Genetic diversity and demography of Bufo japonicus and B. torrenticola (Amphibia: Anura: Bufonidae) influenced by the Quaternary climate

Abstract

The Quaternary climate affected the present species richness and geographic distribution patterns of amphibians by limiting their activities during the glacial period. The present study examined the phylogenetic relationships of Japanese toads (Bufo japonicus and B. torrenticola) and the demography of each lineage from the past to the present based on mitochondrial sequences and ecological niche models. Japanese toads are a monophyletic group with two main clades (clades A and B). Clade A represents B. j. formosus, including three clades (clades A1, A2, and A3). Clade B contains three clades, two of which corresponded to B. j. japonicus (clades B1 and B2) and the other to B. torrenticola. Clade B2 and B. torrenticola made a sister group, and, thus, B. j. japonicus is paraphyletic. Clades A and B diverged in the late Miocene 5.7 million years ago (Mya) during the period when the Japanese archipelago was constructed. The earliest divergence between the three clades of clade A was estimated at 1.8 Mya. Clades A1 and A2 may have diverged at 0.8 Mya, resulting from the isolation in the multiple different refugia; however, the effects of the glacial climate on the divergence events of clade A3 are unclear. Divergences within clade B occurred from the late Pliocene to the early Pleistocene (3.2–2.2 Mya). Niche similarity between the parapatric clade in clade B (clades B1 and B2) indicated their allopatric divergence. It was suggested that niche segregation between B. japonicus and B. torrenticola contributed to a rapid adaptation of B. torrenticola for lotic breeding. All clade of Japanese toads retreated to each refugium at a low elevation in the glacial period, and effective population sizes increased to construct the current populations after the Last Glacial Maximum. Furthermore, we highlight the areas of climate stability from the last glacial maximum to the present that have served as the refugia of Japanese toads and, thus, affected their present distribution patterns.

Larval Body Shape and Eye Size Variation in Japanese Toads (Anura: Bufonidae: Bufo): An Ecological Implication for Lentic and Lotic Habitats

“…In addition, the eye–body allometries of B. torrenticola and B. j. japonicus showed the same growth pattern, i.e., positive growth, while that of B. j. formosus showed a different type of growth, i.e., isometric growth. This difference may reflect the phylogenetic relationships of these toads: ([ B. j. japonicus and B. torrenticola ], B. j. formosus ) (Fukutani et al, 2022). However, there are few studies about the difference of the eye-body allometry in Bufo .…”

“…In contrast, B. torrenticola breeds in running (lotic) water, such as mountainous streams (Matsui, 1975, 1976). In mitochondrial sequences and an ecological niche model, B. torrenticola forms a monophyletic clade with B. j. japonicus and B. j. formosus , and B. torrenticola has been suggested to have changed the morphology drastically in this lotic breeding habitat (Fukutani et al, 2022). This drastic change produces unique stream-adapted morphology in B. torrenticola.…”

“…Thus, breeding habitat shift, from lentic to lotic, causes differentiation in larval ecology, and finally might affect the eye position and size in tadpoles. In order to test this hypothesis, some species of Bufo from Japan, lotic-breeding B. torrenticola and lentic-breeding B. japonicus japonicus and B. j. formosus , are ideal taxa because they form a monophyletic group and the lotic-breeding B. torrenticola is known to have been derived from lentic-breeding B. j. japonicus (Fukutani et al, 2022).…”

Phylogeography of the Miyako Toad, Bufo gargarizans miyakonis (Anura: Bufonidae), Inferred from Mitochondrial Sequence Data

“…A previous morphological analysis suggested that B. g. miyakonis was closely related to a continental population around Shanghai (Matsui, 1984). Several subsequent molecular studies have confirmed that B. g. miyakonis is a member of the B. gargarizans species group (allozyme: Nishioka et al, 1990; mitochondrial (mt) DNA: Igawa et al, 2006, Hase et al, 2012, Fukutani et al, 2022: in these studies, a few samples of the B. gargarizans species group, including B. g. miyakonis , were analyzed as out groups of B. japonicus species group). Igawa et al (2006) estimated that the divergence time between the Miyako population and its close relative, the Beijing lineage, was approximately 0.9 Ma.…”

“…Location names denoted by dots with numerals are further described in Appendix I. Nishioka et al, 1990;mitochondrial (mt) DNA: Igawa et al, 2006, Hase et al, 2012, Fukutani et al, 2022 in these studies, a few samples of the B. gargarizans species group, including B. g. miyakonis, were analyzed as out groups of B. japonicus species group). Igawa et al (2006) estimated that the divergence time between the Miyako population and its close relative, the Beijing lineage, was approximately 0.9 Ma.…”