Distance to coastline modulates morphology and population structure in a coastal amphibian

Abstract

Salinization due to sea-level rise and marine submersions is expected to strongly impact coastal ecosystems. Exposure to salinity can negatively impact biodiversity especially in coastal wetlands. To understand comprehensively the consequences of environmental salinization on coastal biodiversity, it is essential to document how coastal species currently respond to exposure to salinity. In this study, we investigated how variations of environmental salinity relative to the distance to the ocean influence population structure (age ratio and sex ratio), and individual hydro-mineral balance (osmolality) and morphology (size, mass, condition) in the western spadefoot toad (Pelobates cultripes) in two populations from the French Atlantic coast. We show that distance to coastline strongly influences exposure to salt on a small spatial scale. Some variables (e.g., abundances, osmolality, morphology) responded similarly in both sites and may be related to salt deposition due to landward sea-spray. Interestingly, other variables (sex ratio and age ratio) displayed site-specific responses and appeared to be linked to the salinity of breeding sites. Distance to the shoreline appears to be a critical population structuring factor in this coastal salt-tolerant species. Future studies should investigate how distance to shoreline—and thus environmental salinity—can ultimately affect individual performances and fitness.

From the Field to the Lab: Physiological and Behavioural Consequences of Environmental Salinity in a Coastal Frog

“…Our study species can be found in ponds in which the salinity (ranging from 0 to 16 g L −1 ) is similar to those experienced by other species found in coastal marshes ( Hopkins and Brodie, 2015 ). The salinity experienced in the field (0–7 g L −1 ) was correlated with physiological parameters (osmolality, monocytes and eosinophils counts), negatively correlated with body condition and locomotor performance and seems to influence size- and sex-specific habitat selection (see also Lorrain-Soligon et al, 2022b ). Experimentally, we demonstrated that short-term exposure to environmental salinity significantly affects physiological parameters [salt influxes (osmolality), water effluxes (body mass), immunity (leukocyte counts)] and locomotor performance (jumping distances and activity).…”

“…Indeed, adult females mobilize large amount of energy to reproduce ( Wells, 2007 ; Hayward and Gillooly, 2011 ) and energetic constraints of life in brackish water (either directly linked to osmoregulation, or indirectly linked to foraging efficiency, see above) may negatively interact with the energetic requirements of reproduction. Complementarily, such a biased sex-ratio may also be linked to habitat selection processes for which amphibian females have been shown to select less brackish sites to mate and lay their eggs in order to decrease the negative consequences of elevated salinity on embryonic and larval development ( Haramura, 2008 ; Albecker and McCoy, 2017 ; Lorrain-Soligon et al, 2022b ). It is noteworthy that we focused our investigation on pond salinity and we did not assess other parameters.…”

“…In this study, we adopted a comprehensive approach to assess the behavioural and physiological consequences of exposure to environmental salinity in adults of a coastal frog ( Pelophylax sp., N = 156) originating from freshwater and brackish ponds in wetlands from the Atlantic coast of France. First, we used a field-based approach to assess the consequences of pond salinity on 1) physiology [osmolality ( Gomez-Mestre et al, 2004 ), hemoglobin-binding protein ( Wang et al, 2020 ), blood cell composition ( Burraco and Gomez-Mestre 2016 )], 2) locomotor performance [jumping distance, ( Alexander et al, 2012 ; Kearney et al, 2016 ; Sanabria et al, 2018 )] and 3) ecological responses [morphology and sex-ratio ( Lorrain-Soligon et al, 2022b )]. On the same individuals, and for the same measures, we then used an experimental approach to precisely measure the consequences of short-term (48 h) exposure to different levels of salinity (0, 6, 9 or 12 g L −1 ) similar to those recorded in the field (min: 0 g L −1 , max: 16 g L −1 ).…”

Some like it salty: Spatio‐temporal dynamics of salinity differentially affect anurans and caudates in coastal wetlands

“…Finally, these patterns may reveal trade‐offs linked to adaptive processes. Indeed, coastal anurans may have evolved specific physiological adaptations to promote life in hyperosmotic environments (Albecker & McCoy, 2019; Gomez‐Mestre & Tejedo, 2003; Hopkins et al, 2016), notably through mechanisms that allow them to reduce salt intake (or increase excess salt excretion) and/or to increase water influxes (or reduce water effluxes, Lorrain‐Soligon, Bichet, et al, 2022; Lorrain‐Soligon, Robin, et al, 2022). In turn, these mechanisms may become maladaptive in hyposmotic water bodies because of elevated salt loss and excessive water influxes (Lorrain‐Soligon, Bichet, et al, 2022), leading to massive oedema and mortality (L. Lorrain‐Soligon, pers.…”

“…Indeed, most amphibians are characterised by a complex biphasic life cycle, with eggs and tadpoles developing in aquatic habitats and adults displaying various levels of terrestriality (Wells, 2007). Accordingly, eggs and larvae are less tolerant to elevated salinity than adults (Albecker & McCoy, 2017), and some evidence suggest that reproductive individuals can express habitat selection and avoid saline water for egg‐laying (Albecker & McCoy, 2017; Haramura, 2008; Lorrain‐Soligon, Robin, et al, 2022; Viertel, 1999) to improve their reproductive success (Lukens & Wilcoxen, 2020; Tornabene et al, 2021). Taken together, these elements suggest that variability in both within‐ and between‐species susceptibility to salinity could be a major factor determining the structure of amphibian coastal communities (Lorrain‐Soligon et al, 2021) and may significantly affect within‐ and between‐species distribution across the spatial and temporal salinity gradient.…”