Phylogeographic and population insights of the Asian common toad (Bufo gargarizans) in Korea and China: population isolation and expansions as response to the ice ages

Abstract

The effects of ice ages on speciation have been well documented for many European and North American taxa. In contrast, very few studies have addressed the consequences of such environmental and topographical changes in North East Asian species. More precisely, the Korean Peninsula offers a unique model to assess patterns and processes of speciation as it hosts the northern- and eastern-most distribution limit of some widespread Asian taxa. Despite this, studies addressing phylogeographic patterns and population genetics in the peninsula and surrounding countries are few and studies for most families are lacking. Here we inferred the phylogenetic relationships of the common toad (Bufo gargarizans) from South Korea and their North East Asian counterpart populations, based on mitochondrial data. Korean B. gargarizans GenBank BLASTs matched few individuals from nearby China, but the presence of a Korean clade suggests isolation on the Korean Peninsula, previous to the last glacial maximum, linked to sea level resurgence. Molecular clock calibrations within this group were used to date the divergence between clades and their relationship to paleo-climatic events in the area. Lack of genetic structure among South Korean populations and strong homogeneity between the Korean and some Chinese localities suggest weak isolation and recent expansion. Geographical projection of continuous coalescent maximum-clade-credibility trees shows an original Chinese expansion towards the Korean Peninsula through the Yellow Sea circa two million years ago with colonisation events dating circa 800 thousand years ago (K. y. a.). Following this colonisation, the data point to outgoing Korean Peninsula dispersal events throughout different periods, towards the North through land, and West through land bridge formations over the Yellow Sea during sea level falls. In accordance, demographic analyses revealed a population expansion in the Koran Peninsula circa 300 K. y. a., likely attributed to glacial cycle fluctuations.

Yellow sea mediated segregation between North East Asian Dryophytes species

“…; [40]). The same pattern is expected for species distributed across the Yellow sea, such as Bufo gargarizans [41] and Pelophylax nigromaculatus [42]. Other species are expected to have seen their range split during past fluctuations of the sea level, such as Pelophylax chosenicus and P. plancyi [43], and Dryophytes suweonensis and D. immaculatus [44][45][46][47], the focal species of this study.…”

Patterns of morphological variation in the Schlegel’s Japanese gecko (Gekko japonicus) across populations in China, Japan, and Korea

“…Both natural and artificial dispersals could have contributed to this pattern. Natural dispersal could have been facilitated by land connections among the countries during prehistoric glacial periods via three potential routes (via the Ryukyu Islands, around the Yellow Sea or rafting across the East China Sea, Kim et al 2007;Borzee et al 2017;Park et al 2017). Artificial dispersal could have been facilitated by the human shipping connections between cities in the Shandong Peninsula and east coasts of China and cities in Japan and Korea (Fogel 2000;Mitsuhashi et al 2005).…”

The Korean Baekdudaegan Mountains: A Glacial Refugium and a Biodiversity Hotspot That Needs to Be Conserved

“…Such value as a biodiversity reservoir seems to be directly related to the role of the BDDG as a Pleistocene refugium, as shown by recent phylogeographic and palaeoecological studies (plant species reviewed in Chung et al, 2017 ; for animals see Borzée et al, 2017 ; Lee et al, 2018 ). Chung et al ( 2017 ) critically reviewed the literature on genetic diversity and phylogeography of plants for which Korean populations were studied and found clear signals of the role of these mountains as a glacial refugium: [1] Korean populations showed higher intrapopulation genetic diversity than populations located further north (and, in some cases, with latitudinal decreases of genetic variation; i.e., consistent with the “southern richness” vs. “northern purity” paradigm of Quaternary biogeography; Hewitt, 2000 ; Hu et al, 2009 ); [2] Korean populations harbored ancestral haplotypes; and [3] Korean populations exhibited significant amounts of unique haplotypes/alleles (Chung et al, 2017 ).…”

“…Kim et al ( 2013 ) detected eight mitochondrial cytochrome b haplotypes from Korean populations (including some from the BDDG) of the raccoon dog Nyctereutes procyonoides , but only five from the Russian Far East. Borzée et al ( 2017 ) found more mitochondrial haplotypes from populations of the Asian common toad ( Bufo gargarizans ) in the BDDG and its vicinity compared to other lowland localities (mean number of haplotypes; 3.33 vs. 2.43). Similarly, Jo et al ( 2017 ), using five microsatellite loci, found that populations of the striped field mouse (Apodemus agrarius) on the BDDG and its vicinity harbor significantly higher levels of within-population genetic diversity than those from lower habitats (by excluding a population on Jeju Island; H e = 0.864 vs. 0.805, P = 0.017, Mann-Whitney U test).…”