Ecological niche modelling and phylogeography reveal range shifts of pawpaw, a North American understorey tree

Abstract

Aim Predictions of species' responses to accelerating global climate change require an understanding of historical range shifts. However, large‐scale phylogeographical studies of Eastern North American understorey plant taxa are relatively scarce. Here we employ ecological niche modelling and genetic analyses for inference of optimal pawpaw habitat in the past and future. Location In all, 26 states in the eastern United States. Taxon Asimina triloba (L.) Dunal (Annonaceae). Methods The present‐day niche of Asimina triloba was modelled in Maxent using seven bioclimatic variables, elevation and location data from field samples and herbarium specimens. To model historically optimal habitats, the present‐day model was projected onto rasters of seven bioclimatic variables and elevation representing the last glacial maximum (~22,000 years before present [YBP]) and the mid‐Holocene (~6,000 YBP). Predicted habitat suitability for 2070 was also modelled. Additionally, 62 populations were genotyped with nine nuclear microsatellite loci and statistically analysed. Levels and partitioning of genetic variation within and among populations were estimated within a geographical context. Results Models indicate that optimal habitat 22,000 YBP was severely restricted to mostly now‐submerged Gulf of Mexico and southeastern US coastlines. By 2070, models suggest that optimal habitat will expand substantially northward relative to the present. Species‐level genetic diversity (HE = 0.765) is high and genetic structure among populations is moderate (GST = 0.202). Structure indicates that there are two population clusters straddling the Appalachian Mountains. Main conclusions Models suggest that 22,000 YBP A. triloba was restricted to two major refugia in narrow bands of mostly now‐submerged habitat and possibly several small inland refugia. Molecular data are consistent suggesting that the eastern refugia expanded to give rise to the eastern cluster which is characterized by higher genetic diversity. The Gulf of Mexico refugium likely gave rise to populations in the western cluster, which is characterized by lower genetic diversity.

The role of anthropogenic dispersal in shaping the distribution and genetic composition of a widespread North American tree species

“…The two genetic clusters identified by S tructure analysis of all 82 populations are consistent with results for wild populations only (Wyatt et al., 2021 ), with clusters primarily located on either side of the Appalachian Mountains and separated by an east‐west phylogeographic discontinuity along the Tombigbee drainage in Alabama (Figure 2 ). However, some anthropogenic populations (e.g., FCP A , OSF A , SEL A , and SU1 A ) are located outside the geographic boundaries of their inferred genetic cluster, which is consistent with long‐distance human‐mediated dispersal.…”

“…Levels of admixture and K were also estimated separately for putative anthropogenic populations as a part of the present study and wild populations as reported by Wyatt et al (2021). Ten independent simulations at each K-value from 1 to 20 were run, using a burn-in of 500,000 repetitions and a run length of 1,000,000 Markov chain Monte Carlo (MCMC) iterations.…”

“…Summary statistics of A. triloba nuclear genetic diversity in 20 putative anthropogenic and 62 wild populations arranged in order of ascending latitude. Data for wild populations are fromWyatt et al (2021) …”

Interspecific Variance of Suitable Habitat Changes for Four Alpine Rhododendron Species under Climate Change: Implications for Their Reintroductions

“…This rapid change in temperature poses a great threat to alpine plant species and communities [5,6]. Therefore, understanding how alpine species spread to new habitats and how the geographical distribution range changes is crucial for predicting their response to global climate change and facilitating species conservation and reintroduction [7].…”

“…In particular, it requires only species presence data, can deal effectively with limited occurrence data and small sample sizes, and can use continuous and categorical environmental data as input variables. Numerous studies have predicted changes in animal and plant distributions in response to contemporary climate changes using the Maxent model [7,[16][17][18][19][20][21].…”