Speciation in Progress? A Continuum of Reproductive Isolation in Drosophila Bipectinata

Abstract

Incipient species in the early stages of divergence can provide crucial information about the genetic basis of reproductive isolation and the evolutionary forces that promote speciation. In this report, we describe two subspecies of Drosophila bipectinata that show a continuum of reproductive isolation. Crosses between strains of the same subspecies produce fully fertile offspring. At the same time, each subspecies harbors extensive variation for the degree of reproductive isolation from the other subspecies. The percentage of fertile hybrid males varies from 0 to 90%, depending on the origin of parental strains, indicating that the genes responsible for hybrid sterility are not fixed within either subspecies, or even within local populations. Reproductive isolation is non-transitive, so that the extent of hybrid sterility depends on the particular combination of strains. The two subspecies show little or no evidence of genetic differentiation at three nuclear loci, suggesting that they diverged very recently or continue to experience significant levels of gene flow. A hybrid zone between the two subspecies may exist in New Guinea and Northeastern Australia.

Incompatibility Between X Chromosome Factor and Pericentric Heterochromatic Region Causes Lethality in Hybrids Between Drosophila melanogaster and Its Sibling Species

“…Considerable variation in lethality among stocks exists for D. melanogaster/D. simulans hybrids (Watanabe et al 1977;Lee 1978;Orr 1996;Barbash et al 2000;Presgraves 2003), and variation in the strength of postzygotic isolation exists between other pairs of Drosophila species (e.g., Macknight 1939;Crow 1942;Mainland 1942;Patterson and Stone 1952;Ayala et al 1974;Kimura 1987;Kopp and Frank 2005;Orr and Irving 2005;Reed et al 2008), nonDrosophila animal species (Forejt and Ivány 1975;Wade and Johnson 1994;Thomson et al 1995;Shuker et al 2005;Vyskocilová et al 2005;Good et al 2008;Kozlowska et al 2012), and plant species (Stebbins 1958;Christie and Macnair 1987;Sweigart et al 2007). Together, these studies suggest that polymorphism in Dobzhansky-Muller incompatibilities is common.…”

Reproductive Isolation Among Geographical Populations of Drosophila Bipectinata Duda (Diptera, Drosophilidae) with Recognition of Three Subspecies

“…Powell, 1997). As mentioned by Kopp and Frank (2005) the observed sterility of hybrid males between D. bipectinata subspecies appears to be ''genetic''.…”

Wherefore and Whither the Ring Species?

“…The units A, B, and C thus form a single closed genetic system. Nontransitive reproductive interactions do not require a ring-like distribution (Kopp and Frank, 2005;Peterson et al, 2013), but the biogeographic scenario implicit in ring species illustrates how such a situation may evolve.…”