Phenotypic stability of the P-M system in wild populations of Drosophila melanogaster

Abstract

The P element appears to be one of the most recently invaded transposons of D. melanogaster . To study the dynamics and long-term fate of P elements in natural populations of D. melanogaster , 472 isofemale lines newly collected from 27 localities of Japan were examined for the P element-associated characteristics (abilities to induce and repress of P element transposition) and genomic P element composition (size classes and their numbers). There was variation in the P elementrelated phenotypes among local populations, but genomic P composition did not correlate strongly with the phenotype of each line: full-size P and KP elements predominated in their genomes ( FP + KP predominance). Comparison with previous results suggests a stability in the P-M system in local populations over about 15 years. In some populations, phenotypic stability for particularly long times was found: for 30 years or more Q strains predominated in Hikone and Tanushimaru, P or Q strains around Inakadate, and M ' or Q strains around Tozukawa. There was no clear evidence of structural destruction underlying functional variation of P elements during this period. These results suggest that the current evolutionary status of P elements in the gene pool of D. melanogaster is not intermediary stage predicted by the original recent invasion hypothesis, and that several other factors such as the position effect play important roles.

Reexamining the P-Element Invasion of Drosophila melanogaster Through the Lens of piRNA Silencing

“…Similar frequencies of P and Q strains were observed among North American collections from 2001 and 2003 , indicating temporal stability of strain types. By contrast, populations outside of the Americas were mostly composed of M/M9 and Q strains in the early 1970s, and more recent collections also indicate that many regions have stably maintained this strain composition (Itoh et al 2001(Itoh et al , 2004Onder and Kasap 2014). These geographic differences are consistent with theoretical predictions based on an invasion that started in the Americas.…”

“…Because these elements were abundant in P-strain genomes, but rare or absent from M-strain genomes, they were referred to as P elements Rubin et al 1982). Atypical M strains, referred to as M9, were observed to harbor P elements; however, almost all of those elements had internal deletions and were therefore immobile in the absence of autonomous copies Anxolabéhère et al 1985Anxolabéhère et al , 1988Ronsseray et al 1989a;Itoh et al 2001Itoh et al , 2004Ogura et al 2007;Fukui et al 2008). The demonstration of increased P-element transcription and transposition in dysgenic germlines further solidified P elements as the molecular cause of hybrid dysgenesis (Eggleston et al 1988;Lemaitre et al 1993;Khurana et al 2011).…”

“…Q strains, which repress P activity but do not induce hybrid dysgenesis, are also common worldwide, particularly in Europe (Onder and Kasap 2014), Asia (Itoh et al 2001(Itoh et al , 2004, and Oceania (Ogura et al 2007), where P strains are comparatively rare. Because Q strains by definition do not exhibit a maternal effect in reference crosses ( Figure 3B), their regulation of P activity cannot be attributed to piRNA-mediated silencing based on their strain classification.…”

“…The KP element, a type II repressor that was originally identified in a wild-derived strain from Krasnodar, Russia, is widespread in extant genomes (Black et al 1987;Jackson et al 1988;Itoh and Boussy 2002;Itoh et al 2004Itoh et al , 2007Ogura et al 2007;Onder and Kasap 2014) and provides an appealing explanation for the prevalence of zygotic repression. However, evidence that KP elements are important repressors of P activity in wild-derived genomes remains mixed, despite observations that transgenically expressed KP elements confer modest zygotic repression (Simmons et al 2002;Jensen et al 2008).…”

Patterns of hobo elements and their effects in natural populations of Drosophila melanogaster in Japan

“…Th elements are present in most strains from different continents (Periquet et al, 1990). The wide distribution and predominance of the Th elements suggest that they might be analogous to the KP elements hobo elements in Japanese populations of D. melanogaster K Kikuno et al of the P-M system (Black et al, 1987;Jackson et al, 1988;Itoh et al, 2001Itoh et al, , 2004, perhaps even to having a regulatory role. Another defect hobo element, the Kh element of 1.7 kb, a specific defective element described from Korean strains Kim, 1996, 1999), was found in most Japanese populations.…”