Biology subjects

Bagley, R. K.

Publications and source records attributed to Bagley, R. K..

7 recordsLinked to original sources

bioRxiv2023

Multiple mechanisms contribute to isolation-by-environment in the redheaded pine sawfly, Neodiprion lecontei

Isolation by environment (IBE) is a population genomic pattern that arises when ecological barriers reduce gene flow between populations. Although current evidence suggests IBE is common in nature, few studies have evaluated the underlying mechanisms that generate IBE patterns. In this study, we evaluate five proposed mechanisms of IBE (natural selection against immigrants, sexual selection against immigrants, selection against hybrids, biased dispersal, environment-based phenological differences) that may give rise to host-associated differentiation within a sympatric population of the redheaded pine sawfly, Neodiprion lecontei, a species for which IBE has previously been detected. We first characterize the three pine species used by N. lecontei at the site, finding morphological and chemical differences among the hosts that could generate divergent selection on sawfly host-use traits. Next, using morphometrics and ddRAD sequencing, we detect modest phenotypic and genetic differentiation among sawflies originating from different pines that is consistent with recent, in situ divergence. Finally, via a series of laboratory assays - including assessments of larval performance on different hosts, adult mate and host preferences, hybrid fitness, and adult eclosion timing - we find evidence that multiple mechanisms contribute to IBE in N. lecontei. Overall, our results suggest IBE can emerge quickly, possibly due to multiple mechanisms acting in concert to reduce migration between different environments.

evolutionary biology↗

bioRxiv2022

Speciation in Nearctic oak gall wasps is frequently correlated with changes in host plant, host organ, or both.

Quantifying the frequency of shifts to new host plants within diverse clades of specialist herbivorous insects is critically important to understand whether and how host shifts contribute to the origin of species. Oak gall wasps (Hymenoptera: Cynipidae: Cynipini) comprise a tribe of ~1000 species of phytophagous insects that induce gall formation on various organs of trees in the family Fagacae, -- primarily the oaks (genus Quercus; ~435 sp). The association of oak gall wasps with oaks is ancient (~50 my), and most oak species are galled by one or more gall wasp species. Despite the diversity of both gall wasp species and their plant associations, previous phylogenetic work has not identified a strong signal of host plant shifting among oak gall wasps. However, most emphasis has been on the Western Palearctic and not the Nearctic where both oaks and oak gall wasps are considerably more species rich and where oaks are more phylogenetically diverse. We collected 86 species of Nearctic oak gall wasps from 10 of the 14 major clades of Nearctic oaks and sequenced >1000 Ultra Conserved Elements (UCEs) and flanking sequences to infer wasp phylogenies. We assessed the relationships of Nearctic gall wasps to one another and, by leveraging previously published UCE data, to the Palearctic fauna. We then used phylogenies to infer historical patterns of shifts among host tree species and tree organs. Our results indicate that oak gall wasps have moved between the Palearctic and Nearctic at least four times, that some Palearctic clades have their proximate origin in the Nearctic, and that gall wasps have shifted within and between oak tree sections, subsections, and organs considerably more often than the analysis of previous data have suggested. Given that host shifts have been demonstrated to drive reproductive isolation between host-associated populations in other phytophagous insects, our analyses of Nearctic gall wasps suggest that host shifts are key drivers of speciation in this clade, especially in hotspots of oak diversity. Though formal assessment of this hypothesis requires further study, two putatively oligophagous gall wasp species in our dataset show signals of host-associated genetic differentiation unconfounded by geographic distance, suggestive of barriers to gene flow associated with the use of alternative host plants.

evolutionary biology↗

bioRxiv2020

The impact of life stage and pigment source on the evolution of novel warning signal traits

Our understanding of how novel color traits evolve in aposematic taxa is based largely on studies of reproductive stages and organisms with endogenously produced pigmentation. In these systems, genetic drift is often required for novel alleles to overcome strong purifying selection stemming from frequency-dependent predation and positive assortative mating. Here we show that the importance of these mechanisms can differ if selective processes are considered in larval stage instead. By integrating population genomic data, predation experiments and phenotypic measurements of larvae and their host plants, we show that novel white alleles in Neodiprion lecontei (pine sawfly) larvae spread via selection rather than drift. The cost of being rare was not offset by an enhanced aposematic display or immune function. Instead, bottom-up selection via host plants may drive divergence among populations as white larvae were disproportionately abundant on a pine species with a reduced carotenoid content relative to other pine hosts.

evolutionary biology↗

bioRxiv2020

Phylogeny, morphology, and ecology resurrect previously synonymized species of North American Stereum

Stereum is an exceedingly common but taxonomically confounding genus of basidiomycete fungus with a cosmopolitan distribution. Lack of consensus about morphological and geographic boundaries of many Stereum species has resulted in a lack of consistency in identification of physical specimens, a problem that cascades to their associated published DNA sequences. A critical initial step towards addressing these issues is determining the scope of the problem. Here, we first use integrative taxonomy to delimit species in the North American Stereum ostrea complex. We use morphological and ecological characters, alongside ITS rDNA sequences of specimens from midwestern and eastern North America to show that "Stereum ostrea" in this region is a complex of at least three reproductively isolated sister species: S. lobatum, S. fasciatum, and S. subtomentosum. We then extend lessons from this case study to a set of publicly available Stereum ITS sequences to assess the accuracy of species names represented by existing sequence data. ASAP species delimitation successfully discriminates among the three newly revealed species in the S. ostrea species complex, but also reveals considerable cryptic diversity across global Stereum and widespread inconsistency in application of species names. Though ITS alone should not be used to delimit species or describe evolutionary relationships, its application here helps direct new hypotheses and suggests several areas of Stereum taxonomy that require revision. The critical future work of disentangling Stereum taxonomy and evolution should combine a multilocus genetic approach with morphology, ecology, and a global sampling strategy.

evolutionary biology↗

bioRxiv2020

Host shifting and host sharing in a genus of specialist flies diversifying alongside their sunflower hosts

Congeneric parasites are unlikely to specialize on the same tissues of the same host species, likely because of strong multifarious selection against niche overlap. Exceptions where multiple congeneric species overlap on the same tissues may therefore reveal important insights into the ecological factors underlying the origins and maintenance of diversity. Larvae of sunflower maggot flies in genus Strauzia feed on the pith of plants in the family Asteraceae. Although Strauzia tend to be host specialists, some species overlap in their host use. To resolve the origins of host sharing among these specialist flies, we used reduced representation genomic sequencing to infer the first multi-locus phylogeny of genus Strauzia. Our results show that Helianthus tuberosus and Helianthus grosseserratus each host three different fly species, and that the flies co-occurring on a host are not one anothers closest relatives. Though this pattern implies that host sharing is most likely the result of host shifts, these may not be host shifts in the conventional sense of an insect moving onto an entirely new plant. Many hosts of Strauzia belong to a young (1-2 MYA) clade of perennial sunflowers noted for their frequent introgression and hybrid speciation events. In at least one case, flies may have converged upon a host after their respective ancestral host plants hybridized to form a new sunflower species (H. tuberosus). Broadly, we suggest that rapid and recent adaptive introgression and speciation in this group of plants may have instigated the diversification of their phytophagous fly associates, including the convergence of >1 species onto the same shared host plants.

evolutionary biology↗

bioRxiv2018

Long-distance dispersal, ice sheet dynamics, and mountaintop isolation underlie the genetic structure of glacier ice worms

Disentangling the contemporary and historical factors underlying the spatial distributions of species is a central goal of biogeography. For species with broad distributions but little capacity to actively disperse, disconnected geographic distributions highlight the potential influence of passive, long-distance dispersal (LDD) on their evolutionary histories. However, dispersal alone cannot completely account for the biogeography of any species, and other factors-e.g., habitat suitability, life history-must also be considered. North American ice worms (Mesenchytraeus solifugus) are ice-obligate annelids that inhabit coastal glaciers from Oregon to Alaska. Previous studies identified a complex biogeographic history for ice worms, with evidence for genetic isolation, unexpectedly close relationships among geographically disjunct lineages, and contemporary migration across large (> 1,500 km) areas of unsuitable habitat. In this study, we analyzed genome-scale sequence data for most of the known ice worm range. We found clear support for divergence between populations along the Pacific Coast and the inland flanks of the Coast Mountains (mean FST = 0.60), likely precipitated by episodic ice sheet expansion and contraction during the Pleistocene. We also found support for LDD of ice worms from Alaska to Vancouver Island, perhaps mediated by migrating birds. Our results highlight the power of genomic data for disentangling complex biogeographic patterns, including the presence of LDD.

evolutionary biology↗

bioRxiv2018

Quantifying the unquantifiable: why Hymenoptera -- not Coleoptera -- is the most speciose animal order

BackgroundWe challenge the oft-repeated claim that the beetles (Coleoptera) are the most species-rich order of animals. Instead, we assert that another order of insects, the Hymenoptera, are more speciose, due in large part to the massively diverse but relatively poorly known parasitoid wasps. The idea that the beetles have more species than other orders is primarily based on their respective collection histories and the relative availability of taxonomic resources, which both disfavor parasitoid wasps. Though it is unreasonable to directly compare numbers of described species in each order, the ecology of parasitic wasps - specifically, their intimate interactions with their hosts - allows for estimation of relative richness. We present a simple logical model that shows how the specialization of many parasitic wasps on their hosts suggests few scenarios in which there would be more beetle species than parasitic wasp species. We couple this model with an accounting of what we call the \"genus-specific parasitoid-host ratio\" from four well-studied genera of insect hosts, a metric by which to generate extremely conservative estimates of the average number of parasitic wasp species attacking a given beetle or other insect host species. Synthesis of our model with data from real host systems suggests that the Hymenoptera may have 2.5 - 3.2x more species than the Coleoptera. While there are more described species of beetles than all other animals, the Hymenoptera are almost certainly the larger order.

zoology↗