Effects of Salinity and Density on Tadpoles of Two

Effects of Salinity and Density on Tadpoles of Two Anurans from the Río Salado, Puebla, Mexico Author(s): Guillermo A. Woolrich-Piña, Geoffrey R. Smith, and Julio A. Lemos-Espinal Source: Journal of Herpetology, 49(1):17-22. Published By: The Society for the Study of Amphibians and Reptiles URL: http://www.bioone.org/doi/full/10.1670/13-127

BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder.

BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research.

Journal of Herpetology, Vol. 49, No. 1, 17–22, 2015 Copyright 2015 Society for the Study of Amphibians and Reptiles

Effects of Salinity and Density on Tadpoles of Two Anurans from the Rıó Salado, Puebla, Mexico GUILLERMO A. WOOLRICH-PINÃ,1,2 GEOFFREY R. SMITH,3

AND JULIO

A. LEMOS-ESPINAL4,5

1

IPN ESIA Ticomań ‘‘Ciencias de la Tierra,’’ Laboratorio de Paleontologıá y Geobiologıá, Av. Ticomań #600, Col. San Jose´ Ticomań, Del. Gustavo A. Madero, Me´xico Districto Federal, Mexico 2 ´ Bolı´var, Av. Rıó Mixcoac No.48, Col. Insurgentes Mixcoac, Del. Benito Jua´rez, Me´xico D.F. C.P. 03920 Universidad Simon 3 Department of Biology, Denison University, Granville, Ohio 43023 USA 4 ´ Laboratorio de Ecologıá, UBIPRO, FES Iztacala, Universidad Nacional Autonoma de Me´xico, Av. De los Barrios #1, Col. Los Reyes Iztacala, Tlalnepantla, Estado de Me´xico, Me´xico

ABSTRACT.—Numerous studies have explored environmental factors that drive the distributions of anuran larvae. However, the causal links between physical or chemical factors and tadpole distributions often remain untested. The Rıó Salado is an intermittent, naturally saline river in Puebla, Mexico, that is increasingly being impacted by removal of water for commercial salt production. Using tadpoles of Exerodonta xera (Hylidae; Puebla Treefrog) and Incilius occidentalis (Bufonidae; Pine Toad), we experimentally examined the hypothesis that the distribution of tadpoles along the Rıó Salado results from the effects of salinity on tadpole survivorship, growth, and metamorphosis. We also examined the effect of tadpole density and the interaction of tadpole density and salinity, because pool size likely affects tadpole density. Increased salinity did not affect survivorship in I. occidentalis but reduced survivorship in E. xera by approximately 20% at both 0.4 parts per thousand (ppt) (0.4 g L-1) and 0.8 ppt (0.8 g L-1). Higher salinities delayed metamorphosis by up to 9 wk in E. xera and by 3 or 4 d in I. occidentalis. Tadpole density had a nonlinear effect on survivorship in E. xera, and higher densities delayed metamorphosis in I. occidentalis. There were no significant interactions between salinity and tadpole density in either species. Our results suggest that even though they can be found in pools averaging 0.8 ppt, tadpoles may not emerge from such pools because of delayed metamorphosis at salinities around 0.8 ppt. Decreasing pool volume and increasing tadpole density may further delay emergence of I. occidentalis. The removal of water from the Rıó Salado to produce salt may threaten amphibians that use the river for breeding. ´ de renacuajos; sin embargo, los RESUMEN.—Numerosos estudios han examinado los factores ambientales que influyen en la distribucion ´ de renacuajos frecuentemente permanecen sin probarse. El Rıó Salado es un rıó vıńculos entre factores fı´sicos o quı´micos y la distribucion ´ de agua para la produccion ´ comercial de sal. Utilizando salino localizado en Puebla, Me´xico que esta´ siendo muy impactado por la extraccion ´ ´ de los renacuajos a lo renacuajos de Exerodonta xera e Incilius occidentalis, experimentalmente examinamos la hipotesis que la distribucion largo del Rıó Salado es el resultado de los efectos de la salinidad sobre la sobrevivencia, crecimiento y metamorfosis de los renacuajos. Tambień ´ de la densidad de renacuajos y la salinidad, ya que el tamanõ de las pozas examinamos el efecto de la densidad de renacuajo y la interaccion probablemente afecta la densidad de los renacuajos. El incremento de la salinidad no afecto la supervivencia de I. occidentalis pero redujo la sobrevivencia de E. xera en aproximadamente 20% tanto en tratamientos de 0.4 como de 0.8 partes por mil (ppm). Salinidades ma´s altas retrasaron la metamorfosis hasta por nueve semanas en E. xera y por tres o cuatro dıás en I. occidentalis. La densidad de renacuajos tuvo un efecto no lineal sobre la supervivencia en E. xera y las densidades ma´s altas retrasaron la metamorfosis en I. occidentalis. No hubo interacciones significativas entre la salinidad y densidad de renacuajos en ninguna de las dos especies. Nuestros resultados sugieren que aunque estas especies pueden ocupar pozas con un promedio de 0.8 ppm, los renacuajos podrıán no salir de estas pozas que se estań secando debido al retraso en la metamorfosis en salinidades de alrededor 0.8 ppm. Disminuyendo el volumen de las pozas e incrementando la densidad de los ´ de renacuajos de I. occidentalis. La extraccion ´ de agua del Rıó Salado para producir sal puede renacuajos puede retrasar la transformacion amenazar la habilidad de los anfibios que utilizan el Rıó Salado para reproducirse.

Numerous studies have examined environmental factors that drive distributions of anuran larvae, both within and among bodies of water (e.g., ponds, lakes, rivers). For example, the presence or absence of fish can explain the distribution of several species of tadpoles, with many species being absent in the presence of fish (Porej and Hetherington, 2005; McGarvie Hirner and Cox, 2007; Hamer and Parris, 2011). Other studies have found that physical or chemical factors can also influence the distribution of tadpoles (Welch and MacMahon, 2005; Girish and Krishnamurthy, 2009; Woolrich-Pinã et al., 2010a), including salinity, a factor that is often negatively correlated with the presence of amphibians (Smith et al., 2007; Collins and Russell, 2009; Woolrich-Pinã et al., 2010a, 2011). Salinity is of particular concern for amphibians, and other freshwater organisms, because in many regions of the world, freshwater habitats are becoming increasingly saline. In northern temperate regions, salinization occurs as a function of the use of road-deicing salts (Godwin et al., 2003; Thunqvist, 5

Corresponding Author. E-mail: [email protected]

DOI: 10.1670/13-127

2004; Ramakrishna and Viraraghavan, 2005). In warmer and more arid regions, salinization is increasing because of increased use of groundwater by humans (e.g., irrigation) that draw down aquifers causing saltwater intrusion (Williams, 1987, 2001; Cardona et al., 2004). In Mexico, salinization is threatening some rivers in arid and semiarid regions (Contreras-B. and Lozano-V., 1994). Furthermore, elevated salinity has been shown to affect the behavior, activity, and demography of a variety of amphibians negatively (Sanzo and Hecnar, 2006; Squires et al., 2008; Denoel¨ et al., 2010) along with their growth (Wu and Kam, 2009; Squires et al., 2010), development (Sanzo and Hecner, 2006; Wu and Kam, 2009), and survivorship (Dougherty and Smith, 2006; Karraker et al. 2008, 2010; Brown and Walls, 2013; Hua and Pierce, 2013). We have studied the distribution of tadpoles along the Rıó Salado, an intermittent river in Puebla, Mexico. Salinities in the Rıó Salado gradually increase from 0.5 parts per thousand (ppt) (0.5 g L-1) in the vicinity of Zapotitlań Salinas to 6.2 ppt (6.2 g L-1) near San Gabriel Chilac because of accumulation of salts from the rocks through which the river flows (Woolrich-Pinã, 2010). This last concentration is much greater than those found

˜ A ET AL. G. A. WOOLRICH-PIN

18

in regions of the river occupied by tadpoles of Incilius (formerly Bufo) occidentalis (Camerano, 1879) (Barbosa-Morales, 2008, Aquino-Caballero, 2010; Pine Toad), Exerodonta (formerly Hyla) xera (Mendelson and Campbell, 1994) (Hernańdez-Rıós, 2010; Puebla Treefrog), Hyla arenicolor (Woolrich-Pinã et al., 2011; Canyon Treefrog), and Lithobates spectabilis (Woolrich-Pinã, pers. obs.; Showy Leopard Frog). Our field observations demonstrated significant relationships between the distribution of tadpoles and various physical and chemical parameters among pools along the Rıó Salado. The distribution of I. occidentalis tadpoles is influenced by pool size and volume, distance from the main river channel, dissolved oxygen, salinity, and vegetative cover (Woolrich-Pinã et al., 2010a). The distribution of E. xera tadpoles is related to salinity, dissolved oxygen, and pool volume (Woolrich-Pinã et al., pers. obs.). However, causal links between physical or chemical factors and tadpole distribution remain untested. Using E. xera and I. occidentalis tadpoles, we experimentally examined the hypothesis that their distribution along the Rıó Salado is limited by the effects of salinity on tadpole survivorship, growth, and metamorphosis. We were particularly interested in salinity because, in addition to being naturally saline, the Rıó Salado is increasingly being impacted by human activities. In particular, water is removed from the Rıó Salado by ‘‘salineras’’ that extract salt from river water via evaporation. Removing water from the Rıó Salado for ‘‘salineras’’ decreases the volume of water flowing in the river and thus reduces the volume of water in pools, affecting hydroperiod and potentially influencing salinity. For instance, removal of water from rivers for irrigation or other uses can increase salinity (Williams, 2001). Indeed, size and depth of pools found along the Rıó Salado can vary significantly across the year, with mean depths of persisting pools dropping to approximately 10 cm at the end of the summer (Woolrich-Pinã et al., 2010a,b). We predicted that both species would be negatively affected by increasing salinity. MATERIALS

AND

METHODS

Study Species.—Exerodonta xera is endemic to the Valle de Tehuacań where it typically breeds in temporary streams during July and August (Woolrich-Pinã et al., 2005). In Puebla, I. occidentalis typically occurs in pine forest and dry tropical ´ deciduous forests (Oliver-Lopez et al., 2000). Incilius occidentalis in the Valle de Zapotitlań Salinas breeds during the rainy season (November–February) in pools and slow-moving water in rivers ´ or in pools along rivers (Oliver-Lopez et al., 2000; Smith and Lemos-Espinal, 2010). Methods.—We collected tadpoles of each species used in this experiment from pools in the main channel of the Rıó Salado shortly after hatching and transported them back to the laboratory (collection localities for I. occidentalis were Rıó Salado, near to Jardin Botańico, 18819 0 25.4 00 N, 97828 0 37.4 00 W, 1,460 m; and for E. xera were near Tilapa, 18816 0 22.6 00 N, 97829 0 14.2 00 W, 1,620 m). Salinity in pools where we collected the tadpoles was 0.1 ppt. Tadpoles were maintained before and during the experiment in plastic containers (20 cm · 32 cm · 11 cm) with 2 L of dechlorinated tapwater, with constant aeration and food available ad libitum (ground Purina Rabbit Chow added every 3 d). Water temperature was maintained between 23 and 24.2 8C before and during the experiment, a range that was 1–28C lower than the mean temperatures of pools in the Rıó Salado during the period when tadpoles are present in nature (November– February; Woolrich-Pinã et al., 2010a,b). After 4 d, tadpoles had

reached Gosner stage 26–27 (Gosner, 1960) and were placed into experimental treatments (initial snout–vent length [SVL] = 9–11 mm). Our experimental design was a fully factorial 3 · 3 design with three density treatments (two, four, and eight tadpoles) and three salinity treatments (0, 0.4, and 0.8 ppt) replicated three times for each species. Densities of tadpoles used correspond to one, two, and four tadpoles L-1, densities that fall within the range of densities we have observed along the Rıó Salado (Woolrich-Pin˜ a et al., pers. obs.). We chose our salinity treatments to include conditions that tadpoles experience in pools along the Rıó Salado (I. occidentalis: overall range 0.3–0.9 ppt, Woolrich-Pinã et al., 2010b; H. arenicolor: overall range 1.2– 2.8 ppt, Woolrich-Pinã et al., 2011). We used InstantOceant Synthetic Sea Salt that is primarily Na+ and Cl-, but that includes other ions as well (e.g., Mg2+, SO42-, Ca2+, K+) in lesser quantities, to create salinity treatments (see Christy and Dickman, 2002 for details on the chemical composition of InstantOcean). Overall salinity levels were confirmed using a YSI model 85-10 FT hand-held meter. Water was changed (refreshing the treatments) and containers were cleaned weekly. We recorded when each tadpole metamorphosed (Gosner stage 46; tail fully reabsorbed) and then measured their SVL with a transparent ruler. We analyzed each species separately. We used a two-way multivariate analysis of variance (MANOVA) to analyze the effects of salinity, tadpole density, and their interaction on each species, with survivorship, time to metamorphosis (in weeks), and size at metamorphosis as the dependent variables. A significant MANOVA was followed by univariate analyses of variance (ANOVAs) on each dependent variable. We used Tukey’s honestly significant difference (HSD) post hoc tests when a univariate ANOVA was significant to determine which treatments were significantly different. Before analyses, we transformed tadpole survivorship using an arcsine-square root transformation. Data analyses were conducted using JMP 10.0 (SAS Institute, Cary, NC). RESULTS Exerodonta xera.—There was a significant effect of salinity in the MANOVA (Roy’s greatest root = 2.30; F3,17 = 13.05, P = 0.0001). There was also a significant effect of density (Roy’s greatest root = 0.595; F3,17 = 3.37, P = 0.043). The interaction of salinity and density was not significant in the MANOVA (Roy’s greatest root = 0.094; F4,18 = 2.34, P = 0.094). Survivorship was slightly lower in the 0.4 ppt (0.76 6 0.06) and 0.8 ppt (0.79 6 0.11) treatments compared with the control (0.96 6 0.03), but this difference only approached statistical significance (F2,18 = 3.03, P = 0.073). Survivorship was lowest in the four tadpole density and highest in the two tadpole density treatments and intermediate at the eight tadpole density (Fig. 1A; F2,18 = 4.04, P = 0.035). The interaction between salinity and tadpole density was not significant (F4,18 = 0.60, P = 0.66). Time to metamorphosis for E. xera increased with salinity (Fig. 1B; F2,18 = 13.06, P = 0.0003). Time to metamorphosis was not affected by tadpole density (F2,18 = 1.68, P = 0.21). The interaction between salinity and density treatments was not significant (F4,18 = 1.06, P = 0.40). Size (SVL) at metamorphosis was similar in the 0 and 0.8 ppt salinity treatments and lowest in the 0.4 ppt salinity treatment (Fig. 1C; F2,18 = 4.80, P = 0.02). Tadpole density had no effect on

´ SALADO SALINITY EFFECTS ON TADPOLES OF THE RIO

19

FIG. 2. Effect of (A) salinity and (B) tadpole density on the time to metamorphosis in Incilius occidentalis tadpoles from the Rıó Salado, Puebla, Mexico. Means are given 61 SE. Means not sharing letters are significantly different (Tukey’s HSD post hoc test, P 0.05).

FIG. 1. The effect of (A) tadpole density on survivorship and salinity treatments on (B) time to metamorphosis and (C) size (SVL) at metamorphosis of Exerodonta xera tadpoles from the Rıó Salado, Puebla, Mexico. Means are given 61 SE. Means not sharing letters are significantly different (Tukey’s HSD post hoc test, P 0.05).

size at metamorphosis (F2,18 = 1.48, P = 0.25). The interaction term was not significant (F4,18 = 1.44, P = 0.26). Incilius occidentalis.—In the MANOVA, there was a significant effect of salinity on I. occidentalis (Roy’s greatest root = 0.823; F3,17 = 4.66, P = 0.015). There was also a significant density effect (Roy’s greatest root = 2.35; F3,17 = 13.3, P = 0.0001). The interaction between salinity and density was not significant in the MANOVA (Roy’s greatest root = 0.21; F4,18 = 0.94, P = 0.46).

Survivorship was not affected by salinity treatments (F2,18 = 1.78, P = 0.20). Survivorship did not differ among the tadpole density treatments (F2,18 = 0.27, P = 0.76). The interaction between salinity and tadpole density was also not significant (F4,18 = 0.22, P = 0.92). Metamorphosis was delayed in the 0.8 ppt salinity treatment relative to the 0 ppt and the 0.4 ppt salinity treatments (Fig. 2A; F2,18 = 3.77, P = 0.043). Time to metamorphosis was significantly higher in the eight tadpole density treatment compared with the two and four tadpole density treatments (Fig. 2B; F2,18 = 13.2, P = 0.0003). The interaction between salinity and density treatments was not significant (F4,18 = 0.31, P = 0.87). Size (SVL) at metamorphosis was not affected by salinity treatment (F2,18 = 1.02, P = 0.38). Tadpole density had no effect on size at metamorphosis (F2,18 = 0.53, P = 0.60). The interaction term was also not significant (F4,18 = 0.80, P = 0.54). DISCUSSION Increased salinity did not affect survivorship in the tadpoles of either I. occidentalis or E. xera, although there was a trend for survivorship in E. xera to be lower in both the low and high salinity treatments (reduction in survivorship approximately

20


20% in both treatments). Salinity treatments had sublethal effects, with higher salinities delaying metamorphosis in both species, and intermediate salinities reducing size at metamorphosis in E. xera. Marginally significant effects on survivorship were only observed in E. xera. However, the reduction of survivorship of E. xera in the salinity treatments was not large (approximately 20% in both treatments). The fact that salinity levels we used in our experiment did not have large negative effects on survivorship is consistent with our observations of tadpole distributions in pools along the Rıó Salado. Pools in which we observed tadpoles of I. occidentalis had a mean salinity of 0.8 ppt, whereas pools that did not have tadpoles averaged 1.2 ppt (Woolrich-Pinã et al., 2010b). Pools in which tadpoles of E. xera were observed had a mean salinity of 0.3 ppt, and pools without E. xera tadpoles had a mean salinity of 1.8 ppt (Woolrich-Pinã et al., pers. obs.). Thus, tadpoles of both these species can tolerate extended exposure to salinities up to 0.8 ppt for most of their larval period without suffering large increases in mortality. It may be that the brief interval (4 d) that the tadpoles were kept in freshwater before being placed in the experiment reduced the effects of the salinity treatments (see Kuznetsov and Lobachyov, 2007; Squires et al., 2010). Compared with other species for which tolerance to chronic exposure to increased salinity has been examined, E. xera and I. occidentalis show similar tolerances. For example, tadpoles of Rana temporaria exposed to a salinity of 1.5 ppt for 2 mo (Denoel ¨ et al., 2010); tadpoles of Lithobates clamitans (Green Frog) exposed to a salinity of 0.945 ppt for 58 d (Karraker, 2007); and Lithobates catesbeianus (American Bullfrog) exposed to a salinity of 1 ppt for 60 d (Matlaga et al., 2014) showed no reduction in survivorship. In contrast, Lithobates sylvaticus (Wood Frog) tadpoles showed reduced survivorship with exposure to 1.03 ppt for 90 d (Sanzo and Hecnar, 2006) and to 0.945 ppt for 70 d (Karraker et al., 2008). Thus, the responses seen in our experiment do not appear to be atypical (i.e., these species do not appear to have an exceptional tolerance for salinity). However, we do note that a congener of I. occidentalis, Incilius nebulifer (Gulf Coast Toad), showed increased mortality when acutely exposed to salinities as low as 0.44 ppt (Hua and Pierce, 2013). Our results also suggest that even though they can be found in pools with salinities above 0.5 ppt, these tadpoles may not be able to successfully emerge from such pools. In both species, metamorphosis was delayed by several days (I. occidentalis) or weeks (E. xera) in the high salinity treatment (0.8 ppt). This contrasts with the acceleration of metamorphosis by L. sylvaticus exposed to 1.03 ppt (Sanzo and Hecnar, 2006) and Fejervarya limnocharis exposed to up to 13 ppt (Wu and Kam, 2009). The delay we observed could result in the inability of tadpoles to successfully metamorphose because of pools drying, especially in E. xera that showed delays of almost 5 wk at 0.4 ppt and 9 wk at 0.8 ppt. For I. occidentalis, the delay of 4 or 5 d may not have much impact on the ability to successfully emerge from pools along the Rıó Salado because they breed when the size of pools is relatively constant and when pools are at their deepest (Woolrich-Pinã et al., 2010a). However, E. xera breeds during a period (July–August; Woolrich-Pinã et al., 2005) when depth and size of pools along the Rıó Salado are declining rapidly and isolated pools are drying up (Woolrich-Pinã et al., 2010a). Indeed, given that the window for breeding in this species is approximately 8–9 wk in July and August, delays of 5 to 9 wk could have a dramatic effect on their ability to successfully emerge. It therefore appears that pools with salinities >0.4–0.8 ppt may be harmful to these populations because eggs are laid

in them (up to at least 1.2 ppt; Smith and Lemos-Espinal, 2010). Tadpoles can survive in these pools but none may emerge before the pools dry because of the delayed metamorphosis. Plasticity of time to metamorphosis in response to pond drying appears to be related to the permanence and predictability of the hydroperiod experienced by a species (e.g., Richter-Boix et al., 2006). The ability to accelerate metamorphosis in response to pool drying might ameliorate some of the observed delays in metamorphosis, although we have no information about the ability of E. xera and I. occidentalis to accomplish this relationship. Some species of hylids (e.g., Richter-Boix et al., 2006) and bufonids (Wilbur, 1987; Marquez-Garcia et al., 2009; Perotti et al., 2011) do show such plasticity, but some do not (e.g., hylids: Leips et al., 2000; bufonids: Boone and James, 2003; Boone et al., 2004), including a congener of I. occidentalis, I. nebulifer (Vogel and Pechmann, 2010). Further experiments examining the interaction of pool drying, salinity, and tadpole density may help elucidate the extent of the threat to these populations. However, given the delays we observed, it would seem more likely such plasticity might help I. occidentalis overcome the delayed metamorphosis (delay of 4–5 d), but not E. xera (delay of 5–9 wk). We did not assess the relative tolerance of tadpoles at Rıó Salado to salinity compared with tadpoles from other populations inhabiting streams with lower or higher salinities. However, other species of amphibians show the ability to adapt to increased salinity (Brady, 2012; Hopkins et al., 2012), with populations from higher salinity habitats showing increased tolerance compared with populations from lower salinity habitats (Gomez-Mestre and Tejedo, 2003, 2004). In addition, some species of tadpoles demonstrate an ability to acclimate to increasing levels of salinity (Hsu et al., 2012; Wu et al., 2014), but in some cases exposure to sublethal levels of salinity decreases subsequent tolerance of salinity (Hua and Pierce, 2013). It would be enlightening to conduct additional experiments comparing the relative tolerances within these two species, and other species of anurans that occur along the Rıó Salado (e.g., H. arenicolor), and their abilities to acclimate to salinity. Tadpole density had a negative effect on survivorship in E. xera, but not in a linear manner (i.e., the biggest effect was at intermediate density; Fig. 1A), and did not affect size at or time to metamorphosis. In I. occidentalis, the highest tadpole density delayed metamorphosis, but tadpole density did not affect survivorship or size at metamorphosis. The effects of density on the tadpoles in our experiment are to be expected given the numerous previous studies that have shown that density can affect tadpole survivorship or time to metamorphosis negatively in hylids (Warner et al., 1993; Smith et al., 2004) and bufonids (Brockelman, 1969; Saidapur and Girish, 2001; Distel and Boone, 2011). The sizes of the pools along the Rıó Salado can change dramatically throughout the year (Woolrich-Pinã et al., 2010a,b). Such changes likely alter the density that tadpoles experience in these pools; thus, the effects of density on the tadpoles of E. xera and I. occidentalis that we observed in our experiment are likely relevant to tadpoles in nature (Leips et al., 2000). Removal of water by ‘‘salineras’’ may decrease the amount of water in the Rıó Salado and in turn may result in a river that is a series of pools connected by very little flow. As these pools lose water during the dry season, they will likely become increasingly saline, smaller, and have shorter hydroperiods. Our results suggest that ‘‘salineras’’ may threaten amphibian populations along the Rıó Salado by affecting salinity and hydroperiod of pools and leading to major reductions in successful metamor-

´ SALADO SALINITY EFFECTS ON TADPOLES OF THE RIO phosis of these species. Indeed, there has been a recent decline in the distribution and abundance of anurans along the Rıó Salado. At the end of the 1990s, it was common to observe tadpoles of four species of anurans in the Rıó Salado and its associated pools (Canseco-Ma´rquez et al., 2003; Woolrich-Pinã and J. Lemos-Espinal, pers. obs.). However, in the last 5–6 yr, there has been an obvious decline in amphibian populations along the Rıó Salado, with no other apparent change in the environment that might explain the decline (Woolrich-Pinã and J. Lemos-Espinal, pers. obs.). Our results suggest that the impacts of similar anthropogenic changes in the freshwater rivers and streams in the arid tropics worldwide (Williams, 1987, 2001; Cardona et al., 2004) need to be examined experimentally, because simple observational surveys may not reflect the underlying fitness consequences of such changes accurately. Acknowledgments.—This research was part of the doctoral dissertation of GAW-P submitted to the Universidad Nacional ´ Autonoma de Me´xico. We thank E. Aquino Caballero and A. Hernandez Rios for logistical support to carry out this part of the project that led to the realization of their professional theses. We also thank anonymous reviewers for helpful comments on previous versions of this manuscript. Financial support was provided by project PAPIIT IN 221707 and projects PAPCA 2008–2009 and 2009–2010. CONACYT provided a scholarship to support GAW-P during this study. All necessary regulations pertaining to the collection of these species that were in place at the time of this research were followed and the experiments were approved by the Denison University Institutional Animal Care and Use Committee (07-004).

LITERATURE CITED AQUINO-CABALLERO, E. 2010. Efecto de la Salinidad y Densidad Poblacional en el Desempenõ de las Larvas del Sapo de los Pinos Ollotis occidentalis (Anura: Bufonidae) Provenientes de las Pozas Asociadas al Rıó Salado, Puebla. Unpub. B.S. thesis, Universidad ´ Nacional Autonoma de Me´xico, Mexico City, Mexico. ´ de las Pozas Asociadas al BARBOSA-MORALES, M. 2008. Caracterizacion Rıó Salado, Puebla, Me´ xico (Larvas de Anfibios y Factores ´ ´ Abioticos). Unpub. B.S. thesis, Universidad Nacional Autonoma de Me´xico, Mexico City, Mexico. BOONE, M. D., AND S. M. JAMES. 2003. Interactions of an insecticide, herbicide, and natural stressors in amphibian community mesocosms. Ecological Applications 13:829–841. BOONE, M. D., E. E. LITTLE, AND R. D. SEMLITSCH. 2004. Overwintered bullfrog tadpoles negatively affect salamanders and anurans in native amphibian communities. Copeia 2004:683–690. BRADY, S. P. 2012. Road to evolution? Local adaptation to road adjacency in an amphibian (Ambystoma maculatum). Scientific Reports 2:235, doi:10.1038/srep00235. BROCKELMAN, W. Y. 1969. An analysis of density effects and predation in Bufo americanus tadpoles. Ecology 50:632–644. BROWN, M. E., AND S. C. WALLS. 2013. Variation in salinity tolerance among larval anurans: implications for community composition and the spread of an invasive, non-native species. Copeia 2013:543–551. CAMERANO, L. 1879. Di alcune anfibii anuri esistenti nelle collezioni del R. Museo Zoologico di Torino. Atti della Reale Accademia della Scienze di Torino 866–897. CANSECO-MARQUEZ, L., G. GUTIE´RREZ-MAYEŃ, AND J. R. MENDELSON. 2003. Distribution and natural history of the hylid frog Hyla xera (Anura: Hylidae) in the Tehuacań-Cuicatlań Valley, with a description of the tadpole. Southwestern Naturalist 48:670–675. CARDONA, A., J. J. CARILLO-RIVERA, R. HUIZAR-A´ LVAREZ, AND E. GRANIELCASTRO. 2004. Salinization in coastal aquifers of arid zones: an example from Santo Domingo, Baja California Sur, Mexico. Environmental Geology 45:350–366.

21

CHRISTY, M. T., AND C. R. DICKMAN. 2002. Effects of salinity on tadpoles of the green and golden bell frog (Litoria aurea). Amphibia-Reptilia 23: 1–11. COLLINS, S. J., AND R. W. RUSSELL. 2009. Toxicity of road salt to Nova Scotia amphibians. Environmental Pollution 157:320–324. CONTRERAS-B. S., AND M. L. LOZANO-V. 1994. Water, endangered fishes, and development perspectives in arid lands of Mexico. Conservation Biology 8:379–387. ¨ , M., M. BICHOT, G. F. FICETOLA, J. DELCOURT, M. YLIEFF, P. DENOEL KOSTEMONT, AND P. PONCIN. 2010. Cumulative effects of road de-icing salt on amphibian behavior. Aquatic Toxicology 99:275–280. DISTEL, C. A., AND M. D. BOONE. 2011. Pesticide has asymmetric effects on two tadpole species across density gradient. Environmental Toxicology and Chemistry 30:650–658. DOUGHERTY, C. K., AND G. R. SMITH. 2006. Acute effects of road de-icers on the tadpoles of three anurans. Applied Herpetology 3:87–93. GIRISH, K. G., AND S. V. B. KRISHNAMURTHY. 2009. Distribution of tadpoles of large wrinkled frog Nyctibatrachus major in central Western Ghats: influence of habitat variables. Acta Herpetologica 4:153–160. GODWIN, K. S., S. D. HAFNER, AND M. F. BUFF. 2003. Long-term trends in sodium an chloride in the Mohawk River, New York: the effect of fifty years of road-salt application. Environmental Pollution 124:273– 281. GOMEZ-MESTRE, I., AND M. TEJEDO. 2003. Local adaptation of an anuran amphibian to osmotically stressful environments. Evolution 57:1889– 1899. ———. 2004. Contrasting patterns of quantitative and neutral genetic variation in locally adapted populations of the Natterjack toad, Bufo calamita. Evolution 58:2343–2352. GOSNER, K. L. 1960. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16:183–190. HAMER, A. J., AND K. M. PARRIS. 2011. Local and landscape determinants of amphibian communities in urban ponds. Ecological Applications 21:378–390. HERNAŃDEZ-RIÓS, A. 2010. Efecto de la Salinidad y Densidad Poblacional en Larvas de Hyla xera que Habitan en el Valle de Zapotitlań Salinas, Puebla, Me´ xico. Unpub. B.S. thesis, Universidad Nacional ´ Autonoma de Me´xico, Mexico City, Mexico. HOPKINS, G. R., S. S. FRENCH, AND E. D. BRODIE JR. 2012. Potential for local adaptation in response to an anthropogenic agent of selection: effects of road-deicing salts on amphibian embryonic survival and development. Evolutionary Applications 6:384–392. HSU, W.-T., C.-S. WU, J.-C. LAI, Y.-K. CHAO, C.-H. HSU, AND Y.-C. KAM. 2012. Salinity acclimation affects survival and metamorphosis of crab-eating frog tadpoles. Herpetologica 68:14–21. HUA, J., AND B. A. PIERCE. 2013. Lethal and sublethal effects of salinity on three common Texan amphibians. Copeia 2013:562–566. KARRAKER, N. E. 2007. Are embryonic and larval green frogs (Rana clamitans) insensitive to road deicing salt? Herpetological Conservation and Biology 2:35–41. KARRAKER, N. E., J. P. GIBBS, AND J. R. VONESH. 2008. Impacts of road deicing salt on the demography of vernal pool-breeding amphibians. Ecological Applications 18:724–734. KARRAKER, N. E., J. ARRIGONI, AND D. DUDGEON. 2010. Effects of increased salinity and an introduced predator on lowland amphibians in southern China: species identity matters. Biological Conservation 143:1079–1086. KUZNETSOV, V. A., AND Y. A. LOBACHYOV. 2007. Effects of salinity fluctuations on growth and development of the larvae of marsh frog (Rana ridibunda L). Hydrobiological Journal 43:71–79. LEIPS, J., M. G. MCMANUS, AND J. TRAVIS. 2000. Response of treefrog larvae to drying ponds: comparing temporary and permanent pond breeders. Ecology 81:2997–3008. MARQUEZ-GARCIA, M., M. CORREA-SOLIS, M. SALLABERRY, AND M. A. MENDEZ. 2009. Effects of pond drying on morphological and lifehistory traits in the anuran Rhinella spinulosa (Anura: Bufonidae). Evolutionary Ecology Research 11:803–815. MATLAGA, T. H., C. A. PHILLIPS, AND D. J. SOUCEK. 2014. Insensitivity to road salt: an advantage for the American bullfrog? Hydrobiologia 721:1–8. MCGARVIE HIRNER, J. L., AND S. P. COX. 2007. Effects of rainbow trout (Oncorhynchus mykiss) on amphibians in productive recreational fishing lakes of British Columbia. Canadian Journal of Fisheries and Aquatic Science 64:1770–1780. MENDELSON, J. R., III, AND J. A. CAMPBELL. 1994. Two new species of the Hyla sumichrasti group (Amphibia: Anura: Hylidae) from Mexico. Proceedings of the Biological Society of Washington 107:398–409.

22


OLIVER-LO´ PEZ, L., A. RAMI´REZ-BAUTISTA, AND J. A. LEMOS-ESPINAL. 2000. Bufo occidentalis. Fecundity. Herpetological Review 31:39–40. PEROTTI, M. G., F. G. JARA, AND C. A. UBEDA. 2011. Adaptive plasticity of life-history traits to pond drying in three species of Patagonian anurans. Evolutionary Ecology Research 13:414–429. POREJ, D., AND T. E. HETHERINGTON. 2005. Designing wetlands for amphibians: the importance of predatory fish and shallow littoral zones in structuring of amphibian communities. Wetlands Ecology and Management 13:445–455. RAMAKRISHNA, D., AND T. VIRARAGHAVAN. 2005. Environmental impact of chemical deicers—a review. Water, Air and Soil Pollution 166:49–63. RICHTER-BOIX, A., G. A. LLORENTE, AND A. MONTORI. 2006. A comparative analysis of the adaptive developmental plasticity hypothesis in six Mediterranean anuran species along a pond permanency gradient. Evolutionary Ecology Research 8:1139–1154. SAIDAPUR, S. K., AND S. GIRISH. 2001. Growth and metamorphosis of Bufo melanostictus tadpoles: effects of kinship and density. Journal of Herpetology 35:249–254. SANZO, D., AND S. J. HECNAR. 2006. Effects of road de-icing salt (NaCl) on larval wood frogs (Rana sylvatica). Environmental Pollution 140:247– 256. SMITH, G. R., AND J. A. LEMOS-ESPINAL. 2010. Observations of amplexus and oviposition in Ollotis [Bufo] occidentalis in the Rıó Salado, Puebla, Mexico. IRCF Reptiles and Amphibians 17:46–47. SMITH, G. R., H. A. DINGFELDER, AND D. A. VAALA. 2004. Asymmetric competition between Rana clamitans and Hyla versicolor tadpoles. Oikos 105:626–632. SMITH, M. J., E. S. G. SCHREIBER, M. P. SCROGGIE, M. KOHOUT, K. OUGH, J. POTTS, R. LENNIE, D. TURNBULL, C. JIN, AND T. CLANCY. 2007. Associations between anuran tadpoles and salinity in a landscape mosaic of wetlands impacted by secondary salinisation. Freshwater Biology 52:75–84. SQUIRES, Z. E., P. C. E. BAILEY, R. D. REINA, AND B. B. B. M. WONG. 2008. Environmental deterioration increase tadpole vulnerability to predation. Biology Letters 4:392–394. ———. 2010. Compensatory growth after transient salinity stress. Marine and Freshwater Research 61:219–222. THUNQVIST, E.-L. 2004. Regional increase of mean chloride concentration in water due to the application of deicing salt. Science of the Total Environment 325:29–37. VOGEL, L. S., AND J. H. K. PECHMANN. 2010. Response of Fowler’s toad (Anaxyrus fowleri) to competition and hydroperiod in the presence of

the invasive coastal plain toad (Incilius nebulifer). Journal of Herpetology 44:382–389. WARNER, S. C., J. TRAVIS, AND W. A. DUNSON. 1993. Effect of pH variation on interspecific competition between two species of hylid tadpoles. Ecology 74:183–194. WELCH, N. E., AND J. A. MACMAHON. 2005. Identifying habitat variables important to the rare Columbia spotted frog in Utah (USA): an information theoretic approach. Conservation Biology 19:473–481. WILBUR, H. M. 1987. Regulation of structure in complex systems: experimental temporary pond communities. Ecology 68:1437–1452. WILLIAMS, W. D. 1987. Salinization of rivers and streams: an important environmental hazard. Ambio 16:180–185. ———. 2001. Anthropogenic salinisation of inland waters. Hydrobiologia 466:329–337. ´ Hidrologica ´ del Valle de WOOLRICH-PINÃ, G. A. 2010. Caracterizacion ´ de los Zapotitlań Salinas (Puebla) y su Influencia en la Distribucion ´ ´ Anfibios: Aspects Geogra´ficos, Ecologicos y de Conservacion. ´ Unpub. Ph.D. diss., Universidad Nacional Autonoma de Me´xico, Mexico City, Mexico. WOOLRICH-PINÃ, G. A., L. OLIVER-LO´ PEZ, AND J. A. LEMOS-ESPINAL. 2005. Anfibios y Reptiles del Valle de Zapotitla´ n Salinas, Puebla. CONABIO, Mexico City, Mexico. WOOLRICH-PINÃ, G. A., G. R. SMITH, L. OLIVER-LO´ PEZ, M. BARBOSA MORALES, AND J. A. LEMOS-ESPINAL. 2010a. Distribution of Ollotis occidentalis (Amphibia: Anura: Bufonidae) along the Rıó Salado, Puebla, Me´xico. Acta Herpetologica 5:151–160. ———. 2010b. Factors influencing the distribution of Poeciliopsis fasciata along the Rıó Salado (Puebla, Mexico). Journal of Freshwater Ecology 25:127–133. WOOLRICH-PINÃ, G. A., J. A. LEMOS-ESPINAL, G. R. SMITH, R. MONTOYAAYALA, AND L. OLIVER-LO´ PEZ. 2011. Distribution of tadpoles (Hyla arenicolor) in the pools associated with the Rıó Salado, Puebla, Mexico. Bulletin of the Maryland Herpetological Society 47:47–50. WU, C.-S., AND Y.-C. KAM. 2009. Effects of salinity on the survival, growth, development, and metamorphosis of Fejervarya limnocharis tadpoles living in brackish water. Zoological Science 26:476–482. WU, C.-S., W.-K. YANG, T.-H. LEE, I. GOMEZ-MESTRE, AND Y.-C. KAM. 2014. Salinity acclimation enhances salinity tolerance in tadpoles living in brackish water through increased Na+, K+-ATPase expression. Journal of Experimental Zoology 321A:57–64. Accepted: 28 February 2014.