Disentangling the Impacts of Speciation, Sympatry and the Island Effect on the Morphology of Seven Hynobius sp. Salamanders

Abstract

Closely related individuals from different areas can see their morphologies change based on differences between clades, but also ecological variables such as the island effect or sympatry. This is the case of salamanders, which have adapted to a broad range of ecological niches, ranging from underground dwellers in xeric landscape to tropical arboreal habitats. On the Korean Peninsula, salamanders from the Hynobius clade are widespread on the mainland and islands, with several partially sympatric clades and candidate species. Currently, seven lineages have been identified based on mtDNA, four of them matching named species and three others for which the species status remains untested. While the morphology of Korean Hynobius is known to be variable between genetically segregated clades, we hypothesise that (1) the candidate species are morphologically different, and that (2) the island effect and (3) the sympatric status have significant impacts on the morphology of individuals within the genus. Here we measured 329 Hynobius salamanders from all seven clades, in areas of sympatry and allopatry, and on islands and on the mainland (Graphical Abstract A). We determined that the island effect had a significant impact on the morphology of the genus, with mainland individuals generally displaying a broader range of morphology than islandic individuals (Graphical Abstract B). We also determined that sympatry had an impact on morphology, with the sizes of individuals from clades in sympatric areas diverging from each other (Graphical Abstract C). Finally, we demonstrated that all seven clades have significantly different morphologies, and we described the three candidate species that had already been isolated based on mtDNA and microsatellite data: Hynobius notialis sp. nov., Hynobius geojeensis sp. nov. and Hynobius perplicatus sp. nov. We conclude that looking at morphology alone would be misleading about the true diversity of Hynobius species, and species in general, because of the island and patry effects.

Potential Distribution of Amphibians with Different Habitat Characteristics in Response to Climate Change in South Korea

“…According to the Korean Society of Herpetologists, there are 20 amphibian species in South Korea ( , accessed on 20 July 2021), and three more Hynobius species were reported very recently [ 25 ]. Among those 23 amphibians, we obtained occurrence data from the 3rd Natural Ecosystem Survey ( Figure 3 ) [ 26 ], and a total of 18 amphibian species were identified [ 27 ].…”

Citizen science and roadkill trends in the Korean herpetofauna: The importance of spatially biased and unstandardized data

“…In this study, we used the list of Korean herpetofauna provided by the Korean Society of Herpetologists (http:// www.krsh.co.kr/html/sub0201.html) as a reference taxonomic framework. To this list we added the three recently described Hynobius species (Borzée and Min, 2021) and Bufo sachalinensis (reassigned from B. gargarizans for population on the Korean Peninsula; Othman et al, 2022), but we did not include the newly described Onychodactylus species (Borzée et al, 2022). However, the taxonomy used herein differs slightly from that used by iNaturalist.…”

“…For some species, there are clear biases stemming from the lack of sampling. For instance, H. leechii was the only Hynobius species detected by both the iNaturalist and literature datasets, even though there are seven species of Hynobius described in R Korea (Borzée and Min, 2021). H. leechii is the most common and widely distributed species of the genus in R Korea and it migrates across roads in large numbers during the breeding season (A Borzée, pers.…”

“…However, as only a few roadkills of this species were detected, the true magnitude of roadkill affecting this species is likely to be greatly underrepresented in the iNaturalist data. On the other hand, all seven species of Hynobius in R Korea form a clade of lentic breeders with similar ecologies (Borzée and Min, 2021). However, the other species of the genus less common than H. leechii have a relatively small distribution range and are found in more rural areas, which in combination with their secretive lifestyles and habitat characteristics might reduce the potential risk of roadkill and explain the lack of records.…”

“…Among the 23 amphibian species, 12 are endemic to the Korean Peninsula and one is invasive (the American Bullfrog, Lithobates catesbeianus). In addition, 11 species are either currently listed as nationally threatened or have been identified as threatened by previous studies (Borzée et al, 2020(Borzée et al, , 2022Borzée and Min, 2021), and two are listed as globally threatened (NIBR, 2019; https://www. iucnredlist.org/; accessed October 4, 2021).…”