The clock gene cryptochrome of Bactrocera cucurbitae (Diptera: Tephritidae) in strains with different mating times

Abstract

Differences in mating time between populations can give rise to premating reproductive isolation. Tephritid fruit flies exhibit large variation in mating time among intra-or inter-specific populations. We previously cloned the clock gene period from two strains of melon fly, Bactrocera cucurbitae; in one the individuals mate early during the day, whereas in the other the individuals mate later. These strains were originally established by divergent artificial selection for developmental time, 'short' and 'long', with early and late mating times, respectively. The deduced amino acid sequences of PERI-OD proteins for these two strains were reported to be identical. Here we cloned another clock gene cryptochrome (cry) from the two strains, and found two stable amino acid substitutions in the strains. In addition, the allele frequency at the two polymorphic sites of cry gene correlated with the circadian locomotor period (t) across strains, whereas the expression pattern of cry mRNA in the heads of flies taken from the short strain significantly differed from that from the long strain. These findings suggest that variation in the cry gene is related to differences in the circadian behaviour in the two strains, thus implying that the cry gene may have an important role in reproductive isolation.

Comparison of two polymorphic sites in the clock gene cryptochrome in the Taiwan strain of the melon fly, Bactrocera cucurbitae (Diptera: Tephritidae): a possible quick method to estimate the mating time of trapped invading flies

“…The negative relationship between circadian period and S-type allele frequency at the cry1212 site is coincident with that observed among the populations from Okinawa (Fuchikawa et al 2010), while no relationship was observed at cry1865. We previously failed to determine which site (cry1212 or cry1865) is responsible for the mating time (Fuchikawa et al 2010).…”

“…We previously failed to determine which site (cry1212 or cry1865) is responsible for the mating time (Fuchikawa et al 2010). In the present study, Taiwan strains exhibited different patterns of combinations of alleles at the sites from the Okinawa strains.…”

“…1). S means the allele observed in the S strain, and L means the allele in the L strain (Miyatake 1995;Fuchikawa et al 2010). Circadian period is expressed as mean ± SE.…”

“…Allele characterization at sites 1212 and 1865 of the cry gene by PCR To examine whether the two stable amino acid polymorphisms found in the S (short development period and earlier mating time) and L (long development period and later mating time) strains (originally established in Miyatake 1995) of the Okinawa populations relate to overt behavioral rhythmicity (Fuchikawa et al 2010), we investigated individual genotypes at two polymorphic sites using polymerase chain reaction (PCR) of the two B. cucurbitae strains from Taiwan described above. Two single nucleotide polymorphisms (SNP) at sites 1212 (cry1212) and 1865 (cry1865) of the cry gene (EMBL/GenBank/DDBJ accession no.…”

“…We previously identified two polymorphic sites that are closely related to mating time (Fuchikawa et al 2010) in the circadian photoreceptor gene, cryptochrome (cry) Stanewsky et al 1998). (1) We collected the allele frequency data of polymorphic sites of the cry gene in several populations of B. cucurbitae derived from Taiwan because it is most likely to invade Japan (Kohama and Kuba 1996).…”