natural interspecific spawning behaviors are rare (e.g., Moyer 1981). The Indo-Pacific pomacentrid fish Abudefduf vaigiensis (Quoy & Gaimard, 1825) was first observed in the Hawaiian Islands in the early 1990s (Severns and Fiene-Severns 1993, Mundy 2005) and now exists in both monospecific schools and mixed schools with the Pacific Science (2007), vol. 61, no. 2:211–221 : 2007 by University of Hawai‘i Press All rights reserved 1 Support for this study was provided by Hawai‘i Institute of Marine Biology and the Honolulu Chapter of Achievement Rewards for College Scientists (K.P.M.) and Hawai‘i Coral Reef Initiative (K.A.P.). This is contribution no. 1254 from Hawaii Institute of Marine Biology. Manuscript accepted 28 June 2006. 2 Corresponding author. 3 Hawai‘i Institute of Marine Biology, 46-007 Lilipuna Road, Kāne‘ohe, Hawai‘i 96744 (phone: 808-2367466; fax: 808-236-7443; e-mail: [email protected]). 4 Department of Zoology, University of Hawai‘i at Mānoa, 2538 The Mall, Honolulu, Hawai‘i 96822. 5 Department of Botany and Department of Ecology, Evolution and Conservation Biology, University of Hawai‘i at Mānoa, 3190 Maile Way, Honolulu, Hawai‘i