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  1. Abstract

    Fish population surveys in north‐temperate lakes are often conducted in the fall or spring when individuals are easy to capture with traditional fisheries techniques. Because some fishes are preparing to spawn or are spawning during these seasons, there is a critical need to better understand the potential influences of these surveys on decisions related to fish reproduction. We tested whether spring mark‐recapture surveys using fyke nets followed by electrofishing affect reproductive behaviors of male Smallmouth BassMicropterus dolomieuin a northern Wisconsin lake. Fyke‐netting, electrofishing, and whole‐lake nest snorkeling surveys were conducted during 2001‐2008, and Floy‐tagged males were tracked across years to test whether capture in the fyke nets only, or capture in the electrofishing survey influenced inter‐year nest site fidelity and reproductive timing. The mark‐recapture surveys were conducted preceding Smallmouth Bass spawning, and returning males caught in the electrofishing survey nested ~50 m farther from their prior year's nest than both males captured only in fyke nets and males that were captured by neither method. Average inter‐year nest distances were ~200 m and median inter‐year nest distances were ~90 m for males not captured in the electrofishing survey. Electrofishing and fyke netting did not influence timing of reproduction. Spring electrofishing surveys for Smallmouth Bass have the potential to displace breeding males from preferred nesting habitats. If displacement negatively influences fitness (i.e., age‐0 survivorship to maturation), spring electrofishing surveys would not be recommended for assessing Smallmouth Bass populations. However, spring population surveys often occur soon after ice off, and surveys conducted at these colder temperatures are typically less stressful and less likely to result in mortality. Future research should test for fitness implications of reduced nest site fidelity following electrofishing in Smallmouth Bass, while considering potential fitness trade‐offs if surveys are moved later in the year.

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    Free, publicly-accessible full text available October 3, 2024
  2. The seasonal onset of reproduction is constrained in many systems by a need to first accumulate energetic reserves. Consequently, the observation that larger individuals reproduce earlier may be due to a negative relationship between size and mass‐specific basal metabolic rate that is shared across diverse taxa. However, an untested prediction of this hypothesis is that individuals should be metabolically efficient enough to escape energetic constraints above a certain size threshold. Seasonally reproducing species, such as temperate fishes, that must recover winter energy losses before reproduction and exhibit indeterminate growth are ideal models to test this prediction. We harness decade‐long behavioral data on parental male smallmouth bass,Micropterus dolomieu, to investigate contributions of energetic allometry to differences in reproductive timing. At the population level, peak seasonal reproductive timing (i.e. the median date on which eggs were found in nests each year) was negatively related to degree days – a measure of thermal energy experienced – before reproduction. At the individual level, degree days accumulated by males before reproduction was related to male size and condition in every year, but the impact of temperature on reproductive timing by the largest males was relaxed in most years. Additionally, we used our data to replicate the analyses of two previous studies ofM. dolomieupopulations and found virtually identical negative associations between male body size and degree days accumulated before reproduction. Our results suggest that in smallmouth bass the onset of seasonal reproduction is constrained by basal metabolic rate – as indicated by total length – and that large individuals can escape size‐associated energetic constraints. We reveal a more complicated relationship between size and reproductive timing than earlier studies, which may be relevant for many species. Knowledge of this relationship is critical to understanding how a changing climate will influence population dynamics of economically, ecologically and recreationally important species likeM. dolomieu.

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    Free, publicly-accessible full text available June 1, 2024
  3. Mikó, István (Ed.)
    Abstract Several recent reappraisals of supposed generalist parasite species have revealed hidden complexes of species, each with considerably narrower host ranges. Parasitic wasps that attack gall-forming insects on plants have life history strategies that are thought to promote specialization, and though many species are indeed highly specialized, others have been described as generalist parasites. Ormyrus labotus Walker (Hymenoptera: Ormyridae) is one such apparent generalist, with rearing records spanning more than 65 host galls associated with a diverse set of oak tree species and plant tissues. We pair a molecular approach with morphology, host ecology, and phenological data from across a wide geographic sample to test the hypothesis that this supposed generalist is actually a complex of several more specialized species. We find 16–18 putative species within the morphological species O. labotus, each reared from only 1–6 host gall types, though we identify no single unifying axis of specialization. We also find cryptic habitat specialists within two other named Ormyrus species. Our study suggests that caution should be applied when considering host ranges of parasitic insects described solely by morphological traits, particularly given their importance as biocontrol organisms and their role in biodiversity and evolutionary studies. 
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  4. Abstract

    Host races represent an important step in the speciation process of phytophagous insects as they reflect the maintenance of genetically divergent host‐associated populations in the face of appreciable gene flow. The red‐shouldered soapberry bug,Jadera haematoloma(Herrich‐Schäffer) (Hemiptera: Rhopalidae), is an oligophagous seed predator with a history of host race evolution on plant associations in the (soapberry) family Sapindaceae. Soapberry bugs are a model group for understanding rapid ecological adaptation to their hosts, and hence good candidates for investigating evolutionary divergence in host associations over short timescales. Here, we describe the recent discovery of Mexican buckeye,Ungnadia speciosaEndl., as a host ofJ. haematolomain a region of the Chihuahuan desert including west Texas and southeastern New Mexico, USA. This host differs fromJ. haematoloma’s previously recorded hosts in the Sapindaceae in seed chemistry, ecology, and phylogeny. The tendency toward rapid, host‐associated adaptations by populations ofJ. haematolomaand the unique biology of the newly discoveredUngnadiahost create the opportunity for potential host race formation, as it overlaps geographically with two previously recorded host plants in this region – the native western soapberry tree,Sapindus saponariavar.drummondii(Hook & Arn.), and the non‐native goldenrain tree,Koelreuteria paniculataLaxm. We explore the possibility of host race formation onUngnadia‐associated insects by testing for host‐associated differentiation in morphology and feeding behaviors. We find evidence of differentiation in the length of the mouth parts, which is an ecologically relevant feeding trait between host plant species with larger or smaller seed capsules. This divergence is maintained in the face of potential gene flow by reproductive isolation in the form of habitat isolation, which we detect in host preference trials. Together, our results demonstrate that soapberry bugs associated with this newly discovered host exhibit morphological and behavioral traits consistent with host race formation, but additional work is required to confirm its state along the speciation continuum.

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  5. Studies assessing the predictability of evolution typically focus on short-term adaptation within populations or the repeatability of change among lineages. A missing consideration in speciation research is to determine whether natural selection predictably transforms standing genetic variation within populations into differences between species. Here, we test whether and how host-related selection on diapause timing associates with genome-wide differentiation during ecological speciation by comparing ancestral hawthorn and newly formed apple-infesting host races of Rhagoletis pomonella to their sibling species Rhagoletis mendax that attacks blueberries. The associations of 57 857 single nucleotide polymorphisms in a diapause genome-wide-association study (GWAS) on the hawthorn race strongly predicted the direction and magnitude of genomic divergence among the three fly populations at a field site in Fennville, MI, USA. The apple race and R. mendax show parallel changes in the frequencies of putative inversions on three chromosomes associated with the earlier fruiting times of apples and blueberries compared to hawthorns. A diapause GWAS on R. mendax revealed compensatory changes throughout the genome accounting for the earlier eclosion of blueberry, but not apple flies. Thus, a degree of predictability, although not complete, exists in the genomics of diapause across the ecological speciation continuum in Rhagoletis . The generality of this result is placed in the context of other similar systems. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers'. 
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