skip to main content


Title: Integrating environmental, molecular, and morphological data to unravel an ice‐age radiation of arctic‐alpine Campanula in western N orth A merica
Abstract

Many arctic‐alpine plant genera have undergone speciation during the Quaternary. The bases for these radiations have been ascribed to geographic isolation, abiotic and biotic differences between populations, and/or hybridization and polyploidization. The CordilleranCampanulaL. (Campanulaceae Juss.), a monophyletic clade of mostly endemic arctic‐alpine taxa from western North America, experienced a recent and rapid radiation. We set out to unravel the factors that likely influenced speciation in this group. To do so, we integrated environmental, genetic, and morphological datasets, tested biogeographic hypotheses, and analyzed the potential consequences of the various factors on the evolutionary history of the clade. We created paleodistribution models to identify potential Pleistocene refugia for the clade and estimated niche space for individual taxa using geographic and climatic data. Using 11 nuclear loci, we reconstructed a species tree and tested biogeographic hypotheses derived from the paleodistribution models. Finally, we tested 28 morphological characters, including floral, vegetative, and seed characteristics, for their capacity to differentiate taxa. Our results show that the combined effect of Quaternary climatic variation, isolation among differing environments in the mountains in western North America, and biotic factors influencing floral morphology contributed to speciation in this group during the mid‐Pleistocene. Furthermore, our biogeographic analyses uncovered asynchronous consequences of interglacial and glacial periods for the timing of refugial isolation within the southern and northwestern mountains, respectively. These findings have broad implications for understanding the processes promoting speciation in arctic‐alpine plants and the rise of numerous endemic taxa across the region.

 
more » « less
NSF-PAR ID:
10196872
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Ecology and Evolution
Volume:
4
Issue:
20
ISSN:
2045-7758
Format(s):
Medium: X Size: p. 3940-3959
Size(s):
["p. 3940-3959"]
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We present a phylogeographic study of at least six reproductively isolated lineages of new world harvester ants within thePogonomyrmex barbatusandP. rugosusspecies group. The genetic and geographic relationships within this clade are complex: Four of the identified lineages show genetic caste determination (GCD) and are divided into two pairs. Each pair has evolved under a mutualistic system that necessitates sympatry. These paired lineages are dependent upon one another because theirGCDrequires interlineage matings for the production of F1 hybrid workers, and intralineage matings are required to produce queens. ThisGCDsystem maintains genetic isolation among these interdependent lineages, while simultaneously requiring co‐expansion and emigration as their distributions have changed over time. It has also been demonstrated that three of these fourGCDlineages have undergone historical hybridization, but the narrower sampling range of previous studies has left questions on the hybrid parentage, breadth, and age of these groups. Thus, reconstructing the phylogenetic and geographic history of this group allows us to evaluate past insights and hypotheses and to plan future inquiries in a more complete historical biogeographic context. Using mitochondrialDNAsequences sampled across most of the morphospecies’ ranges in the U.S.A. and Mexico, we conducted a detailed phylogeographic study. Remarkably, our results indicate that one of theGCDlineage pairs has experienced a dramatic range expansion, despite the genetic load and fitness costs of theGCDsystem. Our analyses also reveal a complex pattern of vicariance and dispersal inPogonomyrmexharvester ants that is largely concordant with models of late Miocene, Pliocene, and Pleistocene range shifts among various arid‐adapted taxa in North America.

     
    more » « less
  2. Abstract Aim

    We aim to test the biogeographic drivers of diversification and gene‐flow at the Isthmus of Panama using a species complex of suboscine birds as a case study. We specifically evaluate whether diversification in these birds is better explained by continuous parapatry or a Refuge Model of periodic isolation and gene‐flow due glacial cycling.

    Location

    The Isthmus of Panama (Neotropics).

    Taxon

    Pachyramphus aglaiaeandPachyramphus homochrous(Aves: Tityridae).

    Methods

    We develop an approach to distinguish among the two biogeographic hypotheses—parapatric ecological speciation versus climatically mediated speciation—by making explicit predictions for demographic history, niche evolution and change in geographic connectivity over time. We sequenced genome‐wide markers (ultraconserved elements) to estimate the evolutionary and demographic history of this group. We applied both phylogenomic network analyses and demographic modelling using a supervised machine learning approach. These genetic analyses were combined with a novel distribution modelling method that estimates the probability of interspecies contact as a function of climatic conditions through time.

    Results

    We found that both spatial and genetic analyses revealed concordant results. All speciation events occurred during the Pleistocene and were characterized by non‐continuous gene‐flow, supporting a scenario of climate‐mediated diversification. Spatial connectivity was highest at present, consistent with our best demographic model of secondary contact.

    Main conclusions

    This study exemplifies a mechanism by which speciation, dispersal and introgression unfold in an important region for Neotropical diversification—the Isthmus of Panama—where periods ofbothisolation and introgression probably drive diversification. Overall, our results are consistent with the Refuge Model of biotic diversification, but suggest that introgression may be a crucial yet underappreciated component of this classic paradigm.

     
    more » « less
  3. Abstract Aim

    We test the predictions of the Stockholm Paradigm, a synthesis of eco‐evolutionary theory explaining the nature of faunal assembly, host range and parasite diversification. Faunal diversification and assembly, manifested in patterns of host colonization, co‐adaptation and parasite speciation, are predicted to emerge as a consequence of alternating episodes of ecological disruption and stability. Specifically, for a diverse cestode genus (Arostrilepis), we evaluate the number and direction of Pleistocene dispersal events across Beringia, the number and relative timing of host colonization events and the relationship between host and parasite biogeographic histories and associations through time.

    Location

    Beringia and adjacent temperate to arctic biomes in North America and Eurasia.

    Taxon

    Arostrilepis(Cyclophyllidea: Hymenolepididae) and its rodent hosts.

    Methods

    Multi‐locus phylogenetic reconstruction and biogeographic ancestral range estimation.

    Results

    Arostrilepislineages crossed Beringia eastward into North America a minimum of four times and westward into Asia twice in association with temporally disjunct geographic expansions of three major tribes of cricetid rodents (Arvicolini, Myodini, Lemmini). Inferences of ancestral host associations support at least nine instances of host colonization involving shifts from one rodent tribe or family to another. Several previously unrecognized lineages ofArostrilepisare revealed.

    Main conclusions

    Consistent with expectations of the Stockholm Paradigm, episodes of intercontinental dispersal were both frequent in the history ofArostrilepisand preceded a majority of inferred host‐colonization events. Events of historical geographic expansion created numerous opportunities for development of novel host–parasite associations through ecological fitting, as parasites tracked historically conserved resources available across diverse host taxa. Beringia played a major role in shaping rodent/parasite assemblages by mediating dispersal between the northern continents during glacial episodes of the Pleistocene, rather than by serving as a zone of refugial isolation.

     
    more » « less
  4. Premise

    The distributions of plant clades are shaped by abiotic and biotic factors as well as historical aspects such as center of origin. Dispersals between distant areas may lead to niche evolution when lineages are established in new environments. Alternatively, dispersing lineages may exhibit niche conservatism, moving between areas with similar environmental conditions. Here we test these contrasting hypotheses in the Datureae clade (Solanaceae).

    Methods

    We used maximum likelihood methods to estimate the ancestral range of Datureae along with the history of biogeographic events. We then characterized the niche of each taxon using climatic and soil variables and tested for shifts in environmental niche optima. Finally, we examined how these shifts relate to the niche breadth of taxa and clades within Datureae and the degree of overlap between them.

    Results

    Datureae originated in the Andes and subsequently expanded its range to North America and non‐Andean regions of South America. The ancestral niche, and that of mostDaturaandTrompettiaspecies, is dry, whileBrugmansiaspecies likely shifted toward a more mesic environment. Nonetheless, most Datureae present moderate to high overlap in niche breadth today.

    Conclusions

    The expansion of Datureae into North America was associated with niche conservatism, with dispersal into similarly dry areas as occupied by the ancestral lineage. Subsequent niche evolution, including the apparent shift to a mesic niche inBrugmansia, diversified the range of habitats occupied by species in the tribe Datureae but also led to significant niche overlap among the three genera.

     
    more » « less
  5. Abstract

    Rapid speciation events, with taxa generated over a short time period, are among the most investigated biological phenomena. However, molecular systematics often reveals contradictory results compared with morphological/phenotypical diagnoses of species under scenarios of recent and rapid diversification. In this study, we used molecular data from an average of over 29 000 loci per sample from RADseq to reconstruct the diversification history and delimit the species boundary in a short‐winged grasshopper species complex (Melanoplus scudderigroup), where Pleistocene diversification has been hypothesized to generate more than 20 putative species with distinct male genitalic shapes. We found that, based on a maximum likelihood molecular phylogeny, each morphological species indeed forms a monophyletic group, contrary to the result from a previous mitochondrial DNA sequence study. By dating the diversification events, the species complex is estimated to have diversified during the Late Pleistocene, supporting the recent radiation hypothesis. Furthermore, coalescent‐based species delimitation analyses provide quantitative support for independent genetic lineages, which corresponds to the morphologically defined species. Our results also showed that male genitalic shape may not be predicted by evolutionary distance among species, not only indicating that this trait is labile, but also implying that selection may play a role in character divergence. Additionally, our findings suggest that the rapid speciation events in this flightless grasshopper complex might be primarily associated with the fragmentation of their grassland habitats during the Late Pleistocene. Collectively, our study highlights the importance of integrating multiple sources of information to delineate species, especially for a species complex that diversified rapidly, and whose divergence may be linked to ecological processes that create geographic isolation (i.e. fragmented habitats), as well as selection acting on characters with direct consequences for reproductive isolation (i.e. genitalic divergence).

     
    more » « less