Conspecific Sperm Precedence Is an Effective Barrier to Hybridization Between Closely Related Species

Abstract

Abstract.-Conspecific sperm precedence is widespread in animals, appears to evolve rapidly, and is thought to have the potential to prevent hybridization between closely related species. However, to date no study has tested the isolating potential of such a barrier in mixed populations of two taxa under conditions in which other potential barriers to gene flow are controlled for or are prevented from operating. We tested the isolating potential of conspecific sperm precedence in the ground crickets Allonemobius fasciatus and A. socius in population cage experiments in which the frequency of the two species was varied. Despite the observation of abundant interspecific matings, the proportions of hybrid progeny were low and differed statistically from the proportions expected in the absence of conspecific sperm precedence. The results demonstrate that conspecific sperm precedence can severely limit gene flow between closely related species, even when one species is less abundant than the other. Key words.s-Allonemobius, barrier to fertilization, conspecific sperm precedence, cricket, hybridization, reproductive isolation, speciation.Received July 15, 1997. Accepted January 28, 1998 Postmating but prezygotic barriers to fertilization have begun to attract wide attention among evolutionists, as a large number of recent studies suggest that such barriers arise quickly and may represent the primary isolating barrier between many species of animals

Absence of pollinator-mediated premating barriers in mixed-ploidy populations of Gymnadenia conopsea s.l. (Orchidaceae)

“…Pre-zygotic breeding barriers prevent individuals from wasting their gametes in the formation of unviable seeds or unfit hybrid individuals, bearing the potential to undergo natural selection and reinforcing any pre-existing postzygotic mating barriers (Dobzhansky 1940;Howard 1993). In our study we investigated various pre-zygotic barriers, except spatial separation of cytotypes or the cryptic reproductive barriers acting after pollination but before fertilization as a result of pollen competition and interactions between male gametophytes and female reproductive tissues (gametic isolation, Howard et al 1998). Furthermore, this mechanism of sexual isolation may be asymmetrical, such that the gametic interactions depend on the direction of mating between the parental taxa (Rieseberg et al 1995;Arnold et al 1996).…”

An introgression approach to mapping differences in mating success and sperm competitive ability in Drosophila simulans and D. sechellia

“…In cages containing equal proportions of the two sister species of ground crickets Allonemobius fasciatus and A. socius, an average 40 % heterospecific matings were recorded. However, hybrids were rare, ranging from none to 6 % (Howard et al, 1998). Laboratory cage experiments with D. melanogaster females and mixtures of D. melanogaster and D. simulans males resulted in an average 24 % of females producing hybrid progeny.…”

Cryptic gametic interactions confer both conspecific and heterospecific advantages in the Chrysochus (Coleoptera: Chrysomelidae) hybrid zone

“…Such cryptic reproductive barriers are important, not only because they can substantially limit genetic exchange between species (e.g., Howard et al 1998;Ramsey et al 2003;Matsubayashi and Katakura 2009), but also because their existence can influence the evolution of other reproductive barriers. For example, Servedio and Noor (2003) discussed how, in response to low hybrid fitness, selection might favor the evolution of conspecific sperm precedence (CSP), the establishment of which would reduce the cost of mating 'mistakes' for females.…”

“…Until recently, the great majority of research in reproductive barriers has examined the nature and evolution of either premating barriers or late-acting postzygotic barriers such as hybrid sterility and inviability (Markow 1997;Howard 1999;Coyne and Orr 2004). However, cryptic barriers that are realized within the reproductive systems of hybridizing females have received increasing attention (e.g., Rieseberg et al 1995;Howard et al 1998;Price et al 2000;Chang 2004;Fricke and Arnqvist 2004a;Rahmé et al 2009). As a result, it is now clear that cryptic post-mating barriers can take a variety of forms (Eberhard 2009), including the failure of heterospecific sperm (or pollen) to survive or remain motile (Price et al 2000), the incompatibility of heterospecific sperm and eggs (Palumbi and Metz 1991), the tendency for conspecific sperm to outcompete heterospecific sperm in fertilizing the eggs of multiply-mated females (Howard 1999), the reduced fecundity of females that mate with heterospecific males (Nosil and Crespi 2006), and the early abortion of F1 embryos (Matsubayashi and Katakura 2009).…”