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Comparison between sexual and asexual reproduction

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Conceived and designed the experiments: All Comparison between sexual and asexual reproduction relevant data are within the paper. But the evolution of sexual reproduction remains unclear, because we have limited examples that demonstrate the relative success of sexual lineages in the face of competition from asexual lineages in the same environment.

Here we investigated a sympatric occurrence of sexual and asexual reproduction in the pineapple mealybug, Dysmicoccus brevipes.

This pest invaded southwestern Japan, including Okinawa and Ishigaki Islands, in the s in association with imported pineapple plants. Our recent censuses demonstrated that on Okinawa sexually reproducing individuals can coexist with and even dominate asexual individuals in the presence of habitat and resource competition, which is considered to be severe for this nearly immobile insect. Molecular phylogeny based on partial DNA sequences in the mitochondrial and nuclear genomes, as well as the endosymbiotic bacterial genome, revealed that the asexual lineage diverged from a common sexual ancestor in the relatively recent past.

In contrast, only the asexual lineage exhibiting obligate apomictic thelytoky was discovered on Ishigaki. Co-existence of the two lineages cannot be explained by the results of laboratory experiments, which Comparison between sexual and asexual reproduction that the intrinsic rate of increase in the sexual lineage was not obviously superior to that of the asexual lineage.

This biological system offers a unique opportunity to assess the relative success of sexual versus asexual lineages with an unusual morphology and life cycle.

Asexual reproduction, in which offspring arise from a single female organism, occurs in a variety of eukaryotes including plants, fungi, and animals. It is assumed to confer some advantages over a sexual reproduction, in which individuals of two genders, females and males, must be involved but only females can give birth to new individuals [ 1 — 10 ].

Although a variety of theories have been proposed to explain the genetic and ecological fitness associated with sexual reproduction, the evolution of sexuality and reproductive systems remains as one of the major unresolved puzzles in biology [ 4 ].

In particular, there are few examples that demonstrate the success and persistence of sexual lineages in the face of competition from asexual lineages in natural environments [ 1112 ]. Coccoideawhich include mealybugs Pseudococcidaeare interesting for studies of the evolution and ecology of sexuality and asexuality, because this taxon exhibits various systems that control sex determination, sexual development, sex ratio, and mode of reproduction [ 1314 ].

Such an extraordinary diversity of genetic systems is considered to be, at least partly, associated Comparison between sexual and asexual reproduction their unusual morphology Fig 1 and life cycle [ 1315 ]. Scale insects are plant sap feeders closely related to aphids and whiteflies and are characterized by their unusual shapes.

Adult females show development with retention of juvenile physical characters neoteny and are relatively immobile, lacking wings and often even legs.

They produce body-covering secretions that act like protective shells, and they can be long-lived sometimes up to several months [ 15 ]. In contrast, adult males are winged and mobile, but they are tiny and fragile and have a limited life span of a few days at most [ 1516 ].

Such extreme sexual dimorphism exposes the immobile females to high levels of competition over mate resources represented by the fragile and short-lived males [ 17 ], which may lead to the evolution of reproductive systems that depend less on males [ 14 ].

In fact, males are either very rare or unknown in many scale insects, particularly in mealybugs: Comparison between sexual and asexual reproduction pineapple mealybug, Dysmicoccus brevipes Cockerellis one such parthenogenetic species. It is a known vector of pineapple wilt—associated viruses, which severely reduce pineapple yields [ 19 ], and this species also attacks many Comparison between sexual and asexual reproduction agricultural crops [ 2021 ].

Dysmicoccus brevipes was first described in Jamaica and is apparently native to the New World [ 22 ], but it now has a cosmopolitan distribution associated with pineapple transportation and cultivation.

Many previous studies [ 23 — 27 ] conducted in a variety of areas indicated that this species reproduces by obligate apomictic thelytokous parthenogenesis [ 18 ], although the presence of adult males has been reported [ 22 ]. At least on the Hawaiian Islands, only parthenogenetic females are found; males have yet to be discovered and are probably not present [ 22 ].

These findings suggest that both sexual and asexual reproductive systems are included in the same or a very closely related lineage, and thus D. However, little is known about the distributions of sexual and asexual D. Therefore, in the present study we first surveyed the occurrences and frequencies of sexual and asexual individuals in D.

These findings suggest that both...

Comparison between sexual and asexual reproduction The sexual and asexual lineages co-exist on one of the islands, whereas only the asexual lineage is present in the other. We then measured their fecundity and growth rates under laboratory conditions to examine the basic elements of competition between the lineages.

Finally, we attempted to elucidate their molecular phylogeny by using partial sequences of genomes of mitochondria, nuclei, and the primary endosymbiotic bacterium, Candidatus Tremblaya princeps, which is ubiquitously present in the cytoplasm of mealybug bacteriocytes and is maternally inherited [ 2829 ].

Gravid ovoviviparous females of D. Each mealybug was collected from a different colony in order to avoid sampling bias.

They were placed individually in a tight-sealed laboratory dish 5. The offspring were transferred to a larger tight-sealed laboratory dish 9. For sexual mealybugs, the adults that emerged were allowed to copulate for 1 day. Pregnant females were transferred to a new dish with fresh food.

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Development times, pre-parturition durations, parturition durations, and numbers of offspring were assessed using laboratory-reared mealybugs under the conditions described above. For the assessment of development times, freshly born nymphs were transferred individually to a germinated broad bean plant placed in a tight-sealed dish and were monitored daily.

"Comparison between sexual and asexual reproduction" made cocoons and became pupae after three molts, whereas females matured to adulthood after three molts without pupal metamorphosis. To assess reproductive performance parameters, a fresh adult female just after the final molt was placed individually in a tight-sealed dish and fed with a germinated broad bean plant.

Each female of the sexual lineages was housed with one adult male that was randomly chosen from stock culture, and copulation was confirmed visually.

Offspring borne by each female were counted every day until the female stopped parturition. The mitochondrial cytochrome oxidase subunit I CO1 gene ca. The following internal sequencing primers were used in the sequencing reaction: Planococcus citriPlanococcus minorPlanococcus kraunhiaePseudococcus comstockiPseudococcus cryptusCrisicoccus matsumotoiand Dysmicoccus neobrevipes. The gene sequences were aligned using ClustalX software [ 31 ]. The final alignment was inspected and corrected manually, and only unambiguous nucleotide sites were used for analyses.

Maximum likelihood trees with bootstrap values based on resamplings were constructed using TreeFinder [ 32 ].

Two completely different reproductive systems were observed in the pineapple mealybugs collected on Okinawa: Females from the female-only broods produced only female offspring without copulation, indicating thelytokous parthenogenesis.

Females from the broods with both sexes were able to produce both male and female offspring only after copulation and never produced offspring without copulation, indicating sexual reproduction. As far as we observed, both of the reproductive systems were maternally hereditable and completely obligatory. The sex ratios of offspring in some matrilines are shown in S1 Fig.

On the other hand, only an asexual lineage was found in a pineapple field on Ishigaki; the matrilines collected during three censuses were examined but no sexual reproduction was observed.