Reproductive and genetic evidence for a reticulate evolutionary history of mass-spawning corals

Abstract

Reef-building corals, which reproduce through simultaneous multispecies spawning, are thought to hybridize frequently, and it is hypothesized that they have evolved in repeated rounds of species separation and fusion. We conducted cross-fertilization experiments and molecular analyses with a number of mass-spawning coral species in the genus Acropora. A high rate of interspecific fertilization occurred between some species despite very different morphologies. The hybrid larvae developed normally and contained an allelic sequence transmitted from each parent, suggesting common diploid hybridization. Molecular phylogenetic analyses provided strong evidence for a gene pool shared between the hybridizing species. These reproductive and genetic characteristics are consistent with a species complex formed under the separation/fusion processes predicted for a reticulate evolutionary history.

The New Systematics of Scleractinia: Integrating Molecular and Morphological Evidence

“…These markers, along with the primers used to amplify them, are often clade specific. Among the nuclear loci that are still in use today, some of the earliest to be developed include the intron region of the mini-collagen gene (Wang et al 1995), used almost exclusively to investigate the evolutionary history of Acropora (Hatta et al 1999;Vollmer and Palumbi 2002;Fukami et al 2003;Palumbi et al 2012;Suzuki and Fukami 2012). The Pax-C 46/47 intron, introduced by van Oppen et al (2000van Oppen et al ( , 2001, continues to be used for Acropora phylogenetics (Richards et al 2008(Richards et al , 2013 and taxonomically broader reconstructions (Fig.…”

“…However, data from such studies are limited in terms of taxonomic and geographic coverage. Crosses have been tested for a variety of Acropora species and interspecific fertilisation observed in several combinations (Willis et al 1997;Hatta et al 1999;Fukami et al 2003;Isomura et al 2013). Nevertheless, interspecific fertilisation rates tend to be lower than intraspecific ones (Wei et al 2012), allowing species boundaries to be defined (Willis et al 2006).…”

The future of coral reefs

“…Similarly, subtle temporal differences in spawning times between species whose gametes are otherwise compatible (28) would be less effective if, for example, unfertilized eggs from an early spawning species remained near populations of later spawning species. Laboratory experiments do clearly suggest that many species are capable of hybridization, including species with very different morphologies (30,31). However, the potential evolutionary impact of hybridization between morphologically and ecologically distinct taxa is difficult to evaluate empirically, because of long generation times and the difficulty of maintaining corals in captivity for determining long-term survival and fertility of hybrids.…”

Mechanisms of Reproductive Isolation Among Sympatric Broadcast-Spawning Corals of the Montastraea Annularis Species Complex

“…In the Indowest Pacific, for example, more than 100 species spawn simultaneously during annual mass-spawning events (Harrison et al 1984;Babcock et al 1986). Most work on species boundaries has focused on the species-rich genus Acropora, where hybrids may be commonly produced in laboratory crosses, and clear genetic differences between described species have been difficult to establish (Willis et al1997;Hatta et al 1999;van Oppen et al 2001van Oppen et al , 2002Marquez et al 2002aMarquez et al , 2002b. High intraspecific genetic heterogeneity (Odorico and Miller 1997) and chromosomal numbers (Kenyon 1997) are also suggestive of hybridization and reticulate evolution.…”