Relationship between maternal transfer of immunity and mother fecundity in an insect

Trans-generational immune priming (TGIP) corresponds to the plastic adjustment of offspring immunity as a result of maternal immune experience. TGIP is expected to improve mother's fitness by improving offspring individual performance in an environment where parasitism becomes more prevalent. However, it was recently demonstrated that maternal transfer of immunity to the offspring is costly for immune-challenged female insects. Thus, these females might not provide immune protection to all their offspring because of the inherent cost of other fitness-related traits. Females are therefore expected to adjust their investment to individual offspring immune protection in ways that maximize their fitness. In this study, we investigated how bacterially immune-challenged females of the mealworm beetle, Tenebrio molitor, provision their eggs with immune protection according to egg production. We found that immune-challenged females provide a variable number of their eggs with internal antibacterial activity along egg-laying bouts. Furthermore, within the first immune-protected egg-laying bout (2-4 days after the maternal immune challenge), the number of eggs protected was strongly dependent on the number of eggs produced. Immune-challenged females might therefore adjust their investment into TGIP and fecundity according of their individual perception of the risk of dying from the infection and the expected parasitic conditions for the offspring.     

Previous encapsulation response enhances within individual protection against fungal parasite in the mealworm beetle Tenebrio mofitor

Immune defenses of insects show either broad reactions or specificity and durability of induced protection against attacking parasites and pathogens. In this study, we tested whether encapsulation response against nylon monofilament increases between two attempts of activation of immune system in mealworm beetles Tenebrio molitor, and whether previous exposure to nylon monofilament may also increase protection against an entomopathogenic fungus. We found that survival of beetles subjected to immune activation by nylon implant and subsequent fungal exposure a week later was significantly higher than survival of beetles which had been subjected to fimgal infection only. This result suggests that previous immune activation by the nylon implant may be considered as broad spectrum ＂immune priming＂ which helps to fight not only the same intruder but also other parasites.     

Is there a role for antioxidant carotenoids in limiting self-harming immune response in invertebrates?

Innate immunity relies on effectors, which produce cytotoxic molecules that have not only the advantage of killing pathogens but also the disadvantage of harming host tissues and organs. Although the role of dietary antioxidants in invertebrate immunity is still unknown, it has been shown in vertebrates that carotenoids scavenge cytotoxic radicals generated during the immune response. Carotenoids may consequently decrease the self-harming cost of immunity. A positive relationship between the levels of innate immune defence and circulating carotenoid might therefore be expected. Consistent with this hypothesis, we show that the maintenance and use of the prophenoloxidase system strongly correlate with carotenoid concentration in haemolymph within and among natural populations of the crustacean Gammarus pulex.     

Use it or lose it: reproductive implications of ecological specialization in a haematophagous ectoparasite

Using experimentally induced disruptive selection, we tested two hypotheses regarding the evolution of specialization in parasites. The 'trade-off' hypothesis suggests that adaptation to a specific host may come at the expense of a reduced performance when exploiting another host. The alternative 'relaxed selection' hypothesis suggests that the ability to exploit a given host would deteriorate when becoming obsolete. Three replicate populations of a flea Xenopsylla ramesis were maintained on each of two rodent hosts, Meriones crassus and Dipodillus dasyurus, for nine generations. Fleas maintained on a specific host species for a few generations substantially decreased their reproductive performance when transferred to an alternative host species, whereas they generally did not increase their performance on their maintenance host. The results support the 'relaxed selection' hypothesis of the evolution of ecological specialization in haematophagous ectoparasites, while suggesting that trade-offs are unlikely drivers of specialization. Further work is needed to study the extent by which the observed specializations are based on epigenetic or genetic modifications.     

Divergent host plant specialization as the critical driving force in speciation between populations of a phytophagous ladybird beetle

Detecting the isolating barrier that arises earliest in speciation is critically important to understanding the mechanism of species formation. We tested isolating barriers between host races of a phytophagous ladybird beetle, Henosepilachna diekei (Coleoptera: Coccinellidae: Epilachnine), that occur sympatrically on distinct host plants. We conducted field surveys for the distribution of the beetles and host plants, rearing experiments to measure six potential isolating factors (adult host preference, adult and larval host performance, sexual isolation, egg hatchability, F(1) hybrid inviability, and sexual selection against F(1) hybrids), and molecular analyses of mitochondrial ND2 and the nuclear ITS2 sequences. We found significant genetic divergence between the host races, and extremely divergent host preference (i.e. habitat isolation) and host performance (i.e. immigrant inviability), but no other isolating barriers. The fidelity to particular host plants arises first and alone can prevent gene flow between differentiating populations of phytophagous specialists.     

Do mosquitoes filter the access of Plasmodium cytochrome b lineages to an avian host?

Many parasites show fidelity to a set of hosts in ecological time but not evolutionary time and the determinants of this pattern are poorly understood. Malarial parasites use vertebrate hosts for the asexual stage of their life cycle but use Dipteran hosts for the sexual stage. Despite the potential evolutionary importance of Dipteran hosts, little is known of their role in determining a parasite's access to vertebrate hosts. Here, we use an avian malarial system in Panama to explore whether mosquitoes act as an access filter that limits the range of vertebrate hosts used by particular parasite lineages. We amplified and sequenced Plasmodium mitochondrial DNA (mtDNA) from Turdus grayi (clay-coloured robin) and from mosquitoes at the same study site. We trapped and identified to species 123 141 female mosquitoes and completed polymerase chain reaction (PCR) screening for Plasmodium parasites in 435 pools of 20 mosquitoes per pool (8700 individuals total) spanning the 11 most common mosquito species. Our primers amplified nine Plasmodium lineages, whose sequences differed by 1.72%–10.0%. Phylogenetic analyses revealed partial clustering of lineages that co-occurred in mosquito hosts. However PAN3 and PAN6, the two primary parasite lineages of T. grayi , exhibited sequence divergence of 8.59% and did not cluster in the phylogeny. We detected these two lineages exclusively in mosquitoes from different genera — PAN3 was found only in Culex (Melanoconion) ocossa , and PAN6 was found only in Aedeomyia squamipennis . Furthermore, each of these two parasite lineages co-occurred in mosquitoes with other Plasmodium lineages that were not found in the vertebrate host T. grayi . Together, this evidence suggests that parasite–mosquito associations do not restrict the access of parasites to birds but instead may actually facilitate the switching of vertebrate hosts that occurs over evolutionary time.     

Dynamics of host plant use and species diversity in Polygonia butterflies (Nymphalidae)

The ability of insects to utilize different host plants has been suggested to be a dynamic and transient phase. During or after this phase, species can shift to novel host plants or respecialize on ancestral ones. Expanding the range of host plants might also be a factor leading to higher levels of net speciation rates. In this paper, we have studied the possible importance of host plant range for diversification in the genus Polygonia (Nymphalidae, Nymphalini). We have compared species richness between sistergroups in order to find out if there are any differences in number of species between clades including species that utilize only the ancestral host plants ('urticalean rosids') and their sisterclades with a broader (or in some cases potentially broader) host plant repertoire. Four comparisons could be made, and although these are not all phylogenetically or statistically independent, all showed clades including butterfly species using other or additional host plants than the urticalean rosids to be more species-rich than their sisterclade restricted to the ancestral host plants. These results are consistent with the theory that expansions in host plant range are involved in the process of diversification in butterflies and other phytophagous insects, in line with the general theory that plasticity may drive speciation.     

Coexistence of competitive species with a stage-structured life cycle

Ecological theory provides explanations for exclusion or coexistence of competing species. Most theoretical works on competition dynamics that have shaped current perspectives on coexistence assume a simple life cycle. This simplification, however, may omit important realities. We present a simple two-stage structured competition model to investigate the effects of life-history characteristics on coexistence. The achievement and the stability of coexistence depend not only on competition coefficients but also on a set of life-history parameters that reflect the viability of an individual, namely, adult death rate, maturation rate, and birth rate. High individual viability is necessary for a species to persist, but it does not necessarily facilitate coexistence. Intense competition at the juvenile or adult stage may require higher or lower viability, respectively, for stable coexistence to be possible. The stability mechanism can be explained by the refuge effect of the less competitive stage, and the birth performance, which preserves the less competitive stage as a refuge. Coexistence might readily collapse if the life-history characteristics, which together constitute individual viability, change, even though two species have an inherent competitive relation conducive to stable coexistence.