Evolution of reproductive traits have no apparent life-history associated cost in populations of Drosophila melanogaster selected for cold shock resistance

Background In insect species like Drosophila melanogaster, evolution of increased resistance or evolution of particular traits under specific environmental conditions can lead to energy trade-offs with other crucial life-history traits. Adaptation to cold stress can, in principle, involve modification of reproductive traits and physiological responses. Reproductive traits carry a substantial cost; and therefore, the evolution of reproductive traits in response to cold stress could potentially lead to trade-offs with other life-history traits. We have successfully selected replicate populations of Drosophila melanogaster for increased resistance to cold shock for over 33 generations. In these populations, the ability to recover from cold shock, mate, and lay fertile eggs 24 h post cold shock is under selection. These populations have evolved a suite of reproductive traits including increased egg viability, male mating ability, and siring ability post cold shock. These populations also show elevated mating rate both with and without cold shock. In the present study, we quantified a suite of life-history related traits in these populations to assess if evolution of cold shock resistance in these populations comes at a cost of other life-history traits. Results To assess life-history cost, we measured egg viability, mating frequency, longevity, lifetime fecundity, adult mortality, larva to adult development time, larvae to adults survival, and body weight in the cold shock selected populations and their controls under two treatments (a) post cold chock and (b) without cold shock. Twenty-four hours post cold shock, the selected population had significantly higher egg viability and mating frequency compared to control populations indicating that they have higher cold shock resistance. Selected populations had significantly longer pre-adult development time compared to their control populations. Females from the selected populations had higher body weight compared to their control populations. However, we did not find any significant difference between the selected and control populations in longevity, lifetime fecundity, adult mortality, larvae to adults survival, and male body weight under the cold chock or no cold shock treatments. Conclusions These findings suggest that cold shock selected populations have evolved higher mating frequency and egg viability. However, there is no apparent life-history associated cost with the evolution of egg viability and reproductive performances under the cold stress condition.

The Costs and Benefits of Two Secondary Symbionts in a Whitefly Host Shape Their Differential Prevalence in the Field

Insects commonly harbor maternally inherited intracellular symbionts in nature, and the microbial partners often exert influence on host reproduction and fitness to promote their prevalence. Here, we investigated composition of symbionts and their biological effects in the invasive Bemisia tabaci MED species of a whitefly complex. Our field surveys revealed that populations of the MED whitefly, in addition to the primary symbiont Portiera, mainly contain two secondary symbionts Hamiltonella, which is nearly fixed in the host populations, and Cardinium with infection frequencies ranging from 0 to 86%. We isolated and established Cardinium-positive and Cardinium-free whitefly lines with a similar nuclear genetic background from a field population, and compared performance of the two whitefly lines. The infection of Cardinium incurred significant fitness costs on the MED whitefly, including reduction of fecundity and egg viability as well as delay in development. We then selectively removed Hamiltonella from the Cardinium-free whitefly line and compared performance of two whitefly lines, one harboring both Portiera and Hamiltonella and the other harboring only Portiera. While depletion of Hamiltonella had little or only marginal effects on the fecundity, developmental rate, and offspring survival, the Hamiltonella-free whitefly line produced very few female offspring, often reducing the progeny female ratio from about 50% to less than 1%. Our findings indicate that the varying costs and benefits of the association between these two symbionts and the MED whitefly may play an important role in shaping their differential prevalence in the field.

Microbial Polymers as Sustainable Agents for Mitigating Health Risks of Plant-Based Endocrine Disruptors in Surface Water

This study investigated the binding abilities of extracellular polymers produced by an environmentally isolated strain of Enterococcus hirae towards phytoestrogen endocrine disruptors—biochanin A, formonetin, genistein and daidzein. The extracellular biopolymer exhibited notable binding and removal for all four phytoestrogens, with a maximum removal of daidzein (87%) followed by genistein (72%) at a 1–1.5 mg/mL concentration. Adsorption proceeded rapidly at ambient temperature. The adsorption data fitted well with the Langmuir isotherm. Based on the adsorption energy, the biopolymer binding of phytoestrogens was inferred as daidzein > genistein > biochanin A > formononetin. Toxicity of the biopolymer (5–250 µg/mL) evaluated using RAW 264.7 cell lines indicated no significant (p < 0.05) changes in viability. In biopolymer-challenged Caenorhabditis elegans previously exposed to daidzein, complete protection to developmental toxicity, such as reduced egg-laying capacity, egg viability and progeny counts of the worm, was observed. The results of this study offer valuable insights into understanding the potential role of microbial extracellular biopolymers in binding and removal of phytoestrogens with sustainable technological implications in modulating the toxic effect of high levels of endocrine disruptors in the environment.

Rapid stress hardening in the Antarctic midge improves male fertility by increasing courtship success and preventing decline of accessory gland proteins following cold exposure

Rapid hardening is a process that quickly improves an animal's performance following exposure to a potentially damaging stress. In this study of the Antarctic midge, Belgica antarctica (Diptera, Chironomidae), we examine how rapid hardening in response to dehydration (RDH) or cold (RCH) improves male pre- and post-copulatory function when the insects are subsequently subjected to a damaging cold exposure. Neither RDH nor RCH improved survival in response to lethal cold stress, but male activity and mating success following sublethal cold exposure was enhanced. Egg viability decreased following direct exposure of the mating males to sublethal cold but improved following RCH and RDH. Sublethal cold exposure reduced expression of four accessory gland proteins, while expression remained high in males exposed to RCH. Though rapid hardening may be cryptic in males, this study shows that it can be revealed by pre- and post-copulatory interactions with females.

Predation and oviposition rates of Gaeolaelaps aculeifer and Parasitus bituberosus (Acari: Laelapidae and Parasitidae) on pre-pupae/pupae of Thrips tabaci (Thysanoptera: Thripidae)

Thrips tabaci Lindeman is one of the main insect pests of onion (Allium cepa L.) in Colombia and several other countries. Strategies for its control are currently based on the use of chemical products. In a recent survey, Gaeolaelaps aculeifer (Canestrini) and Parasitus bituberosus Karg, two soil-dwelling predatory mite species (Acari: Mesostigmata), were found associated with this crop at Boyacá department, Colombia. Given that T. tabaci spends its pre-pupal and pupal stages in the soil, this study was conducted to evaluate the predation and oviposition of G. aculeifer and P. bituberosus on these developmental stages under laboratory conditions. The predators consumed up to 6.8 ± 0.52 and 6.9 ± 0.45 T. tabaci pre-pupae/ pupae, respectively, when offered 6 –10 prey a day. The maximum oviposition rates were 4.4 ± 0.25 eggs/female/day for G. aculeifer and 6.9 ± 0.26 eggs/female/day for P. bituberosus, with a mean egg viability higher than 91% for both predators. These results suggest that the evaluated predators may affect the population of T. tabaci under field conditions, and that the conduction of complementary studies on those predators is warranted, envisioning their practical use for T. tabaci control in Colombia.

Oocyte Ageing in Zebrafish Danio rerio (Hamilton, 1822) and Its Consequence on the Viability and Ploidy Anomalies in the Progeny

Fish egg quality can be markedly influenced by the oocyte age after ovulation. In this study, we examined the duration of oocyte ageing in the zebrafish (Danio rerio) and whether prolonged ageing is associated with the incidence of ploidy anomalies in the resulting embryos. Oocytes were incubated in vitro for 6 h post-stripping (HPS) at 26 °C and fertilized at 2-h intervals. Meanwhile, for eggs fertilized immediately after stripping, the fertilization, embryo survival, and hatching rates started at ~80%; these rates decreased to 39%, 24%, and 16%, respectively, for oocytes that had been stored for 4 h (p ˂ 0.05), and there was an almost complete loss of egg viability at 6 HPS. Furthermore, almost 90% of the embryos derived from 6-h aged oocytes died prior to hatching, and all larvae originating from 4- and 6-h aged oocytes showed malformations. The proportion of ploidy abnormal embryos was significantly greater at 4 HPS (18.5%) than at either 0 or 2 HPS (4.7% and 8.8%, respectively). The results revealed that zebrafish oocytes retained their fertilization potential for up to 2 h after stripping at 26 °C and indicated the contribution of post-ovulatory oocyte ageing in the occurrence of ploidy anomalies in the resulting embryos.

Rapid stress hardening in the Antarctic midge improves male fertility by increasing courtship success and preventing the decline of accessory gland proteins following cold exposure

Rapid hardening is a process that quickly improves animal performance following exposure to a potentially damaging stress. Features of reproduction can be improved by rapid hardening, but little is known about how rapid hardening may contribute to physiological responses in the cold environment of Antarctica. In this study of the Antarctic midge, Belgica antarctica (Diptera, Chironomidae), we examine how rapid hardening in response to dehydration (RDH) or cold (RCH) improves male pre- and post-copulatory function related to fertility when the insects are subsequently subjected to a damaging cold exposure. Neither RDH nor RCH improved survival in response to lethal cold stress, but male activity following sublethal cold exposure was enhanced. Both RCH and RDH improved mating success of males compared to those subjected directly to a sublethal bout of cold. Egg viability decreased following direct exposure to sublethal cold, but improved following RCH and RDH. Sublethal cold exposure reduced expression of four accessory gland proteins, while expression remained high in males exposed to RCH. Though rapid hardening may be cryptic in males, this study shows that it can be revealed by pre- and post-copulatory interactions with females.

Lethal and Sublethal Effects of Long-term Cold Storage on Indoor-reared Harmonia Axyridis Adults

Indoor-reared natural enemy with high quality after long-term cold storage is crucial for sustainable pest management. However, besides survivals, the sublethal effects were not widely been reported. In this study, Harmonia axyridis (Pallas), an important biological control agent in Asia, was reared with β-carotene-amended artificial diet (Ha-Car) before storing at 6°C. After 30, 60, 90 and 120 days of storage, a series of biological parameters were measured to evaluate the fitness of H. axyridis. We found that: (1) Survivals significantly decreased with prolonged storage, and more Ha-Car individuals survived at day 120 compared to Ha-CK (control); (2) The contents of glycogen and trehalose dramatically decreased following storage, and the weight losses gradually increased; (3) The average egg production and hatch rates within 15 days were not significantly different among treatments Ha-Car and Ha-CK following long-term storage (90 and 120 days), while the daily hatch rates gradually decreased from relatively high to zero at day 14 and 15; (4) The number of micropyles deposited on eggs also gradually decreased along with oviposition period. After re-mating with a new non-stored partner, the egg viability gradually increased again, while low egg viability was still detected in F1 generation. Moreover, reduced number of micropyles were detected on their eggs. In summary, Ha-Car can be cold stored for about 120 days with relatively high survivals and fecundity, but long-term storage produced remarkable intra- and trans-generational negative effects on fertility. Even though, the cold-stored H. axyridis had great potential being used in biological control program with inevitable promiscuity with field individuals.