Morphometrics of two sympatric species of tree frogs in Korea: a morphological key for the critically endangeredHyla suweonensisin relation toH. japonica

Abstract

Although DNA taxonomy is readily available, morphological keys are still valuable for quick and easy identification of species on site. In Korea, Hyla japonica is widespread throughout the country, whereas Hyla suweonensis occurs in the lowlands of western central Korea. H. suweonensis is rapidly disappearing and was consequently designated as critically endangered by the Korean government. We measured 19 characters for male individuals of the two tree frog species to develop a morphological key for identification. Our morphometric analyses indicated that the two tree frog species differed significantly in means of all morphological characters. In general, H. suweonensis was smaller and more slender than H. japonica. Moreover, the distributions of five characters related to head width and the angle between eyes and ipsilateral nostrils did not overlap in the two species and may be used for species identification. Because the character differences between the two species are small, all five characters should be used together to reliably distinguish the two tree frog species. Besides being used as a morphological key, our result in size difference leads to several research questions about microhabitat niche selection and competition between the two Korean tree frog species.

Interference competition driven by hydric stress in Korean Hylids

“…It is so far unclear if the low sample size is the reason for the non-significance in distance to the edge of the submerged field between the two species, or if females move around to lay eggs in a random fashion to increase offspring survivorship, such as in Bibron's toadlet (Pseudophryne bibronii Günther, 1859; Byrne & Keogh, 2009). The outcome of the physical interaction may be the result of morphological differences between the two species as males D. japonicus are on average 5.22 % larger than males of D. suweonensis for snout-vent length (Borzée et al, 2013). Another explanation is that despite male-male physical confrontations being common in D. japonicus, this is the first such observation for D. suweonensis and the species may not express this behaviour.…”

Interspecific Variation in Seasonal Migration and Brumation Behavior in Two Closely Related Species of Treefrogs

“…The five sections used to distinguish between experiments are based on the seasonal succession of activities, from prehibernation to emergence from hibernation. We conducted all experiments with the agreement of the Ministry of Environment from the Republic of Korea under permit numbers 2013-16, 2014-04, 2014-08, 2014-20, 2015-3, 2015-4, 2015-6, 2015-28, and 2016-5. Dryophytes suweonensis is slender and smaller than D. japonicus (Borzée et al, 2013), and the earlier species is active earlier in the afternoon than the latter, although both species are principally active at night (Borzée et al, 2016b). Dryophytes japonicus is widespread on the Asian mainland until central Mongolia and the Baikal lake region in Russia (Dufresnes et al, 2016;Kuzmin et al, 2017) but the two species only co-occur on the western lowlands of the Korean Peninsula, where the distribution of D. suweonensis is restricted to agricultural wetlands due to widespread habitat modification (Roh et al, 2014;Borzée and Jang, 2015;Borzée et al, 2015aBorzée et al, , 2018aBorzée and Seliger, 2018).…”

“…We conducted the transects at the forest sites along a 250-m approximately straight line due to the topology of the field. Each hylid frog found was hand caught, and the species identified based on morphology (Borzée et al, 2013) when calls were not available (Park et al, 2013). We detected D. suweonensis during 20 surveys, and D. japonicus during 29 surveys.…”

Temporal and spatial differentiation in microhabitat use: Implications for reproductive isolation and ecological niche specification

“…Evolution of ecological specialization may arise to lessen competition over resource use (Graham et al 2004;Duré & Kehr 2001). Male H. suweonen-sis are on average 5% smaller (snout-vent length) than male H. japonica (Borzée et al 2013). This size difference, as well as the differentiation in microhabitat use, could be a resulting correlate of the different ecologies and niche requirements.…”

“…Almost everywhere male H. suweonensis are heard calling, male H. japonica are also producing advertisement calls. These 2 species are morphologically similar, albeit not identical (Borzée et al 2013), and exhibit a microhabitat differentiation for their calling location in rice paddies. H. suweonensis calls from the center of rice paddies while H. japonica calls from the edges, with an average separation of 8.14 m (Borzée et al 2013, unpubl.…”