A maximum likelihood approach to generate hypotheses on the evolution and historical biogeography in the Lower Volga Valley regions (southwest Russia)

Abstract

The evolution of the diverse flora in the Lower Volga Valley (LVV) (southwest Russia) is complex due to the composite geomorphology and tectonic history of the Caspian Sea and adjacent areas. In the absence of phylogenetic studies and temporal information, we implemented a maximum likelihood (ML) approach and stochastic character mapping reconstruction aiming at recovering historical signals from species occurrence data. A taxon-area matrix of 13 floristic areas and 1018 extant species was constructed and analyzed with RAxML and Mesquite. Additionally, we simulated scenarios with numbers of hypothetical extinct taxa from an unknown palaeoflora that occupied the areas before the dramatic transgression and regression events that have occurred from the Pleistocene to the present day. The flora occurring strictly along the river valley and delta appear to be younger than that of adjacent steppes and desert-like regions, regardless of the chronology of transgression and regression events that led to the geomorphological formation of the LVV. This result is also supported when hypothetical extinct taxa are included in the analyses. The history of each species was inferred by using a stochastic character mapping reconstruction method as implemented in Mesquite. Individual histories appear to be independent from one another and have been shaped by repeated dispersal and extinction events. These reconstructions provide testable hypotheses for more in-depth investigations of their population structure and dynamics.

Invasive plant distributions recapitulate patterns found in native plant assemblages in a heterogeneous landscape

“…We investigated the southern part of the Volga River, which encompasses 11 distinct local floristic areas forming the strictly defined LVV (reviewed in Mavrodiev et al 2012;Fig. 1; see Table 1 for floristic areas size and other summary statistics).…”

“…A1) includes all putative alien plants, naturalized plants, invasive plants, weeds, and transformers (Richardson et al 2000). The matrix of 1006 presumably native species with distributions within 11 floristic regions was modified from (Mavrodiev et al 2012).…”

“…The Astrakhan region of Russia comprises the most southern part of the Volga River with 11 floristic areas forming the strictly defined Valley of Volga (LVV) (reviewed in Mavrodiev et al 2012) and also two floristic areas that include Mountain Bolshoe Bogdo and Lake Baskunchak (reviewed in Mavrodiev et al 2012). The LVV is a 500 km long valley ending in the delta of the Volga River in the Caspian Sea (e. g., Mavrodiev et al 2012). Within strictly defined LVV, which is the subject of our primary interest, the native plant communities date back approximately 10,000 years to the period when the Caspian Sea last receded (Dumont 1998).…”

On biodiversity and conservation of the Iris hexagona complex (Phaeiris, Iridaceae)

“…Modern phylogenetic methods, especially molecular approaches, have made it possible to identify many cryptic, unrecognized, or simply forgotten taxonomic entities (e.g., Mavrodiev et al 2012 a , b , c , 2013, 2014, 2015 a , Yurtseva et al 2016 a , b , among others), some of which are potentially in need of conservation attention. Such new analyses have also provided new information on the prevalence of previously unrecognized areas of endemism (Mavrodiev et al 2012 a , b ) as well as on the importance of environmental variables that may be fully congruent with the observed biodiversity (Mavrodiev et al 2015 b ). In this context, the challenging of traditional taxonomic circumscriptions suspected to contain hidden taxa can also be an important tool for both ecologists and conservation biologists, especially when linked with actual or potential biodiversity hot spots (e.g., Mavrodiev et al 2012 a , b , Sokoloff et al 2019, see also Liu et al 2019).…”

“…Such new analyses have also provided new information on the prevalence of previously unrecognized areas of endemism (Mavrodiev et al 2012 a , b ) as well as on the importance of environmental variables that may be fully congruent with the observed biodiversity (Mavrodiev et al 2015 b ). In this context, the challenging of traditional taxonomic circumscriptions suspected to contain hidden taxa can also be an important tool for both ecologists and conservation biologists, especially when linked with actual or potential biodiversity hot spots (e.g., Mavrodiev et al 2012 a , b , Sokoloff et al 2019, see also Liu et al 2019).…”