Romer’s tree frog
Tadpoles are small. The length of the tail is approximately four times its width. The upper and lower fins are the same width and shorter than the width of the muscle at the base of the tail (Smith 1953).
Based on molecular data (Yang et al. 2015), the genus Liuixalus is comprised of six species: L. romeri (Smith1953), L. ocellatus (Liu et al. 1973), L. hainanus (Liu et al. 2004), L. calcarius (Milto et al. 2013), L. feii (Yang et al. 2015), and L. schiwandashan (Qin et al. 2015). Liuixalus romeri can be distinguished from congenerics based on a combination of traits (traits for L. romeri in parenthesis): when appressed to the body, the tibiotarsal articulation reaches between the anterior corner of the eye and snout in L. ocellatus, and over the tip of the snout in L. hainanus (tibiotarsal articulation reaches the nostril) (Liu et al., 1973; Liu et al., 2004); L. calcarius has an off-white belly and granular skin on the dorsal section of the limbs (darker color on the ventral side) (Milto et al., 2013); L. schiwandashan has prominent dermal fringes on the fingers (dermal fringe absent) (Qin et al., 2015).
Liuixalus romeri can be distinguished from its closest relative, L. feii, based on the following traits present in L. feii (traits for L. romeri in parenthesis; Yang et al. 2015): males have a small tympanum-to-snout-vent-length ratio of 0.056 (males have tympanum-to-snout-vent-length of 0.088); the snout is larger than the diameter of eye (snout shorter than eye diameter); adults lack webbing on fingers (weak webbing present between fingers III and V); small amount of webbing on toes (webbing covers one third of the toe’s length) (Yang et al. 2015). A main difference reported between L. romeri and L. feii is the larvae, L. romeri has a free larvae stage, whereas L. feii is assumed to be deposited in tree holes. However, according to the original description this behavior is not confirmed (Yang et al. 2015).
In life, L. romeri has a tan brown dorsum coloration, a dark brown line in between the eyes, dark coloration on the post tympanic fold, and brown spots around the lips (Smith 1953). This species has a distinctive “x” shape on the dorsum, the dark markings making the “x” extend from behind the eyes to the region in between the arms, where the lines forming the “x” do not always meet in the center (Karsen et al. 1986, Chan et al. 2005 Friends). The lines then extend throughout the dorsum towards the inguinal region, outlining an irregular chevron shape extending from the “x” cross intersection to the middle of the body (Karsen et al. 1986). The hind limbs have transverse, dark brown bars with an irregular pattern. The sides of the body and edges of forelimbs and hindlimbs have an irregular spotted pattern (Karsen et al. 1986, Chan et al. 2005 Friends). The ventral side of the holotype was described as cream with dark spots (Smith 1953). Ventral coloration of subsequent specimens has been described as a uniform white color (Karsen et al. 1986, Chan et al. 2005 Friends)
Tadpoles are brown and have a translucent tail with brown spots (Smith 1953).
Females are larger than the males, with females reaching up to 2.5 cm and males on average 1.5 cm (Chan et al. 2005 Friends). Males have white nuptial pads on fingers 1 and 2 and a single external subgular vocal sac (Banks et al. 2008). Some individuals have slightly larger webbing in between the toes (Smith 1953). The color intensity of the “x” shape on the dorsum is variable (Karsen et al. 1986; Chan et al. 2005 Friends).
Distribution and Habitat
Due to the construction of the Hong Kong International Airport on Chek Lap Kok, the population at Scenic Hill was relocated in 1992 to seven localities: Kadoorie Farm and Botanic Garden, Pat Sin Leng Country Park, Tai Po Kau Special Area, Tai Lam Country Park, Tsiu Hang Special Area, Hong Kong Zoological and Botanical Gardens, and Tai Tam (Lau 1998, Chan et al. 2005 Hong). This species prefers a microhabitat of leaf litter and understory vegetation, and can be found in habitats that include areas close to caves, woodlands, forest, and plantations (Lau 1998, Chan 2005 Friends, 2005 Hong).
Until 2005, all relocated populations survived, except for Tai Lam Country Park. Liuixalus romeri is considered an abundant species within the protected areas of Lantau Island and Tsiu Hang. Recent surveys (Michael W.N. Lau and Yik Hei Sung personal communication) did not find any individuals in three sites (Tai Lam Country Park and Kadoorie Farm and Botanic Garden and Hong Kong Zoological and Botanical Gardens), while three of the relocated populations are expanding (Pat Sin Leng Country, Tai Tam, and Tsiu Hang) (Lau personal communication). The population status in each of the relocation sites are regularly monitored and evaluated by the Agriculture, Fisheries and Conservation Department (AFCD) of the Hong Kong Government.
Life History, Abundance, Activity, and Special Behaviors
Romer’s tree frog is strictly nocturnal (Lau 1998).
Non-breeding individuals inhabit forest, plantations, and contact zones in between. The breeding season lasts from March to September, and breeding sites include forest and shrubland. This species prefers shaded areas with slow-flow water to breed, particularly places free of fish and with low nutrient content (Chan et al. 2005 Friends, 2005 Hong).
The male call is composed by short bursts of a high-pitched croak (cricket-like). Females deposit up to 120 eggs in small pools of water with plant debris, within stones or in vegetation (Chan et al. 2005 Friends, 2005 Hong).
Larvae complete metamorphosis in 4 – 6 weeks. Eggs and tadpoles are predated by fish and other frogs (Chan et al. 2005 Hong).
The frogs feed on small arthropods (e.g. termites) (Lau 1998).
Trends and Threats
Liuixalus romeri has an international IUCN Redlist status of “Endangered” because of habitat loss and destruction (Lau and Zhao 2004).
According to the Wildlife Protection Ordinance (Cap. 170), offenders will be subject to a fine up to HKD 100,000 (~ USD 12,500) for hunting, disturbing, keeping captive, selling, or exporting this species at any stage of development.
The construction of the Chek Lap Kok Airport threatened key core populations of this species. In 1991 – 1992 over 200 individuals (220 adults, 13 juveniles, 8 tadpoles, and 7 egg clutches) were rescued for captive breeding at the University of Hong Kong and Melbourne Zoo (Lau 1998, Banks et al. 2008). Captive breeding of these individuals produced 1,100 frogs and 1,600 tadpoles. In 1993 – 1994, approximately 90 individuals were released at each of the seven localities (see distribution section for details) (Lau 1998). The Herpetofauna Working Group of AFCD monitors the population status and the habitat of L. romeri, performing annual surveys during the breeding season since the translocations happened in 1994.
Eleutherodactylus planirostris have been introduced to Hong Kong since 2000 (Lee et al. 2016) and they are sympatric with L. romeri in a number of localities (e.g. Tai Tam, Tsiu Hang and Tung Chung). Given their similar size and microhabitat use, they may share a similar niche and potential interspecific competition may occur.
Possible reasons for amphibian decline
General habitat alteration and loss
Liuixalus romeri was originally described in the genus Philautus (Smith 1953). Philautus romeri was then placed in the genus Chirixalus due to its free larval stage (Bossuyt and Dubois 2001). In 2006, Frost et al. synonymized Chirixalus with Chiromantis due to the lack of evidence for the monophyly of Chirixalus. Finally, Li et al. (2008), using Bayesian methods on 12s and 16s mitochondrial markers, assigned the species to the genus Liuixalus, with the genus Liuixalus being the sister lineage to the remaining members of the family Racophoridae. Monophyly of Liuixalus has been confirmed in consequent molecular studies (Li et al. 2009, Li et al. 2013, Nguyen et al. 2014, Yang et al. 2015, Chan et al. 2018).
Based on molecular data, as of 2020, the genus Liuixalus is composed of six valid species distributed in southern China (including Hong Kong), Hainan, and Vietnam (Frost 2020): L. romeri (Smith 1953), L. ocellatus (Liu et al. 1973), L. hainanus (Liu et al. 2004), L. calcarius (Milto et al. 2013), L. feii (Yang et al. 2015), and L. schiwandashan (Li et al. 2015). Two additional species were described for the genus but were later invalidated using molecular markers: L. jinxiuensis (Qin et al. 2015) was synonymized with L. feii, and L. catbaensis (Nguyen et al. 2014) was synonymized with L. calcarius.
Li et al. (2009) estimated a phylogeny based on a mitochondrial fragment of 16s, 12s and t-val. Their hypothesis suggested L. romeri was most closely related to L. hainanus and L ocellatus. Yang et al. (2015) used Bayesian methods to analyze the dataset of the mitochondrial gene 16s and recovered L. romeri as the sister species to the clade comprised of L calcarius, L catbaensis, and L. feii. A multilocus phylogeny estimated for the family Racophoridae included eight species of Liuixalus (six valid and two synonymized species) (Chan et al. 2018). Based on two nuclear (Rag-1 and Tyrosinase) and two mitochondrial (16s and Cytochrome-b) genes, this study recovered L. romeri in the same clade as L. feii and L. jinxicenensis. The genetic divergence among those three species was low, and the results suggested L. romeri, L. feii, and L. jinxicenensis constitute a single species. However, the taxonomy for those three species is still unresolved. The clade including L. romeri, L. feii, and L. jinxicenensis was recovered as the sister lineage of a clade composed of two groups, one including L calcarius and L. catabaensis and one composed by L. ocellatus and L. shiwandashan.
The species was dedicated to Mr. J. D. Romer, who discovered the species living in a cave by the sea on Lamma Island, Hong Kong (Smith 1953).
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Wildlife Protection Ordinance, Cap. 170 (2012) https://www.elegislation.gov.hk/hk/cap170 Downloaded May 2020
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Written by Itzue W. Caviedes-Solis, Jonathan J. Fong, Yik Hei Sung (itzuecaviedessolis AT ln.edu.hk), Science Unit, Lingnan University
First submitted 2020-08-24
Edited by Ann T. Chang (2020-08-26)
Species Account Citation: AmphibiaWeb 2020 Liuixalus romeri: Romer’s tree frog <http://amphibiaweb.org/species/4450> University of California, Berkeley, CA, USA. Accessed Nov 25, 2020.
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Citation: AmphibiaWeb. 2020. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 25 Nov 2020.
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