Postcopulatory, prezygotic isolation: intraspecific and interspecific sperm precedence in Tribolium spp., flour beetles

Abstract

We investigated intraspecific and interspecific patterns of paternity in Tribolium castaneum, the flour beetle, by mating females either to pairs of conspecific males or to one conspecific and one heterospecific male of the closely related species, T freemani. Females of both species store sperm in the spermatheca after copulation and postcopulatory, prezygotic reproductive isolation has been reported between this pair of species. When conspecific males of contrasting genotype were mated simultaneously to T. castaneum females, we observed extremely high levels of variation among females in the pattern of sperm precedence as shown by the offspring genotypes. In contrast, T. castaneum females mated simultaneously to a conspecific and a heterospecific male produced over 99 per cent conspecific progeny. When conspecific males were mated sequentially to T castaneum females, within 3-7 days, all offspring were sired by the second male. In contrast, when a conspecific male was replaced with a T freemani male, most females continued to produce only first-male, conspecific offspring for the next 10 days. When a heterospecific male was replaced with a conspecific male, T castaneum females changed from producing hybrid to conspecific offspring within 3 days. We discuss the evolutionary implications of these findings.

Sperm competition and the maintenance of polymorphism

“…Gregory and Howard (1994) and Howard et al (1998) found that the major barrier to hybridization between two related ground crickets was postmating conspecific sperm precedence. Robinson et al (1994), in double-mating studies with Tribolium castaneum and T. freemani, found strong conspecific sperm precedence, which they characterized as postcopulatory prezygotic isolation. Price (1997) performed tests of sperm competition among D. simulans, mauritiana and sechellia by mating females with conspecific males followed by heterospecific males and vice versa.…”

Rapid Speciation via Parallel, Directional Selection on Regulatory Genetic Pathways

“…One form of reproductive isolation, prezygotic isolation, occurs when fewer than expected hybrid zygotes are produced, and may be due to such factors as di!erences in mating song and other aspects of courtship behavior (Noor & Aquadro, 1998;Wells and Henry, 1998) or conspeci"c sperm precedence (e.g. Bella et al, 1992;Robinson et al, 1994;Howard et al, 1998). Reproductive isolation can also occur postzygotically, after the production of hybrid zygotes, via reduced hybrid viability Carvajal et al, 1996;Orr et al, 1997;Gadau et al, 1999) or fertility (Coyne, 1984;Orr et al, 1987;.…”

Incipient speciation in the flour beetle, Tribolium confusum: premating isolation between natural populations

“…These findings are different from those previously reported in crosses between two other species in this genus, T castaneum and T freemani. In this pairing, the isolation is postmating but prezygotic (Wade et al, 1993;Robinson et al, 1994) and hybrids of both sexes are sterile . Furthermore, the interspecific hybrids exhibit Haldane's rule in that hybrid males are infrequent and also tend to be morphologically deformed .…”

“…The sterile interspecific hybrids between T castaneum and T freemani have been studied in a series of papers (Wade et a!., 1993Robinson et a!., 1994;. These two species exhibit reciprocal postmating, prezygotic reproductive isolation (Robinson et al, 1994;. T confusum has not been reported to hybridize with other species in the genus nor has reproductive iso-lation among different populations of this species been reported.…”

“…This species has been placed in a separate dade from the T castaneum species group, which includes T freemani, based upon morphological, genetic, karyotypic and molecular data (Hinton, 1948;Sokoloff, 1974;Brownlee & Sokoloff, 1988;Juan et al, 1993;. The sterile interspecific hybrids between T castaneum and T freemani have been studied in a series of papers (Wade et a!., 1993Robinson et a!., 1994;. These two species exhibit reciprocal postmating, prezygotic reproductive isolation (Robinson et al, 1994;.…”