Aphid Sex Research Articles

Latitudinal trend in the reproductive mode of the pea aphid Acyrthosiphon pisum invading a wide climatic range.

The maintenance of sexuality is a puzzling phenomenon in evolutionary biology. Many universal hypotheses have been proposed to explain the prevalence of sex despite its costs, but it has been hypothesized that sex could be also retained by lineage‐specific mechanisms that would confer some short‐term advantage. Aphids are good models to study the maintenance of sex because they exhibit coexistence of both sexual and asexual populations within the same species and because they invade a large variety of ecosystems. Sex in aphids is thought to be maintained because only sexually produced eggs can persist in cold climates, but whether sex is obligate or facultative depending on climatic conditions remains to be elucidated. In this study, we have inferred the reproductive mode of introduced populations of the pea aphid Acyrthosiphon pisum in Chile along a climatic gradient using phenotypic assays and genetic‐based criteria to test the ecological short‐term advantage of sex in cold environments. Our results showed a latitudinal trend in the reproductive mode of Chilean pea aphid population from obligate parthenogenesis in the north to an intermediate life cycle producing both parthenogenetic and sexual progeny in the southernmost locality, where harsh winters are usual. These findings are congruent with the hypothesis of the ecological short‐term advantage of sex in aphids.

Molecular markers linked to breeding system differences in segregating and natural populations of the cereal aphid Rhopalosiphum padi L.

The aphid Rhopalosiphum padi shows coexistence of sexual and asexual populations, providing an opportunity to study the evolution of breeding system variation in the context of theories on the origin and maintenance of sex. However, assessments of the distribution of sexual and asexual lineages of this aphid are complicated by the difficulties in rapidly characterizing their breeding system. To facilitate this task and to gain insight into the genetic relatedness between sexual and asexual genotypes, molecular markers linked to breeding system differences were recently developed. In this study, we have successfully converted a random amplified polymorphic DNA (RAPD) marker associated with life-cycle variation in R. padi into a codominant sequences-characterized amplified region (SCAR). Segregating and natural populations of known breeding systems were examined to evaluate the life cycle-SCAR marker association. Complete linkage was found in segregating populations while the association averaged 94% in field populations. Detailed analysis of allelic distribution and sequence divergence of the SCAR locus among sexual and asexual populations provides further evidence for a unique and apparently ancient loss of sexuality in this aphid. It also suggests that occasional gene flow occurs between populations differing in their breeding system, mediated by males produced by 'asexual' lineages. This system provides the possibility for the recurrent emergence of new asexual lineages, ensuring the longer persistence of asexuality, and would have important implications for the assessment of costs and benefits of sex in aphids.

Different Tolerance to High Temperatures Between Male and Female Embryos of the AphidMegoura viciae

Summary The total fecundity and pattern of reproduction were studied in the aphid Megoura viciae, under different postnatal temperature and photoperiod conditions, after prenatal exposure to long (16L:8D) or short (8L:16B) photoperiods. In the 13–27°C temperature range, total fecundity is markedly reduced by higher temperatures; postnatal photoperiod is without effect. In the temperature range 13–24°C, no difference was detected between aphids exposed prenatally to long and short photoperiods, respectively, whereas at 27°C fecundity of females exposed prenatally to short photoperiods is significantly lower. This reduced fecundity is due to the selective death of male embryos at a late developmental stage. The results provide a further case of low viability of the male sex in aphids.

Cost of Sex in Aphids: Size of Males at Birth and the Primary Sex Ratio in Sitobion avenae (F.)

Although Sitobion avenae (F.) was less fecund under sexual-inducing photoperiods it did not produce a significantly lower biomass of offspring than apterae reared under long daylength. The lower fecundity is due to the cost of developing the larger male embryos; at birth males were significantly heavier and denser than females. The primary sex ratio in S. avenae is approximately two females to one male but is equal in terms of biomass. Key-words: Sitobion avenae, sex ratio, aphids, reproductive cost

Temperature prediction and the timing of sex in aphids.

The aphid life cycle contains a series of parthenogenetic, viviparous generations, followed usually by a sexual generation that produces resistant overwintering eggs. Since the decision to produce sexually-reproducing offspring ends the period of rapid growth of the clone, it should be postponed as late as is compatible with successful oviposition. The time of leaf fall determines the latest possible time of oviposition, and is itself determined mainly by daylength. The time required for the development of the final generations of aphid depends on temperature. The decision to end the sequence of parthenogenetic generations should thus depend on temperature and photoperiod. This paper calculates the optimal combination of daylength and temperature for the cueing of this decision in Rhopalosiphum padi. It is shown that the experimental data of Dixon and Glen (1971) are in agreement with the predictions, and that, in the field, the time of production of male R. padi does vary adaptively with July temperature.