Herpetological Conservation and Biology 16(2):259–270. Submitted: 16 May 2020; Accepted 7 April 2021: Published: 31 August 2021. POTENTIAL EFFECTS OF DAMS IN THE GEOGRAPHIC RANGE EXPANSION OF HYLID FROGS ASSOCIATED WITH AQUATIC MACROPHYTES PABLO J. TORRES1, JUAN M. BOERIS1, JUAN A. INSAURRALDE2, DIEGO BALDO1, 1,3 AND ANDRÉS E. BRUNETTI 1Laboratorio de Genética Evolutiva “Claudio Juan Bidau,” Instituto de Biología Subtropical (IBS, UNaM-CONICET), Félix de Azara 1552, Posadas, 3300, Misiones, Argentina 2Instituto de Biología Subtropical (IBS, UNaM-CONICET), Bertoni 85, Puerto Iguazú, 3370, Misiones, Argentina 3Corresponding author: [email protected] Abstract.—The Fluorescent Frog (Boana punctata) and the Uruguay Harlequin Frog (Lysapsus limellum) are two hylid species found in seasonal swamps and along large rivers in South America. Despite their wide distribution in the Amazon and Paraná River basins, they had never been recorded along the margins of the more than 340 km of the Paraná River in the provinces of Misiones, Itapúa, and Alto Paraná in Argentina and Paraguay. Comparisons of historical and recent satellite images and analyses of the Paraná River structure indicate that the lake formed after the construction of the Yacyretá Dam (140,000-160,000 ha), which has made novel lentic and semi-lentic environments in the tributary streams identified as large inlets, bays, and lagoons. These transformations favored permanent settlement of aquatic macrophytes, mainly Water Hyacinth (Eichhornia crassipes) and floating ferns (Salvinia sp.), which are the characteristic habitat of L. limellum and B. punctata. Because of these changes, we conducted surveys by boat and from shore to determine whether these frog species colonized the novel environments. We found L. limellum and B. punctata at several localities on the margins of Paraná River within the boundaries of the Yacyretá Lake. Because all observations of both species were at sites with abundant macrophytes, and because neither of them were found in field surveys we conducted before 2011 (i.e., when the Yacyretá Lake filled to maximum capacity), our results support the hypothesis that the new records are related to the artificial wetlands created after the construction of the Yacyretá Dam. Key Words.—amphibians; aquatic plants; Boana punctata; habitat loss riverine; Lysapsus limellum; Misiones; tree frogs; Yacyretá Dam INTRODUCTION mainly to produce hydropower (Bonetto et al. 1989; Agostinho et al. 1994). The Yacyretá Dam is the second Aquatic macrophytes are essential components of largest dam on the Paraná River and was constructed riverine ecosystems (Wetzel 2001) and provide habitat between Argentina and Paraguay (27°28′58.01″ S, to a rich micro- and macroinvertebrate fauna (Collins 56°44′8.99″ W). In 2011, the reservoir of Yacyretá and Williner 2006; Battauz et al. 2017). Because reached its maximum height (83 m above sea level), annual fluctuations of the hydrometric levels of large creating an artificial lake of 140,000-160,000 ha (Fulco rivers displace extensive beds of macrophytes (Battauz 2011; Brites and Catullo 2016). When Yacyretá Lake et al. 2017), suppression of flood pulses by dam filled, the water from the main reservoir inundated large construction has profound effects on the distribution of sections of tributaries that drain into the river (Fontana and this type of vegetation (Finer and Jenkins 2012). One Iriarte 2016; Fulco 2011), creating inlets or bays. These of the main effects of reservoirs upstream of dams is the inlets have spatial and seasonal characteristics such as transformation of lotic ecosystems into lentic or semi- shallow waters, increased nutrient input, protection from lentic environments that changes the biotic composition wind, and higher sedimentation rates that create favorable and the viability of populations of many riverine species environments for the colonization and settlement of (Bunn and Arthington 2002; Agostinho et al. 2008). aquatic macrophytes (Thomaz et al. 1999). Although the The Paraná River is the main river within del Plata effect of habitat modification on fish fauna was assessed Basin, the second largest in South America. It has an in reservoirs from the Upper Paraná section (Benedicto- annual discharge of 500 million m3, with peak flows of Cecilio et al. 1997; Agostinho et al. 1994, 2008), no 65,000 m3s-1, extensive fertile lands, and is one of the research has examined the impact of habitat alteration as most important rivers in the world (Bonetto et al. 1989). a consequence of dam construction in the Paraná River on Besides these natural characteristics, the Paraná River is amphibian diversity. the most intensively dammed river of South America, Several Neotropical hylid frogs (Anura: Hylidae: particularly in the Upper and High sections, which serve Hylinae) live near or by the margins of large rivers Copyright © 2021. Pablo J. Torres 259 All Rights Reserved. Torres et al.—Potential effects of dams in the range expansion of amphibians. (particularly in floodplains and slow-flowing river as potential habitats for the establishment of B. punctata channels), where they are strongly associated with and L. limellum. For the temporal variable, we compiled aquatic macrophytes such as Water Hyacinth (Eichhornia a list of geo-referenced locality records for both species crassipes), Horsetail Paspalum (Paspalum repens), and in the Paraná River Basin based on published literature Floating Primrose-Willow (Ludwigia peploides; Hödl (Brusquetti and Lavilla 2006; Weiler et al. 2013), 1977; Manzano et al. 2004). Some of these frogs possess available biodiversity databases (Global Biodiversity morphological adaptations for living in water, such as a Information Facility. 2020. Available from https://doi. paddle-like autopodium (species of the tribe Pseudini; org/10.15468/dl.5ffqhq [Accessed 07 May 2020]), and Goldberg and Fabrezi 2008). The reproductive activities information from the Herpetological Collection of the of the species living in these environments are tightly Laboratorio de Genética Evolutiva (LGE). Reports associated with aquatic macrophytes and vary in relation covered a wide span including the period before Yacyretá to the class and height of the vegetation used (Hödl Dam creation in 1998 (about 1900–1998), the period 1977; Prado et al. 2005; Brunetti et al. 2014, 2015). For from creation till the Yacyretá lake reached its maximum instance, males of the Uruguay Harlequin Frog (Lysapsus height in 2011, and the period from 2011 till present. We limellum) use plants that lie flat on the water surface like considered observations at sites surveyed by members of species of floating ferns (Salvinia sp.) and Water Cabbage our laboratory before 2011 as pre-maximum height data. (Pistia stratiotes; Hödl 1977). In contrast, the Fluorescent We located these on maps using satellite images from Frog (Boana punctata) uses plants with vertical structure the years 1990, 2005 and 2020, and applied identifying like E. crassipes; males emit territorial calls at heights of water indices according to McFeeters et al. (1996) and approximately 40–70 cm or perform complex courtship two vegetation indices, Green Chlorophyll Index and behaviors at the water surface level (Brunetti et al. 2014). Normalized Difference Vegetation Index (Ahamed et Boana punctata and L. limellum are common hylid al. 2011; Hunt et al. 2011). We processed the satellite frogs with a wide distribution in South America. In images with the Google Earth Engine platform using the Argentina, both species have a high degree of sympatry in Landsat 5 and 8 image collections (Gorelick et al. 2017). the provinces of Chaco, Formosa, Corrientes, Entre Ríos, We examined satellite images for 2019 (Google Earth and Santa Fe along the Paraná and Paraguay Rivers (Vaira Pro v.7.3.2.5776) to account for spatial variation and et al. 2012). Despite their common occurrence, they categorize the habitats likely having macrophytes along were never reported in the more than 340 km of Paraná the shores of the High Section of the Paraná River for River in the provinces of Misiones, likely because the approximately 340 km in the province of Misiones, river structure was characterized by a single and narrow Argentina. Because aquatic macrophytes represent the channel (Peso et al. 2013), which lacked the suitable lentic characteristic habitat of B. punctata and L. limellum, we habitat conditions for these species (Hödl 1977; Manzano identified four habitats, small inlets, large inlets, bays, and et al. 2004). Here, we analyze the alterations on the lagoons, where this type of vegetation likely accumulates shape and structure of the Paraná River generated by the within the boundaries of the Yacyretá Lake, as follows. construction of the Yacyretá upstream of the boundaries of Inlets formed when lower parts of the tributaries draining the Yacyretá Lake aiming to (1) investigate the presence into the Paraná River were flooded. In satellite images, of B. punctata and L. limellum, (2) compare these they are distinguishable by a narrow channel, which presence/absence data with our amphibian surveys before connects the tributaries to the reservoir, and by a wetted 2011 (i.e., prior to the lake filling to maximum capacity), width that is permanently inundated. We categorized and (3) connect the presence of these hylid frogs to the these inlets as large when the length was ≥ 3 km, or small altered structure of the Paraná River and the diversity and when it was ≥ 500 m and < 3 km (measured with Google abundance of aquatic macrophytes. We predict that the Earth Pro v.7.3.2.5776; Fig. 3). Bays are similar to inlets novel lentic environments created by damming the river but connect to the river by a wide mouth (i.e., width > generated habitats that became occupied by amphibian 2 km length), and in most cases, not related to seasonal species typical of these environments, which were not rains that flood tributaries (Fig. 3). Lagoons are flooded previously registered at this high section of the Paraná areas where the long axis parallels the flow direction of River.