Speciation along a latitudinal gradient: The origin of the Neotropical cycad sister pair Dioon sonorense–D. vovidesii (Zamiaceae)

Abstract

Latitude is correlated with environmental components that determine the distribution of biodiversity. In combination with geographic factors, latitude‐associated environmental variables are expected to influence speciation, but empirical evidence on how those factors interplay is scarce. We evaluated the genetic and environmental variation among populations in the pair of sister species Dioon sonorense–D. vovidesii , two cycads distributed along a latitudinal environmental gradient in northwestern Mexico, to reveal their demographic histories and the environmental factors involved in their divergence. Using genome‐wide loci data, we determined the species delimitation, estimated the gene flow, and compared multiple demographic scenarios of divergence. Also, we estimated the variation of climatic variables among populations and used ecological niche models to test niche overlap between species. The effect of geographic and environmental variables on the genetic variation among populations was evaluated using linear models. Our results suggest the existence of a widespread ancestral population that split into the two species ~829 ky ago. The geographic delimitation along the environmental gradient occurs in the absence of major geographic barriers, near the 28th parallel north, where a zonation of environmental seasonality exists. The northern species, D. vovidesii , occurs in more seasonal environments but retains the same niche of the southern species, D. sonorense . The genetic variation throughout populations cannot be solely explained by stochastic processes; the latitudinal‐associated seasonality has been an additive factor that strengthened the species divergence. This study represents an example of how speciation can be achieved by the effect of the latitude‐associated factors on the genetic divergence among populations.

Phenology of Zamia boliviana (Zamiaceae), a threatened species from a seasonally dry biodiversity hotspot in South America

“…The reproductive events of Z. boliviana were seasonal, with sex‐to‐sex synchrony in terms of strobili production, peak intensity, and activity, and subsequent dehiscence of seeds coincided with the dry season. The reproductive success of this cycad undoubtedly depends on reproductive synchrony, in addition to other biotic and abiotic factors (e.g., number of reproductive adults, pollen availability, effective pollination, seed dispersal, adaptation to seasonal niches) (Gutiérrez‐Ortega et al, 2021; Mora et al, 2013; Morellato, 2004; Octavio‐Aguilar, Iglesias‐Andreu, et al, 2017; Pérez‐Farrera & Vovides, 2004; Velasco García et al, 2016). Overall, our study not only allows the acquisition of basic information but is also a contribution to the knowledge of cycads and Zamia spp.…”

Ceratozamia aurantiaca (Zamiaceae): A New Cycad Species from the Northern Rainforests of Oaxaca, Mexico

“…These patterns of distribution suggest that the Ceratozamia species are products of geographic isolation leading to allopatric speciation, as has been demonstrated in another cycad species in this geographic area [14]. After gaining geographic isolation, cycads seem to be prone to experience local adaptation through the retention/acquisition of anatomical features [8,15] and stochastic, demographic processes [14,16]. Ceratozamia aurantiaca is likely to have originated through similar evolutionary processes.…”

Evolutionary and ecological trends in the Neotropical cycad genus Dioon (Zamiaceae): An example of success of evolutionary stasis

“…The Edule, Purpusii, and Tomasellii clades diversified around during the Miocene. However, this model estimated that the median values for the species pairs occurred from the late Miocene, being earlier than estimated when using approximate Bayesian computation (ABC) (a coalescent-based method) in two previous studies (Gutiérrez-Ortega et al, 2020;Gutiérrez-Ortega, Molina-Freaner, et al, 2021). In D. merolae and D. salas-moralesiae (labeled as D. merolae-WestB in Gutiérrez-Ortega et al, 2020) were estimated to diverge 3.15 Ma (HPD 95% 1.55-5.62), whereas the estimate obtained in this article was 7.11 Ma (HPD 95% 2.83-9.65).…”

“…However, disparate local environmental pressures may allow species to shift/drift toward distinct ecological tolerances over time, at macroevolutionary scale. Clarifying such trends among closely related species can contribute to clarify the factors shaping the evolution of Dioon throughout its wide distribution range, but unfortunately, studies applying ENMs in Dioon are almost non-existent (only in Gutiérrez-Ortega et al, 2020;Gutiérrez-Ortega, Molina-Freaner, et al, 2021;Rubio-Méndez et al, 2020), and are very limited in cycad research in general (only in Bamigboye & Tshisikhawe, 2022;Carvajal-Hern andez et al, 2020;Gutiérrez-Ortega, Pérez-Farrera, Lopez, & Vovides, 2023;Gutiérrez-Ortega, Pérez-Farrera, Matsuo, et al, 2023;Laidlaw & Forster, 2012;Martínez-Domínguez et al, 2021;Mudannayake et al, 2019;Pradhan & Chettri, 2017;Swart et al, 2018). Here, we aim to fill that knowledge gap by following a common method, as we describe below, to construct ENMs by using geographic coordinates of localities where Dioon populations occur and environmental data obtained from geographic information systems.…”

“…Among the three genera in Mexico ( Zamia , Ceratozamia , and Dioon ), D. tomasellii , D. sonorense , and D. vovidesii are the only cycad species that reached northwestern Mexico (Vovides et al, 2003), which might suggest that Dioon was able to disperse earlier than other cycad genera in Mexico, or that it was the only cycad genus able to adapt to the seasonally dry forests and highly seasonal oak forests and xeric scrublands from western Mexico during its northward dispersal. In a recent study on the northernmost species pair D. sonorense – D. vovidesii , it was found that the temperature seasonality associated to the latitudinal gradient seems to be an important factor determining the genetic differentiation among populations (Gutiérrez‐Ortega, Molina‐Freaner, et al, 2021).…”