Biology subjects

Baldwin, B. G.

Publications and source records attributed to Baldwin, B. G..

6 recordsLinked to original sources

bioRxiv2026

Patterns of species richness and endemism in bee and plant communities in California

Understanding the spatial distribution of species and their patterns of endemism is necessary for establishing effective conservation priorities. Despite the vital pollination services bees provide, Californias native bee distribution patterns remain largely unexplored relative to plants and butterflies. We analyzed bee species richness and endemism across California and their concordance with plant distributions. Richness was high across areas of the California Floristic Province, including the Sierra Nevada, San Francisco Bay Area and Central Coast, South Coast Ranges, and the Transverse and Peninsular ranges. Bee endemism was more localized, concentrated in the San Joaquin Valley, eastern Sierra Nevada and adjacent Great Basin, Sierra Nevada foothills, and California deserts. Because richness and endemism appear to operate at different spatial scales and likely respond to different environmental drivers, effective conservation strategies must address both. Additionally, conservation plans that incorporate both plant and bee diversity are needed to achieve more comprehensive biodiversity protection.

ecology↗

bioRxiv2026

A tribal-scale phylogenomic perspective on ancestry and major lineages of the allotetraploid Hawaiian silversword alliance (Madieae, Compositae)

Premise of the studyDisentangling ancestry of insular plant lineages is important for resolving their evolutionary histories but often complicated by polyploidy, an overrepresented condition in remote island floras. A phylogenomic approach was used to study the origin of subgenomes of the tetraploid Hawaiian silversword alliance and advance understanding of this major example of adaptive radiation. MethodsSequences from 461 target-capture nuclear loci were phased to subgenomes of the tetraploid silversword alliance (Compositae) using assemblies from diploid North American tarweeds as clade references. Maximum-likelihood and multispecies- coalescent analyses of phased loci were conducted with and without representatives of diploid lineages throughout tribe Madieae. Key resultsAn allopolyploid origin of the silversword alliance was corroborated, with Subgenome-A phased consistently to Anisocarpus madioides and Subgenome-B phased to diploid representatives of each of three other sublineages of the "Madia" lineage. Phylogenomic analyses indicate Anisocarpus madioides is more closely related to Subgenome-A than to other tarweeds, including Anisocarpus scabridus. Subgenome trees for the silversword alliance are highly congruent with each other and with structural genomic differences between lineages. ConclusionsThese results indicate an even closer relationship of the silversword alliance to extant California tarweeds than previously understood. Anisocarpus madioides has chromosomal and ecological traits anticipated in an ancestor of the silversword alliance, with the widest geographic range among perennial tarweeds and sticky bracts completely enveloping fruits. Within the silversword alliance, robust support for four major clades reinforces the phylogenetic value of chromosomal interchanges and taxonomic insights by Asa Gray regarding the enigmatic liana Dubautia latifolia.

evolutionary biology↗

bioRxiv2025

The Goldilocks effect drives plant diversification on middle-aged Hawaiian islands

Islands are natural laboratories for studying dispersal, speciation, and extinction, yet the historical dynamics of many insular radiations remain poorly understood because of the difficulty aligning the tempo and mode of diversification with paleogeography during phylogenetic inference. We introduce a phylogenetic modeling framework, named TimeFIG, that combines data about species ranges and genetic variation with paleogeographic information to simultaneously infer divergence times, ancestral ranges, and historical diversification rates, without relying on fossils to time-calibrate the phylogeny. Applying TimeFIG to the spectacular radiation of Hawaiian Kadua (Rubiaceae) points to colonization of either modern Kaua'i or ancient now-eroded islands, with island isolation as the strongest correlate of dispersal, and with a tendency for net diversification to be highest on "middle-aged" islands. Modeling diversification within an explicit spatiotemporal context, while accounting for historical uncertainty regarding the timing and placement of phylogenetic and biogeographic events, enables the rigorous testing of foundational hypotheses in island biology and evolutionary theory for clades beyond Kadua.

evolutionary biology↗

bioRxiv2022

Edaphic specialization onto bare, rocky outcrops as a factor in the evolution of desert angiosperms

Understanding the processes that enable organisms to shift into more arid environments as they emerge is critical for gauging resilience to climate change, yet these forces remain poorly known. In a comprehensive clade-based study, we investigate recent shifts into North American deserts in the rock daisies (Perityleae), a diverse tribe of desert sunflowers (Compositae). We sample Perityleae across two separate contact zones between tropical deciduous forest and desert biomes in western North America and infer a time-calibrated phylogeny based on target capture sequence data. We reconstruct biome shifts using Bayesian inference with paleobiome-informed models and find evidence for seven independent shifts into desert habitats since the onset of aridification in the late Miocene epoch. The earliest shift occurred out of tropical deciduous forests and led to an extensive radiation throughout North American deserts that accounts for the majority of extant desert Perityleae. Reconstructions of life history and micro-habitat in Perityleae reveal a correlation between a suffrutescent perennial life history and edaphic endemism onto rocky outcrops, an ecological specialization that evolved prior to establishment and diversification in deserts. That the insular radiation of desert rock daisies stemmed from ancestors pre-adapted for dry conditions as edaphic endemics in otherwise densely vegetated tropical deciduous forests in northwest Mexico underscores the crucial role of exaptation and dispersal for shifts into arid environments. Significance StatementThe environmentally stressful conditions found in desert regions have often been implicated as the main factor in the evolution of drought tolerance in desert plants. Yet many iconic desert plant lineages evolved prior to the recent emergence of widespread arid climates, suggesting an important role for pre-adaptation (exaptation). In the desert rock daisies (Perityleae), we provide empirical support for this view by showing that life history evolution associated with their ecological specialization onto rock outcrops was a precursor to their establishment and extensive diversification in North American deserts. We caution against assuming the presence of ancient dry biomes based on time-calibrated phylogenies and we emphasize the fundamental roles that exaptation and dispersal play during community assembly in novel environments.

evolutionary biology↗

bioRxiv2020

Natural selection maintains species despite widespread hybridization in the desert shrub Encelia

Natural selection is an important driver of genetic and phenotypic differentiation between species. A powerful way to test the role of natural selection in the formation and maintenance of species is to study species complexes in which potential gene flow is high but realized gene flow is low. For a recent radiation of New World desert shrubs (Encelia: Asteraceae), we use fine-scale geographic sampling and population genomics to determine patterns of gene flow across two hybrid zones formed between two independent pairs of species with parapatric distributions. After finding evidence for extremely strong selection at both hybrid zones, we use a combination of field experiments, high-resolution imaging, and physiological measurements to determine the ecological basis for selection at one of the hybrid zones. Our results identify multiple ecological mechanisms of selection (drought, salinity, herbivory, and burial) that together are sufficient to maintain species boundaries despite high rates of hybridization. Given that multiple pairs of species hybridize at ecologically divergent parapatric boundaries in the adaptive radiation of Encelia, such mechanisms may maintain species boundaries throughout this group. SIGNIFICANCE STATEMENTIn Baja California, the deserts meet the coastal dunes in a narrow transition visible even from satellite images. We study two species pairs of desert shrubs (Encelia) that occur across this transition. Although these species can interbreed, they remain distinct. Using a combination of genetics, field experiments, 3D-imaging, and physiological measurements, we show that natural selection counteracts the homogenizing effects of gene exchange. The different habitats of these species create multiple mechanisms of selection - drought, salinity, herbivory, and burial, which together maintain these species in their native habitats and their hybrids in intermediate habitats. This study illustrates how environmental factors influence traits and fitness and how this in turn maintain species, highlighting the importance of natural selection in speciation.

evolutionary biology↗

bioRxiv2018

Retracing the Hawaiian silversword radiation despite phylogenetic, biogeographic, and paleogeographic uncertainty

The Hawaiian silversword alliance (Asteraceae) is an iconic adaptive radiation of 33 species. However, like many island plant lineages, no fossils have been assigned to the clade. As a result, the clades age and diversification rate are not known precisely, making it difficult to test biogeographic hypotheses about the radiation. In lieu of fossils, paleo-geographically structured biogeographic processes may inform species divergence times; for example, an island must first exist for a clade to radiate upon it. We date the silversword clade and test biogeographic hypotheses about its radiation across the Hawaiian Archipelago by modeling interactions between species relationships, molecular evolution, biogeographic scenarios, divergence times, and island origination times using the Bayesian phylogenetic framework, RevBayes. The ancestor of living silverswords most likely colonized the modern Hawaiian Islands once from the mainland approximately 5.1 Ma, with early surviving silversword lineages first appearing approximately 3.5 Ma. In testing the progression rule of island biogeography, we found strong positive evidence of the dispersal process preferring old-to-young directionality, but strong negative evidence for speciation occurring on islands during their young growth phase. This work serves as a general example for how diversification studies benefit from incorporating biogeographic and paleogeographic components.

evolutionary biology↗