Quantitative trait loci involved in the reproductive success of a parasitoid wasp

Dissecting the genetic basis of intraspecific variations in life history traits is essential to understand their evolution, notably for potential biocontrol agents. Such variations are observed in the endoparasitoid Cotesia typhae (Hymenoptera: Braconidae), specialized on the pest Sesamia nonagrioides (Lepidoptera: Noctuidae). Previously, we identified two strains of C. typhae that differed significantly for life history traits on an allopatric host population. To investigate the genetic basis underlying these phenotypic differences, we used a quantitative trait locus (QTL) approach based on restriction site‐associated DNA markers. The characteristic of C. typhae reproduction allowed us generating sisters sharing almost the same genetic content, named clonal sibship. Crosses between individuals from the two strains were performed to generate F2 and F8 recombinant CSS. The genotypes of 181 clonal sibships were determined as well as the phenotypes of the corresponding 4,000 females. Informative markers were then used to build a high‐quality genetic map. These 465 markers spanned a total length of 1,300 cM and were organized in 10 linkage groups which corresponded to the number of C. typhae chromosomes. Three QTLs were detected for parasitism success and two for offspring number, while none were identified for sex ratio. The QTLs explained, respectively, 27.7% and 24.5% of the phenotypic variation observed. The gene content of the genomic intervals was investigated based on the genome of C. congregata and revealed 67 interesting candidates, as potentially involved in the studied traits, including components of the venom and of the symbiotic virus (bracovirus) shown to be necessary for parasitism success in related wasps.     

Errors in egg-laying by female Common Cuckoo Cuculus canorus in nests of its common host

Dozens of studies have documented that brood parasites are well adapted to a brood parasitic lifestyle but not all parasitism events are successful. Co-evolution between brood parasites and their hosts is a dynamic process so it is reasonable to expect that a female brood parasite may commit errors during egg deposition by laying her eggs outside the laying period of the host, with consequent impacts on her fitness. Using an extensive dataset from a long-term study, we evaluated egg-laying patterns and errors related to the timing of egg-laying in the Common Cuckoo Cuculus canorus (hereafter ‘Cuckoo’). Specifically, we tested whether the Cuckoo avoids laying before or on the day of host clutch initiation to reduce the risk of rejection of parasitic eggs, whether laying errors will be more frequent in periods with a lack of active host nests, and whether the laying errors will be more frequent in periods with intense Cuckoo parasitism and a consequent lack of suitable host nests. We found that about one-third of Cuckoo eggs were laid on the host clutch initiation day or 1 day before, and the percentage of Cuckoo eggs laid decreased thereafter. Surprisingly, the probability of Cuckoo egg acceptance by the hosts was not affected by the egg-laying stage of the host clutch. Errors in the timing of egg-laying with fatal consequences (i.e. those precluding Cuckoo hatching because of laying in incubated or deserted clutches) were recorded in about 5% of cases. Only laying date of a Cuckoo egg had a significant effect on the probability of errors, which increased during the breeding season. This may be related to the higher number of deserted and incubated host nests at the site at the end of the breeding season. Errors in egg-laying may be attributed to young and inexperienced females but also impaired body condition or intraspecific competition may cause this behaviour. Future studies, which will test these possible explanations, will help to understand better the mechanism of co-evolutionary arms races and differences between host specialist and generalist brood parasites in various host–parasite systems.     

Impact of brood parasitism and predation on nest survival of the fan-tailed gerygone in New Caledonia

Predation and brood parasitism are common reasons for nesting failure in passerine species and the additive impact by invasive species is a major conservation concern, particularly on tropical islands. Recognising the relative contribution of the different components of nesting failure rates is important to understand co-evolutionary interactions within brood parasite–host systems. In the remote archipelago of New Caledonia, the fan-tailed gerygone Gerygone flavolateralis is the exclusive host of the brood-parasitic shining bronze-cuckoo Chalcites lucidus. Additionally, invasive rodents also possibly have an impact on breeding success. To estimate the impact of potential nest predators, we 1) video monitored nests to identify predators, 2) estimated the probability of predation based on nest visibility and predator abundance and 3) tested the possibility that the location of experimental nests and lack of odour cues decrease the predation by rodents. In addition, we estimated nest survival rates using data collected in different habitats over the course of eight breeding seasons. Nesting success of fan-tailed gerygones was relatively low and predation was the main cause of nesting failure. We recorded mainly predation by native birds, including the shining bronze-cuckoo, whereas predation by rats was rare. In open habitats predation by cuckoos was much lower than predation by other avian predators. Neither predator activity around nests nor nest visibility influenced the probability of predation. Experimental nests in more accessible locations and containing an odorous bait were more exposed to rodent predation. Apparently, the fan-tailed gerygone has either never been specifically vulnerable to predation by rats or has developed anti-predator adaptations.     

Heritability of resting metabolic rate in a wild population of blue tits

We report the first study with the aim to estimate heritability in a wild population, a nest box breeding population of blue tits. We estimated heritability as well as genetic and phenotypic correlations of resting metabolic rate (RMR), body mass and tarsus length with an animal model based on data from a split cross‐fostering experiment with brood size manipulations. RMR and body mass, but not tarsus length, showed significant levels of explained variation but for different underlying reasons. In body mass, the contribution to the explained variation is mainly because of a strong brood effect, while in RMR it is mainly because of a high heritability. The additive variance in RMR was significant and the heritability was estimated to 0.59. The estimates of heritability of body mass (0.08) and tarsus length (0.00) were both low and based on nonsignificant additive variances. Thus, given the low heritability (and additive variances) in body mass and tarsus length the potential for direct selection on RMR independent of the two traits is high in this population. However, the strong phenotypic correlation between RMR and mass (0.643 ± 0.079) was partly accounted for by a potentially strong, although highly uncertain, genetic correlation (1.178 ± 0.456) between the two traits. This indicates that the additive variance of body mass, although low, might still somewhat constrain the independent evolvability of RMR.     

Begging and cowbirds: brood parasites make hosts scream louder

Avian brood parasites have evolved striking begging abilitythat often allows them to prevail over the host progeny in competitionfor parental resources. Host young are therefore selected bybrood parasites to evolve behavioral strategies that reducethe cost of parasitism. We tested the prediction that the intensityof nestling begging displays functioning to attract parentalcare increases across species with the frequency of parasitismby the brown-headed cowbird (Molothrus ater). This was expectedbecause host young should try to prevail over highly competitiveparasitic broodmates in scramble interactions, act more selfishlywhen frequency of parasitism is high because brood parasitesoften affect more severely host condition than conspecific broodmates,and discount the kin selection costs of subtracting resourcesto unrelated parasites. Across 31 North American host species,begging loudness positively covaried with parasitism rate inPasserines, and such effect was stronger in species with smallcompared with large clutches. Begging loudness increased withbrood parasitism and nest predation among the most suitablehost species. These results held after controlling for concomitantecological factors and for common ancestry effects. Our resultssupport the hypothesis that avian brood parasitism has playeda role in the evolution of begging behavior of host young.     

A meta-analysis of parasite virulence in nestling birds

Parasitism is a common cause of host mortality, but little is known about the ecological factors affecting parasite virulence (the rate of mortality among infected hosts). We reviewed 117 field estimates of parasite-induced nestling mortality in birds, showing that there was significant consistency in mortality among host and parasite taxa. Virulence increased towards the tropics in analyses of both species-specific data and phylogenetic analyses. We found evidence of greater parasite prevalence being associated with reduced virulence. Furthermore, bird species breeding in open nest sites suffered from greater parasite-induced mortality than hole-nesting species. By contrast, parasite specialization and generation time of parasites relative to that of hosts explained little variation in virulence. Likewise, there were little or no significant effects of host genetic variability, host sociality, host migration, host insular distribution or host survival on parasite virulence. These findings suggest that parasite-induced nestling mortality in birds is mainly determined by geographical location and to a smaller extent nest site and prevalence.     

Incidence of lamprey marks on Lake Sturgeon (Acipenser fulvescens Rafinesque, 1817) in the St. Clair – Detroit River System: Implications for Sea Lamprey (Petromyzon marinus Linnaeus, 1758) effects

Laurentian Great Lakes Lake Sturgeon (Acipenser fulvescens) are hosts to lamprey species, including native Silver Lamprey (Ichthyomyzon unicuspis) and invasive Sea Lamprey (Petromyzon marinus). Silver Lamprey coevolved with Lake Sturgeon and cause negligible mortality, but Sea Lamprey can negatively affect Lake Sturgeon populations. Sea Lamprey abundance in Lake Erie has been above targets set by resource managers, with the St. Clair – Detroit River System (SCDRS) suspected as a source of Sea Lamprey production into Lake Erie. This study summarizes lamprey marking on Lake Sturgeon captured during agency assessment surveys in the SCDRS since 1996 and provides insight on the potential for Sea Lamprey to negatively affect Lake Sturgeon in the SCDRS. Lamprey marks (any lamprey species) were noted on 48.2% of Lake Sturgeon (2.5 marks/fish) and 3.3% of Lake Sturgeon assumed to be susceptible to mortality by Sea Lamprey (<760 mm TL; 0.06 marks/fish). Silver Lamprey were the only lamprey species found attached to Lake Sturgeon and there was no difference between oral disc diameters of Silver Lamprey and marks measured on Lake Sturgeon in Lake St. Clair and the lower St. Clair River (p = .45). Based on logistic regression, probability of at least one lamprey mark increased with Lake Sturgeon total length and was highest in Lake St. Clair. The probability of observing at least one lamprey mark on a 760 mm Lake Sturgeon was 8.1% or less for each sampling location in the SCDRS aside from Lake St. Clair (28.1%). Results suggest that parasitism of Lake Sturgeon by Sea Lamprey in the SCDRS is rare, particularly for Lake Sturgeon <760 mm TL. Low incidence of lamprey marks on Lake Sturgeon assumed to be susceptible to mortality from Sea Lamprey parasitism and zero occurrence of Sea Lamprey being observed attached to a Lake Sturgeon suggest Sea Lamprey at their current abundance likely have little effect on the Lake Sturgeon population in the SCDRS. Caution should be taken when using mark size to assign marks to lamprey species as there is substantial overlap among species oral disc diameters, potentially inflating the perceived impact of Sea Lamprey on Lake Sturgeon in areas with native lampreys.     

The poor health of deep-water species in the context of fishing activity and a warming climate: will populations of Molva species rebuild or collapse?

Many deep-water fish populations, being K-selected species, have little resilience to overexploitation and may be at serious risk of depletion as a consequence. Sea warming represents an additional threat. In this study, the condition, or health, of several populations of common ling (Molva molva), blue ling (Molva dypterygia) and Mediterranean or Spanish ling (Molva macrophthalma) inhabiting different areas in the North Atlantic and the Mediterranean was evaluated, to shed light on the challenges these deep-water species are facing in the context of fishing activity and a warming climate. The data on the condition of Molva populations which are analysed here have been complemented with data on abundance and, for the southernmost species (Mediterranean ling), with two other health indicators (parasitism and hepato-somatic index). Despite some exceptions (e.g., common ling in Icelandic waters), this study shows that the condition of many populations of Molva species in the northeastern Atlantic and the Mediterranean Sea has worsened, a trend which, in recent decades, has usually been found to be accompanied by a decline in their abundance. In addition, the poor health status of most populations of common ling, blue ling and Mediterranean ling considered in this analysis points to a lower sustainability of these populations in the future. Overall, the health status and abundance of Molva populations in the northeastern Atlantic and the Mediterranean suggest that only some populations located in the North Atlantic may be able to rebuild, whereas the populations in southern North Atlantic and the Mediterranean, which are probably most at risk from sea warming, are facing serious difficulties in doing so. In the context of fisheries and global warming, this study's results strongly indicate that management bodies need to consider the health status of many of the populations of Molva species, particularly in southern European waters, before implementing their decisions.